CN119269391A

CN119269391A - Refractive index measuring device, measuring equipment and measuring method

Info

Publication number: CN119269391A
Application number: CN202310834242.XA
Authority: CN
Inventors: 谈宜东; 阿玛尼·阿里雷扎
Original assignee: Tsinghua University
Current assignee: Tsinghua University
Priority date: 2023-07-07
Filing date: 2023-07-07
Publication date: 2025-01-07

Abstract

The application provides a refractive index measuring device, measuring equipment and a measuring method. The refraction of the measuring light emitted by the light source through the linear zone plate and then through the sample can form a diffraction pattern containing a plurality of linear light spots on the imaging sensor. The diffraction patterns corresponding to the reference sample and the diffraction patterns corresponding to the sample to be measured are respectively obtained by the measuring device, and the refractive index of the sample to be measured can be determined according to the two diffraction patterns and the refractive index of the reference sample. The measuring device, the measuring equipment and the measuring method provided by the application have the advantages of high accuracy of refractive index measuring results, wide measuring range, and wide application in measuring liquid refractive index and solid refractive index, and are particularly suitable for the field of HPCL.

Description

Refractive index measuring device, refractive index measuring apparatus, and refractive index measuring method

Technical Field

The present application relates to the field of optics, and in particular, to a refractive index measurement device, a refractive index measurement apparatus, and a refractive index measurement method.

Background

The critical angle measurement method, the phase change measurement method, the interference fringe difference method, the light diffraction method and the like can be used for measuring the refractive index of the material, and the measurement methods often need to obtain measurement results with higher precision under more severe conditions, so that the application of the test device using the test methods in gradient chromatography is limited to a certain extent.

How to improve the accuracy of refractive index measurement is a considerable problem.

Disclosure of Invention

The application provides a refractive index measuring device, measuring equipment and a measuring method, wherein a diffraction pattern comprising a plurality of linear light spots can be formed on an imaging sensor after measuring light rays are diffracted through a linear zone plate, and the refractive index of a sample to be measured obtained by measuring the diffraction pattern is higher in accuracy. The refractive index measuring device provided by the embodiment of the application can be applied to refractive index measurement in the field of HPLC.

In a first aspect, a refractive index measurement device is provided that includes a light source for emitting measurement light, a zone plate including a plurality of prisms parallel to one another, and an imaging sensor for receiving measurement light passing through the zone plate, a reference sample, and/or a reference sample.

In one possible implementation, the refractive index measurement device comprises a reference sample, the refractive index of which is known.

With reference to the first aspect, in certain implementations of the first aspect, the diffraction pattern formed by the measuring light on the imaging sensor includes a plurality of linear light spots.

With reference to the first aspect, in certain implementations of the first aspect, the measurement device further includes a measurement compartment for accommodating a reference sample and/or a sample to be measured, the measurement compartment being located on a side of the zone plate remote from the light source.

A zone plate may also be referred to as a fresnel zone plate, and a plurality of prisms parallel to one another contained in the zone plate may also be referred to as a narrow band. A fresnel zone plate comprising a plurality of prisms parallel to each other may also be referred to as a linear fresnel zone plate. The measuring light can be diffracted when being incident on the prisms of the zone plate, and a diffraction pattern comprising a linear light spot is easier to form.

The measurement cabin can be used for accommodating the reference sample and the sample to be measured at the same time, and can also be used for accommodating only one of the reference sample or the sample to be measured. It should be understood that the reference sample refers to a sample of known refractive index.

Compared with a common diffraction grating, the diffraction pattern formed by using the zone plate for diffraction can form linear diffraction fringes, the diffraction fringes are clearer, and the position information of the diffraction fringes is easier to determine. Since the accuracy (or error) of the difference between the refractive index of the sample to be measured and the refractive index of the reference sample is positively correlated with the measurement accuracy (or error) of the position information of the diffraction fringes, the accuracy of the refractive index of the sample to be measured by the refractive index measuring device provided by the application is higher.

With reference to the first aspect, in certain implementations of the first aspect, the apparatus further includes a moving platform, the moving platform is located on a side of the measurement pod away from the zone plate, the imaging sensor is located on the moving platform, and the imaging sensor is movable on the moving platform along an optical axis direction of the zone plate.

In some examples, the imaging sensor may be a camera or imaging device comprising a CCD or CMOS.

Compared with a refractive index measuring device with a fixed position of the imaging sensor, the imaging sensor of the refractive index measuring device provided by the technical scheme can move along the optical axis direction of the zone plate on the moving platform, and the refractive index of the sample to be measured can be determined by receiving the measuring light passing through the sample to be measured as much as possible through the moving imaging sensor no matter the deflection angle of the measuring light caused by the sample to be measured (i.e. no matter the refractive index of the sample to be measured). The refractive index measuring device provided by the technical scheme can measure the refractive index in a wider range. To a certain extent, the refractive index measuring device provided by the technical scheme has higher accuracy of refractive index measuring results near the measuring boundary value.

With reference to the first aspect, in some implementations of the first aspect, the apparatus further includes a first mirror, a second mirror, a beam splitter, and a moving platform, where the moving platform is located on a side of the measurement chamber away from the zone plate, the first mirror is located on the moving platform, and the first mirror is movable on the moving platform along an optical axis direction of the zone plate;

The measuring light beam is incident to the first reflecting mirror along a first light path, and is reflected by the first reflecting mirror and then is incident to the imaging sensor along a second light path;

the first light path sequentially passes through the beam splitter, the second reflector, the zone plate and the measuring cabin, and the second light path sequentially passes through the measuring cabin, the zone plate, the second reflector and the second beam splitter.

According to the technical scheme, the first reflecting mirror and the second reflecting mirror are utilized to change the light path of the measuring light, so that the measuring light can pass through the reference sample and/or the sample to be measured twice, namely, in a measuring process, the measuring light can deflect twice. Compared with a method for measuring the refractive index of a sample to be measured by only one deflection, the method for measuring the refractive index by two deflection is beneficial to reducing relative errors caused by factors such as measurement errors and the like and is beneficial to improving the accuracy of the measurement result of the refractive index measuring device. On the other hand, the reflector is used for adjusting the propagation path of the measuring light, so that the utilization rate of the internal space of the refractive index measuring device is improved to a certain extent, and the volume of the refractive index measuring device is reduced.

With reference to the first aspect, in some implementations of the first aspect, the apparatus further includes a second mirror disposed near the zone plate, and the measurement light is incident to the imaging sensor along a third optical path, where the third optical path passes through the second mirror, the zone plate, and the measurement pod in order.

In the technical scheme, the second reflecting mirror is utilized to change the light path of the measuring light, so that the space layout of different devices in the measuring device can be adjusted, the volume of the measuring device can be reduced, and the space utilization rate of the measuring device can be improved.

With reference to the first aspect, in certain implementations of the first aspect, the second mirror is a collimating mirror.

In some possible implementations, the collimating mirror may be an adjustable parabolic mirror.

In the technical scheme, a collimating reflector is used on a propagation light path of measuring light rays, and originally divergent measuring light rays are converted into mutually parallel light beams as much as possible. When the parallel light beam is incident on the zone plate to be diffracted, the formed derivative pattern is clearer. The implementation of the technical scheme is beneficial to improving the accuracy of the refractive index measurement result and reducing the measurement error.

With reference to the first aspect, in certain implementations of the first aspect, the measurement compartment includes a first accommodation compartment and a second accommodation compartment for accommodating the reference sample and/or the sample to be measured.

In some examples, the measurement pod is a quadrangular prism, and the first and second pods are triangular prisms of equal volume, the first and second pods being isolated from each other.

In the technical scheme, the measurement cabin is provided with two accommodation cabins, namely, a reference sample and a sample to be measured can be accommodated at the same time, measurement errors caused by sample pollution of a measurement environment are reduced, and accuracy of refractive index measurement results is improved.

With reference to the first aspect, in certain implementations of the first aspect, the measurement pod is configured to accommodate the sample to be measured, the reference sample is plate-shaped, and the reference sample is located between the zone plate and the measurement pod, or the measurement pod is configured to accommodate the reference sample, and the sample to be measured is plate-shaped, and the sample to be measured is located between the zone plate and the measurement pod.

In the technical scheme, the plate-shaped reference sample is used for replacing the reference sample accommodated in the measurement cabin, so that the structure of the measurement cabin is simplified, the operation process of refractive index measurement is simplified, and the accuracy of the refractive index measurement result is improved to a certain extent.

With reference to the first aspect, in certain implementations of the first aspect, the measuring light is coherent light, and a wavelength of the measuring light is within a threshold range.

