Optical system of autocorrelator and device for measuring pulse width of laser pulse

Abstract

The application provides a self-correlation instrument optical system and a laser pulse width measuring device. The self-correlation instrument optical system comprises an optical path difference generating module, a self-correlation signal generating module and a self-correlation signal receiving module. The optical path difference generating module comprises an optical path adjusting sheet and a Fresnel double prism, which are used for dividing the laser to be measured into two beams of pulse laser with different delays and intersecting at a non-collinear included angle. The self-correlation signal generating module comprises a frequency doubling crystal and a filter sheet, which are used for frequency doubling conversion of the pulse laser, generation of a self-correlation signal and filtering. The self-correlation signal receiving module comprises a CCD module, which is used for receiving an intensity signal of the self-correlation signal and converting the intensity signal into a self-correlation function image for output. The self-correlation function image is used for calculating the pulse width of the laser to be measured through image analysis. The problems that the existing technology is difficult to build and the size of the non-collinear included angle is not easy to adjust due to the use of multiple mirrors are solved.

Description

Technical Field

[0001] This invention belongs to the field of laser pulse width technology, and particularly relates to an autocorrelator optical system. Background Technology

[0002] Over the years, lasers have been continuously developing towards increased power, expanded wavelength range, and shortened pulse width. Today, lasers have entered the ultrafast realm and are increasingly widely used in physics, chemistry, biomedicine, astronomy, and other fields. Therefore, the study of the characteristic properties of ultrafast lasers is becoming increasingly important. Among these, the laser pulse width is one of the crucial parameters for accurately characterizing the properties of ultrafast lasers. For example, in the laser-induced acceleration of charged particles, the laser pulse width is an important indicator of the mass of the accelerated particles. Traditional methods for measuring laser pulse width use an oscilloscope with a photodiode, but this method has a response time on the order of picoseconds, which is unsuitable for ultrafast lasers.

[0003] Currently, the main methods for measuring ultrafast laser pulse width include autocorrelation, spectral phase interferometry for direct electric-field reconstruction (SPIDER), and frequency-resolved optical gating (FROG). FROG can obtain all the information of the laser pulse, but it requires iterative calculations, which is time-consuming and unsuitable for rapid measurements. SPIDER, while fast and accurate, is complex and cumbersome to operate. Autocorrelation, with its simple structure and fast measurement speed, while not providing all the laser information, meets the requirement of obtaining only pulse width information in practical applications. Therefore, autocorrelation is more widely used than the other two methods.

[0004] Existing autocorrelator optical systems have the following shortcomings:

[0005] When the laser beam passes through the beam splitter, it is reflected twice on the front and back surfaces of the lens, resulting in interference fringes that affect the accuracy of the measurement results.

[0006] To introduce more accurate delays, existing autocorrelation techniques require higher precision from the displacement platform, which also increases the cost.

[0007] The use of multiple reflectors increases the difficulty of adjusting the autocorrelator during the setup process, and makes it difficult to adjust the size of the non-collinear angle when there is non-collinear incidence. Summary of the Invention

[0008] Based on the above analysis, the present invention aims to provide an autocorrelator optical system to solve the problems of interference from beam splitters in the prior art, and the increased difficulty in adjusting the autocorrelator during the construction process due to the use of multiple mirrors, as well as the difficulty in adjusting the size of the non-collinear angle when there is non-collinear incidence.

[0009] The objective of this invention is mainly achieved through the following technical solutions:

[0010] On one hand, the present invention provides an autocorrelation instrument optical system, comprising: an optical path difference generation module, an autocorrelation signal generation module, and an autocorrelation signal receiving module;

[0011] The optical path difference generation module includes an optical path adjustment plate and a Fresnel double prism, which are fixedly placed sequentially along the incident direction of the laser to be tested; it is used to split the laser to be tested into two pulsed lasers that cross at a non-collinear angle and have different delays.

[0012] The autocorrelation signal generation module includes a frequency doubling crystal and a filter. The frequency doubling crystal and the filter are fixedly placed behind the Fresnel double prism along the incident direction of the laser to be tested. They are used to perform frequency doubling conversion on two pulsed lasers with different delays, generate an autocorrelation signal, and filter it.

