Dark field thermal wave confocal microscopy apparatus and method based on circular dichroism

Abstract

The application discloses a dark-field thermal wave confocal microscopic measuring device based on circular dichroism, which comprises the following steps: a time division multiplexing circular polarized light generating light path alternately generates left-handed circular polarized light and right-handed circular polarized light in the same period as thermal wave detection light; a thermal wave detection light shaping light path shapes the thermal wave detection light; a thermal wave pump light generating light path generates thermal wave pump light, and after the thermal wave pump light is modulated, the thermal wave pump light is combined with received thermal wave detection light to obtain combined light; a light beam illumination light path irradiates the combined light to a sample to be measured, and receives thermal wave reflection and scattering light; a dark-field balanced detection light path receives the shaped thermal wave detection light, extracts the scattering light of the thermal wave detection light in the thermal wave reflection and scattering light, and obtains a circular dichroism thermal wave dark-field signal according to the difference frequency signal between the reference light and the scattering light of the thermal wave detection light. The application can obtain the chiral information of various physical properties and micro-nano structures of sample defects.

Description

Technical Field

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

[0002] High-performance optical components and materials have wide applications in precision instrument manufacturing and major optical engineering research, forming the foundation of optical system performance. Therefore, high-resolution precision detection of the mechanical structure, chemical composition, and lattice structure defects of optical components and materials at the surface and subsurface levels is crucial. In particular, the chiral structure of defects in optical components can severely affect the optical field distribution of the incident beam, reducing the beam quality.

[0003] Dark-field confocal microscopy, with its advantages of excellent optical tomography capabilities, high imaging resolution, and high imaging contrast due to the dark background, has become an important means of non-destructive three-dimensional inspection of optical components. Conventional optical dark-field confocal microscopy can only detect geometric defects in samples, such as scratches and bubbles, but it cannot obtain other physicochemical properties of these defects.

[0004] Therefore, how to provide a circular dichroism-based dark-field thermal wave confocal microscopy measurement device and method that can more comprehensively detect the defect characteristics of samples and obtain chiral information of micro-nano structures 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 present invention provides a dark-field thermal wave confocal microscopy measurement device and method based on circular dichroism, which can obtain various physical properties of sample defects and chiral information of micro-nano structures.

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

[0007] A dark-field thermal wave confocal microscopy measurement device based on circular dichroism includes: a time-division multiplexed circular polarized light generation optical path, a thermal wave detection light shaping optical path, a thermal wave pump light generation optical path, a beam illumination optical path, and a dark-field balanced detection optical path.

[0008] The time-division multiplexed circularly polarized light generation optical path is used to alternately generate left-handed and right-handed circularly polarized light within the same period T, as thermal wave detection light;

[0009] The heat wave detection light shaping optical path is used to shape the heat wave detection light. The shaped heat wave detection light is incident on one path to the heat wave pump light generation optical path and on the other path to the dark field balance detection optical path.

[0010] The thermal wave pump light generation optical path is used to generate thermal wave pump light. After the thermal wave pump light is modulated, it is combined with the received thermal wave detection light to obtain combined light.

[0011] The beam illumination path is used to illuminate the sample under test with combined beam light and to receive thermal wave reflection and scattered light;

[0012] The dark field balanced detection optical path is used to extract the scattered light of the thermal wave detection light that carries only the sample information from the thermal wave reflected and scattered light. The circular dichroic thermal wave dark field signal is obtained based on the difference frequency signal between the scattered light of the thermal wave detection light and the reference light.

[0013] Furthermore, the time-division multiplexed circularly polarized light generation optical path includes: laser one, half-wave plate one, polarization grating, mirror one, mirror two, acousto-optic modulator one, acousto-optic modulator two, fiber collimator one, fiber collimator two, fiber coupler and fiber collimator three.

[0014] Wherein, the laser emits linearly polarized laser light, the polarization grating splits the linearly polarized laser light emitted by the laser into left-hand circularly polarized light and right-hand circularly polarized light, and the half-wave plate controls the light intensity of the left-hand circularly polarized light and the right-hand circularly polarized light to be the same.