In one possible implementation, the measuring light is monochromatic coherent light.

In the technical scheme, the wavelength and the propagation angle of the measuring light are controlled, so that the definition of a diffraction pattern formed after the measuring light is diffracted by the zone plate is improved, and the accuracy of a refractive index measuring result is improved.

With reference to the first aspect, in certain implementations of the first aspect, the apparatus further includes a polarizer disposed proximate to the light source.

The main vibration direction of the measuring light passing through the polaroid is consistent with the polarization direction of the polaroid.

In the technical scheme, the polarization direction of the measuring light is modulated by the polaroid, so that the polarization direction of the measuring light is as consistent as possible, the diffraction pattern formed after the measuring light is incident into the zone plate for diffraction is clearer, and the accuracy of the refractive index measured by the measuring device is higher.

With reference to the first aspect, in certain implementations of the first aspect, the apparatus further includes a drive control unit for driving the mobile platform.

In one possible implementation, the drive control unit may drive the mobile platform magnetically, electrically, etc. For example, the drive control unit may be a stepper motor. The higher the control accuracy of the drive control unit, the easier the movement distance of the moving platform is controlled, and accordingly the higher the accuracy of the refractive index measurement result of the measuring device is.

The following explanation and description of the beneficial effects in the following technical solutions may refer to the related description in the first aspect, and for brevity, the description is omitted below.

In a second aspect, there is provided a measurement apparatus comprising processing means and measurement means of refractive index in the first aspect and any possible implementation thereof, the processing means being adapted to determine the refractive index of a sample to be measured from the measurement means.

In a possible implementation, the processing device includes a distance measuring unit for determining a moving distance of the imaging sensor in the direction of the optical axis, and a monitoring and analyzing unit for determining a deflection distance of the light rays in the pattern from the diffraction pattern acquired by the measuring device.

In a third aspect, a method for measuring refractive index is provided, the method comprising obtaining a first diffraction pattern corresponding to a reference sample, the first diffraction pattern comprising a first set of linear fringes, the first set of linear fringes comprising a first fringe, obtaining a second diffraction pattern corresponding to a sample to be measured, the second diffraction pattern comprising a second set of linear fringes, the second set of linear fringes comprising a second fringe, determining the refractive index of the sample to be measured according to the first diffraction pattern, the second diffraction pattern, and the refractive index of the reference sample;

Wherein the first stripe corresponds to the second stripe, and the measurement accuracy of the refractive index of the reference sample is positively correlated with the measurement accuracy of the distance between the first stripe and the second stripe.

Since the linear stripes can more easily obtain more accurate results in the position determination and distance measurement, the technical scheme is beneficial to improving the accuracy of the refractive index measurement result by determining the refractive index of the sample to be measured by utilizing the linear stripes in the diffraction pattern corresponding to the reference sample and the linear stripes in the diffraction pattern corresponding to the sample to be measured. On the other hand, in the present technical solution, the accuracy of the measurement result of the refractive index is positively correlated with the measurement accuracy of the displacement variation value between the linear fringes, and in order to further improve the accuracy of the measurement result of the refractive index and reduce the error, the measurement accuracy of the displacement variation value between the linear fringes may be improved, for example, a distance measuring device with higher accuracy may be used.

With reference to the third aspect, in some implementations of the third aspect, a first diffraction pattern formed after the diffracted light passes through the reference sample is obtained, the diffracted light is formed by diffracting the measuring light through a zone plate, and the second diffraction pattern formed after the diffracted light passes through the sample to be measured and the reference sample is obtained.

With reference to the third aspect, in some implementations of the third aspect, the first diffraction pattern is acquired at a first position in an optical axis direction of the zone plate, and the second diffraction pattern is acquired at a second position in the optical axis direction of the zone plate.

In one possible implementation, the first location and the second location are different.

With reference to the third aspect, in some implementations of the third aspect, the refractive index of the sample to be measured is determined according to a first distance, a second distance, and the refractive index of the reference sample, where the first distance is a distance between positions of the imaging sensor when the first diffraction pattern and the second diffraction pattern are acquired, and the second distance is a distance between projections of the first stripe and the second stripe on the imaging sensor.

With reference to the third aspect, in certain implementations of the third aspect, the imaging sensor includes an electrically coupled device CCD.

With reference to the third aspect, in some implementations of the third aspect, the second distance is determined according to a distance between a first pixel point on the imaging sensor and a second pixel point, where the first pixel point is used to indicate a position of the first stripe, and the second pixel point is used to indicate a position of the second stripe.

With reference to the third aspect, in certain implementations of the third aspect, the refractive index of the sample to be measured is determined according to the following formula:

Wherein Δx is the second distance, α is an incident angle of the measuring light on the measuring chamber, d is a wall thickness of the measuring chamber, n is a ratio of a refractive index of the sample to be measured to a refractive index of the reference sample, Δz is the first distance, and the measuring chamber is used for accommodating the reference sample and/or the sample to be measured.

Drawings

Fig. 1 is a schematic diagram of a refractive index measurement principle according to an embodiment of the present application.

Fig. 2 is a schematic diagram of a refractive index measurement device according to an embodiment of the present application.

Fig. 3 is a schematic structural diagram of a zone plate according to an embodiment of the present application.

Fig. 4 is a schematic diagram of a zone plate according to an embodiment of the present application.

Fig. 5 is a schematic structural diagram of a measurement cabin according to an embodiment of the present application.

Fig. 6 is a schematic diagram of a refractive index measurement method according to an embodiment of the present application.

Fig. 7 is a schematic diagram of another refractive index measurement apparatus according to an embodiment of the present application.

Fig. 8 is a schematic view of another refractive index measurement apparatus according to an embodiment of the present application.

Fig. 9 is a schematic view of another refractive index measurement apparatus according to an embodiment of the present application.

Fig. 10 is a schematic diagram of a refractive index measurement device according to an embodiment of the present application.

Fig. 11 is a simulation result of the refractive index measuring device shown in fig. 10.

Fig. 12 is a diffraction pattern obtained by using the refractive index measuring device provided by the embodiment of the present application.

Fig. 13 is another diffraction pattern obtained using the refractive index measuring device provided by the embodiment of the present application.

Fig. 14 is a schematic diagram of a distribution manner of a plurality of wavebands on a zone plate according to an embodiment of the present application.

Fig. 15 is a schematic view of a diffraction pattern and a light intensity distribution in the pattern obtained by using the refractive index measuring device according to the embodiment of the present application.

Fig. 16 is a schematic view showing another diffraction pattern and light intensity distribution in the pattern obtained by using the refractive index measuring device according to the embodiment of the present application.

Fig. 17 is a schematic diagram showing another diffraction pattern and a light frequency distribution in the pattern obtained by using the refractive index measuring device according to the embodiment of the present application.

Fig. 18 is a schematic diagram showing a diffraction pattern and a light frequency distribution in the pattern obtained by using the refractive index measuring device according to the embodiment of the present application.

Fig. 19 is a schematic diagram of a site displacement calculation method according to an embodiment of the present application.

FIG. 20 is a schematic diagram of the relationship between fringe displacement and displacement of a moving platform provided by an embodiment of the application.

Fig. 21 is a schematic diagram showing a relationship between a standard refractive index and a measured refractive index of a sample to be measured according to an embodiment of the present application.

Detailed Description

Reference will now be made in detail to embodiments of the present application, examples of which are illustrated in the accompanying drawings. In the drawings, the same or similar reference numerals denote the same or similar elements or elements having the same or similar functions. The embodiments described below by referring to the drawings are illustrative only and are not to be construed as limiting the application.

Unless defined otherwise, technical or scientific terms used herein should be given the ordinary meaning as understood by one of ordinary skill in the art to which this application belongs. In the description of the present application, it should be understood that the terms "center", "longitudinal", "lateral", "upper", "lower", "front", "rear", "left", "right", "vertical", "horizontal", "top", "bottom", "inner", "outer", etc. indicate orientations or positional relationships based on the orientations or positional relationships shown in the drawings, are merely for convenience in describing the present application and simplifying the description, and do not indicate or imply that the devices or elements referred to must have a specific orientation, be configured and operated in a specific orientation, and thus should not be construed as limiting the present application.

Before describing embodiments of the present application, some terms of art that may be used in the following embodiments will be explained first.

Zone plate (zone plate), which generally refers to an optical element consisting of alternating transparent and opaque rings, can be used to block either the odd or even bands in a fresnel half-wave band. A linear fresnel zone plate (LINEAR FRESNEL zone plate, LFZP), which may also be referred to as a linear zone plate, is a variation of a fresnel zone plate that cuts a circular ring into linear fringes.

