Time super-resolution digital holographic measurement system and method based on frequency division multiplexing technology

Abstract

The invention discloses a time super-resolution digital holographic measurement system and method based on frequency division multiplexing. The system comprises a light source, a collimation and beam expansion system, a beam splitter prism, a digital micromirror device (DMD), three 4f lens systems, a diaphragm, a reflector and a camera. Firstly, a DMD is used as a two-dimensional dynamic grating to be synchronized with camera hardware, and a binary grating pattern is dynamically loaded in a single exposure period of the DMD, so that reference light generates multi-angle diffraction; the first 4f system is combined with a diaphragm to filter out non-+ 1-order diffracted light; the second 4f system ensures that the reference light beams are overlapped on an image plane at different moments; the object light is modulated by an object and then interferes with the multi-direction reference light to generate a frequency division multiplexing hologram. When the refreshing speed of the DMD is higher than the frame rate of the camera, the frame rate of the system breaks through the limitation of the sampling rate of the camera, and time super-resolution imaging is realized; a camera is used for recording the frequency division multiplexing hologram in a single frame mode, dependence of a traditional multi-exposure method on synchronization precision is reduced, the experiment process is simplified, and environmental interference sensitivity is reduced.

Description

Technical Field

[0001] The present invention belongs to the field of digital holographic measurement, and in particular relates to a time super-resolution digital holographic measurement system and method based on frequency division multiplexing technology. Background Art

[0002] Off-axis digital holographic measurement technology has been widely used in the visualization measurement of complex physical fields such as biomedical imaging, industrial inspection, flow fields and acoustic fields due to its advantages in full-field, non-contact and high-precision measurement. Traditional off-axis digital holographic technology usually adopts a single-carrier optical path structure and a single-frame acquisition mechanism of the image sensor, resulting in the system's temporal resolution being limited by the frame rate of the image sensor, making it difficult to meet the measurement requirements of high-speed dynamic processes. Off-axis multiplexed holographic technology can simultaneously record multiple sets of complex amplitude wavefronts in a single interferogram, achieving high-speed imaging far higher than the camera frame rate, while effectively reducing the burden of data storage and transmission. Existing off-axis multiplexed holographic measurement devices are complex in structure, bulky in size and high in cost, which are not conducive to promotion and practical application. Therefore, the development of off-axis multiplexed holographic measurement devices with simple structure, easy construction, strong multiplexing capability and controllable cost has attracted widespread attention from scholars at home and abroad.

[0003] Rajput et al. (Sudheesh K. Rajput, Osamu Matoba, Manoj Kumar, Xiangyu Quan,"Sound wave detection by common-path digital holography,"Opt. Lasers Eng. 137, 106331 (2021)) proposed a common-path off-axis point diffraction digital holographic measurement device. The device uses an inclined spectroscopic prism as a spectroscopic element and sets a double-hole filter in the Fourier plane: the unfiltered light beam that passes completely through one of the light holes is used as the object light, and the other pinhole filters out the object light information as the reference light. Finally, the two beams of light interfere in the camera plane to form a hologram. Since the device uses a spectroscopic prism to separate the object light and the reference light, the tilt angle of the spectroscopic prism is strictly required, and the system adjustment is more difficult. In addition, the structure can only capture a single-carrier hologram in one exposure of the camera, and the frame rate of the system is still limited by the acquisition rate of the camera.

[0004] Anzai et al. (Wataru Anzai, Takashi Kakue, Tomoyoshi Shimobaba,"Temporal super-resolution high-speed holographic video recording based on switching reference lights and angular multiplexing in off-axis digital holography" Opt. Lett. 47(13), 3151-3154(2022)) proposed a temporal super-resolution measurement device based on angular multiplexing, which uses two acousto-optic modulators (AOMs) to achieve high-speed switching of two reference beams with different incident directions, doubling the sampling rate of the system. However, the incident light beam coupled with the AOM must meet specific polarization requirements, so additional optical elements are required to adjust the polarization state of the incident light, which increases the complexity of the optical path design. In addition, the system adds an additional reference light arm to achieve the purpose of two-way multiplexing, making the optical system too large and difficult to construct.

