Single-exposure time-space measurement device and method based on space-frequency multiplexing

Abstract

A kind of single exposure ultra-short pulse space-time measurement device and method based on space-frequency multiplexing, device includes beam splitting module, wavelength gating module, wavefront modulation module and detector. The light beam to be measured is divided into different angle sub-beams by the beam splitting module, the wavelength gating module makes the different angle light beam pass through different narrow-band wavelengths, then the filtered light beam passes through the wavefront modulation module, and finally the diffraction spot is recorded by the detector. The phase retrieval technology of single exposure can recover the wavefront information corresponding to each wavelength. The present application can realize single exposure measurement of wideband light beam, especially for femtosecond pulse wavefront measurement, which can realize femtosecond pulse space-time diagnosis, and has the characteristics of self-reference and high spatial resolution.

Description

Technical Field

[0001] This invention relates to single-shot measurement of spatiotemporal three-dimensional complex amplitude of ultrashort pulses, single-exposure measurement of spatial and spectral phases of ultrashort pulses, and spatiotemporal coupling, especially for wavefront measurement of complex wavefront distributions of ultrafast pulses. Background Technology

[0002] Characterization of ultrashort pulse properties requires obtaining or Four-dimensional information, and general methods for measuring spectral phase include FROG (frequency-resolved optical gating), SPIDER (spectral-phase interferometry for direct electric-field reconstruction), and discrete scanning. However, measuring spatiotemporal characteristics requires combining spatial phase measurement techniques. For example, Shackled FROG and HAMSTER (Hartmann-Shack assisted, multidimensional, shader-based technique for electric-field reconstruction) techniques combined with Hartmann sensors can achieve spatial-spectral phase measurement, but scanning is required. Additionally, the (sTRIPED FISH) spatially and temporally resolved intensity and phase evaluation device: Full Information from a Single Hologram, combined with holographic technology, can achieve spatial-spectral phase measurement in a single exposure, but this method requires a reference beam. This invention proposes a single-exposure phase recovery device and method based on wavelength spectroscopy. This method does not require a reference beam and can reconstruct the wavefront complex amplitude distribution of M wavelengths in a single exposure. Combined with other spectral phase measurement techniques, it can achieve spatial-spectral phase measurement of a single-exposure ultrashort pulse, i.e. or It has the advantages of simple device, high resolution, and high stability. Summary of the Invention

[0003] This invention addresses the limitations of measuring the spatiotemporal coupling characteristics of single-exposure ultrashort pulses by proposing a spatiotemporal measurement device and method based on spatial-frequency multiplexing. A wavefront beam splitter module divides the wavefront into outgoing light at different angles. These outgoing light beams then pass through a narrowband filter, resulting in different wavelengths at different angles. After passing through a modulator, diffraction spots of different wavelengths are recorded at different positions on the detector. A phase retrieval algorithm can be used to reconstruct the spatial complex amplitude of the wavefront corresponding to different wavelengths. Combined with a time-phase measurement method, spatiotemporal phase measurement of ultrashort pulses can be achieved.

[0004] The technical solution of the present invention is as follows:

[0005] A spatiotemporal measurement device for a single-exposure ultrashort pulse based on space-frequency multiplexing, characterized in that it comprises:

[0006] The wavefront beam splitter module is used to split the beam under test into beams according to the energy ratio Q1:Q2, where Q1 and Q2 are determined according to requirements;

[0007] A grating beam splitter module is used to divide the split beam of the test beam into sub-beams at different angles;

[0008] The wavelength gating module allows sub-beams at different angles to pass through different narrowband wavelengths;

[0009] The wavefront modulation module is used to modulate the wavefront under test.

[0010] The detector module is used to record the light intensity of the wavefront after it has been modulated by the wavefront modulation module.

[0011] The time phase measurement module is used to measure the time phase distribution of ultrashort pulses;

[0012] The control and data processing module is used to control the detector module, record and store the diffraction spots in a timely manner, and process the data.

[0013] The aforementioned single-exposure ultrashort pulse spatiotemporal measurement device based on space-frequency multiplexing is characterized in that a laser module is provided on the same optical axis before the wavefront beam splitting module, and the laser module is an ultrashort pulse light source.

