Single-shot imaging apparatus and method based on structured light encoding and transient grating shuttering

Abstract

The application provides a single-shot imaging device and method based on structured light coding and transient grating shutter, the device comprising: an ultrashort pulse laser, a to-be-measured transient event device, an optical beam splitter, an optical path adjusting unit, a structured light coding unit, an optical beam combiner, a transient grating shutter unit, an imaging unit, and a data processing unit in communication connection with the imaging unit, which are sequentially arranged along the laser transmission direction; the ultrashort pulse laser irradiates the to-be-measured transient event device to generate to-be-measured signal light, the to-be-measured signal light is split into multiple sub-beams by the optical beam splitter; the optical path adjusting unit is used for setting time delay for each sub-beam and the structured light coding unit is used for modulation coding, the transient grating shutter unit is used for gating different time slices, and a composite light field image is formed in the imaging unit; the data processing unit is used for restoring light field information of each sub-beam at different times, and femtosecond-level time resolution and high-precision measurement of transient events are realized.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of laser technology and devices, in particular to a single-shot imaging device and method based on structured light coding and transient grating shutter. BACKGROUND

[0002] Ultrafast phenomena exist widely in the natural world and scientific and technological research, reflecting many important basic mechanisms in physics, chemistry and biology. Ultrafast phenomena generally occur in two-dimensional space on a time scale from nanoseconds to femtoseconds, and ultrafast optical imaging technology can realize two-dimensional visualization observation of transient evolution processes, which is an important tool for studying ultrafast dynamics and has attracted widespread attention from researchers in the field of science and technology. For highly repeatable ultrafast phenomena, the classical pump-probe method is usually used to capture the dynamic evolution process of transient events and explore potential influencing mechanisms. However, many ultrafast phenomena are either non-reproducible or difficult to reproduce, such as superstrong laser filamentation, device damage, irreversible chemical reactions, etc. In these cases, the pump-probe method is difficult to play a role. In addition, for transient events with low repetition frequency or significant changes between shots, such as plasma evolution, the pump-probe method not only has low measurement efficiency, but also cannot obtain accurate dynamic evolution information. The pump-probe method is limited to statistical research under reproducible conditions.

[0003] In order to overcome the limitations of the pump-probe method, researchers have proposed a series of single-shot ultrafast optical field imaging techniques in recent years. Single-shot ultrafast optical field imaging technology refers to the acquisition of multiple time and space resolved information of the entire transient event through a single exposure. "Single-shot" means that a single exposure can capture the entire transient event, "ultrafast" means that femtosecond to nanosecond scale time resolution can be achieved, "optical field" means that spectral information from extreme ultraviolet to far infrared can be detected, and "imaging" means that spatial (x, y) dimensional information can be obtained. Single-shot ultrafast optical field imaging technology can characterize transient events under more extensive and arbitrary conditions, opening the door to the study of non-reproducible and difficult-to-reproduce ultrafast phenomena, and has become an essential tool for understanding basic scientific and technological problems and achieving high-precision and high-efficiency measurement.

[0004] The existing single-shot ultrafast light field imaging measurement technology usually uses an ultrashort pulse train as a probe element, actively encodes in the dimensions of space, angle, wavelength, polarization or spatial frequency, and then completes the measurement of transient events. Such a measurement method using an ultrashort pulse train as an illumination probe detects the transient events (such as laser-induced plasma), and it is difficult to measure the light field itself. Another type of single-shot ultrafast light field imaging measurement technology does not require active illumination, and uses an ultrafast photoelectric detector to realize ultrafast time resolution. Although it can measure the light field, it is difficult to meet the requirements of wide spectral range and high spatiotemporal resolution measurement. The ultrafast light field detector mainly includes a framing camera based on fast electronics, an in-situ storage electronic shutter camera and a high-speed sampling camera, etc. Among them, the microchannel plate traveling wave gating type framing camera is relatively mature in development, and its basic principle is to control the gating and amplification of an electric pulse with an extremely narrow pulse width at different times. The developed ultrafast MCP framing camera can realize a minimum gate width of 200 ps. However, due to the problem of spectral response of infrared photodiodes, the MCP framing camera is difficult to meet the wide spectral measurement requirements from ultraviolet to infrared.

[0005] Therefore, the prior art still needs further development. SUMMARY

[0006] The present application aims to overcome the above technical deficiencies, and provides a single-shot imaging device and method based on structured light coding and transient grating shutter, to solve the problems existing in the prior art, and to realize single-shot high spatiotemporal resolution imaging of transient events, while having a wide spectral response range and a simplified system structure.

[0007] To achieve the above technical purpose, according to the first aspect of the present application, the present application provides a single-shot imaging device based on structured light coding and transient grating shutter, comprising:

[0008] An ultrashort pulse laser, a transient event device to be measured, an optical beam splitter, an optical path adjustment unit, a structured light coding unit, an optical beam combiner, a transient grating shutter unit, an imaging unit, and a data processing unit in communication connection with the imaging unit are arranged in sequence along the laser transmission direction.

[0009] Specifically, the ultrashort pulse laser is used to irradiate the transient event device to be measured, and generates a to-be-measured signal light carrying to-be-measured information.

[0010] Specifically, the optical beam splitter is used to split the to-be-measured signal light into a plurality of sub-beams.

