An ultra-short pulse time-slicing measurement device and method based on electro-optic deflection crystal

Abstract

An ultra-short pulse time-slicing measurement device and method based on an electro-optic deflection crystal, wherein a pulse light emitted by an ultra-short pulse light source is deflected by a polarizer and then an electro-optic crystal to form a diffraction light spot which is spatially time-stretched, an intensity detector is used to record the diffraction light spot, and then a multi-mode phase recovery algorithm is used to reconstruct the pulse complex amplitude information at different times. The diffraction light spot recorded by the detector is a diffraction light spot modulated by an encoding plate, and the modulation of the encoding plate improves the convergence performance of the phase recovery algorithm. Finally, an iteration operation is performed on the light spot recorded by the light intensity detector by using a control and data processing module, so that the complex amplitude time of the ultra-short pulse at different times can be obtained, and the space-time coupling condition of the ultra-short pulse can be measured. The present application can measure the complex amplitude information of the ultra-short pulse at different times.

Description

Technical Field

[0001] This invention relates to the measurement of complex amplitude of time slices of ultrashort pulses on time scales from ns to ps, and particularly to the measurement of complex amplitude of complex pulse wavefronts with spatiotemporal characteristics. Background Technology

[0002] Spatiotemporal phase measurement of ultrashort pulses is an important method for determining beam quality. Therefore, it plays a crucial role in studying the mechanism of spatiotemporal coupling of ultrashort pulses. One method for measuring the time slices of ultrashort pulses is the nonlinear FROG (frequency-resolved optical gating) method (R. Trebino, R. Jafari, SAAkturk, P. Bowlan, Z. Guang, P. Zhu, E. Escoto, and G. Steinmeyer, "Highly reliable measurement Of ultrashort laser pulses," J. Appl. Phys. 128, 171103 (2020).). This method can measure the temporal and spectral phase information of fs broadband sources. However, for ns or ps narrowband ultrashort pulses, the traditional FROG method cannot perform complex amplitude measurement on the time slices of the pulse. Another approach involves using a fringe camera to measure the time-slice information of ultrashort pulses. Fringe phase analysis can deflect the light intensity of the ultrashort pulse at different times to different spatial locations within the camera, allowing for the recording of intensity information at each time. Combining this with compressed sensing can achieve higher time-resolution measurement accuracy. However, this method requires an expensive fringe camera and cannot measure spatial phase. Therefore, more efficient, convenient, lower-cost, and more stable measurement techniques are needed for complex amplitude measurements of nanosecond (ns) and ps (ps) ultrashort pulse time slices. Summary of the Invention

[0003] To address the shortcomings of existing technologies, this invention proposes an ultrashort pulse time-slicing measurement device and method based on an electro-optic deflecting crystal. A pulse voltage is applied to the electro-optic deflecting crystal, synchronizing the ultrashort pulse with its rising edge. This allows the intensity information corresponding to different moments of the ultrashort pulse to be deflected to different spatial positions on different detectors, enabling the measurement of the intensity distribution at different times. Since the intensity distributions at different moments spatially overlap, a multimodal phase re-addition algorithm can be used to reconstruct the complex amplitude information at different moments. This method does not require an expensive ultrafast camera or a reference beam, and offers advantages such as stability, low cost, and the ability to simultaneously measure amplitude and phase.

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

[0005] An ultrashort pulse time-slicing measurement device based on an electro-optic deflection crystal, characterized in that it includes:

[0006] The voltage anode and cathode are used to apply pulse voltage to the electro-optic deflecting crystal.

[0007] An electro-optic deflecting crystal, placed between the voltage anode and cathode, is used to generate a nonlinear effect, causing the pulse beam under test to deflect. The magnitude of the deflection angle is related to the magnitude of the applied pulse voltage.

[0008] A pulse voltage source, connected to the voltage anode and cathode, is used to generate a pulse voltage, causing the pulse beam to be measured to generate a time-deflecting spatial stretch pulse at the leading edge of the pulse voltage.

[0009] A wavefront modulator module is used to perform wavefront modulation on the spatial stretching pulse to form a pulse diffraction spot.

[0010] The light intensity detector module is used to collect the pulsed diffraction spot and transmit it to the control and data processing module;

[0011] The control and data processing module is used to store and process the pulse diffraction spot.

[0012] The wavefront modulator 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.

[0013] The ultrashort pulse time slice measurement device based on electro-optic deflection crystal is characterized in that, during measurement, the pulse beam to be measured, the pulse voltage output by the pulse voltage source, and the acquisition time of the light intensity detector module must be synchronized.