[0014] The aforementioned single-exposure ultrashort pulse spatiotemporal measurement device based on space-frequency multiplexing is characterized in that the laser module generating the chirped pulse beam further includes: a dispersive prism A and a dispersive prism B, used to generate spatial chirped pulses.

[0015] The pulsed beam generated by the laser module is converted into a chirped pulse after passing through dispersive prism A and dispersive prism B, which serves as the test beam for the system.

[0016] The single-exposure ultrashort pulse spatiotemporal measurement device based on space-frequency multiplexing is characterized in that, between the wavefront beam splitting module and the grating beam splitting module, a dispersive lens A and a dispersive lens B are sequentially arranged along the optical path to generate spatial chirped pulses.

[0017] The aforementioned single-exposure ultrashort pulse spatiotemporal measurement device based on space-frequency multiplexing is characterized in that the grating beam splitting module is an amplitude-type or phase-type two-dimensional grating.

[0018] The aforementioned single-exposure ultrashort pulse spatiotemporal measurement device based on space-frequency multiplexing is characterized in that the wavefront modulation module is a binary step phase wavefront modulator, a ternary step phase wavefront modulator, a deca-step phase wavefront modulator, a continuous phase modulator, a continuous amplitude phase modulator, or a pure amplitude wavefront modulator.

[0019] The method for performing spatiotemporal measurement of a single-exposure ultrashort pulse using a single-exposure ultrashort pulse spatiotemporal measurement device based on space-frequency multiplexing is characterized by comprising the following steps:

[0020] Step 1) Calibrate the complex amplitude transmittance function T of the wavefront modulation module for a certain wavelength. m m represents the different diffraction orders of the grating, m = 1, 2, 3...M;

[0021] Step 2) The initial guess formula for the complex amplitude distribution of the beam before the wavefront modulation module is as follows:

[0022] Oguess m =Aguess m ·(rand(nx,ny)·exp(i·rand(nx,ny)·π)) m

[0023] In the formula, Aguess m Let nx be the amplitude coefficient of the m-th diffraction order, and rand(nx, ny) be a random matrix that generates nx rows and ny columns, where nx and ny are the rows and columns of the data matrix to be operated on, respectively.

[0024] Step 3) Wavefront iterative calculation process of the control and data processing module:

[0025] ① Forward propagation process: Initial guess wavefront Oguess m After passing through the wavefront modulation module, it becomes the wavefront: P m =Oguess m ·T m Then wavefront P m The wavefront is obtained by propagation to the detector module. in This represents the forward propagation process of the wavefront, where L is the propagation distance.34 The distance between the wavefront modulation module (4) and the detector module (5);

[0026] The diffraction spot IA recorded by the detector module is divided into diffraction spots I corresponding to different wavelengths. m =cut(IA), where cut() is the splitting operation;

[0027] The control and data processing module controls the wavefront IP. m Update: IP' m =I m ·exp(i·angle(IP m The error RMS between the estimated diffraction spot and the recorded diffraction spot is calculated using the following formula:

[0028] RMS = sum(I m ) / (sum(IP′ m 2 )-sum(I m )) 2

[0029] Where sum is the summation of all elements in the matrix, and angle is the phase operation on the wavefront;

[0030] ② Backpropagation process: Updated wavefront IP′ m Backpropagation to the wavefront modulation module yields the wavefront. in This represents the backward propagation process, where L is the propagation distance;

[0031] The wavefront before the wavefront modulation module (4) is obtained using the following update formula:

[0032] Oguess′ m =Oguess m +conj(T m ) / max(conj(T m )·T m )·(P′ m -P m )

[0033] The updated wavefront Oguess' m Propagation to the focal plane yields the focal plane wavefront. Apply the aperture function to update the focal surface wavefront as: F′ m =F m ·R m , where R m Let F′ be the aperture function corresponding to the m-th wavefront; then F′ m The wavefront before the modulation module is obtained before propagation to the wavefront modulation module.

