Confocal Microscopy Apparatus and Method Based on Circular Dichroism Dark-Field Nonlinear Thermal Waves

Abstract

This invention relates to a circular dichroic dark-field nonlinear thermal wave confocal microscopy measurement device and method. The device includes: a time-division multiplexed circularly polarized light generation module for splitting polarized laser light into left- and right-hand circularly polarized light, which are then modulated and coupled; a thermal wave detection light shaping module for shaping the coupled beam into a ring light; a thermal wave pump light generation module for generating thermal wave pump light; a beam illumination module for scanning the sample under test using the beam resulting from the combination of the ring light and the thermal wave pump light; and a dark-field nonlinear thermal wave detection module for filtering out thermal wave scattered light from the scanning beam, obtaining a dark-field thermal wave signal based on the thermal wave scattered light, and demodulating the dark-field thermal wave signal to obtain a circular dichroic dark-field thermal wave imaging result. This invention can obtain three-dimensional distribution information of various geometric defects and detect the chirality of defects.

Description

Technical Field

[0001] This invention relates to the field of optical precision measurement technology, and more specifically to a confocal microscopy measurement device and method based on circular dichroism dark-field nonlinear thermal wave. Background Technology

[0002] High-performance optical components and materials have wide applications in precision instrument manufacturing and major optical engineering research, and are the foundation of optical system performance. The mechanical structure, chemical composition and lattice structure defects on the surface and subsurface of optical components and materials play an important role in high-resolution precision detection. Among them, the chiral structure defects of optical components have a prominent impact, mainly manifested in seriously affecting the light field distribution of the incident beam and reducing the quality of the light spot.

[0003] Currently, dark-field confocal microscopy is an important means of non-destructive three-dimensional inspection of optical components. It has advantages such as good optical tomography capabilities, high imaging resolution, and high imaging contrast due to the dark background. However, ordinary optical dark-field confocal microscopy can only detect geometric defects in samples, such as scratches and bubbles, but cannot detect the chirality of defects.

[0004] Therefore, proposing a dark-field confocal microscopy measurement device and method to more accurately identify and classify defects, and to more comprehensively characterize the defect characteristics of optical components and materials, is a problem that urgently needs to be solved by those skilled in the art. Summary of the Invention

[0005] In view of this, the problem to be solved by the present invention is to provide a confocal microscopy measurement device and method based on circular dichroism dark-field nonlinear thermal wave excitation. This device and method extract the three-dimensional distribution information of geometric defects such as subsurface scratches, wear, subsurface cracks, and bubbles by directly analyzing the thermal wave scattering signal excited by a single circularly polarized pump light; and obtain the chiral information of micro / nano structures by analyzing the difference in thermal wave scattering signals excited by left- and right-handed circularly polarized pump light. The measurement device and method provided by the present invention solve the problem of the single imaging mode of ordinary dark-field confocal techniques and overcome the application bottleneck of being unable to obtain multiple physical properties of defects.

[0006] To achieve the above objectives, the present invention adopts the following technical solution:

[0007] On one hand, the present invention discloses a dark-field nonlinear thermal wave confocal microscopy measurement device based on circular dichroism, including a time-division multiplexed circular polarized light generation module, a thermal wave detection light shaping module, a thermal wave pump light generation module, a beam illumination module, and a dark-field nonlinear thermal wave detection module.

[0008] The time-division multiplexing circular polarizer generation module divides the polarized laser into left-hand circular polarizer and right-hand circular polarizer through a polarization grating. The left-hand circular polarizer and the right-hand circular polarizer are modulated by an acousto-optic modulator and then coupled by an optical fiber coupler to obtain a coupled beam.

[0009] The thermal wave detection light shaping module is used to shape the coupled light beam into a ring light;

[0010] The thermal wave pump light generation module is used to generate thermal wave pump light, which has a component with the same intensity as the left-hand circularly polarized light and the right-hand circularly polarized light.

[0011] The beam illumination module uses the combined beam of the ring light and the thermal wave pump light to scan the sample under test, and obtains the scanned beam.