[0011] Specifically, the optical path adjustment unit is arranged in the optical path of each sub-beam, and the optical path adjustment unit is used to set different time delays for each sub-beam.

[0012] Specifically, the optical path adjustment unit at least includes any one of the following:

[0013] A combination of a dimmable delay line, a mirror assembly, and an electrically driven displacement platform.

[0014] Specifically, the structured light coding unit includes multiple gratings located in different spatial orientations, and the gratings are used to perform spatial frequency domain modulation coding on each sub-beam.

[0015] Specifically, the optical beam combiner is used to combine the modulated and coded sub-beams;

[0016] The transient grating shutter unit includes a Kerr medium and a pump light source;

[0017] The pump light source is used to generate two pump beams, which interfere in the Kerr medium to form a transient grating. Then, the encoded sub-beams are guided to the transient grating for gating different time slices.

[0018] Specifically, the imaging unit is used to receive each sub-beam after being gated by the transient grating shutter and to form a composite light field image;

[0019] The data processing unit is used to perform frequency domain analysis on the composite light field image, and to separate and restore the light field information of each sub-beam at different time slices.

[0020] According to a second aspect of the present invention, a single-shot imaging method based on structured light coding and transient grating shutter is provided, comprising:

[0021] S100. Use an ultrashort pulse laser to irradiate the transient event device under test to generate a test signal light carrying the test information, and use an optical beam splitter to split the test signal light into multiple sub-beams.

[0022] S200: Different time delays are set for each sub-beam using the optical path adjustment unit;

[0023] S300: Spatial frequency domain modulation coding is performed on each sub-bundle using gratings in different spatial orientations in the structured light coding unit to form the coded sub-bundle;

[0024] S400. Combine the encoded sub-bundles using an optical beam combiner to form the first combined beam.

[0025] S500: Pass the first combined beam through the transient grating shutter unit, and use the transient grating shutter unit to select different time slices for each encoded sub-beam;

[0026] S600: Guide the selected sub-beams to the imaging unit to form a composite light field image;

[0027] S700 uses the data processing unit to perform frequency domain analysis on the composite light field image, and separates and restores the light field information of each sub-beam at different time slices.

[0028] Specifically, the composite light field image is subjected to frequency domain analysis by the data processing unit to separate and restore the light field information of each sub-beam at different time slices, including:

[0029] The data processing unit is used for Fourier transform, spatial frequency translation, low-pass filtering and inverse Fourier transform on the composite light field image, so as to separate and restore the light field information of each sub-beam.

[0030] Beneficial effects:

[0031] 1. The present application realizes single-shot ultrafast optical imaging based on structured light encoding and transient grating shutter gating. Multiple time and space resolution images of ultrafast phenomena can be captured in a single exposure by frequency domain identification and analysis. The number of image frames is further improved by using structured light encoding multiplexing. The femtosecond level time resolution is realized by using transient grating shutter gating. Combined with a high spatial resolution optical system, high-precision measurement of transient events is realized. The transient grating shutter uses two pump beams to interfere in a Kerr medium to produce a transient grating to diffract the signal light and realize gating. The diffracted signal appears in the wave vector matching direction, and has the advantages of no background detection and high extinction ratio.

[0032] 2. Based on the image transfer principle, the present application realizes multi-frame imaging in the spatial frequency domain. It does not depend on dispersion encoding, preserves all the spectral information of the measured transient event, has full spectral compatibility, and the spectral range depends on the spectral transmittance of the optical element. Therefore, it can cover a wide spectral range from infrared to ultraviolet, and is suitable for various spectral measurement requirements, providing a powerful tool for ultrafast phenomenon research. The single-shot imaging device in the present application has a simple structure, greatly reducing the cost, and greatly improving the usability and reliability of the present application.

[0033] 3. Based on the single-shot ultrafast imaging device provided by the present application, the measured transient event can be removed, thereby realizing ultrafast time-resolved imaging of the time and space structure of the laser pulse itself. It can be widely used in non-repetitive and reproducible ultrafast phenomenon research, and is not limited to transient events or lasers. It greatly expands the application scenarios of the present application. BRIEF DESCRIPTION OF DRAWINGS

[0034] Figure 1 is the overall structure schematic diagram of the single-shot imaging device based on structured light encoding and transient grating shutter provided in the specific embodiment of the present application;

[0035] Figure 2 is the principle diagram of the transient grating shutter provided in the specific embodiment of the present application;

[0036] Figure 3 is the optical path structure schematic diagram of the single-shot imaging based on structured light encoding and transient grating shutter provided in the specific embodiment of the present application;

[0037] Figure 4 is a schematic diagram of the time resolution of the system when H-ZF73 is used as the optical Kerr medium in the specific embodiments of the present application;

[0038] Figure 5 is a simulation diagram of the influence of the thickness of the Kerr medium and the light intensity on the diffraction efficiency of the transient grating shutter in the specific embodiments of the present application;

[0039] Figure 6 is a composite overlapping image carrying information to be measured at different times in the specific embodiments of the present application;

[0040] Figure 7 is a spatial frequency spectrum distribution diagram corresponding to the composite overlapping image carrying information to be measured at different times in the specific embodiments of the present application;

[0041] Figure 8 is a spatial frequency domain frequency shift diagram of the spatial frequency spectrum of the composite overlapping light field in the specific embodiments of the present application;

[0042] Figure 9 is a frequency spectrum diagram of low-pass filtering the spatial frequency spectrum of the composite overlapping light field in the specific embodiments of the present application;