A zone plate is a special diaphragm. The concentric rings on the optical wave band correspond to Fresnel half-wave bands, and the effect of the concentric rings is that all odd (or even) wave bands pass through the Fresnel half-wave band, and the even (or odd) wave bands are blocked, and complex amplitudes generated by the optical wave bands pass through the Fresnel half-wave band and are overlapped in phase at a certain observation point on the axis, so that the complex amplitude and the light intensity of the point are greatly increased. Since its condensing action is similar to that of a lens and satisfies the relation of object distance, image distance and focal length, it is also called fresnel lens (FRESNEL LENS).

Coherent light (coherent light) can produce a stable and clear interference pattern, and a monochromatic light field is coherent light in a strict sense.

An electrically coupled device (charge coupled device, CCD), which is an influence sensor used in digital cameras, is a chip with its surface covered with tiny photosensitive elements and registers.

A complementary metal oxide semiconductor device (complementary metal oxide semiconductor, CMOS) is an image sensor used on a digital camera.

Fig. 1 schematically provides a schematic diagram of a deflection method for measuring refractive index. Incident light is incident on one surface of the chamber 120 containing the sample to be measured and the reference sample, which is close to the light source 110, at an incident angle alpha after being emitted from the light source 110, and is emitted at an emergent angle from the other surface far away from the light source 110 after being refracted by the sample to be measured and the reference sampleExit, and eventually are captured by imaging sensor 130.

The chamber 120 may house a reference sample and a sample to be measured, where the refractive index of the reference sample is n and the refractive index of the sample to be measured is n+Δn. As shown in fig. 1, the chamber 120 may have a quadrangular prism shape, and the inner space of the chamber 120 may be partitioned into two sub-chambers, for example, a first sub-chamber 120a and a second sub-chamber 120b. Both sub-compartments may be triangular prisms. The two sub-compartments may be used to house a reference sample and a sample to be measured, respectively.

The light source 110, the cabin 120 and the imaging sensor 130 may be sequentially arranged at intervals in the first direction, where a distance between the imaging sensor 130 and the light emitting surface of the cabin 120 in the first direction may be Z.

At one stage of the refractive index measurement process, the same reference sample is contained in both sub-compartments in the compartment 120. In this case, the zeroth incident point of the incident light beam incident on the imaging sensor 130 after being refracted by the sample in the chamber 120 is S ₀.

In another stage of the refractive index measurement process, the reference sample and the sample to be measured are respectively contained in two sub-compartments in the compartment 120, and in this case, the first incident point of the incident light beam incident on the imaging sensor 130 after being refracted by the sample in the compartment 120 is S ₁.

The distance between the zeroth incident point S ₀ and the first incident point S ₁ in the second direction is Δx, and the second direction is perpendicular to the first direction.

The difference between the refractive index (n+Deltan) of the sample to be measured and the refractive index (n) of the reference sample is Deltan, the incident angle alpha and the exit angle of the incident lightThe following relationship is approximately satisfied:

angle of emergence of incident ray 101 It can be approximately determined by the aforementioned interval Δx between the two incident points in the second direction and the interval Z between the imaging sensor 130 and the exit surface in the first direction, and further, a difference between the refractive index (n+ [ Δn) of the sample to be measured and the refractive index (n) of the reference sample is denoted as Δn:

as can be seen from the above equation, the measurement range of the refractive index of the sample to be measured is constrained by three variables Δx, Z and α. For a determined refractive index measurement device, the size of the imaging sensor 130 and the distance between the imaging sensor 130 and the exit surface are generally determined. The value of the distance Δx between different points of incidence on the imaging sensor 130 in the second direction is smaller than the maximum size of the imaging sensor 130 in the second direction, and is therefore also limited.

On the other hand, the incident point on the imaging sensor 130 will not appear in the form of a dot, and is more likely to be a light spot or an aperture, and thus, the measurement error of the pitch Δx of different incident points in the second direction may be larger, and accordingly, the measurement accuracy of the refractive index of the sample to be measured by this method will be limited.

In order to improve the measurement accuracy and measurement range of the refractive index measurement device, the application provides a refractive index measurement device which can be applied to liquid chromatography, in particular to refractive index measurement in high performance liquid chromatography (high performance liquid chromatography, HPLC).

As shown in fig. 2, the refractive index measurement device 200 provided by the embodiment of the present application may include a light source 210, a zone plate 220, a measurement chamber 230, an imaging sensor 240, and a moving platform 250.

The light source 210, zone plate 220, measurement bay 230, imaging sensor 240, and linear motion stage 250 may be sequentially aligned along the axial direction of zone plate 220 (the direction of OO' in fig. 2).

The light source 210 is configured to provide a measuring beam, and in some examples, the light source 210 may emit a coherent beam, that is, the measuring beam incident on the zone plate 220 is a coherent beam.

In some examples, the light source 210 may be a helium-neon (He-Ne) laser light source, and accordingly, the light emitted by the light source 210 is monochromatic light or single frequency light (monochromatic light). The wavelength range of the monochromatic light or the monochromatic light is narrow, for example, the difference between the longest wavelength and the shortest wavelength of the monochromatic light is less than 10 ^-12 m.

The measurement light may diffract as it passes through the zone plate 220, forming a plurality of diffracted light beams that may be incident on the measurement chamber 230. During measurement, diffracted light may pass through the reference sample and/or the sample under test contained in measurement chamber 230 and collect on imaging sensor 240. Here, the reference sample may also be referred to as a standard sample (STANDARD SAMPLE), which refers to a sample having a known refractive index, and is described in the following examples. The sample to be measured refers to a sample with a refractive index to be measured.

The imaging sensor 240 may be mounted on the mobile platform 250 and may be positioned along a track toward or away from the measurement bay 230. Because the refractive index of different samples to be measured is different, the deflection degree of the measuring light passing through the samples to be measured is different, and the position of the measuring light incident on the imaging sensor 240 may be different. For example, for measuring light rays with a large degree of deflection, the location of their incidence on the imaging sensor 240 may be located in the edge region of the imaging sensor, and may not even be captured by the imaging sensor 240. For measuring light rays that are deflected to a lesser extent, their location of incidence on the imaging sensor 240 may be in the central region of the imaging sensor. The imaging sensor 240 mounted on the moving platform 250 can move along a predetermined trajectory to facilitate capturing the measurement light refracted by the samples of different refractive indices.

In one aspect, the movable imaging sensor 240 may be disposed to improve the measurement range of the refractive index measurement device 200 provided by the embodiment of the present application to some extent. On the other hand, the distance that the imaging sensor 240 moves on the moving platform 250 can be quantitatively measured, and the higher the measurement accuracy of the distance that the imaging sensor 240 moves, the higher the measurement accuracy of the refractive index measurement device 200, so that the measurement accuracy of the refractive index measurement device 200 provided by the embodiment of the application is beneficial to improvement.

Fig. 3 schematically illustrates a structure of a zone plate 220 according to an embodiment of the present application, where (a) in fig. 3 is a front view of the zone plate 220, and (b) in fig. 3 is a left side view of the zone plate 220. Zone plate 220 may also be referred to as a linear fresnel zone plate 220, a cylindrical fresnel lens (CYLINDER FRESNEL LENSES) 220, or a fresnel lens 220. Zone plate 220 may be comprised of a plurality of fresnel zones (or zones) parallel to one another, each in a narrow stripe (or band), each of which may also be referred to as a slot. The wave bands 221 in fig. 3 are an example, and each wave band in fig. 3 can be regarded as a rectangular triangular prism.

In some examples, zone plate 220 may include a number of zones of 200, 300, 400, 500, or more, and in some scenarios, the total number of zones contained by zone plate 220 may also be expressed by the number of zones contained within a unit width of zone plate 220, e.g., 20/cm, 30/cm, 50/cm, 70/cm, 80/cm, 100/cm, etc.

Zone plate 220 may be made of a transparent material, such as polymethyl methacrylate (PMMA). Zone plate 220 may have a refractive index, such as 1.49, 1.52, or 1.60, etc.

Zone plate 220 has a thickness H, a length L, and a width W. The plurality of zones 221 included in zone plate 220 may be the same length as zone plate 220, all being L. The widths of the different bands may be different, and a plurality of bands are sequentially arranged along the width direction of the zone plate 220. In some examples, the zone plate 220 has a greater width of zones in the middle region and a smaller width of zones in the edge region. Illustratively, the zone plate 220 includes a plurality of zones having widths that gradually decrease from a middle region to an edge region of the zone plate 220.