[0015] The first reflector and the second reflector correspond one-to-one to reflect left-handed circularly polarized light and right-handed circularly polarized light to the first acousto-optic modulator and the second acousto-optic modulator;

[0016] The acousto-optic modulator one and the acousto-optic modulator two correspond to each other to modulate left-handed circularly polarized light and right-handed circularly polarized light into square waves, and within the same period T, the time delay of the left-handed circularly polarized light square wave and the right-handed circularly polarized light square wave is 0.5T.

[0017] The first fiber collimating lens and the second fiber collimating lens respectively couple left-handed circularly polarized light and right-handed circularly polarized light to the two input ends of the fiber coupler;

[0018] The output end of the fiber coupler is connected to the fiber collimating lens three, and the coupled beam is output in parallel through the fiber collimating lens three to the thermal wave detection light shaping optical path.

[0019] Furthermore, the thermal wave detection light shaping optical path includes: a reflector three, a beam expander, a chopper one, an aperture stop one, and a conical lens group arranged sequentially along the light propagation direction;

[0020] The third reflector reflects the thermal wave detection light to the beam expander for beam expansion. The first chopper modulates the intensity of the expanded thermal wave detection light. The conical lens group shapes the modulated thermal wave detection light into a ring light. The first aperture stop adjusts the inner diameter of the ring light to match the illumination path of the beam.

[0021] Furthermore, the chopper modulates the intensity frequency of the thermal wave detection light to f1, where f1 is greater than 2 / T and ranges from 10kHz to 1MHz.

[0022] Furthermore, the optical path for generating the thermal wave pump light includes: a second laser, a second chopper, a second half-wave plate, a polarizer, and a first non-polarizing beam splitter arranged sequentially along the optical fiber propagation direction;

[0023] The laser 2 emits thermal pump light; the chopper 2 modulates the intensity of the thermal pump light; the half-wave plate 2 and the polarizer adjust the polarization state of the thermal pump light to be the same as the polarization state of left-handed or right-handed circularly polarized light.

[0024] The non-polarized beam splitter combines the modulated thermal wave pump light and thermal wave probe light into the beam illumination path.

[0025] Furthermore, the second chopper modulates the intensity frequency of the thermal wave pump light to f2, where f2 = f1 + 0.1 * f1.

[0026] Furthermore, the beam illumination optical path includes: an aperture stop II, a non-polarizing beam splitter II, an objective lens, and a three-dimensional stage arranged sequentially along the light propagation direction; the sample to be tested is located on the three-dimensional stage and is oriented towards the objective lens;

[0027] The aperture stop II adjusts the outer diameter of the beam combiner to match the aperture of the objective lens; the adjusted beam combiner is incident on the sample under test through the non-polarizing beam splitter II and the objective lens, forming a focused spot on the sample under test.

[0028] The three-dimensional stage moves the sample to be tested according to preset conditions;

[0029] After receiving the thermal wave reflection and scattered light from the sample under test, the objective lens is reflected twice by the non-polarizing beam splitter to the dark field balanced detection optical path.

[0030] Furthermore, the number of scanning points on the three-dimensional stage is N*N, and the dwell time at each point is T.

[0031] Furthermore, the dark field balanced detection optical path includes: filter one, focusing lens one, single-mode fiber one, filter two, aperture stop three, focusing lens two, single-mode fiber two, balanced photodetector and lock-in amplifier.

[0032] The filter one filters out the thermal wave pump light that passes through the non-polarizing beam splitter one and receives the thermal wave detection light emitted from the thermal wave detection light shaping optical path; the focusing lens one focuses the thermal wave detection light into the single-mode fiber one.

[0033] The second filter filters out the heat wave pump light from the reflected and scattered heat wave light, while retaining the heat wave detection light; the aperture of the third aperture is complementary to the annular reflected light of the heat wave detection light, which isolates the annular reflected light of the heat wave detection light and retains only the central scattered light; the second focusing lens focuses the central scattered light into the second single-mode fiber.

[0034] The balanced photodetector collects the output signal of the first single-mode fiber and the output signal of the second single-mode fiber, and detects the difference frequency signal between the two output signals;

[0035] The lock-in amplifier processes the difference frequency signal under the conditions of detection frequency f2-f1 and integration time T>2 / f2, and outputs a circular dichroic thermal dark field signal.