[0013] The autocorrelation signal receiving module includes a CCD module, which is used to receive the intensity signal of the autocorrelation signal and convert it into an autocorrelation function image for output; the autocorrelation function image is used to calculate the pulse width of the laser pulse to be tested through image analysis.

[0014] Furthermore, the optical path adjustment plate is positioned off-center from the central axis of the laser beam to be tested, so that half of the laser beam passes through the optical path adjustment plate and is incident on one side of the right-angled prism of the Fresnel double prism, while the other half of the beam is directly incident on the other side of the right-angled prism.

[0015] The laser beam to be tested is incident perpendicularly to the bottom surface of the Fresnel biprism, and the relationship between the bottom angle of the Fresnel biprism and the non-collinear angle is as follows:

[0016]

[0017] Where β is the base angle of the Fresnel biprism. The non-collinear angle is defined as n1, where n1 is the refractive index of the Fresnel biprism. The non-collinear angle is approximated by a small angle and is typically between 2° and 5°.

[0018] Furthermore, the thickness l of the optical path adjustment plate satisfies:

[0019]

[0020] Where, d beam Let be the beam radius of the laser to be measured. The angle between the two non-collinear axes is c, where c is the speed of light, and τ is the angle between the two axes. p1 n1 is the pulse width calibrated for the laser emitter of the laser under test, and n2 is the refractive index of the optical path adjustment plate.

[0021] Furthermore, the frequency doubling crystal is fixedly placed at the intersection of the two pulsed laser beams after passing through the Fresnel double prism.

[0022] The distance from the center of the frequency doubling crystal to the apex of the Fresnel biprism is:

[0023]

[0024] Where: d beam Let be the radius of the laser beam to be measured, β be the base angle of the Fresnel biprism, and n1 be the refractive index of the Fresnel biprism.

[0025] Furthermore, the thickness d of the frequency doubling crystal satisfies:

[0026]

[0027] in, The non-collinear angle is given by c, where c is the speed of light, n is the refractive index of the frequency-doubled crystal, and τ is the refractive index of the crystal. p1 n1 is the pulse width calibrated for the laser emitter of the laser under test, n2 is the refractive index of the optical path adjustment plate, and l is the thickness of the optical path adjustment plate.

[0028] The aperture size D of the frequency doubling crystal crys satisfy:

[0029]

[0030] Where d is the thickness of the frequency doubling crystal. The non-collinear angle is n, where n is the refractive index of the frequency-doubled crystal, and d is the refractive index of the crystal. beam The radius of the laser beam to be tested is denoted as .

[0031] Furthermore, the autocorrelation optical system provided by the present invention also includes an attenuator, which is fixedly disposed behind the filter along the laser incident direction to attenuate the intensity of the autocorrelation signal.

[0032] On the other hand, the present invention also provides a laser pulse width measurement device, including the aforementioned autocorrelator, and further including a processing terminal, wherein the processing terminal is equipped with an image processing program and is connected to the CCD module of the autocorrelator optical system via a serial port.

[0033] When the image processing program is executed, it is used to implement the following method:

[0034] The full width at half maximum (FWHM) of the autocorrelation function image is obtained from the autocorrelation function image.

[0035] Based on the full width at half maximum (FWHM), the pulse width of the laser under test is calculated using the following formula:

[0036]

[0037] Where, τ p Δd is the pulse width of the laser to be tested, Δx is the full width at half maximum (FWHM) of the autocorrelation function image, Δx is the peak intensity shift distance of the autocorrelation signal received by the CCD module, n1 is the refractive index of the Fresnel biprism, n2 is the refractive index of the optical path adjustment plate, l is the thickness of the optical path adjustment plate, c is the speed of light, and γ is the waveform coefficient of the laser pulse to be tested.