[0043] Figure 10 is a spatial frequency spectrum diagram of the first time separated out in the specific embodiments of the present application;

[0044] Figure 11 is a transient image corresponding to the spatial frequency spectrum diagram of the first time separated out in the specific embodiments of the present application;

[0045] Figure 12 is a spatial frequency spectrum diagram of the second time separated out in the specific embodiments of the present application;

[0046] Figure 13 is a transient image corresponding to the spatial frequency spectrum diagram of the second time separated out in the specific embodiments of the present application;

[0047] Figure 14 is a flowchart of a single-shot imaging method based on structured light coding and a transient grating shutter in the specific embodiments of the present application;

[0048] In the above figures, the reference signs of the figures are as follows:

[0049] 1, ultra-short pulse laser; 2, transient event device to be measured; 3, optical beam splitter; 4, optical path adjustment unit; 5, structured light encoding unit; 6, optical beam combiner; 7, transient grating shutter unit; 8, imaging unit; 9, pump beam splitter; 10, signal light optical path adjustment unit; 11, first pump light optical path adjustment unit; 12, second pump light optical path adjustment unit; 13, first beam splitter; 14, second beam splitter; 15, third beam splitter; 16, fourth beam splitter; 17, focusing lens; 18, first mirror; 19, second mirror; 20, highly tunable climbing mirror group; 21, fifth beam splitter; 25, sixth mirror; 26, Kerr medium; 27, pinhole diaphragm; 401, first optical path adjustment unit; 402, second optical path adjustment unit; 403, third optical path adjustment unit; 501, first structured light encoding unit; 502, second structured light encoding unit; 503, third structured light encoding unit. DETAILED DESCRIPTION

[0050] In order for those skilled in the art to better understand the technical solutions of the present application, the technical solutions of the present application will be described clearly and completely below in combination with the drawings of the present application. Based on the embodiments in the present application, other similar embodiments obtained by those skilled in the art without making creative efforts should all belong to the scope of protection of the present application. In addition, the direction words mentioned in the following embodiments, such as “up”, “down”, “left”, “right” and the like, are only the directions of the drawings, therefore, the direction words used are used for illustration and not for limiting the present application.

[0051] The present application will be further described below in combination with the drawings and preferred embodiments.

[0052] Please refer to Figure 1 The present embodiment provides a single-shot imaging device based on structured light encoding and transient grating shutter, comprising:

[0053] An ultra-short pulse laser 1, a transient event device to be measured 2, an optical beam splitter 3, an optical path adjustment unit 4, a structured light encoding unit 5, an optical beam combiner 6, a transient grating shutter unit 7, an imaging unit 8, and a data processing unit in communication connection with the imaging unit 8 are sequentially arranged along the laser transmission direction.

[0054] It can be understood that the working process of the single-shot imaging device in the embodiment includes: irradiating the device 2 to be measured by the ultra-short pulse laser 1, splitting the signal light carrying the to-be-measured information into a plurality of sub-beams by the optical beam splitter 3, setting different time delays for each sub-beam by the optical path adjustment unit 4, then modulating and coding each sub-beam by the grating in the structural light coding unit 5 in different spatial directions, combining the coded structural light sub-beams by the optical combiner 6, and then irradiating the transient grating shutter of the transient grating shutter unit 7, under the control of the pump light, the transient grating shutter realizes the gating of different time slices of each sub-beam, and finally images on the imaging unit 8, and through the frequency domain recognition and analysis technology of the data processing unit, the light field information at different times is recovered.

[0055] Referring to Figure 1 , the optical beam splitter 3 can include beam splitters arranged on a plurality of different signal light branches, such as 301, 302, … 30n (n is a natural number) in Figure 1 , the optical path adjustment unit 4 can include optical path adjustment units arranged on a plurality of signal light branches, such as 401, 402, 40n in Figure 1 , the structural light coding unit 5 can include structural light coding units arranged on a plurality of signal light branches, such as 501, 502, … 50n in Figure 1 .

[0056] Specifically, the ultra-short pulse laser 1 is used to irradiate the device 2 to be measured to generate the to-be-measured signal light carrying the to-be-measured information.

[0057] Further, the to-be-measured transient event includes ultrafast phenomena in the fields of physics and chemistry, such as transient evolution processes of plasma evolution, crystal phase transition, irreversible chemical reaction, etc. The details of these transient events can be observed by the single-shot imaging device in the embodiment, and the information such as the occurrence mechanism and the intermediate state can be understood, so that the transient evolution process of the related transient event can be further studied.

[0058] Specifically, the optical beam splitter 3 is used to split the to-be-measured signal light into a plurality of sub-beams.

[0059] In a specific embodiment, the optical beam splitter 3 is composed of a series of beam splitters with different splitting ratios, which is used to split the signal light carrying the to-be-measured information into a plurality of sub-beams. Preferably, the splitting ratios of the splitting pieces are adjusted to make the energy of each sub-beam as equal as possible, so as to ensure the accuracy and consistency of the subsequent operation. For the structural light coding unit 5, if the energy difference of the sub-beams is too large, it may cause inaccurate coding information in the coding process, affecting the coding effect. Making the energy of each sub-beam as equal as possible helps to ensure the stability of the whole single-shot ultrafast imaging device.