[0014] The ultrashort pulse time-slice measurement device based on electro-optic deflection crystal is characterized in that it further includes a signal generator, which is connected to a pulsed laser, a pulsed voltage source, and a light intensity detector module that generate the pulse beam to be measured, respectively, and is used to generate a synchronization signal.

[0015] The aforementioned method for measuring the time slice of ultrashort pulses based on electro-optic deflection crystals is characterized by including the following steps:

[0016] Step 1) The spot detector module acquires the pulse diffraction spot I after the pulse beam under test is modulated by the wavefront modulator module, and calibrates the transmittance complex amplitude distribution of the wavefront modulator module as T(x, y).

[0017] Step 2) Using the control and data processing module, iterative calculations are performed on the pulsed diffraction spot I in front of the focal plane (or spectral plane) P1 of the pulse beam under test, the wavefront modulator module plane P2, and the intensity detector module plane P3. The calculation method includes the following iterative steps, and the number of iterations is denoted as k:

[0018] ① Set the complex amplitude distribution before the wavefront modulator module to φ k，n (x, y, t) n ), t n For different times corresponding to the pulse beam under test, n = 1, 2, 3...N; the complex amplitude distribution after modulation by the wavefront modulator module is expressed as:

[0019] ② Complex amplitude distribution The complex amplitude distribution obtained after propagation to plane P3 of the light intensity detector module is as follows: in This represents the free-space propagation of the light beam, which can be achieved using the angular spectrum or Fresnel propagation equation; L1 is the distance between the wavefront modulator module plane P2 and the light intensity detector module plane P3.

[0020] ③Based on the N complex amplitude distributions ψ at different times at the location of the light intensity detector module k，n (x, y, t) n The complex amplitude distribution at this location is updated using the multimodal update formula to obtain:

[0021]

[0022] And calculate the error:

[0023]

[0024] ④ Update the complex amplitude ψ′ k，n (x, y, t) n The updated complex amplitude is fed back to plane P2 of the wavefront modulator module. Then update the complex amplitude of the wavefront modulator module: , where * indicates conjugate;

[0025] ⑤ The complex amplitude φ′ k，n (x, y, t) n The light is transmitted to the focal plane of the wavefront or subjected to a spectral transform. Then, its spatial distribution is constrained using a constraint function to obtain the updated light field:

[0026] or

[0027]

[0028] Where L2 is the distance between plane P2 of wavefront modulator module (4) and focal plane P3. This is for spectrum transformation operation.

[0029] ⑥ The complex amplitude E k，n (x, y, t) n The following complex amplitudes are obtained by feeding back the data to the wavefront modulator module plane P2 or by performing an inverse spectral transform: or in This indicates the inverse spectrum transform operation;

[0030] Then obtain E′ from ⑥ k，n (x, y, t) n Substitute into ①φ k，n (x, y, t) n Proceed to the next iteration, looping ①-⑥ until the error ERROR reaches the ideal error, thus ending the loop. This allows us to obtain the wavefront φ to be measured. n (x, y, t) n The complex amplitude distribution of the corresponding ultrashort pulse at different times.

[0031] The technical advantages of this invention compared to existing technologies are as follows:

[0032] (1) Compared to ultrafast imaging with stripe cameras, it is cheaper and has more stable performance.

[0033] (2) It can simultaneously reconstruct the complex amplitude information of ultrashort pulses, making up for the shortcomings of traditional ultrafast imaging devices and making it more applicable.

[0034] (3) It can be applied to the measurement of complex amplitude of ultrafast phenomena and the spatiotemporal diagnosis of ultrashort pulses, which is of great significance for plasma detection, stress detection and other fields. Attached Figure Description

[0035] Figure 1 This is a schematic diagram of the ultrashort pulse time-slice measurement device based on an electro-optic deflection crystal according to the present invention.

[0036] Figure 2 This is a schematic diagram of Embodiment 1 of the ultrashort pulse time-slice measurement device based on electro-optic deflection crystal of the present invention.

[0037] Figure 3 This is a schematic diagram of Embodiment 2 of the ultrashort pulse time-slice measurement device based on electro-optic deflection crystal of the present invention. Detailed Implementation

[0038] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0039] Please see Figure 1 ,like Figure 1 As shown, an ultrashort pulse time-slice measurement device based on an electro-optic deflecting crystal includes: an electro-optic deflecting crystal 1, used to generate a nonlinear effect to deflect the beam under test, the deflection angle being related to the magnitude of the applied voltage; a pulse voltage source 2, used to generate a pulse voltage, causing the beam to generate a spatially stretched pulse that deflects with time at the leading edge of the pulse voltage; voltage anode and cathode 3, used to apply voltage to the electro-optic deflecting crystal; a wavefront modulator module 4, used to modulate the wavefront under test; a light intensity detector module 5, used to record the diffraction spot modulated by the wavefront modulator module 4 and transmit it to a control and data processing module 6; and a control and data processing module 6, used to store the diffraction spot data recorded by the light intensity detector module 5 and perform algorithm processing.