[0038] The beneficial effects of this technical solution are:

[0039] 1. This invention replaces existing beam splitters and reflectors with Fresnel biprisms, significantly optimizing the autocorrelator structure and achieving miniaturization and convenience. It also eliminates interference caused by beam splitters, improving the accuracy of measurement results. Furthermore, using Fresnel biprisms allows the two beams to intersect at a specific angle, avoiding the need for numerous reflectors, reducing the difficulty of angle adjustment during autocorrelator setup, and simplifying the autocorrelator structure.

[0040] 2. This invention replaces the displacement platform in the prior art with an optical path adjustment plate, making operation simpler and avoiding the cost problems caused by the requirement for excessively high precision of the displacement platform. The delay introduced by the optical path adjustment plate is only related to its thickness, thus solving the problem of precision adjustment of the displacement platform in the prior art.

[0041] Other features and advantages of the invention will be set forth in the following description, and will be apparent in part from the description, or may be learned by practicing the invention. The objects and other advantages of the invention may be realized and obtained by means of the structures particularly pointed out in the written description, claims, and drawings. Attached Figure Description

[0042] The accompanying drawings are for illustrative purposes only and are not intended to limit the invention. Throughout the drawings, the same reference numerals denote the same parts.

[0043] Figure 1 This is a structural diagram of an autocorrelator optical system according to an embodiment of the present invention.

[0044] Figure 2This is a structural diagram of an autocorrelator system in the existing technology.

[0045] Figure 3 This is a schematic diagram of the interference effects produced by using beam splitters in existing technologies.

[0046] Figure label:

[0047] 1-Optical path adjustment plate; 2-Fresnel double prism; 3-French frequency doubling crystal; 4-Filter; 5-Attenuator; 6-CCD module; 7-Processing terminal Detailed Implementation

[0048] The preferred embodiments of the present invention will now be described in detail with reference to the accompanying drawings, which form part of this application and are used together with the embodiments of the present invention to illustrate the principles of the present invention, but are not intended to limit the scope of the present invention.

[0049] One embodiment of the present invention provides an autocorrelation optical system, such as Figure 1 As shown, it includes an optical path difference generation module, an autocorrelation signal generation module, and a laser pulse width calculation module.

[0050] The optical path difference generation module includes an optical path adjustment plate and a Fresnel double prism. The optical path adjustment plate and the Fresnel double prism are fixedly placed sequentially along the incident direction of the laser in the optical path of the laser to be tested. It is used to split the laser to be tested into two pulsed lasers that cross at a non-collinear angle and have different delays.

[0051] In a specific embodiment, the optical path adjustment plate is positioned offset from the central axis of the laser beam under test, such that half of the laser beam passes through the optical path adjustment plate and then enters one side of the right-angled prism of the Fresnel biprism, while the other half of the beam directly enters the other side of the right-angled prism. Furthermore, the laser beam under test is incident perpendicularly to the bottom surface of the Fresnel biprism, and the relationship between the bottom angle of the Fresnel biprism and the non-collinear angle is as follows:

[0052]

[0053] Where β is the base angle of the Fresnel biprism. Let n1 be the refractive index of the Fresnel biprism, and n be the non-collinear angle. Adopting the principle of small-angle approximation, its theoretical value is 2° to 5°.

[0054] Optionally, the Fresnel biprism can be fixed with one bottom corner facing upwards and the other bottom corner facing downwards. The optical path adjustment plate is placed upwards, offset from the central axis of the laser beam under test, so that half of the laser beam under test passes through the optical path adjustment plate and enters the upper right-angle prism of the Fresnel biprism, while the other half of the beam directly enters the lower right-angle prism.

[0055] The optical path adjustment plate can be a thin film made of a different material than that of the Fresnel biprism, or it can be a thin film made of the same material. If a thin film made of the same material is used, that is, the refractive index of the optical path adjustment plate is the same as that of the Fresnel biprism, the computational complexity can be reduced to a certain extent.

[0056] Based on the calibration parameters of the laser emitter of the laser under test, optical path adjustment plates of different thicknesses can be selected to introduce different optical path differences into the optical path system, thereby introducing a delay into the measurement system. Its thickness l is:

[0057]

[0058] Where, d beam Let be the beam radius of the laser to be measured. The angle between the two non-collinear axes is c, where c is the speed of light, and τ is the angle between the two axes. p1 n1 is the pulse width calibrated for the laser emitter of the laser under test, and n2 is the refractive index of the optical path adjustment plate.