[0012] The dark field nonlinear thermal wave detection module is used to filter out the thermal wave scattered light in the scanned beam. The thermal wave scattered light is detected by a lock-in amplifier to obtain a dark field thermal wave signal. The dark field thermal wave signal is demodulated to obtain a circular dichroic dark field thermal wave imaging result.

[0013] Preferably, the time-division multiplexing circularly polarized light generation module includes, in sequence according to the light propagation direction: laser 1, half-wave plate 2, and polarization grating 3. The polarization grating 3 is used to split the light to generate left-hand circularly polarized light and right-hand circularly polarized light. The optical path of the left-hand circularly polarized light includes, in sequence: mirror 4, acousto-optic modulator 6, and fiber collimator 8. The optical path of the right-hand circularly polarized light includes, in sequence: mirror 5, acousto-optic modulator 7, and fiber collimator 9. The light beams output from the optical paths of the left-hand and right-hand circularly polarized light are coupled by fiber coupler 10 and then propagated to the thermal wave detection light shaping module by fiber collimator 11.

[0014] Preferably, the acousto-optic modulator 6 and the acousto-optic modulator 7 are used to modulate the left-handed circularly polarized light and the right-handed circularly polarized light into a pulse form with a period of t, wherein the left-handed circularly polarized light and the right-handed circularly polarized light are delayed by t / 2, and t is greater than the integration time of the lock-in amplifier.

[0015] Preferably, the thermal wave detection light shaping module includes, in sequence according to the direction of light propagation: a reflector 12, a beam expander 13, an aperture stop 14, and a conical lens group 15.

[0016] Preferably, the conical lens group 15 consists of two conical lenses, which are mounted back-to-back.

[0017] Preferably, the thermal wave pump light generation module includes, in sequence according to the light propagation direction: laser 16, chopper 17, half-wave plate 18, polarizer 19, and dichroic mirror 20; the chopper 17 is used to modulate the thermal wave pump light emitted by the laser 16 at a modulation frequency of f, and the dichroic mirror 20 combines the modulated thermal wave pump light and the ring light and propagates them to the beam illumination module.

[0018] Preferably, the beam illumination module includes, in sequence according to the direction of light propagation: aperture stop 21, non-polarizing beam splitter 22, objective lens 23, sample under test 24, and three-dimensional stage 25; the scanned beam reflected by the sample under test propagates in reverse through the objective lens 23 and the non-polarizing beam splitter 22 to the dark field nonlinear thermal wave detection module.

[0019] Preferably, the dark field nonlinear thermal wave detection module includes, in sequence according to the direction of light propagation: a filter 26, an aperture stop 27, a collecting lens 28, a single-mode fiber 29, a photodetector 30, and a lock-in amplifier 31. The detection frequency of the lock-in amplifier 31 is 2f, and the integration time is T, where T>2 / f.

[0020] Preferably, the demodulation process involves extracting the thermal dark field data of the thermal wave under illumination by the left-hand circularly polarized light and the right-hand circularly polarized light respectively, based on the duty cycles of the left-hand circularly polarized light and the right-hand circularly polarized light, and then subtracting the values ​​to obtain the circular dichroic dark field thermal wave imaging result.

[0021] On the other hand, the present invention also discloses a dark-field nonlinear thermal wave confocal microscopy measurement method based on circular dichroism. This method is based on any of the dark-field nonlinear thermal wave confocal microscopy measurement devices based on circular dichroism as described above, and the specific steps include:

[0022] S1. The time-division multiplexing circular polarizer generation module divides the polarized laser into left-hand circular polarizer and right-hand circular polarizer, modulates them into pulse waves, and then couples them.

[0023] S2. The thermal wave detection light shaping module shapes the coupled light beam into a ring light;

[0024] S3. Thermowave pump light is generated by the thermowave pump light generation module, and the thermowave pump light has a component with the same intensity as the left-hand circularly polarized light and the right-hand circularly polarized light.

[0025] S4. The ring light and the thermal wave pump light are combined and then scanned through the beam illumination module to obtain the scanned beam.

[0026] S5. After the scanned beam is filtered by the dark field nonlinear thermal wave detection module, thermal wave scattered light is obtained. Dark field thermal wave signal is obtained based on the thermal wave scattered light, and the dark field thermal wave signal is demodulated to obtain circular dichroism dark field thermal wave imaging result.

