High-performance single-shot contrast measurement device with real-time self-verification of accuracy

Abstract

A high-performance single-shot contrast measurement device with real-time self-verification of accuracy is characterized in that the sampling light of the single-shot contrast measurement device is obtained based on spectral broadening and spectral filtering in a self-phase modulation process, so that the sampling light has high contrast, high energy, and a large difference from the central wavelength of the incident light, and good stability; at the same time, the sampling light introduces a series of intensities through a pulse replication unit to be attenuated in sequence, and is offset at equal intervals in position. The sampling light is also evenly spaced in time for self-verification of the measurement accuracy of the measurement device. This invention realizes the characteristics of single-shot contrast measurement with high measurement dynamic range, wide time window, high time resolution, high measurement fidelity, simple and compact device, and real-time verification of the accuracy of measurement results, providing better support for improving the contrast of ultra-strong and ultra-short laser pulses and related laser-matter interaction experimental research.

Description

Technical Field

[0001] The invention relates to the field of laser pulse contrast single-shot measurement, in particular to a high-performance contrast single-shot measurement device with real-time self-verification of accuracy. Background Art

[0002] With the development of chirped pulse amplification and optical parametric chirped pulse amplification technology, dozens of petawatt laser devices have been built or planned to be built around the world (High Power Laser Sci. Eng. 7, 54 (2019)). The peak focused intensity of ultra-intense ultrashort laser pulses is expected to reach 10 23-24 W / cm 2 This has important applications in the field of high-field laser-matter interactions. For such ultra-intense, ultra-short laser pulses, temporal contrast is a key parameter. Furthermore, because petawatt laser devices typically operate in low-frequency mode and the energy of each shot may fluctuate, measurements can only be made on a single shot basis. Therefore, single-shot contrast measurement of laser pulses becomes extremely important.

[0003] At present, laser pulse contrast single-shot measurement technology has made great progress. However, for various measurement technologies, it is still difficult to simultaneously meet the requirements of high measurement dynamic range, wide time window, high time resolution, high measurement fidelity, simple and compact device, and real-time verification of the accuracy of measurement results.

[0004] In 1993, the third-order autocorrelator was first used to measure single-shot time contrast. The light to be measured and its own frequency-doubled light were used to obtain the cross-correlation signal light based on the sum frequency process. However, at that time, only 10 6 In 2014, the dynamic range was increased to 10 by using a fiber optic array combined with a photomultiplier tube as a detector. 10 , recently reached 10 13 (Adv.Photonics Res.2, 2100105(2021)). Another third-order autocorrelation is to directly use four-wave mixing to obtain sampling light, such as patent CN107063480, but this is a scanning contrast measurement device and cannot achieve single-shot measurement. In the third-order autocorrelation, the time resolution is limited by the group velocity mismatch between the sampling light and the light to be measured. In addition, due to the limited pulse purification ability of the second-order nonlinear process, its measurement fidelity is also affected. Another contrast single-shot measurement method is based on a self-referenced spectral interferometer method, which has a time resolution of up to 20fs, but a dynamic range of only about 10 8, the time window is only about 20 ps, which cannot meet the requirements of high dynamic range and wide time window (Opt. Express 25, 12588-12600 (2017)).

[0005] In order to simultaneously achieve high dynamic range, high temporal resolution, wide time window and high fidelity, the fourth-order autocorrelation device was first proposed in 2019. This method uses a third-order nonlinear process to obtain high-contrast sampling light that is consistent with the central wavelength of the light to be measured. In 2019, the fourth-order autocorrelation device used a cascaded four-wave mixing process, or a self-diffraction process to obtain a clean sampling pulse, and simultaneously obtained a high fidelity of up to 10 11 The dynamic range and time resolution of about 160fs are achieved (Adv.Photonics 1, 056001 (2019), patent CN109632113). However, the cascaded four-wave mixing process and the self-diffraction process require beam splitting, spatial overlap and time synchronization, which makes the device complex and unstable. In 2021, the use of cross-polarization wave generation (XPW) of a single input beam to generate clean sampling pulses can achieve up to 10 12 dynamic range (Appl.Opt.60, 5912-5916(2021)). However, the polarizer that is indispensable in the process of generating cross-polarized waves limits the improvement of the temporal contrast of the sampling pulse, and the purification of the sampling light is limited, which actually affects the fidelity of the measurement. For the fourth-order autocorrelation device, its current disadvantages include the complex sampling light acquisition process, the instability of the device, and the inability to clearly distinguish and separate the central wavelengths of the sampling light and the light to be measured. In this way, the sampling light and the self-harmonic light of the light to be measured and their cross-correlation sum spectrum are little different, which makes it difficult to denoise the cross-correlation signal light, and the surface cleanliness of the mutual light crystal must be guaranteed.

