CN107664648B - A kind of X-ray differential phase contrast microscopic system and its two-dimensional imaging method - Google Patents

Abstract

The invention discloses an X-ray differential phase contrast microscope system and a two-dimensional imaging method thereof. The X-ray differential phase contrast microscope system includes: a light source for generating X-rays; Condenser, central diaphragm, beamsplitter grating, pinhole, sample stage, objective, annular analysis grating and imaging detector. The beneficial effects of the present invention are: the X-ray differential phase contrast microscope system can realize phase contrast quantitative imaging only by adding a beam splitting grating and a ring analysis grating to the traditional X-ray microscope, and has a simple structure and is easy to popularize advantage. In addition, the X-ray light source, condenser lens, and beam splitting grating can be integrated into an X-ray ring grating source element, and the length of the entire X-ray differential phase contrast microscope system can be further shortened, which not only reduces the manufacturing cost of the X-ray microscope system, but also The utilization efficiency of light can also be further improved.

Description

An X-ray differential phase contrast microscope system and its two-dimensional imaging method

technical field

The invention relates to the technical field of nano-resolution X-ray microscope imaging, in particular to an X-ray differential phase contrast microscope system and a two-dimensional imaging method thereof.

Background technique

The effect of matter on X-rays can be represented by the refractive index, n=1-δ+iβ, where δ is the attenuation rate of the real part of the refractive index, and β is the absorption term. The physical meaning of δ is that the X-rays passing through a unit length of matter move relative to the wavefront generated by the X-rays passing through a unit length of vacuum; the physical meaning of β is the decrease in the amplitude of X-rays passing through a unit length of matter. According to the physical meaning of δ and β, after the X-ray passes through a sample, its complex amplitude can be expressed as in

It is the change amount of the X-ray phase passing through the sample relative to the X-ray phase passing through the vacuum of the same length, referred to as the phase shift, and l is the path of the X-ray passing through the sample; because the integral value outside the sample is zero, the upper and lower limits of the integral can be expanded to infinity;

is the absorption, and μ is the linear absorption coefficient. Because δ is more than three orders of magnitude larger than β for light elements in the hard X-ray band, phase changes have the potential to generate light intensity signals that are much larger than absorption changes. Dutch scientist Zernik (Zernik) is the first person in phase contrast imaging. As early as 1935, he proposed the theory and method of phase contrast microscopy in the visible light band, for which he won the 1953 Nobel Prize in Physics. At present, people have successfully extended the Zernike phase contrast microscope method to the X-ray microscope with a zone plate as the objective lens, and successfully developed an X-ray phase contrast microscope that uses a phase shift ring to obtain phase contrast, as shown in Figure 1. The microscope includes an X-ray light source 10, a condenser lens 1, a central diaphragm 2, a pinhole 3, a sample stage 4, an objective lens 5, a phase shift ring 6 and an imaging detector 7 in sequence according to the X-ray propagation direction. However, the phase-contrast imaging invented by Zernike has obvious shortcomings: its application range is limited to weak-phase samples with negligible absorption. When the absorption cannot be ignored, it cannot distinguish between the light intensity response caused by absorption and the light intensity response caused by phase shift; when the sample is not a weak phase object, especially when the phase shift of the sample exceeds π/4, the relationship between phase shift and light intensity response The linear relationship is no longer satisfied, and the light intensity response will oscillate with the phase period. These deficiencies make it difficult to quantitatively study the density structure of samples.

Contents of the invention

One of the objectives of the present invention is to provide an X-ray differential phase contrast microscope system capable of quantitatively studying the density structure of a sample with higher sensitivity than traditional absorption X-ray microscopes.

The second object of the present invention is to provide a two-dimensional imaging method for the high-sensitivity X-ray differential phase contrast microscope system.

According to one aspect of the present invention, an X-ray differential phase contrast microscope system is disclosed, which may include: a light source for generating X-rays; and a condenser lens, a central diaphragm, and a beam splitting grating arranged in sequence along the X-ray propagation direction , pinhole, sample stage, objective lens, annular analysis grating and imaging detector; Wherein, the light source that described X-ray generation is monochromatic X-ray light source; Described condenser is ellipsoid capillary, tapered capillary, zone plate or other The X-ray optical element with focusing function is used to generate a focused beam for illuminating the sample; the central diaphragm is located at the center of the condenser exit and is used to block the through light from the X-ray light source to form a hollow cone beam for illuminating the sample; The beam splitting grating is an absorption grating with a period of micron scale, located behind the central diaphragm at the exit of the condenser, and is used to split the hollow cone beam from the condenser and the central diaphragm, making it a hollow cone beam with a spatially periodic structure ; The pinhole, located behind the beam splitting grating, is used to block the through light and stray light from the X-ray light source; the sample stage, located on the object plane, is used to carry the sample, and can translate and rotate the sample; the objective lens It is a zone plate or other optical element with X-ray lens imaging function, which is used to magnify the nanoscale sample structure on the object plane into an image with micron scale structure on the image plane, and make the beam splitting grating hollow The annular part of the cone beam illumination forms an annular grating image and an annular grating image beam near the rear focal plane of the objective lens; the annular analysis grating is an absorption grating with a period of micron or submicron order, located near the rear focal plane of the objective lens, and its shape and The size is the same as the annular grating image near the rear focal plane of the objective lens, and is used to filter the annular grating image beam attached to the rear focal plane of the objective lens; the imaging detector is located on the image plane, and is used to photograph samples 2D magnified image of .

Optionally, the beam splitting grating and the ring analysis grating are made of gold or other heavy metals.

Optionally, when the thicknesses of the beam splitting grating and the annular analysis grating are not large, the thickness of the beam splitting grating is an odd multiple of the π phase shift, and the thickness of the annular analysis grating is an even multiple of the π phase shift.

According to another aspect of the present invention, a two-dimensional imaging method for the X-ray differential phase contrast microscope system is disclosed, comprising the following steps:

S1, turn on and adjust the light source: aim the X-ray beam generated by the light source at the condenser;

S2, adjust the condenser, central diaphragm and pinhole: make the hollow cone beam generated by the condenser and the central diaphragm align with the position of the sample on the sample stage, so that the central diaphragm and the pinhole block the direct passage from the X-ray light source light and stray light;

S3, adjusting the objective lens: aligning the imaging light beam formed by the objective lens with the imaging detector located on the image plane;

S4, feeding into the beam splitting grating: after the central diaphragm at the exit of the condenser, feed into the beam splitting grating, so that the hollow cone beam illuminates the annular part of the beam splitting grating to form a ring grating image and a ring grating image beam near the rear focal plane of the objective lens;

S5, feed and adjust the ring analysis grating: make the ring analysis grating align with the ring grating image formed by the beam splitting grating near the rear focal plane of the objective lens, adjust the direction of the ring analysis grating bars so that the ring analysis grating bars are parallel to the beam splitting grating grid;

S6, angle measurement signal response curve: move the beam splitting grating step by step along the direction perpendicular to the optical axis and the grating bars, so that the annular grating image of the beam splitting grating has a shear displacement relative to the annular analysis grating, and the imaging detector is used to measure the angle on the image plane. Obtain the angle signal response curve of the brightness changing with the displacement of the annular grating image;

S7, fitting the angle signal response curve with a cosine curve: the angle signal response curve is similar to a cosine curve, and the measured angle signal response curve is fitted with a cosine curve to obtain an analytical expression of a cosine curve;

S8, take a two-dimensional enlarged image of the sample: fix the annular grating image of the beam splitting grating at the valley position, uphill position, peak position, and downhill position of the angle signal response curve respectively, place the sample on the sample stage, and photograph the sample The valley zoom image, uphill zoom image, peak zoom image, downhill zoom image;

S9, extract the quantitative two-dimensional image of the sample in the object space: extract the absorption image, refraction image and scattering image of the sample in the object space from the valley magnification image, uphill magnification image, peak magnification image, and downhill magnification image of the sample ; Extract the absorption, refraction and scattering images of the sample in the object space from any three of the four magnification images.