[0027] As can be seen from the above technical solution, the present invention discloses a confocal microscopy device and method based on circular dichroism dark-field nonlinear thermal waves. Compared with the prior art, its beneficial effects include at least the following:

[0028] By directly analyzing the thermal wave scattering signal excited by a single circularly polarized pump light, the three-dimensional distribution information of geometric defects such as subsurface scratches, wear, subsurface cracks, and bubbles can be extracted; by illuminating with left- or right-hand circularly polarized light and performing circular dichroism analysis on the thermal wave scattering signal, chiral detection of absorption defects can be achieved.

[0029] Another beneficial effect of the present invention is that the use of dark field detection for thermal wave imaging improves the imaging sensitivity of absorption defects, while the use of nonlinear thermal wave detection improves the imaging resolution. Attached Figure Description

[0030] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on the provided drawings without creative effort.

[0031] Figure 1 The attached figure is a schematic diagram of the structure of the circular dichroism dark-field nonlinear thermal wave confocal microscopy measurement device provided by the present invention.

[0032] Figure 2 The attached figure is a flowchart of the dark-field nonlinear thermal wave confocal microscopy measurement method based on circular dichroism according to the present invention.

[0033] Explanation of reference numerals in the attached figures:

[0034] 1. Laser I; 2. Half-wave plate I; 3. Polarizing grating; 4. Mirror I; 5. Mirror II; 6. Acousto-optic modulator I; 7. Acousto-optic modulator II; 8. Fiber collimator I; 9. Fiber collimator II; 10. Fiber coupler; 11. Fiber collimator III; 12. Mirror III; 13. Beam expander; 14. Aperture stop I; 15. Conical lens group; 16. Laser II; 17. Chopper II; 18. Half-wave plate II; 19. Polarizer; 20. Dichroic mirror; 21. Aperture stop II; 22. Unpolarized beam splitter; 23. Objective lens; 24. Sample under test; 25. Three-dimensional stage; 26. Filter; 27. Aperture stop III; 28. Focusing lens; 29. ​​Single-mode fiber; 30. Photodetector; and 31. Lock-in amplifier. Detailed Implementation

[0035] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0036] The dark-field nonlinear thermal wave confocal microscopy measurement device and method based on circular dichroism disclosed in this invention not only improves the sensitivity of dark-field detection to a certain extent, but also can detect absorption defects in samples through nonlinear thermal wave imaging. Furthermore, the chiral information of micro-nano structures can be obtained through the circular dichroism analysis of thermal wave signals, providing a new approach for the detection of micro-nano structures.

[0037] Specifically, the present invention first discloses a dark-field nonlinear thermal wave confocal microscopy measurement device based on circular dichroism, the structure of which mainly includes a time-division multiplexed circular polarized light generation module, a thermal wave detection light shaping module, a thermal wave pump light generation module, a beam illumination module, and a dark-field nonlinear thermal wave detection module.

[0038] Among them, the time-division multiplexing circular polarization generation module divides the polarized laser into left-hand circular polarization and right-hand circular polarization through a polarization grating. The left-hand circular polarization and right-hand circular polarization are modulated by an acousto-optic modulator and then coupled by an optical fiber coupler to obtain a coupled beam.

[0039] The thermal wave detection beam shaping module is used to shape the coupled beam into a ring beam;

[0040] The thermal wave pump light generation module is used to generate thermal wave pump light, wherein the thermal wave pump light has a component with the same intensity as both left-hand circularly polarized light and right-hand circularly polarized light;

[0041] The beam illumination module uses the combined beam of ring light and thermal wave pump light to scan the sample under test, thus obtaining the scanned beam.

[0042] Furthermore, the dark field nonlinear thermal wave detection module is used to filter out the thermal wave scattered light in the scanned beam, and obtain the dark field thermal wave signal based on the thermal wave scattered light. The dark field thermal wave signal is then demodulated to obtain the circular dichroic dark field thermal wave imaging result.

[0043] To make the above-mentioned objects, features and advantages of the present invention more apparent and understandable, the following description is provided in conjunction with the accompanying drawings. Figure 1 The present invention will be described in further detail below.