[0005] Kuang Cuifang and others from Zhejiang University proposed a method and device for ultra-high-speed structured illumination microscopy, as described in CN115327757A. This device splits the illumination beam into a central interference path and three sub-interference paths. An electro-optical modulator controls the phase difference between the different interference paths to produce different illumination patterns, surpassing the speed limitations of conventional phase modulation. A high-speed rotating mirror is used for scanning, dividing the camera target surface into several imaging areas. A single camera exposure can capture multiple images. However, this device involves numerous components, and the optical path differences between the different interference paths must be matched, making the system complex and bulky, and sensitive to external interference. Summary of the Invention

[0006] The purpose of the present invention is to overcome the problems of traditional single-carrier digital holographic measurement device systems being limited by the camera, large data storage capacity, and the existing off-axis multiplexed digital holographic measurement device systems being complex, large and expensive, and to provide a time super-resolution digital holographic measurement system and method based on frequency division multiplexing technology that has a simple structure, easy construction, strong multiplexing capability and controllable cost.

[0007] The purpose of the present invention is achieved through the following technical solutions:

[0008] The time super-resolution digital holographic measurement system based on frequency division multiplexing technology includes a light source, a collimating beam expansion system, first to second beam splitting prisms, a digital micromirror device (DMD), first to sixth lenses, an aperture, first to third reflectors, an object to be measured, a camera and a computer; the light beam emitted by the light source forms a plane light beam after passing through the collimating beam expansion system, and then is divided into reflected light and transmitted light after passing through the first beam splitting prism; the transmitted light is divided into different diffraction orders by the digital micromirror device, and then is focused on the Fourier plane by the first lens, and an aperture is set on the Fourier plane to separate the 0th order and unnecessary orders The selected diffraction order is blocked, and the selected diffraction order is used as a reference beam and passes through the second lens, the first reflector, the third lens, and the fourth lens in sequence, and then is focused by the second beam splitter prism; the reflected light passes through the second reflector and is modulated into object light by the object to be measured, and then passes through the fifth lens, the third reflector, the sixth lens, and the second beam splitter prism in sequence; finally, the reference light and the object light are merged through the second beam splitter prism and interfere on the camera target surface, completing a time slice; the image signal of the camera is input into a computer; when the refresh rate of the digital micromirror device is greater than the frame rate of the camera, the camera will capture a multiplexed hologram within a single exposure cycle of the camera.

[0009] Furthermore, the trigger input of the camera is connected to the hardware trigger output of the digital micromirror device, and the exposure time of the camera is controlled by configuring the control software of the digital micromirror device to ensure synchronization between the camera and the digital micromirror device.

[0010] Furthermore, the distance between the first lens and the second lens is the sum of the focal lengths of the two lenses, and the aperture is placed on the Fourier plane between the two lenses; the distance between the third lens and the fourth lens is the sum of the focal lengths of the two lenses; and the distance between the fifth lens and the sixth lens is the sum of the focal lengths of the two lenses.

[0011] Furthermore, the digital micromirror device is placed perpendicular to the optical axis as a two-dimensional dynamic grating.

[0012] Furthermore, the camera is placed on the target imaging plane behind the second beam splitter prism.

[0013] Furthermore, the light source emits a light beam with a wavelength of λ.

[0014] The time super-resolution digital holographic measurement method based on frequency division multiplexing technology and the time super-resolution digital holographic measurement system based on frequency division multiplexing technology have the following specific steps:

[0015] Step 1: Connect the camera's trigger input to the DMD's hardware trigger output. Configure the DMD's control software to precisely control the camera's exposure time and synchronize the camera and DMD.

[0016] Step 2: Turn on the light source. The light beam passes through the collimating and expanding system to form a plane beam. After passing through the first beam splitter prism, it is split into reflected light and transmitted light. The reflected light enters the object light path, and the transmitted light enters the transmission light path. After the reflected light is diffracted by the digital micromirror device, the 0th order and other diffraction orders are blocked by the aperture, leaving only the +1st order diffraction light as the reference light, which interferes with the object light after the reflected light is modulated by the object. Set the refresh rate of the digital micromirror device to be greater than the camera acquisition speed so that the camera can capture a multiplexed hologram sequence.

