Ultrafast holographic imaging method and system based on compressed frequency domain holographic recording

Abstract

The embodiments of the present application relate to the field of high-speed imaging technology. The embodiments of the present application disclose an ultrafast holographic imaging method based on compressed frequency-domain holographic recording, which combines the frequency-time correspondence of chirped pulses, frequency-domain interference phase recording and reproduction, and compressed dimensionality reduction recording and recovery methods to obtain the changes in the intensity and phase information of continuous spatiotemporal femtosecond ultrafast processes, and adopts a weighted sparse compression model-based reproduction algorithm to achieve compressed recording interference fringes to reproduce multiple continuous intensity and phase distributions, and calculate the three-dimensional space-time intensity and phase information of ultrafast events. The embodiments of the present application also disclose an ultrafast holographic imaging system based on compressed frequency-domain holographic recording. The embodiments of the present application can simultaneously solve the technical problems of complex amplitude recording, recording frame number, and expanding recording dimension.

Description

Technical Field

[0001] The embodiments of the present application relate to the field of high-speed imaging technology. More specifically, the embodiments of the present application relate to an ultrafast holographic imaging method and system based on compressed frequency domain holographic recording. Background Art

[0002] In cutting-edge physics, chemistry and biology research, many important phenomena occur on the atomic time scale and are non-repeatable: such as the generation and evolution of plasma shock waves under ultra-intense lasers, and the acceleration of tailfield electrons driven by ultra-intense and ultra-short lasers. In order to deeply study the laws of these transient events and reveal the scenes and changing laws of atomic motion, it is necessary to record the spatiotemporal evolution of ultrafast phenomena within picoseconds, which requires single-shot ultrafast imaging technology.

[0003] After years of exploration and accumulation, atomic time single-shot imaging technology has made great progress in recent years, and new imaging principles and technologies have continuously emerged. Existing atomic time single-shot ultrafast imaging technologies can be divided into amplitude / intensity imaging and complex amplitude imaging. In terms of amplitude / intensity imaging, the time-series all-optical imaging technology (STAMP) once attracted the attention of the academic community. It uses the spatial and temporal dispersion shaping technology of femtosecond pulses to convert the spatially varying information to be measured into a time-series image signal, achieving a photography frequency of up to 4.4×10 12 The single 6-frame imaging at fps has a frame pixel count of 450×450, a framing time of 299fs, and an exposure time of 733fs. The spatial information recorded in adjacent frames overlaps severely. After that, the project team used a filtering method to improve the STAMP technology (SF-STAMP). At the same time, considering the constraints of the Heisenberg uncertainty principle, the framing time was consistent with the exposure time, reaching 477fs. In addition, the multiple exposure frequency identification (FRAME) technology uses structured light to encode multiple detection pulses with stripes of different densities, and then obtains the results through corresponding spectrum distribution decoding, achieving 4-frame imaging with a time resolution of 200fs. The above-mentioned ultrafast multi-frame intensity imaging technologies are difficult to make major breakthroughs in the number of framing frames due to the limitations of the Nyquist sampling theorem. It was not until 2014 that California Institute of Technology first applied compressed sensing technology to variable image tube streak camera imaging (CUP), achieving 10 11 350 images at fps greatly increased the number of frames, but its spatial resolution was only 0.78lp / mm. Since then, a variety of optimized CUP technologies have been proposed: T-CUP increases the shooting frequency to 10 13 fps; Ultrafast Electro-Optical Deflection Imaging (UEODI) uses electro-optical deflection crystals to replace expensive streak cameras, with a photography frequency of 10 10fps; Hyperspectral Compressed Ultrafast Imaging (HCUP) records spatial, temporal and spectral information simultaneously. There is also Compressed Ultrafast Time Spectroscopy (CUST), which uses the principle of mutual coupling between femtosecond laser time and spectrum, assisted by compressed sensing encoding and decoding algorithms, to successfully achieve wide-spectrum imaging of biological transient events, with a framing frequency of 3.85THz and a framing number of up to 60. Compressed sensing technology is a sparse representation, and the introduction of this method successfully solves the problem of framing frame number.

