Full-field interference measuring instrument and measuring method based on comb-shaped interval scanning source

Abstract

The invention discloses a full-field interference measuring instrument based on a comb-shaped interval scanning source and a measuring method. The full-field interference measuring instrument comprises a light source module, a modulation interferometer, a shaping uniform light path, a measuring interferometer, an acquisition camera and a data processing unit, light rays emitted by the light source module enter the modulation interferometer, the modulation interferometer performs light splitting interference on the entered light rays and then outputs interference light to enter the shaping and dodging light path, and the shaping and dodging light path performs collimation, beam expansion and dodging on the light rays; the shaping and dodging light path outputs processed dodging light as input light to enter the measurement interferometer, the measurement interferometer divides the input light into measurement light and reference light, the measurement light is reflected by a measurement sample and interfered with the reference light and then is imaged on the acquisition camera, and the acquisition camera transmits acquired data to the data processing unit. The measuring instrument can realize rapid imaging on the premise of no mechanical motion, keeps an imaging plane stable, avoids imaging errors caused by mechanical motion, and improves the imaging resolution of the system.

Description

Technical Field

[0001] This invention relates to a full-field measurement interferometer, and more particularly to a full-field interferometric measuring instrument and measurement method based on a comb-shaped interval scanning source. Background Technology

[0002] Optical interferometry utilizes the principle of light interference to achieve micron- to nanometer-level precision in detecting surface morphology, thickness, and optical properties. Traditional interferometers offer larger imaging fields of view and imaging depth and are widely used in materials science, on-site process monitoring, and other fields. Full-field interferometers possess isotropic micron-level resolution and can generate signals close to the true image from the sample in a very short time without further processing of the sample, such as white-light interferometers and phase-shifting interferometers. However, existing full-field interferometry systems are limited by low spatial coherence and wide spectral characteristics, resulting in short coherence lengths. Measurements can only be performed when the optical paths of the measurement and reference optical paths are equal, limiting the field of view and requiring physical displacement to obtain depth information. The scanning process introduces mechanical errors and has low data acquisition efficiency, failing to meet the demands of high-speed online inspection (such as online semiconductor quality inspection and biological in vivo imaging). Mechanical scanning of the reference arm or moving the sample is required to achieve large-scale measurements, leading to limited measurement speed, poor vibration resistance, and difficulty in achieving dynamic process observation. Summary of the Invention

[0003] In view of this, embodiments of the present invention provide a full-field interferometry instrument and measurement method based on a comb-shaped interval scanning source, which achieves three-dimensional topographic imaging with good imaging quality and fast imaging speed without mechanical motion.

[0004] To achieve the above objectives, the present invention adopts the following technical solution: In a first aspect, a full-field interferometric measuring instrument based on a comb-shaped interval scanning source is provided, comprising a light source module, a modulation interferometer, a shaping and homogenizing optical path, a measuring interferometer, a data acquisition camera, and a data processing unit. The light emitted from the light source module enters the modulation interferometer, which performs beam splitting interference on the incoming light and outputs interfering light that enters the shaping and homogenizing optical path. The shaping and homogenizing optical path collimates, expands, and homogenizes the light. The homogenized light output from the shaping and homogenizing optical path is used as input light and enters the measuring interferometer. The measuring interferometer splits the input light into a measuring light and a reference light. After being reflected by the measuring sample, the measuring light interferes with the reference light and forms an image on the data acquisition camera. The data acquisition camera transmits the acquired data to the data processing unit.

[0005] Furthermore, the modulation interferometer includes a first 1*2 fiber coupler, a second 1*2 fiber coupler, a polarization controller, an optical delay line, a fiber stretcher, and a drive controller; the first 1*2 fiber coupler splits the light from the light source module into two beams that enter the sample arm and the reference arm respectively; the polarization controller is arranged on the sample arm; the optical delay line and the fiber stretcher are arranged on the reference arm; the fiber stretcher is connected to the drive controller; the light from the reference arm, after passing through the fiber stretcher and the optical delay line, interferes with the light from the sample arm at the second 1*2 fiber coupler.

[0006] Furthermore, the shaping and homogenizing optical path includes a collimating lens, a beam expander group, and a homogenizing lens group; the collimating lens is an aspherical lens, the beam expander group adopts a Galilean structure, and the homogenizing lens group adopts a structure of two aspherical lenses. After the light passes through the collimating lens, it becomes parallel light. The parallel light passes through the beam expander group for proportional beam expansion, and the light spot diameter becomes larger. Finally, after passing through the homogenizing lens group, the light field energy within the light spot area is uniformly distributed.

