A device and method for measuring material elastic-optic coefficient based on Brillouin scattering

Abstract

The present invention discloses a device and method for measuring the elastic-optic coefficient of a material based on Brillouin scattering, the device comprising: an incident light generating module for generating a measuring laser and converting it into circularly polarized light; a beam transforming module for converting the circularly polarized light into linearly polarized light of a first preset polarization direction, and then collimating and reducing the beam, so that the incident light obtained is incident from the first surface of the sample to be measured; a scattered light collecting module for obtaining scattered light generated by the Brillouin effect in the sample to be measured, and after the scattered light is emitted from the second surface, focusing the scattered light parallel to its own optical axis direction on the aperture of the F-P interferometer; the F-P interferometer is used to form equal-inclination interference using the scattered light, and to image the scattered light after interference, and to determine the elastic-optic coefficient of the sample to be measured by measuring multiple Brillouin scattering spectra. The present invention reduces the error of the elastic-optic coefficient caused by a large solid angle, which is conducive to measuring the elastic-optic coefficient with higher accuracy.

Description

Technical Field

[0001] The invention belongs to the field of measurement technology, and in particular relates to a device and method for measuring the elastic-optic coefficient of a material based on Brillouin scattering. Background Art

[0002] The elastic-optic coefficient is a basic property of materials. It is a tensor that relates the internal strain deformation of the material to the change in the refractive index. The study of the elastic-optic coefficient of materials not only helps to understand the properties of the material itself, but also helps to find high-performance acousto-optic materials. At present, for complex materials with low symmetry, its elastic-optic coefficient is difficult to measure effectively through existing experimental means, and is limited by existing measurement methods. This coefficient is also difficult to measure under complex environmental conditions such as high and low temperatures and high pressures.

[0003] In related technologies, when measuring the elastic-optic coefficient of highly symmetric materials, various methods are used to generate internal strain (density fluctuation) in the material and couple it with the light field to measure the elastic-optic coefficient. The main technical principles used include the following three categories:

[0004] (1) Generate internal strain in the material through external force. This method generates internal strain in the material by applying external force to the material, and uses optical methods such as MZ interferometer to detect strain to achieve the measurement of the elastic-optic coefficient. However, for complex anisotropic materials, the size and direction of the microscopic strain caused by macroscopic stress or pressure are very complex and difficult to obtain quantitatively. Therefore, this method is only applicable to highly symmetric materials or specific directions of anisotropic materials; limited by the volume and mode of action of the experimental instrument, this method is difficult to adapt to measurements in complex environments. At the same time, this method is a contact measurement and is often destructive to the material.

[0005] (2) Applying ultrasound to the material to generate acoustic-optical diffraction. This method adheres a piezoelectric transducer to the surface of the material in a specific tangential direction to generate acoustic waves in the material to form a strain field. This strain field is similar to a grating, causing the incident laser to diffract, and then the material's elastic-optical coefficient is obtained by measuring the ultrasonic diffraction intensity. This method requires bonding the reference material, piezoelectric transducer, and the sample to be tested, and then generating acoustic waves through the transducer for measurement. Switching the acoustic wave mode requires replacing the transducer, which is cumbersome. On the other hand, this method requires designing the direction of acoustic wave propagation according to the sample to be tested, which is easily limited by the properties of the material. In addition, the environment of the instrument and adhesive limits the test to be difficult to conduct in a changing environment, and issues such as bonding quality can affect the test results.

[0006] (3) Material scattering measurement: This method uses the material's own Raman and Brillouin effects to measure the elasto-optic coefficient. Raman scattering measurement is rarely used due to its narrow applicability, and Brillouin scattering measurement is mainly used. However, when using Brillouin scattering to measure the elasto-optic coefficient, its theoretical model has defects in describing the instrument configuration, which limits the practical application of this method. In addition, due to the large collection solid angle, the measurement process will produce elasto-optic coefficient measurement errors caused by the change in the collection solid angle. Summary of the invention

[0007] In order to solve the above problems existing in the prior art, the present invention provides a device and method for measuring the elastic-optical coefficient of a material based on Brillouin scattering. The technical problem to be solved by the present invention is achieved by the following technical solutions:

[0008] In a first aspect, the present invention provides a material elastic-optic coefficient measuring device based on Brillouin scattering, characterized in that it comprises: an incident light generating module, a beam transforming module, a transparent sample to be measured, a scattered light collecting module and an FP interferometer, wherein the optical axes of the incident light generating module, the beam transforming module, the scattered light collecting module and the FP interferometer are coplanar;

[0009] The incident light generating module is used to generate a measuring laser and convert the measuring laser into circularly polarized light;

[0010] The beam conversion module is used to convert the circularly polarized light into linearly polarized light of a first preset polarization direction, and then collimate and shrink the linearly polarized light so that the incident light obtained is incident from the first surface of the sample to be tested; the incident light generating module and the beam conversion module are located on the same optical axis, and the sample to be tested is obliquely arranged between the beam conversion module and the scattered light collecting module;

[0011] The scattered light collection module is used to obtain the scattered light generated by the Brillouin effect in the sample to be tested, and after the scattered light is emitted from the second surface of the sample to be tested, focus the scattered light in the scattering volume that is parallel to the optical axis direction of the scattered light at the aperture of the FP interferometer;

[0012] The FP interferometer is used to form iso-inclined interference using the scattered light, and to image the scattered light after interference, and to determine the elastic-optical coefficient of the sample to be tested by measuring a plurality of Brillouin scattering spectra obtained.