[0036] Furthermore, the lock-in amplifier is available at 0.5T, 1.5T, ..., (N) 2 The output at time -0.5)T is the thermal dark field data under left-handed circularly polarized light illumination, at 0, T, 2T, ..., (N 2 -1) The output at time T is the thermal dark field data under right-hand circularly polarized light illumination. The difference between the two is arranged into an N*N two-dimensional array, which serves as the result of circular dichroism dark field thermal imaging.

[0037] As can be seen from the above technical solution, compared with the prior art, this invention discloses a dark-field thermal wave confocal microscopy measurement device based on circular dichroism. Linearly polarized light is incident on a polarization grating, simultaneously generating left-handed and right-handed circularly polarized light. An acousto-optic modulator is controlled to modulate the beam into a pulsed form, achieving alternating illumination by left-handed and right-handed circularly polarized light within the same period, each accounting for 50% of the time. A chopper modulates the intensity of the pump light and probe light respectively to generate a thermal wave detection signal. A conical lens group shapes the probe light into a ring light. Simultaneously, complementary aperture blocking detection is used to extract the scattered signal. A balanced photodetector is used to perform heterodyne detection on the probe reference light and the scattered signal light. This structure can achieve:

[0038] ① The device uses dark field detection for thermal imaging, which has higher imaging sensitivity for detecting absorption defects. At the same time, it uses a balanced photodetector for heterodyne detection, which improves the contrast and signal-to-noise ratio of the image.

[0039] ② 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;

[0040] ③ By introducing left- and right-hand circularly polarized illumination, analyzing the difference in thermal wave scattering signals under pump light excitation, and performing circular dichroism analysis on the difference in thermal wave scattering signals, the chiral information of micro- and nanostructures can be detected. Attached Figure Description

[0041] 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.

[0042] Figure 1 This is a schematic diagram of the structure provided by the present invention.

[0043] In the diagram: 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. Chopper I, 15. Aperture stop I, 16. Conical lens group, 17. Laser II, 18. Chopper II, 19. Half-wave plate II, 20. Polarizer, 21. Unpolarized beam splitter I, 22. Filter I, 23. Focusing lens I, 24. Single-mode fiber I, 25. Aperture stop II, 26. Unpolarized beam splitter II, 27. Objective lens, 28. Sample under test, 29. Three-dimensional stage, 30. Filter II, 31. Aperture stop III, 32. Focusing lens II, 33. Single-mode fiber II, 34. Balanced photodetector, and 35. Lock-in amplifier. Detailed Implementation

[0044] 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.

[0045] like Figure 1 As shown, this embodiment of the invention discloses a dark-field thermal wave confocal microscopy measurement device based on circular dichroism, including: a time-division multiplexed circularly polarized light generation optical path, a thermal wave detection light shaping optical path, a thermal wave pump light generation optical path, a beam illumination optical path, and a dark-field balanced detection optical path.

[0046] The time-division multiplexed circularly polarized light generation optical path is used to alternately generate left-handed and right-handed circularly polarized light within the same period T, as thermal wave detection light;

[0047] The thermal wave detection light shaping optical path is used to shape the thermal wave detection light. The shaped thermal wave detection light is incident on two paths: one path is sent to the thermal wave pump light generation optical path, and the other path is sent to the dark field balance detection optical path.

[0048] The thermal wave pump light generation optical path is used to generate thermal wave pump light. After the thermal wave pump light is modulated, it is combined with the received thermal wave probe light to obtain combined light.

[0049] The beam illumination path is used to illuminate the sample under test with combined beam light and to receive thermal wave reflections and scattered light;

[0050] The dark field balanced detection optical path is used to extract the scattered light of the thermal wave detection light that carries only the sample information from the thermal wave reflected and scattered light. The circular dichroic thermal wave dark field signal is obtained based on the difference frequency signal between the scattered light of the thermal wave detection light and the reference light.

[0051] The optical path structures described above will be further explained below.