In the step S6, considering the influence of the refraction and scattering of the sample's focal depth thin beam, that is, considering the influence of the angle signal generated by the sample on the imaging process, the sample uses the angle signal function f(x _o , y _o , ψ _x ) is expressed as

Where (x _o , y _o , z _o ) are the spatial coordinates of the sample, M(x _o , y _o ), θ _x (x _o , y _o ) and are the variances of the absorption, refraction and scattering angles of the sample, respectively, and are also the absorption, refraction and scattering images of the sample in the object space required in the two-dimensional quantitative imaging of the X-ray differential phase contrast microscope, and their expressions are

Where (x _o , y _o , z _o ) are the spatial coordinates at the object plane, μ is the linear absorption coefficient, δ is the attenuation rate of the real part of the refractive index, and ω _x is the linear scattering coefficient perpendicular to the direction of the grating bars.

What measure in described step S6 is the angle signal response curve, and it is analytically expressed with fitting cosine curve as

or expressed as

Wherein η is the diffraction efficiency of the objective lens, B ₀ is the brightness of the incident beam at the object plane, and _xp is the position coordinate at the annular analysis grating, is the angular displacement of the annular grating image displacement relative to the object plane, d _o is the object distance of the sample relative to the objective lens, p is the period of the annular analysis grating, is the average value of the angle signal response curve, R _max and R _min are the maximum and minimum values of the angle signal response curve, respectively, is the visibility of the angle signal response curve, n is the modulation parameter, and n=0, 1, 2, 3 correspond to the valley response curve, upslope response curve, peak response curve and downslope response curve respectively.

In said step S8, the two-dimensional enlarged image taken by the imaging detector is described by the angle signal imaging equation, and the angle signal imaging equation is the convolution of the angle signal function and the angle signal response function, and its expression is:

Where (x _o , y _o ) is the coordinates of the object plane, ( _xi , y _i ) is the coordinates of the image plane, η is the diffraction efficiency of the objective lens, B ₀ is the brightness of the incident beam at the object plane, n=0,1,2,3 Corresponding to the valley magnification imaging equation, uphill magnification imaging equation, peak magnification imaging equation and downhill magnification imaging equation.

In the step S8, the annular grating image of the beam splitting grating is fixed at the valley of the angle signal response curve, the sample is placed on the sample stage, and the imaging detector captures the enlarged image of the valley of the sample, and its expression is

In the step S8, the annular grating image of the beam splitting grating is fixed on the slope position of the angle signal response curve, the sample is placed on the sample stage, and the imaging detector captures the uphill enlarged image of the sample, its expression for

In the step S8, the annular grating image of the beam-splitting grating is fixed at the peak position of the angle signal response curve, the sample is placed on the sample stage, and the imaging detector captures an enlarged image of the peak position of the sample, and its expression is

In the step S8, the annular grating image of the beam splitting grating is fixed at the downhill position of the angle signal response curve, the sample is placed on the sample stage, and the imaging detector captures the downhill enlarged image of the sample, its expression for

because

B _V ( _xi ,y _i )+B _P ( _xi ,y _i )＝ _BU ( _xi ,y _i )+B _D ( _xi ,y _i )

Therefore, the three images in the valley magnified image, uphill magnified image, peak magnified image, and downhill magnified image are independent, and any one of them can be expressed by the other three images; among the above formulas, (x _i , y _i ) are the coordinates of the image plane, η is the diffraction efficiency of the objective lens, B ₀ is the brightness of the light beam illuminating the object plane, is the average value of the angle signal response curve, R _max and R _min are the maximum and minimum values of the angle signal response curve respectively, is the visibility of the angle signal response curve, d _o is the object distance of the sample relative to the objective lens, and p is the ring analysis grating period.

In the step S9, the method of extracting the absorption image, refraction image and scattering image of the sample in the object space from the valley magnification image, uphill magnification image, peak position magnification image and downhill magnification image of the sample is as follows:

The formula for extracting the absorption image of the sample in the object space is

The formula for extracting the refraction image of the sample in object space is

Under the condition that the scattering can be ignored, the formula for extracting the refraction image of the sample in the object space is simplified as

The formula for extracting the scattering image of the sample in the object space is

Under the condition that the refraction can be ignored, the formula for extracting the scattering image of the sample in the object space is simplified as

In the above formulas, (x _o , y _o ) are object plane coordinates, ( _xi , y _i ) are image plane coordinates, d _o is the object distance of the sample relative to the objective lens,

As an optional implementation, the X-ray light source, condenser lens and beam splitting grating can be integrated into an element of an X-ray ring grating source whose period is on the order of microns. At this time, at the exit of the X-ray ring grating source Place two ring-shaped light holes in sequence along the optical axis, so that the light beam emitted by the ring-shaped grating source passes through the two ring-shaped light holes to form a hollow cone beam that illuminates the sample, and forms a ring grating near the rear focal plane of the objective lens. The source image and the annular grating source image light beam, the shape and size of the annular analysis grating are the same as the annular grating source image.

The X-ray differential phase contrast microscope system disclosed by the invention can realize phase contrast quantitative imaging only by adding a beam splitting grating and a ring analysis grating to the traditional X-ray microscope, and has the advantages of simple structure and easy popularization. In addition, the X-ray light source, condenser lens, and beam splitting grating can be integrated into an X-ray annular grating source element, and two annular apertures are arranged in sequence along the optical axis at the exit of the annular grating source, and the entire X-ray differential phase contrast The length of the microscope system can be further shortened, not only can reduce the manufacturing cost of the X-ray microscope system, but also can further improve the light utilization efficiency, which has broad application prospects.

Description of drawings

It should be understood that in all the following drawings, the same reference numerals indicate the same or corresponding components and features.

Fig. 1 is a schematic diagram of an optical path of an X-ray phase contrast microscope system in the prior art.

FIG. 2 is a schematic diagram of an X-ray differential phase contrast microscope system according to an embodiment of the present invention.

Fig. 3 is a flowchart of a two-dimensional imaging method of an X-ray differential phase contrast microscope system according to an embodiment of the present invention.

Fig. 4 is a schematic diagram of refraction angle signal imaging of an X-ray differential phase contrast microscope system according to an embodiment of the present invention.