[0013] In a second aspect, the present invention further provides a material elastic-optic coefficient measurement method based on Brillouin scattering, characterized in that it is applied to the material elastic-optic coefficient measurement device based on Brillouin scattering described in the first aspect;

[0014] The material elastic-optic coefficient measurement method comprises:

[0015] Obtaining a reference sample, wherein the reference sample is an isotropic material;

[0016] The ratio of the scattered light power of the sample to be tested to the external energy flux density of the incident light material is calculated to obtain the scattering intensity of the sample to be tested, and the ratio of the scattered light power of the reference sample to the external energy flux density of the incident light material is calculated to obtain the scattering intensity of the reference sample; wherein:

[0017]

[0018]

[0019] Among them, P s Indicates the scattered light power of the sample to be tested, S i Represents the external energy flux density of the first surface of the sample to be tested, V s Represents the scattering volume of the sample to be tested, dΩ D represents the solid angle of the detector outside the sample to be tested, α and β represent the angles between the energy flow direction inside and outside the sample to be tested and the normal direction of the first surface, respectively, P sref represents the scattered light power of the reference sample, S iref Represents the external energy flux density of the incident light material in the reference sample, V ref represents the scattering volume of the reference sample, dΩ Dref represents the solid angle of the detector outside the reference sample, α ref and β ref They respectively represent the angles between the energy flow directions inside and outside the reference sample and the normal direction of the first surface;

[0020] Determining an intermediate parameter R of the sample to be tested according to a ratio of the scattering intensity of the sample to be tested to the scattering intensity of the reference sample;

[0021] The elastic-optical coefficient of the sample to be tested is calculated according to the intermediate parameter R of the sample to be tested.

[0022] Compared with the prior art, the present invention has the following beneficial effects:

[0023] The present invention provides a material elastic coefficient measuring device based on Brillouin scattering, which is suitable for various geometric configurations such as vertical scattering, flat plate scattering and backscattering, and solves the problem of the scattering volume changing with the collection solid angle in the scattering geometric configuration in the prior art. By shrinking the scattered light solid angle and expanding the size of the scattering volume area, the angle deviation corresponding to the collected scattering intensity is reduced, thereby reducing the elastic coefficient error caused by the large solid angle. The device can be used to measure the elastic coefficient with higher accuracy, and at the same time, it can also prevent the scattering volume from changing too much due to manual operation errors.

[0024] The present invention will be further described in detail below with reference to the accompanying drawings and embodiments. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] Figure 1 It is a structural schematic diagram of a material elastic-optical coefficient measuring device based on Brillouin scattering provided in an embodiment of the present invention;

[0026] Figure 2 is another structural schematic diagram of a material elastic-optical coefficient measuring device based on Brillouin scattering provided in an embodiment of the present invention;

[0027] Figure 3 is a flow chart of a method for measuring the elastic-optical coefficient of a material based on Brillouin scattering provided in an embodiment of the present invention;

[0028] Figure 4 is a schematic diagram of the relationship between Brillouin scattering vectors in a material provided by an embodiment of the present invention;

[0029] Figure 5 (a) is a schematic diagram of the light path in the material under the vertical scattering geometric configuration provided by an embodiment of the present invention;

[0030] Figure 5 (b) is a schematic diagram of the light path in the material under the flat plate scattering geometry configuration provided by an embodiment of the present invention;

[0031] Figure 5 (c) is a schematic diagram of the light path inside the material under the backscattering geometric configuration provided by an embodiment of the present invention. DETAILED DESCRIPTION

[0032] The present invention is further described in detail below with reference to specific embodiments, but the embodiments of the present invention are not limited thereto.

[0033] Figure 1-2 Schematic diagram of the structure of the material elastic-optical coefficient measurement device based on Brillouin scattering provided by an embodiment of the present invention. Figure 1-2 , an embodiment of the present invention provides a material elastic-optic coefficient measurement device based on Brillouin scattering, comprising: an incident light generating module, a beam transforming module, a transparent sample to be measured 10, a scattered light collecting module and an FP interferometer, wherein the optical axes of the incident light generating module, the beam transforming module, the scattered light collecting module and the FP interferometer are coplanar;

[0034] An incident light generating module, used for generating a measuring laser and converting the measuring laser into circularly polarized light;

[0035] The beam conversion module is used to convert the circularly polarized light into linearly polarized light of a first preset polarization direction, and then collimate and shrink the linearly polarized light so that the incident light is incident from the first surface of the sample 10 to be tested; the incident light generation module and the beam conversion module are located on the same optical axis, and the sample 10 to be tested is obliquely arranged between the beam conversion module and the scattered light collection module;

[0036] A scattered light collection module is used to obtain scattered light generated by the Brillouin effect in the sample to be tested, and after the scattered light is emitted from the second surface of the sample to be tested, focus the scattered light in the scattering volume parallel to its own optical axis direction at the aperture of the FP interferometer;

[0037] The FP interferometer is used to form iso-inclined interference using scattered light, and to image the scattered light after interference, and to determine the elastic-optical coefficient of the sample to be tested by measuring a plurality of Brillouin scattering spectra obtained.

[0038] When vertical scattering or flat scattering is used, the angle θ2 between the incident light of the sample to be tested and the outgoing scattered light is ≠180°. Figure 1 The material elastic coefficient measuring device under the flat plate scattering or vertical scattering mode is shown. For example, the incident light generating module includes: a laser light source 1, a first lens 2, a second lens 3, a first polarizer 4 and a quarter wave plate 5; wherein,

[0039] A laser light source 1 is used to generate a measuring laser; a first lens 2, a second lens 3, a first polarizer 4 and a quarter wave plate 5 are arranged in sequence along the propagation direction of the measuring laser generated by the laser light source 1;

[0040] The first lens 2 and the second lens 3 are confocal and are used to collimate the measuring laser;

[0041] A first polarizer 4, used for converting the collimated measuring laser into a first sub-beam of a second preset polarization direction, where the second preset polarization direction is the working direction of the quarter-wave plate;

[0042] The quarter wave plate 5 is used to convert the first sub-beam into circularly polarized light.

