DE102023108849A1 - Optical arrangement and method for generating a measuring signal - Google Patents

Abstract

The invention relates, inter alia, to an optical arrangement for generating a measurement signal (M) with a coherent optical radiation source (10), an optically nonlinear device (30), a beam splitter (40), two radiation paths (SP1, SP2) and a measuring device (200) which can detect a photon (P2") modulated with a first and a second oscillation frequency (f1, f2) and evaluate it to form the measurement signal (M).

Description

The invention relates to optical arrangements and methods for generating a measurement signal, for example, among others, to such arrangements and methods in which pump photons are generated with a coherent optical radiation source, entangled photon pairs with photons of the first and second type are formed with optically nonlinear devices, the photons of the first type are exposed to an interaction with a sample body and the consequences of this interaction are measured by detecting the photons of the second type.

Such an arrangement and such a method are described, for example, in the publication “ Microscopy with undetected photons in the mid-infrared” (Kviatkovsky et al., Sci. Adv. 2020; 6: eabd0264, 14 October 2020 ), the content of which is referred to here and the technical content of which is incorporated by reference into the present application.

The invention is based on the object of specifying an improved arrangement or an improved method.

This object is achieved with regard to the arrangement according to the invention by an arrangement according to patent claim 1. Advantageous embodiments of the arrangement according to the invention are specified in subclaims.

According to the invention, an arrangement is provided with a coherent optical radiation source that is suitable for emitting at least one pump photon, an optically non-linear device arranged downstream of the radiation source that can convert the at least one pump photon into an entangled photon pair that comprises a photon of the first type and a photon of the second type, wherein the wavelength of the photon of the first type differs from the wavelength of the photon of the second type, a beam splitter arranged downstream of the non-linear device that outputs the photon of the first type, if it has been generated, on a first radiation path and the photon of the second type, if it has been generated, on a second radiation path or alternatively outputs the pump photon on the second radiation path, a sensor element assigned to the first radiation path and mechanically oscillating at a first oscillation frequency when the arrangement is in operation, which is irradiated by the photon of the first type, if it has been generated, and in the event of irradiation, a sensor environment-dependent modulation of the photon of the first type to form a photon with the first oscillation frequency influenced photon of the first kind, a feedback element assigned to the second radiation path and modulating with a second oscillation frequency during operation of the arrangement, which returns incident radiation to the optically nonlinear device, wherein the first and second oscillation frequencies are non-commensurate, and wherein the optically nonlinear device enables the photon modulated with the first oscillation frequency and the radiation returned by the modulating feedback element to undergo nonlinear interference to form a photon of the second kind modulated with the first and second oscillation frequencies, and wherein a measuring device of the arrangement can detect the photon of the second kind modulated with the first and second oscillation frequencies and evaluate it to form the measuring signal.

A significant advantage of the arrangement according to the invention is that, due to the evaluation of the photons of the second type modulated with the first and second oscillation frequencies, background influences in the range of the photons of the first type, in particular background noise, can be efficiently suppressed, so that the resulting measurement signals have a particularly high quality.

It is advantageous if a stream of pump photons is generated because in such a case the measurement signal can cover a certain wavelength band in the wavelength range of the photons of the first kind. However, just for the sake of clarity, it should be mentioned that the measurement signal can also be formed with a single pump photon; the measurement signal then only refers to the wavelength of the photon of the second kind that corresponds to the respective pump wavelength and indirectly describes properties of the photon of the first kind that are influenced by the sensor element and its environment with regard to the wavelength of the photon of the first kind.

$$\text{mit Es}=\text{Enf}+\text{Ebg}$$

• - wobei Es das Feld des mit der ersten Schwingungsfrequenz f1 modulierten Photons erster Art beschreibt, wobei das Feld Es einen von der ersten Schwingungsfrequenz f1 beeinflussten Nahfeldsignalanteil Enf und einen von der ersten Schwingungsfrequenz weniger oder gar nicht beeinflussten Hintergrundsignalanteil Ebg enthält, und
• - wobei Eref das Feld eines mit der zweiten Schwingungsfrequenz f2 modulierten Photons zweiter Art beschreibt, das die optisch nichtlineare Einrichtung aus der vom modulierenden Rückführelement kommenden und mit der zweiten Schwingungsfrequenz modulierten Strahlung bilden kann.