[0017] Step 3: Restore the original light field of the target based on the acquired multiplexed hologram sequence.

[0018] Furthermore, the frame rate of the camera is set to 500fps, and the quadruple frequency division multiplexing mode is adopted to increase the effective acquisition rate of the temporal super-resolution digital holographic measurement system to 2000fps.

[0019] Furthermore, in step 2, four binary fringe patterns are sequentially loaded into the digital micromirror device in a cyclic manner, and four different reference lights after passing through the aperture are incident on the target surface of the camera from different directions:

[0020]

[0021] Among them, A R represents the amplitude of the reference beam; f x m and f y m They represent the spatial frequencies of the reference beam in the x and y directions when the DMD loads the mth pattern; mod refers to the modular operation; the duration of DMD projecting a pattern is T s , object light wavefront O n for:

[0022]

[0023] Wherein, the subscript n represents the nth moment, x and y represent pixel coordinates; A O and They represent the amplitude and phase of the object light at the nth moment respectively; when the reference light and the object light interfere:

[0024]

[0025] Among them, A represents the autocorrelation term, C n represents the complex amplitude distribution of the object to be measured at the nth time point, * represents the conjugate term; the multiplexed holographic video frame sequence H captured by the camera l , by I within a single exposure n The holographic multiplexed video frame sequence captured by the camera is expressed as:

[0026]

[0027] Wherein, l=0, 1, 2, ... represents the time index of the multiplexed hologram acquired by the camera.

[0028] Furthermore, the step 3 performs the holographic multiplexing video frame sequence H l After applying Fourier transform, bandpass filtering, and inverse Fourier transform, we get the complex amplitude:

[0029]

[0030] Among them, FT and IFT represent Fourier transform and inverse Fourier transform, BPF represents bandpass filtering, Indicates rounding operation;

[0031] The amplitude of the object to be measured is obtained by the following formula:

[0032] A n =abs[C n ]

[0033] The phase of the object to be measured is obtained by the following process:

[0034] To obtain the unwrapped phase to be measured, first perform an inter-frame division operation on the complex amplitudes in the same carrier direction to eliminate the influence of the same type of carrier frequency, carrier frequency error, and static phase error, and obtain the complex amplitude containing the differential phase:

[0035]

[0036] Use the arg function to extract the differential phase from the complex amplitude:

[0037]

[0038] Where arg represents a function that calculates a complex independent variable, and the phase difference between two frames is considered to be a small phase change within the time interval; Integrate along the differential direction to recover the phase to be measured:

[0039]

[0040] Among them, φ n represents the phase of the integral at the nth moment, and ∑ represents the summation.

[0041] The beneficial effects of the present invention are:

[0042] 1. DMD acts as a two-dimensional dynamic grating, changing the propagation direction of the reference light multiple times within a single exposure cycle of the camera. When the refresh rate of the DMD is higher than the frame rate of the camera, a multiplexed hologram can be obtained. The system frame rate will exceed the limitation of the camera sampling rate, achieving temporal super-resolution imaging. This is one of the innovations that distinguishes it from existing technologies.

[0043] 2. Non-mechanical reference light angle control based on pure optical modulation eliminates mechanical motion errors and enhances optical path stability. Using a camera to record frequency-division multiplexed holograms in single frames reduces the reliance on synchronization accuracy of traditional multi-exposure methods, simplifies the experimental process, and reduces sensitivity to environmental interference. This is the second innovation that distinguishes this method from existing technologies.