[0044] First, the time-division multiplexed circularly polarized light generation module includes, in sequence according to the direction of light propagation: laser 1, half-wave plate 2, polarization grating 3, mirror 1, mirror 2, acousto-optic modulator 1, acousto-optic modulator 2, fiber collimator 1, fiber collimator 2, fiber coupler 10, and fiber collimator 3 11.

[0045] Specifically, the polarized laser emitted by laser 1 is used as a thermal wave detection light. In one embodiment, the wavelength of the emitted laser beam is 488nm-532nm. Then, the beam is split by polarization grating 3, and the upper and lower paths are left and right circularly polarized, respectively. The polarization state direction of the incident beam is controlled by half-wave plate 2 so that the left and right circularly polarized beams generated by the beam splitting maintain the same intensity in terms of components. Then, the propagation direction of the two beams is adjusted to be parallel to the main optical axis by reflector 4 and reflector 5. The beam is modulated into a pulse form with a period of t by acousto-optic modulator 1 (6) and acousto-optic modulator 2 (7). The delay between the left and right circularly polarized beams is t / 2, and the period t is greater than the integration time of lock-in amplifier 31, so that the left and right circularly polarized beams alternately illuminate within the same integration period of the lock-in amplifier, and only the left or right circularly polarized beams are in the optical path at the same time.

[0046] In one embodiment, the beam is modulated into a square wave with a duty cycle of 50%, and there is a time delay of 0.5T between the upper and lower paths.

[0047] The modulated left and right circularly polarized light is connected to the two input ends of the fiber coupler 10 by fiber collimating lens 8 and fiber collimating lens 9 respectively, and parallel light is output by fiber collimating lens 11.

[0048] Then, the parallel light enters the thermal wave detection light shaping module;

[0049] The thermal wave detection light shaping module includes, in order of light propagation direction, a reflector 12, a beam expander 13, an aperture stop 14, and a conical lens group 15.

[0050] Aperture stop 14 is used to remodulate the beam expanded by beam expander 13 to the desired inner diameter. In one embodiment, the inner diameter is adjusted to be smaller than the light-transmitting aperture of objective lens 23, with a difference of about 1 mm. The conical lens group (15) consists of two conical lenses mounted back to back to shape the beam into a ring light.

[0051] At this time, a thermal wave pump light is generated by the thermal wave pump light generation module. In the sample, the pump light periodically modulates the refractive index, which is the thermal wave signal. This modulates the phase of the thermal wave detection light, thereby causing periodic intensity changes in the thermal wave detection light. This is then detected by a lock-in amplifier to improve the sensitivity of defect detection.

[0052] The thermal wave pump light generation module includes, in order of light propagation direction, a laser 16, a chopper 17, a half-wave plate 18, a polarizer 19, and a dichroic mirror 20.

[0053] The polarized laser emitted by laser 16 serves as the thermal pump light. In one embodiment, the wavelength of the emitted laser beam is 405nm. The intensity of the thermal pump light is modulated by chopper 17, and in one embodiment, the modulation frequency is f. Furthermore, the polarization state of the modulated thermal pump light is adjusted by half-wave plate 18 and polarizer 19 to be the same as the intensity of the left and right circularly polarized components.

[0054] Finally, the ring light output by the thermal wave detection light shaping module and the adjusted thermal wave pump light are combined through the dichroic mirror 20 and then enter the beam illumination module.

[0055] The beam illumination module includes, in order of light propagation direction: aperture stop 21, non-polarizing beam splitter 22, objective lens 23, sample to be tested 24, and three-dimensional stage 25.

[0056] Aperture stop 21 adjusts the beam size to match the light transmission aperture of the objective lens. The beam passes through objective lens 23 to scan the sample 24 to be tested placed on the three-dimensional stage 25. Then, the beam collected by the objective lens enters the dark field nonlinear thermal wave detection module.

[0057] The dark field nonlinear thermal wave detection module includes, in sequence according to the direction of light propagation: filter 26, aperture stop 27, collecting lens 28, single-mode fiber 29, photodetector 30, and lock-in amplifier 31.