[0007] Furthermore, the measurement interferometer includes a beam splitter, an adjustable attenuator, a focusing lens, a reflecting mirror, and a double telecentric lens. The beam splitter splits the light field after the light has passed through the shaping and homogenizing optical path into a measurement beam and a reference beam. The reference beam is attenuated by the adjustable attenuator and focused by the focusing lens before being focused on the reflecting mirror. After being reflected by the reflecting mirror, the reflected light returns to the beam splitter along the original path. After the measurement beam is reflected on the measurement sample, the reflected light interferes with the light reflected by the reflecting mirror at the beam splitter. The interference beam passes through the double telecentric lens and is captured by the acquisition camera.

[0008] Furthermore, the drive controller is connected to the data processing unit, and the data processing unit sends control signals to the drive controller to control the fiber stretcher to stretch and compress the fiber to modulate the optical phase of the reference arm. The acquisition camera is connected to the data processing unit, and the imaging signal acquired by the acquisition camera is transmitted to the data processing unit for image processing.

[0009] Secondly, the measurement method of the above-mentioned full-field interferometry instrument based on the comb-shaped interval scanning source is provided, and the specific steps are as follows: S1: Transmit the light beam emitted by the light source module to the modulation interferometer; S2: Adjust the modulation interferometer to perform optical path compensation of the reference arm until the modulation interferometer outputs interference light; S3: After passing through the shaping and homogenizing mirror group, the interference light becomes a flat-topped uniform beam. The beam is split into a measurement beam and a reference beam in the measuring interferometer. After the measurement beam and the reference beam interfere, the interference light is focused onto the acquisition camera by the double telecentric lens. S4: Acquisition camera acquires interference signals; S5: Change the optical path difference between the two arms of the modulation interferometer to delay the phase, repeat S3-S4, and collect the interferogram after phase delay by the camera until the entire depth range scan is completed. S6: The data processing unit processes the acquired interferogram, performs envelope detection using the Hilbert transform method, and outputs a three-dimensional surface topography image.

[0010] The beneficial effects of this invention are as follows: The modulation interferometer is used to modulate the light from the light source module. The change in the optical path difference between the two arms of the modulation interferometer changes the spectral period. The modulation interferometer outputs a modulated comb-shaped interval scanning source, which can achieve a large range of axial scanning. The debugging interferometer and the measurement interferometer are separate and independent. The mechanical vibration of the modulation interferometer will not affect the measurement, thus improving system stability and measurement accuracy.

[0011] Because the acquisition camera needs to achieve rapid imaging while also satisfying the requirements of parallel light incidence and emission, a double telecentric lens is chosen as the structure of the imaging system. The double telecentric lens has a large depth of field, and when the interferometer is adjusted to change the optical path for scanning at different depths, there is no need to adjust the system focus or move the camera to focus, and the camera can still capture clear images within the depth of field. Attached Figure Description

[0012] Figure 1 A schematic diagram of the structure of a full-field interferometry instrument based on a comb-shaped interval scanning source provided in an embodiment of the present invention; Figure 2 The interferogram of the interferometric light output by the interferometer provided in this invention.

[0013] Figure 3 The spectrum of the output interference light of the modulation interferometer provided in this invention.

[0014] Figure 4 The flowchart illustrates the measurement steps of the full-field interferometer with a comb-shaped interval scanning source provided by this invention.

[0015] In the diagram: 1. Light source module; 2. First 1*2 fiber coupler; 3. Polarization controller; 4. Sample arm; 5. Second 1*2 fiber coupler; 6. Optical delay line; 7. Fiber stretcher; 8. Reference arm; 9. Drive controller; 10. Data processing unit; 11. Acquisition camera; 12. Double telecentric lens; 13. Collimating lens; 14. Plano-concave lens; 15. Plano-convex lens; 16. Plano-concave aspherical lens; 17. Plano-convex aspherical lens; 18. Beam splitter; 19. Adjustable attenuator; 20. Focusing lens; 21. Reflector; 22. Modulation interferometer; 23. Shaping and homogenizing optical path; 24. Measurement interferometer. Detailed Implementation

[0016] The present invention will be further described in detail below with reference to the accompanying drawings and embodiments, but the invention is not limited to these embodiments.

