Method and device for measuring chirp rate of broadband laser pulse

Abstract

The application discloses a broadband laser pulse chirp rate measuring method and device. The method is as follows: a broadband chirp pulse is divided into two beams, a reflected beam keeps original beam characteristics as a measured light, a transmitted beam becomes narrow pulse width and narrow spectrum light as a probe light after filtering, the two beams are incident in a non-collinear way in a nonlinear crystal to generate sum frequency through space-time coupling, a crystal is optimally adjusted to obtain a maximum intensity sum frequency signal, a spectrometer is used to measure the sum frequency spectrum and record the data; a probe light path is adjusted to change a relative synchronization relationship with the measured light, so that the probe light scans from a front edge to a rear edge of the measured light, and a delay path amount and a corresponding sum frequency spectrum are recorded; and the chirp rate is calculated according to a corresponding relationship between the sum frequency spectrum and the path delay amount. The device for realizing the method comprises a beam splitter, three mirrors, a narrow-band filter, a path delay device, a nonlinear crystal, an electric angle adjusting frame, an absorber group, a lens and a spectrometer.

Description

Technical Field

[0001] This invention relates to the field of laser pulse time-domain information measurement, and in particular to a method and apparatus for measuring the chirp rate of broadband chirped pulses, which can perform chirp rate measurements with absolute significance for chirped pulses with pulse widths in the picosecond to nanosecond time domain range. Background Technology

[0002] In the field of ultrashort laser source generation, ultrashort pulse lasers with broad spectra are accompanied by dispersion effects during transmission. These include material dispersion caused by transmission within materials, angular dispersion caused by transmission at interfaces of materials with unequal thicknesses, and diffraction dispersion caused by transmission and reflection through dispersive elements such as gratings. These dispersion effects affect the ultrashort pulse in both the frequency domain spectral phase and the time domain pulse width. Especially in the field of high-power ultrashort pulse lasers, chirped pulse amplification (CPA) technology is widely used. In CPA technology, stretchers and compressors are used for overall system dispersion control, with the goal of obtaining compressed pulses with Fourier transform limits that are fully compensated for dispersion. Due to the complexity of the laser transmission link, there is a residual dispersion in the terminal compressed pulse, i.e., residual chirp. Accurately measuring this chirp is of guiding significance for feedback control of overall system dispersion and achieving chirp compensation.

[0003] Currently, the mainstream methods for pulse width measurement are based on the autocorrelation principle. Chirp rate measurement methods, such as FROG (Review of Scientific Instruments, 68, 3277-3295, 1997) or SPIDER (Optics letters, 23, 792-794, 1998), add spectral information to the pulse width measurement. These methods use algorithms to reconstruct the spectral phase information of the pulsed laser, thereby indirectly measuring the pulse's chirp rate. Both FROG and SPIDER require interferometric measurement devices. FROG requires a relatively long acquisition time, and SPIDER's increased iterations during algorithm reconstruction may compromise the reliability of reconstructing complex phase profiles. Both methods are limited to pulses with widths within picoseconds. The patent "Measurement Device and Method for Time Waveform and Chirp Rate of Ultrashort Pulses" (CN 104697647B) uses the autocorrelation principle to measure pulse width and a spectrometer to measure spectral width; its measurement capability is also limited to pulse widths within picoseconds. Therefore, the above method can only measure the chirp rate of pulses within a picosecond time window, and cannot measure the chirp rate of pulses within a time window of nearly ten picoseconds or larger.

[0004] This invention proposes a chirp rate measurement method based on time-frequency scanning, which has the following advantages: First, the test light and the probe light are from the same source, ensuring zero synchronization jitter between the two lights; second, the optical path traversed by the test light is a total internal reflection light guide transmission, ensuring its maximum fidelity, and the spectral and intensity changes of the probe light after transmission and narrowband filtering do not affect the measurement accuracy; third, the sum-frequency light spectrum is only related to the injected narrowband probe light and the spatiotemporally coupled test light spectrum, and is independent of crystal matching and the pulse width and waveform of the test pulse, making this method have absolute measurement significance; Fourth, the delay of the probe optical delay path can be very large, resulting in an extremely large scanning pulse width, reaching the nanosecond level. Fifth, the adjustment step size of the probe optical delay path can be very small, such as 1.5 μm, which represents a time resolution of 10 fs. The current electric translation stage can achieve a precision of nanometer level, making the optical time resolution of this measurement method very high, reaching the level of a single pixel in the autocorrelation principle. The overall system resolution depends on the spectral resolution of the spectrometer. Sixth, the method and device have a simple structure, a small nonlinear crystal length, and the non-collinear angle can be freely set within a wide range. Summary of the Invention