[0060] Referring to Figure 3The optical beam splitter 3 comprises a first beam splitter 13, a second beam splitter 14, a third beam splitter 15 and a fourth beam splitter 16.

[0061] Specifically, the optical path adjustment unit 4 is arranged in the optical path of each sub-beam, and is configured to set different time delays for the sub-beams.

[0062] Specifically, the optical path adjustment unit 4 comprises at least one of the following:

[0063] A combination of an adjustable optical delay line, a mirror group and an electrically driven displacement platform.

[0064] In a specific embodiment, the optical path adjustment unit 4 is arranged in the optical path of each sub-beam, and is generally composed of a mirror group and an electrically driven displacement platform, and can also be composed of an adjustable optical path delay line, and is configured to set different time delays for the sub-beams.

[0065] Referring to Figure 3 The optical path adjustment unit 4 comprises a first optical path adjustment unit 401, a second optical path adjustment unit 402 and a third optical path adjustment unit 403.

[0066] Specifically, the structured light encoding unit 5 comprises a plurality of gratings arranged at different spatial orientations, and the gratings are configured to perform spatial frequency domain modulation encoding on the sub-beams.

[0067] In a specific embodiment, the structured light encoding unit 5 can select a Ronchi grating or a sinusoidal amplitude grating, and each sub-beam has a different spatial orientation. Different spatial orientation encoding is significant to avoid the far field of the encoded sub-beams from overlapping in the spatial frequency domain, which will adversely affect the spatial frequency domain analysis and interfere with the entire imaging effect. Therefore, by assigning different spatial orientation encoding to each sub-beam, the occurrence of such a situation can be effectively avoided, thereby ensuring that the information of each sub-beam can be accurately distinguished in the spatial frequency domain, and providing clear and accurate encoding information basis for subsequent imaging measurement.

[0068] Specifically, the optical beam combiner 6 is configured to combine the modulated and encoded sub-beams.

[0069] Further, the optical beam combiner 6 is generally composed of a plurality of stages of beam combiners.

[0070] The transient grating shutter unit 7 comprises a Kerr medium 26 and a pump light source.

[0071] The pump light source is used to generate two beams of pump light, which interfere to form a transient grating in the Kerr medium 26, and then each sub-beam after coding is guided to the transient grating for gating of different time slices.

[0072] In a specific embodiment, the Kerr medium 26 can be selected as H-ZF73, which has multiple excellent properties, such as high nonlinear refractive index, which enables it to produce significant optical nonlinear effects when interacting with pump light, which plays a key role in forming a transient grating, fast medium polarization response speed, which can quickly respond to changes in the electric field caused by pump light, thereby ensuring that the transient grating can be formed in a very short time, which is very important for achieving ultrafast time resolution, and H-ZF73 also has the advantage of good transmission surface, which means that the light can maintain good propagation characteristics when passing through the medium, reducing adverse effects such as scattering and deformation of the light, which is beneficial to improve the imaging quality and measurement accuracy of the entire system, and can achieve ultrafast time resolution.

[0073] Referring to Figure 2 In the Kerr medium 26, the wave vectors of the two beams of pump light (k1 and k2) and the probe signal light (k3) are arranged at the three vertices of a square, and the fourth beam of diffracted signal light will appear at the remaining vertex of the square. The four wave vectors automatically satisfy the phase matching condition of four-wave mixing. The transient grating shutter is induced by the interference of the two high-power pump light beams in the Kerr medium 26 to form a transient refractive index structure. The third beam of signal light is incident into the Kerr medium 26 to modulate the transient refractive index structure to generate the fourth beam of diffracted light. The fourth beam of diffracted light corresponds to the third beam of signal light and carries the same transient event modulation information as the third beam of light. The direction of the fourth beam of diffracted light is different from the first three beams of light. The transient grating time shutter can realize local detection-free, high extinction ratio, and higher diffraction switching efficiency than the Kerr gate. Moreover, it does not require a high polarization extinction ratio device, further simplifying the structure of the entire optical system, reducing the construction cost, and greatly improving the stability and adaptability of the optical system in different environments.

[0074] Specifically, the imaging unit 8 is configured to receive each sub-beam after being gated by the transient grating shutter and form a composite light field image.

[0075] The data processing unit is configured to perform frequency domain analysis on the composite light field image to separate and restore the light field information of each sub-beam at different time slices.

[0076] Please refer to Figures 6-13 The working principle of the single-shot ultrafast imaging technology scheme based on structured light coding and transient grating shutter gating is explained below by using theoretical analysis and simulation verification of the physical feasibility of the scheme:

[0077] Assume that the to-be-measured signal light I(x, y, t) carrying transient event information is divided into two beams by an optical beam splitter 3, denoted as I 10 (x, y, t) and I 20 (x, y, t), respectively, and the sub-beams are grating-encoded by using thin sinusoidal amplitude gratings, the first grating and the second grating can be described as:

[0078]

[0079]

[0080] wherein G1(x, y) represents the first grating, G2(x, y) represents the second grating, x and y represent two-dimensional spatial coordinates, corresponding to horizontal and vertical directions, respectively, t represents a time coordinate, I 10 (x, y, t) represents the first beam of to-be-measured signal light, I 20 (x, y, t) represents the second beam of to-be-measured signal light, m represents an amplitude, and represents a phase;

[0081] The grating-encoded optical field can be described as:

[0082] I1(x, y, t) = I 10 (x, y, t)G1(x, y)

[0083] I2(x, y, t) = I 20 (x, y, t)G2(x, y), (2)

[0084] wherein I1(x, y, t) represents the first optical field, and I2(x, y, t) represents the second optical field;

[0085] After being selected by the transient grating shutter unit 7, the optical fields at two different times are:

[0086] ΔI1(x, y, t) = I 10 (x, y, Δt1)G1(x, y)

[0087] ΔI2(x, y, t) = I 20 (x, y, Δt2)G2(x, y), (3)

[0088] wherein ΔI1(x, y, t) represents the optical field at the first time, ΔI2(x, y, t) represents the optical field at the second time, and Δt1 and Δt2 represent the first time and the second time, respectively;

[0089] After the two beams of light are combined, they are received by the same camera, and the optical field received by the camera is represented as:

[0090] ΣI(x, y, t) = ΔI1(x, y, t) + ΔI2(x, y, t), (4)

[0091] The Fourier transform is performed on the signal received by the camera, and the light field frequency domain is represented as:

[0092]

[0093] wherein AF(ξ,η) is represented as a light field frequency domain, ξ,η represent discrete variables in a spatial frequency domain, respectively represent the Fourier transform of the light field at the first time and the second time;

[0094] As can be seen from formula (5), after encoding by the sinusoidal grating modulation, there are 0th and ±1st orders of light fields at different times on the spectrum plane. By using sinusoidal gratings with different frequencies and orientations, the ±1st orders of the first light field and the second light field are separated on the spectrum space. After band-pass filtering, the inverse Fourier transform is performed to obtain the separated light fields, i.e., the time-resolved light fields.

[0095] As shown in Figures 6-13 , the simulation of the encoding and analysis process of the transient event further simulates the whole process of encoding, acquisition, frequency shift, low-pass filtering and restoration of the light field image: first, the scenes of the transient event with large feature differences at different times (the first time and the second time) are selected, which are also used as the two light fields at different times after beam splitting. The original frequency distributions of the two images are located near zero frequency. After the light field images at different times are encoded by gratings with different orientations, they are overlapped together. The composite overlapped light field and its spectrum are shown in Figure 6 and Figure 7 The center of the spatial frequency domain is the spectrum of the first time and the second time mixed together, which is difficult to distinguish. The four spectrum areas on the periphery are the ±1st order spectra of the first time and the second time separated, respectively. After frequency shift and low-pass filtering are performed on the composite overlapped light field spectrum, Figure 8 is a spatial frequency domain frequency shift diagram performed on the composite overlapped light field spectrum, Figure 9 is a spectrum diagram of low-pass filtering performed on the composite overlapped light field spectrum. Then, the inverse Fourier transform is performed to restore the separated transient events at different times, Figure 10 is a spatial spectrum diagram of the first time separated, Figure 11 is a transient image corresponding to the spatial spectrum diagram of the first time separated, Figure 12 is a spatial spectrum diagram of the second time separated, Figure 13 is a transient image corresponding to the spatial spectrum diagram of the second time separated.

[0096] In summary, the theoretical analysis and simulation show that the single-shot ultrafast imaging technology scheme based on structured light coding and transient grating shutter gating has physical feasibility. It can not only image and measure typical transient events such as the evolution process of laser-induced plasma, but also clearly capture the evolution process of plasma in a very short time by the cooperation of various components. The structured light coding unit can accurately encode the signal light related to the transient event, and the transient grating shutter unit can accurately select the appropriate time slice, thereby providing a powerful imaging means for studying the physical properties of plasma. This technical scheme also has the ability to image the light field itself. By imaging the light field itself, important characteristics such as the distribution and intensity variation of the light field can be deeply explored, providing a new perspective and tool for the study of light field, breaking through the limitations of existing technology, and having strong expansibility and high upper limit of measurement.

[0097] Please refer to Figures 3-5 The specific parameter design and selection scheme of the single-shot imaging device based on structured light coding and transient grating shutter gating proposed in the embodiment, and the working mechanism of the device, are described in detail below through a specific example:

[0098] The overall design scheme of the device is as follows:

[0099] The ultra-short pulse laser 1 is divided into signal light and pump light by the pump beam splitter 9. The signal light irradiates the measured transient event device 2. The measured signal light carrying the transient event is divided into three sub-beams by a series of optical beam splitters 3. Then, an electric displacement platform and two mirrors are used as an optical path adjustment unit 4 to set three different time delays for the three sub-beams, respectively, and select 0 ps / 0.3 ps / 0.6 ps. Next, the three sub-beams are spatially modulated and coded by gratings with spatial orientations of 0°, ±8.3°, respectively, to form coded structured light sub-beams. After the coded sub-beams are combined by a combiner, they are incident into the H-ZF73 optical Kerr medium 26. In addition, the pump light is divided into two beams by a series of optical beam splitters 3. The optical path of the first pump light and the second pump light is adjusted to be equal by a pump light path adjustment unit, and the laser energy is as consistent as possible. The optical path delay of the three structured light sub-beams is adjusted by a signal light path adjustment unit 10 to realize strict synchronization with the pump light, that is, the 0 time of the pump light coincides with the 0 time of the signal light. Then, the two pump beams interfere to generate a transient grating in the Kerr medium 26. The diffraction of the three measured structured light sub-beams by the transient grating realizes time gating, and the transient events at different times are intercepted. Finally, the gated light field information is imaged on the camera, and three light field images at different times are recovered by a frequency domain identification and analysis unit.