[0017] like Figure 1 As shown, this embodiment of the invention provides a full-field interferometric measuring instrument based on a comb-shaped interval scanning source, including a light source module 1, a modulation interferometer 22, a shaping and homogenizing optical path 23, a measuring interferometer 24, a data acquisition camera 11, and a data processing unit 10. The light emitted from the light source module 1 enters the modulation interferometer 22, which performs beam splitting interference on the incoming light and outputs interference light into the shaping and homogenizing optical path 23. The shaping and homogenizing optical path 23 collimates, expands, and homogenizes the light. The homogenized light output from the shaping and homogenizing optical path 23 is used as input light into the measuring interferometer 24. The measuring interferometer 24 splits the input light into a measuring light and a reference light. The measuring light, after being reflected by the measuring sample, interferes with the reference light and forms an image on the data acquisition camera 11. The data acquisition camera 11 transmits the acquired data to the data processing unit 10.

[0018] The modulation interferometer 22 of this invention is used to modulate the light from the light source module 1. The change in the optical path difference between the two arms of the modulation interferometer 22 alters the spectral period. The modulation interferometer 22 outputs a modulated comb-shaped interval scanning source, enabling a large-range axial scan. The adjustment interferometer 22 is separate and independent from the measurement interferometer 24. The mechanical vibration of the modulation interferometer 22 will not affect the measurement, improving system stability and measurement accuracy. Since the acquisition camera 11 requires rapid imaging and must satisfy parallel light incidence and emission, a double telecentric lens 12 is selected as the structure of the imaging system. The double telecentric lens 12 has a large depth of field. When the adjustment interferometer 22 changes the optical path for scanning at different depths, there is no need for system focusing or camera refocusing; the camera can still capture clear images within the depth of field.

[0019] In this embodiment, the laser emitted by the laser in the light source module 11 has a center wavelength of 840nm and a bandwidth of 50nm, and its spectrum is as follows: Figure 3 As shown in (a) of the diagram.

[0020] In one embodiment, the modulation interferometer 22 is used to modulate a broadband laser beam into a comb-shaped spaced light source, the spectrum of which is as follows: Figure 3As shown in (b) of the diagram. The modulation interferometer 22 includes a first 1*2 fiber coupler 2, a second 1*2 fiber coupler 5, a polarization controller 3, an optical delay line 6, a fiber stretcher 7, and a drive controller 9. The first 1*2 fiber coupler 2 splits the light from the light source module 1 into two beams, which enter the sample arm 4 and the reference arm 8 respectively. The polarization controller 3 is arranged on the sample arm 4 to adjust the polarization state of the light in the sample arm 4, so that the light in the sample arm 4 and the reference arm 8 are in the same polarization state. The optical delay line 6 and the fiber stretcher 7 are arranged on the reference arm 8 to adjust the optical path of the reference arm 8 and compensate for the optical path difference between the sample arm 4 and the reference arm 8. The fiber stretcher 7 is used to squeeze the fiber and modulate the phase of the reference arm 8. The fiber stretcher 7 is connected to the drive controller 9. After passing through the fiber stretcher 7 and the optical delay line 6, the light from the reference arm 8 interferes with the light from the sample arm 4 at the second 1*2 fiber coupler 5.

[0021] In this embodiment, the shaping and homogenizing optical path 23 includes a collimating lens, a beam expander group, and a homogenizing lens group. The collimating lens is an aspherical lens 13, the beam expander group adopts a Galilean structure (composed of a plano-concave lens 14 and a plano-convex lens 15 according to the Galilean structure), and the homogenizing lens group adopts a structure of two aspherical lenses (composed of a plano-concave aspherical lens 16 and a plano-convex aspherical lens 17). After the light passes through the collimating lens, it becomes parallel light. The parallel light passes through the beam expander group for proportional beam expansion, and the light spot diameter becomes larger. Finally, after passing through the homogenizing lens group, the light field energy within the light spot area is uniformly distributed.