[0005] To address the shortcomings of current chirp rate measurement techniques in terms of measurement accuracy and small measurement time windows, this invention provides a novel absolute chirp rate measurement method and its implementation device. This invention features a simple structure, using optical path delay to achieve time and frequency domain scanning. The measurement data is directly related to the optical path delay, thus possessing absolute measurement significance. It boasts femtosecond-level time resolution, and the measurement time window can range from picoseconds to nanoseconds. It can not only obtain the linear chirp rate of pulses but also further analyze higher-order nonlinear chirps. Existing chirp rate measurement techniques are all limited to the picosecond range.

[0006] The technical solution of the present invention is as follows:

[0007] A method for measuring the chirp rate of a broadband laser pulse, characterized by comprising:

[0008] The chirped pulse to be tested is split into two beams. One beam is used as the test beam, and the other is used as the probe beam. The probe beam has a narrow spectrum and narrow pulse width, with a center wavelength of λ. p ;

[0009] The light under test and the probe light are spatiotemporally coupled in the nonlinear crystal in a nonlinear phase-matching manner to generate sum-frequency light;

[0010] The optical path delay of the probe light is gradually adjusted to ensure that the probe light scans the test light from the leading edge to the trailing edge within the nonlinear crystal, and the results are recorded at different optical path delays L. i Below, the wavelength λ of the sum-frequency light generated by the probe light and the light to be tested is... i The total number of records is N sets, i = 1, 2, ..., N;

[0011] Calculate the chirp rate CR of the chirped pulse to be tested. j The formula is as follows:

[0012]

[0013] In the formula, c is the speed of light in a vacuum, and δL j =L j -L j-1 ,δλ j =λ j -λ j-1 , j = 2, 3…N.

[0014] Calculate the phase φ of the chirped pulse to be measured. i The formula is as follows:

[0015]

[0016] In the formula, i = 1, 2, 3...N.

[0017] Two beams of light achieve spatiotemporal coupling and generate a sum frequency within the crystal in a non-collinear phase-matched manner. By adjusting the angle of the nonlinear crystal, the sum frequency light signal is made the strongest.

[0018] A broadband laser pulse chirp rate measuring device, characterized in that it comprises: a beam splitter 1, a first reflector 2, a narrowband filter 3, a second reflector 4, an optical path delay module 5, a third reflector 6, a nonlinear crystal 7, an electric angle adjustment frame 8 for placing the nonlinear crystal 7, a lens 10, a spectrometer 11, and a computer 12.

[0019] Its key feature is its structure: the chirped pulse to be tested is split into reflected light and transmitted light by the beam splitter 1. The reflected light, as the test light, is incident on the nonlinear crystal 7 through the first reflecting mirror 2. The transmitted light, as the probe light, is incident on the nonlinear crystal 7 after passing through the narrowband filter 3, and then sequentially through the second reflecting mirror 4, the optical path delay module 5, and the third reflecting mirror 6. The test light and the probe light undergo spatiotemporal coupling in the nonlinear crystal in a non-collinear phase-matched manner, and the resulting sum-frequency light is focused by the lens 10 and injected into the spectrometer 11.

[0020] The computer 12 is connected to the optical path delay module 5 and controls it to scan the light to be measured from the leading edge to the trailing edge. The computer 12 is also connected to the electric angle adjustment frame 8 and controls its rotation to change the angle of the nonlinear crystal, thereby making the sum-frequency optical signal the strongest.

[0021] The computer 12 is connected to the spectrometer 11 to collect sum-frequency light wavelengths λ. i and the corresponding probe optical path delay L i .

[0022] The absorber group 9 is used to absorb the remaining test light and remaining probe light emitted by the nonlinear crystal 7.

[0023] The beam splitter 1 is within the broadband spectrum of the light to be measured, and the incident surface is coated with a broadband beam splitting film with a splitting ratio of 50%:50%, while the back surface is coated with a broadband high-transmission film.