[0044] 3. The system of the present invention uses DMD to achieve frequency division multiplexing, instead of AOM with strict requirements on incident light or SLM with very low refresh rate. It is simple to operate and easy to implement, and can achieve high-speed imaging using a low-speed camera at low cost. By optimizing the optical path design and signal processing method, the present invention realizes the synchronous acquisition of complex amplitude information at multiple moments in a single-frame interference pattern, which not only reduces data storage pressure but also significantly improves measurement efficiency. BRIEF DESCRIPTION OF THE DRAWINGS

[0045] Figure 1 Schematic diagram of the time super-resolution digital holographic measurement system based on frequency division multiplexing technology;

[0046] Figure 2 The multiplexed hologram obtained by the embodiment of this system;

[0047] Figure 3 The spatial spectrum diagram obtained by the embodiment of this system;

[0048] Figure 4 A schematic diagram of the spectrum provided by an embodiment of this system;

[0049] Figure 5 An example of time super-resolution provided for an embodiment of the system of the present invention. DETAILED DESCRIPTION

[0050] The present invention will be further described below with reference to the accompanying drawings.

[0051] The present invention provides a time-super-resolution digital holographic measurement system and method based on frequency division multiplexing technology. The system includes a light source 1 with a wavelength of λ, a collimating and expanding beam system 2, a first beam splitter prism 3, a digital micromirror device (DMD) 4, a first lens 5, an aperture 6, a second lens 7, a first reflector 8, a third lens 9, a fourth lens 10, a second beam splitter prism 16, a second reflector 11, a fifth lens 13, a sixth lens 15, a third reflector 14, an object to be measured 12, a camera 17, and a computer 18. First, the trigger input of camera 17 is connected to the hardware trigger output of DMD 4. By configuring the control software of DMD 4, the exposure time of camera 17 is precisely controlled to ensure perfect synchronization between camera 17 and DMD 4. According to the light propagation path, the light beam emitted by light source 1 passes through collimating and expanding system 2, becoming a parallel beam. It then passes through first beam splitter prism 3, splitting the parallel beam into two: an object beam path and a reference beam path. In the reference beam path, the reference beam passes through DMD 4, where it is diffracted into multiple orders. This is focused on the Fourier plane by first lens 5, with diaphragm 6 blocking unwanted orders. The selected orders then continue to propagate through second lens 7, first reflector 8, third lens 9, and fourth lens 10. In the object beam path, the beam passes through second reflector 11, where it is modulated by object 12 to form the object beam. The beam then passes through fifth lens 13, third reflector 14, and sixth lens 15. The reference and object beams merge through second beam splitter prism 16, causing superposition interference on the image plane of camera 17. DMD 4 completes a deflection, and camera 17 captures a single time slice. When the refresh rate of DMD4 exceeds the camera's frame rate, it deflects multiple times within a single exposure cycle of camera 17, allowing camera 17 to capture a frequency-division multiplexed hologram. The image signal output of camera 17 is connected to the image signal input of computer 18. The first and second lenses 5 and 7 form a first 4f system, the third and fourth lenses 9 and 10 form a second 4f system, and the fifth and sixth lenses 13 and 15 form a third 4f system. The DMD4 is positioned perpendicular to the optical axis as a two-dimensional dynamic grating. The aperture 6 is placed on the Fourier plane of the first 4f system.

[0052] The implementation of a temporal super-resolution digital holographic measurement system based on frequency division multiplexing technology is as follows: First, connect the trigger input of camera 17 to the hardware trigger output of DMD4. By configuring the DMD4 control software, the exposure time of camera 17 is precisely controlled to ensure perfect synchronization between camera 17 and DMD4. Then, the optical system is constructed according to the schematic diagram. A light beam with a wavelength of λ is emitted from light source 1. It is split by collimating and expanding system 2 and first beam splitter prism 3 into two paths: a reference beam path and an object beam path. In the reference beam path, after passing through DMD4, it is diffracted into multiple beams. It then passes through first lens 5, aperture 6, and second lens 7, and is reflected and diverged by first reflector 8. It then passes through third lens 9 and fourth lens 10. The object beam path is reflected by second reflector 11, modulated by the information of the object to be measured 12, and then passes through fifth lens 13, third reflector 14, and sixth lens 15. The reference and object beams are then combined by second beam splitter prism 16 and interfere on the target surface of camera 17, completing a time slice. When the refresh rate of DMD4 is greater than the frame rate of camera 17, camera 17 will capture a multiplexed hologram within a single exposure period of camera 4, thereby improving the system frame rate.