One of the opposite sides of the zone plate 220 in the thickness direction may be regarded as a plane (e.g., the right side of (a) in fig. 3), and the other side may be regarded as a convex side (e.g., the left side of (a) in fig. 3). In some examples, light rays are incident from a convex side of the zone plate 220, exit from a planar side of the zone plate 220 after being diffracted by multiple zones on the zone plate 220.

Fig. 4 shows a schematic optical path of the parallel light after it is incident on the surface of the zone plate 220. For convenience of description, the width direction of the zone plate 220 is defined herein as the x-axis direction, the optical axis direction of the zone plate 220 or the thickness direction of the zone plate 220 is defined herein as the z-axis direction, and the length direction of the zone plate 220 is defined herein as the y-axis direction.

The parallel light beam enters from the convex side of the zone plate 220, is diffracted by a plurality of zones in the zone plate 220, exits from the plane side of the zone plate 220, and is converged at the main focus Z ₀ of the zone plate 220. Light rays incident from different wavebands exit the zone plate 220 and propagate to the focal point Z ₀ with different optical paths. Let x _i be the distance between the optical axis and the ith (i is an integer greater than or equal to 1) zone from the optical axis of zone plate 220 to both sides, the optical path of incident light, which enters from the ith zone and propagates to focal point Z ₀ after exiting from zone plate 220, be Si, which satisfies the following relationship:

S_i＝Z₀+iλ (3)

The perpendicular distance between each band in the zone plate 200 and the optical axis can be determined to approximately satisfy the following relationship with the wavelength λ and the focal length Z ₀ of the zone plate 200:

where Z ₀ is the focal length of zone plate 200, λ is the wavelength of the light, and x _i is the distance of the ith zone from the optical axis.

As can be further seen from the above equation, the optical path difference generated at the focal point by the diffracted light of two adjacent wavebands on the same side of the optical axis by the zone plate 220 is λ. In other words, in the case where the measurement light is coherent light, diffracted light of two adjacent bands generates pi phase difference at the focal point of the band 220. In other words, the measuring light is diffracted by the linear fresnel zone plate 220 (zone plate 220) to form a diffraction pattern (thin line) with alternate brightness and darkness on the focal plane.

Unlike a lens with converging action, the measuring light beam after being diffracted by the zone plate 220 may form a plurality of converging thin lines when being incident on the imaging sensor 240, instead of converging into one light spot. The distance between the thin lines of alternating light and dark is more easily determined, and thus the use of the zone plate 220 is advantageous for improving the accuracy of the refractive index measurement.

It should be noted that, the measuring light emitted from the zone plate may be converged not only on the focal plane where the primary focus is located, but also on the secondary focus (e.g.Etc.), it is understood that the effect of the convergence of diffracted light at different focal planes is different, i.e., the intensity of the diffraction pattern formed at different focal planes, etc.

The diffraction effects of different zone plates 220 for different wavelengths are different, and in some examples, zone plates 220 may diffract light waves having wavelengths in the range 400nm to 1100 nm.

Fig. 5 illustrates a structure of a measurement chamber 230 according to an embodiment of the present application, where the measurement chamber 230 may be used to hold a sample to be measured and/or a reference sample, and the measurement chamber 230 may also be referred to as a sample chamber 230. The measuring chamber 230 may be made of a material having a certain transparency, such as transparent glass or the like. In order to improve the corrosion resistance of the measuring chamber 230 to the sample, the measuring chamber 230 may also be made of a transparent material having a certain corrosion resistance.

In some examples, the measurement pod 230 may include a first pod 231 and a second pod 232, and the first pod 231 and the second pod 232 may each be triangular prism-shaped. The volume of the first receiving compartment 231 and the volume of the second receiving compartment 232 may be equal, or the first receiving compartment 231 and the second receiving compartment 232 may receive equal volumes of the sample.

In some examples, the measurement pod 230 is a triangular prism, the first pod 231 and the second pod 232 are each triangular prisms, and the volumes of the first pod 231 and the second pod 232 are each one-half the volume of the measurement pod 230.

The first receiving compartment 231 and the second receiving compartment 232 may each be provided with one or more sample inlets and outlets. In some examples, as shown in fig. 5, the first receiving compartment 231 may be provided with a first sample inlet 231a and a first sample outlet 232b, and the second receiving compartment 232 may be provided with a second sample inlet 232a and a second sample outlet 232b.

In some examples, the reference sample and the sample to be measured may both be liquid, or the reference sample may be a liquid sample to be measured as a solid, or the reference sample may be a solid sample to be measured as a liquid, or both the reference sample and the sample to be measured are solids.

The outer case of the measuring compartment 230 may have a certain transparency so that the measuring light may be incident into the measuring compartment 230 from the outside space of the measuring compartment 230 and exit after passing through the measuring compartment 230.

In some examples, the measurement pod 230 may be used only to house a sample to be measured, and the reference sample may be placed outside of the measurement pod 230. In particular, reference may be made to the relevant description of fig. 7 below.

The refractive index measuring device 200 may further include a driving control unit 260, and the driving control unit 260 may be used to drive the moving platform 250 to linearly move according to a preset track. Illustratively, the movable stage 250 may be linearly moved along the optical axis of the zone plate 220 under the driving of the driving control unit 260.

The refractive index measurement device 200 may further include a distance measurement unit 270, and the distance measurement unit 270 may be used to record and determine different positions of the mobile platform 250 at different times during the refractive index measurement, and thus may determine a moving distance of the mobile platform 250, or determine a distance of the mobile platform 250 from an initial position.

The moving distance of the moving platform 250 may have higher accuracy, thereby being beneficial to improving the accuracy of the measurement result of the refractive index measuring device. The driving control unit 260 may drive the moving platform 250 in a variety of different manners, such as magnetic driving, electric driving, etc. In some examples, the motion stage 250 may be a high precision (e.g., the resolution of the position may be well less than 1 nanometer) linear motion stage, the drive control unit 260 may be a stepper motor, or the like.

In some examples, in the event that the imaging sensor 240 located on the moving platform cannot receive the measuring light, the driving control unit 260 may drive the moving platform 250 to move in a direction of the optical axis toward the measuring chamber 230 or away from the measuring chamber 230 until the imaging sensor 240 can capture the measuring light.

In some examples, where the linear spot displayed on the imaging sensor 240 is blurred, the drive control unit 260 may drive the moving platform 250 to move in the direction of the optical axis toward the measurement pod 230 or away from the measurement pod 230 until the pattern displayed on the imaging sensor 240 is clear.

The imaging sensor 240 may be used to capture measurement light passing through the measurement chamber 230, or the imaging sensor 240 may be used to present linear fringes of measurement light after passing through the sample under test and/or the reference sample. The imaging sensor 240 may be mounted on the moving platform 250 such that the imaging sensor 240 may move along a corresponding track when the driving control unit 260 drives the moving platform 250. The distance measuring unit 270 may determine the moving distance of the imaging sensor 240 by determining the moving distance of the moving platform 250.

The imaging sensor 240 may be an optical sensor, and in some examples, the imaging sensor 240 may be a camera or imaging device including a CCD, or the imaging sensor 240 may be a camera or imaging device including a CMOS.

The imaging sensor 240 may be a camera including a CCD, for example. Before the measurement process begins, the camera may be initialized, calibrated, and the field of view (FOV) of the camera fixed. In some examples, the sampling rate of the camera and the size of the frame (picture) may also be set, for example, to 38fps, with the frame size being 2448×2048 pixels.

In some examples, the accuracy of the deflection value of the measuring light measured on the linear movement stage 250 by mounting the imaging sensor 240 may reach 2×10 ^-8 m.

Because different optical sensors have certain optical resolution, for different samples to be measured, the refractive indexes of the different optical sensors are different, and deflection of measurement light after passing through the samples to be measured is also different, so that under the condition that the positions of the imaging sensors 240 are fixed, straight lines generated by the measurement light corresponding to different samples to be measured may partially exceed the resolution of the imaging sensors 240 and cannot be captured by the imaging sensors 240.

The moving platform 250 is arranged, and the imaging sensor 240 is arranged on the moving platform 250, so that the refractive index measuring device provided by the application can capture straight stripes corresponding to different samples to be measured through the moving imaging sensor 240, and the refractive index measuring range of the measuring device can be enlarged.