[0034] With the updated wavefront U m Instead of the initial guess of wavefront Oguess m The iteration continues until the error RMS is less than a predetermined value, at which point the iteration process ends. This yields the wavefront distribution before the wavefront modulation module for each wavelength. Propagating the wavefront allows us to obtain the spatial phase distribution of the beam at other locations with different wavelengths, denoted as... n = 1, 2, 3, ... N.

[0035] Step 4): The complex amplitude corresponding to different times can be measured by the time phase measurement module, and its complex amplitude is expressed as... Combined with the results obtained in step 3) n = 1, 2, 3, ... N, can be... Spatiotemporal coupling is achieved to obtain the wavefront distribution of the pulse under test.

[0036] Compared with existing technologies, the advantages of this invention are: this method does not require the introduction of a reference beam, and can reconstruct the wavefront complex amplitude distribution of M wavelengths in a single exposure. Combined with other spectral phase measurement techniques, it can achieve spatial-spectral phase measurement of a single-exposure ultrashort pulse. It has the advantages of simple device, high resolution, and high stability. Attached Figure Description

[0037] Figure 1 A spatiotemporal measurement device for single-exposure ultrashort pulses based on space-frequency multiplexing;

[0038] Figure 2 A spatiotemporal measurement device for single exposure based on space-frequency multiplexing of an ultrashort pulse light source;

[0039] Figure 3 A prism dispersion single-exposure spatiotemporal measurement device based on an ultrashort pulse light source;

[0040] Figure 4 Spatiotemporal measurement device for single exposure of dispersive lens based on ultrashort pulse light source; Detailed Implementation

[0041] The present invention will be further described in conjunction with embodiments and accompanying drawings to address different types of measurement requirements, but the scope of protection of the present invention should not be limited by these embodiments.

[0042] Example 1

[0043] like Figure 3The prism dispersion single-exposure spatiotemporal measurement device based on an ultrashort pulse light source includes: a wavefront beam splitting module (1) for splitting the beam to be measured into beams according to an energy ratio Q1:Q2, where Q1 and Q2 are determined according to requirements; a grating beam splitting module (2) for splitting the beam to be measured into sub-beams at different angles; a wavelength gating module (3) for passing sub-beams at different angles through different narrowband wavelengths; a wavefront modulation module (4) for performing wavefront modulation on the wavefront to be measured; a detector module (5) for recording the light intensity of the wavefront after modulation by the wavefront modulation module (4); a time phase measurement module (6) for measuring the time phase distribution of ultrashort pulses, such as Frequency Resolved Optical Gating (FROG) or Spectral-phase Interferometry For Direct Electric-field Reconstruction (sPIDER); and a control and data processing module (7) for controlling the detector module (5), recording and storing the diffraction spots in a timely manner, and processing the data.

[0044] The laser module (8) uses a femtosecond high repetition rate pulsed laser with a pulse width of 30 femtoseconds and a bandwidth of 780-820nm.

[0045] The process for generating the chirped pulse beam includes: a dispersive prism A (9) for generating spatial dispersion; and a dispersive prism B (10) which works in conjunction with dispersive prism A (9) to generate the chirped pulse. The dispersive prism is a symmetrical quartz right-angle prism.

[0046] After beam expansion, the femtosecond pulse to be measured is passed through dispersive prism A (9) and dispersive prism B (10) to generate a chirped pulse, which serves as the beam to be measured in the system.

[0047] Grating beam splitting module (2): 6×6 two-dimensional Damman grating with a beam splitting angle of 3°.

[0048] The wavelength gating module (3) uses an 800nm ​​narrowband filter.

[0049] The wavefront modulation module (4) is a binary step phase wavefront modulator that modulates the wavefront transmitted through the wavelength gating module (3).

[0050] Example 2

[0051] like Figure 4The spatiotemporal measurement device for a single exposure of a dispersive lens based on an ultrashort pulse light source includes: a wavefront beam splitting module (1) for splitting the beam to be measured into beams of different energy ratios Q1:Q2, where Q1 and Q2 are determined according to requirements; a grating beam splitting module (2) for splitting the beam to be measured into sub-beams of different angles; a wavelength gating module (3) for passing sub-beams of different angles through different narrowband wavelengths; a wavefront modulation module (4) for modulating the wavefront to be measured; a detector module (5) for recording the light intensity of the wavefront after modulation by the wavefront modulation module (4); a time phase measurement module (6) for measuring the time phase distribution of ultrashort pulses, such as Frequency Resolved Optical Gating (FROG) or Spectral-phase Interferometry For Direct Electric-field Reconstruction (SPIDER) measurement devices; and a control and data processing module (7) for controlling the detector module (5), recording and storing the diffraction spots in a timely manner, and processing the data.