[0053] The technical solutions in the examples of the present invention are described clearly and completely below in conjunction with the drawings in the examples of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, rather than all the embodiments.

[0054] Figure 1 The time super-resolution digital holographic measurement device based on frequency division multiplexing technology includes the following steps:

[0055] Step 1: Connect the camera's trigger input to the DMD's hardware trigger output. Configure the DMD's control software to precisely control the camera's exposure time, ensuring perfect synchronization between the camera and DMD and avoiding crosstalk between scenes at different time points within the same frame.

[0056] Step 2: After the light beam is diffracted by the DMD, a specific order is selected as the reference light to interfere with the object light modulated by the object. When the refresh rate of the DMD is greater than the acquisition speed of the camera, the camera acquires a multiplexed hologram sequence. The camera frame rate is set to 500fps. The limited spatial sampling depth of the camera will limit the frequency domain sampling rate. To avoid undersampling of frequency domain information, quadruple frequency division multiplexing is selected, and the acquisition rate of the temporal super-resolution system is 2000fps.

[0057] The four binary fringe patterns are loaded into the DMD in turn. After the reference beam undergoes diffraction, it will produce diffraction orders with different propagation directions. Use the aperture to block the 0th order and the unnecessary diffraction order, and keep the +1 order. Then, the four different reference beams are incident on the target surface of the camera from different directions. The reference beam sequence can be expressed as

[0058]

[0059] Among them, A R represents the amplitude of the reference beam; f x m and f y m They represent the spatial frequencies of the reference beam in the x and y directions when the DMD is loaded with the mth pattern; mod refers to the modulo operation. The duration of DMD projecting a pattern is T s , object light wavefront O n It can be expressed as:

[0060]

[0061] Wherein, the subscript n represents the nth moment, x and y represent pixel coordinates; A O and They represent the amplitude and phase of the object light at the nth moment respectively. When the reference light and the object light interfere, they can be expressed as:

[0062]

[0063] Among them, A represents the autocorrelation term, C n Represents the complex amplitude distribution of the object under test at the nth time point, and “*” represents the conjugate term. The multiplexed holographic video frame sequence H captured by the camera l , can be seen as the I n The holographic multiplexed video frame sequence captured by the camera can be expressed as:

[0064]

[0065] Wherein, l=0, 1, 2, ... represents the time index of the multiplexed hologram acquired by the camera.

[0066] Step 3: Restore the target original light field according to the multiplexed holographic video frame sequence. Specifically, the following method can be used:

[0067] For H l After applying Fourier transform, bandpass filtering, and inverse Fourier transform, we get the complex amplitude:

[0068]

[0069] Among them, FT and IFT represent Fourier transform and inverse Fourier transform, BPF represents bandpass filtering, Indicates the rounding operation. Then, the amplitude of the object to be measured can be obtained as follows:

[0070] An =abs[C n ]

[0071] To obtain the unwrapped phase to be measured, first perform an inter-frame division operation on the complex amplitudes in the same carrier direction to eliminate the influence of the same type of carrier frequency, carrier frequency error, and static phase error, and obtain the complex amplitude containing the differential phase:

[0072]

[0073] The differential phase is then extracted from the complex amplitude using the arg function:

[0074]

[0075] Where arg represents a function that calculates a complex independent variable, and the phase difference between two frames can be considered as a small phase change within the time interval. The phase to be measured can be recovered by summing along the differential direction:

[0076]

[0077] Among them, φ n represents the phase at the nth moment, and ∑ represents the sum.