[0059] Due to its special optical path structure, according to the law of refraction, when a laser beam is incident from the bottom edge of a Fresnel biprism, the incident beam is split into two beams, and the beams exiting from its two sides are both deflected toward the central axis; that is, the incident pulse beam is split into two beams and intersects at a certain angle, forming a non-collinear angle.

[0060] Specifically, in order to meet the phase matching conditions of the frequency doubling crystal and maximize its frequency doubling conversion efficiency, the non-collinear angle is approximated by a small angle, theoretically ranging from 2° to 5°.

[0061] For an optical path adjuster with thickness l and refractive index n2, the resulting optical path difference is δ = n2l; then the delay added to the laser pulse incident on the Fresnel biprism after passing through the optical path adjuster is:

[0062] Where c is the speed of light and n2 is the refractive index of the optical path adjustment plate;

[0063] After introducing a delay, the intersection point of the two beams after passing through the Fresnel double prism, i.e., the peak value of the spatial intensity distribution function S(x) of the autocorrelation signal, will shift. According to geometric relationships, the relationship between the introduced delay Δτ and the peak shift distance Δx of the autocorrelation signal S(x) is as follows:

[0064]

[0065] in, Since the angle is non-collinear, according to the relationship between the non-collinear angle and the base angle of a Fresnel biprism:

[0066]

[0067] Calculations show that:

[0068]

[0069] Where n2 is the refractive index of the optical path adjustment plate, Δx is the shift distance of the peak intensity of the autocorrelation signal received by the CCD module, and l is the thickness of the optical path plate.

[0070] It should be noted that, theoretically, the value of the non-collinear angle can be determined by the phase matching condition of the frequency doubling crystal, thus determining the bottom angle value of the Fresnel biprism. Furthermore, without the need for an optical path adjuster to introduce delay, the pulse width of the laser pulse under test can also be obtained. The formula for pulse width measurement is:

[0071]

[0072] However, errors are easily introduced during the processing of Fresnel biprisms and frequency doubling crystals, so the actual angle needs to be measured during the measurement process. However, the angle measurement method is cumbersome and prone to measurement errors. To solve the above problems, this invention adds an optical path adjustment plate, introducing a delay into the measurement system, transforming the angle measurement into the measurement of the optical path adjustment plate thickness. The thickness measurement is easier and more accurate. The pulse width measurement formula of this invention becomes:

[0073]

[0074] Where l is the thickness of the optical path adjustment plate.

[0075] Therefore, the autocorrelation system of this invention can measure the peak shift distance of the autocorrelation signal corresponding to different thicknesses of the optical path adjustment plate by adjusting the thickness of the optical path adjustment plate, thereby replacing the measurement of the bottom angle of the Fresnel biprism. This avoids the errors caused by cumbersome angle measurement and improves the measurement accuracy. In addition, by using the optical path adjustment plate and the Fresnel biprism instead of the displacement platform in the prior art, the accuracy problem of the displacement platform and the interference effect of the beam splitter in the prior art are solved. The use of reflectors is reduced, the adjustment difficulty of the system is reduced, and the structure of the autocorrelation instrument is simplified. Moreover, while reducing the number of optical components used, the measurement accuracy is further improved, the construction cost is reduced, and the autocorrelation measurement system is made more miniaturized and portable.

[0076] Furthermore, the autocorrelation signal generation module includes a frequency doubling crystal and a filter. The frequency doubling crystal and the filter are sequentially fixed behind the Fresnel double prism along the incident direction of the laser to be tested, and are used to perform frequency doubling and filtering of the incident laser and generate an autocorrelation signal.

[0077] Specifically, the frequency doubling crystal in the autocorrelation signal generation module is placed at the intersection of the two pulse beams. The two pulse beams undergo frequency doubling in the frequency doubling crystal, generating a second harmonic at the angle bisector of their included angle, which is the autocorrelation signal. The second harmonic is filtered out by a filter to remove the fundamental frequency component.

