Method and apparatus for single-shot measurement of three-dimensional spatiotemporal wave packets of ultrafast laser

Abstract

Disclosed in the present invention are a method and apparatus for single-short measurement of three-dimensional spatiotemporal wave packets of an ultrafast laser. The apparatus comprises a beam-splitting grating, an ultra-narrowband filter, a shearing interferometer, a spectral phase measurement device, and a control and calculation device. A light beam under test is split by the beam splitting grating into replicated beams with different propagation directions; the ultra-narrowband filter enables the light beams under test at different angles to pass through with different central wavelengths, and filtered light beams are incident upon the shearing interferometer; and an interferogram is recorded by means of a detector. The interferogram is analyzed to recover wavefront information corresponding to each wavelength. The present invention has the characteristics of a simple and reliable principle, strong anti-interference capability, high precision, a high spatiotemporal bandwidth product and high speed, and thus is particularly suitable for the online measurement of the three-dimensional optical field distribution of short-pulse lasers.

Description

A method and apparatus for single measurement of three-dimensional spatiotemporal wave packets using ultrafast laser Technical Field

[0001] This invention belongs to the field of laser measurement technology, specifically relating to a single-shot measurement device and method for ultrafast laser three-dimensional spatiotemporal wave packets. It enables single-frame measurement of structured spatiotemporal wave packets with high spatiotemporal resolution, simultaneously extracting spatial and spectral phase information and resolving spatiotemporal coupling issues. It can be widely applied in fields such as particle acceleration, fusion energy, secondary light source generation, and optical communication, providing support for the efficient characterization of complex optical fields. Background Technology

[0002] The ability to characterize the spatiotemporal wave packets of ultrafast laser pulses is becoming increasingly important for revealing the physical nature of these pulses and for demanding industrial applications, including particle acceleration, fusion energy, secondary light sources, and optical communications. Complete characterization of structural spatiotemporal wave packets requires high-resolution four-dimensional information E(x,y,z,t) or E(x,y,z,w). Therefore, the most significant challenge in measuring such spatiotemporal wave packets is how to efficiently acquire dense, complex three-dimensional spatiotemporal optical field data cubes E(x,y,t).

[0003] [Amended according to Rule 26, 09.01.2026] Traditional spatiotemporal three-dimensional measurement methods, such as electric field full reconstruction techniques based on Michelson interferometer time scanning (TERMITES), laser-coupled fast acquisition techniques based on narrowband filters (FALCON), multispectral camera Hartmann aperture technology (MSC HM), and spatiotemporal resolution intensity-phase evaluation single hologram full information extraction techniques (STRIPED FISH), are limited by problems such as low scanning, low number of channels, need for additional reference light or space, and low spectral resolution, making them difficult to apply. Another type of method, based on compressed sensing light field mapping technology (COFT) or computational optical broadband single-layer stacked imaging technology (BBSSP), can achieve three-dimensional measurement of short pulses, but the process of separating overlapping spectra sacrifices considerable reconstruction accuracy and resolution, and requires extremely high computational complexity, which limits accurate and high-throughput fast feedback.

[0004] Currently, commonly used methods for three-dimensional measurement of structure-time-space wave packets employ mechanical components to perform interferometric scanning in the time or spectral dimensions. However, these systems typically suffer from drawbacks such as large size and time-consuming operation, especially in high-power applications with low repetition rates (<1 Hz). Summary of the Invention

[0005] To overcome the shortcomings of the prior art, the present invention provides a method and apparatus for single measurement of ultrafast laser three-dimensional spatiotemporal wave packets, aiming to achieve high spatiotemporal resolution three-dimensional light field reconstruction through a single measurement.

[0006] The working principle of this invention is as follows: First, a beam splitter is used to obtain replica sub-beams of the pulse to be measured in different directions. A twisted ultra-narrowband filter selects the required wavelength according to the incident angle. An interferometer is used to collect the interferogram. Thus, wavefront interference information of multiple spectral components can be extracted simultaneously in a single frame measurement, realizing single-frame wavefront measurement of the three-dimensional light field distribution of ultrafast laser.

[0007] The technical solution of the present invention is as follows:

[0008] A method for single measurement of three-dimensional spatiotemporal wave packets using ultrafast lasers, characterized by the following steps:

[0009] Beam splitting and filtering: The laser pulse to be measured is split into a reflecting arm and a transmitting arm by a beam splitter. The reflecting arm is input to a spectral phase measuring device to obtain spectral phase information. The transmitting arm generates a multi-angle replica sub-beam array through a beam splitter grating, and then passes through an ultra-narrowband filter to select quasi-monochromatic light of different center wavelengths according to the incident angle.