[0024] The bandpass spectrum of the narrowband filter 3 belongs to any band within the spectrum range to be measured, so that the transmitted light is a narrow spectral pulse, and the narrower the spectrum, the better. Further preferred, the bandwidth of the bandpass filter belongs to the center band of the spectrum of the pulse to be measured.

[0025] The nonlinear crystal 7 is mounted on the electric angle adjustment frame 8. Its surface is coated with a double-sided high-transmittance film with a chirped pulse spectrum and its sum-frequency spectrum range. The cutting direction of the nonlinear crystal is the sum-frequency matching direction between the center wavelength of the light under test and the probe light under non-collinear matching conditions. The crystal thickness is in the sub-millimeter to millimeter range. The nonlinear crystal can be BBO, LBO, YCOB, LN, DKDP, KTP, etc.

[0026] The distance between the lens 10 and the nonlinear crystal 7 is more than twice the focal length of the lens on the object side, so that the sum-frequency light converges within twice the focal length of the image side. The spectrometer 11 is placed on the image side of the lens, so that the sum-frequency light is focused within the probe of the spectrometer 11, and the complete sum-frequency spectrum is measured.

[0027] The optical path delay module 5 includes an electric translation stage and a beam retroreflector. The adjustment step accuracy of the electric translation stage determines the scanning time resolution. Its range must be greater than four times the product of the full width at half maximum (FWHM) pulse width and the speed of light to ensure full-range scanning. The movement direction of its guide rail is parallel to the incident probe light. The retroreflector is mounted on the electric translation stage and has high reflectivity for the probe light, reflecting the probe light 180° after spatial misalignment.

[0028] The optical path delay module 5, whose maximum delay is twice the quotient of the speed of light, is the maximum pulse width of the chirped pulse to be measured that it can support. The step accuracy of its delay determines the measurement sampling rate, and the spectral resolution of the spectrometer determines the data recording accuracy.

[0029] The first reflector 2, the second reflector 4, and the third reflector 6 can have a 45° high-reflectivity broadband dielectric film or a high-reflectivity metal film facing the light, and the back surface is roughened to eliminate stray light.

[0030] Compared with the prior art, the technical effects of the present invention are as follows:

[0031] 1) The light to be measured and the probe light are from the same source, ensuring zero synchronization jitter between the two lights. The sum-frequency light spectrum is only related to the spectrum of the injected narrowband probe light and the spatiotemporally coupled light to be measured, and is independent of the pulse width and waveform of the pulse to be measured, making this method have absolute measurement significance; 2) The delay of the probe light delay path can be very large, making the scanning pulse width of this method extremely large, reaching the nanosecond level. The adjustment step size of the probe light delay path can be very small, making the sampling time resolution of this measurement method very high, reaching the level of the autocorrelation principle. The overall system resolution depends on the spectral resolution of the spectrometer; 3) The method and device have a simple structure, a small nonlinear crystal length, and the non-collinear angle can be freely set within a large range. Attached Figure Description

[0032] Figure 1 This is a schematic diagram of the broadband laser pulse chirp rate measuring device of the present invention.

[0033] The diagram shows: beam splitter 1, first reflector 2, narrowband filter 3, second reflector 4, optical path delay module 5, third reflector 6, nonlinear crystal 7, motorized angle adjustment frame 8 for placing the nonlinear crystal 7, lens 10, spectrometer 11, and computer 12.

[0034] Figure 2 This is a schematic diagram of the phase matching angle of the nonlinear crystal BBO under different non-collinear angle settings in an embodiment of the broadband laser pulse chirp rate measurement device of the present invention, with the light to be measured in the 800nm ​​band.

[0035] Figure 3 This is a schematic diagram showing the correspondence between the preset time delay (dashed line) and the time delay (solid line) obtained by experimental measurement using the method of this invention, and the wavelength in an embodiment of the broadband laser pulse chirp rate measuring device of this invention.

[0036] Figure 4 This is a schematic diagram showing the correspondence between the difference between the preset time delay and the experimentally measured value and the wavelength in an embodiment of the broadband laser pulse chirp rate measuring device of the present invention.