[0078] Preferably, in order to prevent the intensity of the autocorrelation signal light from damaging the signal receiving module, an attenuator is provided between the autocorrelation signal generation module and the signal receiving module to attenuate its intensity, so as to avoid damaging the CCD camera used to receive the autocorrelation intensity signal.

[0079] The appropriate frequency doubling crystal is selected based on the different wavelengths of the incident laser pulse. The relationship between the placement of the frequency doubling crystal and the bottom angle of the Fresnel biprism is as follows:

[0080]

[0081] Where L is the distance from the center of the frequency doubling crystal to the apex of the Fresnel biprism, and d beam Where is the radius of the laser beam to be measured, β is the base angle of the Fresnel double prism, and n1 is the refractive index of the optical path adjustment plate;

[0082] Since the second harmonic is generated at the point where the two pulses completely overlap in time and space, in order to generate the second harmonic and maximize its intensity, the two pulses must completely overlap in the frequency doubling crystal. Simultaneously, it is necessary to ensure that, even after introducing a delay, the overlap position of the two pulses remains within the frequency doubling crystal. Therefore, the thickness d of the frequency doubling crystal must satisfy the following:

[0083]

[0084] The aperture size D of the frequency doubling crystal crys Must meet:

[0085]

[0086] Where d is the thickness of the frequency doubling crystal. The non-collinear angle is n, where n is the refractive index of the frequency-doubled crystal, and d is the refractive index of the crystal. beam The radius of the laser beam to be tested is denoted as .

[0087] The autocorrelation signal receiving module includes a CCD module, which is used to receive the intensity signal of the autocorrelation signal and convert it into an autocorrelation function image for output; the autocorrelation function image is used to calculate the pulse width of the laser pulse to be tested through image analysis.

[0088] The autocorrelation signal generated by the autocorrelation signal generation module has a high intensity and needs to be attenuated by an attenuator before entering the CCD module. The attenuator needs to be selected according to the parameters of the CCD camera. When building the autocorrelation instrument optical system, multiple attenuators can be inserted first, and then the number of attenuators can be gradually reduced until the CCD camera can receive and output clear autocorrelation signal intensity information.

[0089] Specifically, the CCD camera receives the autocorrelation signal intensity information. After secondary development of the CCD camera through LabVIEW and adjusting the optical path adjustment plates of different thicknesses, the value of the peak shift distance Δx of the autocorrelation signal spatial intensity distribution function curve can be displayed in real time. The full width at half maximum (FWHM) Δd of the autocorrelation spatial intensity distribution function S(x) can be displayed through the processing terminal connected to the CCD. Therefore, the intensity signal of the autocorrelation signal is output through the processing terminal, and the pulse width information of the incident pulse can be obtained through the signal image output by the processing terminal.

[0090] Another embodiment of the present invention also provides a laser pulse width measurement device, including an autocorrelator and a processing terminal of any of the foregoing embodiments, wherein the processing terminal is equipped with an image processing program and is connected to the CCD module of the autocorrelator optical system via a serial port;

[0091] When the image processing program is executed, it is used to implement the following method:

[0092] The full width at half maximum (FWHM) of the autocorrelation function (AFM) image is obtained from the AFM image. Specifically, the FWHM of the AFM refers to the image width corresponding to half of the peak value of the AFM image. Based on the obtained AFM image, the width of the AFM image corresponding to half of the peak value can be read in the image processing program to obtain the full WHM of the AFM image.

[0093] The pulse width of the laser under test is calculated using the following formula based on the full width at half maximum (FWHM) of the autocorrelation function graph:

[0094]

[0095] Where, τ p Δd is the pulse width of the laser under test, Δx is the full width at half maximum (FWHM) of the autocorrelation function image, Δx is the peak intensity shift distance of the autocorrelation signal received by the CCD module, n1 is the refractive index of the Fresnel biprism, n2 is the refractive index of the optical path adjustment plate, l is the thickness of the optical path adjustment plate, c is the speed of light, and γ is the waveform coefficient of the laser pulse under test. The waveform coefficient of the laser under test is determined by the laser transmitter calibrated; specifically, the waveform coefficient of the Gaussian laser is 1.414, and the waveform coefficient of the hyperbolic secant laser is 1.543.