The refractive index measuring device 200 may further comprise a monitoring and analyzing unit 280, which monitoring and analyzing unit 280 may be adapted to obtain diffraction patterns captured by the imaging sensor 240 and to determine differences in the deflection of the measuring light generated at different measuring process stages from the diffraction patterns of the different frames. In some examples, the monitoring and analysis unit 280 may also determine the refractive index of the sample to be measured from the acquired data.

The refractive index measuring device 200 according to the embodiment of the present application is further described below with reference to fig. 6 through a measurement process of an actual refractive index.

S601, a reference sample is loaded into the first sub-pod 231 and the second sub-pod 232, and a first diffraction pattern is acquired.

With the refractive index of the reference sample as a reference, both sub-compartments of the measurement compartment 230 may now be filled with the reference sample. When the measuring light is incident on the surface of the measuring capsule 230 near the zone plate 220 after being diffracted by the zone plate 220, the measuring light is incident into the measuring capsule 230 at an incident angle α as shown in fig. 6. The measuring light is emitted at an angle after passing through the reference sample loaded in the first and second sub-containers 231 and 232And (5) emergent.

In some examples, the reference sample may satisfy the condition that, after passing through the measurement bin 230, the diffracted rays of the measurement rays just converge on the principal focal plane of the zone plate 220. In other words, in the case where the imaging sensor 240 is located at the focal position (z=z ₀) of the zone plate 220 on the moving stage 250, if both sub-holding tanks in the measurement tank 230 are loaded with reference samples, the linear fringes produced by the diffraction of the measurement light can just be captured by the imaging sensor.

To facilitate measuring the difference in refractive index of the sample under test and the refractive index of the reference sample, the imaging sensor 240 may store a captured diffraction pattern, which may be referred to as a first diffraction pattern, which may be used to determine the location of the different linear fringes on the pattern.

S602, the first sub-accommodation chamber 231 is filled with the sample to be measured, the second sub-accommodation chamber 232 is filled with the reference sample, and the second diffraction pattern is obtained.

Before S602 is performed after the measurement operation of S601 is completed, the sample in the measurement chamber 230 may be purged by washing and drying (for example, drying with nitrogen gas) a plurality of times to reduce the influence of the sample residue on the accuracy of the measurement result.

The operation in S601 is repeated by replacing the reference sample in the first accommodation compartment 231 or the second accommodation compartment 232 in the measurement compartment 230 with the sample to be measured. The measuring light is emitted from the surface of the measuring cabin 230 far away from the zone plate 220, and the emission angle of the light isBy driving the imaging sensor 240 on the moving platform 250 to move, the linear fringes produced by the diffraction of the measuring light can be collected on the imaging sensor 240.

Similar to S601, the photosensitive element 240 may hold a captured diffraction pattern, which may be referred to as a second diffraction pattern, which may be used to determine the location of the different linear fringes on the pattern.

S603, the axial displacement of the imaging sensor 240 and the displacement of the same point (e.g., the same point on the same diffraction stripe) in the first diffraction pattern and the second diffraction pattern are acquired.

The distance by which the imaging sensor 240 moves in the positive direction of the optical axis can be determined as Δz by the distance measurement unit 270. The displacement of the same point can be determined from the first diffraction pattern and the second diffraction pattern described above.

According to the refraction ration (snell's law), when a light ray propagates from a first propagation medium into a second propagation medium (refractive index n), the lateral deflection displacement Δx of the light ray can be calculated by the following formula:

Where α is the angle of incidence, d is the wall thickness of the measurement chamber 230, n is the ratio of the refractive index of the test sample to the refractive index of the reference sample, T is the temperature in K, where n is also dependent on the temperature T. According to an embodiment of the present application, it may be assumed that the parameter N.A =n× sinn =0.45 when light is refracted between air (N.A) and the objective lens.

The longitudinal deflection Δz of the light ray can be calculated by the following equation:

Where d is the wall thickness of the measurement chamber 230 and n is the ratio of the refractive index of the test sample to the refractive index of the reference sample.

In some examples, to reduce the effect of the measurement pod 230 itself on the deflection of the measurement light, the deflection value Δz ₁ of the measurement light caused by the measurement pod 230 may be measured without the measurement pod 230 enclosing a reference sample or sample to be measured (i.e., empty). In the case that the reference sample or the sample to be measured is loaded in the measurement chamber 230, the measured longitudinal deflection value of the measuring light is Δz ₂, and the longitudinal deflection value Δz' of the measuring light caused by the reference sample or the sample to be measured can be calculated by the following formula:

Δz'=ΔZ₁-ΔZ₂ (8)

In some examples, for the case that the reference sample and the sample to be measured are both solid blocks, the measurement cabin 230 may not be provided in the refractive index measurement device 200, in this case, the refractive index measurement process of the sample to be measured is similar to that described above, and the settlement principle of the refractive index of the sample to be measured is also similar to that described above, so that for brevity, the description will not be repeated here.

S604, determining the refractive index difference between the sample to be tested and the reference sample and the refractive index of the sample to be tested.

The refractive index difference between the sample to be measured and the reference sample can be determined according to the measured deltax and deltaz, and the refractive index of the sample to be measured can be determined according to the refractive index of the reference sample. The detailed calculation process is further described below and is not described in detail here.

Another refractive index measurement device 700 provided in accordance with an embodiment of the present application is shown in fig. 7, wherein the refractive index measurement device 700 may include a light source 210, a zone plate 220, a reference sample 710, a measurement chamber 720, an imaging sensor 240, and a moving stage 250.

The nature and structure of the light source 210, zone plate 220, mobile platform 250 and imaging sensor 240 may be described in relation to fig. 6, and for brevity, will not be described in detail herein.

In some examples, the refractive index measurement device 700, the measurement chamber 720 may be used only to hold the sample to be measured, or the measurement chamber 720 may be provided with only one chamber for holding the sample to be measured. The reference sample 710 is not contained within the measurement chamber 720, but may be replaced with one or more (e.g., 3) pieces of flat glass having a known refractive index. In particular, the one or more flat glasses may be mounted vertically between the zone plate 220 and the measurement bay 720.

In other examples, the refractive index measurement device 700, the measurement chamber 720 may be configured to receive only the reference sample, or the measurement chamber 720 may be configured with only one chamber configured to receive the reference sample. The sample to be measured may not be accommodated in the measurement chamber 720, for example, in the case where the sample to be measured is a bulk solid, the reference sample may be disposed between the zone plate 220 and the measurement chamber 720.

In the process of measuring the refractive index using the refractive index measuring device 700, a measuring process may be performed with the measuring cell 720 empty and loaded with a sample, respectively, to obtain a diffraction linear fringe of the measuring light under the refraction of the reference sample and a diffraction linear fringe of the measuring light under the co-refraction of the reference sample and the sample to be measured, respectively. The refractive index of the sample to be measured is determined from the linear fringes obtained from the two measurements.

In some examples, the refractive index measurement device 700 may further include a driving unit, and the related descriptions of the functions of the driving unit are similar to those in the example shown in fig. 6, and are not repeated herein for brevity.

The embodiment of the application also provides a measuring device, which may include the refractive index measuring device 700 shown in fig. 7 and a processing device, where the processing device may determine the refractive index of the sample to be measured according to the information (such as a diffraction pattern, etc.) acquired by the refractive index measuring device 700.

In some examples, the processing means may comprise the monitoring and analysis unit and the distance measurement unit shown in the previous embodiments, which may be referred to in the relevant description above.

The refractive index measuring device 700 provided in fig. 7 uses a plate-shaped reference sample instead of the reference sample accommodated in the measuring chamber 720, which is beneficial to simplifying the structure of the measuring chamber 720, simplifying the operation process of refractive index measurement, and improving the accuracy of the refractive index measurement result to a certain extent.

Fig. 8 shows yet another refractive index measurement device 800 according to an embodiment of the present application, wherein the refractive index measurement device 800 includes a light source 210, an objective lens 810, a polarizer (polarizing filter) 820, a collimating mirror 830, a zone plate 220, a measurement pod 230, a moving stage 250, and an imaging sensor 240.

Wherein the objective lens 810 is disposed close to the light source 210, and a polarizer or polarizer 820 is located on a side of the objective lens 810 away from the light source 210. A collimating mirror 830 is arranged obliquely with respect to the optical axis, which collimating mirror 830 is used to direct the measuring light to the zone plate 220. The zone plate 220, the measurement chamber 230, and the imaging sensor 240 are sequentially disposed along the direction of the optical axis, and the imaging sensor 240 may be mounted on the moving platform 250 and configured to move along the direction of the optical axis.