[0037] Figure 5 This is a schematic diagram showing the correspondence between the preset theoretical chirp rate (dashed line) obtained by numerical analysis and the chirp rate (solid line) obtained by experimental measurement using the method of this invention, and the wavelength in an embodiment of the broadband laser pulse chirp rate measurement device of this invention. Detailed Implementation

[0038] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to the accompanying drawings and embodiments. The specific embodiments described herein are only for explaining the invention and do not limit the invention.

[0039] A method and apparatus for measuring the chirp rate of a broadband laser pulse, wherein the method is described as follows:

[0040] In the first step, the chirped pulse is split into two beams by a beam splitter. The transmitted beam is filtered by a narrow-band filter to become a probe beam with a narrow spectrum and narrow pulse width, while the reflected beam retains the chirped characteristics of the light to be tested and serves as the light to be tested.

[0041] In the second step, the light to be tested is incident on the nonlinear crystal through the light guide mirror, and the probe light is passed through the electric optical path delayer and guided into the nonlinear crystal by the reflector. The two beams of light achieve spatiotemporal coupling and generate sum frequency in the crystal in a non-collinear phase-matched manner.

[0042] The third step is to adjust the nonlinear crystal to make the sum-frequency signal the strongest, and then measure and record the sum-frequency spectrum.

[0043] Fourth step: Gradually adjust the optical path delay of the probe light and repeat step three so that the probe light scans the light to be measured from the leading edge to the trailing edge. At the same time, record the sum-frequency spectrum and the corresponding optical path delay of the probe light.

[0044] The fifth step is to analyze the relationship between the sum-frequency spectrum and the optical path delay. The chirp rate and phase of the light under test can be obtained through calculation and analysis.

[0045] Please see Figure 1 , Figure 1 This is a schematic diagram of the optical path of the present invention, as shown below. Figure 1 As shown, the device includes: a beam splitter 1, a first reflector 2, a narrowband filter 3, a second reflector 4, an optical path delay module 5, a third reflector 6, a nonlinear crystal 7, an electric angle adjustment frame 8 for placing the nonlinear crystal 7, a lens 10, a spectrometer 11, and a computer 12.

[0046] Along the optical path transmission direction, the following sequence occurs: the chirped pulse to be tested is split into reflected light and transmitted light by the beam splitter 1. The reflected light, as the test light, is incident on the nonlinear crystal 7 via the first reflecting mirror 2. The transmitted light, as the probe light, is incident on the nonlinear crystal 7 via the narrowband filter 3, the second reflecting mirror 4, the optical path delay module 5, and the third reflecting mirror 6. The test light and the probe light undergo spatiotemporal coupling within the nonlinear crystal in a non-collinear phase-matched manner. The resulting sum-frequency light is converged by the lens 10 and injected into the spectrometer 11. The computer 12 is connected to the optical path delay module 5 and controls it to scan the test light from the leading edge to the trailing edge. The computer 12 is also connected to the electric angle adjustment frame 8 and controls its rotation to change the angle of the nonlinear crystal, thereby maximizing the sum-frequency light signal. The computer 12 is connected to the spectrometer 11 and collects the sum-frequency light wavelength λ. i and the corresponding probe optical path delay L i Absorber group 9 is used to absorb the remaining test light and remaining probe light emitted through the nonlinear crystal 7.

[0047] The beam splitter 1 is a surface beam splitter, not a volume beam splitter, within the broadband spectrum of the light to be measured. The incident surface is coated with a broadband beam splitting film with a splitting ratio of 50%:50%, and the back surface is coated with a broadband high-transmission film.

[0048] The bandpass spectrum of the narrowband filter 3 belongs to any band within the spectrum range to be measured, so that the transmitted light is a narrow spectral pulse, and the narrower the spectrum, the better. Further preferred, the bandwidth of the bandpass filter belongs to the center band of the spectrum of the pulse to be measured.

[0049] The nonlinear crystal 7 is mounted on the electric angle adjustment frame 8. Its surface is coated with a double-sided high-transmittance film covering the range of chirped pulse spectroscopy and its sum-frequency spectroscopy. The cutting direction of the nonlinear crystal is the sum-frequency matching direction between the center wavelength of the light under test and the probe light under non-collinear matching conditions. The phase matching angles under different non-collinear angle settings within the BBO crystal are shown in the diagram. Figure 2 As shown, the crystal thickness is in the sub-millimeter to millimeter range, and the nonlinear crystal can be BBO, LBO, YCOB, LN, DKDP, KTP, etc.