[0006] Furthermore, real-time verification of the accuracy of each single-shot measurement is a crucial issue for single-shot measurement instruments. The spot pattern of the light being measured and the proficiency of the operator directly influence the accuracy and validity of each measurement. However, there is currently no method to monitor the accuracy of each shot in real time. Summary of the Invention

[0007] The present invention proposes a high-performance single-shot contrast measurement device with real-time self-verification of accuracy. The device achieves the unified results of high measurement dynamic range, wide time window, high time resolution, high measurement fidelity, simple and compact device, and real-time verification of measurement accuracy for single-shot contrast measurement. The device is characterized in that the sampling light of the single-shot contrast measurement device is obtained by spectral broadening and further filtering based on the self-phase modulation process, so that the sampling light has high contrast, high energy, good stability, and a large difference from the center wavelength of the light to be measured. At the same time, the sampling light introduces a series of sampling lights with attenuated intensity and shifted position through a pulse replication unit for self-verification of the measurement accuracy of the measurement device.

[0008] The technical solutions of the present invention are as follows:

[0009] A high-performance single-shot contrast measurement device with real-time self-verification of accuracy is characterized in that its structure includes a beam splitter, incident light is divided into reflected light and transmitted light by the beam splitter, the transmitted light sequentially passes through a long-pass filter, a focusing element, a first third-order nonlinear thin plate, a second third-order nonlinear thin plate, a short-pass filter, a first concave reflector, a second concave reflector, and a pulse duplicator to output sampling light, the reflected light sequentially passes through a first plane reflector, a second plane reflector, and a third concave reflector to output light to be measured, the sampling light and the light to be measured are simultaneously incident on a second-order nonlinear material, the signal light output by the second-order nonlinear material sequentially passes through an imaging lens, a third plane reflector, a bandpass filter, and finally input into a signal acquisition and analysis device.

[0010] The pulse replicator can be a glass plate or two parallel thin sheets. The transmitted light is incident on the pulse replicator at an angle in the vertical direction. Based on multiple reflections on the front and back surfaces of the pulse replicator, a series of sampling lights can be obtained, with intensities attenuated proportionally, distributed at equal intervals in time, and distributed at equal intervals in the vertical direction in space.

[0011] The long-pass filter and the short-pass filter have the same cut-off frequency, and the central wavelength of the obtained sampling light is greatly different from the central wavelength of the light to be measured.

[0012] The nonlinear thin slice can be a transparent material with a high third-order nonlinear coefficient, such as white sapphire or fused quartz cut into a wedge angle. Based on the self-phase modulation effect, the spectrum of the transmitted light is broadened.

[0013] The signal acquisition and analysis device has high spatial resolution, such as an sCMOS camera.

[0014] Compared with the prior art, the present invention has the following significant features:

[0015] 1. The device of the present invention obtains sampling light based on the self-phase modulation process and further spectral filtering. It only requires a beam of incident light. The sampling light has high energy and high contrast, and the central wavelength is significantly different from the light to be measured. At the same time, it has the characteristics of simple structure, stability and compactness.

[0016] 2. The present invention uses a pulse duplicator to obtain a series of reference small pulses, whose pulse intensities are proportionally attenuated, distributed at equal intervals in time, and sequentially shifted by the same scale in space. These pulses can be used as a scale to monitor the measurement results in real time, thereby achieving real-time self-verification of the measurement results of the measuring device.

[0017] 3. The pulse duplicator used in the present invention can be a simple inclined glass sheet of a certain thickness, or a parallel thin plate with a certain interval, and the structure is very simple;

[0018] 4. The present invention realizes the unity of high measurement dynamic range, wide time window, high time resolution, high measurement fidelity, simple and compact device design, and real-time self-verification of measurement result accuracy in contrast single-shot measurement.