In some examples, the refractive index measurement device 800 may further include an interference aperture (INTERFERENCE APERTURE) 840, the interference aperture 840 being disposed proximate to the zone plate 220 and on a side of the zone plate 220 remote from the measurement chamber 230. The measuring light rays are emitted by the collimating mirror 830, pass through the interference hole 840 and then are incident on the zone plate 240.

The properties and structures of the light source 210, the zone plate 220, the measurement chamber 230, the mobile platform 250, and the imaging sensor 240 are described in detail with reference to fig. 6, and are not described herein for brevity.

The polarizer 820, the collimating mirror 830, and the interference hole 840 in the refractive index measuring device 800 are explained below.

When the measuring light is incident on the polarizer 820, a portion where the vibration direction of the measuring light is not coincident with the polarization direction of the polarizer 820 cannot pass through the polarizer 820. In other words, the divergent measuring light may be filtered into polarized light having a vibration direction identical to the polarization direction of the polarizer 820 after passing through the polarizer 820.

The collimating mirror 830, which may be an adjustable parabolic mirror (adjustable parabolic mirror) in some examples, may modulate the divergent measuring light rays into light rays that are parallel to each other. The collimating mirror 830 may be disposed obliquely with respect to the optical axis of the zone plate 220, and the divergent measuring rays may be modulated into non-spherical parallel rays after incidence on the collimating mirror 830.

The measurement light rays parallel to each other need to pass through the interference hole 840 before entering the zone plate 220, that is, the measurement light rays having propagation paths within the aperture range of the interference hole 840 can pass through the interference hole 840, and the measurement light rays having propagation paths outside the aperture range of the interference hole 840 cannot pass through the interference hole 840.

In some examples, the refractive index measurement device 800 may further include a driving unit, and the related descriptions of the functions of the driving unit are similar to those in the example shown in fig. 6, and are not repeated herein for brevity.

The embodiment of the application also provides a measuring device, which may include the refractive index measuring device 800 shown in fig. 8 and a processing device, where the processing device may determine the refractive index of the sample to be measured according to the information (such as a diffraction pattern, etc.) acquired by the refractive index measuring device 800.

By arranging the polarizer 820, the collimating mirror 830 and the interference hole 840, the vibration direction, the incidence angle and the propagation range of the measuring light incident on the zone plate 220 can be regulated and controlled, so that the measuring light can be diffracted to form relatively clear linear stripes after passing through the zone plate 220 to a certain extent, and the measuring accuracy of the distance between the stripes is improved, thereby being beneficial to improving the accuracy of the measuring result of the refractive index measuring device.

As shown in fig. 9, a refractive index measuring device 900 according to an embodiment of the present application may further include a beam splitter and a reflective mirror, relative to the refractive index measuring device 800 shown in fig. 8.

Specifically, the refractive index measurement device 900 may include a light source 210, an objective lens 810, a polarizer 820, a beam splitter (beam splitter mirror) 910, a collimating mirror 830, a zone plate 220, a measurement pod 230, a moving stage 250, a mirror 920, and an imaging sensor 240.

Wherein the objective lens 810 is disposed close to the light source 210, and a polarizer or polarizer 820 is located on a side of the objective lens 810 away from the light source 210. Beam splitter 910 is positioned between polarizer 820 and collimating mirror 830. A collimating mirror 830 may be disposed obliquely with respect to the optical axis of the zone plate 220, the collimating mirror 830 being used to direct the measurement light to the zone plate 220.

The zone plate 220, the measurement chamber 230, and the mirror 920 may be sequentially disposed along the direction of the optical axis, and the mirror 920 may be mounted on the moving platform 250 and configured to be movable along the direction of the optical axis.

The imaging sensor 240 is disposed at the other side of the beam splitter 910 opposite to the polarizer 820. The measuring light exiting the collimating mirror 830 and entering the zone plate 220 may obtain a first-order diffracted light after being diffracted by the zone plate 220. The first-order diffracted light may be incident upon the mirror 920 after passing through the measurement chamber 230. The primary diffracted light may pass through the measurement chamber 230 after being reflected by the mirror 920 and be incident on the zone plate 220, and may be obtained by the diffraction of the zone plate 220, where the secondary diffracted light may be captured by the imaging sensor 240 after being reflected by the collimating mirror 830 and the beam splitter 910.

The moving stage 250 may be configured to move in the axial direction so that the aforementioned primary diffracted light can be converged on the mirror.

In some examples, the refractive index measurement device 900 may further include an interference aperture 840, the interference aperture 840 being disposed proximate to the zone plate 220 and on a side of the zone plate 220 remote from the measurement chamber 230. The measuring light rays are emitted by the collimating mirror 830, then pass through the interference hole 840 and then enter the zone plate 220.

The nature and structure of polarizer 820, collimating mirror 830 and interference aperture 840 are described with reference to those described above with reference to fig. 8, and for brevity, no further description is provided herein.

The beam splitter 910 is disposed between the polarizer 820 and the collimating mirror 830, and the measuring light may pass through the beam splitter 910 and propagate to the collimating mirror 830 when the measuring light is incident on the first surface of the beam splitter 910 after passing through the polarizer 820. When the second diffracted light beam is reflected by the collimating mirror 830 and then enters the second surface (the second surface is the opposite surface to the first surface) of the beam splitter 910, the second diffracted light beam may be reflected on the second surface, so as to adjust the propagation direction, which is beneficial to be captured by the imaging sensor 240.

In some examples, the refractive index measurement device 900 may further include a driving unit, and the related descriptions of the functions of the driving unit are similar to those in the example shown in fig. 6, and are not repeated herein for brevity.

The embodiment of the application also provides a measuring device, which may include the refractive index measuring device 700 shown in fig. 9 and a processing device, where the processing device may determine the refractive index of the sample to be measured according to the information (such as the diffraction pattern) acquired by the refractive index measuring device 900.

In the refractive index measuring device 900 provided in this embodiment, the measuring light passes through the measuring chamber 230 twice in sequence, in other words, the measuring light deflects twice before being captured by the imaging sensor 240, and both of the deflections are caused by refraction of the sample to be measured contained in the measuring chamber 230. Compared with a method for measuring the refractive index of a sample to be measured by only one deflection, the method for measuring the refractive index by two deflection is beneficial to reducing relative errors caused by factors such as measurement errors and the like and is beneficial to improving the accuracy of the measurement result of the refractive index measuring device 900. On the other hand, by adjusting the propagation path of the measurement light using the mirror, it is advantageous to improve the utilization of the internal space of the refractive index measuring device 900 to some extent, and to reduce the volume of the refractive index measuring device 900.

Taking the refractive index measuring device 200 as an example, simulation results shown in fig. 10 and 11 can be obtained by performing simulation using Zemax OpticStudio. Fig. 10 shows an optical device corresponding to the refractive index measuring device 200 used in the simulation, and fig. 11 shows a diffraction pattern captured on the imaging sensor 240 obtained by the simulation. As shown in fig. 11, the simulated diffraction pattern substantially exhibited linear fringes with alternating light and dark.

Fig. 12 and 13 show diffraction patterns of the measurement light captured by the imaging sensor 240 during the refractive index measurement test. Wherein fig. 12 can be regarded as a diffraction pattern of only the reference sample loaded in the measurement chamber 230, and fig. 13 can be regarded as a diffraction pattern of both the reference sample and the sample to be measured loaded in the measurement chamber 230.

In connection with fig. 12 and 13, the bright linear stripe in the center area of fig. 12 has moved to the left edge area in fig. 13. Similarly, the linear stripes in the left region of fig. 12 are not shown in the screen shown in fig. 13, and the linear stripes in the right region of fig. 12 correspondingly move to the left of the screen to form the screen shown in fig. 13.

In some examples, the distribution of the plurality of bands along the x-axis direction on the zone plate 220 may be generally expressed by the following formula, and fig. 14 exemplarily provides a schematic structural diagram of the zone plate 220 under the distribution rule.

For the zone plate 220 with the above-mentioned zone distribution rule, the function T (x ₀) of the diffraction pattern obtained by measuring the light after being diffracted by the zone plate can be obtained by performing convolution processing on the aperture function of the zone plate 220. The convolution result is developed according to the fourier series, and the following formula can be obtained:

The above can be considered as a series expansion of the measured light transmittance distribution using a type III sinc function of the zone plate. If the width of the zone of zone plate 220 is small, the diffraction pattern captured by imaging sensor 240 will be a series of peak functions, which corresponds to the convolution result of the narrow flat-squared pulse (narrow flat-topped square pulse) function of T (x ₀). In some examples, the diffraction pattern may be adjusted to peak as much as possible by tailoring the size of the zones of zone plate 220, controlling the distance of zone plate 220 from imaging sensor 240, and measuring the wavelength of the light.