[0100] The specific design and selection scheme of the single-shot imaging device based on structured light coding and transient grating shutter gating proposed in the embodiment, and the working mechanism of the device, are described in detail below through a specific example:

[0101] As Figure 3As shown, the super short pulse laser with a center wavelength of 1030 nm, a pulse width of 1 ps and a diameter of 3 mm is used as the super short pulse laser 1, the super short pulse laser is divided into signal light and pump light by the pump beam splitter 9, and the beam splitting ratio of the pump beam splitter 9 is 30:70, 70% of the laser energy is used as the pump light, and 30% of the laser energy is used as the signal light.

[0102] After the signal light irradiates the device to be tested 2, it is divided into three sub-beams by the optical beam splitter 3. Each sub-beam is precisely adjusted in time by the optical path adjustment unit 4, which includes a first optical path adjustment unit 401, a second optical path adjustment unit 402 and a third optical path adjustment unit 403, which are respectively arranged on the optical paths of the three sub-beams. Then, spatial frequency domain adjustment coding is performed by the structured light coding unit 5, and the first structured light coding unit 501, the second structured light coding unit 502 and the third structured light coding unit 503 are respectively arranged on the optical paths of the three sub-beams. The above-mentioned optical path adjustment unit 4 is composed of an electrically driven translation stage and two mirrors at an angle of 90°, the structured light coding unit 5 uses a Ronchi grating coding of 10 lp / mm, the focal length of the focusing lens 17 is 150 mm, and the separation distance of the 0th order diffraction and the 1st order diffraction in the far field frequency spectrum space is 1.55 mm. In order to realize 3 division, the focal spots of different sub-beams do not coincide, and the offset angle of the grating in the beam cross-section direction (the direction of perpendicular light incidence) is 8.3°, and the spatial orientations of the three gratings are 0, ±8.3° respectively. Since the specification of the commercial grating is square (1 inch*1 inch), in order to realize accurate adjustment of the spatial orientation of the grating, a square-circular adapter clamp is customized and processed, and here a 1 inch square grating is embedded in a 2 inch circular wave plate holder and fixed by the adapter clamp. There is a time delay difference between the signal light sub-beams, and the time delay of 0 ps, 0.3 ps and 0.6 ps relative to the pump light is set by adjusting the electrically driven translation stage. Finally, the three sub-beams after delay coding are coaxially combined together by the optical combiner 6, the spatial incidence angle is adjusted by the first mirror 18 and the second mirror 19, and then the signal light is incident on the Kerr medium 26.

[0103] The pump light is divided into first pump light and second pump light by the fifth beam splitter 21, and the first pump light and the second pump light are precisely delayed and synchronized by the first pump light path adjustment unit 11 and the second pump light path adjustment unit 12 respectively. Subsequently, the first pump light and the second pump light are adjusted in spatial incidence angle by the height-adjustable climbing mirror group 20 and the sixth mirror 25 respectively, and then the first pump light and the second pump light are incident on the Kerr medium 26. It should be noted that the first pump light, the second pump light and the signal light sub-beam need to meet the four-wave mixing phase matching condition. In the design of the present scheme, the spatial angle is designed skillfully, and a rhombus spatial orientation is adopted, so that the first pump light and the signal light sub-beam only need to adjust the angle in the horizontal direction, and the second pump light only needs to adjust the angle in the vertical direction, which reduces the complexity of angle adjustment and is more conducive to meeting the phase matching condition.

[0104] Kerr medium 26 is selected from H-ZF73, which has a high nonlinear refractive index coefficient of 87e-7cm. 2 / GW. like Figure 5 As shown, the diffraction efficiency variation of H-ZF73 medium under the combined variation of dielectric thickness and power density was simulated based on Kogelnik theory at a power density of 1 GW / cm². 2 Under pump light excitation, the switching efficiencies of H-ZF73 with thicknesses of 10 mm, 20 mm, and 30 mm were 0.26, 0.76, and 1, respectively. The switching efficiency increased with increasing dielectric thickness and pump light power density. When the pump light beam was expanded, the power density decreased; therefore, increasing the dielectric thickness could compensate for the decrease in switching efficiency. This was particularly effective for dielectric thicknesses ranging from 0 to 40 mm and power densities from 0 to 3 GW / cm². 2 Within the parameter range, the diffraction efficiency of H-ZF73 changes by one cycle. The processing technology of H-ZF73 is relatively mature, and the surface shape is good. Considering the defects of CS2, such as its slight toxicity and volatility, and the fact that liquid transmission surface shape is not as good as solid, this invention uses H-ZF73 medium. In order to construct the transient grating shutter unit 7, H-ZF73 glass is placed on a precision optical platform, and its position is adjusted to ensure that the pump light and signal light can be accurately focused into the glass.

[0105] The time response characteristics of H-ZF73 were tested using a step-scan method. The test equipment included an electric displacement platform, an energy calorimeter, a camera, and an oscilloscope. First, the signal light and pump light were synchronized, and the time gating signal was observed on the energy calorimeter (camera or oscilloscope). The excitation time of the pump light was changed by the electric displacement platform, and the response amplitude of the signal light was measured synchronously. The time response curve of H-ZF73 was measured point by point. Figure 4 When H-ZF73 is used as the optical Kerr medium 26, the system's time resolution is 1.57 ps (half-width at half maximum) and 5.77 ps (10% bottom width).

