Broadband laser pulse chirp rate measurement method and device

Abstract

The invention discloses a broadband laser pulse chirp rate measuring method and device. The method comprises the steps that a broadband chirped pulse is divided into two beams, a reflected beam keeps original beam characteristics to serve as light to be measured, a transmitted beam becomes narrow-pulse-width narrow-spectrum light after being filtered to serve as probe light, and the two beams of laser are incident into a nonlinear crystal in a non-collinear mode to be subjected to space-time coupling to generate sum frequency; optimizing and adjusting crystal matching to obtain a maximum intensity sum frequency signal, measuring a sum frequency spectrum by using a spectrograph, and recording the data; adjusting the optical path of the probe light, changing the relative synchronization relation between the probe light and the to-be-measured light, enabling the probe light to scan from the front edge of the to-be-measured light to the rear edge, recording the delay optical path amount and the corresponding sum frequency spectrum, and calculating the chirp rate according to the corresponding relation between the sum frequency spectrum and the optical path delay amount. The device for realizing the method comprises a beam splitter, three reflectors, a narrow-band filter, an optical path delayer, a nonlinear crystal, an electric angle adjusting frame, an absorber group, a lens, a spectrograph and a computer.

Description

Technical Field

[0001] The present invention relates to the field of laser pulse time domain information measurement, in particular to a chirp rate measurement method and device for broadband chirped pulses, which can perform chirp rate measurement with absolute significance on chirped pulses with pulse widths in the time domain range of picoseconds to nanoseconds. Background Art

[0002] In the field of ultrashort laser light source generation, ultrashort pulse lasers with a wide spectrum are accompanied by dispersion effects during transmission, including material dispersion caused by transmission within the material, angular dispersion effects caused by transmission at the interface of materials of unequal thickness, and diffraction dispersion effects during the transflection process of dispersive elements such as gratings. The influence of these dispersion effects on ultrashort pulses is reflected in the frequency domain spectral phase and 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 full system dispersion control, with the goal of obtaining Fourier transform-limited compressed pulses with fully compensated dispersion. Due to the complexity of the laser transmission link, there is residual dispersion in the terminal compressed pulse, that is, residual chirp. Accurately measuring this chirp is of guiding significance for feedback control of full system dispersion and realization of chirp compensation.

[0003] At present, the mainstream method of pulse width measurement is based on the principle of autocorrelation. The chirp rate measurement method adds spectral information to the pulse width measurement, such as FROG (Review of Scientific Instruments, 68, 3277-3295, 1997) or SPIDER (Optics letters, 23, 792-794, 1998), which uses algorithms to reconstruct the spectral phase information of the pulse laser, thereby indirectly measuring the chirp rate of the pulse. Both FROG and SPIDER require interferometric measurement devices, and FROG requires a long acquisition time. In the process of algorithm reconstruction, SPIDER increases the number of iterations, which may destroy the reliability of complex phase profile reconstruction. Both methods are limited to pulses within a few picoseconds. The patent "Measurement device and method for measuring the time waveform and chirp rate of ultrashort pulses" (CN 104697647B) uses the autocorrelation principle to measure pulse width, and the spectrometer measures the spectral width. Its measurement capability is also limited to a few picoseconds of pulse width. Therefore, the above method can only measure the chirp rate of pulses in a time window of picoseconds, and cannot measure the chirp rate of pulses in a time window of nearly ten picoseconds or more.

[0004] The present invention proposes a chirp rate measurement method based on time-frequency scanning, which has the following advantages: first, the light to be measured and the probe light are of the same source, ensuring zero synchronization jitter of the two lights; second, the optical path of the light to be measured is total reflection light transmission, ensuring its maximum fidelity, and after the probe light is transmitted and narrow-band filtered, its spectrum and intensity changes do not affect the measurement accuracy; third, the sum frequency light spectrum is only related to the injected narrow-band probe light and the time-space coupled light spectrum of the light to be measured, and has nothing to do with crystal matching, and has nothing to do with the pulse width and waveform of the pulse to be measured, so that this method has absolute measurement significance; Fourth, the delay amount of the probe light delay optical path can be very large, which makes the scanning pulse width of this method extremely large, which can reach the nanosecond level; fifth, the adjustment step size of the probe light delay optical path can be very small, such as 1.5μm represents a time resolution of 10fs, and the current electric translation stage accuracy can reach the nanometer level, which makes the optical time resolution of this measurement method very high, reaching the level of single pixel in the autocorrelation principle, and the resolution of the entire system 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 large range. Summary of the invention

