Dark-field confocal microscopic measurement device and method based on frequency mismatch demodulation

Abstract

A dark-field confocal microscopic measurement device and method based on frequency mismatch demodulation, which relates to a dark-field confocal microscopic measurement device and method. The present invention aims to solve the problem that the traditional non-destructive detection technology for subsurface defects in dark-field confocal microscopy relies on a complex beam shaping mechanism, which affects the lateral and axial resolutions and reduces the stability of the microscopic system. The device of the present invention includes a dual-channel waveform generator, a modulation illumination module, an optical scanning module, a mismatch demodulation module, and an axial displacement stage; the sample is placed on the axial displacement stage, one channel of the dual-channel waveform generator is connected to the modulation illumination module, the laser emitted by the modulation illumination module is irradiated on the sample through the optical scanning module, and the return light of the sample is collected by the mismatch demodulation module. The present invention belongs to the field of optical precision measurement technology.

Description

Technical Field

[0001] The present invention relates to a dark-field confocal microscopic measurement device and method, belonging to the technical field of optical precision measurement. Background Technique

[0002] During the processing of high-performance advanced optical components, it is inevitable to generate defects such as impurities, scratches, and microcracks below the surface, that is, subsurface defects, which easily affect the mechanical properties and service life of the components. Especially in high-energy laser systems, the existence of subsurface defects reduces the fracture stress of the material, provides a space for light-absorbing impurities, and strongly scatters and modulates the incident high-energy laser, greatly reducing the laser damage threshold of optical components. How to effectively detect and suppress subsurface defects has become a "bottleneck" problem restricting the manufacturing precision of optical components, the production efficiency of core components, and the high-energy laser power density.

[0003] The dark-field confocal microscopic measurement technology has good optical tomography ability, high imaging resolution, and signal-to-noise ratio, and has become an important means for detecting surface and subsurface defects of optical components. However, the traditional non-destructive detection technology for subsurface defects in dark-field confocal microscopy relies on a complex beam shaping mechanism, which affects the lateral and axial resolutions and reduces the stability of the microscopic system. Therefore, achieving dark-field imaging without beam shaping can effectively improve the reliability of subsurface defect detection. Summary of the Invention

[0004] The present invention aims to solve the problem that the traditional non-destructive detection technology for subsurface defects in dark-field confocal microscopy relies on a complex beam shaping mechanism, which affects the lateral and axial resolutions and reduces the stability of the microscopic system, and further provides a dark-field confocal microscopic measurement device and method based on frequency mismatch demodulation.

[0005] The technical solution adopted by the present invention to solve the above problems is as follows: The dark-field confocal microscopic measurement device of the present invention includes a dual-channel waveform generator, a modulation illumination module, an optical scanning module, a mismatch demodulation module, and an axial displacement stage; the sample is placed on the axial displacement stage, one channel of the dual-channel waveform generator is connected to the modulation illumination module, the laser emitted by the modulation illumination module is irradiated on the sample through the optical scanning module, and the reflected light of the sample is collected by the mismatch demodulation module.

[0006] Further, the modulation illumination module includes an LD laser, a single-mode optical fiber, an optical fiber collimator, and a non-polarizing beam splitter; the LD laser, the single-mode optical fiber, the optical fiber collimator, and the non-polarizing beam splitter are arranged in sequence from left to right, the LD laser is connected to one channel of the dual-channel waveform generator, and the laser emitted by the LD laser is incident on the optical scanning module through the single-mode optical fiber, the optical fiber collimator, and the non-polarizing beam splitter.

[0007] Further, the optical scanning module includes a galvanometer, a scanning lens, a tube lens, and an objective lens; the galvanometer, the scanning lens, the tube lens, and the objective lens are arranged in sequence. The LD laser passes through a single-mode optical fiber, a fiber collimator, and a non-polarizing beam splitter in sequence and then enters the galvanometer, and then irradiates on the sample after passing through the scanning lens, the tube lens, and the objective lens in sequence.

[0008] Further, the mismatch demodulation module includes a focusing lens, a pinhole, a PMT detector, and a lock-in amplifier; the return light of the sample is focused by the focusing lens to the pinhole and collected by the PMT detector, and the output electrical signal of the PMT detector is connected to the input channel of the lock-in amplifier.