[0004] Compared with amplitude / intensity ultrafast imaging, complex amplitude imaging can obtain phase information at the same time, which has unique advantages for studying laser-induced plasma, the interaction between ultrashort pulses and matter, etc. At present, atomic time complex amplitude transient imaging is mostly realized by coding technology, such as spatial coding, wavelength coding, polarization coding, etc. Holographic imaging technology was first applied to this field due to its multi-parameter and easy multi-frame coding characteristics. Domestic and foreign scholars have also achieved good results in this regard. However, these spatial domain holographic imaging technology methods all record multiple holograms on the same medium at the same time, requiring their respective Fourier spectra to be fully separated in space, which greatly limits the application. Based on this, scholars consider transferring spatial domain holographic technology to frequency domain implementation and solving this problem through the characteristics of frequency domain. Frequency domain holography (FDH) transfers the observation of time dimension to spectrum dimension, converts continuous time change records into spatial spectrum measurements, and restores the time domain change information of ultrafast processes through frequency-time correspondence. This technology is proposed on the basis of frequency domain interferometry (FDI) technology. The linear chirp technology is applied to FDI, and a single interferometric measurement can obtain the information on the change of the complex amplitude of ultrafast events over time. In 2006, the research group used FDH for the first time to measure the electron density perturbation of the laser-excited plasma tail field at a higher plasma density, and obtained an image of the refractive index change caused by plasma oscillation within 1ps. The time resolution of the measurement reached 30fs, and the spatial resolution (one-dimensional) reached 3μm. FDH technology is a major breakthrough in ultrafast imaging technology. It fully utilizes the advantages of chirped pulse technology and frequency domain interferometry technology. A single measurement can obtain the space-time perturbation information within the atomic time period of transient events. However, this technology is also limited by the real-time spectrum measurement method. A single record can only obtain the change information (xt or yt) along the time dimension in the one-dimensional spatial direction (the direction of the spectrometer slit), resulting in the loss of high-dimensional spatial information. Summary of the invention

[0005] One purpose of the embodiments of the present application is to solve the above-mentioned problems and provide corresponding beneficial effects.

[0006] Another purpose of the embodiments of the present application is to provide an ultrafast holographic imaging method and system based on compressed frequency domain holographic recording, which solves the technical problems of complex amplitude recording, recording frame number and expanding recording dimension. The embodiments of the present application are mainly implemented through the following technical solutions:

[0007] <First aspect of the embodiment of the present application>

[0008] A first aspect provides an ultrafast holographic imaging method based on compressed frequency domain holographic recording, comprising:

[0009] Splitting a femtosecond laser pulse into an excitation beam and a recording beam;

[0010] forming an ultrafast event excitation region according to the excitation light beam;

[0011] Broadening the recording light beam to form a chirped pulse;

[0012] Performing spectroscopic processing on the chirped pulse to obtain a first chirped pulse and a second chirped pulse;

[0013] Passing the first chirped pulse through the ultrafast event excitation region to perform intensity and phase modulation to obtain a first modulated pulse;

[0014] Passing the second chirped pulse through a delayed optical path to form a reference pulse in frequency domain interferometry;

[0015] Combining the first modulated pulse and the reference pulse to form a record and reference pulse separated in front and back of the visual time dimension;

[0016] Performing beam expansion processing on the recording and reference pulses to obtain beam expanded pulses;

[0017] Performing two-dimensional sparse sampling modulation on the beam expansion pulse to form a second modulated pulse, and obtaining a sparse sampling result;

[0018] Perform frequency domain interference on the second modulated pulse after light splitting to obtain two-dimensional frequency domain interference fringes, compress and superimpose the records, and obtain an interference fringe superposition intensity image;

[0019] The three-dimensional space-time (X, Y, T) intensity and phase information is calculated using a weighted sparse compression model reconstruction algorithm.

[0020] In some technical solutions, in the step of performing frequency domain interference on the second modulated pulse after light splitting to obtain two-dimensional frequency domain interference fringes, compressing and superimposing the records, and obtaining the interference fringe superposition intensity image, the step of obtaining the interference fringe superposition intensity image includes:

[0021] ① The compressed recorded image of the two-dimensional frequency domain interference fringes is:

[0022]

[0023] Wherein, I(x, y, ω) is the interference fringes obtained by two-dimensional spatial frequency domain interference (i.e., two-dimensional frequency domain interference fringes); M is the combination of the grating spectroscopic deflection operation S of the imaging spectrometer and the DMD intensity random sparse sampling C, that is, M=S·C;

[0024] ② The compressed recorded image is converted to the time domain using Fourier transform to obtain:

[0025]

[0026] in represents Fourier transform, W0(t), W(t-τ0), W * (-t-τ0) represents the time domain 0-level and positive and negative 1-level intensity, respectively, and G represents the time domain intensity coefficient;

[0027] ③Extract the first-level spectrum and use inverse Fourier transform to obtain:

[0028]

[0029] in, represents the reference pulse frequency domain electric field distribution, represents the frequency domain electric field distribution of the detection light pulse, represents the frequency domain phase distribution of the detected ultrafast process, τ0 represents the time difference between the detection pulse and the reference pulse;

[0030] ④ The formula for calculating the difference between the first-order spectrum phase angle of the compressed recorded interference fringes and the first-order spectrum phase angle of the compressed reference interference fringes is:

[0031]

[0032] Wherein, M is the combination of the grating spectroscopic deflection operation S of the imaging spectrometer and the random sparse sampling C of the DMD intensity, that is, M=S·C, represents the frequency domain phase distribution of the detected ultrafast process, τ0 represents the time difference between the detection pulse and the reference pulse;

[0033] ⑤ Based on the local linearity of the tangent function, it is converted to:

[0034]

[0035] Usually, the phase shift of transient events in ultrafast recording is small.