[0040] The device described above can be used to implement an ultrashort pulse time slice measurement method, including the following steps:

[0041] Step 1) Record the diffraction spot of the pulse beam under test after being modulated by the wavefront modulator module 4 through the spot detector module 5, and denote it as I; calibrate the transmittance complex amplitude distribution of the wavefront modulator module 4 as T(x, y).

[0042] Step 2) Using the control and data processing module 6, iterative calculations are performed on the diffraction spot I in front of the focal plane (or spectral plane) P1 of the pulse beam under test, the plane P2 of the wavefront modulator module 4, and the plane P3 of the intensity detector module 5. The calculation method includes the following iterative steps (the number of iterations is denoted as k):

[0043] ① Set the complex amplitude distribution before wavefront modulator module 4 to φ k，n (x, y, t) n ), t n Let n = 1, 2, 3…N, corresponding to different times of the pulse beam under test. The complex amplitude distribution modulated by wavefront modulator module 4 is expressed as follows:

[0044] ② Complex amplitude The complex amplitude distribution obtained after propagation to plane P3 of light intensity detector module 5 is as follows: in This represents the free-space propagation of the light beam, which can be achieved using angular spectrum or Fresnel propagation equations. L1 is the distance between plane P2 of wavefront modulator module 4 and plane P3 of intensity detector module 5.

[0045] ③ Calculate the N complex amplitude distributions ψ at different times at the location of the light intensity detector module 5 using steps ① and ②. k，n (x, y, t) n The complex amplitude distribution at this location is updated using the multimodal update formula to obtain: And calculate the error

[0046]

[0047] ④ The complex amplitude ψ′ k，n (x, y, t) n The updated complex amplitude is fed back to plane P2 of wavefront modulator module 4: Then, the wavefront preceding wavefront modulator module 4 is obtained using the following update formula: The asterisk (*) indicates conjugate.

[0048] ⑤ The complex amplitude φ′ k，n (x, y, t) n The light is transmitted to the focal plane of the wavefront or subjected to a spectral transform. Then, its spatial distribution is constrained using a constraint function to obtain the updated light field:

[0049] or

[0050]

[0051] Where L2 is the distance between plane P2 of wavefront modulator module 4 and focal plane P3. This is for taking the spectrum of the wavefront.

[0052] ⑥ The complex amplitude E k，n (x, y, t) n The following complex amplitudes are obtained by transmitting the data back to plane P2 of the wavefront modulator module 4 or by performing an inverse spectral transform: or in This indicates the inverse spectral transform operation on the wavefront.

[0053] Then obtain E′ from ⑥ k，n (x, y, t) n Substitute into ①φ k，n (x, y, t) n Proceed to the next iteration, looping ①-⑥ until the error ERROR reaches the ideal error, thus ending the loop. This allows us to obtain the wavefront φ to be measured. n (x, y, t) nThe complex amplitude distribution of the corresponding ultrashort pulse at different times.

[0054] Example 1:

[0055] Please see Figure 2 , Figure 2 This is a schematic diagram of Embodiment 1 of the ultrashort pulse time-slicing measurement device based on an electro-optic deflection crystal according to the present invention. As shown in the figure, an ultrashort pulse time-slicing measurement device based on an electro-optic deflection crystal also requires a pulse generation and synchronization optical path, including: a pulsed laser 7 for generating ns pulse beams; a collimator modulator 8 for generating the required pulse beam to be measured; a signal generator 9 for generating a synchronization signal; a synchronization pulsed laser 7; a pulse voltage source 2; and a light intensity detector module 5. In this embodiment, the wavefront modulator module 4 is set as a binary stepped phase wavefront modulator with a phase delay of 0 or π, and the element size is randomly distributed, with the smallest element size being 5 μm × 5 μm. The pulsed laser 7 uses an ultrashort pulse with a pulse width of 7 ns and a wavelength of 1064 nm.

[0056] Example 2:

[0057] The ultrashort pulse time-slice measurement device based on electro-optic deflection crystal described in this embodiment also requires an optical path for generating the ultrashort pulse to be measured, such as... Figure 3 Its features include:

[0058] The pulse beam splitter 11 splits the light into two pulses: the transmitted light is used as the probe pulse, and the reflected light is used as the wavefront modulation pulse. The wavefront modulation pulse is used to generate the required ultrashort pulse.