[0009] Further, a channel of the dual-channel waveform generator outputs a square-wave pulse sequence with a frequency of f to the LD laser, where 500 kHz ≤ f ≤ 10 MHz, and the LD laser outputs intensity-modulated linearly polarized laser with a modulation frequency of f.

[0010] Further, another channel of the dual-channel waveform generator outputs a trigonometric function signal with a frequency of f + Δf to the lock-in amplifier as a reference waveform, the output electrical signal of the PMT detector is connected to the input channel of the lock-in amplifier, and Δf is set to f / 10.

[0011] Further, the lock-in amplifier demodulates at a frequency of f + Δf, acquires and outputs an analog signal, and reconstructs the dark-field microscopic imaging result synchronously with the galvanometer scanning.

[0012] The steps of the dark-field confocal microscopic measurement method of the present invention include:

[0013] Step 1: A channel of the dual-channel waveform generator outputs a square-wave pulse sequence with a frequency of f to the LD laser, and the LD laser outputs intensity-modulated linearly polarized laser with a modulation frequency of f;

[0014] Step 2: The single-mode optical fiber couples the laser and then outputs collimated light through the fiber collimator, enters the optical scanning module through the non-polarizing beam splitter, and is focused on the sample by the galvanometer, the scanning lens, the tube lens, and the objective lens;

[0015] Step 3: The galvanometer scans the position of the focused spot, and controls the scanning rate of the galvanometer so that the residence time of each scanning point is greater than 2 / f;

[0016] Step 4: The return light of the sample is focused by the focusing lens to the pinhole and collected by the PMT detector;

[0017] Step 5: The output electrical signal of the PMT detector is connected to the input channel of the lock-in amplifier, and another channel of the dual-channel waveform generator outputs a trigonometric function signal with a frequency of f + Δf to the reference channel of the lock-in amplifier;

[0018] Step 6: The lock-in amplifier demodulates the frequency of f+Δf with the external reference mode, collects the output analog signal, and reconstructs the tomographic microscopy result synchronously with the galvanometer scanning.

[0019] Step 7: The axial displacement stage is scanned step by step to move the axial position of the sample. After moving one step value, repeat Steps 1-6.

[0020] The beneficial effects of the present invention are as follows:

[0021] 1. The present invention uses a solid focused spot to illuminate the sample, which is more uniform in the field of view, and the system resolution is higher than that of the annular light illumination dark-field confocal microscopy system.

[0022] 2. The present invention uses the lock-in amplification demodulation technology to achieve higher sensitivity defect detection. Description of the Drawings

[0023] Figure 1 It is a schematic structural diagram of the dark-field confocal microscopy measurement device described in the present invention. Detailed Embodiments

[0024] Detailed Embodiment 1: In combination with Figure 1 This embodiment is described. The dark-field confocal microscopy measurement device based on frequency mismatch demodulation described in this embodiment includes a dual-channel waveform generator 1, a modulation illumination module, an optical scanning module, a mismatch demodulation module, and an axial displacement stage 11; the sample 10 is placed on the axial displacement stage 11. One channel of the dual-channel waveform generator 1 is connected to the modulation illumination module, and the laser emitted by the modulation illumination module irradiates the sample 10 through the optical scanning module. The return light of the sample 10 is collected by the mismatch demodulation module.

[0025] Detailed Embodiment 2: In combination with Figure 1 This embodiment is described. The modulation illumination module of the dark-field confocal microscopy measurement device based on frequency mismatch demodulation described in this embodiment includes an LD laser 2, a single-mode optical fiber 3, an optical fiber collimator 4, and a non-polarizing beam splitter 5; the LD laser 2, the single-mode optical fiber 3, the optical fiber collimator 4, and the non-polarizing beam splitter 5 are arranged in sequence from left to right. The LD laser 2 is connected to one channel of the dual-channel waveform generator 1, and the laser emitted by the LD laser 2 is incident on the optical scanning module through the single-mode optical fiber 3, the optical fiber collimator 4, and the non-polarizing beam splitter 5.