[0036]

[0037]

[0038] The above formula converts to:

[0039]

[0040] ⑥ The formula for converting the interference fringe intensity superposition into phase superposition is obtained:

[0041]

[0042] Where ΔΨ(x,ω) is the compressed recorded phase image, represents the frequency domain phase distribution of the detected ultrafast process, M is the combination of the grating spectroscopic deflection operation S of the imaging spectrometer and the random sparse sampling C of the DMD intensity, that is, M = S·C;

[0043] ⑦ Extract the Fourier transform 0-level spectrum and obtain the weighted superposition formula of intensity:

[0044]

[0045] Wherein, ΔΠ(x,ω) is a compressed recorded intensity image, and M is a combination of the grating spectroscopic deflection operation S of the imaging spectrometer and the DMD intensity random sparse sampling C, that is, M=S·C.

[0046] In some technical solutions, the constraint formula of the weighted sparse compression model reproduction algorithm is:

[0047]

[0048]

[0049] in,

[0050]

[0051]

[0052] Among them, λ is the adjustment coefficient; is the phase information; Δ|E(x,y,ω)| 2 is the intensity information. TV[·] indicates total variation calculation, +1 indicates the value of the adjacent scale. They are respectively expressed as discrete differences of phase in the spatial x and y dimensions and the frequency domain dimension. Similarly, Δ|E(x,y,ω)| 2 The parts represent the discrete differences in the intensity of each dimension.

[0053] In some technical solutions, after the step of forming an ultrafast event excitation region according to the excitation light beam, the ultrafast holographic imaging method based on compressed frequency domain holographic recording further includes:

[0054] Computationally recover ultrafast events such as the propagation of space plasma and its speed.

[0055] <Second Aspect of the Embodiments of the Present Application>

[0056] The second aspect provides an ultrafast holographic imaging system based on compressed frequency domain holographic recording, which is used to implement the ultrafast holographic imaging method based on compressed frequency domain holographic recording provided in the first aspect of the embodiment of the present application, and the ultrafast holographic imaging system based on compressed frequency domain holographic recording includes:

[0057] A first beam splitting module, used for splitting a femtosecond laser pulse into an excitation beam and a recording beam;

[0058] An ultrafast event excitation module, used to form an ultrafast event excitation region according to the excitation light beam;

[0059] A pulse stretching module, used for stretching the recording light beam to form a chirped pulse;

[0060] A second light splitting module, used for performing light splitting processing on the chirped pulse to obtain a first chirped pulse and a second chirped pulse;

[0061] A modulation module, used for passing the first chirped pulse through the ultrafast event excitation region to perform intensity and phase modulation to obtain a first modulated pulse;

[0062] A delay module, used for passing the second chirped pulse through a delay optical path to form a reference pulse in frequency domain interferometry;

[0063] A light combining module, used for combining the first modulated pulse and the reference pulse to form a recording pulse and a reference pulse separated in time dimension;

[0064] A beam expansion module, used for performing beam expansion processing on the recording and reference pulses to obtain beam expanded pulses;

[0065] A sparse sampling module, used for performing two-dimensional sparse sampling modulation on the beam expansion pulse to form a second modulated pulse and obtain a sparse sampling result;

[0066] A compression superposition recording module, used for performing frequency domain interference on the second modulated pulse after light splitting to obtain two-dimensional frequency domain interference fringes, compressing and superposing the records, and obtaining an interference fringes superposition intensity image;

[0067] The calculation module is used to calculate and obtain three-dimensional space-time intensity and phase information using a weighted sparse compression model reconstruction algorithm.

[0068] In some technical solutions, the ultrafast holographic imaging system based on compressed frequency domain holographic recording further includes:

[0069] A femtosecond laser is used to generate the femtosecond laser pulse.

[0070] In some technical solutions, the first light splitting module is a first light splitting element.

[0071] In some technical solutions, the ultrafast event excitation module includes:

[0072] A frequency doubling crystal, used for incident upon the excitation light beam to form a frequency doubling light beam and emit it;

[0073] at least one first reflecting element, used to reflect the frequency-doubled light beam;

[0074] The focusing element is used to focus the reflected double frequency light beam to excite the spatial ultrafast event and form the ultrafast event excitation area.

[0075] In some technical solutions, the pulse stretching module is a pulse stretching element.

[0076] In some technical solutions, the second light splitting module is a second light splitting element.

[0077] In some technical solutions, the modulation module is a second reflective element.

[0078] In some technical solutions, the delay module includes a plurality of third reflective elements.

[0079] In some technical solutions, the light combining module is a light combining element.

[0080] In some technical solutions, the beam expansion module is a lens group.

[0081] In some technical solutions, the sparse sampling module is a DMD chip.

[0082] In some technical solutions, the compressed superposition recording module includes an imaging spectrometer.