[0058] The beam collected by the objective lens is reflected by the non-polarizing beam splitter 22. First, the thermal wave pump light is filtered out by the filter 26, retaining the thermal wave detection light. Then, the reflected thermal wave detection light is isolated by the aperture stop 27, which is complementary to the thermal wave detection ring light. Only the thermal wave scattered light carrying the information of the sample 24 is allowed to pass through. The thermal wave scattered light is focused by the focusing lens 28 and enters the single-mode fiber 29. The output signal of the single-mode fiber 29 is collected and detected by the photodetector 30 to obtain the thermal wave signal. Further, the output signal of the photodetector 30 is connected to the lock-in amplifier 31, which detects the thermal wave signal to obtain the dark field thermal wave signal. Since the lock-in amplifier 31 detects a nonlinear signal, which is equivalent to the second harmonic of the thermal wave, the detection frequency of the lock-in amplifier 31 is set to 2f, and the integration time is set to T, where T>2 / f, to ensure that the lock-in amplifier 31 receives the signal of the entire cycle and avoids distortion in the intensity of the extracted periodic signal.

[0059] Finally, the dark-field thermal wave signal is demodulated to obtain the circular dichroic dark-field thermal wave imaging result. Specifically, the demodulation process involves extracting the thermal wave dark-field data under left-handed and right-handed circular polarization illumination from the thermal wave scattered light according to the duty cycles of left-handed and right-handed circular polarization, respectively, and then subtracting the values ​​to obtain the circular dichroic dark-field thermal wave imaging result.

[0060] In one embodiment, the three-dimensional stage 25 has N*N scanning points, and the dwell time of each point is T. As mentioned above, the duty cycle of the left and right circularly polarized light is 50%. At this time, the output of the lock-in amplifier 31 at 0.5T, 1.5T, ..., (N2-0.5)T is extracted as thermal dark field data under left-handed illumination, and the output of the lock-in amplifier 31 at 0, T, 2T, ..., (N2-1)T is extracted as thermal dark field data under right-handed illumination. The difference between the two is arranged into an N*N two-dimensional array, which is the circular dichroic dark field thermal imaging result.

[0061] On the other hand, based on the dark-field nonlinear thermal wave confocal microscopy measurement device based on circular dichroism, the present invention also provides a measurement method, which mainly includes the following steps, such as... Figure 2 As shown:

[0062] S1. The polarized laser is divided into left-hand circular polarizer and right-hand circular polarizer by the time-division multiplexing circular polarizer generation module, and then coupled after being modulated into pulse waves.

[0063] S2, The thermal wave detection light shaping module shapes the coupled light beam into a ring light;

[0064] S3. Thermo-wave pump light is generated by the thermo-wave pump light generation module. The thermo-wave pump light has a component with the same intensity as the left-hand circularly polarized light and the right-hand circularly polarized light.

[0065] S4, the ring light and the thermal wave pump light are combined and then scanned through the beam illumination module to obtain the scanned beam;

[0066] S5. After the scanned beam is filtered by the dark field nonlinear thermal wave detection module, thermal wave scattered light is obtained. The dark field thermal wave signal is obtained based on the thermal wave scattered light, and the dark field thermal wave signal is demodulated to obtain the circular dichroic dark field thermal wave imaging result.

[0067] In one embodiment, see Appendix Figure 1 The specific steps of this detection process are as follows:

[0068] Step a: The laser-1 emits a thermal wave detection beam, which is split by the polarization grating 3 into two paths: left and right circularly polarized beams, respectively. The half-wave plate 2 adjusts the left and right circularly polarized beams to make their light intensities the same.

[0069] Step b: Adjust the propagation direction of the two beams to be parallel to the main optical axis using reflector 4 and reflector 5 respectively, and use acousto-optic modulator 6 and acousto-optic modulator 7 to modulate the light waves into square waves in the time domain with a period of T and a delay of 0.5T between the square waves.

[0070] Step c: The upper and lower beams are coupled into the two input ends of the fiber coupler 10 by fiber collimating lens 18 and fiber collimating lens 29 respectively, and the output end is connected to fiber collimating lens 311 to output parallel light;

[0071] Step d: After the beam diameter is adjusted by aperture stop 14, the beam is incident on the cone lens group 15, which consists of two cone lenses placed back to back, and modulated into a ring light.