[0078] Example:

[0079] The effectiveness of the system was verified by analyzing the rotation angle difference between consecutive frames of the circular protractor. The circular protractor was mounted on a rotating motor with a speed of 10 rpm, equivalent to a rotation speed of 60° / s. The camera sampling rate was set to 100 fps, and after time multiplexing, the system sampling rate reached 400 fps. Therefore, the scale difference between consecutive frames of the protractor should be 0.15°. Figure 5 (a)-(b) show the multiplexed holograms and their spatial spectra collected by the proposed system. In order to clearly identify the scale changes of the protractor, an intensity map is shown every 10 frames. Figure 5 (c) It can be observed that the scale of the circular protractor changes by 1.5° every 10 frames, thus demonstrating that the proposed system achieves temporal super-resolution.

[0080] Figure 5 (d)-(e) show the off-axis single-carrier hologram and its spatial spectrum. Figure 5 (f) shows the reconstructed amplitude. The sampling rate of the camera and the speed of the motor remain unchanged, and the scale difference between adjacent reconstructed frames is 0.6°. For the sake of comparison, an intensity map is also shown every 10 frames. Figure 5 As can be seen in (f), the scale of the circular protractor changes by 6° every 10 frames, which indicates that the acquisition rate of the hologram is 100 fps, which is the same as the preset camera sampling rate.

[0081] The foregoing description is merely a preferred embodiment of the present invention and is not intended to limit the present invention. Those skilled in the art will readily appreciate that various modifications and variations of the present invention are possible. Any modifications, equivalent substitutions, or improvements made within the spirit and principles of the present invention are intended to be within the scope of protection of the present invention.

Claims

1. A time super-resolution digital holographic measurement system based on frequency division multiplexing technology, characterized by: The invention comprises a light source (1), a collimating beam expansion system (2), first to second beam splitting prisms (3, 16), a digital micromirror device (4), first to sixth lenses (5, 7, 9, 10, 13, 15), an aperture (6), first to third reflectors (8, 11, 14), an object to be measured (12), a camera (17) and a computer (18); a light beam emitted by the light source (1) forms a plane light beam after passing through the collimating beam expansion system (2), and then is divided into reflected light and transmitted light after passing through the first beam splitting prism (3); the transmitted light is divided into different diffraction orders after passing through the digital micromirror device (4), and then is focused on the Fourier plane after passing through the first lens (5); an aperture (6) is set on the Fourier plane to block the 0th order and unnecessary orders, and the selected diffraction orders are used as the diffraction order. The reference light beam passes through the second lens (7), the first reflector (8), the third lens (9), and the fourth lens (10) in sequence and is focused by the second beam splitter prism (16); the reflected light passes through the second reflector (11) and is modulated into object light by the object to be measured (12), and then passes through the fifth lens (13), the third reflector (14), the sixth lens (15), and the second beam splitter prism (16) in sequence; finally, the reference light and the object light pass through the second beam splitter prism (16) and converge and interfere on the target surface of the camera (17), completing a time slice; the image signal of the camera (17) is input to the computer (18); when the refresh rate of the digital micromirror device (4) is greater than the frame rate of the camera (17), the camera (17) will capture a multiplexed hologram within a single exposure cycle of the camera (17).

2. The time super-resolution digital holographic measurement system based on frequency division multiplexing technology according to claim 1 is characterized in that: The trigger input of the camera (17) is connected to the hardware trigger output of the digital micromirror device (4), and the exposure time of the camera (17) is controlled by configuring the control software of the digital micromirror device (4), thereby ensuring synchronization between the camera (17) and the digital micromirror device (4).

3. The time super-resolution digital holographic measurement system based on frequency division multiplexing technology according to claim 1, characterized in that: The distance between the first lens (5) and the second lens (7) is the sum of the focal lengths of the two lenses, and the aperture (6) is placed on the Fourier plane between the two lenses; the distance between the third lens (9) and the fourth lens (10) is the sum of the focal lengths of the two lenses; and the distance between the fifth lens (13) and the sixth lens (15) is the sum of the focal lengths of the two lenses.

4. The time super-resolution digital holographic measurement system based on frequency division multiplexing technology according to claim 1, characterized in that: The digital micromirror device (4) is placed perpendicular to the optical axis as a two-dimensional dynamic grating.

5. The time super-resolution digital holographic measurement system based on frequency division multiplexing technology according to claim 1, characterized in that: The camera (17) is placed on the target imaging plane behind the second beam splitter prism (16).