[0106] The coded imaging optical path is designed based on the single-lens 2f imaging principle. The object plane is located at the grating, and the structured light coding unit 5 of each sub-beam is equidistant from the optical Kerr medium 26, at twice the focal length. A camera is placed at twice the focal length behind the optical Kerr medium 26, enabling imaging of the signal light to be measured at different time segments. Based on the image transfer imaging principle, it can adapt to a wide spectrum of light sources, is not limited to a specific wavelength range, and is suitable for various spectral measurement needs. Furthermore, a pinhole aperture 27 is placed in front of the imaging measurement to filter out stray light other than diffracted light, achieving high signal-to-noise ratio and background-free detection.

[0107] It should be noted that the present application realizes single-shot ultrafast optical imaging based on structured light encoding and transient grating shutter gating, can capture multiple time and space resolution images of the whole light field evolution in a single exposure through frequency domain identification analysis, further improves the image frame number by using structured light encoding multiplexing, realizes femtosecond-level time resolution by using transient grating shutter gating, realizes high-precision measurement of transient events in combination with a high spatial resolution optical system, realizes gating by using the diffraction of signal light by a transient grating generated by the interference of two pump lights in a Kerr medium, the diffraction signal appears in the wave vector matching direction, has the advantages of no background detection and high extinction ratio, and based on the single-shot ultrafast imaging device provided by the present application, the placement of the to-be-measured transient event can be cancelled, the ultrafast time-resolved imaging of the time and space evolution of the laser pulse itself can be realized, the application range of the present application is greatly expanded, the present application realizes multi-frame imaging in the spatial frequency domain based on the image transfer principle, does not depend on dispersion encoding, retains all spectral information of the to-be-measured transient event, has full-spectrum compatibility, and the spectral range depends on the spectral transmittance of the optical element, so it can cover a wide spectral range from infrared to ultraviolet, is suitable for various spectral measurement requirements, and provides a powerful tool for ultrafast phenomenon research, and the single-shot imaging device in the present application has a simple composition, greatly reduces the cost, and greatly improves the usability and reliability of the present application.

[0108] Please refer to Figure 14 The embodiment provides a single-shot imaging method based on structured light encoding and transient grating shutter, which comprises the following steps:

[0109] S100, an ultra-short pulse laser 1 is used to irradiate a to-be-measured transient event device 2, to generate to-be-measured signal light carrying to-be-measured information, and an optical beam splitter 3 is used to split the to-be-measured signal light into multiple sub-beams;

[0110] S200, an optical path adjusting unit 4 is used to set different time delays for each sub-beam;

[0111] S300, a grating in different spatial directions in a structured light encoding unit 5 is used for spatial frequency domain modulation and encoding of each sub-beam, to form an encoded sub-beam;

[0112] S400, the encoded sub-beam is combined by an optical combiner 6 to form a first combined beam;

[0113] S500, the first combined beam passes through a transient grating shutter unit 7, and the transient grating shutter unit 7 is used for gating of different time slices of the encoded sub-beams;

[0114] S600, each gated sub-beam is guided to an imaging unit 8 to form a composite light field image;

[0115] S700, performing frequency domain analysis on the composite light field image by using the data processing unit to separate and restore the light field information of each sub-beam in different time slices.

[0116] Specifically, the data processing unit performs frequency domain analysis on the composite light field image to separate and restore the light field information of each sub-beam in different time slices, including:

[0117] The data processing unit performs Fourier transform, spatial frequency translation, low-pass filtering, and inverse Fourier transform on the composite light field image to separate and restore the light field information of each sub-beam.

[0118] It can be understood that the data processing unit mainly includes Fourier transform, spatial frequency translation, low-pass filtering, and inverse Fourier transform, which are used to perform frequency domain analysis on the composite light field image to separate and restore the light field information of each sub-beam. After being modulated by gratings in different directions, each sub-beam has 0th and ±1st orders in the spatial frequency spectrum. Since the directions of the sub-beams are different, the ±1st orders of the sub-beams are separated in the frequency spectrum. After band-pass filtering the ±1st orders of each sub-beam, inverse Fourier transform can obtain the separated sub-beam light field. In addition, by canceling the placement of the to-be-measured transient event, the ultrafast time-resolved imaging of the spatiotemporal evolution of the laser pulse itself can be realized, greatly expanding the application scenarios of the present application.

[0119] It should be noted that the present application realizes single-shot ultrafast optical imaging based on structured light encoding and transient grating shutter gating. Through frequency domain identification and analysis, multiple time and space resolution images of the entire light field evolution can be captured in a single exposure. The use of structured light encoding multiplexing further improves the number of image frames. The use of transient grating shutter gating enables femtosecond-level time resolution. Combined with a high spatial resolution optical system, high-precision measurement of transient events is achieved. The transient grating shutter uses the interference of two pump beams in a Kerr medium to generate a transient grating to diffract the signal light and achieve gating. The diffracted signal appears in the wave vector matching direction, has the advantages of no background detection and high extinction ratio. Based on the single-shot ultrafast imaging device provided by the present application, the placement of the to-be-measured transient event can be canceled, and ultrafast time-resolved imaging of the spatiotemporal evolution of the laser pulse itself can be realized, greatly expanding the application range of the present application. Based on the image transfer principle, the present application realizes multi-frame imaging in the spatial frequency domain, does not rely on dispersion encoding, preserves all the spectral information of the to-be-measured transient event, has full-spectrum compatibility, and the spectral range depends on the spectral transmittance of the optical element. Therefore, it can cover a wide spectral range from infrared to ultraviolet, suitable for various spectral measurement needs, and provides a powerful tool for ultrafast phenomenon research.