[0010] Interference information acquisition: The filtered sub-beams enter the shearing interferometer, which includes a two-dimensional beam splitter grating and a camera. Multispectral interferograms are generated through spatial shearing and captured by the camera in a single shot.

[0011] Data processing and reconstruction: The control and calculator perform the following processing on the interferogram:

[0012] -Based on the center position (X,Y) and wavelength (W) determined by calibration, the interferogram is cropped into a three-dimensional multispectral interferometric cube (H);

[0013] - Perform a two-dimensional Fourier transform on the interferogram of each wavelength channel to extract the DC component and first harmonic in the frequency domain, and separate the phase gradient matrix in the orthogonal directions (x, y).

[0014] - Perform an inverse Fourier transform on the first harmonic to obtain the phase gradients in the x and y directions, integrate to generate the two-dimensional wavefront phase, and subtract the wavefront tilt angle (θ) recorded during the calibration phase.

[0015] - Combining the spectral phase obtained by the spectral phase measuring device, perform an inverse Fourier transform along the frequency axis to reconstruct the three-dimensional spatiotemporal distribution E(x,y,t) of the light field to be measured.

[0016] Furthermore, the beam splitting grating is a Damman grating, used to uniformly split the transmission arm beam into a multi-angle sub-beam array.

[0017] Furthermore, the ultra-narrowband filter is a transmission or reflection type ultra-narrowband pass filter, and its center wavelength has a linear mapping relationship with the incident angle of the sub-beam.

[0018] Furthermore, the spectral phase measuring device can be any time-domain spectral phase metrology device, such as a frequency-resolved optical switch (FROG) system or a self-referenced spectral interferometry (SRSI) system.

[0019] Furthermore, the two-dimensional beam-splitting grating of the shearing interferometer is a periodic transmission grating with a beam splitting quantity of 2×2, used to generate orthogonal shearing interference fringes.

[0020] Second, the present invention also provides an ultrafast laser three-dimensional spatiotemporal wave packet single measurement device, characterized in that it includes:

[0021] A beam splitter is used to divide the laser beam under test into a reflecting arm and a transmitting arm.

[0022] A spectral phase measuring device, connected to the reflector arm, is used to measure the spectral phase;

[0023] A beam splitter grating is set in the optical path of the transmission arm to generate a multi-angle replica sub-beam array;

[0024] Ultra-narrowband filter, which selects quasi-monochromatic light of different center wavelengths according to the incident angle of the sub-beam;

[0025] A shearing interferometer, comprising a two-dimensional beam splitter and a camera, is used to generate and record multispectral interferograms.

[0026] A controller and calculator are used to synchronously trigger the spectral phase measuring device and the camera, and to perform the data processing and reconstruction steps as described in any one of claims 1-5.

[0027] Furthermore, the control and calculator includes:

[0028] The calibration module is used to store the wavelength (W), center position (X,Y) and wavefront tilt angle (θ) obtained during calibration.

[0029] The measurement module is used to capture the spectral phase of a single pulse and the interferogram of multiple spectral channels;

[0030] The solution module is used to perform two-dimensional Fourier transform, frequency domain filtering, phase gradient integration, and time-frequency domain inverse transform to output a three-dimensional light field distribution.

[0031] Compared with the prior art, the present invention has the following beneficial effects:

[0032] 1) By co-designing beam-splitting gratings and ultra-narrowband filters, employing a self-referenced shearing interferometry encoding scheme, and utilizing a low-complexity solution algorithm, high spatiotemporal resolution three-dimensional light field reconstruction was achieved in a single measurement. This solved long-standing technical challenges in traditional methods, such as the contradiction between spectral and spatial resolution, excessive system complexity, and low computational efficiency.

[0033] 2) The use of ultra-narrowband filters provides sufficiently high spectral resolution, avoiding the insufficient spectral resolution of pixel-level Bayer filters. The use of only planar optics avoids complex beam manipulations such as lenses, and systematic errors introduced by planar optics can be eliminated by a standard light source, thus providing extremely high measurement accuracy. The interferogram of this method is self-referenced, avoiding the use of an additional reference beam. The interference fringes on the sensor are independent of each spectral channel, and the self-referenced interferogram avoids the use of an additional reference beam, resulting in low computational complexity for solving the light field data cube.

[0034] 3) Suitable for high-precision, high-spatiotemporal resolution structured spatiotemporal wave packet online characterization applications. Attached Figure Description

[0035] Figure 1 is a schematic diagram of an embodiment of the ultrafast laser three-dimensional spatiotemporal wave packet single measurement device of the present invention.

[0036] Figure 2 is a flowchart of the solution process for the single measurement method of ultrafast laser three-dimensional spatiotemporal wave packets of the present invention. Detailed Implementation

[0037] The present invention will now be described in detail with reference to the accompanying drawings and embodiments. It should be understood that the scope of protection of the present invention is not limited to such specific statements and embodiments.