[0005] In view of the shortcomings of the current chirp rate measurement technology in terms of measurement accuracy and small measurement time window, the present invention provides a new absolute chirp rate measurement method and provides a device for implementing the method. The present invention has a simple structure and realizes time domain and frequency domain scanning by optical path delay. The measurement data is directly related to the optical path delay, so it has absolute measurement significance and has a femtosecond time resolution. The measurement time window can be from picoseconds to nanoseconds. Not only can the linear chirp rate of the pulse be obtained, but also the high-order nonlinear chirp rate can be further analyzed. The existing chirp rate measurement technologies are all limited to a few picoseconds.

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

[0007] A broadband laser pulse chirp rate measurement method, characterized by comprising:

[0008] The chirped pulse to be measured is divided into two beams, one of which is used as the measured light and the other as the probe light. The probe light has a narrow spectrum and a narrow pulse width, and its central wavelength is λ p ;

[0009] The light to be measured and the probe light are spatially coupled in a non-collinear phase matching manner in the nonlinear crystal 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 light to be measured from the leading edge to the trailing edge in the nonlinear crystal, and the light is recorded at different optical path delays L. i The wavelength λ of the sum frequency light generated by the probe light and the light to be measured is i , the total number of recorded data is N groups, i = 1, 2...N;

[0011] Calculate the chirp rate CR of the chirped pulse to be measured j , the formula is as follows:

[0012]

[0013] Where c is the speed of light in vacuum, 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] The two beams of light are spatiotemporally coupled in a non-collinear phase matching manner within the crystal and generate sum-frequency signals. By adjusting the angle of the nonlinear crystal, the sum-frequency optical signal is made the strongest.

[0018] A broadband laser pulse chirp rate measuring device, characterized in that it 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.

[0019] The invention is characterized in that the chirped pulse to be measured is divided into reflected light and transmitted light by the beam splitter 1, wherein the reflected light is incident on the nonlinear crystal 7 via the first reflector 2 as the light to be measured, and the transmitted light is incident on the nonlinear crystal 7 via the narrowband filter 3, and then sequentially via the second reflector 4, the optical path delay module 5 and the third reflector 6 as the probe light, and then incident on the nonlinear crystal 7; the light to be measured and the probe light are spatiotemporally coupled in the nonlinear crystal in a non-collinear phase matching manner, and the generated sum frequency light is converged by the lens 10 and then injected into the spectrometer 11;

[0020] The computer 12 is connected to the optical path delay module 5 to control the probe light to scan the light to be measured from the leading edge to the trailing edge. The computer 12 is connected to the electric angle adjustment frame 8 to control its rotation, thereby changing the angle of the nonlinear crystal to make the sum frequency optical signal the strongest.

[0021] The computer 12 is connected to the spectrometer 11 to collect and spectrally analyze the wavelength λ of the light. i and its corresponding probe light path delay L i .

[0022] The absorber group 9 is used to absorb the remaining light to be measured and the 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 beam splitting ratio of 50%:50%, and the backlight surface is coated with a broadband high-transmittance film.

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

[0025] The nonlinear crystal 7 is mounted on the electric angle adjustment frame 8, and the surface coating is a double-sided high-transmittance film in the 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 to be measured 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 outside 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 to measure the complete sum frequency spectrum.