[0043] The beam transformation module includes: a second polarizer 6, a third lens 7, a fourth lens 8 and a first aperture 9, and the second polarizer 6, the third lens 7, the fourth lens 8 and the first aperture 9 are arranged in sequence along the propagation direction of the circularly polarized light; wherein,

[0044] A second polarizer 6, used for converting the circularly polarized light into a second sub-beam of a first preset polarization direction, where the first preset polarization direction is the direction of the electric displacement vector of the incident light;

[0045] The third lens 7 and the fourth lens 8 are confocal and are used to collimate and reduce the second sub-beam;

[0046] The first aperture 9 is used to limit the size of the second sub-beam after collimation and contraction to obtain the incident light; the incident light is incident from the first surface of the sample to be tested 10, and the Brillouin effect occurs in the sample to be tested 10, and the generated scattered light is emitted from the second surface of the sample to be tested 10; the first surface of the sample to be tested 10 is parallel to the second surface, and the normal of the first surface is coplanar with the optical axis of the beam conversion module and the optical axis of the scattered light collection module.

[0047] Specifically, in order to select the appropriate laser energy and polarization direction, the polarization direction required for scattering intensity measurement is first determined. The second polarizer 6 can be rotated according to the polarization direction requirement of the incident light in the intensity calculation theory, so that the circularly polarized light emitted by the incident light generating module is converted into linearly polarized light (second sub-beam) of the first preset polarization direction after passing through the second polarizer 6. The adjustment of the polarization direction here will not affect the amplitude of the linearly polarized light, that is, the incident light energy; then, the third lens 7 and the fourth lens 8 of the confocal point collimate and shrink the second sub-beam, and the first aperture 9 is used to limit the second sub-beam after shrinking, and the obtained incident light is incident from the first surface of the sample 10 to be measured.

[0048] It should be noted that in some other embodiments of the present application, the fourth lens 8 in the beam transformation module can also be replaced by a plano-concave lens that is confocal with the third lens 7, that is, the Kepler configuration is changed to the Galilean configuration. The third lens 7 is combined with the plano-concave lens to also achieve the function of beam reduction and collimation.

[0049] Further, Figure 2 The Brillouin scattering material elastic-optical coefficient measuring device shown also includes an annihilation target plate 11 , and at least part of the scattered light is emitted from the second surface of the sample 10 to be measured and then absorbed by the annihilation target plate 11 .

[0050] The scattered light collection module includes: a second aperture 12, a third polarizer 13, a fifth lens 14, a sixth lens 15 and a seventh lens 16, which are arranged in sequence along the propagation direction of the scattered light; wherein,

[0051] The second aperture 12 is used to limit the size of the scattered light to form a third sub-beam;

[0052] A third polarizer 13, used for converting the third sub-beam into a fourth sub-beam with a third preset polarization direction, where the third preset polarization direction is the direction of the electric displacement vector of the scattered light;

[0053] The fifth lens 14, the sixth lens 15 and the seventh lens 16 are confocal, and the fifth lens 14 and the sixth lens 15 are used to convert at least part of the fourth sub-beam parallel to the optical axis direction of the scattered light collection module into parallel light, and the seventh lens 16 is used to focus the parallel light at the aperture of the FP interferometer.

[0054] Specifically, when the incident light enters the sample 10 to be tested, the irradiated area inside the sample 10 to be tested will radiate scattered waves in any direction due to the Brillouin scattering effect, that is, the irradiated area inside the sample 10 to be tested can be regarded as a volume light source, and the light emitted by the volume light source is irradiated onto the second aperture 12, and only the light beam within the aperture of the second aperture 12 can pass through to obtain a third sub-beam; the third polarizer 13 is used to screen the fourth sub-beam from the third sub-beam according to the polarization direction of the scattered light required in the scattering intensity measurement; further, the fifth lens 14 , the sixth lens 15 and the seventh lens 16 are cofocal, and the image (rear) focus of the seventh lens 16 is located at the clear aperture of the FP interferometer, that is, the aperture of the FP interferometer, wherein the fifth lens 14 collects scattered light parallel to the optical axis and focuses it on the object (front) focus of the sixth lens 15, and the light at the object focus of the sixth lens 15 is converted into parallel light after passing through the sixth lens 15, and is collected by the seventh lens 16 and focused at the aperture of the FP interferometer. The aperture size mainly affects the solid angle of the scattered light collection module to the sample 10 to be measured.

[0055] For the FP interferometer, the laser incident from the aperture diaphragm 17 can be regarded as an extended light source, which is located at the focus of the lens 18. The light emitted by the light source is reflected by the prism pair composed of the prism 19 and the prism 20, and then repeatedly passes through the refractive plates 21 and 22 to form equal-inclined interference. Finally, the scattered light after interference is imaged on the focal plane of the lens through the interferometer outlet 24 by the lens 23. A scattering detector 25 is placed on the focal plane. The Brillouin peak at the corresponding frequency shift is obtained by reading the light intensity information of the scattered light. The detector is a single-photon detector, which accumulates the scattered photons after spectral separation for a certain period of time to form a Brillouin scattering spectrum.

[0056] It should be understood that Figure 1 In the scattered light collection module shown, the fifth lens 14 can also be replaced with a plano-concave lens, and achieve the same function by cooperating with the sixth lens 15; in addition, the specific parameters (free spectral range, resolution, etc.) and optical path settings of the FP interferometer applied to Brillouin scattering are different, but as long as the entrance aperture determines the size of the light source and the imaging is located on the exit focal plane, it will be sufficient.