[0052] In one specific embodiment, the time-division multiplexed circularly polarized light generation optical path includes: laser 1, half-wave plate 2, polarization grating 3, mirror 4, mirror 5, acousto-optic modulator 6, acousto-optic modulator 7, fiber collimator 8, fiber collimator 9, fiber coupler 10, and fiber collimator 31.

[0053] Among them, laser-1 emits linearly polarized laser light, polarization grating 3 splits the linearly polarized laser light emitted by laser-1 into left-hand circularly polarized light and right-hand circularly polarized light, and half-wave plate 2 controls the light intensity of left-hand circularly polarized light and right-hand circularly polarized light to be the same.

[0054] Reflector 4 and reflector 5 correspond one-to-one to reflect left-handed and right-handed circularly polarized light to acousto-optic modulator 6 and acousto-optic modulator 7, respectively.

[0055] Acousto-optic modulator 6 and acousto-optic modulator 7 correspond one-to-one to modulate left-handed and right-handed circularly polarized light into square waves. The period T of the square wave is equal to the integration time of the lock-in amplifier 35, and the duty cycle is 50%. Within the same period T, the time delay of the left-handed and right-handed circularly polarized light square waves is 0.5T.

[0056] Fiber collimating lens 8 and fiber collimating lens 9 respectively couple left-handed circularly polarized light and right-handed circularly polarized light to the two input ends of fiber coupler 10;

[0057] The output end of the fiber optic coupler 10 is connected to the fiber optic collimating lens 311. The coupled beam is output in parallel through the fiber optic collimating lens 311 to the reflector 32 in the thermal wave detection light shaping optical path.

[0058] In one specific embodiment, the thermal wave detection light shaping optical path includes: a reflector 12, a beam expander 13, a chopper 14, an aperture stop 15, and a conical lens group 16 arranged sequentially along the light propagation direction.

[0059] Reflector 12 reflects the thermal detection light to beam expander 13 for beam expansion. Chopper 14 performs a second light intensity modulation on the expanded thermal detection light. Conical lens group 16 shapes the modulated thermal detection light into a ring light. Aperture stop 15 adjusts the inner diameter of the ring light to match the illumination path of the beam. Specifically, aperture stop 15 adjusts the inner diameter of the ring light to be smaller than the aperture of objective lens 27, with a difference of approximately 1 mm.

[0060] Among them, the chopper-14 modulates the intensity frequency of the thermal wave detection light to f1, where f1 is greater than 2 / T and ranges from 10kHz to 1MHz.

[0061] In one specific embodiment, the thermal wave pump light generation optical path includes: a laser 17, a chopper 18, a half-wave plate 19, a polarizer 20, and a non-polarizing beam splitter 21 arranged sequentially along the optical fiber propagation direction.

[0062] Laser 17 emits X-ray polarized laser light as thermal pump light; chopper 18 modulates the intensity of thermal pump light; half-wave plate 19 and polarizer 20 adjust the polarization state of thermal pump light to be the same as that of left-hand circularly polarized light or right-hand circularly polarized light.

[0063] The non-polarized beam splitter 21 combines the modulated thermal wave pump light and thermal wave probe light into the beam illumination path.

[0064] Specifically, chopper 218 modulates the frequency of the heat wave pump light to f2, where f2 = f1 + 0.1 * f1.

[0065] In one embodiment, the beam illumination optical path includes: an aperture stop 25, a non-polarizing beam splitter 26, an objective lens 27, and a three-dimensional stage 29 arranged sequentially along the light propagation direction; the sample to be tested 28 is located on the three-dimensional stage 29 and is positioned facing the objective lens 27.

[0066] Aperture stop 25 adjusts the outer diameter of the beam combiner to match the aperture of objective lens 27; the adjusted beam combiner is incident on the sample under test through non-polarizing beam splitter 26 and objective lens 27, forming a focused spot on the sample under test.

[0067] The three-dimensional stage 29 moves the sample to be tested according to preset conditions to achieve beam scanning of the sample to be tested;

[0068] After receiving the thermal wave reflection and scattered light from the sample under test, the objective lens 27 is reflected by the non-polarizing beam splitter 26 to the filter 30 in the dark field balanced probe optical path.