It is particularly advantageous if the nonlinear interference provides an intensity I of the photon of the second kind modulated with the first and second oscillation frequencies, which is given by: $$\begin{array}{l}\text{I}={\left(\text{It}\left(\text{f1}\right)+\text{Eref}\left(\text{f2}\right)\right)}^2={\left(\text{Enf}\left(\text{f1}\right)+\text{Ebg}+\text{Eref}\left(\text{f2}\right)\right)}^2=\\ \text{Enf}{\left(\text{f1}\right)}^2+{\text{Ebg}}^2+\text{Eref}{\left(\text{f2}\right)}^2+2\cdot \text{Enf}\left(\text{f1}\right)\cdot \text{Eref}\left(\text{f2}\right)+\\ 2\cdot \text{Enf}\left(\text{f1}\right)\cdot \text{Eref}\left(\text{f2}\right)+2\cdot \text{Ebg}\cdot \text{Eref}\left(\text{f2}\right)\end{array}$$

$$\text{with Es}=\text{Enf}+\text{Ebg}$$

• - where Es describes the field of the photon of the first kind modulated with the first oscillation frequency f1, where the field Es has a near-field signal component Enf influenced by the first oscillation frequency f1 and a near-field signal component Enf influenced by the first oscillation frequency less or not at all contains unaffected background signal component Ebg, and
• - where Eref describes the field of a photon of the second kind modulated with the second oscillation frequency f2, which the optically nonlinear device can form from the radiation coming from the modulating feedback element and modulated with the second oscillation frequency.

The measuring device preferably comprises a detector which detects the photon of the second type modulated with the first and second oscillation frequencies to form a detection signal.

The measuring device preferably comprises an evaluation device arranged downstream of the detector, which evaluates only that signal component of the detection signal which contains both the first oscillation frequency and the second oscillation frequency.

wobei fsum die Summenfrequenz oder Differenzfrequenz, f1 die erste Schwingungsfrequenz und f2 die zweite Schwingungsfrequenz bezeichnet und n eine beliebige natürliche Zahl und m eine beliebige ganze Zahl ist.It is particularly advantageous if the evaluation device only evaluates the signal component of the detection signal that corresponds to the specified sum frequencies or difference frequencies according to $$\text{fsum}=\text{n f1}+\text{m f2}$$

where fsum is the sum frequency or difference frequency, f1 is the first oscillation frequency and f2 is the second oscillation frequency and n is any natural number and m is any integer.

The measuring device is or preferably contains a dispersive spectrometer.

The measurement signal preferably indicates the respective wavelength of the received photon of the second kind.

The measuring device or the spectrometer preferably comprises a wavelength-dependent grating and a multipixel detector associated with the grating, the pixels of which are each associated with a wavelength of the received photons.

The coherent optical radiation source is preferably designed to emit a stream of pump photons that vary in wavelength.

The measuring device preferably outputs the measuring signal as a function of the wavelength of the respective detected photons of the second kind.

In an embodiment variant considered to be advantageous, it is provided that the optically non-linear device has an optically non-linear element into which the at least one pump photon of the radiation source, the radiation returned by the modulating feedback element and the photon of the first type modulated with the first modulation frequency, if it has been generated, are radiated, and the said optically non-linear element carries out the optical interference.

In another embodiment variant considered to be advantageous, it is provided that the optically nonlinear device has a first optically nonlinear element and a second optically nonlinear element, wherein the pump photon of the radiation source is fed into the first optically nonlinear element and the radiation returned by the modulating feedback element and the photon of the first type modulated with the first modulation frequency are radiated into the second optically nonlinear element and the second optically nonlinear element carries out the optical interference.