[0050] The distance between the lens 10 and the nonlinear crystal 7 is more than twice the focal length of the lens on the object side, so that the sum-frequency light converges within twice the focal length of the image side. The spectrometer 11 is placed on the image side of the lens, so that the sum-frequency light is focused within the probe of the spectrometer 11, and the complete sum-frequency spectrum is measured.

[0051] The optical path delay module 5 includes an electric translation stage and a beam retroreflector. The adjustment step accuracy of the electric translation stage determines the scanning time resolution. Its range must be greater than four times the product of the full width at half maximum (FWHM) pulse width and the speed of light to ensure full-range scanning. The movement direction of its guide rail is parallel to the incident probe light. The retroreflector is mounted on the electric translation stage and has high reflectivity for the probe light, reflecting the probe light 180° after spatial misalignment.

[0052] The optical path delay module 5, whose maximum delay is twice the quotient of the speed of light, is the maximum pulse width of the chirped pulse to be measured that it can support. The step accuracy of its delay determines the measurement sampling rate, and the spectral resolution of the spectrometer determines the data recording accuracy.

[0053] The first reflector 2, the second reflector 4, and the third reflector 6 can have a 45° high-reflectivity broadband dielectric film or a high-reflectivity metal film facing the light, and the back surface is roughened to eliminate stray light.

[0054] Example

[0055] Please see Figure 1 , Figure 1 This is a schematic diagram of the optical path of the pulse chirp rate measuring device of the present invention.

[0056] In this embodiment, the chirped pulse parameters are: center wavelength 808nm, spectral range 778nm-838nm, half-width at half maximum (WHM) pulse width preset to about 22ps; single pulse energy 50mJ, circular spot diameter 7mm, and repetition frequency 1Hz.

[0057] Component parameter settings include:

[0058] The beam splitter 1 has a reflectivity to transmittance ratio of 50% to 50% on its light-facing surface within the range of 778nm-838nm, and a high transmittance coating on its back surface within the same range. The surfaces of the first reflector 2, the second reflector 4, the third reflector 6, and the light return mirror have a 45° high reflectivity within the range of 778nm-838nm. The narrowband filter 3 is a filter with a center wavelength of 808nm and a FWHM bandwidth of 3nm. The optical path delay module 5 has a transmission range of not less than 4cm. The electric angle adjustment bracket 8 has an angle adjustment range of ±2°. The lens 10 has a high transmittance coating on its front and rear surfaces within the spectral range of 390nm-420nm, and its focal length is 100mm. The distance between the nonlinear crystal 7 and the lens 10 is set to 250mm. The distance between the probe of the spectrometer 11 and the lens 10 is approximately 170mm. The spectral optical resolution of the spectrometer 11 is 0.5nm. The parameters of nonlinear crystal 7 are as follows: the nonlinear crystal is β-phase barium borate (β-BBO), the sum frequency is the first type of phase matching mode, the non-collinear angle within BBO is set to 1.5°, the crystal cutting angle (θ=29.25°), the crystal thickness is 0.8mm, and the size is 12mm×12mm.

[0059] In this embodiment, the chirped pulse is obtained by: using a grating-compressor to measure the pulse width of the output pulse, which is then fed back by an autocorrelator to achieve a Fourier transform-limited pulse width. Based on this, the grating pair spacing is increased to a micrometer precision, introducing dispersion into the output pulse, resulting in a pulse width of approximately 22 ps. This constructs chirped pulses with precise dispersion at each order. The chirped pulse is injected into the device of this invention, and the measured dispersion at each order is compared with preset values ​​to verify the measurement accuracy of the invention. The offset of the grating pair spacing relative to the Fourier transform-limited pulse width grating pair spacing is G, where G is 24 mm. The grating line density is D, where D is 1740 lines / mm. Therefore, the grating line spacing is d, where d = 1 / D = 1 / 1.74 micrometers. The laser incident angle is γ, where γ is 56°. The above parameters determine the preset output chirped pulse spectral phase φ. set CR set They are respectively:

[0060]

[0061] Where θ is the diffraction angle, satisfying the relationship sinγ + sin(γ - θ) = mλ / d, m = 1. Based on the above expression, the spectral phase φ of the preset output chirped pulse can be plotted. set CR set The curve.