6. The time super-resolution digital holographic measurement system based on frequency division multiplexing technology according to claim 1, characterized in that: The light source (1) emits a light beam with a wavelength of λ.

7. A method for measuring time super-resolution digital holography based on frequency division multiplexing technology, and a system for measuring time super-resolution digital holography based on frequency division multiplexing technology according to any one of claims 1 to 6, characterized in that: The specific steps are as follows: Step 1: Connect the trigger input of the camera (17) to the hardware trigger output of the digital micromirror device (4), and configure the control software of the digital micromirror device (4) to accurately control the exposure time of the camera (17) so that the camera (17) and the digital micromirror device (4) Synchronize between Step 2: Turn on the light source (1), the light beam passes through the collimating beam expansion system (2) to form a plane light beam, and then passes through the first diffraction prism (3) to be divided into reflected light and transmitted light, the reflected light enters the object light path, and the transmitted light enters the transmission light path; after the reflected light is diffracted by the digital micromirror device (4), the 0th order and other diffraction orders are blocked by the aperture (6), and only the +1st order diffraction light is retained as the reference light, and the reflected light is interfered with the object light after being modulated by the object; the refresh rate of the digital micromirror device (4) is set to be greater than the acquisition speed of the camera (17), so that the camera (17) acquires a multiplexed hologram sequence; Step 3: Restore the original light field of the target based on the acquired multiplexed hologram sequence.

8. The time super-resolution digital holographic measurement method based on frequency division multiplexing technology according to claim 7, characterized in that: The frame rate of the camera (17) is set to 500fps, and a quadruple frequency division multiplexing mode is adopted to increase the effective acquisition rate of the time super-resolution digital holographic measurement system to 2000fps.

9. The time super-resolution digital holographic measurement method based on frequency division multiplexing technology according to claim 7, characterized in that: In step 2, four binary fringe patterns are sequentially loaded into the digital micromirror device (4) in a cyclic manner, and four different reference lights passing through the aperture (6) are incident on the target surface of the camera (17) from different directions: Among them, A R represents the amplitude of the reference beam; f x m and They represent the spatial frequencies of the reference beam in the x and y directions when the DMD loads the mth pattern; mod refers to the modular operation; the duration of DMD projecting a pattern is T s , object light wavefront O n for: Wherein, the subscript n represents the nth moment, x and y represent pixel coordinates; A O and They represent the amplitude and phase of the object light at the nth moment respectively; when the reference light and the object light interfere: Among them, A represents the autocorrelation term, C n represents the complex amplitude distribution of the object to be measured at the nth time point, * represents the conjugate term; the multiplexed holographic video frame sequence H captured by the camera l , by I within a single exposure n The holographic multiplexed video frame sequence captured by the camera is expressed as: n=4l+m Wherein, l=0, 1, 2, ... represents the time index of the multiplexed hologram acquired by the camera.

10. The time super-resolution digital holographic measurement method based on frequency division multiplexing technology according to claim 9, characterized in that: The step 3 performs a multi-processing on the holographic multiplexed video frame sequence H l After applying Fourier transform, bandpass filtering, and inverse Fourier transform, we get the complex amplitude: Among them, FT and IFT represent Fourier transform and inverse Fourier transform, BPF represents bandpass filtering, Indicates rounding operation; The amplitude of the object to be measured is obtained by the following formula: A n =abs[C n ] The phase of the object to be measured is obtained by the following process: To obtain the unwrapped phase to be measured, first perform an inter-frame division operation on the complex amplitudes in the same carrier direction to eliminate the influence of the same type of carrier frequency, carrier frequency error, and static phase error, and obtain the complex amplitude containing the differential phase: Use the arg function to extract the differential phase from the complex amplitude: Where arg represents a function that calculates a complex independent variable, and the phase difference between two frames is considered to be a small phase change within the time interval; Integrate along the differential direction to recover the phase to be measured: Among them, φ n represents the phase of the integral at the nth moment, and ∑ represents the summation.

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