It is advantageous if a first vibration device is present with which the first vibration frequency is generated and the sensor element is excited to vibrate.

Preferably, a second oscillation device is provided, with which the second oscillation frequency is generated and the feedback element is excited to modulate. The second oscillation frequency can be generated by mechanical oscillation or alternatively in another way: For example, the second oscillation frequency can be generated by a phase modulator that is electrically controlled and causes the phase modulation by an electrical change in the refractive index (e.g. charge carrier injection, electro-optical effects) in a material that conducts the radiation.

The sensor element preferably tapers in a needle-shaped manner along a longitudinal direction.

The sensor element is preferably excited to oscillate along the longitudinal direction at the first oscillation frequency.

The modulating feedback element is preferably at least two-part and preferably comprises a modulator unit and a feedback unit separate from the modulator unit.

The modulating feedback element can be one-piece and the modulator function can be integrated into the feedback unit.

The invention also relates to a method for generating a measurement signal, in which for example, including an arrangement as described above. According to the invention, the method provides that at least one pump photon is emitted with a coherent optical radiation source, the pump photon is fed into an optically non-linear device arranged downstream of the radiation source, which can convert the at least one pump photon into an entangled photon pair comprising a photon of the first type and a photon of the second type, wherein the wavelength of the photon of the first type differs from the wavelength of the photon of the second type, the photon of the first type, if it has been generated, is output on a first radiation path and the photon of the second type, if it has been generated, is output on a second radiation path or alternatively the pump photon is output on the second radiation path, a sensor element mechanically oscillating at a first oscillation frequency is irradiated with the photon of the first type, if it has been generated, and in the event of irradiation, a sensor environment-dependent modulation of the photon of the first type is brought about to form a photon of the first type modulated with the first oscillation frequency, the radiation of the second radiation path is modulated with a modulated with a feedback element modulating a second oscillation frequency and fed back to the optically nonlinear device, wherein the first and second oscillation frequencies are non-commensurable, the optically nonlinear device enables the photon modulated with the first oscillation frequency and the radiation fed back by the modulating feedback element to undergo nonlinear interference to form a photon of the second type modulated with the first and second oscillation frequencies, and the photon of the second type modulated with the first and second oscillation frequencies is detected and evaluated to form the measurement signal.

With regard to the advantages of the method according to the invention and advantageous embodiments of the method according to the invention, reference is made to the above statements in connection with the arrangement according to the invention and its advantageous embodiments.

• 1 ein erstes Ausführungsbeispiel für eine optische Anordnung zum Erzeugen eines Messsignals,
• 2 ein zweites Ausführungsbeispiel für eine optische Anordnung zum Erzeugen eines Messsignals, und
• 3 ein weiteres Ausführungsbeispiel für eine nichtlineare Einrichtung, die bei den Anordnungen gemäß den 1 und 2 eingesetzt werden kann.

The invention is explained in more detail below using exemplary embodiments, which show, for example:

• 1 a first embodiment of an optical arrangement for generating a measuring signal,
• 2 a second embodiment of an optical arrangement for generating a measuring signal, and
• 3 another embodiment of a non-linear device which can be used in the arrangements according to the 1 and 2 can be used.

The 1 shows a first embodiment of an optical arrangement for generating a measuring signal M.

The arrangement comprises a coherent optical radiation source 10 which emits a continuous stream of pump photons Pp with a wavelength of, for example, 660 nm. The pump photons Pp vary slightly in their wavelength within a conventional range.

An optically nonlinear device 30 is arranged downstream of the radiation source 10 via a wavelength-selective beam splitter element 20, which can convert each of the pump photons Pp into an entangled photon pair comprising a photon P1 of the first kind and a photon P2 of the second kind within the framework of an SPDC (spontaneous parametric down-conversion) process and will also convert them with a certain probability.

The wavelength of the photon P1 of the first kind differs from the wavelength of the photon P2 of the second kind. It is advantageous if the device 30 is selected such that the wavelength of the photons P1 of the first kind is in the mid-infrared range and the wavelength of the photons P2 of the second kind is in the near-infrared range.