[0072] Step e: The laser 16 outputs a thermal wave pump light, which is intensity modulated by the chopper 17 at a modulation frequency f.

[0073] Step f: The half-wave plate 18 and polarizer 19 are adjusted to ensure that the thermal wave pump light and the left-hand circularly polarized light component have the same intensity.

[0074] Step g: The thermal wave pump light and the thermal wave detection light are strictly combined by the dichroic mirror 20 and input into the subsequent optical path. The outer diameter of the light spot is adjusted by the aperture stop 21 to match the light transmission aperture of the objective lens 23.

[0075] In step h, in the signal path of the dark field balance detection module, the reflected and scattered thermal wave detection light collected by objective lens 23 is reflected by non-polarized beam splitter 22 and filtered out by filter 26. The ring reflected light is isolated by aperture stop 27, while the central thermal wave scattered light is retained and focused into single-mode fiber 29 by focusing lens 28.

[0076] Step i: Connect the single-mode fiber 29 to the photodetector 30 for dark field thermal wave signal detection;

[0077] Step g: Input the detection signal of the photodetector 30 into the lock-in amplifier 31. The operating frequency of the lock-in amplifier 31 is set to 2f to detect the nonlinear thermal wave dark field signal excited by left- or right-hand circularly polarized thermal wave pump light.

[0078] Step k: Demodulate the nonlinear chiral thermal wave dark field signal according to the time sequence to obtain the circular dichroic dark field thermal wave imaging result.

[0079] The various embodiments in this specification are described in a progressive manner, with each embodiment focusing on its differences from other embodiments. Similar or identical parts between embodiments can be referred to interchangeably. For the apparatus disclosed in the embodiments, since they correspond to the methods disclosed in the embodiments, the description is relatively simple; relevant parts can be referred to the method section.

[0080] The above description of the disclosed embodiments enables those skilled in the art to make or use the invention. Various modifications to these embodiments will be readily apparent to those skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of the invention. Therefore, the invention is not to be limited to the embodiments shown herein, but is to be accorded the widest scope consistent with the principles and novel features disclosed herein.

Claims

1. A confocal microscopy measurement device based on circular dichroism dark-field nonlinear thermal waves, characterized in that, It includes a time-division multiplexed circularly polarized light generation module, a thermal wave detection light shaping module, a thermal wave pump light generation module, a beam illumination module, and a dark-field nonlinear thermal wave detection module. The time-division multiplexing circular polarizer generation module divides the polarized laser into left-hand circular polarizer and right-hand circular polarizer through a polarization grating. The left-hand circular polarizer and the right-hand circular polarizer are modulated by an acousto-optic modulator and then coupled by an optical fiber coupler to obtain a coupled beam. The thermal wave detection light shaping module is used to shape the coupled light beam into a ring light; The thermal wave pump light generation module is used to generate thermal wave pump light and modulate the thermal wave pump light by a chopper at a modulation frequency of f. The thermal wave pump light has a component with the same intensity as the left-hand circularly polarized light and the right-hand circularly polarized light. The beam illumination module uses the combined beam of the ring light and the thermal wave pump light to scan the sample under test, and obtains the scanned beam. The dark field nonlinear thermal wave detection module is used to filter out the thermal wave scattered light in the scanned beam. The thermal wave scattered light is detected to obtain a dark field thermal wave signal. The dark field nonlinear thermal wave detection module includes a lock-in amplifier, which detects the thermal wave scattered signal at a frequency of 2f. The dark field thermal wave signal is demodulated to obtain the circular dichroic dark field thermal wave imaging result.