[0069] The three-dimensional stage 29 has N*N scanning points, and the dwell time for each point is T.

[0070] In one specific embodiment, the dark field balanced detection optical path includes: filter 22, focusing lens 23, single-mode fiber 24, filter 30, aperture stop 31, focusing lens 32, single-mode fiber 33, balanced photodetector 34, and lock-in amplifier 35.

[0071] Filter 22 filters out the heat wave pump light that passes through the non-polarizing beam splitter 21 and receives the heat wave detection light emitted from the heat wave detection light shaping optical path; focusing lens 23 focuses the heat wave detection light into the single-mode fiber 24.

[0072] Filter 2 30 filters out the heat wave pump light in the reflected and scattered heat wave light, while retaining the heat wave detection light; the aperture of aperture 3 31 is complementary to the ring reflection light of the heat wave detection light, which isolates the ring reflection light of the heat wave detection light and retains only the central scattered light; focusing lens 2 32 focuses the central scattered light into single-mode fiber 2 33.

[0073] The balanced photodetector 34 collects the output signal of single-mode fiber 24 and the output signal of single-mode fiber 33, and detects the difference frequency signal between the two output signals.

[0074] The lock-in amplifier 35 processes the difference frequency signal under the conditions of detection frequency f2-f1 and integration time T>2 / f2, and outputs a circular dichroic thermal dark field signal.

[0075] By analyzing the thermal wave scattering signal collected by a balanced photodetector under single circularly polarized pump light excitation, the three-dimensional distribution information of geometric defects such as subsurface scratches, wear, subsurface cracks, and bubbles can be extracted; by analyzing the difference between the thermal wave scattering signals of left and right circularly polarized detectors under pump light excitation, the chiral detection of absorption defects can be achieved.

[0076] Specifically, the lock-in amplifier 35 is used at 0.5T, 1.5T, ..., (N) 2 The output at time -0.5)T is the thermal dark field data under left-handed circularly polarized light illumination, at 0, T, 2T, ..., (N 2 -1) The output at time T is the thermal dark field data under right-hand circularly polarized light illumination. The difference between the two is arranged into an N*N two-dimensional array, which serves as the result of circular dichroism dark field thermal imaging.

[0077] This invention also provides a measurement method based on the above-described measuring device, comprising the following steps:

[0078] Step a: The heat wave detection beam emitted by laser 1 is split by polarization grating 3, and the upper and lower paths are left and right circularly polarized light, respectively. The half-wave plate 2 is adjusted to make the intensity of the left and right circularly polarized light the same.

[0079] 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.

[0080] Step c: The upper and lower beams are coupled into the two input ends of the fiber coupler 10 by fiber collimating lens 8 and fiber collimating lens 9 respectively. The output end of the fiber coupler 10 is connected to fiber collimating lens 11. The coupled beams are output in parallel through fiber collimating lens 11.

[0081] Step d: The beam enters the beam expander 13 through the reflector 12. After being expanded by the beam expander (13), the light intensity is modulated by the chopper 14. Its frequency f1 is greater than 2 / T and ranges from 10kHz to 1MHz.

[0082] Step e: After adjusting the beam diameter with aperture stop 15, the beam is incident on the cone lens group 16, which consists of two cone lenses placed back to back, and modulated into a ring light.

[0083] Step f: The laser 17 outputs a thermal wave pump light, which is intensity modulated by the chopper 18 at a frequency of f2, where f2 is f1 + 0.1 * f1.

[0084] Step g: Adjust half-wave plate 19 and polarizer 20 to make the thermal wave pump light have the same intensity in the left-hand circularly polarized light component;

[0085] In step h, the thermal wave pump light and the thermal wave detection light are strictly combined by the non-polarization beam splitter 21 and input into the subsequent optical path. The outer diameter of the light spot is adjusted by the aperture stop 25 to match the light transmission aperture of the objective lens 27.

[0086] In step i, the dark field balanced detection optical path, the modulated and shaped thermal wave detection light is reflected by the non-polarized beam splitter 21 and filtered out by the filter 22, and then focused into the single-mode fiber 24 by the focusing lens 23.