[0120] The application is not limited to the foregoing specific embodiments, nor to the foregoing described application scenarios, and can be applied to any filtering scenario, and the application does not limit this. Furthermore, the application extends to any novel one, or any new combination, of the characteristics disclosed in this specification, as well as to any novel method or process steps, or any new combination, disclosed.

[0121] All characteristics disclosed in this specification, or steps in any method or process disclosed, can be combined in any way, except where this is impermissible from a theoretical standpoint or is technically impossible.

[0122] Any one of the characteristics disclosed in this specification can be replaced by other equivalent or analogous characteristics, unless there are specific statements to the contrary. That is, unless there are specific statements to the contrary, each characteristic is merely an example of a range of equivalent or analogous characteristics.

[0123] The technical features described above can be combined in any way. Although not all possible combinations of the technical features are described, any combination of the technical features should be considered as covered by the present specification, as long as such a combination does not lead to a contradiction.

[0124] The foregoing detailed description of the application has been presented for the purposes of illustration and description. It is not intended to be exhaustive or to limit the application to the precise form disclosed. Many modifications and variations are possible in light of the above teachings. It is intended that the scope of the application be limited not with this detailed description, but rather by the claims appended hereto.

Claims

1. A single-shot imaging device based on structured light coding and transient grating shutter, characterized in that, include: The following components are arranged sequentially along the laser transmission direction: an ultrashort pulse laser (1), a transient event device to be tested (2), an optical beam splitter (3), an optical path adjustment unit (4), a structured light coding unit (5), an optical beam combiner (6), a transient grating shutter unit (7), an imaging unit (8), and a data processing unit that is communicatively connected to the imaging unit (8). The structured light coding unit (5) includes multiple gratings located in different spatial orientations, and the gratings are used to perform spatial frequency domain modulation coding on each sub-beam; The optical beam combiner (6) is used to combine the modulated and encoded sub-beams. The transient grating shutter unit (7) includes a Kerr medium (26) and a pump light source; The pump light source is used to generate two pump beams, which interfere in the Kerr medium (26) to form a transient grating. Then, the encoded sub-beams are guided to the transient grating for gating different time slices.

2. The single-shot imaging device based on structured light coding and transient grating shutter according to claim 1, characterized in that, The ultrashort pulse laser (1) is used to irradiate the transient event device (2) under test, and generate a test signal light carrying the test information.

3. The single-shot imaging device based on structured light coding and transient grating shutter according to claim 1, characterized in that, The optical beam splitter (3) is used to split the signal light to be tested into multiple sub-beams.

4. The single-shot imaging device based on structured light coding and transient grating shutter according to claim 3, characterized in that, The optical path adjustment unit (4) is located in the optical path of each sub-beam, and the optical path adjustment unit (4) is used to set different time delays for each sub-beam.

5. The single-shot imaging device based on structured light coding and transient grating shutter according to claim 4, characterized in that, The optical path adjustment unit (4) includes at least one of the following: A combination of a dimmable delay line, a mirror assembly, and an electrically driven displacement platform.

6. The single-shot imaging device based on structured light coding and transient grating shutter according to claim 1, characterized in that, The imaging unit (8) is used to receive each sub-beam after being selected by the transient grating shutter and to form a composite light field image; The data processing unit is used to perform frequency domain analysis on the composite light field image, and to separate and restore the light field information of each sub-beam at different time slices.

7. A single-shot imaging method based on structured light coding and transient grating shutter, characterized in that, The method employs the single-shot imaging device based on structured light coding and transient grating shutter as described in any one of claims 1 to 6, the method comprising: S100. Use an ultrashort pulse laser (1) to irradiate the transient event device (2) under test to generate a signal light carrying the information to be tested. Use an optical beam splitter (3) to split the signal light under test into multiple sub-beams. S200, using the optical path adjustment unit (4) to set different time delays for each sub-beam; S300. Using gratings in different spatial orientations in the structured light coding unit (5), each sub-bundle is spatially frequency-domain modulated and coded to form the coded sub-bundle. S400, The encoded sub-bundles are combined using an optical combiner (6) to form the first combined bundle; S500, the first combined beam is passed through the transient grating shutter unit (7), and the transient grating shutter unit (7) is used to select different time slices for each encoded sub-beam; S600, guide the selected sub-beams to the imaging unit (8) to form a composite light field image; S700 uses the data processing unit to perform frequency domain analysis on the composite light field image, and separates and restores the light field information of each sub-beam at different time slices.

8. The single-shot imaging method based on structured light coding and transient grating shutter according to claim 7, characterized in that, The process of using a data processing unit to perform frequency domain analysis on the composite light field image, separating and reconstructing the light field information of each sub-beam at different time slices, includes: The data processing unit performs Fourier transform, spatial frequency shift, low-pass filtering, and inverse Fourier transform on the composite light field image, thereby separating and restoring the light field information of each sub-beam.

Images