[0057] It should be noted that the incident light generating module and the beam transforming module are coaxial, and the angle between the optical axes of the two and the optical axis of the scattered light collecting module is θ, and the sample 10 to be tested is placed obliquely between the incident light generating module and the beam transforming module, and is tilted along the angle bisector of θ1. In addition, in the vertical scattering configuration, the angle between the optical axis of the incident light and the optical axis of the scattered light is 90°, and at this time, the sample 10 to be tested is a cuboid, and the first surface where the incident light enters and the second surface where the scattered light emerges are perpendicular to each other.

[0058] When backscattering, the angle between the incident light of the sample to be tested and the outgoing scattered light is θ2 = 180°. Figure 2 The figure shows a device for measuring the elastic-optical coefficient of a material in a backscattering mode; Figure 2 As shown, the incident light generation module and Figure 1 The incident light generating modules shown are exactly the same, so they will not be described again here.

[0059] Please continue to see Figure 2 The beam transformation module includes: a fourth polarizer 6', an eighth lens 7' and a ninth lens 8', and the fourth polarizer 6', the eighth lens 7' and the ninth lens 8' are arranged in sequence along the propagation direction of the circularly polarized light; wherein,

[0060] a fourth polarizer 6', used for converting the circularly polarized light into a fifth sub-beam of a first preset polarization direction, where the first preset polarization direction is the direction of the electric displacement vector of the incident light;

[0061] The eighth lens 7 ′ and the ninth lens 8 ′ are confocal and are used to collimate and reduce the fifth sub-beam.

[0062] The scattered light collection module includes: a third aperture 11', a semi-transparent and semi-reflective mirror 12', a tenth lens 13', an eleventh lens 14', a fifth polarizer 15' and a twelfth lens 16'; wherein,

[0063] A semi-transparent and semi-reflective mirror 12' is used to transmit at least part of the fifth sub-beam after being collimated and reduced to the third aperture 11';

[0064] The third aperture 11' is used to limit the size of at least part of the fifth sub-beam after transmission, so that the incident light is incident from the first surface of the fourth polarizer 6', and the scattered light generated by the Brillouin effect in the fourth polarizer 6' is emitted from the second surface of the fourth polarizer 6', and the size of the scattered light is limited. After the sixth sub-beam is obtained, at least part of the sixth sub-beam is further allowed to enter the tenth lens 13' through the semi-transparent and semi-reflective mirror 12';

[0065] The tenth lens 13', the eleventh lens 14' and the twelfth lens 16' are confocal, and the tenth lens 13' and the eleventh lens 14' are used to filter out non-parallel light in at least part of the sixth sub-beam entering the tenth lens 13' and retain parallel light;

[0066] a fifth polarizer 15', used for converting the parallel light into a seventh sub-beam of a fourth preset polarization direction, where the fourth preset polarization direction is the direction of the electric displacement vector of the incident light;

[0067] The twelfth lens 16 ′ is used to focus the seventh sub-beam onto the aperture of the FP interferometer.

[0068] In this embodiment, the semi-transparent and semi-reflective mirror 12' is tilted at an angle of 45° to the incident light path of the fifth sub-beam after collimation and focusing. Optionally, the material elastic-optical coefficient measurement device based on Brillouin scattering also includes an annihilation target plate 9', which is located on the side of the fourth polarizer 6' away from the third aperture 11', and at least part of the incident light is absorbed by the annihilation target plate 9' after passing through the fourth polarizer 6'; in addition, the optical axis direction of the scattered light collection module is the propagation direction of the scattered light, which is perpendicular to the propagation direction of the incident light.

[0069] Figure 3 1 is a flow chart of a method for measuring the material elastic-optical coefficient based on Brillouin scattering provided by an embodiment of the present invention. Figure 3 As shown, an embodiment of the present invention further provides a material elastic-optic coefficient measurement method based on Brillouin scattering, which is applied to the material elastic-optic coefficient measurement device based on Brillouin scattering;

[0070] The material elastic-optic coefficient measurement method comprises:

[0071] S1. Obtain a reference sample, which is an isotropic material;

[0072] S2. Calculate the ratio of the scattered light power of the sample to be tested to the external energy flux density of the incident light material to obtain the scattering intensity of the sample to be tested, calculate the ratio of the scattered light power of the reference sample to the external energy flux density of the incident light material to obtain the scattering intensity of the reference sample; wherein:

[0073]

[0074]

[0075] Among them, P s Indicates the scattered light power of the sample to be tested, S i Represents the external energy flux density of the first surface of the sample to be tested, V s Represents the scattering volume of the sample to be tested, dΩ Drepresents the solid angle of the detector outside the sample to be tested, α and β represent the angles between the energy flow direction inside and outside the sample to be tested and the normal direction of the first surface, respectively, P sref represents the scattered light power of the reference sample, S iref Represents the external energy flux density of the incident light material in the reference sample, V ref represents the scattering volume of the reference sample, dΩ Dref represents the solid angle of the detector outside the reference sample, α ref and β ref They respectively represent the angles between the energy flow directions inside and outside the reference sample and the normal direction of the first surface;

[0076] S3, determining an intermediate parameter R of the sample to be tested according to the ratio of the scattering intensity of the sample to be tested to the scattering intensity of the reference sample;

[0077] S4. Calculate the elastic-optical coefficient of the sample to be tested according to the intermediate parameter R of the sample to be tested.