[0083] In some technical solutions, the compression superposition recording module also includes a fourth reflection element.

[0084] In some technical solutions, the recording pixels on the DMD chip have a scale correspondence with the pixels on the imaging spectrometer.

[0085] The beneficial effects of this application include:

[0086] This application combines the chirped pulse frequency-time correspondence, frequency domain interference phase recording and reproduction, and compressed dimension reduction recording and recovery methods to obtain the changes in the intensity and phase information of continuous spatiotemporal femtosecond ultrafast processes, and adopts a weighted sparse compression model-based reproduction algorithm to achieve compression recording interference fringes to reproduce multiple continuous intensity and phase distributions, and calculate the three-dimensional space-time intensity and phase information of ultrafast events. Therefore, this application can simultaneously solve the technical problems of complex amplitude recording, recording frame number, and expanding recording dimensions.

[0087] The chirped pulse frequency response is to widen the recording light beam to form a chirped pulse.

[0088] The frequency domain interference phase recording and reproduction is to pass the first chirped pulse through the ultrafast event excitation region, perform intensity and phase modulation, and obtain a first modulated pulse.

[0089] The compressed dimension reduction recording and recovery method is to perform two-dimensional sparse sampling modulation on the beam expansion pulse to form a second modulated pulse to obtain a sparse sampling result.

[0090] The present application places a DMD intensity random sparse sampling template in the frequency domain holographic imaging optical path, and compresses and records the interference fringe superposition intensity image. Based on the analysis of the relationship between the compression phase, compression intensity and each separated phase and intensity of the compressed frequency domain holographic recording image, the space-time three-dimensional intensity and phase can be restored.

[0091] Unless defined otherwise, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention belongs.

[0092] The various features and embodiments of the present invention mentioned in the above aspects may be applied to other aspects with appropriate modifications, as appropriate. Therefore, specific features in one aspect may be appropriately combined with specific features in other aspects.

[0093] Other advantages, objectives and features of the present invention will be embodied in part through the following description, and in part will be understood by those skilled in the art through study and practice of the present invention. BRIEF DESCRIPTION OF THE DRAWINGS

[0094] In order to more clearly illustrate the technical solutions of the embodiments of the present application, the drawings required for use in the description of the embodiments of the present application will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present application. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying any creative labor.

[0095] Figure 1Schematic diagram of the optical path and structure of the ultrafast holographic imaging system based on compressed frequency domain holographic recording of the present invention in some embodiments;

[0096] Figure 2 A compressed recording optical path diagram of an ultrafast holographic imaging system based on compressed frequency domain holographic recording in some embodiments of the present invention;

[0097] Figure 3 A diagram showing the phase wavefront change in some embodiments of the present invention after ultrafast event plasma excitation;

[0098] Description of Figure Numbers:

[0099] 1. The first optical splitter module;

[0100] 2. Ultrafast event excitation module; 21. Frequency doubling crystal; 22. First reflection element; 23. Focusing element;

[0101] 3. Pulse stretching module;

[0102] 4. The second optical splitter module;

[0103] 5. Modulation module;

[0104] 6. Delay module; 61. Third reflective element;

[0105] 7. Light combining module;

[0106] 8. Beam expansion module;

[0107] 9. Sparse sampling module;

[0108] 10. Compression superposition recording module;

[0109] F. Femtosecond laser. DETAILED DESCRIPTION

[0110] In order to make the purpose, technical solution and advantages of the present invention more clear, the technical solution in the embodiment of the present application will be clearly and completely described below in conjunction with the drawings in the embodiment of the present application. Obviously, the described embodiment is a part of the embodiment of the present application, not all of the embodiments. Based on the embodiments in the present application, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of this application.

[0111] The terms "first" and "second" in the description of the embodiments of the present application are used to distinguish different objects rather than to describe a specific order of the objects. For example, the first beam splitter element and the second beam splitter element are used to distinguish different beam splitters rather than to describe a specific order of the beam splitters.

[0112] In the embodiments of the present application, words such as "exemplary" or "for example" are used to indicate examples, illustrations or descriptions. Any embodiment or design described as "exemplary" or "for example" in the embodiments of the present application should not be interpreted as being more preferred or more advantageous than other embodiments or designs. Specifically, the use of words such as "exemplary" or "for example" is intended to present related concepts in a specific way.

[0113] It should be noted that, in this document, the terms "comprises", "includes" or any other variations thereof are intended to cover non-exclusive inclusion. For example, a process, method, system, product or apparatus comprising a series of steps or units is not necessarily limited to those steps or units explicitly listed, but may include other steps or units not explicitly listed or inherent to these processes, methods, products or apparatus.

[0114] It should be noted that X, Y and T mentioned in this article refer to two-dimensional space and three dimensions of time.

[0115] The specific implementation of the present application is further described below in conjunction with the accompanying drawings.