[0027] The optical path delay module 5 comprises an electric translation stage and a beam retroreflecting mirror. The adjustment step accuracy of the electric translation stage determines the scanning time resolution. Its measuring range must be greater than 4 times the product of the half-height full-width pulse width of the light to be measured and the speed of light to ensure full-domain time scanning. The moving direction corresponding to its guide rail is parallel to the incident probe light. The retroreflecting mirror is installed on the electric translation stage and has a high reflectivity to the probe light, reflecting the probe light 180° after spatial dislocation.

[0028] The optical path delay module 5 has a quotient of twice the maximum optical path delay and the speed of light, which is the maximum pulse width of the chirped pulse to be measured. The stepping accuracy of the delay determines the measurement sampling rate, and the spectral resolution of the spectrometer determines the data recording accuracy.

[0029] The light-facing surfaces of the first reflector 2, the second reflector 4, and the third reflector 6 can be 45° high-reflectivity broadband dielectric films or high-reflectivity metal films, and the backlight surfaces are roughened to eliminate stray light.

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

[0031] 1) The measured light and the probe light are of the same origin, ensuring zero synchronization jitter of the two lights. The sum-frequency light spectrum is only related to the injected narrow-band probe light and the measured light spectrum part coupled in time and space, and has nothing to do with the pulse width and waveform of the measured pulse, making this method have absolute measurement significance; 2) The delay amount of the probe light delay optical path can be very large, making the scanning pulse width of this method extremely large, which can reach the nanosecond level, and the adjustment step size of the probe light delay optical path can be very small, making the sampling time resolution of this measurement method very high, reaching the level of the autocorrelation principle, and the resolution of the entire system 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. BRIEF DESCRIPTION OF THE DRAWINGS

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

[0033] In the figure: 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.

[0034] Figure 2 It 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, when the light to be measured is in the 800nm ​​band.

[0035] Figure 3 It is a schematic diagram of the corresponding relationship between the preset time delay (dashed line) and the time delay (solid line) obtained by experimental measurement using the method of the present invention and the wavelength in an embodiment of the broadband laser pulse chirp rate measurement device of the present invention.

[0036] Figure 4 It is a schematic diagram of the corresponding relationship between the difference between the preset time delay and the experimental measurement value and the wavelength in the embodiment of the broadband laser pulse chirp rate measurement device of the present invention.

[0037] Figure 5 It is a schematic diagram of the corresponding relationship between the preset chirp rate theoretical value (dashed line) obtained by numerical analysis and the chirp rate (solid line) obtained by experimental measurement using the method of the present invention and the wavelength in an embodiment of the broadband laser pulse chirp rate measurement device of the present invention. DETAILED DESCRIPTION

[0038] In order to make the purpose, technical solution and advantages of the present invention more clearly understood, the present invention is further described in detail below in conjunction with the accompanying drawings and embodiments. The specific embodiments described herein are only used to explain the present invention and are not intended to limit the present invention.

[0039] A broadband laser pulse chirp rate measurement method and device, 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 light with a narrow spectrum and narrow pulse width, and the reflected beam retains the chirp characteristics of the light to be measured as the light to be measured.

[0041] In the second step, the light to be measured is incident on the nonlinear crystal through the light guide mirror, and the probe light is guided into the nonlinear crystal through the electric optical path delay device by the reflector. The two beams of light are spatiotemporally coupled in the crystal in a non-collinear phase matching manner and generate sum frequency.

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

[0043] Step 4: gradually adjust the optical path delay of the probe light, repeat step 3, so that the probe light scans the light to be measured from the leading edge to the trailing edge, and at the same time, record the sum frequency spectrum and its corresponding optical path delay of the probe light;