Due to the already mentioned certain fluctuations in the wavelength of the pump photons Pp and due to stochastic tolerances in the photon conversion, the wavelength of the photons P1 of the first and second kind will fluctuate: For example, the wavelength of the photons P1 of the first kind can be in a range between 3.4 µm and 4.3 µm for a nominal pump wavelength of 660 nm, and the wavelength of the photons P2 of the second kind can be in a range between 780 nm and 820 nm.

For example, a ppKTP (periodically poled potassium titanyl phosphate) crystal can be used as the optically nonlinear device 30, as described in the publication “Microscopy with undetected photons in the mid-infrared” ( Kviatkovsky et al., Sci. Adv 2020; 6: eabd0264 October 14, 2020 ) is described.

Downstream of the non-linear device 30 is a wavelength-selective beam splitter 40 which outputs each photon P1 of the first type, if it has been generated, on a first radiation path SP1 and outputs each photon P2 of the second type, if it has been generated, on a second radiation path SP2. The wavelength-selective beam splitter 40 can be a dichroic filter which Radiation with the pump wavelength and radiation in the near infrared range are reflected and radiation in the mid-infrared range is allowed to pass.

If the optically nonlinear device 30 has not converted individual pump photons Pp, they are output by the wavelength-selective beam splitter 40 on the second radiation path SP2.

A mechanically oscillating sensor element 50 is assigned to the first radiation path SP1. The sensor element 50 is connected to a first oscillation device 60, which excites the sensor element 50 to oscillate, specifically with a first oscillation frequency f1. The sensor element 50 is preferably needle-shaped and tapers to a point along a longitudinal direction L, forming a needle tip 51.

The needle-shaped sensor element 50 is excited by the first vibration device 60 to vibrate along the longitudinal direction L, so that the distance between the needle tip 51 and a 1 in the x- and y-direction extending surface 90 of a sample body 91 to be analyzed on the surface varies.

The area B of the needle tip 51 of the sensor element 50 is irradiated by the photons P1 of the first type, provided that they have been generated, after they have passed through deflection elements 70 and 80. The irradiation of the area B of the needle tip 51 of the sensor element 50 causes a sensor-environment-dependent modulation of the photons P1 of the first type, forming a stream of photons P1' of the first type influenced by the first oscillation frequency f1, which returns to the device 30 via the first radiation path SP1.

If the needle tip 51 of the needle-shaped sensor element 50 is now moved over the surface 90 of the sample body 91, the interaction of the needle tip 51 with the surface 90 of the sample body 91 causes a change in the photons P1' with regard to the phase and the amplitude, which depends on the location (x, y) of the needle tip 51 and on the nature of the surface at the respective location (x, y); this can be used to analyze the nature of the surface 90, as will be explained in more detail below in connection with the formation of the measurement signal M.

A feedback element 100 modulating with a second oscillation frequency f2 is arranged downstream of the second radiation path SP2, which returns the radiated radiation in a modulated manner to the optically nonlinear device 30. If the respective pump photon Pp was converted in the upstream optically nonlinear device 30, a modulated photon P2' of the second type passes from the modulating feedback element 100 back to the optically nonlinear device 30 on the second radiation path SP2. If the respective pump photon Pp was not converted in the upstream optically nonlinear device 30, a correspondingly modulated pump photon Pp' passes from the modulating feedback element 100 back to the optically nonlinear device 30 on the second radiation path SP2.

In the embodiment according to 1 the modulating feedback element 100 comprises a modulator unit and a feedback unit separate from the modulator unit. The feedback unit is a mirror 101 which is excited to oscillate at the second oscillation frequency f2 by a second oscillation device 102 forming the modulator unit. The mirror 101 preferably oscillates in a direction of movement which is perpendicular to the mirror surface of the mirror 101.

The first oscillation frequency f1 and the second oscillation frequency f2 are “non-commensurable”.