[0116] <Ultrafast holographic imaging system based on compressed frequency domain holographic recording>

[0117] See also Figure 1 , Figure 1 This is a schematic diagram of the optical path and structure of the ultrafast holographic imaging system based on compressed frequency domain holographic recording in this application. Figure 1 In the present application, the ultrafast holographic imaging system based on compressed frequency domain holographic recording includes:

[0118] A first beam splitting module 1, used for splitting a femtosecond laser pulse into an excitation beam and a recording beam;

[0119] An ultrafast event excitation module 2, used for forming an ultrafast event excitation region according to the excitation light beam;

[0120] A pulse stretching module 3, used for stretching the recording light beam to form a chirped pulse;

[0121] A second light splitting module 4, used for performing light splitting processing on the chirped pulse to obtain a first chirped pulse and a second chirped pulse;

[0122] A modulation module 5, configured to pass the first chirped pulse through the ultrafast event excitation region to perform intensity and phase modulation to obtain a first modulated pulse;

[0123] A delay module 6, used for passing the second chirped pulse through a delay optical path to form a reference pulse in frequency domain interferometry;

[0124] A light combining module 7, used for combining the first modulated pulse and the reference pulse to form a recording pulse and a reference pulse separated in time dimension;

[0125] A beam expansion module 8, used for performing beam expansion processing on the recording and reference pulses to obtain beam expanded pulses;

[0126] A sparse sampling module 9 is used to perform two-dimensional sparse sampling modulation on the beam expansion pulse to form a second modulated pulse and obtain a sparse sampling result;

[0127] A compression superposition recording module 10 is used to perform frequency domain interference after light splitting the second modulated pulse to obtain two-dimensional frequency domain interference fringes, compress and superpose the records, and obtain an interference fringe superposition intensity image;

[0128] The calculation module (not shown in the figure) is used to calculate and obtain three-dimensional space-time intensity and phase information using a weighted sparse compression model reconstruction algorithm.

[0129] It should be noted that the femtosecond laser pulse may be a femtosecond laser pulse with a wavelength of 800 nm.

[0130] The first light splitting module 1 is a first light splitting element, and the first light splitting element may be a beam splitter.

[0131] The ultrafast event excitation module 2 includes a frequency doubling crystal 21, at least one first reflective element 22 and a focusing element 23. The number of the at least one first reflective element 22 is set to six. In other embodiments, the number of the first reflective elements 22 can be set by those skilled in the art according to actual needs.

[0132] The excitation light beam passes through the frequency doubling crystal 21 to form a frequency doubling light beam with a wavelength of 400 nm. The frequency doubling light beam is reflected to the focusing element 23 through six (or more) first reflecting elements 22 in sequence. The focusing element 23 focuses the frequency doubling light beam to excite an ultrafast event, thereby forming an ultrafast event excitation area.

[0133] The pulse stretching module 3 is a pulse stretching element. The pulse stretching element may be a prism pair. The recording light beam is incident on the pulse stretching element to form a 6ps chirped pulse.

[0134] The second light splitting module 4 is a second light splitting element. The second light splitting element may be a beam splitter. The first chirped pulse split by the second light splitting element is emitted through a recording optical path, and the second chirped pulse is emitted through a delay optical path.

[0135] The modulation module 5 is a second reflection element. The second reflection element reflects the first chirped pulse, passes through the ultrafast event excitation region, and reaches the light combining module 7.

[0136] The delay module 6 includes a plurality of third reflective elements 61. In the embodiment of the present application, the number of the third reflective elements 61 is five. In other embodiments, the number of the third reflective elements 61 can be set by a person skilled in the art. The purpose of setting the plurality of third reflective elements 61 is to extend the optical path of the second chirped pulse propagating to the light combining module 7.

[0137] The light combining module 7 is a light combining element.

[0138] The beam expansion module 8 is a lens group. In this embodiment, the lens group is a lens pair.

[0139] The sparse sampling module 9 is a DMD chip. The resolution of the DMD chip is 911x1139, and each pixel is rectangular, with a length and a width of 10.8 μm and 5.4 μm respectively. The DMD chip is used to encode and sample the femtosecond change process for restoration and reproduction.

[0140] The compression superposition recording module 10 includes an imaging spectrometer. The compression superposition recording module 10 also includes a fourth reflecting element, and the fourth reflecting element is used to reflect the expanded beam to the imaging spectrometer.

[0141] The beam expansion pulse is incident on the sparse sampling module 9 and propagates to the compression recording optical path diagram of the compression superposition recording module 10. Figure 2 ,exist Figure 2 In the figure, label A is a continuous signal in time, label B is grating spectroscopy, label C is the forward and backward expansion in the Y dimension, label D is the intensity superposition recorded on the imaging spectrometer surface, label E is the image of the integrated imaging at the same position on the imaging surface of the imaging spectrometer, and the light is staggered forward and backward in the time dimension.