Fig. 5 is a schematic diagram of scattering angle signal imaging of an X-ray differential phase contrast microscope system according to an embodiment of the present invention.

Fig. 6 is a curve diagram of four angle signal response functions of the X-ray differential phase contrast microscope system.

Fig. 7 is a schematic diagram of an X-ray differential phase contrast microscope system based on a ring grid source according to another embodiment of the present invention.

A brief description of each reference sign in the accompanying drawings is as follows:

1: Condenser

2: Central aperture

3: pinhole

4: Sample stage

5: objective lens

6: Phase shift ring

7: Imaging detector

3': beam splitting grating

6': Ring analysis grating

10: X-ray light source

10': X-ray ring grid source

20: The first annular light hole

30: the second annular light hole.

Detailed ways

The X-ray differential phase contrast microscope system of the embodiment disclosed in the present invention and the two-dimensional imaging method used in the system will be described in detail below with reference to the accompanying drawings.

FIG. 2 is a schematic diagram of an X-ray differential phase contrast microscope system according to an embodiment of the present invention. As shown in Figure 2, the X-ray differential phase contrast microscope system 100 includes an X-ray light source 10 (not shown in the figure), a condenser lens 1, a central diaphragm 2, a beam splitting grating 3', and a pinhole in sequence according to the X-ray propagation direction. 3. A sample stage 4, an objective lens 5, an annular analysis grating 6' and an imaging detector 7 are formed. The nature, structure and function of each component are described as follows:

X-ray source 10: The X-ray objective lens is generally a diffractive optical element with lens imaging function, such as a zone plate, so the X-ray source 10 used in the X-ray differential phase contrast microscope system can be a monochromatic X-ray source, such as electron impact X-ray sources with characteristic spectral lines produced by metal targets, laser plasma X-ray sources, and synchrotron radiation monochromatic X-ray sources.

Condenser 1: It can be an ellipsoidal capillary, a tapered capillary, a zone plate or other X-ray optical elements with a focusing function, and its function is to provide a focused illumination beam for the sample.

Central diaphragm 2: located at the center of the exit of condenser 1, it is used to block the excessively strong through light from the X-ray source from illuminating the sample and detector, so that the focused beam illuminating the sample becomes a hollow cone beam.

Beam splitting grating 3': It can be an absorption grating with a period of micron order, located behind the central diaphragm 2 at the exit of the condenser 1, and is used to split the hollow cone beam from the condenser 1 and the central diaphragm 2, making it a Hollow cone beam with spatially periodic structure.

Pinhole 3: Located in front of the sample stage behind the beam splitting grating 3', it is used to block the excessively strong through light and stray light from the X-ray light source to illuminate the sample and detector.

Sample stage 4: Located between the pinhole 3 and the objective lens 5, it is used to carry the sample, translate and rotate the sample, and the plane perpendicular to the optical axis is called the object plane.

Objective lens 5: It can be an optical element with X-ray lens imaging function, such as a zone plate, which is a circular grating whose period gradually becomes smaller as the radius increases. It has a lens function for monochromatic X-rays, so it is called X-ray Lens; it has two functions. The first function is to magnify and image the nanometer-scale sample structure on the object surface on the image plane to form an image with a micron-scale structure. The annular portion illuminated by the hollow cone beam is imaged near the rear focal plane of the objective lens 5 to form an annular grating image and an annular grating image beam.

Annular analysis grating 6': It can be an absorption grating with a period of micron or submicron level, located near the rear focal plane of the objective lens 5, and its shape and size are the same as the annular part of the beam splitting grating 3' illuminated by the hollow cone beam when there is no sample The annular grating image near the rear focal plane of the objective lens 5 is the same, and is used to filter the annular grating image beam near the rear focal plane of the objective lens 5 .

Imaging detector 7: Arranged by two-dimensional area array pixels (such as X-ray CCD), each pixel has the function of independently detecting light intensity, which is used to measure the angle signal response curve, detect the spatial position change of light intensity, and photograph samples The magnified image of , the plane where its position is perpendicular to the optical axis is called the image plane.

Further, although the beam splitting grating 3' and the annular analysis grating 6' are both absorption gratings, when the thickness of the grating is not large, some X-rays will pass through the grating strips, causing the passing X-rays to generate a phase shift, In order to avoid the negative effect brought by the phase shift, the thickness of the beam splitting grating 3' is an odd multiple of the π phase shift, and the thickness of the annular analysis grating 6' is an even multiple of the π phase shift.

In addition, the beam splitting grating 3' and the ring analysis grating 6' are made of gold or other heavy metals.

The X-ray differential phase contrast microscope system of the embodiment of the present invention is a traditional X-ray microscope combined with a beam splitting grating 3' and an annular analysis grating 6'. On the basis of the imaging process of the traditional X-ray microscope system, an additional Two aspects of physical content are discussed: first, consider the influence of refraction and scattering of the narrow beam at the focal depth of the sample, that is, consider the influence of the angle signal generated by the sample on the imaging process; second, consider the angle signal of the sample to regulate the annular The shear displacement of the grating image on the annular analysis grating makes the angle signal obtain the light intensity response.

Fig. 3 is a flow chart of a two-dimensional imaging method of an X-ray differential phase contrast microscope system according to an embodiment of the present invention. As shown in Fig. 3, the two-dimensional An imaging method, comprising the steps of:

S1, turn on and adjust the light source: aim the X-ray beam generated by the light source at the condenser;

S2, adjust the condenser, central diaphragm and pinhole: make the hollow cone beam generated by the condenser and the central diaphragm align with the position of the sample on the sample stage, so that the central diaphragm and the pinhole block the direct passage from the X-ray light source light and stray light;

S3, adjusting the objective lens: aligning the imaging light beam formed by the objective lens with the imaging detector located on the image plane;

S4, feeding into the beam splitting grating: after the central diaphragm at the exit of the condenser, feed into the beam splitting grating, so that the hollow cone beam illuminates the annular part of the beam splitting grating to form a ring grating image and a ring grating image beam near the rear focal plane of the objective lens;

S5, feed and adjust the ring analysis grating: make the ring analysis grating align with the ring grating image formed by the beam splitting grating near the rear focal plane of the objective lens, adjust the direction of the ring analysis grating bars so that the ring analysis grating bars are parallel to the beam splitting grating grid;

S6, angle measurement signal response curve: move the beam splitting grating step by step along the direction perpendicular to the optical axis and the grating bars, so that the annular grating image of the beam splitting grating has a shear displacement relative to the annular analysis grating, and the imaging detector is used to measure the angle on the image plane. The angle signal response curve of the brightness changing with the image displacement of the ring grating is obtained; the angle signal response curves measured on each pixel of the imaging detector are basically the same, and when the angle signal response curve is measured, the stronger the light intensity signal obtained by the detector, the more The denser the moving step of the beam grating, the higher the signal-to-noise ratio of the measured data; when the annular grating image of the beam splitting grating and the annular analysis grating completely overlap, the beam passing rate of the annular grating image is the lowest, and the entire field of view becomes a dark field. The lowest position of the signal response curve corresponds to the valley position; when the annular grating image of the beam splitting grating and the annular analysis grating are staggered by a quarter period, half of the annular grating image beam passes through, and the other half is blocked, and the entire field of view becomes a semi-bright field , corresponding to the uphill position of the angle signal response curve; when the annular grating image of the beam splitting grating and the annular analysis grating are staggered by one-half period, the beam passing rate of the annular grating image is the highest, and the entire field of view becomes a bright field, which is consistent with the angular signal response The highest position of the curve corresponds to the peak position; when the annular grating image of the beam splitting grating and the annular analysis grating are staggered by three quarters of the period, half of the beam of the annular grating image is blocked, and the other half passes through, and the entire field of view becomes a semi-bright field, which is the same as The angle signal corresponds to the downhill position of the shift curve;