[0087] In step g, in the dark field balanced detection optical path, the thermal wave reflected and scattered light collected by objective lens 27 is reflected by non-polarized beam splitter 26 and then filtered out by filter 30 to remove the thermal wave pump light, while retaining the reflected and scattered light of thermal wave detection light. The reflected and scattered light of thermal wave detection light is isolated by aperture stop 31 to isolate the ring reflected light, while retaining the central scattered light, and is focused into single-mode fiber 33 by focusing lens 32.

[0088] Step h: Connect single-mode fiber 1 24 and single-mode fiber 2 33 to the balanced detector 34 for difference frequency detection;

[0089] Step i: The output signal of the balanced detector 34 is input into the lock-in amplifier 35. The operating frequency of the lock-in amplifier 35 is set to f2-f1 to detect the thermal dark field signal excited by the left-hand circularly polarized thermal wave pump light.

[0090] Step j: Demodulate the circular dichroic thermal dark field signal according to the time sequence.

[0091] 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.

[0092] 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 dark-field thermal wave confocal microscopy measurement device based on circular dichroism, characterized in that, include: Time-division multiplexing circularly polarized light generation optical path, thermal wave detection light shaping optical path, thermal wave pump light generation optical path, beam illumination optical path, and dark field balance detection optical path; The time-division multiplexed circularly polarized light generation optical path is used to alternately generate left-handed and right-handed circularly polarized light within the same period T, as thermal wave detection light; The heat wave detection light shaping optical path is used to shape the heat wave detection light. The shaped heat wave detection light is incident on one side to the heat wave pump light generating optical path and on the other side to the dark field balance detection optical path as a reference light. The thermal wave pump light generation optical path is used to generate thermal wave pump light. After the thermal wave pump light is modulated, it is combined with the received thermal wave detection light to obtain combined light. The beam illumination path is used to illuminate the sample under test with combined beam light and to receive thermal wave reflection and scattered light; The dark field balanced detection optical path is used to extract the scattered light of the thermal wave detection light that carries only the sample information from the thermal wave reflected and scattered light. The circular dichroic thermal wave dark field signal is obtained based on the difference frequency signal between the scattered light of the thermal wave detection light and the reference light. The thermal wave detection light shaping optical path includes: a reflector three (12), a beam expander (13), a chopper one (14), an aperture stop one (15), and a conical lens group (16) arranged sequentially along the light propagation direction. The chopper (14) modulates the intensity frequency of the heat wave detection light to... f 1, f 1 is greater than 2 / T, ranging from 10kHz to 1MHz; The heat wave pump light generation optical path includes: a laser second (17), a chopper second (18), a half-wave plate second (19), a polarizer (20), and a non-polarized beam splitter first (21) arranged sequentially along the optical fiber propagation direction. The second laser (17) emits thermal pump light; the second chopper (18) modulates the intensity of the thermal pump light; the second half-wave plate (19) and the polarizer (20) adjust the polarization state of the thermal pump light to be the same as that of left-hand circularly polarized light or right-hand circularly polarized light. The non-polarization beam splitter (21) combines the modulated thermal wave pump light and thermal wave probe light into the beam illumination path. The second chopper (18) modulates the intensity frequency of the heat wave pump light to... f 2, f 2= f 1+0.1* f 1.

2. The dark-field thermal wave confocal microscopy measuring device based on circular dichroism according to claim 1, characterized in that, The time-division multiplexing circularly polarized light generation optical path includes: laser one (1), half-wave plate one (2), polarization grating (3), mirror one (4), mirror two (5), acousto-optic modulator one (6), acousto-optic modulator two (7), fiber collimator one (8), fiber collimator two (9), fiber coupler (10) and fiber collimator three (11). Among them, the laser one (1) emits linearly polarized laser, the polarization grating (3) splits the linearly polarized laser emitted by the laser one (1) into left-hand circularly polarized light and right-hand circularly polarized light, and the half-wave plate one (2) controls the light intensity of the left-hand circularly polarized light and the right-hand circularly polarized light to be the same. The first reflector (4) and the second reflector (5) reflect left-handed circularly polarized light and right-handed circularly polarized light to the first acousto-optic modulator (6) and the second acousto-optic modulator (7) respectively. The acousto-optic modulator one (6) and the acousto-optic modulator two (7) modulate left-handed circularly polarized light and right-handed circularly polarized light into square waves in a one-to-one correspondence, and within the same period T, the time delay of the left-handed circularly polarized light square wave and the right-handed circularly polarized light square wave is 0.5T. The first fiber collimator (8) and the second fiber collimator (9) respectively couple left-handed circularly polarized light and right-handed circularly polarized light to the two input ends of the fiber coupler (10); The output end of the fiber coupler (10) is connected to the fiber collimating mirror three (11), and the coupled beam is output in parallel through the fiber collimating mirror three (11) to the thermal wave detection light shaping optical path.