[0026] Detailed Embodiment 3: In combination with Figure 1Describing this embodiment, the optical scanning module of the dark-field confocal microscopic measurement device based on frequency mismatch demodulation described in this embodiment includes a galvanometer 6, a scanning lens 7, a tube lens 8, and an objective lens 9; the galvanometer 6, the scanning lens 7, the tube lens 8, and the objective lens 9 are arranged in sequence. The LD laser 2 is incident on the galvanometer 6 after passing through a single-mode optical fiber 3, an optical fiber collimator 4, and a non-polarizing beam splitter 5 in sequence, and then irradiates on the sample 10 after passing through the scanning lens 7, the tube lens 8, and the objective lens 9 in sequence.

[0027] Specific Embodiment Four: Combining Figure 1 Describing this embodiment, the mismatch demodulation module of the dark-field confocal microscopic measurement device based on frequency mismatch demodulation described in this embodiment includes a focusing lens 12, a pinhole 13, a PMT detector 14, and a lock-in amplifier 15; the return light of the sample 10 is focused by the focusing lens 12 onto the pinhole 13 and collected by the PMT detector 14, and the output electrical signal of the PMT detector 14 is connected to the input channel of the lock-in amplifier 15.

[0028] Specific Embodiment Five: Combining Figure 1 Describing this embodiment, one channel of the dual-channel waveform generator 1 of the dark-field confocal microscopic measurement device based on frequency mismatch demodulation outputs a square wave pulse sequence with a frequency of f to the LD laser 2, where 500 kHz ≤ f ≤ 10 MHz, and the LD laser 2 outputs intensity-modulated linearly polarized laser with a modulation frequency of f.

[0029] Specific Embodiment Six: Combining Figure 1 Describing this embodiment, the other channel of the dual-channel waveform generator 1 of the dark-field confocal microscopic measurement device based on frequency mismatch demodulation outputs a trigonometric function signal with a frequency of f + Δf to the lock-in amplifier 15 as a reference waveform. The output electrical signal of the PMT detector 14 is connected to the input channel of the lock-in amplifier 15, and Δf is set to f / 10.

[0030] Specific Embodiment Seven: Combining Figure 1 Describing this embodiment, the lock-in amplifier 15 of the dark-field confocal microscopic measurement device based on frequency mismatch demodulation demodulates at a frequency of f + Δf, acquires and outputs an analog signal, and reconstructs the dark-field microscopic imaging result synchronously with the scanning of the galvanometer 6.

[0031] Specific Embodiment Eight: Combining Figure 1 Describing this embodiment, the steps of the dark-field confocal microscopic measurement method based on frequency mismatch demodulation described in this embodiment include:

[0032] Step 1: One channel of the dual-channel waveform generator 1 outputs a square wave pulse sequence with a frequency of f to the LD laser 2, and the LD laser 2 outputs intensity-modulated linearly polarized laser with a modulation frequency of f;

[0033] Step 2: After the single-mode optical fiber 3 is coupled with the laser, collimated light is output by the fiber collimator 4, enters the optical scanning module through the non-polarizing beam splitter 5, and is focused on the sample 10 by the galvanometer 6, the scanning lens 7, the tube lens 8, and the objective lens 9;

[0034] Step 3: The galvanometer 6 scans the position of the focused spot, and controls the scanning rate of the galvanometer 6 so that the residence time of each scanning point is greater than 2 / f;

[0035] Step 4: The return light of the sample 10 is focused by the focusing lens 12 onto the pinhole 13 and collected by the PMT detector 14;

[0036] Step 5: The electrical signal output by the PMT detector 14 is connected to the input channel of the lock-in amplifier 15, and the other channel of the dual-channel waveform generator 1 outputs a trigonometric function signal with a frequency of f + Δf to the reference channel of the lock-in amplifier 15;

[0037] Step 6: The lock-in amplifier 15 demodulates at a frequency of f + Δf, in the external reference mode, collects and outputs the analog signal, and reconstructs the tomographic microscopy result synchronously with the galvanometer scanning.

[0038] Step 7: The axial displacement stage 11 is moved step by step to scan the axial position of the sample. After moving one step value, steps 1-6 are repeated.

[0039] The above is only a preferred embodiment of the present invention, and does not impose any form of limitation on the present invention. Although the present invention has been disclosed above with a preferred embodiment, it is not intended to limit the present invention. Any person skilled in the art, within the scope of the technical solution of the present invention, can make some changes or modifications to equivalent embodiments with equivalent changes by using the disclosed technical content. However, as long as it does not depart from the content of the technical solution of the present invention, according to the technical essence of the present invention, any simple modification, equivalent replacement, and improvement of the above embodiments within the spirit and principle of the present invention still fall within the protection scope of the technical solution of the present invention.