As described in the above experiment, the zone plate 220 is disposed at a position of z=0 on the Z axis, and the zone plate 220 is irradiated with a parallel light beam parallel to the optical axis of the zone plate 220, the distribution function U (x _i,Z₀) of diffracted light shown in the following formula can be obtained.

Where λ is the wavelength of the measuring light and k is the wave vector of the plane wave. Let n=1 in the above equation, which can be used to explain the converging light beam focused at the principal focal length, the focal point of the light beam is shown as Z ₀ in fig. 4.

In addition, the light generated by diffraction of zone plate 220 is concentrated at the position of the secondary focus, i.e1, ±2..Degree.) are located. That is, the zone plate 220 may be used not only to concentrate parallel incident light at the position of the primary focus (primary focal plane), but also to concentrate parallel incident light at the position of the secondary focus. In the above formula, not only n is 1, but also n is 0, ±3, ±5.± (2 m-1) contributes to the diffraction pattern of the zone plate 220.

Fig. 15 (a) is a diffraction pattern that the imaging sensor 240 can capture when the imaging sensor 240 is placed in the zone plate 220 at the location of the principal focal plane (z=z ₀), and fig. 15 (b) is a relative value of the intensity of each linear stripe in the pattern.

Fig. 16 (a) is a diffraction pattern that the imaging sensor 240 can capture when the imaging sensor 240 is placed in the zone plate 220 at the secondary principal focal plane (z=3z ₀), and fig. 16 (b) is a relative value of the intensity of each linear stripe in the pattern.

In some examples, equation (11) may be simplified where the initial phases of the parallel beams incident on zone plate 220 are the same, resulting in the following equation (the last term in equation (11) is the total complex field of the original object wave except the constant term and the exponential term, which is the ideal term of the equation):

wherein A and B are both constant coefficients.

In some examples, the optical system provided in the refractive index measurement device provided by the present application may determine the object scanning diffraction fringe pattern by using a time-varying fresnel zone plate (TDFZP) equation.

Taking the physical structure of the refractive index measuring device 200 shown in fig. 4 as an example, a point light source located on the optical axis can be expanded to form a plane wave. The pattern shown in fig. 12 or 13 may be regarded as a diffraction pattern formed at a certain time after the scanning beam passes through the zone plate 220, for example, at time t=t ₀ =0. The zone plate 220 in this case may also be referred to as a static zone plate or a static fresnel zone plate. If the time varies according to equation (11), a linear stripe that continuously moves toward the middle of the pattern can be obtained.

When studying the quadratic spatial dependence of a zone plate, the spatial rate of change of the zone plate phase (e.g. the rate of change along the x-axis) can be calculated by:

This is a local fringe frequency that increases linearly with spatial coordinates. In other words, for linear fringes that are farther from the center of the region, the higher the local spatial frequency. Accordingly, as shown in fig. 17 and 18, for one fixed (local) point on the imaging sensor 240, depth information of the point can be acquired. In particular, the depth information of the fixed point may be determined by looking for the local fringe frequency of the light of a given wavelength. For point sources on the axis (e.g., point sources with zero ordinate and Z ₀ distance from the imaging sensor), the local fringe frequency of the aforementioned fixed point also depends on the center of the area. When the zone plate is disposed on the optical axis, as shown in fig. 17 and 18, depth information of the partial fringes is encoded in the linear zone plate.

Fig. 17 (a) is a diffraction pattern that the imaging sensor 240 can capture when the imaging sensor 240 is placed in the zone plate 220 at the location of the principal focal plane (z=z ₀), and fig. 17 (b) is a relative value of the spatial frequency distribution of each linear stripe in the pattern.

Fig. 18 (a) shows a diffraction pattern that the imaging sensor 240 can capture when the imaging sensor 240 is placed in the zone plate 220 at the secondary main focal plane (z=3z ₀), and fig. 18 (b) shows the relative value of the spatial frequency distribution of each linear stripe in the pattern.

Fig. 17 and 18 show the local spatial frequency of the zone plate 220 along the optical axis, the zone plate characteristics as a function of depth parameters, when we change the value of Z, for example, adjust Z from Z ₀ to 3Z ₀, the local fringes change from dense to sparse. This conclusion can also be drawn from equation (13).

Thus, one or more regions may be formed on the imaging sensor 240, each of the one or more regions containing lateral position information and depth information for each individual point, from the local fringe frequency of the linear fringes. From the lateral position information and depth information of the points, the distance between the object point and the plane in which the imaging sensor is located can be determined. The distance between the two is very important for the refractive index measuring device provided by the application to determine the refractive index of the sample to be measured. Based on the above theory, the measurement of the fringe offset of the platform can be controlled by using MATLAB codes.

The imaging sensor 240 may be configured to receive the converging light fringes from the zone plate and convert the light fringes into a digital signal. The refractive index measuring device provided by the application can be used for detecting the movement stripe pattern of the object and calculating the displacement of the movement of the object. Specifically, moving objects can be detected in the order of images, processed by MATLB software and using an optical flow method.

In some examples, the foregoing monitoring and analyzing unit 280 may be used to monitor the change of pixel positions in the moving stripe from the initial stage to the final stage, and the monitoring and analyzing unit 280 may also divide the video signal into a plurality of images (frames).

In some examples, the image size may be 2448 x 2048 pixels.

The first image or initial position 1910 in fig. 19, which may also be referred to as a reference position, may be used to represent a reference pixel value for comparison purposes, and the second image or target position 1920, which may also be referred to as an "input", the second image 1920 matches the first image 1910, and the second image 1920 contains a moving object therein. The starting position of the light beam on the imaging sensor 240 may be regarded as a zero point, and in order to measure the difference in refractive index between the sample to be measured and the reference sample, it may be assumed that the deflection distance of the light beam at the starting position on the imaging sensor is zero. By comparing the first image and the second image and calculating the difference in pixel values, the distance between the pixel points, the number of images included in each period of time, the speed at which the object moves, and the amount of light deflection due to the difference in refractive index between the sample to be measured and the reference can be calculated, thereby obtaining the refractive index of the sample.

Also shown in fig. 19 are integer pixels and a pixel array determined according to a conventional motion estimation method. Displacement vectors between the first image 1910 and the second image 1920 can be obtained by optical flow processingThe refractive index of the sample to be measured may be calculated by determining the distance of corresponding pixels within the first image 1910 and the second image 1920.

The movable imaging sensor 240 may capture target light and reference light fringes in a sequence of frames that may be used to measure object movement. Specifically, the movement of the object may be measured by measuring the displacement of the light stripe at the position of the imaging sensor 240 surface. The displacement of the light fringes can vary with the moving imaging sensor 240. The displacement of the light ray stripes can be calculated by the Euclidean distance formula. Taking the first pixel point 1911 and the second pixel point 1921 in the two continuous frame images in fig. 19 as an example, the distance between the two pixel points can be calculated by the following equation. In some examples, first pixel point 1911 and second pixel point 1921 may represent positions of corresponding pixel points on the initial stage and final stage moving object, respectively.

Wherein x _i and y _i are positions of pixel points, i is equal to or more than 0 and equal to or less than n-1, j is equal to or less than i+1 and equal to or less than n, and n is the total number of captured pictures.

Fig. 20 shows a comparison of the measured displacement of the stripe and the authenticated displacement of the moving platform, and as can be seen from fig. 20, the displacement of the stripe measured by the refractive index measuring device provided by the application has a good linear relationship with the displacement of the moving platform, and the measurement error is smaller.

The moving platform 250 may be directly driven by the control driving unit 270 by magnetic force or other means, and thus the longitudinal displacement amount of the image may be easily determined by using the movable platform 150. In some examples, the refractive index measurement device provided by the application can use a high-resolution physical instrument optical nano encoder (Physik Intrumente Optical nanometrology Encoder, PIOne) with smaller linear error and a mobile platform 250 with higher precision, and the resolution of the displacement measurement result of the linear stripes can reach 2× ^-8 m.

The amount of displacement of the linear fringes is proportional to the change in position of the light and thus also to the difference in refractive index. The method for measuring the displacement of the linear stripes is beneficial to improving the accuracy of the refractive index measurement result of the refractive index measurement device provided by the application and expanding the refractive index measurement range of the refractive index measurement device provided by the application.