[0062] Under the above parameter settings, the pulse chirp rate measurement method is described in detail below:

[0063] In the first step, the chirped pulse to be tested is split into two beams by a beam splitter. The transmitted beam is filtered by a narrow-band filter to become a probe beam with a narrow spectrum and narrow pulse width. The probe beam has a pulse width of about 1.5 ps, a spectral width of 3 nm, and a center wavelength of 808 nm. The reflected beam retains the chirped characteristics of the light to be tested and is used as the light to be tested. The pulse width of the light to be tested is about 22 ps, the spectral width is about 60 nm, and the center wavelength is 808 nm.

[0064] The second step involves the light to be tested passing through a light guide mirror and entering the nonlinear crystal, while the probe light passes through an optical path delayer and enters the nonlinear crystal. The optical path delayer is adjusted so that the two beams, after passing through equal optical paths, achieve spatiotemporal coupling and generate sum-frequency in the crystal in a non-collinear phase-matched manner.

[0065] The third step is to adjust the nonlinear crystal BBO to make the sum-frequency signal the strongest, measure and record the sum-frequency spectrum, and the center wavelength of the sum-frequency spectrum is 404nm.

[0066] The fourth step involves adjusting the electric translation stage in 15μm increments, resulting in a single-step optical path delay of 30μm. This allows for the increase or decrease of the probe light's optical path relative to the light under test. The time-domain scanning accuracy is 100fs. Step three is repeated to scan the light under test from the center to the rear and front edges, recording the sum-frequency spectrum and its corresponding probe light optical path delay.

[0067] The fifth step is to analyze the relationship between the frequency spectrum and the optical path delay. Based on expressions (1) and (2), the chirp rate and phase of the light to be measured are obtained.

[0068] After completing the above measurement steps, the experimental results were compared with the theoretical preset values ​​as shown in the diagram. Figure 3 , Figure 4 and Figure 5 As shown,

[0069] The relationship between the preset time delay (dashed line) and the time delay (solid line) experimentally measured using the method of this invention and the wavelength is as follows: Figure 3 As shown, the two curves are very close; the difference between the preset time delay and the experimental measurement is as follows: Figure 4 As shown, with a spectral width of 60 nm and a theoretical pulse width of 22 ps, the difference between the experimental measurement and the theoretical expectation is <0.5 ps, with an error ratio of ~2%, indicating that the measurement accuracy of the present invention is high.

[0070] The relationship between the theoretical value of the preset chirp rate obtained from numerical analysis (dashed line) and the chirp rate (solid line) obtained experimentally using the method of this invention and the wavelength is as follows: Figure 5 As shown, the experimentally measured chirp rate CR at a probe light wavelength of 808 nm is 0.3595 ps / nm, which deviates from the preset theoretical value of 0.3666 ps / nm by 1.94%. This indicates that the present invention has extremely high accuracy in chirp rate measurement.

[0071] Those skilled in the art will readily understand that the main bottleneck in the measurement accuracy of this invention lies in the resolution of the spectrometer. The accuracy of reading the sum-frequency spectrum determines the accuracy of the inverted light under test. In the embodiments of this invention, it can be demonstrated that even with a spectrometer resolution of 0.5 nm, the measured value of the chirp rate at the center wavelength can achieve extremely high accuracy. On the other hand, those skilled in the art will also readily understand that in this embodiment, the practice of deviating the grating spacing of the grating to the compressor from the Fourier transform limit position inevitably introduces uncontrollable higher-order dispersion into the light under test due to the imperfection of actual operation. This results in the actual output pulse chirp characteristics not being entirely equal to the theoretical preset value. Therefore, the accuracy of the measurement results in the embodiments of this invention is actually higher than the 1.94% described above.