In a subsequent second step, the optically nonlinear device 30 now enables each photon P1' of the first type modulated with the first oscillation frequency and the radiation returned by the modulating feedback element 100 to undergo nonlinear interference, forming a photon P2" of the second type modulated with both the first and the second oscillation frequencies f1 and f2.

$$\text{mit Es}=\text{Enf}+\text{Ebg}$$

The latter nonlinear interference yields an intensity I of the photon P2" of the second kind modulated with the first and second oscillation frequencies, which is given by: $$\begin{array}{l}\text{I}=\left(\text{It}\left(\text{f1}\right)+\text{Eref}\left(\text{f2}\right)\right)2=\left(\text{Enf}\left(\text{f1}\right)+\text{Ebg}+\text{Eref}\left(\text{f2}\right)\right)2=\\ \text{Enf}\left(\text{f1}\right)2+\text{Ebg2}+\text{Eref}\left(\text{f2}\right)2+2\cdot \text{Enf}\left(\text{f1}\right)\cdot \text{Eref}\left(\text{f2}\right)+\\ 2\cdot \text{Enf}\left(\text{f1}\right)\cdot \text{Eref}\left(\text{f2}\right)+2\cdot \text{Ebg}\cdot \text{Eref}\left(\text{f2}\right)\end{array}$$

$$\text{with Es}=\text{Enf}+\text{Ebg}$$

In the above equation, "Es" describes the field of the photon P1' of the first kind modulated with the first oscillation frequency f1, whereby the field Es contains a near-field signal component Enf influenced by the first oscillation frequency f1 and a background signal component Ebg less or not at all influenced by the first oscillation frequency f1. In the above equation, Eref describes the field of a photon P2' of the second kind modulated with the second oscillation frequency f2, which optically non-linear device 30 from the radiation coming from the modulating feedback element 100 and modulated with the second oscillation frequency f2.

The photons P2" of the second type modulated with the first and second oscillation frequencies reach a downstream measuring device 200 via the beam splitter element 20, which can also be a dichroic filter, and further deflection elements 110 and 120. The measuring device 200 detects the photons P2" of the second type modulated with the first and second oscillation frequencies and evaluates them to form the measurement signal M.

The beam splitting element 20 is preferably designed such that it reflects radiation with the pump wavelength and allows radiation in the near infrared range to pass through.

The measuring device 200 can be a dispersive spectrometer. Such a spectrometer makes it possible to form a measuring signal M that indicates the respective wavelength of the received photon P2" of the second kind. For this purpose, the dispersive spectrometer can prepare the light to be examined in such a way that it hits a dispersive optical component (such as a prism or grating), which deflects the light to be examined by a wavelength-dependent angle, and that after the dispersive optical element the change in angle is converted into a change in position for the purpose of detection (for example on a CCD camera, CCD line or CMOS sensor).

The 1 The measuring device 200 shown or the spectrometer shown there comprises a wavelength-dependent grating 210 and a multipixel detector 220 assigned to the grating 210, the pixels of which are each assigned to a wavelength λ of the received photons.

The multipixel detector 220 detects the photons P2" of the second kind modulated with the first and second oscillation frequencies to form a detection signal DS(λ) dependent on the wavelength λ of the respective photon, namely as a function of the wavelength λ in the near infrared range.

wobei fsum die Summenfrequenz oder Differenzfrequenz, f1 die erste Schwingungsfrequenz und f2 die zweite Schwingungsfrequenz bezeichnet und n eine beliebige natürliche Zahl und m eine beliebige ganze Zahl ist.The 1 The measuring device 200 shown also comprises an evaluation device 230 arranged downstream of the multipixel detector 220, which evaluates the amplitude and phase of the detection signal DS(A), but preferably only with regard to that signal component which corresponds to a predetermined sum frequency or difference frequency according to $$\text{fsum}=\text{n f1}+\text{m f2}$$

where fsum is the sum frequency or difference frequency, f1 is the first oscillation frequency and f2 is the second oscillation frequency and n is any natural number and m is any integer.