[0022] In this embodiment, the measurement interferometer 24 includes a beam splitter 18, an adjustable attenuator 19, a focusing lens 20, a reflecting mirror 21, and a double telecentric lens 12. The beam splitter 18 splits the light field after passing through the shaping and homogenizing optical path 23 into a measurement light and a reference light. The reference light is attenuated by the adjustable attenuator 19 and focused by the focusing lens 20 before being focused on the reflecting mirror 21. After being reflected by the reflecting mirror 21, the reflected light returns to the beam splitter 18 along the original path. After the measurement light is reflected on the measurement sample, the reflected light interferes with the light reflected by the reflecting mirror 21 at the beam splitter 18. The interference light passes through the double telecentric lens 12 and is captured by the acquisition camera 11.

[0023] The adjustable attenuator 19 attenuates the light energy of the reference light to reduce the energy of the reference light and improve the contrast of the interference between the reference light and the measurement light. The focusing lens 20 is used to focus the beam and prevent the loss of the returning light due to the slight tilt of the reflector 21. The returning measurement light and the reference light interfere at the beam splitter 18. The interference light enters the double telecentric lens. The double telecentric lens has a large depth of field and is used to eliminate the image quality changes caused by the change of the object position and maintain a constant magnification.

[0024] In this embodiment, the data processing unit 10 is connected to the drive controller 9 and the acquisition camera 11. The data processing unit 10 outputs pulse information to the drive controller 9, controlling the fiber stretcher 7 to stretch and compress the fiber to modulate the optical phase of the reference arm 8, thus achieving phase modulation. When the optical phase is modulated, the modulating interferometer 22 outputs a modulated laser beam, which appears as a comb-shaped spaced beam. The comb-shaped spaced beam is reflected on the surface of the test sample and interferes at the beam splitter 18. The acquisition camera 11 then acquires the interference image. The acquisition camera 11 is connected to the data processing unit 10 and transmits the acquired interference image to the data processing unit 10 for image processing. After acquiring the data, the data processing unit 10 outputs a three-dimensional surface topography image. The data processing unit 10 can be a computer or an embedded microcontroller system, but is not limited to these. The drive controller 9 can be a servo motor driver, but is not limited to these.

[0025] The basic principle of optical path transmission of the full-field interferometer based on the comb-spaced scanning source in this embodiment is as follows: The intensity at the output of interferometer 24 is measured under monochromatic light conditions. It can be given by the following formula: (1) I ( k ) represents the light intensity corresponding to wavenumber k. It is the intensity of the light source. It is the wave number. These are the lengths of sample arm 4 and reference arm 8 of modulation interferometer 22, respectively. The measurements are of the lengths of the sample arm 4 and the reference arm 8 of the interferometer 24, respectively. If the light source has bandwidth, the measurement is of the intensity at the output of the interferometer 24. This can be obtained in the following way: (2) The intensity of the interferogram is based on the optical path difference of the corresponding measuring interferometer 24. Let be the spectral density of the light source. The light source spectrum has a Gaussian beam splitting form, as shown in the following formula: (3) in It is the center wavenumber of the light source spectrum. It is the spectral width, corresponding to the half-width at the spectral maximum value 1 / e. Substituting formulas (1) and (3) into (2), we get: (4) (5) (6) (7) in It is the coherence length of the light source.

[0026] Formula (4) represents the output intensity of the measuring interferometer 24, such as Figure 2 As shown, the interference information consists of three chirps, with the middle chirp corresponding to the one in the equation. The term, the chirping on both sides corresponds to the term in equation (4). and In equations (6) and (7), the distance between the lateral chirp and the center is equal to the chirp distance. The existence of lateral chirping indicates that even in absolute values... It is constant and greater than the coherence length. The interference at the output of the measuring interferometer 24 is also observable. When When the difference changes, the secondary reference also changes.

[0027] When the optical path difference in the modulated interferometer 22 is zero, the peak value of the central interferogram is the output. The peak values ​​of the interferograms on both sides centered on the central peak are the result of measuring the interference signal in the interferometer 24, and are ultimately used as the relative depth information of the sample. That is, one of these peaks can be selectively observed to obtain a depth image of the sample.

[0028] This embodiment also provides an interferometric measurement method using a full-field interferometer based on a comb-spaced scanning source, such as... Figure 4 As shown, the specific steps are as follows: S1: Transmit the light beam emitted by the light source module 1 to the modulation interferometer 22; Specifically, the light emitted by the light source module 1 enters the first 1*2 fiber optic coupler 2 of the modulation interferometer 22, splitting the light from the light source module 1 into two beams that enter the sample arm 4 and the reference arm 8 respectively. The light from the sample arm 4 and the light from the reference arm 8 interfere at the second 1*2 fiber optic coupler 5.