[0038] A method for single measurement of three-dimensional spatiotemporal wave packets using ultrafast lasers, comprising a calibration stage, a measurement stage, and a solution stage;

[0039] The calibration phase consists of the following steps:

[0040] S11: Input a standard planar broadband laser and use a spectrometer to record the center wavelength W of each quasi-monochromatic light output from the ultra-narrowband filter.

[0041] S12: Input a standard planar broadband laser, and use the control and calculator 7 to control the shearing interferometer to record the center position (X,Y) and wavefront tilt angle θ of each sub-pulse.

[0042] The measurement phase involves the following steps:

[0043] The laser under test is split into two paths by beam splitter 1. The reflected light enters the spectral phase measuring device 2, and the transmitted light enters the beam splitting grating, ultra-narrowband filter, and shearing interferometer in sequence. The spectral phase measuring device and shearing interferometer are triggered by the control and computer, and the spectral phase of a single pulse and the interferogram of multiple spectral channels are captured at the same time.

[0044] The solution phase, as shown in Figure 2, involves the following steps:

[0045] S21. The original interferogram acquired by the camera is cropped into a three-dimensional multispectral interferogram cube H, wherein the cropping center (X,Y) and wavelength W are determined according to the calibration data;

[0046] S22. Perform a two-dimensional Fourier transform on the three-dimensional interferogram cube H of each wavelength channel obtained in S21 along the 1st and 2nd dimensions to obtain the frequency domain cube;

[0047] S23: Calculate the position of the first harmonic corresponding to the frequency domain diagram, then use an appropriate filter window to extract the first harmonics in two orthogonal directions, and obtain the phase gradient matrix in two orthogonal directions by inverse Fourier transform along the 1st and 2nd dimensions.

[0048] S24: Retrieve the two-dimensional integral for each wavelength, subtract the tilt θ obtained in calibration step S12, and calculate the phase of each spectral component of the light under test.

[0049] S25: Using the spectral phase measurement device, the phases of each spectral component of the light under test in S24 are spliced ​​together. Combined with the spatial amplitude information of the low frequency of the interferogram, the frequency domain light field cube is obtained. Then, the three-dimensional spatiotemporal distribution of the light field under test is obtained by inverse Fourier transform along the coordinates of the spectrum.

[0050] Figure 1 is a schematic diagram of an embodiment of the ultrafast laser three-dimensional spatiotemporal wave packet single measurement device of the present invention, as shown in the figure, including:

[0051] Beam splitter 1 divides the wave packet to be measured with a wavelength of 800nm ​​and 30fs into a reflecting arm and a transmitting arm. The reflecting arm is injected into the spectral phase measuring device 2, and the transmitting arm is injected into the beam splitting grating 3.

[0052] Phase measuring device 2, using FROG technology, measures the phase of pulse spectrum through a 10μm thick Class I crystal.

[0053] Beam splitter grating 3 divides the wave packet under test into sub-beam arrays at different angles. Here, a 6×6 Dammann beam splitter grating with a period of 10µm is selected.

[0054] An ultra-narrowband filter 4 is installed after the beam splitter grating 3 with a slight twist. It selects different narrowband wavelengths according to the incident angle of the sub-beams to achieve spectral separation. In this embodiment, a filter with a transmission half-width of 0.1 nm is selected.

[0055] The shearing interferometer includes a two-dimensional beam splitter grating 5, which is used to re-split the sub-beam to be tested. Here, a 2×2 two-dimensional transmission grating with a period of 40 μm is selected. The camera 6 is placed behind the two-dimensional beam splitter grating 5, and the distance is adjusted according to the phase gradient to be tested. The camera 6 records the interference fringes.

[0056] Control and calculator 7 are used for wave packet reconstruction. As shown in Figure 2: The first step is to crop the interferogram into a multispectral array and determine the center of the aberration-free beam. The corresponding frequency w is provided by the spectrometer under a reference pulse. Subsequently, wavefront extraction is performed on each interferogram, followed by a two-dimensional Fourier transform. An appropriate window size is selected, containing the DC component U0. ω The first-order frequency Ux in the x and y directions ω and Uy ω The light field intensity I(x,y,ω) is expressed through a clipped DC component U0. ω The inverse Fourier transform of the two dimensions is then used to obtain the wavefront gradients along the x and y directions. The inverse Fourier transform is then applied to the clipped first-order carrier frequency to obtain the wavefront gradients. and To eliminate the additional wavefront tilt caused by the first grating Perform the same extraction operation on a pre-captured reference map without spatiotemporal aberrations, and subtract the reference phase gradient before integration to obtain a more accurate reconstruction result:

[0057] Where F -1 Urefx represents the inverse Fourier transform. ω This is the first-order frequency of the reference light clipped in the Fourier domain. Then, the gradients in the two orthogonal directions are integrated in two dimensions to obtain the measured wavefront W. ω The relative phase between the various spectra is missing. Eliminating this uncertainty requires measuring the spectral phase at a given point in space, typically obtained using FROG at the beam center. The phase is now corrected to:

[0058] The inverse Fourier transform along the frequency direction yields the complete optical field in the time domain E(x, y, t):

Claims

1. A method for single measurement of three-dimensional spatiotemporal wave packets using ultrafast laser, characterized in that, Includes the following steps: Beam splitting and filtering: The laser pulse to be measured is split into a reflecting arm and a transmitting arm by a beam splitter (1). The reflecting arm is input into a spectral phase measuring device (2) to obtain spectral phase information. The transmission arm generates a multi-angle replica sub-beam array through a beam splitter grating (3), and selects quasi-monochromatic light of different center wavelengths according to the incident angle through an ultra-narrowband filter (4); Interference information acquisition: The filtered sub-beam enters the shearing interferometer, which includes a two-dimensional beam splitter grating (5) and a camera (6). A multispectral interferogram is generated through spatial shearing and captured by the camera (6) in a single shot. Data processing and reconstruction: Control and calculator (7) perform the following processing on the interferogram: -Based on the center position (X,Y) and wavelength (W) determined by calibration, the interferogram is cropped into a three-dimensional multispectral interferometric cube (H); - Perform a two-dimensional Fourier transform on the interferogram of each wavelength channel to extract the DC component and first harmonic in the frequency domain, and separate the phase gradient matrix in the orthogonal directions (x, y). - Perform an inverse Fourier transform on the first harmonic to obtain the phase gradients in the x and y directions, integrate to generate the two-dimensional wavefront phase, and subtract the wavefront tilt angle (θ) recorded during the calibration phase. - Combine the spectral phase obtained by the spectral phase measuring device (2), perform an inverse Fourier transform along the frequency axis to reconstruct the three-dimensional spatiotemporal distribution E(x,y,t) of the light field to be measured.

2. The method for single measurement of ultrafast laser three-dimensional spatiotemporal wave packets according to claim 1, characterized in that, The beam splitter grating (3) is a phase-type, phase-amplitude hybrid, or metasurface two-dimensional grating used to uniformly split the transmission arm beam into a multi-angle sub-beam array.

3. [Revised according to Rule 26, 09.01.2026] The method for single measurement of ultrafast laser three-dimensional spatiotemporal wave packets according to claim 1 is characterized in that, The ultra-narrowband filter (4) is a transmission or reflection type ultra-narrowband pass filter, and its center wavelength is linearly mapped to the incident angle of the sub-beam.

4. The method for single measurement of ultrafast laser three-dimensional spatiotemporal wave packets according to claim 1, characterized in that, The spectral phase measuring device (2) can be any time-domain spectral phase measurement device, such as a frequency-resolved optical switch (FROG) system or a self-referenced spectral interferometer (SRSI) system.

5. The method for single measurement of ultrafast laser three-dimensional spatiotemporal wave packets according to claim 1, characterized in that, The two-dimensional beam-splitting grating (5) of the shearing interferometer is a periodic transmission grating with a beam splitting number of 2×2, used to generate orthogonal shearing interference fringes.

6. A device for single measurement of three-dimensional spatiotemporal wave packets using ultrafast laser, characterized in that, include: Beam splitter (1) is used to split the laser to be tested into a reflecting arm and a transmitting arm; A spectral phase measuring device (2) is connected to a reflective arm for measuring the spectral phase; Beam splitting grating (3) is set in the optical path of the transmission arm to generate a multi-angle replica sub-beam array; Ultra-narrowband filter (4) selects quasi-monochromatic light of different center wavelengths according to the incident angle of the sub-beam; A shearing interferometer, comprising a two-dimensional beam splitter grating (5) and a camera (6), is used to generate and record multispectral interferograms; A control and calculator (7) is used to synchronously trigger the spectral phase measuring device (2) and the camera (6) and to perform the data processing and reconstruction steps as described in any one of claims 1-5.

7. The ultrafast laser three-dimensional spatiotemporal wave packet single-shot measurement device according to claim 6, characterized in that, The control and calculator (7) includes: The calibration module is used to store the wavelength (W), center position (X,Y) and wavefront tilt angle (θ) obtained during calibration. The measurement module is used to capture the spectral phase of a single pulse and the interferogram of multiple spectral channels; The solution module is used to perform two-dimensional Fourier transform, frequency domain filtering, phase gradient integration, and time-frequency domain inverse transform to output a three-dimensional light field distribution.

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