If, as already mentioned, the needle tip 51 of the needle-shaped sensor element 50 is now moved over the surface 90 of the sample body 91, the interaction of the needle tip 51 of the sensor element 50 with the surface 90 of the sample body 91 causes a change in the phase and amplitude of the photons P1' of the first type, which depends on the respective location (x, y) of the needle tip 51; this phase and amplitude change occurring in the mid-infrared range is later transferred to the phase and amplitude of the photons P2" of the second type by the interference in the device 30, so that the phase and amplitude change occurring in the mid-infrared range can be detected by measuring the detection signal DS in the near-infrared range. In other words, information relating to the mid-infrared range is detected by a measurement in the near-infrared range.

If, for example, a material absorbing radiation for a wavelength λ0 in the mid-infrared range is located at a location (x0, y0), this will be reflected in the amplitude and phase of the detection signal for the wavelength λ'0 in the near infrared range corresponding to the respective wavelength λ0 when measuring the photons P2" of the second kind in the near infrared range.

Thus, a measurement of surface properties of the surface 90 relevant in the mid-infrared range can be carried out in the near-infrared range because information is transmitted by the interference in the device 30.

The 2 shows a second embodiment of an optical arrangement for generating a measuring signal M.

In the second embodiment, the modulating feedback element 100 is formed by a curved waveguide 102 with an integrated phase modulator 103 which modulates the phase with the second oscillation frequency f2. The integrated phase modulator 103 can be based on charge carrier injection or on an electro-optical effect.

Furthermore, the above statements apply in connection with the 1 for the second embodiment according to 2 accordingly.

The 3 shows a further embodiment of a non-linear device 30 which is used in the arrangements according to the 1 and 2 can be used.

The optically nonlinear device 30 according to 3 comprises a first optically nonlinear element 31 and a second optically nonlinear element 32. The two optically nonlinear elements 31 and 32 can be, for example, ppKTP (periodically poled potassium titanyl phosphate) crystals, as described in the publication “ Microscopy with undetected photons in the mid-infrared” (Kviatkovsky et al., Sci. Adv. 2020; 6: eabd0264, 14 October 2020 ) are described.

The pump photons of the radiation source 10 are fed into the first optically nonlinear element 31. The first optically nonlinear element 31 can convert each of the pump photons into a photon P1 of the first type and a photon P2 of the second type and feed these into a first radiation path SP1 and a second radiation path SP2, as already explained above.

The radiation returned by the modulating feedback element 100 and the photons of the first kind modulated with the first modulation frequency are radiated into the second optically nonlinear element 32 and the second optically nonlinear element 32 carries out the optical interference.

Furthermore, the above statements apply in connection with the 1 and 2 accordingly.

Finally, it should be mentioned that the features of all embodiments described above can be combined with each other in any way to form further other embodiments of the invention.

All features of subclaims can also be combined with each of the subordinate claims, either individually or in any combination with one or more other subclaims, in order to obtain further other embodiments.

QUOTES INCLUDED IN THE DESCRIPTION

This list of documents listed by the applicant was generated automatically and is included solely for the better information of the reader. The list is not part of the German patent or utility model application. The DPMA assumes no liability for any errors or omissions.

Cited non-patent literature

• Microscopy with undetected photons in the mid-infrared” (Kviatkovsky et al., Sci. Adv. 2020; 6: eabd0264, 14 October 2020 [0002, 0059]
• Kviatkovsky et al., Sci. Adv 2020; 6: eabd0264 October 14, 2020 [0033]

Claims (14)