[0096] It should be noted that the autocorrelator optical system provided by this invention can read laser pulse width information in real time through the processing terminal, which solves the problem that the calculation of existing methods such as FROG is complicated and cannot achieve real-time measurement.

[0097] The basic structure of existing autocorrelators is as follows: Figure 2 As shown, the pulse to be measured is split into two identical pulses after passing through the beam splitter (1). One pulse is reflected by mirrors (3) and (4) fixed on the displacement platform (2), and then incident into the frequency doubling crystal (8) through mirror (7). The other pulse is reflected by mirrors (5) and (6), and then incident into the nonlinear crystal (8) at a certain angle with the first pulse. The filter (9) filters out the fundamental frequency light passing through the frequency doubling crystal, and the generated second harmonic is attenuated by the attenuator (10) and finally incident into the CCD (11). The pulse width information of the laser is obtained by analyzing the autocorrelation signal at the PC (12).

[0098] For existing autocorrelation techniques, firstly, when the laser passes through the beam splitter, it undergoes two reflections on the front and back surfaces of the lens, respectively, such as... Figure 3 As shown, the reflected light satisfies the interference conditions, thus interference occurs before and after the mirror, producing interference fringes and affecting the measurement results. Secondly, existing autocorrelation techniques require high precision from the displacement platform to introduce accurate delays into the measurement system; however, higher precision comes at a higher cost. Furthermore, the use of multiple mirrors increases the difficulty of adjusting the autocorrelation instrument during setup and makes it difficult to adjust the size of the non-collinear angle when incident light is non-collinear.

[0099] The optical path difference generation module of this invention replaces the beam splitter, reflector and other devices in the prior art with an optical path adjustment plate and a Fresnel double prism, which greatly optimizes the structure of the autocorrelator and solves the interference effect of the beam splitter in the prior art. During the construction process, only the thickness of the optical path adjustment plate needs to be adjusted, making the autocorrelator more miniaturized and portable, reducing the difficulty and cost of construction, and improving the measurement accuracy.

[0100] Those skilled in the art will understand that all or part of the processes of the methods described in the above embodiments can be implemented by a computer program instructing related hardware, and the program can be stored in a computer-readable storage medium. The computer-readable storage medium may be a disk, optical disk, read-only memory, or random access memory, etc.

[0101] The above description is only a preferred embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any changes or substitutions that can be easily conceived by those skilled in the art within the scope of the technology disclosed in the present invention should be included within the scope of protection of the present invention.