[0142] In some embodiments, the ultrafast holographic imaging system based on compressed frequency domain holographic recording further includes:

[0143] The femtosecond laser F is used to generate the femtosecond laser pulses.

[0144] In some embodiments, the recording pixels on the DMD chip have a scale correspondence with the pixels on the imaging spectrometer.

[0145] The beam expansion pulse is incident on the DMD chip, and each pixel on the DMD chip modulates the spatial light intensity before entering the back-end interference processing optical path.

[0146] The surface of the DMD chip corresponds linearly to the imaging surface of the imaging spectrometer. Each point on the DMD chip is imaged as a line on the imaging spectrometer (spectrometer SPC), and the center of the line segment corresponds to the corresponding point on the SPC (uDMD ,v DMD )→(u SPC ,v SPC ).

[0147] Since the process of the second modulated pulse from the DMD chip to the imaging spectrometer is a linear correspondence, a polynomial can be used to represent this correspondence, and the polynomial parameters are fitted by calibrating the points of the image:

[0148]

[0149] Among them, u SPC , v SPC ,u DMD , v DMD are the horizontal and vertical coordinates on the spectrometer imaging plane and the DMD modulation plane, respectively. are the polynomial coefficients of the horizontal and vertical coordinates on the spectrometer imaging surface to the horizontal and vertical coordinates on the DMD modulation surface, are the polynomial coefficients of the horizontal and vertical coordinates on the DMD modulation surface to the horizontal and vertical coordinates on the spectrometer imaging surface.

[0150] <Ultrafast holographic imaging method based on compressed frequency domain holographic recording>

[0151] The present application provides an ultrafast holographic imaging method based on compressed frequency domain holographic recording, which is applied to the ultrafast holographic imaging system based on compressed frequency domain holographic recording provided by the present application. It includes:

[0152] Splitting a femtosecond laser pulse into an excitation beam and a recording beam;

[0153] forming an ultrafast event excitation region according to the excitation light beam;

[0154] Broadening the recording light beam to form a chirped pulse;

[0155] Performing spectroscopic processing on the chirped pulse to obtain a first chirped pulse and a second chirped pulse;

[0156] Passing the first chirped pulse through the ultrafast event excitation region to perform intensity and phase modulation to obtain a first modulated pulse;

[0157] Passing the second chirped pulse through a delayed optical path to form a reference pulse in frequency domain interferometry;

[0158] Combining the first modulated pulse and the reference pulse to form a recording pulse and a reference pulse separated in time dimension;

[0159] Performing beam expansion processing on the recording and reference pulses to obtain beam expanded pulses;

[0160] Performing two-dimensional sparse sampling modulation on the beam expansion pulse to form a second modulated pulse, and obtaining a sparse sampling result;

[0161] Perform frequency domain interference on the second modulated pulse after light splitting to obtain two-dimensional frequency domain interference fringes, compress and superimpose the records, and obtain an interference fringe superposition intensity image;

[0162] The three-dimensional space-time (X, Y, T) intensity and phase information is calculated using a weighted sparse compression model reconstruction algorithm.

[0163] In some embodiments, the step of obtaining an interference fringe superposition intensity image comprises:

[0164] ① The compressed recorded image of the two-dimensional frequency domain interference fringes is:

[0165]

[0166] Wherein, I(x, y, ω) is the interference fringes obtained by two-dimensional spatial frequency domain interference (i.e., two-dimensional frequency domain interference fringes); M is the combination of the grating spectroscopic deflection operation S of the imaging spectrometer and the DMD intensity random sparse sampling C, that is, M=S·C;

[0167] ② The compressed recorded image is converted to the time domain using Fourier transform to obtain:

[0168]

[0169] in, represents Fourier transform, W0(t), W(t-τ0), W * (-t-τ0) represents the time domain 0-level and positive and negative 1-level intensity, respectively, and G represents the time domain intensity coefficient;

[0170] ③Extract the first-level spectrum and use inverse Fourier transform to obtain:

[0171]

[0172] in, represents the reference pulse frequency domain electric field distribution, represents the frequency domain electric field distribution of the detection light pulse, represents the frequency domain phase distribution of the detected ultrafast process, τ0 represents the time difference between the detection pulse and the reference pulse;

[0173] ④ The formula for calculating the difference between the first-order spectrum phase angle of the compressed recorded interference fringes and the first-order spectrum phase angle of the compressed reference interference fringes is:

[0174]

[0175] Wherein, M is the combination of the grating spectroscopic deflection operation S of the imaging spectrometer and the random sparse sampling C of the DMD intensity, that is, M=S·C, represents the frequency domain phase distribution of the detected ultrafast process, τ0 represents the time difference between the detection pulse and the reference pulse;

[0176] ⑤ Based on the local linearity of the tangent function, it is converted to:

[0177]

[0178] Usually, the phase shift of transient events in ultrafast recording is small.