[0052] The laser module (8) uses a femtosecond high repetition rate pulsed laser with a pulse width of 30 femtoseconds and a bandwidth of 780-820nm.

[0053] The generation of the chirped pulse beam also includes: a dispersive lens A (11) and a dispersive lens B (12) for generating spatial dispersion. The pulse beam generated by the laser module (8) is transformed into a chirped pulse after passing through the dispersive lens A (11) and the dispersive lens B (12), which serves as the beam to be tested in the system.

[0054] Grating beam splitting module (2): 6×6 two-dimensional Damman grating with a beam splitting angle of 3°.

[0055] The wavelength gating module (3) uses an 800nm ​​narrowband filter.

[0056] The wavefront modulation module (4) is a binary continuous phase wavefront modulator that modulates the wavefront transmitted through the wavelength gating module (3).

[0057] The single-exposure phase recovery device based on wavelength spectroscopy described in Examples 1 and 2 is characterized by the following steps:

[0058] Step 1) Calibrate the wavefront modulation module (4) for the complex amplitude transmittance function T of a certain wavelength. m m represents the different diffraction orders of the grating, m = 1, 2, 3...M;

[0059] Step 2) The initial guess formula for the complex amplitude distribution of the beam before the wavefront modulation module (4) is as follows:

[0060] Oguess m =Aguess m ·(rand(nx,ny)·exp(i·rand(nx,ny)·π)) m

[0061] In the formula, Aguess m Let nx be the amplitude coefficient of the m-th diffraction order, and rand(nx, ny) be a random matrix that generates nx rows and ny columns, where nx and ny are the rows and columns of the data matrix to be operated on, respectively.

[0062] Step 3) Control and data processing module (7) Wavefront iterative calculation process:

[0063] ① Forward propagation process: The initial guessed wavefront Oguessm becomes the wavefront after passing through the wavefront modulation module (4): P m =Oguess m ·T m Then wavefront P m The wavefront is obtained by propagating to the detector module (5). in This represents the forward propagation process of the wavefront, where L is the propagation distance. 34 The distance between the wavefront modulation module (4) and the detector module (5);

[0064] The diffraction spot IA recorded by the detector module (5) is divided into diffraction spots I corresponding to different wavelengths. m =cut(IA), where cut() is the splitting operation;

[0065] The control and data processing module (7) controls the wavefront IP. m Update: IP' m =I m ·exp(i·angle(IP m The error RMS between the estimated diffraction spot and the recorded diffraction spot is calculated using the following formula:

[0066] RMS = sum(I m ) / (sum(IP′ m 2 )-sum(I m )) 2

[0067] Where sum is the summation of all elements in the matrix, and angle is the phase operation on the wavefront;

[0068] ② Backpropagation process: Updated wavefront IP′ m The wavefront is obtained by backpropagation to the wavefront modulation module (4). in This represents the backward propagation process, where L is the propagation distance;

[0069] The wavefront before the wavefront modulation module (4) is obtained using the following update formula:

[0070] Oguess′ m =Oguess m +conj(T m ) / max(conj(T m )·T m )·(P′ m -P m )

[0071] The updated wavefront Oguess' m Propagation to the focal plane yields the focal plane wavefront. Apply the aperture function to update the focal surface wavefront as: F′ m =F m ·R m , where R m Let F′ be the aperture function corresponding to the m-th wavefront; then F′ m The wavefront before the wavefront is propagated to the wavefront modulation module (4) is obtained.

[0072] With the updated wavefront U m Instead of the initial guess of wavefront Oguess m The next iteration is performed until the error RMS is less than the predetermined value, at which point the iteration process ends. The wavefront distribution before the wavefront modulation module (4) corresponding to each wavelength is obtained. By propagating the wavefront, the spatial phase distribution of the beams to be measured at different wavelengths at other positions can be obtained, which is represented as follows: n = 1, 2, 3, ... N.