Claims

1. A dark-field confocal microscopic measurement device based on frequency mismatch demodulation, characterized in that: The dark-field confocal microscopy measurement device based on frequency mismatch demodulation includes a dual-channel waveform generator (1), a modulation illumination module, an optical scanning module, a mismatch demodulation module, and an axial displacement stage (11); a sample (10) is placed on the axial displacement stage (11), one channel of the dual-channel waveform generator (1) is connected to the modulation illumination module, the laser emitted by the modulation illumination module irradiates the sample (10) through the optical scanning module, the return light of the sample (10) is collected by the mismatch demodulation module, and the modulation illumination module includes an LD laser (2), a single-mode optical fiber (3), an optical fiber collimator (4), and a non-polarizing beam splitter (5); Another channel of the dual-channel waveform generator (1) outputs a trigonometric function signal with a frequency of f + Δf to a lock-in amplifier (15) as a reference waveform, the output electrical signal of the PMT detector (14) is connected to the input channel of the lock-in amplifier (15), Δf is set to f / 10, and the modulation frequency is f; The optical scanning module includes a galvanometer (6), a scanning lens (7), a tube lens (8), and an objective lens (9); the galvanometer (6), the scanning lens (7), the tube lens (8), and the objective lens (9) are arranged in sequence, the laser emitted by the LD laser (2) passes through the single-mode optical fiber (3), the optical fiber collimator (4), and the non-polarizing beam splitter (5) in sequence and then enters the galvanometer (6), and then passes through the scanning lens (7), the tube lens (8), and the objective lens (9) in sequence and then irradiates the sample (10); The mismatch demodulation module includes a focusing lens (12), a pinhole (13), a PMT detector (14), and a lock-in amplifier (15); the return light of the sample (10) is focused by the focusing lens (12) onto the pinhole (13) and collected by the PMT detector (14), and the output electrical signal of the PMT detector (14) is connected to the input channel of the lock-in amplifier (15); The lock-in amplifier (15) demodulates at a frequency of f + Δf, acquires and outputs an analog signal, and reconstructs the dark-field microscopy imaging result synchronously with the scanning of the galvanometer (6).

2. The dark-field confocal microscopic measurement device based on frequency mismatch demodulation according to claim 1, wherein: One channel of the dual-channel waveform generator (1) outputs a square wave pulse sequence with a frequency of f to the LD laser (2), 500 kHz ≤ f ≤ 10 MHz, and the LD laser (2) outputs intensity-modulated linearly polarized laser light.

3. A dark-field confocal microscopic measurement method for the dark-field confocal microscopic measurement device according to claim 1 or 2, characterized in that: The steps of the dark-field confocal microscopy measurement method based on frequency mismatch demodulation include: Step 1: One channel of the dual-channel waveform generator (1) outputs a square wave pulse sequence with a frequency of f to the LD laser (2), and the LD laser (2) outputs intensity-modulated linearly polarized laser light with a modulation frequency of f; Step 2: After the single-mode optical fiber (3) couples the laser, collimated light is output by the optical fiber collimator (4), enters the optical scanning module through the non-polarizing beam splitter (5), and is focused on the sample (10) by the galvanometer (6), the scanning lens (7), the tube lens (8), and the objective lens (9); Step 3: The galvanometer (6) scans the position of the focused spot, and controls the scanning rate of the galvanometer (6) so that the residence time of each scanning point is greater than 2 / f; Step 4: The return light of the sample (10) is focused by the focusing lens (12) onto the pinhole (13) and collected by the PMT detector (14); Step 5: The electrical signal output by the PMT detector (14) is connected to the input channel of the lock-in amplifier (15), and the other channel of the dual-channel waveform generator (1) outputs a trigonometric function signal with a frequency of f + Δf to the reference channel of the lock-in amplifier (15). Step 6: The lock-in amplifier (15) demodulates at a frequency of f + Δf, in the external reference mode, collects and outputs the analog signal, and reconstructs the tomographic microscopy result synchronously with the galvanometer scanning. Step 7: The axial displacement stage (11) is moved step by step to scan the axial position of the sample. After moving one step value, repeat Steps 1-6.

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