2. The circular dichroic dark-field nonlinear thermal wave confocal microscopy measurement device according to claim 1, characterized in that, The time-division multiplexing circular polarizer generation module includes, in order of light propagation direction, a laser (1), a half-wave plate (2), and a polarization grating (3). The polarization grating (3) is used to split the light to generate left-hand circular polarizer and right-hand circular polarizer. The optical path of the left-hand circular polarizer includes, in order, a reflector (4), an acousto-optic modulator (6), and a fiber collimator (8). The optical path of the right-hand circular polarizer includes, in order, a reflector (5), an acousto-optic modulator (7), and a fiber collimator (9). The light beams output from the optical paths of the left-hand and right-hand circular polarizers are coupled by a fiber coupler (10) and then propagated by a fiber collimator (11) to the thermal wave detection light shaping module.

3. The circular dichroic dark-field nonlinear thermal wave confocal microscopy measurement device according to claim 2, characterized in that, The first acousto-optic modulator (6) and the second acousto-optic modulator (7) are used to modulate the left-hand circularly polarized light and the right-hand circularly polarized light into a pulse form with a period of t, wherein the left-hand circularly polarized light and the right-hand circularly polarized light are delayed by t / 2.

4. The circular dichroic dark-field nonlinear thermal wave confocal microscopy measurement device according to claim 1, characterized in that, The thermal wave detection light shaping module includes, in sequence according to the direction of light propagation: a third reflector (12), a beam expander (13), an aperture stop (14), and a conical lens group (15).

5. The circular dichroic dark-field nonlinear thermal wave confocal microscopy measurement device according to claim 4, characterized in that, The conical lens group (15) consists of two conical lenses, which are installed back to back.

6. The circular dichroic dark-field nonlinear thermal wave confocal microscopy measurement device according to claim 1, characterized in that, The thermal wave pump light generation module includes, in sequence according to the direction of light propagation: laser II (16), chopper (17), half-wave plate II (18), polarizer (19) and dichroic mirror (20); the chopper (17) is used to modulate the thermal wave pump light emitted by laser II (16), and the dichroic mirror (20) combines the modulated thermal wave pump light and the ring light and propagates them to the beam illumination module.

7. The circular dichroic dark-field nonlinear thermal wave confocal microscopy measurement device according to claim 1, characterized in that, The beam illumination module includes, in sequence according to the direction of light propagation: aperture stop II (21), non-polarizing beam splitter (22), objective lens (23), sample to be tested (24), and three-dimensional stage (25); the scanned beam reflected by the sample to be tested propagates in reverse through the objective lens (23) and the non-polarizing beam splitter (22) to the dark field nonlinear thermal wave detection module.

8. The circular dichroic dark-field nonlinear thermal wave confocal microscopy measurement device according to claim 1, characterized in that, The dark field nonlinear thermal wave detection module includes, in sequence according to the direction of light propagation: a filter (26), an aperture stop (27), a collecting lens (28), a single-mode fiber (29), a photodetector (30), and a lock-in amplifier (31). The integration time of the lock-in amplifier (31) is T, where T>2 / f.

9. The circular dichroic dark-field nonlinear thermal wave confocal microscopy measurement device according to claim 1, characterized in that, The demodulation process involves extracting the thermal dark field data under illumination by the left-hand circularly polarized light and the right-hand circularly polarized light from the thermal wave scattered light according to their respective duty cycles, and then subtracting the values ​​to obtain the circular dichroic dark field thermal wave imaging result.

10. A confocal microscopy method based on circular dichroism dark-field nonlinear thermal waves, characterized in that, The specific steps of the circular dichroic dark-field nonlinear thermal wave confocal microscopy measurement device according to any one of claims 1-9 include: S1. The time-division multiplexing circular polarizer generation module divides the polarized laser into left-hand circular polarizer and right-hand circular polarizer, modulates them into pulse waves, and then couples them. S2. The thermal wave detection light shaping module shapes the coupled light beam into a ring light; S3. Thermowave pump light is generated by the thermowave pump light generation module, and the thermowave pump light has a component with the same intensity as the left-hand circularly polarized light and the right-hand circularly polarized light. S4. The ring light and the thermal wave pump light are combined and then scanned through the beam illumination module to obtain the scanned beam. S5. After the scanned beam is filtered by the dark field nonlinear thermal wave detection module, thermal wave scattered light is obtained. Dark field thermal wave signal is obtained based on the thermal wave scattered light, and the dark field thermal wave signal is demodulated to obtain circular dichroism dark field thermal wave imaging result.

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