[0073] Step 4): The complex amplitude corresponding to different times can be measured by the time phase measurement module (6), and its complex amplitude is expressed as follows: Combined with the results obtained in step 3) n = 1, 2, 3, ... N, can be... Spatiotemporal coupling is achieved to obtain the wavefront distribution of the pulse under test.

Claims

1. A spatiotemporal measurement device for a single-exposure ultrashort pulse based on space-frequency multiplexing, characterized in that, include: Wavefront beam splitter (1) is used to split the beam to be tested according to the energy ratio Q1:Q2, where Q1 and Q2 are determined according to requirements; The grating beam splitting module (2) is used to divide the beam to be measured after beam splitting into sub-beams at different angles; Wavelength gating module (3) enables sub-beams at different angles to pass through different narrowband wavelengths; The wavefront modulation module (4) is used to perform wavefront modulation on the wavefront to be measured. The detector module (5) is used to record the light intensity of the wavefront after modulation by the wavefront modulation module (4); The time phase measurement module (6) is used to measure the time phase distribution of ultrashort pulses; The control and data processing module (7) is used to control the detector module (5), record and store the diffraction spots in a timely manner, process the data, reconstruct the wavefront complex amplitude distribution corresponding to each wavelength through a single exposure phase recovery algorithm, and achieve spatiotemporal coupling by combining the time phase measurement results to obtain the spatiotemporal wavefront distribution of the pulse under test, specifically including: Step 1) Calibrate the wavefront modulation module (4) for the complex amplitude transmittance function of a certain wavelength. Where m represents the different diffraction orders of the grating, m = 1, 2, 3...M; Step 2) The initial guess formula for the complex amplitude distribution of the beam before the wavefront modulation module (4) is as follows: In the formula, Let be the amplitude coefficient of the m-th diffraction order. To generate OK, A random matrix of columns, and These are the rows and columns of the data matrix being operated on; Step 3) Control and data processing module (7) Wavefront iterative calculation process: ① Forward propagation process: Initial guess of wavefront After passing through the wavefront modulation module (4), it becomes a wavefront: Then wavefront The wavefront is obtained by propagating to the detector module (5). ,in This indicates the forward propagation process of the wavefront. For transmission distance, The distance between the wavefront modulation module (4) and the detector module (5); The diffraction spot recorded by the detector module (5) For diffraction spots Divided into diffraction spots corresponding to different wavelengths , For the segmentation operation; The control and data processing module (7) controls the wavefront. Update: And calculate the error between the estimated diffraction spot and the recorded diffraction spot. The formula is as follows: in, To sum all elements in the matrix, To perform a phase-taking operation on the wavefront; ② Backpropagation process: The updated wavefront The wavefront is obtained by backpropagation to the wavefront modulation module (4). ,in Indicates the backpropagation process. For the distance of propagation; The wavefront before the wavefront modulation module (4) is obtained using the following update formula: The updated wavefront Propagation to the focal plane yields the focal plane wavefront. Applying the aperture function updates the focal surface wavefront as follows: ,in Let m be the aperture function corresponding to the m-th wavefront; then... The wavefront before the wavefront is propagated to the wavefront modulation module (4) is obtained. ; With the updated wavefront Instead of the initial guess wavefront The next iteration is performed until the error RMS is less than the predetermined value, and the iteration process ends. The wavefront distribution before the wavefront modulation module (4) corresponding to each wavelength is obtained. The wavefront is propagated to obtain the spatial phase distribution of the beam under test at other positions with different wavelengths, which is expressed as follows: n=1,2,3,…N; Step 4): The complex amplitude corresponding to different times can be measured by the time phase measurement module (6), and its complex amplitude is expressed as... Combined with the results obtained in step 3) n=1,2,3,…N, can be N items Spatiotemporal coupling is achieved to obtain the wavefront distribution of the pulse under test. .

2. The single-exposure ultrashort pulse spatiotemporal measurement device based on spatial frequency multiplexing according to claim 1, characterized in that, A laser module (8) is provided on the same optical axis before the wavefront beam splitter module (1), and the laser module (8) is an ultrashort pulse light source.