[0059] The pulse reflector 12 is used to reflect the wavefront modulated pulse reflected by the pulse beam splitter 11.

[0060] Pulse reflector 13 is used to reflect the wavefront modulated pulse reflected by pulse reflector 12.

[0061] The optical path delay module 14 is used to adjust the time delay of the probe pulse to ensure that the probe pulse and the wavefront modulation pulse are synchronized at the position of the pulse modulation medium 15.

[0062] The pulse modulation medium 15 is used to modulate the ultrashort pulse required to form by changing the instantaneous refractive index of the probe pulse.

[0063] Although embodiments of the invention have been shown and described, it will be understood by those skilled in the art that various changes, modifications, substitutions and alterations can be made to these embodiments without departing from the principles and spirit of the invention, the scope of which is defined by the appended claims and their equivalents.

Claims

1. An ultra-short pulse time-slicing measurement device based on an electro-optic deflection crystal, characterized by, include: Voltage anode and cathode (3) are used to apply pulse voltage to the electro-optic deflection crystal (1); An electro-optic deflection crystal (1) is placed between the voltage anode and cathode (3) to generate a nonlinear effect, causing the pulse beam to be measured to deflect. The magnitude of the deflection angle is related to the magnitude of the applied pulse voltage. The pulse voltage source (2) is connected to the voltage anode and cathode (3) to generate a pulse voltage, so that the pulse beam to be measured generates a spatial stretching pulse that deflects with time at the leading edge of the pulse voltage; Wavefront modulator module (4) is used to perform wavefront modulation on the spatial stretching pulse to form a pulse diffraction spot. The light intensity detector module (5) is used to collect the pulse diffraction spot and transmit it to the control and data processing module (6). The control and data processing module (6) is used to store and process the pulse diffraction spot; During measurement, the pulse beam to be measured, the pulse voltage output by the pulse voltage source (2), and the acquisition time of the light intensity detector module (5) must be synchronized. It also includes a signal generator (9), which is connected to the pulse laser (7), pulse voltage source (2) and light intensity detector module (5) that generate the pulse beam to be measured, respectively, and is used to generate a synchronization signal.

2. The electro-optic deflection crystal based ultra-short pulse time- slicing measurement apparatus of claim 1, wherein, The wavefront modulator 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.

3. A slice measurement method using the ultra-short pulse time-slicing measurement apparatus based on an electro-optic deflection crystal according to claim 1, characterized by, Includes the following steps: Step 1) the light intensity detector module (5) collects the pulse diffraction light spot I of the pulse light beam to be measured after modulation by the wavefront modulator module (4), and the transmittance complex amplitude distribution of the wavefront modulator module (4) is calibrated as ​ Step 2) Iterative calculation is performed on the pulse diffraction spot I before the focal plane (or spectral plane) P1 of the pulse beam to be measured, the plane P2 of the wavefront modulator module (4) and the plane P3 of the light intensity detector module (5) by using the control and data processing module (6). The calculation method includes the following iterative steps, and the number of iterations is denoted as n. : The complex amplitude distribution before setting the wavefront modulator module (4) is , is the different time corresponding to the measured pulse light beam, n = 1, 2, 3…N; the complex amplitude distribution after modulation by the wavefront modulator module (4) is represented as ; Complex amplitude distribution The complex amplitude distribution obtained by propagating to plane P3 of the light intensity detector module (5) is as follows: ,in The free-space propagation of a beam can be represented by angular spectrum or Fresnel propagation equations; The distance between plane P2 of wavefront modulator module (4) and plane P3 of light intensity detector module (5); Based on the complex amplitude distributions at different times at the positions of the light intensity detector module (5) The complex amplitude distribution at this location is updated using the multimodal update formula to obtain: ; And calculate the error: ； Updated complex amplitude The updated complex amplitude is fed back to plane P2 of the wavefront modulator module (4): Then update the complex amplitude of the wavefront modulator module (4) before: , where * indicates taking the conjugate; complex amplitude The light is transmitted to the focal plane of the wavefront or subjected to a spectral transform. Then, its spatial distribution is constrained using a constraint function to obtain the updated light field: or in The distance between plane P2 and focal plane P3 of wavefront modulator module (4) For spectrum transformation operation; complex amplitude The following complex amplitudes are obtained by transmitting the data back to the wavefront modulator module (4) plane P2 or by performing an inverse spectral transform: or ,in This indicates the inverse spectrum transform operation; Then obtain ⑥ Substitute into ① Proceed to the next iteration, looping ①-⑥ until the error ERROR reaches the ideal error, then the loop ends, thus obtaining the wavefront to be measured. The complex amplitude distribution corresponding to different moments of the ultrashort pulse.

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