Claims

1. A method for measuring the chirp rate of a broadband laser pulse, characterized in that, include: The chirped pulse to be tested is split into two beams. One beam is used as the test beam, and the other is used as the probe beam. The probe beam has a narrow spectrum and narrow pulse width, with a center wavelength of λ. p ; The light under test and the probe light are spatiotemporally coupled in the nonlinear crystal in a nonlinear phase-matching manner to generate sum-frequency light; The optical path delay of the probe light is gradually adjusted to ensure that the probe light scans the test light from the leading edge to the trailing edge within the nonlinear crystal, and the results are recorded at different optical path delays L. i Below, the wavelength λ of the sum-frequency light generated by the probe light and the light to be tested is... i The total number of records is N sets, i=1,2…N; Calculate the chirp rate CR of the chirped pulse to be tested. j The formula is as follows: （1） In the formula, c is the speed of light in a vacuum. , , j=2,3…N.

2. The broadband laser pulse chirp rate measurement method as described in claim 1 further includes: Calculate the phase φ of the chirped pulse to be measured. i The formula is as follows: （2） In the formula, i = 1, 2, 3...N.

3. The broadband laser pulse chirp rate measurement method as described in claim 1 or 2, wherein two beams of light achieve spatiotemporal coupling and generate a sum frequency in the crystal in a non-collinear phase-matched manner, and the sum frequency light signal is made strongest by adjusting the angle of the nonlinear crystal.

4. A broadband laser pulse chirp rate measuring device for implementing the method of any one of claims 1-3, characterized in that, include: Beam splitter, first reflector, narrowband filter, second reflector, optical path delay module, third reflector, nonlinear crystal, motorized angle adjustment frame for placing the nonlinear crystal, lens, spectrometer and computer; The chirped pulse to be tested is split into reflected light and transmitted light by the beam splitter. The reflected light, as the test light, is incident on the nonlinear crystal through the first reflector. The transmitted light, as the probe light, is filtered by the narrowband filter into a narrow-spectrum, narrow-pulse-width beam, and then incident on the nonlinear crystal through the second reflector, the optical path delay module, and the third reflector in sequence. The light to be tested and the probe light are spatiotemporally coupled in the nonlinear crystal in a nonlinear phase-matched manner, and the resulting sum-frequency light is focused by the lens and injected into the spectrometer. The computer is connected to the optical path delay module and controls it to scan the light to be measured from the leading edge to the trailing edge. The computer is also connected to the electric angle adjustment frame and controls its rotation to change the angle of the nonlinear crystal, thereby making the sum-frequency optical signal the strongest. The computer is connected to the spectrometer to collect sum-frequency light wavelengths λ. i and the corresponding probe optical path delay L i， The chirp rate of the chirped pulse under test is directly calculated based on this data.

5. The broadband laser pulse chirp rate measuring device as described in claim 4, characterized in that, It also includes an absorber assembly for absorbing the remaining test light and remaining probe light emitted through the nonlinear crystal.

6. The broadband laser pulse chirp rate measuring device as described in claim 4, characterized in that, The beam splitter is within the broadband spectrum of the light to be measured, and the incident surface is coated with a broadband beam splitting film with a splitting ratio of 50%:50%, while the back surface is coated with a broadband high-transmission film.

7. The broadband laser pulse chirp rate measuring device as described in claim 4, characterized in that, The narrowband filter has a bandpass spectrum that falls within any band of the spectrum to be measured, making the transmitted light a narrow-spectral pulse, and the narrower the spectrum, the better.

8. The broadband laser pulse chirp rate measuring device as described in claim 4, characterized in that, The nonlinear crystal surface coating is a double-sided high-transmittance film with a chirped pulse spectrum and its sum-frequency spectrum range. The cutting direction of the nonlinear crystal is the sum-frequency matching direction of the center wavelength of the light under test and the probe light under non-collinear matching conditions. The crystal thickness is in the sub-millimeter to millimeter range.

9. The broadband laser pulse chirp rate measuring device as described in claim 4, characterized in that, The distance between the lens and the nonlinear crystal is more than twice the focal length of the lens on the object side, so that the sum-frequency light converges within twice the focal length on the image side. The spectrometer is placed on the image side of the lens, so that the sum-frequency light is focused within the spectrometer probe to measure the complete sum-frequency spectrum.

10. The broadband laser pulse chirp rate measuring device as described in claim 4, characterized in that, The translation range of the optical path delay module is greater than four times the product of the full width at half maximum (FWHM) pulse width of the light under test and the speed of light, ensuring full-domain time scanning.

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