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

[0045] See also Figure 1 , Figure 1 It is a schematic diagram of the optical path of the present invention, such as 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] The transmission direction of the optical path is as follows: the chirped pulse to be measured is divided into reflected light and transmitted light by the beam splitter 1, wherein the reflected light is incident on the nonlinear crystal 7 via the first reflector 2 as the light to be measured, and the transmitted light is incident on the nonlinear crystal 7 via the second reflector 4, the optical path delay module 5 and the third reflector 6 as the probe light after passing through the narrowband filter 3; the light to be measured and the probe light are spatiotemporally coupled in the nonlinear crystal in a non-collinear phase matching manner, and the generated sum frequency light is converged by the lens 10 and then injected into the spectrometer 11; the computer 12 is connected to the optical path delay module 5 to control it to make the probe light scan the light to be measured from the leading edge to the trailing edge, and the computer 12 is connected to the electric angle adjustment frame 8 to control its rotation, thereby changing the angle of the nonlinear crystal to make the sum frequency light signal the strongest; the computer 12 is connected to the spectrometer 11 to collect the sum frequency light wavelength λ i and its corresponding probe light path delay L i The absorber group 9 is used to absorb the remaining light to be measured and the remaining probe light emitted by 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, and the incident surface is coated with a broadband beam splitting film with a splitting ratio of 50%:50%, and the backlight surface is coated with a broadband high-transmittance film.

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

[0049] The nonlinear crystal 7 is mounted on the electric angle adjustment frame 8, and the surface coating is a double-sided high-transmittance film in the chirped pulse spectrum and its sum frequency spectrum range. The cutting direction of the nonlinear crystal is the sum frequency matching direction of the central wavelength of the light to be measured and the probe light under the non-collinear matching condition. The phase matching angles under different non-collinear angle settings in the BBO crystal are shown in the figure. Figure 2 As shown, the crystal thickness is in the sub-millimeter to millimeter range, and the nonlinear crystal may be BBO, LBO, YCOB, LN, DKDP, KTP, and the like.

[0050] The distance between the lens 10 and the nonlinear crystal 7 is outside 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 to measure the complete sum frequency spectrum.

[0051] The optical path delay module 5 comprises an electric translation stage and a beam retroreflecting mirror. The adjustment step accuracy of the electric translation stage determines the scanning time resolution. Its measuring range must be greater than 4 times the product of the half-height full-width pulse width of the light to be measured and the speed of light to ensure full-domain time scanning. The moving direction corresponding to its guide rail is parallel to the incident probe light. The retroreflecting mirror is installed on the electric translation stage and has a high reflectivity to the probe light, reflecting the probe light 180° after spatial dislocation.

[0052] The optical path delay module 5 has a quotient of twice the maximum optical path delay and the speed of light, which is the maximum pulse width of the chirped pulse to be measured. The stepping accuracy of the delay determines the measurement sampling rate, and the spectral resolution of the spectrometer determines the data recording accuracy.

[0053] The light-facing surfaces of the first reflector 2, the second reflector 4, and the third reflector 6 can be 45° high-reflectivity broadband dielectric films or high-reflectivity metal films, and the backlight surfaces are roughened to eliminate stray light.

[0054] Example

[0055] See also Figure 1 , Figure 1 It 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: central wavelength 808nm, spectral range 778nm-838nm, half-maximum full width pulse width preset to be about 22ps; single pulse energy 50mJ, circular spot diameter 7mm, repetition frequency 1Hz.

[0057] Component parameter settings include:

[0058] The light-facing surface of the beam splitter 1 is coated with a (reflectivity: transmittance) range of (50%:50%) within the range of 778nm-838nm, and the backlight surface is coated with a high transmittance within the range of 778nm-838nm; the first reflector 2, the second reflector 4, the third reflector 6 and the light retroreflector surface have a high reflectivity of 45° within the range of 778nm-838nm; the narrowband filter 3 is a filter with a central wavelength FWHM of 808nm and a bandwidth of 3nm, the transmission range of the optical path delay module 5 is not less than 4cm, the angle adjustment amount of the electric angle adjustment frame 8 is ±2°, the front and rear surfaces of the lens 10 are coated with a high transmittance 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 probe of the spectrometer 11 is about 170mm away from the lens 10, and the spectral optical resolution of the spectrometer 11 is 0.5nm. The parameters of nonlinear crystal 7 are: the nonlinear crystal is β-phase barium borate (β-BBO), the sum frequency is the first type phase matching mode, the non-collinear angle in BBO is set to 1.5°, the crystal cutting angle is (θ=29.25°), the crystal thickness is 0.8mm, and the size is 12mm×12mm.