[0078] Among them, ω s Indicates the scattered light frequency of the sample to be tested, k B represents the Boltzmann constant, T represents the absolute temperature, φ s ,φ i are the angles between the electric displacement vector and the electric field intensity vector of the scattered light and the incident light inside the sample to be tested, T s 、T i are the transmittance when incident on and out of the sample to be tested, c represents the speed of light, n s 、n i are the refractive indices of incident light and scattered light in the sample to be tested, ρ represents the material density, and v B represents the sound velocity corresponding to the Brillouin peak, d s and d i They represent the unit electric displacement vectors of the incident light and scattered light in the sample to be tested, u represents the unit vector of the phonon vibration direction, and q represents the wave vector direction of the phonon.

[0079] Figure 4 Schematic diagram of the relationship between the Brillouin scattering vectors in the material provided by the embodiment of the present invention. Figure 4 Brillouin scattering is explained as follows: Figure 4 As shown, the direction of the external wave vector of the material is k io After the incident light enters the material, the direction is k ii , if the light wave vector direction corresponding to the collection direction of the scattered light outside the material is k so , the corresponding wave vector direction inside the material is k si , k ii With k siThe absolute values ​​of can be regarded as equal, and the angle between them is the internal scattering angle θ of the material. i , the incident light in the material is scattered by the acoustic wave vector with wave vector q, and the direction of the acoustic wave vector is the vector sum direction of the incident light and scattered light wave vectors in the material. Obviously, after determining the position of the material and the incident and collection directions, the wave vector relationship in the material is uniquely determined.

[0080] In this embodiment, in order to calculate the elastic-optical coefficient from the Brillouin scattering spectrum, the scattering intensity of the sample to be tested is first required. R and the scattering intensity of the reference sample In view of the order of magnitude difference in intensity between the incident light and the scattered light in the measurement, the comparative measurement method is used in the measurement, that is, after measuring the Brillouin intensity of the reference sample with a known elastic-optical coefficient, the Brillouin intensity of the sample to be measured is measured, and the intensity difference of the Brillouin scattering spectra of the two is compared. At the same time, the shape of the reference sample is kept consistent with the sample to be measured as much as possible, or the geometric parameter relationship between the two can be obtained by the geometric scaling method. When the incident light power and the incident light path and the scattered light path are kept unchanged, the ratio of the scattering intensities of the two is expressed as:

[0081]

[0082] in, ω s represents the scattered light frequency, ω s =ω0±ω i , the incident light frequency ω0, k B is the Boltzmann constant, T is the absolute temperature; φ s ,φ i are the angles between the electric displacement vector and the electric field intensity vector of the scattered light and the incident light inside the material, T s 、T i are the transmittance of the incident material and the output material, respectively, n s 、n i are the refractive indices of the incident light and scattered light materials, ρ is the material density, and v B The speed of sound corresponding to the Brillouin peak can be calculated by the Brillouin frequency shift. F represents the corresponding Brillouin tensor element. The vector elements inside it need to be normalized to obtain the corresponding unit vector, d s and d i are the unit electric displacement vectors in the materials for the incident light and scattered light respectively. After determining the incident and scattered wave vectors outside the material, u is the unit vector of the phonon vibration direction. For the determined phonon wave vector direction q, the privileged vibration directions of the three phonons can be determined. Their sound velocities are different and they are separated from each other in the Brillouin scattering spectrum.

[0083] It should be noted that when the incident light of the same light source intensity and the same light path are used, the incident light material external energy flux density of the reference sample and the sample to be tested can be considered equal, that is, S iref =S i .

[0084] Furthermore, it is known that k io and k so After that, T s 、T i 、n s 、n i ,φ s ,φ i d s d i All of these can be calculated through geometric parameters, so the effective elastic-optical coefficient It can be correlated with the Brillouin intensity. Through this scattering intensity calculation model, the optical path design and calculation method of related parameters under the scattering geometric configuration can be clarified.

[0085] It should be noted that in order to complete the Brillouin method measurement of the elastic-optic coefficient of the sample to be tested, it is necessary to obtain or measure some parameters of the sample to be tested and the reference sample in advance, such as the density, corresponding mode sound velocity, refractive index, absorptivity of the sample to be tested and the reference sample, and the elastic-optic coefficient of the reference sample. Usually, there are reference data tables for the performance parameters of materials in different environments, but if the accuracy needs to be improved, on-site measurements can also be performed.

[0086] Among them, the material density can be calculated if the volume and weight of the material are known, and the corresponding mode sound velocity of the material can be directly read from the Brillouin scattering spectrum, which will not be repeated here; the refractive index of the material can be measured by using a Brillouin scattering instrument, or it can be measured by reference using methods such as interference method and minimum deflection angle method; when measuring the absorptivity of the material, the material can be placed in the laser light path, and the laser energy without the material and the reflected light energy and transmitted light energy of the material after the material is added are measured, and the difference between the laser energy without the material and the reflected light intensity and the transmitted light intensity of the material after the material is added is calculated; generally speaking, the absorptivity of the reference sample is much less than 1%, so it can be ignored; the reference elastic-optic coefficient of the material is the basis for conducting comparative tests. The test generally selects a high-symmetry material with low absorption rate for the laser wavelength as the reference material. At present, the method that can directly obtain the elastic-optic coefficient of the material is to apply external force to generate internal strain in the material and detect it through light. The most common method is to apply unidirectional stress to generate strain, obtain the material pressure-optic coefficient by photoelastic method or interference method, and obtain the elastic-optic coefficient of the reference sample based on the transformation relationship between the pressure-optic tensor and the elastic-optic tensor of the high-symmetry material.