[0179]

[0180]

[0181] The above formula converts to:

[0182]

[0183] ⑥ The formula for converting the interference fringe intensity superposition into phase superposition is obtained:

[0184]

[0185] Where ΔΨ(x,ω) is the compressed recorded phase image, represents the frequency domain phase distribution of the detected ultrafast process, M is the combination of the grating spectroscopic deflection operation S of the imaging spectrometer and the random sparse sampling C of the DMD intensity, that is, M = S·C;

[0186] ⑦ Extract the Fourier transform 0-level spectrum and obtain the weighted superposition formula of intensity:

[0187]

[0188] Wherein, ΔΠ(x,ω) is a compressed recorded intensity image, and M is a combination of the grating spectroscopic deflection operation S of the imaging spectrometer and the DMD intensity random sparse sampling C, that is, M=S·C.

[0189] In some implementations, the constraint formula of the weighted sparse compression model reproduction algorithm is:

[0190]

[0191]

[0192] in,

[0193]

[0194]

[0195] Among them, λ is the adjustment coefficient; is the phase information; Δ|E(x,y,ω)| 2 is the intensity information. TV[·] indicates total variation calculation, +1 indicates the value of the adjacent scale. They are respectively expressed as discrete differences of the phase in the spatial x and y dimensions and the frequency domain dimension. Similarly, Δ|E(x,y,ω)| 2 The parts represent the discrete differences in the intensity of each dimension.

[0196] In some embodiments, after the step of forming an ultrafast event excitation region according to the excitation light beam, the ultrafast holographic imaging method based on compressed frequency domain holographic recording further includes:

[0197] Computationally recover ultrafast events such as the propagation of space plasma and its speed.

[0198] For example, the X sampling is cut into 11 scales, and the YT section at the middle position scale 6, X=81 μm, is selected. The forward propagation of the phase over time (such as Figure 3 ). Use Figure 3 The 0.8 phase line is equal to the curve mark in the figure, and a straight line Y relative to T is fitted (i.e. Figure 3 The slope is the speed of plasma propagation in space, which is calculated to be: 2.73*10 8 m / s.

[0199] The above is an example of the best implementation method of this application, and the parts not described in detail are common knowledge of ordinary technicians in this field. The protection scope of this application shall be based on the content of the claims, and any equivalent transformation based on the technical enlightenment of this application is also within the protection scope of this application.

Claims

1. An ultrafast holographic imaging method based on compressed frequency domain holographic recording, characterized in that: include: Splitting a femtosecond laser pulse into an excitation beam and a recording beam; forming an ultrafast event excitation region according to the excitation light beam; Broadening the recording light beam to form a chirped pulse; Performing spectroscopic processing on the chirped pulse to obtain a first chirped pulse and a second chirped pulse; Passing the first chirped pulse through the ultrafast event excitation region to perform intensity and phase modulation to obtain a first modulated pulse; Passing the second chirped pulse through a delayed optical path to form a reference pulse in frequency domain interferometry; Combining the first modulated pulse and the reference pulse to form a recording pulse and a reference pulse separated in time dimension; Performing beam expansion processing on the recording and reference pulses to obtain beam expanded pulses; Performing two-dimensional sparse sampling modulation on the beam expansion pulse to form a second modulated pulse, and obtaining a sparse sampling result; Perform frequency domain interference on the second modulated pulse after light splitting to obtain two-dimensional frequency domain interference fringes, compress and superimpose the records, and obtain an interference fringe superposition intensity image; The three-dimensional space-time intensity and phase information is calculated by using a weighted sparse compression model reconstruction algorithm. The step of obtaining the interference fringe superposition intensity image includes: ① The compressed recorded image of the two-dimensional frequency domain interference fringes is: Wherein, I(x, y, ω) is the interference fringe obtained by two-dimensional spatial frequency domain interference; M is the combination of the grating spectroscopic deflection operation S of the imaging spectrometer and the random sparse sampling C of the DMD intensity, that is, M = S·C; ② The compressed recorded image is converted to the time domain using Fourier transform to obtain: in, represents Fourier transform, W0(t), W(t-τ0), W * (-t-τ0) represents the time domain 0-level and positive and negative 1-level intensity, respectively, and G represents the time domain intensity coefficient; ③Extract the first-level spectrum and use inverse Fourier transform to obtain: in, represents the reference pulse frequency domain electric field distribution, represents the frequency domain electric field distribution of the detection light pulse, represents the frequency domain phase distribution of the detected ultrafast process, τ0 represents the time difference between the detection pulse and the reference pulse; ④ The formula for calculating the difference between the first-order spectrum phase angle of the compressed recorded interference fringes and the first-order spectrum phase angle of the compressed reference interference fringes is: Wherein, M is the combination of the grating spectroscopic deflection operation S of the imaging spectrometer and the random sparse sampling C of the DMD intensity, that is, M=S·C, represents the frequency domain phase distribution of the detected ultrafast process, τ0 represents the time difference between the detection pulse and the reference pulse; ⑤ Based on the local linearity of the tangent function, it is converted to: when The above formula converts to: ⑥ The formula for converting the interference fringe intensity superposition into phase superposition is obtained: Where ΔΨ(x,ω) is the compressed recorded phase image, represents the frequency domain phase distribution of the detected ultrafast process, M is the combination of the grating spectroscopic deflection operation S of the imaging spectrometer and the random sparse sampling C of the DMD intensity, that is, M = S·C; ⑦ Extract the Fourier transform 0-level spectrum and obtain the weighted superposition formula of intensity: Wherein, ΔΠ(x,ω) is the compressed recorded intensity image, M is the combination of the grating spectroscopic deflection operation S of the imaging spectrometer and the random sparse sampling C of the DMD intensity, that is, M=S·C, The constraint formula of the weighted sparse compression model reproduction algorithm is: in, Among them, λ is the adjustment coefficient; is the phase information; Δ|E(x, y, ω)| 2 is the intensity information, TV[·] indicates total variation calculation, +1 indicates the value of the adjacent scale, They are respectively expressed as discrete differences of phase in spatial x, y dimensions and frequency domain dimensions, Δ|E(x+1, y, ω)| 2 -Δ|E(x, y, ω)| 2 ,Δ|E(x,y+1,ω)| 2 -Δ|E(x, y, ω)| 2 ,Δ|E((x,y,ω+1)| 2 -Δ|E(x, y, ω)| 2 Represents the discrete difference of the intensity in the x and y dimensions of space.