S7, fitting the angle signal response curve with a cosine curve: the angle signal response curve is similar to a cosine curve, and the measured angle signal response curve is fitted with a cosine curve to obtain an analytical expression of a cosine curve; wherein, the fitting angle signal response When the curve is drawn, the stronger the light intensity signal obtained by the detector, the denser the moving step of the beam splitting grating, the higher the signal-to-noise ratio of the measured data, and the more accurate the fitted cosine curve;

S8, take a two-dimensional enlarged image of the sample: fix the annular grating image of the beam splitting grating at the valley position, uphill position, peak position, and downhill position of the angle signal response curve respectively, place the sample on the sample stage, and photograph the sample The valley zoom image, uphill zoom image, peak zoom image, downhill zoom image;

S9, extract the quantitative two-dimensional image of the sample in the object space: extract the absorption image, refraction image and scattering image of the sample in the object space from the valley magnification image, uphill magnification image, peak magnification image, and downhill magnification image of the sample ; Because the sum of the valley magnification and the peak magnification is equal to the sum of the uphill magnification and the downhill magnification, only three of the above four magnifications are independent, and can be obtained from the four magnifications. Extract the absorption image, refraction image and scattering image of the sample in the object space from any three magnified images.

In the step S6 of the two-dimensional imaging method of the X-ray differential phase contrast microscope system, the influence of refraction and scattering of the narrow beam in the focal depth of the sample is considered, that is, the influence of the angle signal generated by the sample on the imaging process is considered, so , it is necessary to establish a mathematical model of the sample’s action on X-rays, and obtain the mathematical expression of the sample’s angle signal function. The specific method is as follows:

Define the Cartesian coordinate system (x _o , y _o , z _o ) of the sample, and define a point in the sample. In two-dimensional imaging, a point (x _o , y _o ) on the object surface where the sample is located is not a two-dimensional geometric point , but an object area element ΔxΔy centered on (x _o , y _o ), the size of Δx and Δy is determined by the numerical aperture of the objective lens and the resolution of the detector. It is specially stated here that the object point mentioned below means the object area element.

Absorption (including inelastic scattering) is a dissipation process in which X-ray energy is converted into heat energy in the sample. A point (x _o , y _o ) in the sample absorbs the focal depth thin beam, causing the brightness of the focal depth thin beam to attenuate. The absorption of a point (x _o , y _o ) in the sample to the focal depth thin beam passing through this point can be expressed as:

in Represents the Dirac function (to avoid confusion with the real part of the refractive index decay rate δ, marked with the top band represents the Dirac function), is the deflection angle vector of the depth-of-focus thin beam incident on the sample,

Where μ(x _o , y _o , z _o ) is the linear absorption coefficient of the sample. The physical meaning of formula (1) is that the energy loss of the depth-of-focus thin beam is caused by absorption, which leads to the decrease of the brightness of the depth-of-focus thin beam, but does not change the propagation direction of the depth-of-focus thin beam, which is a zero-angle signal. Equation (1) can also be expressed in component form:

where ψ _x and ψ _y are respectively Components along the x _o direction and y _o direction.

Fig. 4 is a schematic diagram of refraction angle signal imaging of the X-ray differential phase contrast microscope system according to an embodiment of the present invention, and the arrows in the partially enlarged diagram depict the refraction direction of the depth-of-focus thin beam. As shown in Figure 4, the hollow cone beam focused on the sample from the beam splitting grating can be split into multiple depth-of-focus beamlets on the object plane, and each depth-of-focus beamlet illuminates an object point (x _o , y _o ), The object point (x _o , y _o ) refracts the focal depth thin beam passing through this point, causing the annular grating image near the rear focal plane of the objective lens to shift relative to the annular analysis grating, so that the image point (x The number of photons of _i , y _i ) increases or decreases, and the relationship between (x _o , y _o ) and ( _xi , y _i ) is a conjugate imaging relationship, which uniquely corresponds to each other.

Refraction is a process of energy conservation. According to Fig. 4, the refraction of a point (x _o , y _o ) in the sample at the focal depth of the thin beam can be expressed as

in is the refraction angle vector, and the physical meaning of formula (4) is that refraction changes the propagation direction of the depth-of-focus thin beam, but does not lose the energy of the depth-of-focus thin beam, and does not cause the brightness of the depth-of-focus thin beam to decrease. Equation (4) can also be written in component form,

Where θ _x (x _o , y _o ) and θ _y (x _o , y _o ) are respectively Components along the x-direction and y-direction. Let δ(x _o ,y _o ,z _o ) represent the attenuation rate of the real part of the refractive index of the sample, then The component expression in (x _o , y _o ) Cartesian coordinate system is

FIG. 5 is a schematic diagram of scattering angle signal imaging of an X-ray differential phase contrast microscope system according to an embodiment of the present invention. The arrows in the partially enlarged figure depict that scattering causes the focal depth thin beam to expand from one propagation direction to multiple directions. As shown in Figure 5, the hollow cone beam focused on the sample from the beam splitting grating can be split into multiple depth-of-focus beamlets on the object plane, and each depth-of-focus beamlet illuminates an object point (x _o , y _o ), The object point (x _o , y _o ) scatters the focal depth thin beam passing through this point, which causes the fringes of the annular grating image near the back focal plane of the objective lens to be blurred, so that the image point (x _i , y The number of photons in _i ) increases or decreases, and the relationship between (x _o , y _o ) and ( _xi , y _i ) is a conjugate imaging relationship, which uniquely corresponds to each other.

Scattering (referring to the refraction caused by small particles inside the area element) is a process of energy conservation. The difference between scattering and refraction is that refraction studies an area element on the sample surface as a whole, that is, the sample surface The last area element is used as a prism, and the scattering uses this area element as a piece of frosted glass to study the inhomogeneous properties inside it, such as particles, bubbles, microcrystals, impurities, etc. inside the area element. Therefore, for each area element, the exiting depth-of-focus beamlet has only one refraction direction, but multiple scattering directions. In other words, scattering is a process in which the focal depth of a thin beam is dispersed. Because the sample has a certain thickness, along the propagation direction of the focal depth thin beam inside the area element, the distribution of each small particle is random, and the refraction produced by the two small particles before and after is independent of each other, and each refraction of the small particle deviates from the depth of focus thin beam The angle of the incident direction is random, so according to the central limit theorem, the scattering angle is a normal statistical distribution centered on the incident angle, and the variance can be used to describe the distribution range of the scattering angle.