The refractive index measuring device provided by the application is suitable for refractive index testing of liquid and flat plate samples, and is especially suitable for liquid chromatography and flat plate samples with wider thickness and size ranges. The device can be suitable for measuring liquids with different refractive indexes, and the preparation method of the sample to be measured is simple. The device has simple structure, high accuracy of the measurement result and wide measurement range. In some examples, the refractive index measurement device provided by the embodiment of the application can be applied to refractive index measurement of HPLC.

Fig. 21 exemplarily provides a relationship between a measured value and an authenticated value of a refractive index of a sample to be tested, including, but not limited to, distilled water, ethanol, a fused silica plate, BK7 borosilicate glass, and a Sapphire window (Sapphire window), which is tested using the refractive index measuring apparatus provided by the present application. As can be seen from FIG. 21, the measured value of the refractive index of the sample to be measured has a good linear relationship with the authentication value, and the measurement error is small.

The uncertainty of the measured refractive index of the sample to be measured by the refractive index measuring device provided by the application is determined by the minimum change of the longitudinal displacement on the diffraction pattern, and the minimum change corresponds to the change of the pixel position which can be detected by the imaging sensor. By employing a high-precision and high-resolution moving platform, the refractive index structure measured by the refractive index measuring device provided by the application can reach 10 ^-4 refractive index units (REFRACTIVE INDEX UNIT, RIU), and the precision can be further improved by using a more sensitive sensor. Meanwhile, as the moving platform has a longer length, for samples to be measured with different refractive indexes, the imaging sensor positioned on the moving platform has enough displacement space to measure the longitudinal displacement (for example, 20mm to 150 mm) on the diffraction pattern, so that the refractive index measuring device provided by the application can measure the refractive index of the samples to be measured with a wider range.

Reference in the specification to "one embodiment" or "some embodiments" or the like means that a particular feature, structure, or characteristic described in connection with the embodiment is included in one or more embodiments of the application. Thus, appearances of the phrases "in one embodiment," "in some embodiments," "in other embodiments," and the like in the specification are not necessarily all referring to the same embodiment, but mean "one or more but not all embodiments" unless expressly specified otherwise. The terms "comprising," "including," "having," and variations thereof mean "including but not limited to," unless expressly specified otherwise.

The foregoing is merely illustrative of the present application, and the present application is not limited thereto, and any person skilled in the art will readily recognize that variations or substitutions are within the scope of the present application. Therefore, the protection scope of the present application shall be subject to the protection scope of the claims.

Claims

1. A refractive index measuring device is characterized by comprising a light source (210), a zone plate (220) and an imaging sensor (240),

The light source (210) is used for emitting measuring light;

The zone plate (220) comprises a plurality of prisms parallel to each other;

the imaging sensor (240) is configured to receive the measuring light passing through the zone plate (220), a reference sample and/or a sample to be measured.

2. The measurement device of claim 1, wherein the diffraction pattern of the measurement light rays on the imaging sensor comprises a plurality of linear light spots.

3. The measurement device according to claim 1 or 2, further comprising a measurement compartment (230), the measurement compartment (230) being adapted to house a reference sample and/or a sample to be measured, the measurement compartment (230) being located at a side of the zone plate (220) remote from the light source (210).

4. A measuring device according to claim 3, characterized in that the device further comprises a moving platform (250), the moving platform (250) being located on a side of the measuring capsule (230) remote from the zone plate (220), the imaging sensor (240) being located on the moving platform (250), the imaging sensor (240) being movable on the moving platform (250) in the direction of the optical axis of the zone plate (220).

5. The measurement device of claim 3, further comprising a first mirror (920), a second mirror, a beam splitter (910), and a moving platform (250),

The mobile platform (250) is positioned at one side of the measuring cabin (230) far away from the zone plate (220), the first reflecting mirror (920) is positioned on the mobile platform (250), and the first reflecting mirror (920) can move on the mobile platform (250) along the optical axis direction of the zone plate (220);

The optical axis of the second reflector is inclined to the optical axis of the zone plate (220);

the light source (210) and the imaging sensor (240) are respectively positioned at two sides of the beam splitter (910);

The measuring light rays are incident to a first reflecting mirror (920) along a first light path, and the measuring light rays are reflected by the first reflecting mirror (920) and then are incident to the imaging sensor (240) along a second light path;

The first light path sequentially passes through the beam splitter (910), the second reflector, the zone plate (220) and the measurement cabin (230), and the second light path sequentially passes through the measurement cabin (230), the zone plate (220), the second reflector and the second beam splitter.

6. The measurement device of claim 3, further comprising a second mirror disposed proximate to the zone plate (220), the measurement light rays being incident on the imaging sensor (240) along a third optical path,

The third light path sequentially passes through the second reflecting mirror, the zone plate (220) and the measuring cabin (230).

7. The measurement device according to claim 5 or 6, wherein the second mirror is a collimating mirror (830).

8. The measurement device according to any one of claims 3 to 7, characterized in that the measurement compartment (230) comprises a first accommodation compartment (231) and a second accommodation compartment (232), the first accommodation compartment (231) and the second accommodation compartment (232) being adapted to accommodate the reference sample and/or the sample to be measured.

9. The measuring device according to any one of claims 3 to 7, wherein,

The measuring chamber (230) is used for accommodating the sample to be measured, the reference sample is plate-shaped, and the reference sample is positioned between the zone plate (220) and the measuring chamber (230), or

The measuring cabin (230) is used for accommodating the reference sample, the sample to be measured is plate-shaped, and the sample to be measured is positioned between the zone plate (220) and the measuring cabin (230).

10. The measurement device of any one of claims 1 to 9, wherein the measurement light is coherent light and the wavelength of the measurement light is within a threshold range.

11. The measurement device according to any one of claims 1 to 10, further comprising a polarizer (820), the polarizer (820) being arranged close to the light source (210).

12. The measurement device according to any one of claims 1 to 11, further comprising a drive control unit (260), the drive control unit (260) being adapted to drive the mobile platform (250).

13. A measuring device comprising processing means for determining the refractive index of a sample to be measured from the measuring means and measuring means according to any one of claims 1 to 12.

14. A method of measuring refractive index, comprising:

acquiring a first diffraction pattern corresponding to a reference sample, wherein the first diffraction pattern comprises a first group of linear stripes, and the first group of linear stripes comprises first stripes;

Obtaining a second diffraction pattern corresponding to the sample to be detected, wherein the second diffraction pattern comprises a second group of linear stripes, and the second group of linear stripes comprises second stripes;

determining the refractive index of the sample to be measured according to the refractive indexes of the first diffraction pattern, the second diffraction pattern and the reference sample;

15. The method of measuring according to claim 14, wherein,

The acquiring a first diffraction pattern corresponding to a reference sample includes:

Obtaining a first diffraction pattern formed after a diffraction ray passes through the reference sample, wherein the diffraction ray is formed by diffracting a measuring ray through a zone plate;

The obtaining a second diffraction pattern corresponding to the sample to be measured comprises the following steps:

And obtaining the second diffraction pattern formed after the diffracted light passes through the sample to be detected and the reference sample.

16. The method of measuring according to claim 15, wherein,

The acquiring a first diffraction pattern corresponding to a reference sample further includes:

acquiring the first diffraction pattern at a first position in the optical axis direction of the zone plate;

the obtaining a second diffraction pattern corresponding to the sample to be measured further includes:

and acquiring the second diffraction pattern at a second position in the optical axis direction of the zone plate.

17. The measurement method according to any one of claims 14 to 16, wherein the determining the refractive index of the sample to be measured from the refractive indices of the first diffraction pattern, the second diffraction pattern, and the reference sample includes:

determining the refractive index of the sample to be measured according to the first distance, the second distance and the refractive index of the reference sample;

The first distance is the distance between the positions of the imaging sensor when the first diffraction pattern and the second diffraction pattern are acquired, and the second distance is the distance between the projections of the first stripe and the second stripe on the imaging sensor.

18. The method of measuring according to claim 17, wherein,

The imaging sensor comprises an electrically coupled device CCD.

19. The method of measuring according to claim 18, wherein,

The second distance is determined according to a distance between a first pixel point and a second pixel point on the imaging sensor, the first pixel point is used for indicating the position of the first stripe, and the second pixel point is used for indicating the position of the second stripe.

20. The method of any one of claims 17 to 19, wherein the refractive index of the sample to be measured is determined according to the formula:

wherein Δx is the second distance, α is an incident angle of a measuring light on a measuring cabin, d is a wall thickness of the measuring cabin, n is a ratio of a refractive index of the sample to be measured to a refractive index of the reference sample, Δz is the first distance, and the measuring cabin is used for accommodating the reference sample and/or the sample to be measured.