3. The dark-field thermal wave confocal microscopy measuring device based on circular dichroism according to claim 1, characterized in that, The third reflector (12) reflects the thermal wave detection light to the beam expander (13) for beam expansion. The first chopper (14) modulates the intensity of the expanded thermal wave detection light. The conical lens group (16) shapes the modulated thermal wave detection light into a ring light. The first aperture stop (15) adjusts the inner diameter of the ring light to match the illumination path of the beam.

4. The dark-field thermal wave confocal microscopy measuring device based on circular dichroism according to claim 1, characterized in that, The beam illumination optical path includes: an aperture stop II (25), a non-polarizing beam splitter II (26), an objective lens (27), and a three-dimensional stage (29) arranged sequentially along the light propagation direction; the sample to be tested (28) is located on the three-dimensional stage (29) and is positioned facing the objective lens (27); The aperture stop II (25) adjusts the outer diameter of the beam combined to match the aperture of the objective lens (27); the adjusted beam combined is incident on the sample to be tested through the non-polarizing beam splitter II (26) and the objective lens (27), forming a focused spot on the sample to be tested; The three-dimensional stage (29) moves the sample to be tested according to preset conditions; After receiving the thermal wave reflection and scattered light from the sample to be tested, the objective lens (27) is reflected by the non-polarizing beam splitter (26) to the dark field balanced detection optical path.

5. The dark-field thermal wave confocal microscopy measuring device based on circular dichroism according to claim 4, characterized in that, The number of scanning points of the three-dimensional stage (29) is N*N, and the dwell time of each point is T.

6. The dark-field thermal wave confocal microscopy measuring device based on circular dichroism according to claim 4, characterized in that, The dark field balanced detection optical path includes: filter one (22), focusing lens one (23), single-mode fiber one (24), filter two (30), aperture stop three (31), focusing lens two (32), single-mode fiber two (33), balanced photodetector (34) and lock-in amplifier (35). The filter (22) filters out the heat wave pump light that passes through the non-polarizing beam splitter (21) and receives the heat wave detection light emitted from the heat wave detection light shaping optical path; the focusing lens (23) focuses the heat wave detection light into the single-mode fiber (24). The second filter (30) filters out the heat wave pump light in the heat wave reflection and scattered light, and retains the heat wave detection light; the aperture of the third aperture (31) is complementary to the ring reflection light of the heat wave detection light, and it isolates the ring reflection light of the heat wave detection light, retaining only the central scattered light; the second focusing lens (32) focuses the central scattered light into the second single-mode fiber (33); The balanced photodetector (34) collects the output signal of the first single-mode fiber (24) and the output signal of the second single-mode fiber (33), and detects the difference frequency signal between the two output signals; The lock-in amplifier (35) processes the difference frequency signal under the conditions of detection frequency f2-f1 and integration time T>2 / f2, and outputs a circular dichroic thermal dark field signal.

7. The dark-field thermal wave confocal microscopy measuring device based on circular dichroism according to claim 6, characterized in that, The lock-in amplifier (35) operates at 0.5T, 1.5T, ..., (N) 2 The output at time -0.5)T is the thermal dark field data under left-handed circularly polarized light illumination, at 0, T, 2T, ..., (N 2 -1) The output at time T is the thermal dark field data under right-hand circularly polarized light illumination. The difference between the two is arranged into an N*N two-dimensional array, which serves as the result of circular dichroism dark field thermal imaging.

Images