[0019] 5. The present invention can introduce reference pulses with controllable intensity values, spatial positions, and time domain distribution into the measurement process. These reference pulses can be used as a scale for accurate and real-time verification of measurement results, making the measurement results more convincing and more convenient for the practical application of the measuring device. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] Figure 1 This is a structural principle diagram of the high-performance single-shot contrast measurement device with real-time self-verification of accuracy according to the present invention.

[0021] Figure 2 Parameters of the sampled light.

[0022] Figure 3 Intensity distribution of signal light on the camera.

[0023] Figure 4 Recovered contrast measurement results. DETAILED DESCRIPTION

[0024] The present invention will be further described in detail below with reference to the accompanying drawings and embodiments, but the scope of protection of the present invention should not be limited thereto.

[0025] Please see the attached Figure 1 , Figure 1 The schematic diagram of the structure of the high-performance single-shot contrast measurement device with real-time self-verification of accuracy of the present invention is as follows: Figure 1As shown in the figure, it can be seen that the accuracy real-time self-verification high-performance contrast single-shot measurement device of the present invention includes a beam splitter 1, incident light is divided into reflected light and transmitted light through the beam splitter 1, the transmitted light passes through a long-pass filter 2, a focusing element 3, a first third-order nonlinear thin plate 4, a second third-order nonlinear thin plate 5, a short-pass filter 6, a first concave reflector 7, a second concave reflector 8 and a pulse duplicator 9 in sequence to output sampling light, the reflected light passes through a first plane reflector 10, a second plane reflector 11, and a third concave reflector 12 in sequence to output light to be measured, the sampling light and the light to be measured are simultaneously incident on a second-order nonlinear material 13, the signal light output by the second-order nonlinear material 13 passes through an imaging lens 14, a third plane reflector 15, a band-pass filter 16 in sequence, and finally inputs into a signal acquisition and analysis device 17.

[0026] The pulse duplicator 9 can be a glass plate or two parallel thin sheets. The transmitted light is incident on the pulse duplicator 9 at an angle in the vertical direction. Based on multiple reflections on the front and rear surfaces of the pulse duplicator 9, a series of sampling lights with proportional attenuation of intensity, equal intervals in time, and equal intervals in the vertical direction in space can be obtained.

[0027] The long-pass filter 2 and the short-pass filter 6 have the same cutoff frequency, and the central wavelength of the obtained sampling light is greatly different from the central wavelength of the light to be measured.

[0028] The nonlinear thin slice 4 can be a transparent material with a high third-order nonlinear coefficient, such as white sapphire or fused quartz with a wedge-shaped angle. Based on the self-phase modulation effect, the spectrum of the transmitted light is broadened.

[0029] The signal acquisition and analysis device 17 has high spatial resolution, such as an sCMOS camera.

[0030] The device has the characteristics of high measurement dynamic range, wide time window, high time resolution, high measurement fidelity, simple and compact device, and real-time self-verification of measurement result accuracy.

[0031] Example

[0032] The invented device was tested using a Ti:Sapphire femtosecond amplifier output pulse (5.5 mJ / 1 kHz / 60 fs). The incident light was split into two beams by a wedge-shaped beamsplitter 1: the reflected light served as the measured light, and the transmitted light was used to generate high-contrast sampling light. The transmitted light first passed through a longpass filter 2 with a cutoff frequency of 780 nm to remove components with wavelengths greater than 780 nm. It was then focused onto two wedge-shaped glass plates by a cylindrical lens 3. The spectrum of the incident light was broadened by self-phase modulation. A shortpass filter 6 with a cutoff wavelength of approximately 780 nm was then used to generate high-energy, high-contrast sampling light. After passing through a 3 mm thick, vertically tilted glass plate, the sampling light and the measured light were finally focused into a BBO crystal. A cross-correlated signal light was generated based on a sum-frequency process. Finally, the spatial distribution of the correlated signal light intensity was captured using an sCMOS camera. A bandpass filter 16 with a center wavelength of 400 nm was further used to mitigate the effects of stray noise on the measured and sampled light. As can be seen in the accompanying figures, the entire measurement setup is economical and compact.