[0087] Once the parameters of the sample to be tested, the direction of the incident light outside the material, and the direction of the scattered light collection are known, the parameters inside the material can be determined. io , then the normal direction of the material surface is related to k io The direction constitutes the incident surface, and k can be obtained by the law of refraction ii direction, at this time the directions of the two polarized photoelectric displacement vectors corresponding to the incident light and They are perpendicular to k in the incident plane. ii and perpendicular to the incident plane. The refractive index of the incident light material is equal to the material refractive index, φ i = 0, considering the incident light outside the material with known polarization direction, the polarization direction and relative amplitude of the incident light inside the material and the polarization direction and relative amplitude of the reflected light can be obtained through the tangential conservation condition of the electromagnetic field on the surface of the material, and then the transmission coefficient T can be obtained. i . For scattered light k so Similarly, I will not go into details here.

[0088] If the sample to be tested is an anisotropic material, the refractive index ellipsoid method needs to be used to iteratively solve the two specific polarization directions. Similarly, the normal direction of the material surface is related to k io The direction constitutes the incident surface, and the intersection of the incident surface and the material surface, the material surface normal and the direction of the incident surface normal constitute the incident surface coordinate system. The corresponding relationship with the material principal axis coordinate system can be determined. By measuring the material properties, the elements corresponding to the three principal axes of the material refractive index tensor matrix n can be obtained. For biaxial crystal materials, there are three different refractive indices, and for uniaxial crystal materials, there are two. The average value of the refractive index elements is taken as the initial value, and substituting it into the refractive index formula can obtain k ii The initial value of the iteration is transformed into the direction vector in the crystal principal axis coordinate system, with k ii The refractive index ellipsoid cut by the surface with the normal line is an ellipse, and the major and minor axis directions of the ellipse are the directions of the two polarized light special electric displacement vectors. and The length is the refractive index n of the two polarized lights. i1 and n i2 Size. io Substitute n i1 and n i2 And the refractive index formula can be used to obtain the new laser wave vector direction k in the material ii1 and k ii2 , repeatedly iterate to obtain the wave vector direction and electric displacement vector direction of the two special polarized lights. Through the relationship between the electric displacement vector d and the electric field intensity vector e, φ can be obtained. i , s=e×h=e×(e×d) can be used to obtain the direction of the energy flow vector in the material, and then obtain the angle between it and the normal line of the material surface. Similar to the isotropic case, T can be obtained through the tangential conservation condition of the electromagnetic field on the material surface.i The same method is used for the scattered light collection direction, which will not be repeated here.

[0089] The geometric parameters include the external scattering solid angle of the material to be tested and its corresponding internal scattering volume of the material. The determination of the geometric parameters can be done through the above-mentioned material elasto-optical coefficient measurement device based on Brillouin scattering, using the ray optics theory approximation. The external scattering solid angle of the material is uniquely determined by the entrance aperture and parallelism requirements of the FP interferometer, and the change in the internal scattering volume of the material corresponding to the change in the solid angle is very small. The change in the internal scattering volume of the material caused by the change in the solid angle can be ignored, and it is considered that the scattering volume corresponding to any solid angle is exactly the same. In this way, the influence of the solid angle can be ignored in the formula and only the influence of the scattering volume on the final scattering intensity is considered, which solves the error caused by the failure to consider the influence of the scattering angle on the scattering volume in the existing scattering geometric configuration.

[0090] In the optical path of the above-mentioned material elastic-optical coefficient measuring device, the incident light is filtered by the aperture to form a plane light with a circular cross section. After entering the material, the cross section on the surface of the material may be circular or elliptical due to different incident angles. The cross section is stretched along the direction of the light in the material to form a column. The scattered light source volume is the overlapping area of ​​the column and the material. The scattered light collected by the aperture is similar, so the scattered light collection volume is the overlapping area of ​​the column and the material, and the overlapping area of ​​the scattered light source area and the collection area is the scattering volume.

[0091] Figure 5 a is a schematic diagram of the light path inside the material under the vertical scattering geometric configuration provided by an embodiment of the present invention. Figure 5 In (a), 1 and 3 are the light paths at the edge of the incident light spot, 2 is the light path in the direction of the incident light axis, and the radius of the incident light spot is Figure 5 The distance between the light rays 2 or 3 and 1 in (a) is determined by the incident light aperture. Figure 5 In (a), 4 and 6 are the edge light paths of the scattered light collection area. Figure 5 In (a), 5 is the light path of the scattered light in the direction of the optical axis, and the radius of the scattered light collection area is determined by the scattered light aperture. Figure 5 b is a schematic diagram of the light path in the material under the flat plate scattering geometry configuration provided by an embodiment of the present invention. Figure 5 (b) is the scattering volume cross section under flat plate scattering conditions, Figure 5 In (b), 1 and 3 are the edge light paths of the incident light spot, 2 is the light path in the direction of the incident light axis, 4 and 6 are the edge light paths of the scattered light collection area, and 5 is the light path in the direction of the scattered light axis. Figure 5 (c) is a schematic diagram of the light path inside the material under the backscattering geometric configuration provided by an embodiment of the present invention. Figure 5In (c), 1 and 3 are the edge light paths of the incident light spot, 4 and 5 are the edge light paths of the scattered light collection area, and 2 is the light path in the direction of the incident light axis and the light path in the direction of the scattered light axis, which overlap. Changing the material refractive index matrix will cause the scattering volume to change synchronously. This change can be easily obtained through spatial geometric calculations and then substituted into the comparison method measurement formula.

[0092] The above parameter calculations are packaged in the form of an algorithm package. The value of the elastic-optical coefficient can be directly obtained by calling the algorithm package program with a given optical path and corresponding material parameters.