Optical arrangement for generating a measurement signal (M) with - a coherent optical radiation source (10) which is suitable for emitting at least one pump photon (Pp), - an optically non-linear device (30) arranged downstream of the radiation source (10) which can convert the at least one pump photon (Pp) into an entangled photon pair comprising a photon (P1) of the first type and a photon (P2) of the second type, wherein the wavelength of the photon (P1) of the first type differs from the wavelength of the photon (P2) of the second type, - a beam splitter (40) arranged downstream of the non-linear device (30) which outputs the photon (P1) of the first type, if it has been generated, on a first radiation path (SP1) and the photon (P2) of the second type, if it has been generated, on a second radiation path (SP2) or alternatively the pump photon (Pp) on the second radiation path (SP2), - a sensor element (50) assigned to the first radiation path (SP1) and mechanically oscillating at a first oscillation frequency (f1) when the arrangement is in operation, which is irradiated by the photon (P1) of the first type, if it has been generated, and in the event of irradiation causes a modulation of the photon (P1) of the first type depending on the sensor environment, forming a photon (P1') of the first type influenced by the first oscillation frequency (f1), - a feedback element (100) assigned to the second radiation path (SP2) and modulating at a second oscillation frequency (f2) when the arrangement is in operation, which returns incident radiation to the optically nonlinear device (30), the first and second oscillation frequencies (f1, f2) being non-commensurate, and - the optically nonlinear device (30) is assigned to the photon (P1') modulated at the first oscillation frequency (f1) and the modulating feedback element (100) enables non-linear interference to form a photon (P2") of the second type modulated with the first and second oscillation frequencies (f1, f2) and - wherein a measuring device (200) of the arrangement can detect the photon (P2") of the second type modulated with the first and second oscillation frequencies (f1, f2) and evaluate it to form the measuring signal (M). Optical arrangement according to claim 1 , characterized in that the non-linear interference provides an intensity I of the photon (P2") of the second kind modulated with the first and second oscillation frequencies (f1, f2), which is obtained according to: $$\begin{array}{l}\text{I}={\left(\text{It}\left(\text{f1}\right)+\text{Eref}\left(\text{f2}\right)\right)}^2={\left(\text{Enf}\left(\text{f1}\right)+\text{Ebg}+\text{Eref}\left(\text{f2}\right)\right)}^2=\\ \text{Enf}{\left(\text{f1}\right)}^2+{\text{Ebg}}^2+\text{Eref}{\left(\text{f2}\right)}^2+2\cdot \text{Enf}\left(\text{f1}\right)\cdot \text{Eref}\left(\text{f2}\right)+\\ 2\cdot \text{Enf}\left(\text{f1}\right)\cdot \text{Eref}\left(\text{f2}\right)+2\cdot \text{Ebg}\cdot \text{Eref}\left(\text{f2}\right)\end{array}$$

$$\text{with Es}=\text{Enf}+\text{Ebg}$$

- where Es describes the field of the photon (P1') of the first type modulated with the first oscillation frequency (f1), the field Es containing a near-field signal component Enf influenced by the first oscillation frequency (f1) and a background signal component Ebg less or not at all influenced by the first oscillation frequency (f1), and - where Eref describes the field of a photon (P2") of the second type modulated with the second oscillation frequency (f2), which the optically nonlinear device (30) can form from the radiation coming from the modulating feedback element (100) and modulated with the second oscillation frequency (f2). Optical arrangement according to one of the preceding claims, characterized in that the measuring device (200) comprises a detector (220) which detects the photon (P2") of the second type modulated with the first and second oscillation frequencies (f1, f2) to form a detection signal (DS). Optical arrangement according to claim 3 , characterized in that the measuring device (200) comprises an evaluation device (230) arranged downstream of the detector (220), which evaluates only that signal component of the detection signal (DS) which contains both the first oscillation frequency (f1) and the second oscillation frequency (f2). Optical arrangement according to claim 4 , characterized in that the evaluation device (230) evaluates only the signal portion of the detection signal (DS) which corresponds to the predetermined sum frequencies or difference frequencies according to $$\text{fsum}=\text{n f1}+\text{m f2}$$