Claims

1. An optical system for an autocorrelator, characterized in that, include: Optical path difference generation module, autocorrelation signal generation module, and autocorrelation signal receiving module; The optical path difference generation module includes an optical path adjustment plate and a Fresnel double prism. The optical path adjustment plate and the Fresnel double prism are fixedly placed sequentially along the incident direction of the laser beam under test. The optical path adjustment plate is positioned offset from the central axis of the laser beam under test, so that half of the laser beam passes through the optical path adjustment plate and then enters a right-angled prism on one side of the Fresnel double prism, while the other half of the beam directly enters the other right-angled prism. This is used to split the laser beam under test into two pulsed laser beams that cross at a non-collinear angle and have different delays. The thickness l of the optical path adjustment plate satisfies: Where, d beam Let be the beam radius of the laser to be measured. The angle between the two non-collinear axes is c, where c is the speed of light, and τ is the angle between the two axes. p1 n1 is the pulse width calibrated for the laser emitter of the laser under test, and n2 is the refractive index of the optical path adjustment plate. The autocorrelation signal generation module includes a frequency doubling crystal and a filter. The frequency doubling crystal and the filter are fixedly placed behind the Fresnel double prism along the incident direction of the laser to be tested. They are used to perform frequency doubling conversion on two pulsed lasers with different delays, generate an autocorrelation signal, and filter it. The distance from the center of the frequency doubling crystal to the apex of the Fresnel biprism is: Where: d beam Where is the radius of the laser beam to be measured, β is the base angle of the Fresnel biprism, and n1 is the refractive index of the Fresnel biprism. The autocorrelation signal receiving module includes a CCD module, which receives the intensity signal of the autocorrelation signal and converts it into an autocorrelation function image for output. Optical path adjustment plates of different thicknesses are selected according to the calibration parameters of the laser emitter of the laser under test, introducing different optical path differences into the optical path system. Based on the autocorrelation function image, the peak intensity shift distance of the autocorrelation signal corresponding to different thicknesses of the optical path adjustment plates is obtained, and the pulse width of the laser under test is calculated using the following formula: Where, τ p Δd is the pulse width of the laser to be tested, Δd is the full width at half maximum (FWHM) of the autocorrelation function image, Δx is the shift distance of the peak intensity of the autocorrelation signal received by the CCD module, n1 is the refractive index of the Fresnel biprism, n2 is the refractive index of the optical path adjustment plate, l is the thickness of the optical path adjustment plate, c is the speed of light, and γ is the waveform coefficient of the laser pulse to be tested.

2. The autocorrelator optical system according to claim 1, characterized in that, The laser beam to be tested is incident perpendicularly to the bottom surface of the Fresnel biprism, and the relationship between the bottom angle of the Fresnel biprism and the non-collinear angle is as follows: Where β is the base angle of the Fresnel biprism. The angle between the two non-collinear prisms is n1, where n1 is the refractive index of the Fresnel biprism. The non-collinear included angle adopts the principle of small angle approximation, with a value of 2° to 5°.

3. The autocorrelator optical system according to claim 1, characterized in that, The frequency doubling crystal is fixedly placed at the intersection of the two pulsed laser beams after passing through the Fresnel double prism.

4. The autocorrelator optical system according to claim 1, characterized in that, The thickness d of the frequency doubling crystal satisfies: in, The non-collinear angle is given by c, where c is the speed of light, n is the refractive index of the frequency-doubled crystal, and τ is the refractive index of the crystal. p1 n1 is the pulse width calibrated for the laser emitter of the laser under test, n2 is the refractive index of the optical path adjustment plate, and l is the thickness of the optical path adjustment plate.

5. The autocorrelator optical system according to claim 4, characterized in that, The aperture size D of the frequency doubling crystal crys satisfy: Where d is the thickness of the frequency doubling crystal. The non-collinear angle is n, where n is the refractive index of the frequency-doubled crystal, and d is the refractive index of the crystal. beam The radius of the laser beam to be tested is denoted as .

6. The autocorrelator optical system according to claim 1, characterized in that, It also includes an attenuator, which is fixedly disposed behind the filter along the incident direction of the laser, and is used to attenuate the intensity of the autocorrelation signal.

7. A laser pulse width measuring device, characterized in that, The autocorrelator according to any one of claims 1-6 further includes a processing terminal, wherein the processing terminal is equipped with an image processing program and is connected to the CCD module of the autocorrelator optical system via a serial port. When the image processing program is executed, it is used to implement the following method: By adjusting the thickness of the optical path adjustment plate, and based on the autocorrelation function image, the peak intensity shift distance of the autocorrelation signal corresponding to different thicknesses of the optical path adjustment plate and the full width at half maximum (FWHM) of the autocorrelation function image are obtained. Based on the full width at half maximum (FWHM), the pulse width of the laser under test is calculated using the following formula: Where, τ p Δd is the pulse width of the laser to be tested, Δd is the full width at half maximum (FWHM) of the autocorrelation function image, Δx is the shift distance of the peak intensity of the autocorrelation signal received by the CCD module, n1 is the refractive index of the Fresnel biprism, n2 is the refractive index of the optical path adjustment plate, l is the thickness of the optical path adjustment plate, c is the speed of light, and γ is the waveform coefficient of the laser pulse to be tested.

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