According to Figure 5, when the depth-of-focus thin beam enters the sample, as the depth-of-focus thin beam travels through the sample, the refraction events of small particles inside the area element continue to occur, and the variance of the scattering angle gradually widens. Since the angle signal of the sample is collected by a grating, it is necessary to decompose the scattering angle signal. The component expression of the scattering of the focused deep thin beam at the sample point (x _o , y _o ) in the (x _o , y _o ) Cartesian coordinate system is

in and is the variance of the scattering angle generated by the overall thickness of the sample at point (x _o , y _o ) in the x _o direction and y _o direction, respectively. According to Equation (7) and Equation (8), although scattering does not lose beam energy, scattering causes an increase in the spread angle of the narrow beam at the depth of focus. make represents the scattering angle variance of the overall thickness of the sample, the subscript κ can be x or y, then is the differential scattering angle variance of a series of Δz _o slices along the X-ray path The sum of , so the variance of the scattering angle across the thickness of the sample can be expressed as the integral of the variance of the differential scattering angle, namely:

where ω _κ (x _o , y _o , z _o ) is the linear scattering coefficient perpendicular to the beam along the κ direction.

Considering the above three effects comprehensively, the effect of a point (x _o , _{y o )} in the sample on the focal depth thin beam passing through this point can be expressed as _:

where the subscript κ can be x or y.

According to formula (10), it can be seen that along the κ direction perpendicular to the beam, the outgoing X-rays carry three angle signals of the sample, zero angle signal: M(x _o , y _o ), refraction angle signal: θ _κ (x _o ,y _o ), scattering angle signal: All of them can be expressed as line integrals, which lays a mathematical foundation for computer tomography to use projection data to obtain the three-dimensional structure of samples.

In the step S6 of the two-dimensional imaging method of the X-ray differential phase contrast microscope system, considering the angle signal of the sample to regulate the shear displacement of the ring grating image of the beam splitting grating on the ring analysis grating, the angle signal is obtained by optical Strong response. Therefore, it is necessary to establish the angle signal response function of the X-ray differential phase contrast microscope system, and the specific method is as follows:

In a conventional X-ray microscope, the beam propagation process without a sample can be described as follows. The diffuse beam from the X-ray source is converged by the condenser and blocked by the central diaphragm to form a hollow cone beam focused on the sample. The focused hollow cone beam can be divided into multiple focal depth thin beams on the object surface according to the spatial coherence area. A depth-of-focus thin beam illuminates an object point position. Inside the depth-of-focus thin beams is coherent light, while two adjacent depth-of-focus thin beams are incoherent. After passing through the object plane, each depth-of-focus thin beam becomes a diffused coherent hollow cone beam. After the focusing effect of the objective lens, each diffused coherent hollow cone beam becomes a focused coherent hollow cone beam. Each image point is formed. In the process of propagation, there is coherence inside the coherent hollow cone beams, but incoherence between two coherent hollow cone beams. When focusing, each coherent hollow cone beam forms a thin beam of focal depth and is separated from each other on the object plane and image plane, but before and after focusing, such as in the position of the condenser lens, the central diaphragm, the objective lens, and the back focal plane of the objective lens, these coherent Hollow cone beams are mutually coincident in space. In the traditional X-ray microscope imaging theory, only the absorption and phase shift of the sample are considered, and the refraction and scattering of the sample are not considered, or even if there is refraction and scattering in the sample, there is no response mechanism that converts refraction and scattering into light intensity. The traditional X-ray microscope imaging theory believes that after the sample is placed, the beam propagation process is the same as when there is no sample, except that the beam brightness decreases and the phase shift is caused by the absorption of the sample.

A beam splitting grating is inserted behind the exit of the condenser lens and the central diaphragm of the traditional X-ray microscope system, and an annular analysis grating is inserted near the rear focal plane of the objective lens, forming the X-ray differential phase contrast in an embodiment of the present invention microscope. The function of the beam splitting grating is to split the hollow cone beam into hollow cone beams with spatial structure, and make the annular part of the beam splitting grating illuminated by the hollow cone beam form a ring grating image and a ring grating image beam near the rear focal plane of the objective lens. The shape and size of the annular analysis grating are exactly the same as that of the annular part of the beam splitting grating illuminated by the hollow cone beam to form an annular grating image near the rear focal plane of the objective lens, and its function is to filter the annular grating image beam near the rear focal plane of the objective lens . It can be seen that in the X-ray differential phase contrast microscope, the beam propagation process when there is no sample can be described as follows: the hollow cone beam from the condenser and the central diaphragm is split by the beam splitting grating to form a beam with a spatial structure focused on Hollow cone beam of the sample. According to the spatial coherence area on the object plane, the focused hollow cone beam is divided into multiple depth-of-focus thin beams, and each depth-of-focus thin beam illuminates an object point. Inside the depth-of-focus thin beams is coherent light, while two adjacent depth-of-focus thin beams are incoherent. After passing through the object plane, each depth-of-focus thin beam becomes a diffused coherent hollow cone beam. After the focusing effect of the objective lens, each diffused coherent hollow cone beam becomes a focused coherent hollow cone beam, not only in the objective lens Respective annular grating image beams are formed near the back focal plane, and image points are formed on the image plane. Although the annular grating image beams formed by the coherent hollow cone beams near the back focal plane of the objective lens coincide with each other, they propagate independently and are independent of each other.

If the sample is placed on the object surface of the X-ray differential phase contrast microscope, a point in the sample will refract and scatter the focal depth thin beam passing through this point, causing the focal depth thin beam to produce two angle signals of deflection and divergence , these two kinds of angle signals will inevitably cause the position shift and fringe blurring of the annular grating image of the depth-of-focus thin beam on the annular analysis grating, which will cause the number of photons passing through the annular analysis grating to increase or decrease, and the angle signal of a point in the sample will be The light intensity response is obtained on the image points of the image plane. Therefore, the filtering effect of the ring analysis grating on the ring grating image of the beam splitting grating provides an angle signal response imaging mechanism for the X-ray differential phase contrast microscope. Because the refraction of the sample causes the position of the annular grating image of the beam-splitting grating to move, which is equivalent to moving the beam-splitting grating artificially when there is no sample, so when there is no sample, the beam-splitting grating can be artificially moved, and the annular grating can be measured with one pixel of the imaging detector The light intensity response generated by the shear displacement between the image and the annular analysis grating is used to measure the angular signal response function of the X-ray differential phase contrast microscope to a point on the object surface. As for the fringe blurring of the ring grating image of the beam splitting grating caused by sample scattering, it can be regarded as the irregular shear displacement of each part of the ring grating image relative to the ring analysis grating, and the resulting light intensity response can also be measured by the angle signal The response function is explained. Because the ring grating images of each object point are coincident near the rear focal plane of the objective lens, a beam splitting grating and a ring analysis grating can be used to convert the angle signal of each object point on the object plane into each image point on the image plane light intensity response. In other words, the mechanism of converting the refraction angle signal and scattering angle signal at each point of the sample into the response light intensity is the same, and has a unified angle signal response function. Therefore, when there is no sample, the beam-splitting grating can be manually stepped once, and each pixel of the imaging detector can be used to measure the respective angular signal response functions in parallel.