[0029] S2: Adjust the modulation interferometer 22 to perform optical path compensation for the reference arm 8 until the modulation interferometer 22 outputs interference light; Specifically, the optical delay line 6 and the fiber stretcher 7 of the reference arm 8 are used to adjust the optical path of the reference arm 8 and compensate for the optical path difference between the sample arm 4 and the reference arm 8. The drive controller 9 controls the fiber stretcher 7 to squeeze the fiber and modulate the phase of the reference arm 8. The modulated interference light is output from the second 1*2 fiber coupler 5.

[0030] S3: After passing through the shaping and homogenizing lens group, the interference light becomes a flat-topped uniform beam. The beam is split into a measurement beam and a reference beam in the measuring interferometer 24. After the measurement beam and the reference beam interfere, the interference light is focused onto the acquisition camera 11 by the double telecentric lens 12. Specifically, after the interference light is collimated by the aspherical mirror 13, it is expanded by a beam expander composed of a plano-concave lens 14 and a plano-convex lens 15. After the expanded beam is homogenized by a homogenizing mirror group composed of a plano-concave aspherical lens 16 and a plano-convex aspherical lens 17, the homogenized beam enters the measuring interferometer 24. The measuring interferometer 24 splits the incoming beam into a measuring beam and a reference beam. The measuring beam is reflected on the sample, and the reference beam is reflected on the reflecting mirror 21. After the reflected measuring beam and reference beam are interfered by the beam splitter 18, they are focused onto the acquisition camera 11 by a dual telecentric lens.

[0031] S4: Camera 11 acquires interference signals; Specifically, the acquisition camera 11 is a CMOS area array camera. In step S3, the interference signal is imaged onto the CMOS area array camera through a dual telecentric lens. Each pixel on the CMOS area array camera corresponds to each object point on the sample surface.

[0032] S5: Change the optical path difference between the two arms of the modulation interferometer 22 to delay the phase, repeat S3-S4, and the acquisition camera 11 acquires the interferogram after the phase delay until the entire depth range scan is completed. Specifically, the fiber stretcher 7 of the modulation interferometer 22 is adjusted with nm-level precision. The entire phase modulation range is 1~5mm. Steps S3-S4 are repeated to gradually complete the modulation of the entire phase range. During the modulation process of the entire range, the acquisition camera 11 acquires the interference signal of the phase modulation process in real time until the entire depth scan is completed.

[0033] S6: The data processing unit 10 processes the acquired interferogram, performs envelope detection using the Hilbert transform method, and outputs a three-dimensional surface topography image.

[0034] Specifically, the data processing unit 10 is a computer. The computer receives and processes a series of two-dimensional data collected by the acquisition camera 11, performs envelope detection on the interference signal intensity of the two-dimensional pixel array using the Hilbert transform method, arranges and assembles all the two-dimensional data into three-dimensional data in the time dimension, and outputs the three-dimensional surface morphology of the measured sample.

[0035] In this example, the interference signal is a cosine signal modulated by a Gaussian envelope in the time dimension. The signal intensity can be detected using the envelope curve fitting method, which treats the signal as a cosine signal whose amplitude is modulated by a low-frequency band signal. The peak point of the low-coherence interference signal coincides with the peak point of the carrier signal. The envelope curve fitting method extracts the envelope of the interference signal and fits the envelope curve using the least squares method. Finally, the position corresponding to the peak point of this envelope curve is taken as the location of the zero optical path difference point.

[0036] In this embodiment, the Hilbert transform method, as an envelope detection method, can be used to deencapsulate broadband information and solve for the instantaneous frequency of the signal for any signal function. Its Hilbert transform is defined as and The convolution, i.e.: (8) Hilbert's inverse transform is: (9) in, for The Hilbert transform result, For signal Hilbert transform, It is the integral variable.

[0037] The frequency response formula of the Hilbert transform is: (10) in, The Hilbert transform of the frequency term, Where is the signal frequency, and j is the imaginary unit, representing a 90° phase shift of the signal.