[0033] Finally, the sampled light energy we obtained can reach 120μJ, and the conversion efficiency is about 6%. The spectra of the pulse to be measured, the pulse after long-pass filtering, the pulse after self-phase modulation spectrum broadening, and the sampled pulse obtained after short-pass filtering are shown in Figure 2. Figure 2 (a) shows the spectrum of the sampling pulse covering from 720nm to 780nm, and its central wavelength is quite different from the central wavelength of the light to be measured. Since the generation of the sampling light only requires one beam and there is no spatial and temporal synchronization, the sampling light is very stable, with an energy stability of 0.9% RMS for half an hour and a spectral stability of Figure 2 (b) At the same time, we also used a second-order autocorrelator to measure the pulse width of the sampling light to be 65fs, which is very close to the pulse width of the incident light, 60fs, as shown in Figure 2 (c) Although the input laser beam has a Gaussian spatial profile, after focusing in the vertical direction, the intensity of the sampling light changes by less than one order of magnitude in the horizontal direction, as shown in Figure 2 (d) shown.

[0034] The intensity distribution of the signal light collected by the camera is as follows Figure 3 As shown, the intensity distribution of the signal light on the camera represents the contrast information of the light to be measured. The pixel intensity is summed in the vertical direction and converted into time delay in the horizontal direction based on the time-space conversion ear, and the measurement result is restored as follows Figure 4 As shown, the dynamic range measurement capability is 2.5×10 compared to the camera noise floor. -11 , time resolution 200fs, time window 68ps, thus verifying that the present invention has the characteristics of high dynamic range, high time resolution and wide time window; the signal light generated by the small pulse introduced by the tilted glass sheet is marked as follows Figure 3 The I and II marked in the figure are separated by 31 ps. Relative to the intensity of the main pulse, they decay by about three orders of magnitude in sequence, which is consistent with the result calculated based on the reflectivity of the front and back surfaces of the glass sheet. Moreover, they are located above the cross-correlated signal light and will not be overwhelmed by the intensity of the cross-correlated signal light, thereby realizing real-time comparative monitoring of the measurement results, thereby verifying the ability of the invention to verify the measurement accuracy in real time; at the same time, the sampling light of the invention is obtained by a third-order nonlinear process, and the high fidelity of the measurement results is also guaranteed.

[0035] Experiments show that the high-performance single-shot contrast measurement device with real-time self-verification of accuracy of the present invention realizes the characteristics of single-shot contrast measurement with high measurement dynamic range, wide time window, high time resolution, high measurement fidelity, simple and compact device, and real-time verification of measurement result accuracy.

Claims

1. A high-performance single-shot contrast measurement device with real-time self-verification of accuracy, characterized by: The invention comprises a beam splitter (1), incident light is divided into reflected light and transmitted light by the beam splitter (1), the transmitted light sequentially passes through a long-pass filter (2), a focusing element (3), a first third-order nonlinear thin plate (4), a second third-order nonlinear thin plate (5), a short-pass filter (6), a first concave reflector (7), a second concave reflector (8) and a pulse replicator (9), wherein the long-pass filter (2) and the short-pass filter (6) have the same cutoff frequency, after the transmitted light sequentially passes through the first third-order nonlinear thin plate (4) and the second third-order nonlinear thin plate (5), the spectrum is broadened based on the self-phase modulation effect, and sampling light is obtained after passing through the short-pass filter (6); the sampling light is obliquely incident into the pulse replicator (9), and is reflected by the front and rear surfaces of the pulse replicator (9) multiple times to obtain a series of sampling lights with proportional attenuation of intensity, equal time interval distribution, and equal vertical space interval distribution; The reflected light sequentially passes through the first plane reflector (10), the second plane reflector (11), and the third concave reflector (12) to output the light to be measured; The sampling light and the light to be measured are incident on the second-order nonlinear material (13) at the same time, and the signal light output by the second-order nonlinear material (13) passes through the imaging lens (14), the third plane reflector (15), the bandpass filter (16) in sequence and is finally input into the signal acquisition and analysis device (17).

2. The high-performance single-shot contrast measurement device with real-time self-verification of accuracy according to claim 1 is characterized in that: The pulse duplicator (9) is a glass plate or two parallel thin plates.

3. The high-performance single-shot contrast measurement device with real-time self-verification of accuracy according to claim 1 is characterized in that: The nonlinear thin slice is a transparent material with a high third-order nonlinear coefficient of white sapphire or fused quartz cut into a wedge angle, and based on the self-phase modulation effect, the spectrum of the transmitted light is broadened.

4. The high-performance single-shot contrast measurement device with real-time self-verification of accuracy according to claim 1 is characterized in that: The signal acquisition and analysis device (17) has high spatial resolution.

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