Since the beam splitting grating and the annular analysis grating can only produce light intensity responses to the angle signal perpendicular to the direction of the grating bars, but have no response to the angle signal parallel to the direction of the grating bars, so only the angle signal function perpendicular to the direction of the grating bars needs to be considered . According to the ring grating image of the beam splitting grating and the shear displacement of the ring analysis grating, it can be known that the measured angle signal response curve is a periodic oscillation curve. Since both refraction and scattering are small-angle signals, it is not the entire angle signal response curve that is at work, but the angle signal response curve is locally at work. Therefore, according to the different start points of the beam-splitting grating step scan, the angle signal response function curves can be divided into four types:

(i) The ring-shaped grating image of the beam-splitting grating and the ring-shaped analysis grating completely coincide as the zero point. With the step-by-step scanning of the beam-splitting grating, the ring-shaped grating image of the beam-splitting grating undergoes a shear displacement relative to the ring analysis grating, and the measured brightness gradually increases The curve is called the valley response curve;

(ii) Taking the staggered quarter period between the annular grating image of the beam splitting grating and the annular analysis grating as the zero point, along with the step scanning of the beam splitting grating, the shear displacement of the annular grating image of the beam splitting grating relative to the annular analysis grating occurs along the Along the direction of increasing shear displacement, the measured brightness gradually increases linearly, and along the direction of shear displacement decreases, the measured brightness gradually decreases linearly, which is called the uphill response curve;

(iii) The ring grating image of the beam splitting grating and the ring analysis grating are staggered by half of the period as the zero point. With the step scanning of the beam splitting grating, the ring grating image of the beam splitting grating has a shear displacement relative to the ring analysis grating. The curve that the brightness gradually decreases is called the peak response curve;

(iv) Taking the staggered three-quarters cycle of the annular grating image of the beam splitting grating and the annular analysis grating as the zero point, along with the step scanning of the beam splitting grating, the shear displacement of the annular grating image of the beam splitting grating relative to the annular analysis grating occurs along the Along the direction of shear displacement increase, the measured brightness gradually decreases linearly, and along the direction of shear displacement decreases, the measured brightness gradually increases linearly, which is called the downhill response curve.

Fig. 6 is a curve diagram of four angle signal response functions of the X-ray differential phase contrast microscope system. According to Figure 6, it can be seen that the angle signal response curve is similar to a cosine curve, which can be approximated by fitting a cosine curve, so that the angle signal response curve can be analytically expressed by a fitted cosine curve, and

or expressed as

Where x _p is the position coordinates of the annular analysis grating, is the angular displacement of the annular grating image displacement of the beam splitting grating relative to the object plane, d _o is the object distance of the sample relative to the objective lens, p is the period of the annular analysis grating, is the average value of the angle signal response curve, R _max and R _min are the maximum and minimum values of the angle signal response curve, respectively, is the visibility of the angle signal response curve, n is the modulation parameter, and n=0, 1, 2, 3 respectively correspond to (a) valley response curve, (b) uphill response curve, (c) peak position in Figure 6 Response curves and (d) downhill response curves.

According to the derivation process of the angle signal response function, it can be seen that the angle signal response function describes the angle signal of an object point and regulates the pass rate of the imaging photon number of the object point when passing through the annular analysis grating.

According to the constant brightness theorem, in an ideal optical system without energy attenuation, brightness is a conserved quantity. Although the transmission efficiency of a real optical system cannot reach 100%, the brightness of a real optical system on the image plane can be regarded as the product of the plane brightness and a transmission efficiency. In the X-ray differential phase contrast microscope system, from the object plane to the image plane, in addition to the decrease in brightness caused by the absorption of the sample, the main contribution to the decrease in brightness comes from the diffraction efficiency of the objective lens and the pass rate of the annular analysis grating, so the brightness of the image plane can be Look at the brightness of the crop surface and the product of the diffraction efficiency of the objective lens and the pass rate of the annular analysis grating. When there is no sample, assuming that the brightness of the incident beam at the object plane is B ₀ , and the diffraction efficiency of the objective lens is η, then the brightness of the beam-splitting ring grating image near the rear focal plane of the objective lens is ηB ₀ . According to formula (12), when there is no sample, the pass rate of the annular analysis grating is the angle signal response function, so the brightness behind the annular analysis grating, or the brightness of the image plane is

Equation (13) is the angular signal response function considering the diffraction efficiency of the objective lens.

In step S8 of the two-dimensional imaging method of the X-ray differential phase contrast microscope system, the two-dimensional enlarged image captured by the imaging detector is described by an angle signal imaging equation. Therefore, it is necessary to establish an angle signal imaging equation, and the specific method is as follows:

For sample magnification imaging, the imaging of each pixel of the detector to each point of the object plane is parallel and independent of each other. Therefore, the X-ray differential phase contrast can be established only by discussing the imaging of a pixel of the detector to a point in the sample. Microscopy imaging equation. Because the mechanism of refraction and scattering conversion into light intensity at each point of the sample is the same, and it has translation invariance on the object plane, the X-ray differential phase contrast microscope can be deduced according to the convolution of the above angle signal function and angle signal response function. Angle signal imaging equation. It needs to be specially explained here that the convolution operation is the convolution operation of the refraction angle, scattering angle and angle signal response function in the angle signal function, and the convolution operation has nothing to do with the spatial coordinates; the absorption in the angle signal function is a zero-angle signal and does not participate in convolution operation.

After the sample is put in, the absorption of the focal depth thin beam passing through this point by an object point (x _o , y _o ) on the object surface will cause the brightness of the annular grating image to decrease near the rear focal plane of the objective lens, and the refraction will cause The position of the ring grating image will be shifted near the surface, and the scattering will cause the ring grating image to appear fringe blur near the back focal plane of the objective lens. After the ring analysis grating filter, the brightness of the image point ( _xi , y _i ) on the image plane is the convolution of the angle signal function and the angle signal response function. Since the beam splitting grating and the annular analysis grating can only produce light intensity responses to the angle signal perpendicular to the direction of the grating bars, but have no response to the angle signal parallel to the direction of the grating bars, so only the angle signal function perpendicular to the direction of the grating bars needs to be considered and the convolution of the angle signal response function. Therefore there is

Where (x _o , y _o ) is the coordinates of the object plane, ( _xi , y _i ) is the coordinates of the image plane, B( _xi , y _i ,ψ _x ) is the depth of focus passing through the object point (x _o , y _o ) The brightness of the thin beam at the image point ( _xi , _yi ). Equation (17) is the angle signal imaging equation established by the X-ray differential phase contrast microscope.