[0038] The interference terms for the interferogram are: (11) After the Hilbert transform, it can be expressed as: (12) in, The original signal strength, For signal amplitude, Here, is the Hilbert transform of the original signal, and z is the scanning height of the test sample. It is phase. It is angular frequency; Analysis of the above equation yields the analytic signal of the envelope: (13) Where h(z) is the analytic signal, The original signal, The Hilbert transform of the original signal is obtained, and the envelope curve is fitted using the least squares method. The amplitude of the above analytical signal can be obtained to get the signal envelope. Finally, the position corresponding to the peak point of the envelope curve is taken as the position of the zero optical path difference point.

[0039] The above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A full-field interferometer based on comb-like interval scanning source, comprising a light source module, a modulation interferometer, a shaping and homogenizing light path, a measurement interferometer, a collection camera, and a data processing unit; light emitted by the light source module enters the modulation interferometer, the modulation interferometer splits the incoming light and outputs the split light as interference light into the shaping and homogenizing light path, the shaping and homogenizing light path collimates, expands, and homogenizes the light, and the shaping and homogenizing light path outputs the processed homogenized light as input light into the measurement interferometer, the measurement interferometer splits the input light into measurement light and reference light, the measurement light is reflected by a measurement sample and interferes with the reference light, and the interference light is imaged on the collection camera, and the collection camera transmits collected data to the data processing unit.

2. The comb spacing scanning source based full-field interferometer of claim 1, wherein, The modulation interferometer comprises a first 1*2 optical fiber coupler, a second 1*2 optical fiber coupler, a polarization controller, an optical delay line, an optical fiber stretcher, and a drive controller. The first 1*2 optical fiber coupler splits the light from the light source module into two beams of light that enter a sample arm and a reference arm, respectively, the sample arm is provided with a polarization controller, the reference arm is provided with an optical delay line and an optical fiber stretcher, the optical fiber stretcher is connected to the drive controller, and the light from the reference arm passes through the optical fiber stretcher and the optical delay line and then interferes with the light from the sample arm at the second 1*2 optical fiber coupler.

3. The comb-spacing scanning source based full-field interferometer of claim 1, wherein, The shaping and homogenizing light path comprises a collimating lens, an expansion mirror group, and a homogenizing mirror group. The collimating lens is an aspheric lens, the expansion mirror group adopts a Galileo structure, and the homogenizing mirror group adopts a structure of two aspheric lenses, the light becomes parallel light after passing through the collimating lens, the parallel light is expanded at a constant ratio by the expansion mirror group, the spot diameter becomes larger, and finally the light field energy in the spot range is uniformly distributed after passing through the homogenizing mirror group.

4. The comb spacing scanning source based full-field interferometer according to claim 1 or 3, characterized in that, The measurement interferometer comprises a beam splitter, an adjustable attenuator, a focusing lens, a mirror, and a double-telecentric lens. The beam splitter splits the light field after the shaping and homogenizing light path into measurement light and reference light, the reference light is attenuated by the adjustable attenuator and focused by the focusing lens, and then focused on the mirror, the reflected light returns to the beam splitter after being reflected by the mirror, the measurement light is reflected by the measurement sample, and then the reflected light interferes with the light reflected by the mirror at the beam splitter, the interference light passes through the double-telecentric lens and is imaged on the collection camera.

5. The comb spacing scanning source based full-field interferometer of claim 2, wherein, The drive controller is connected to the data processing unit, the data processing unit sends a control signal to the drive controller to control the optical fiber stretcher to stretch and squeeze the optical fiber to modulate the phase of the light from the reference arm, the collection camera is connected to the data processing unit, the collection camera collects imaging signals and transmits the imaging signals to the data processing unit for image processing.

6. The measurement method of the comb-spaced-scan-source-based full-field interferometer according to claim 1, wherein, The specific steps are as follows: S1: transmitting the light beam emitted by the light source module to the modulation interferometer; S2: adjusting the modulation interferometer to compensate the optical path of the reference arm until the modulation interferometer outputs interference light; S3: the interference light becomes a flat-top uniform light beam after passing through the shaping and homogenizing mirror group, the light beam is split into measurement light and reference light in the measurement interferometer, the measurement light and the reference light interfere with each other, and the interference light is focused on the collection camera by the double-telecentric lens; S4: the collection camera collects interference signals; S5: change the optical path difference of the two arms of the modulation interferometer to perform phase delay, repeat S3-S4, and collect the interferogram after phase delay by the camera until the entire depth range scanning is completed; S6: the data processing unit performs data processing on the collected interferogram, performs envelope detection by the Hilbert transform method, and outputs a three-dimensional surface topography image.

Images