[0093] It can be seen from the above embodiments that the beneficial effects of the present invention are:

[0094] The present invention provides a material elastic coefficient measuring device based on Brillouin scattering, which is suitable for various geometric configurations such as vertical scattering, flat plate scattering and backscattering, and solves the problem of the scattering volume changing with the collection solid angle in the scattering geometric configuration in the prior art. By shrinking the scattered light solid angle and expanding the size of the scattering volume area, the angle deviation corresponding to the collected scattering intensity is reduced, thereby reducing the elastic coefficient error caused by the large solid angle. The device can be used to measure the elastic coefficient with higher accuracy, and at the same time, it can also prevent the scattering volume from changing too much due to manual operation errors.

[0095] In the description of the present invention, it should be understood that the terms "center", "longitudinal", "lateral", "length", "width", "thickness", "up", "down", "front", "back", "left", "right", "vertical", "horizontal", "top", "bottom", "inside", "outside", "clockwise", "counterclockwise" and the like indicate orientations or positional relationships based on the orientations or positional relationships shown in the accompanying drawings, and are only for the convenience of describing the present invention and simplifying the description, rather than indicating or implying that the referred device or element must have a specific orientation, be constructed and operated in a specific orientation, and therefore should not be understood as limiting the present invention.

[0096] In addition, the terms "first" and "second" are used for descriptive purposes only and should not be understood as indicating or implying relative importance or implicitly indicating the number of the indicated technical features. Therefore, the features defined as "first" and "second" may explicitly or implicitly include one or more of the features. In the description of the present invention, the meaning of "plurality" is two or more, unless otherwise clearly and specifically defined.

[0097] In the description of this specification, the description with reference to the terms "one embodiment", "some embodiments", "example", "specific example", or "some examples" etc. means that the specific features, structures, materials or characteristics described in conjunction with the embodiment or example are included in at least one embodiment or example of the present invention. In this specification, the schematic representations of the above terms do not necessarily refer to the same embodiment or example. Moreover, the specific features, structures, materials or characteristics described may be combined in any one or more embodiments or examples in a suitable manner. In addition, those skilled in the art may combine and combine different embodiments or examples described in this specification.

[0098] Although the present application is described herein in conjunction with various embodiments, in the process of implementing the claimed application, those skilled in the art may understand and implement other variations of the disclosed embodiments by reviewing the drawings, the disclosure, and the appended claims. Certain measures are recorded in mutually different dependent claims, but this does not mean that these measures cannot be combined to produce good results.

[0099] The above contents are further detailed descriptions of the present invention in combination with specific preferred embodiments, and it cannot be determined that the specific implementation of the present invention is limited to these descriptions. For ordinary technicians in the technical field to which the present invention belongs, several simple deductions or substitutions can be made without departing from the concept of the present invention, which should be regarded as falling within the protection scope of the present invention.

Claims

1. A material elastic coefficient measurement device based on Brillouin scattering, characterized in that: include: An incident light generating module, a beam transforming module, a transparent sample to be tested, a scattered light collecting module and an FP interferometer, wherein the optical axes of the incident light generating module, the beam transforming module, the scattered light collecting module and the FP interferometer are coplanar; The incident light generating module is used to generate a measuring laser and convert the measuring laser into circularly polarized light; The beam conversion module is used to convert the circularly polarized light into linearly polarized light of a first preset polarization direction, and then collimate and shrink the linearly polarized light so that the incident light obtained is incident from the first surface of the sample to be tested; the incident light generating module and the beam conversion module are located on the same optical axis, and the sample to be tested is obliquely arranged between the beam conversion module and the scattered light collecting module; The scattered light collection module is used to obtain the scattered light generated by the Brillouin effect in the sample to be tested, and after the scattered light is emitted from the second surface of the sample to be tested, focus the scattered light in the scattering volume that is parallel to the optical axis direction of the scattered light itself at the aperture of the FP interferometer; The FP interferometer is used to form iso-inclined interference using the scattered light, and to image the scattered light after interference, and to determine the elastic-optical coefficient of the sample to be tested by measuring a plurality of Brillouin scattering spectra; When vertical scattering or flat scattering is used, the beam transformation module includes: a second polarizer, a third lens, a fourth lens and a first aperture, and the second polarizer, the third lens, the fourth lens and the first aperture are arranged in sequence along the propagation direction of the circularly polarized light; wherein, The second polarizer is used to convert the circularly polarized light into a second sub-beam of a first preset polarization direction, where the first preset polarization direction is the direction of the electric displacement vector of the incident light; The third lens and the fourth lens are confocal and are used to collimate and reduce the second sub-beam; The first aperture is used to limit the size of the second sub-beam after collimation and focusing to obtain incident light; the incident light is incident from the first surface of the sample to be tested, and the Brillouin effect occurs in the sample to be tested, and the generated scattered light is emitted from the second surface of the sample to be tested; the first surface of the sample to be tested is parallel to the second surface, and the normal of the first surface is coplanar with the optical axis of the beam transformation module and the optical axis of the scattered light collection module.

2. The material elastic-optical coefficient measuring device based on Brillouin scattering according to claim 1, characterized in that: The incident light generation module includes: a laser light source, a first lens, a second lens, a first polarizer and a quarter wave plate; wherein, The laser light source is used to generate a measuring laser; the first lens, the second lens, the first polarizer and the quarter wave plate are arranged in sequence along the propagation direction of the measuring laser generated by the laser light source; The first lens and the second lens are confocal and are used to collimate the measuring laser; The first polarizer is used to convert the collimated measuring laser into a first sub-beam of a second preset polarization direction, where the second preset polarization direction is the working direction of the quarter-wave plate; The quarter wave plate is used to convert the first sub-beam into circularly polarized light.