[0059] In this embodiment, the chirped pulse is injected and obtained in the following way: the pulse output by the grating pair compressor reaches the Fourier transform limited pulse width under the feedback of the pulse width measured by the autocorrelator, and the grating pair spacing is increased with micron accuracy, and the output pulse is introduced into the dispersion amount, so that the pulse width reaches about 22ps, thereby constructing a chirped pulse with accurate dispersion of each order. The chirped pulse is injected into the device of the present invention, and the measured dispersion of each order is compared with the preset value to verify the measurement accuracy of the present invention. The offset of the grating spacing of the grating pair compressor relative to the Fourier transform limited pulse width grating pair spacing is G, and G is 24mm. The grating line density is D, and D is 1740 lines / mm. Then the grating line spacing is d, d=1 / D=1 / 1.74 microns, and the laser incident angle is γ, and γ is 56°. The spectral phase φ of the preset output chirped pulse determined by the above parameters set , chirp rate CR set They are:

[0060]

[0061] Where θ is the diffraction angle, which satisfies the relationship sinγ+sin(γ-θ)=mλ / d, m=1. According to the above expression, the spectral phase φ of the preset output chirped pulse can be plotted: set , chirp rate CR set curve.

[0062] Under the above parameter settings, the pulse chirp rate measurement method is described as follows:

[0063] In the first step, the chirped pulse to be measured is evenly divided into two beams by a beam splitter. The transmitted beam is filtered by a narrow-band filter to become a probe light with a narrow spectrum and narrow pulse width. The pulse width of the probe light is about 1.5ps, the spectrum width is 3nm, and the central wavelength is 808nm. The reflected beam maintains the chirp characteristics of the light to be measured as the light to be measured. The pulse width to be measured is about 22ps, the spectrum width is about 60nm, and the central wavelength is 808nm.

[0064] In the second step, the light to be measured is incident on the nonlinear crystal through the light guide mirror, and the probe light is incident on the nonlinear crystal through the optical path delay device. The optical path delay device is adjusted so that the two beams of light can achieve time-space coupling and frequency sum generation in the crystal in a non-collinear phase matching manner after passing through equal optical paths.

[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 is to adjust the electric translation stage with a step length of 15 μm, and the single-step optical path delay is 30 μm, so that the optical path of the probe light can be increased or decreased relative to the optical path of the light to be measured. The time domain scanning accuracy is 100 fs. Repeat step 3 so that the probe light scans the light to be measured from the center to the back edge and the front edge, and record the sum frequency spectrum and its corresponding optical path delay of the probe light;

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

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

[0069] The corresponding relationship between the preset time delay (dashed line) and the time delay (solid line) obtained by experimental measurement using the method of the present invention and the wavelength is shown in FIG. Figure 3 As shown in the figure, the two curves are very close; the difference between the preset time delay and the experimental measurement is shown in Figure 4 As shown, in the case of 60nm spectrum width and 22ps theoretical pulse width, the difference between experimental measurement and theoretical expectation is <0.5ps, and the error ratio is ∼2%, indicating that the measurement accuracy of the present invention is relatively high.

[0070] The corresponding relationship between the preset chirp rate theoretical value (dashed line) obtained by numerical analysis and the chirp rate (solid line) obtained by experimental measurement using the method of the present invention and the wavelength is shown in FIG. Figure 5 As shown, the experimental measurement value of the chirp rate near the probe light wavelength of 808 nm is CR=0.3595 ps / nm, which is 1.94% different from the preset theoretical value of 0.3666 ps / nm, indicating that the present invention has extremely high accuracy in chirp rate measurement.