3. The single-exposure ultrashort pulse spatiotemporal measurement device based on spatial frequency multiplexing according to claim 2, characterized in that, The laser module (8) that generates a chirped pulse beam also includes: a dispersive prism A (9) and a dispersive prism B (10) for generating spatial chirped pulses; The pulsed beam generated by the laser module (8) is converted into a chirped pulse after passing through the dispersive prism A (9) and the dispersive prism B (10) as the beam to be tested.

4. The single-exposure ultrashort pulse spatiotemporal measurement device based on space-frequency multiplexing according to claim 2, characterized in that, Between the wavefront beam splitter module (1) and the grating beam splitter module (2), a dispersive lens A (11) and a dispersive lens B (12) are sequentially arranged along the optical path to generate spatial chirped pulses.

5. The single-exposure ultrashort pulse spatiotemporal measurement device based on spatial frequency multiplexing according to any one of claims 1-4, characterized in that, The grating beam splitting module (2) is an amplitude-type or phase-type two-dimensional grating.

6. The single-exposure ultrashort pulse spatiotemporal measurement device based on spatial frequency multiplexing according to any one of claims 1-4, characterized in that, The wavefront modulation module (4) is a binary step phase wavefront modulator, a ternary step phase wavefront modulator, a deca-step phase wavefront modulator, a continuous phase modulator, a continuous amplitude phase modulator, or a pure amplitude wavefront modulator.

7. A method for performing spatiotemporal measurement of a single-exposure ultrashort pulse using the spatiotemporal measurement device based on spatial frequency multiplexing as described in any one of claims 1-6, characterized in that, The method includes the following steps: Step 1) Calibrate the wavefront modulation module (4) for the complex amplitude transmittance function of a certain wavelength. Where m represents the different diffraction orders of the grating, m = 1, 2, 3...M; Step 2) The initial guess formula for the complex amplitude distribution of the beam before the wavefront modulation module (4) is as follows: In the formula, Let be the amplitude coefficient of the m-th diffraction order. To generate OK, A random matrix of columns, and These are the rows and columns of the data matrix being operated on; Step 3) Control and data processing module (7) Wavefront iterative calculation process: ① Forward propagation process: Initial guess of wavefront After passing through the wavefront modulation module (4), it becomes a wavefront: Then wavefront The wavefront is obtained by propagating to the detector module (5). ,in This indicates the forward propagation process of the wavefront. For transmission distance, The distance between the wavefront modulation module (4) and the detector module (5); The diffraction spot recorded by the detector module (5) For diffraction spots Divided into diffraction spots corresponding to different wavelengths , For the segmentation operation; The control and data processing module (7) controls the wavefront. Update: And calculate the error between the estimated diffraction spot and the recorded diffraction spot. The formula is as follows: in, To sum all elements in the matrix, To perform a phase-taking operation on the wavefront; ② Backpropagation process: The updated wavefront The wavefront is obtained by backpropagation to the wavefront modulation module (4). ,in Indicates the backpropagation process. For the distance of propagation; The wavefront before the wavefront modulation module (4) is obtained using the following update formula: The updated wavefront Propagation to the focal plane yields the focal plane wavefront. Applying the aperture function updates the focal surface wavefront as follows: ,in Let m be the aperture function corresponding to the m-th wavefront; then... The wavefront before the wavefront is propagated to the wavefront modulation module (4) is obtained. ; With the updated wavefront Instead of the initial guess wavefront The next iteration is performed until the error RMS is less than the predetermined value, and the iteration process ends. The wavefront distribution before the wavefront modulation module (4) corresponding to each wavelength is obtained. The wavefront is propagated to obtain the spatial phase distribution of the beam under test at other positions with different wavelengths, which is expressed as follows: n=1,2,3,…N; Step 4): The complex amplitude corresponding to different times can be measured by the time phase measurement module (6), and its complex amplitude is expressed as... Combined with the results obtained in step 3) n=1,2,3,…N, can be N items Spatiotemporal coupling is achieved to obtain the wavefront distribution of the pulse under test. .

Images