3. The material elastic-optical coefficient measuring device based on Brillouin scattering according to claim 1, characterized in that: The scattered light collection module comprises: a second aperture, a third polarizer, a fifth lens, a sixth lens and a seventh lens, wherein the second aperture, the third polarizer, the fifth lens, the sixth lens and the seventh lens are sequentially arranged along the propagation direction of the scattered light; wherein, The second aperture is used to limit the size of the scattered light to form a third sub-beam; The third polarizer is used to convert the third sub-beam into a fourth sub-beam with a third preset polarization direction, where the third preset polarization direction is the direction of the electric displacement vector of the scattered light; The fifth lens, the sixth lens and the seventh lens are confocal, the fifth lens and the sixth lens are used to convert at least part of the fourth sub-beam parallel to the optical axis direction of the scattered light collection module into parallel light, and the seventh lens is used to focus the parallel light at the aperture of the FP interferometer.

4. The material elastic-optical coefficient measuring device based on Brillouin scattering according to claim 3 is characterized in that: The angle between the optical axes of the incident light generating module and the light beam transforming module and the optical axis of the scattered light collecting module is θ, and the sample to be tested is tilted along the angle bisector of θ1.

5. The material elastic-optical coefficient measuring device based on Brillouin scattering according to claim 2, characterized in that: When backscattering, the beam transformation module includes: a fourth polarizer, an eighth lens and a ninth lens, and the fourth polarizer, the eighth lens and the ninth lens are arranged in sequence along the propagation direction of the circularly polarized light; wherein, The fourth polarizer is used to convert the circularly polarized light into a fifth sub-beam of a first preset polarization direction, where the first preset polarization direction is the direction of the electric displacement vector of the incident light; The eighth lens and the ninth lens are cofocal and are used to collimate and reduce the fifth sub-beam.

6. The material elastic-optical coefficient measuring device based on Brillouin scattering according to claim 5, characterized in that: The scattered light collection module includes: a third aperture, a semi-transparent and semi-reflective mirror, a tenth lens, an eleventh lens, a fifth polarizer and a twelfth lens; wherein, The semi-transparent and semi-reflective mirror is used to transmit at least part of the fifth sub-beam after collimation and contraction to the third aperture; The third aperture is used to limit the size of at least part of the fifth sub-beam after transmission, so that the incident light is incident from the first surface of the sample to be tested, and the scattered light generated by the Brillouin effect in the sample to be tested is emitted from the second surface of the sample to be tested, and the size of the scattered light is limited. After the sixth sub-beam is obtained, at least part of the sixth sub-beam is further allowed to enter the tenth lens through the semi-transparent and semi-reflective mirror; The tenth lens, the eleventh lens and the twelfth lens are confocal, and the tenth lens and the eleventh lens are used to filter out non-parallel light in at least part of the sixth sub-beam entering the tenth lens and retain parallel light; The fifth polarizer is used to convert the parallel light into a seventh sub-beam of a fourth preset polarization direction, where the fourth preset polarization direction is the direction of the electric displacement vector of the incident light; The twelfth lens is used to focus the seventh sub-beam at the aperture of the FP interferometer.

7. The material elastic-optical coefficient measuring device based on Brillouin scattering according to claim 6, characterized in that: The semi-transparent and semi-reflective mirror is tilted at an angle of 45° to the incident light path of the fifth sub-light beam after being collimated and reduced.

8. A method for measuring the elastic-optical coefficient of a material based on Brillouin scattering, characterized in that: The material elastic-optical coefficient measuring device based on Brillouin scattering applied to any one of claims 1 to 7; The material elastic-optic coefficient measurement method comprises: Obtaining a reference sample, wherein the reference sample is an isotropic material; The ratio of the scattered light power of the sample to be tested to the external energy flux density of the incident light material is calculated to obtain the scattering intensity of the sample to be tested, and the ratio of the scattered light power of the reference sample to the external energy flux density of the incident light material is calculated to obtain the scattering intensity of the reference sample; wherein: Among them, P s Indicates the scattered light power of the sample to be tested, S i Represents the external energy flux density of the first surface of the sample to be tested, V s Represents the scattering volume of the sample to be tested, dΩ D represents the solid angle of the detector outside the sample to be tested, α and β represent the angles between the energy flow direction inside and outside the sample to be tested and the normal direction of the first surface, respectively, P sref represents the scattered light power of the reference sample, S iref Represents the external energy flux density of the incident light material in the reference sample, V ref represents the scattering volume of the reference sample, dΩ Dref represents the solid angle of the detector outside the reference sample, α ref and β ref They respectively represent the angles between the energy flow directions inside and outside the reference sample and the normal direction of the first surface; Determining an intermediate parameter R of the sample to be tested according to a ratio of the scattering intensity of the sample to be tested to the scattering intensity of the reference sample; The elastic-optical coefficient of the sample to be tested is calculated according to the intermediate parameter R of the sample to be tested.

9. The method for measuring the material elastic-optical coefficient based on Brillouin scattering according to claim 8, characterized in that: Among them, ω s Indicates the scattered light frequency of the sample to be tested, k B represents the Boltzmann constant, T represents the absolute temperature, φ s ,φ i are the angles between the electric displacement vector and the electric field intensity vector of the scattered light and the incident light inside the sample to be tested, T s , T i are the transmittance when incident on and out of the sample to be tested, c represents the speed of light, n s 、n i are the refractive indices of incident light and scattered light in the sample to be tested, ρ represents the material density, and v B represents the sound velocity corresponding to the Brillouin peak, d s and d i They represent the unit electric displacement vectors of the incident light and scattered light in the sample to be tested, u represents the unit vector of the phonon vibration direction, q represents the wave vector direction of the phonon, Represents the effective elastic-optical coefficient.

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