2. The ultrafast holographic imaging method based on compressed frequency domain holographic recording according to claim 1, characterized in that: After the step of forming an ultrafast event excitation region according to the excitation light beam, the ultrafast holographic imaging method based on compressed frequency domain holographic recording further includes: Computational recovery of ultrafast events.

3. Ultrafast holographic imaging system based on compressed frequency domain holographic recording, characterized in that: The ultrafast holographic imaging method based on compressed frequency domain holographic recording according to claim 1 comprises: A first beam splitting module, used for splitting a femtosecond laser pulse into an excitation beam and a recording beam; An ultrafast event excitation module, used to form an ultrafast event excitation region according to the excitation light beam; A pulse stretching module, used for stretching the recording light beam to form a chirped pulse; A second light splitting module, used for performing light splitting processing on the chirped pulse to obtain a first chirped pulse and a second chirped pulse; A modulation module, used for passing the first chirped pulse through the ultrafast event excitation region to perform intensity and phase modulation to obtain a first modulated pulse; A delay module, used for passing the second chirped pulse through a delay optical path to form a reference pulse in frequency domain interferometry; A light combining module, used for combining the first modulated pulse and the reference pulse to form a recording pulse and a reference pulse separated in time dimension; A beam expansion module, used for performing beam expansion processing on the recording and reference pulses to obtain beam expanded pulses; A sparse sampling module, used for performing two-dimensional sparse sampling modulation on the beam expansion pulse to form a second modulated pulse and obtain a sparse sampling result; A compression superposition recording module, used for performing frequency domain interference on the second modulated pulse after light splitting to obtain two-dimensional frequency domain interference fringes, compressing and superposing the records, and obtaining an interference fringes superposition intensity image; The calculation module is used to calculate and obtain three-dimensional space-time intensity and phase information using a weighted sparse compression model reconstruction algorithm.

4. The ultrafast holographic imaging system based on compressed frequency domain holographic recording according to claim 3, characterized in that: The ultrafast holographic imaging system based on compressed frequency domain holographic recording also includes: A femtosecond laser is used to generate the femtosecond laser pulse.

5. The ultrafast holographic imaging system based on compressed frequency domain holographic recording according to claim 4, characterized in that: The first light splitting module is a first light splitting element; The pulse stretching module is a pulse stretching element; The second light splitting module is a second light splitting element; The modulation module is a second reflective element; The delay module includes a plurality of third reflective elements; The light combining module is a light combining element; The beam expansion module is a lens group; The sparse sampling module is a DMD chip; The compression superposition recording module includes an imaging spectrometer.

6. The ultrafast holographic imaging system based on compressed frequency domain holographic recording according to claim 5, characterized in that: The ultrafast event excitation module comprises: A frequency doubling crystal, used for incident upon the excitation light beam to form a frequency doubling light beam and emit it; at least one first reflecting element, used to reflect the frequency-doubled light beam; The focusing element is used to focus the reflected double frequency light beam to excite the spatial ultrafast event and form the ultrafast event excitation area.

7. The ultrafast holographic imaging system based on compressed frequency domain holographic recording according to claim 6, characterized in that: The compression superposition recording module further includes a fourth reflection element.

8. The ultrafast holographic imaging system based on compressed frequency domain holographic recording according to claim 7, characterized in that: The recording pixels on the DMD chip and the pixels on the imaging spectrometer have a scale corresponding relationship.

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