In the step S8 of the two-dimensional imaging method of the X-ray differential phase contrast microscope system, the annular grating image of the beam splitting grating is fixed at the valley position of the angle signal response curve, the sample is placed on the sample stage, and the imaging The detector captures the magnified image of the valley of the sample. The specific method of taking a two-dimensional magnified image in the experiment is as follows:

Before placing the sample, the ring grating image is fixed at the valley of the angle signal response curve, that is, ψ _x = 0, n = 0, and then the sample is placed, and the detector can capture the enlarged image of the valley of the sample, and its expression is

In the step S8 of the two-dimensional imaging method of the X-ray differential phase contrast microscope system, the annular grating image of the beam splitting grating is fixed at the uphill position of the angular signal response curve, and the enlarged image of the sample uphill position is taken The method: before placing the sample, fix the ring grating image at the uphill position of the angle signal response curve, that is, set ψ _x = 0, n = 1, then place the sample, the detector can take the uphill magnified image of the sample, Its expression is

In the step S8 of the two-dimensional imaging method of the X-ray differential phase contrast microscope system, the method of fixing the ring grating image of the beam splitting grating at the peak position of the angle signal response curve, and taking the enlarged image of the peak position of the sample : Before placing the sample, fix the ring grating image at the peak position of the angle signal response curve, that is, set ψ _x = 0, n = 2, and then place the sample, the detector can capture the peak magnified image of the sample, its expression for

In the step S8 of the two-dimensional imaging method of the X-ray differential phase contrast microscope system, the annular grating image of the beam splitting grating is fixed at the downhill position of the angular signal response curve, and the downhill magnified image of the sample is taken The method: before placing the sample, fix the ring grating image at the downhill position of the angle signal response curve, that is, set ψ _x = 0, n = 3, and then place the sample, the detector can take a downhill magnified image of the sample, Its expression is

In the step S9 of the two-dimensional imaging method of the X-ray differential phase contrast microscope system, the sample is extracted from the valley magnified image, the uphill magnified image, the peak magnified image, and the downhill magnified image of the sample. The absorption image, refraction image and scattering image method of the object space are as follows: the formula for extracting the absorption image of the sample in the object space is:

The formula for extracting the refraction image of the sample in object space is:

Under the condition that the scattering can be ignored, the formula for extracting the refraction image of the sample in the object space is simplified as:

The formula for extracting the scattering image of the sample in the object space is:

Under the condition that the refraction can be ignored, the formula for extracting the scattering image of the sample in the object space is simplified as:

In addition, as an optional implementation, the X-ray light source 10, the condenser lens 1, and the beam-splitting grating 3' can be integrated into one component, that is, an X-ray ring grating source with a period of micron order, as shown in FIG. 7 . At the same time, two annular light-through holes 20 and 30 are placed in sequence along the optical axis at the exit of the X-ray annular grid source, so that the light beam from the X-ray annular grid source passes through the two annular light-through holes 20 and 30 to form an illumination sample. It also has a hollow cone beam with a spatially periodic structure, and forms a ring source image and a ring source image beam near the rear focal plane of the objective lens 5. The shape and size of the ring analysis grating 6' are the same as that of the ring source image. The X-ray differential phase contrast microscope system 100' based on the ring grid source can further shorten the length of the entire X-ray differential phase contrast microscope system, which can not only reduce the manufacturing cost of the X-ray microscope system, but also improve the light utilization efficiency. It can be further improved and has broad application prospects.

Due to the above-mentioned two-dimensional imaging method based on the ring grating source, the ring grating source image and the ring analysis grating X-ray differential phase contrast microscope system, compared with the aforementioned X-ray based on the beam splitting grating, the ring grating image of the beam splitting grating and the ring analysis grating The two-dimensional imaging method of the ray differential phase contrast microscope system is similar and will not be repeated here.

The above description is only a preferred embodiment of the present application and an illustration of the applied technical principle. Those skilled in the art should understand that the scope of the invention involved in this application is not limited to the technical solution formed by the specific combination of the above-mentioned technical features, but should also cover the technical solution formed by the above-mentioned technical features without departing from the inventive concept. Other technical solutions formed by any combination of or equivalent features thereof. For example, a technical solution formed by replacing the above-mentioned features with technical features with similar functions disclosed in (but not limited to) this application.

Claims (10)