[0071] Those skilled in the art can easily understand that the main bottleneck of the measurement accuracy of the present invention lies in the resolution of the spectrometer, and the reading accuracy of the sum frequency spectrum determines the accuracy of the inverted light to be measured. In the embodiments of the present invention, it can be proved that even when the resolution of the spectrometer is 0.5nm, the measurement value of the chirp rate at the central wavelength can also achieve extremely high accuracy; on the other hand, those skilled in the art can also easily understand that in this embodiment, the practice of deviating the grating spacing of the grating pair compressor from the Fourier transform limit position will inevitably introduce uncontrollable high-order dispersion into the light to be measured, because the actual operation cannot be perfect, so that the actual output pulse chirp characteristics are not exactly equal to the theoretical preset values. Therefore, the accuracy of the measurement result of the embodiment of the present invention is actually higher than the 1.94% described above.

Claims

1. A broadband laser pulse chirp rate measurement method, characterized in that: include: The chirped pulse to be measured is divided into two beams, one of which is used as the measured light and the other as the probe light. The probe light has a narrow spectrum and a narrow pulse width, and its central wavelength is λ p ; The light to be measured and the probe light are spatially coupled in a non-collinear phase matching manner in the nonlinear crystal to generate sum frequency light; The optical path delay of the probe light is gradually adjusted to ensure that the probe light scans the light to be measured from the leading edge to the trailing edge in the nonlinear crystal, and the light is recorded at different optical path delays L. i The wavelength λ of the sum frequency light generated by the probe light and the light to be measured is i , the total number of recorded data is N groups, i = 1, 2...N; Calculate the chirp rate CR of the chirped pulse to be measured j , the formula is as follows: Where c is the speed of light in vacuum, δL j =L j -L j-1 ,δλ j =λ j -λ j-1 , j=2,3…N.

2. The broadband laser pulse chirp rate measurement method according to claim 1, further comprising: Calculate the phase φ of the chirped pulse to be measured i , the formula is as follows: 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 are spatiotemporally coupled in a non-collinear phase matching manner in the crystal and generate sum frequency, and the sum frequency optical signal is made strongest by adjusting the angle of the nonlinear crystal.

4. A broadband laser pulse chirp rate measurement device, characterized in that: include: 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; The chirped pulse to be measured is divided into reflected light and transmitted light by the beam splitter 1, wherein the reflected light is incident on the nonlinear crystal 7 via the first reflector 2 as the light to be measured, and the transmitted light is incident on the nonlinear crystal 7 via the narrowband filter 3, and then sequentially via the second reflector 4, the optical path delay module 5 and the third reflector 6 as the probe light. The light to be measured and the probe light are spatiotemporally coupled in the nonlinear crystal in a non-collinear phase matching manner, and the generated sum frequency light is converged by the lens 10 and then injected into the spectrometer 11. The computer 12 is connected to the optical path delay module 5 to control the probe light to scan the light to be measured from the leading edge to the trailing edge. The computer 12 is connected to the electric angle adjustment frame 8 to control its rotation, thereby changing the angle of the nonlinear crystal to make the sum frequency light signal the strongest. The computer 12 is connected to the spectrometer 11 to collect and spectrally analyze the wavelength λ of the light. i and its corresponding probe light path delay L i .

5. The broadband laser pulse chirp rate measuring device according to claim 4, characterized in that: It also includes an absorber group 9 for absorbing the remaining light to be measured and the remaining probe light emitted by the nonlinear crystal 7 .

6. The broadband laser pulse chirp rate measuring device according to claim 4, characterized in that: 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 beam splitting ratio of 50%:50%, and the backlight surface is coated with a broadband high-transmittance film.

7. The broadband laser pulse chirp rate measuring device according to claim 4, characterized in that: The passband 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 spectrum pulse, and the narrower the spectrum, the better.

8. The broadband laser pulse chirp rate measuring device according to claim 4, characterized in that: The surface coating of the nonlinear crystal 7 is a double-sided high-transmittance film in the 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 to be measured 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 according to claim 4, characterized in that: The distance between the lens 10 and the nonlinear crystal 7 is outside 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 to measure the complete sum frequency spectrum.

10. The broadband laser pulse chirp rate measuring device according to claim 4, characterized in that: The translation range of the optical path delay module 5 is greater than 4 times the product of the half-maximum full-width pulse width of the light to be measured and the speed of light, thereby ensuring full-domain temporal scanning.

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