where fsum is the sum frequency or difference frequency, f1 is the first oscillation frequency (f1) and f2 is the second oscillation frequency (f2) and n is any natural number and m is any integer. Optical arrangement according to one of the preceding claims, characterized in that the measuring device (200) is a dispersive spectrometer and the measuring signal (M) is the respective wavelength of the received photon (P2") of the second kind. Optical arrangement according to one of the preceding claims, characterized in that the measuring device (200) or the spectrometer comprises a wavelength-dependent grating (210) and a multipixel detector (220) assigned to the grating (210), the pixels of which are each assigned to a wavelength of the received photons (P2"). Optical arrangement according to one of the preceding claims, characterized in that - the coherent optical radiation source (10) is designed to emit a stream of pump photons (Pp) which vary in wavelength, and - the measuring device (200) outputs the measuring signal (M) as a function of the wavelength of the respectively detected photons (P2") of the second type. Optical arrangement according to one of the preceding claims, characterized in that - the optically non-linear device (30) has an optically non-linear element into which the at least one pump photon (Pp) of the radiation source (10), the radiation returned by the modulating feedback element (100) and the photon (P1') of the first type modulated with the first frequency, if it has been generated, are radiated, and - said optically non-linear element carries out the optical interference. Optical arrangement according to one of the preceding Claims 1 until 8 , characterized in that - the optically nonlinear device (30) has a first optically nonlinear element (31) and a second optically nonlinear element (32), - the pump photon (Pp) of the radiation source (10) is fed into the first optically nonlinear element (31) and - the radiation fed back by the modulating feedback element (100) and the photon (P1') of the first type modulated with the first oscillation frequency (f1) are radiated into the second optically nonlinear element (32) and the second optically nonlinear element carries out the optical interference. Optical arrangement according to one of the preceding claims, characterized in that - a first oscillation device (60) is provided, with which the first oscillation frequency (f1) is generated and the sensor element (50) is excited to oscillate, and - a second oscillation device (102) is provided, with which the second oscillation frequency (f2) is generated and the feedback element (100) is excited to modulate. Optical arrangement according to one of the preceding claims, characterized in that the sensor element (50) tapers in a needle-like manner along a longitudinal direction (L) and the sensor element (50) is excited to oscillate along the longitudinal direction (L) at the first oscillation frequency (f1). Optical arrangement according to one of the preceding claims, characterized in that - the modulating feedback element (100) is at least two-part and comprises a modulator unit (102) and a feedback unit (101) separate from the modulator unit or - the modulating feedback element (100) is one-part and the modulator function is integrated into the feedback unit. Method for generating a measurement signal (M), for example using an arrangement according to one of the preceding claims, wherein in the method - at least one pump photon (Pp) is emitted with a coherent optical radiation source (10), - the pump photon (Pp) is fed into an optically non-linear device (30) arranged downstream of the radiation source (10), which can convert the at least one pump photon (Pp) into an entangled photon pair comprising a photon (P1) of the first type and a photon (P2) of the second type, wherein the wavelength of the photon (P1) of the first type differs from the wavelength of the photon (P2) of the second type, - the photon (P1) of the first type, if it has been generated, is output on a first radiation path (SP1) and the photon (P2) of the second type, if it has been generated, on a second radiation path (SP2) or alternatively the pump photon (Pp) on the second radiation path (SP2) is output, - a sensor element (50) mechanically oscillating at a first oscillation frequency (f1) is irradiated with the photon (P1) of the first type, if it has been generated, and in the case of irradiation, a sensor-environment-dependent modulation of the photon (P1) of the first type is brought about to form a photon (P1') of the first type modulated with the first oscillation frequency (f1), - the radiation of the second radiation path (SP2) is modulated with a feedback element (100) modulating with a second oscillation frequency (f2) and is fed back to the optically nonlinear device (30), wherein the first and second oscillation frequencies (f1, f2) are non-commensurate - the optically non-linear device (30) enables the photon (P1') modulated with the first oscillation frequency (f1) and the radiation returned from the modulating feedback element (100) to undergo non-linear interference to form a photon (P2") of the second type modulated with the first and second oscillation frequencies (f1, f2), and - the photon (P2") of the second type modulated with the first and second oscillation frequencies (f1, f2) is detected and evaluated to form the measurement signal (M).

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