1. An X-ray differential phase contrast microscope system, comprising: a light source for generating X-rays; and a condenser lens, a central diaphragm, a beam splitting grating, a pinhole, a sample stage, an objective lens, Annular analytical gratings and imaging detectors, where: The light source used to generate X-rays is a monochromatic X-ray light source; The condenser is an ellipsoidal capillary, a tapered capillary, a zone plate or other X-ray optical elements with a focusing function, which are used to generate a focused beam for illuminating the sample; The central diaphragm is located at the center of the exit of the condenser, and is used to block the through light from the X-ray light source to form a hollow cone beam for illuminating the sample; The beam-splitting grating is an absorption grating whose period is on the order of microns, located behind the central diaphragm, and is used to split the hollow cone beam from the condenser lens and the central diaphragm to make it have a spatial period Structured hollow cone beams; The pinhole is located behind the beam splitting grating and is used to block the through light and stray light from the X-ray light source; The sample stage is located on the object plane, used to carry the sample, and can translate and rotate the sample; The objective lens is a zone plate or other optical elements with X-ray lens imaging function, which is used to amplify the nanoscale sample structure located on the object plane into an image with a micron scale structure on the image plane, so that the sample structure with a micron scale The imaging detector of the order of magnitude pixels can take the magnified image of the sample, and make the annular part of the beam splitting grating illuminated by the hollow cone beam form an annular grating image and an annular grating image beam near the rear focal plane of the objective lens; The annular analysis grating is an absorption grating with a period of micron or submicron order, located near the back focal plane of the objective lens, and its shape and size are the same as the annular grating image of the beam splitting grating near the back focal plane of the objective lens. Filtering the annular grating image beam near the rear focal plane of the objective lens; The imaging detector is located on the image plane and is used to take a two-dimensional enlarged image of the sample. 2. The X-ray differential phase contrast microscope system according to claim 1, wherein the materials of the beam splitting grating and the ring analysis grating are gold or other heavy metals. 3. The X-ray differential phase contrast microscope system according to claim 1, when the thickness of the beam splitting grating and the annular analysis grating is not large, the thickness of the beam splitting grating is an odd multiple of π phase shift, The thickness of the annular analysis grating is an even multiple of the π phase shift. 4. A two-dimensional imaging method for the X-ray differential phase contrast microscope system described in any one of claims 1-3, comprising the steps of: S1, turn on and adjust the light source: aim the X-ray beam generated by the light source at the condenser; S2, adjust the condenser, central diaphragm and pinhole: make the hollow cone beam generated by the condenser and the central diaphragm align with the position of the sample on the sample stage, so that the central diaphragm and the pinhole block the direct passage from the X-ray light source light and stray light; S3, adjusting the objective lens: aligning the imaging light beam formed by the objective lens with the imaging detector located on the image plane; S4, feeding into the beam splitting grating: after the central diaphragm at the exit of the condenser, feed into the beam splitting grating, so that the hollow cone beam illuminates the annular part of the beam splitting grating to form a ring grating image and a ring grating image beam near the rear focal plane of the objective lens; S5, feed and adjust the ring analysis grating: make the ring analysis grating align with the ring grating image formed by the beam splitting grating near the rear focal plane of the objective lens, adjust the direction of the ring analysis grating bars so that the ring analysis grating bars are parallel to the beam splitting grating grid; S6, angle measurement signal response curve: move the beam splitting grating step by step along the direction perpendicular to the optical axis and the grating bars, so that the annular grating image of the beam splitting grating has a shear displacement relative to the annular analysis grating, and the imaging detector is used to measure the angle on the image plane. Obtain the angle signal response curve of the brightness changing with the displacement of the annular grating image; S7, fitting the angle signal response curve with a cosine curve: the angle signal response curve is similar to a cosine curve, and the measured angle signal response curve is fitted with a cosine curve to obtain an analytical expression of a cosine curve; S8, take a two-dimensional enlarged image of the sample: fix the annular grating image of the beam splitting grating at the valley position, uphill position, peak position, and downhill position of the angle signal response curve respectively, place the sample on the sample stage, and photograph the sample The valley zoom image, uphill zoom image, peak zoom image, downhill zoom image; S9, extract the quantitative two-dimensional image of the sample in the object space: extract the absorption image, refraction image and scattering image of the sample in the object space from the valley magnification image, uphill magnification image, peak magnification image, and downhill magnification image of the sample ; Extract the absorption, refraction and scattering images of the sample in the object space from any three of the four magnification images. 5. The two-dimensional imaging method of the X-ray differential phase contrast microscope system according to claim 4, wherein, in the step S6, considering the influence of refraction and scattering of the sample focal depth thin beam, that is, considering the sample The influence of the generated angle signal on the imaging process, so the sample is expressed by the angle signal function f(x _o ,y _o ,ψ _x ) as where M(x _o ,y _o ), θ _x (x _o ,y _o ) and are the variances of the absorption, refraction and scattering angles of the sample, respectively, and are also the absorption, refraction and scattering images of the sample in the object space required in the two-dimensional quantitative imaging of the X-ray differential phase contrast microscope, and their expressions are Where (x _o , y _o , z _o ) are the spatial coordinates at the object plane, μ is the linear absorption coefficient, δ is the attenuation rate of the real part of the refractive index, and ω _x is the linear scattering coefficient perpendicular to the direction of the grating bars. 6. the two-dimensional imaging method of X-ray differential phase contrast microscope system according to claim 4, what measure in described step S6 is the angle signal response curve, and it is analytically expressed as by fitting cosine curve or expressed as Wherein η is the diffraction efficiency of the objective lens, B ₀ is the brightness of the incident beam at the object plane, and _xp is the position coordinate at the annular analysis grating, is the angular displacement of the annular grating image displacement relative to the object plane, d _o is the object distance of the sample relative to the objective lens, p is the period of the annular analysis grating, is the average value of the angle signal response curve, R _max and R _min are the maximum and minimum values of the angle signal response curve, respectively, is the visibility of the angle signal response curve, n is the modulation parameter, and n=0, 1, 2, 3 correspond to the valley response curve, upslope response curve, peak response curve and downslope response curve respectively. 7. The two-dimensional imaging method of the X-ray differential phase contrast microscope system according to claim 4, in said step S8, the two-dimensional enlarged image taken by the imaging detector is described by an angle signal imaging equation, and the angle signal imaging equation is the convolution of the angle signal function and the angle signal response function, and its expression is: Where (x _o , y _o ) is the coordinates of the object plane, ( _xi , y _i ) is the coordinates of the image plane, η is the diffraction efficiency of the objective lens, B ₀ is the brightness of the incident beam at the object plane, n=0,1,2,3 Corresponding to the valley magnification imaging equation, uphill magnification imaging equation, peak magnification imaging equation and downhill magnification imaging equation, f(x _o , y _o ,ψ _x ) is the angle signal function, ηB ₀ R _n (ψ _x ) is the angle signal response function. 8. The two-dimensional imaging method of the X-ray differential phase contrast microscope system according to claim 4, wherein, In the step S8, the annular grating image of the beam splitting grating is fixed at the valley of the angle signal response curve, the sample is placed on the sample stage, and the imaging detector captures the enlarged image of the valley of the sample, and its expression is In the step S8, the annular grating image of the beam splitting grating is fixed on the slope position of the angle signal response curve, the sample is placed on the sample stage, and the imaging detector captures the uphill enlarged image of the sample, its expression for In the step S8, the annular grating image of the beam-splitting grating is fixed at the peak position of the angle signal response curve, the sample is placed on the sample stage, and the imaging detector captures an enlarged image of the peak position of the sample, and its expression is In the step S8, the annular grating image of the beam splitting grating is fixed at the downhill position of the angle signal response curve, the sample is placed on the sample stage, and the imaging detector captures the downhill enlarged image of the sample, its expression for because B _V ( _xi ,y _i )+B _P ( _xi ,y _i )＝ _BU ( _xi ,y _i )+B _D ( _xi ,y _i ) Therefore, the three images in the valley magnified image, the uphill magnified image, the peak magnified image, and the downhill magnified image are independent, and any one of them can be expressed by the other three images; among the above formulas, (x _i , y _i ) are the coordinates of the image plane, η is the diffraction efficiency of the objective lens, B ₀ is the brightness of the light beam illuminating the object plane, is the average value of the angle signal response curve, R _max and R _min are the maximum and minimum values of the angle signal response curve respectively, is the visibility of the angle signal response curve, d _o is the object distance of the sample relative to the objective lens, and p is the ring analysis grating period. 9. The two-dimensional imaging method of the X-ray differential phase contrast microscope system according to claim 4, in the step S9, the enlarged image from the valley, the enlarged image on the slope, and the enlarged image from the peak of the sample , and downhill magnification images to extract the absorption image, refraction image and scattering image of the sample in the object space as follows: The formula for extracting the absorption image of the sample in the object space is The formula for extracting the refraction image of the sample in object space is Under the condition that the scattering can be ignored, the formula for extracting the refraction image of the sample in the object space is simplified as The formula for extracting the scattering image of the sample in the object space is Under the condition that the refraction can be ignored, the formula for extracting the scattering image of the sample in the object space is simplified as In the above formulas, (x _o , y _o ) are object plane coordinates, ( _xi , y _i ) are image plane coordinates, d _o is the object distance of the sample relative to the objective lens, is the visibility of the angle signal response curve, is the average value of the angle signal response curve, R _max and R _min are the maximum value and minimum value of the angle signal response curve respectively, p is the period of the ring analysis grating, B _V is the enlarged image of the valley, _BU is the enlarged image of the uphill, B _P is the magnified image of the peak position, B _D is the magnified image of the downhill, and B ₀ is the brightness of the light beam illuminating the object plane. 10. The X-ray differential phase contrast microscope system according to claim 1, the X-ray light source, the condenser lens and the beam splitting grating are integrated into an X-ray annular grating source element whose period is on the order of micrometers, and at this time in the At the exit of the X-ray annular grid source, two annular light holes are placed in sequence along the optical axis, so that the light beam emitted by the annular grid source passes through the two annular light holes to form a hollow cone beam that illuminates the sample, and passes through the objective lens. A ring source image and a ring source image beam are formed near the back focal plane, and the shape and size of the ring analysis grating are the same as the ring source image.