Ultra-short light pulse transverse second harmonic measurement system for inhibiting retroreflection light

Abstract

The invention relates to an ultra-short light pulse transverse second harmonic device for suppressing retroreflection light, which comprises a polarizing beam splitter arranged in the direction of a detected ultra-short pulse light beam, and is used for transmitting a first polarized component of the detected ultra-short pulse to form a first polarized light beam and reflecting a second polarized component of the detected ultra-short pulse to form a second polarized light beam; the first wave plate is used for converting the first polarized light beam into first turning circularly polarized light to form a first converted light beam; the second wave plate is used for converting the second polarized light beam into second turning circularly polarized light to form a second converted light beam; and the first reflector group and the second reflector group respectively enable the first conversion light beam and the second conversion light beam to vertically enter the disordered nonlinear medium in opposite directions and generate transverse second harmonics in the disordered nonlinear medium. By adopting the ultra-short light pulse transverse second harmonic device for inhibiting the retroreflection light, the retroreflection light introduced into a reverse collinear light path can be inhibited at low cost, and the damage to front-end systems such as a light source and the like is prevented.

Description

Technical Field

[0001] The present invention relates to the technical field of ultrafast optical measurement and characterization, and particularly to an ultrashort optical pulse transverse second harmonic measurement system for suppressing retroreflected light. Background Art

[0002] With the continuous iterative update of laser science and technology, ultrashort optical pulses have gradually become widely used light sources and are increasingly applied in various industries, becoming an essential tool in all fields. Common industrial applications include optical communication, laser cutting, and microfabrication, etc.; they are also widely used in scientific research, such as in applications like ultrafast spectroscopy analysis, observing the dynamic behavior of electrons, measuring the dynamic characteristics of complex DNA molecules, and monitoring chemical reactions. Therefore, the demand for ultrashort optical pulses in various fields is becoming increasingly stringent. To ensure the precise application of these ultrashort optical pulses in these fields, it is crucial to accurately monitor the parameters of ultrashort optical pulses.

[0003] Traditional ultrashort optical pulse measurement systems use nonlinear crystals to generate and measure sum-frequency second harmonics. However, due to complex problems such as phase matching conditions and temperature tuning, they have high requirements for instrument accuracy and high operating costs. Some scholars have proposed the idea of using the transverse second harmonic effect to perform single-shot measurement of the ultrashort pulse width to overcome the problems of strict phase matching conditions required by conventional nonlinear materials, dependence on temperature, and narrow matching bandwidth. However, the reported technical methods will generate high-intensity retroreflected light, posing a major safety threat to front-end instruments such as femtosecond laser sources. Summary of the Invention

[0004] Based on this, the objective of the present invention is to provide an ultrashort optical pulse transverse second harmonic measurement system for suppressing retroreflected light, which can achieve high-precision single-shot measurement of ultrashort optical pulses while being able to completely suppress the retroreflected light introduced in the reverse collinear optical path and prevent damage to front-end systems such as light sources.

[0005] An ultrashort optical pulse transverse second harmonic device for suppressing retroreflected light includes a polarization beam splitter disposed in the direction of the ultrashort pulse to be measured, which transmits the first polarization component of the ultrashort pulse to be measured to form a first polarized beam and reflects the second polarization component of the ultrashort pulse to be measured to form a second polarized beam; wherein, the first polarization component and the second polarization component are orthogonal;

[0006] A first wave plate that converts the first polarized beam into a first circularly polarized light of a first rotation direction to form a first conversion beam;

[0007] A second wave plate that converts the second polarized beam into a second circularly polarized light of a second rotation direction to form a second conversion beam; wherein, the first rotation direction and the second rotation direction are opposite rotations;

[0008] The first mirror group changes the propagation direction of the first converted light beam to form a first incident light beam;

[0009] The second mirror group changes the propagation direction of the second converted light beam to form a second incident light beam; and

[0010] A disordered nonlinear medium, where the first incident light beam and the second incident light beam are incident perpendicular to the surface of the disordered nonlinear medium; wherein, the first incident light beam and the second incident light beam generate a transverse second harmonic wave and a corresponding transverse second harmonic wave autocorrelation signal inside the disordered nonlinear medium.

[0011] Compared with the existing ultrashort light pulse transverse second harmonic wave device, the ultrashort light pulse transverse second harmonic wave device for suppressing retroreflected light of the present invention can achieve suppression of retroreflected light in the optical path at low cost by using a quarter-wave plate to generate two circularly polarized light beams with opposite rotation directions and using these two circularly polarized light beams to excite the transverse second harmonic wave autocorrelation signal, ensuring the safety of the front-end system in the optical path.

[0012] Further, both the first wave plate and the second wave plate are quarter-wave plates, which respectively convert two linearly polarized light beams from a polarization beam splitter into circularly polarized light beams and restore the circularly polarized light beams returned after passing through the disordered nonlinear medium to linearly polarized light beams in the original polarization state.

[0013] Further, the first mirror group includes a first mirror and a second mirror, and the first mirror is arranged between the second mirror and the first wave plate; the second mirror group includes a third mirror and a fourth mirror, and the third mirror is arranged between the fourth mirror and the second wave plate.

[0014] Further, it further includes at least one translation stage, and the translation stage is arranged at the first mirror and the second mirror. By controlling the translation stage to move the first mirror and the second mirror, the optical path of the first converted light beam is changed, so that the coincidence position of the first incident light beam and the second incident light beam inside the disordered nonlinear medium moves along the collinear direction of the first incident light beam and the second incident light beam.

[0015] Further, it further includes at least one translation stage, and the translation stage is arranged at the first mirror and the third mirror. By controlling the translation stage to move the first mirror and the third mirror, the coincidence position of the first incident light beam and the second incident light beam inside the disordered nonlinear medium moves along the direction perpendicular to the collinearity of the first incident light beam and the second incident light beam.

[0016] Further, it further includes a first aperture diaphragm and a second aperture diaphragm. The first aperture diaphragm is disposed between the disordered nonlinear medium and the first mirror group to change the energy attenuation degree of the first incident light beam. The second aperture diaphragm is disposed between the disordered nonlinear medium and the second mirror group to change the energy attenuation degree of the second incident light beam.

[0017] Further, it further includes a focusing lens. The focusing lens is disposed between the laser generating unit and the polarization beam splitter to focus the initial light beam so that the initial light beam is focused inside the disordered nonlinear medium.

[0018] Further, it includes the above-mentioned ultrashort optical pulse transverse second harmonic generation device for suppressing retroreflected light and a measurement unit. The measurement unit receives the transverse second harmonic and the corresponding transverse second harmonic autocorrelation signal, measures the spatial intensity distribution of the transverse second harmonic autocorrelation signal therein and performs image analysis to obtain the parameter information of the initial ultrashort optical pulse.

[0019] Further, the measurement unit includes an imaging amplification system, a CCD, and a processor. The imaging amplification system collects the transverse second harmonic and the corresponding autocorrelation signal generated inside the disordered nonlinear medium and performs amplification processing on them. The CCD records the amplified signal image. The processor is connected to the CCD, and the signal image is displayed in real time on the processor window and the parameter information of the initial ultrashort optical pulse is analyzed and obtained.

[0020] Further, the parameter information of the initial ultrashort optical pulse is processed and analyzed in the following manner: The first acquisition image when the autocorrelation signal can be observed is recorded by the CCD. The first acquisition image includes the autocorrelation signal and the background signal. The translation stage is adjusted to move the autocorrelation signal out of the lens of the CCD, and the second acquisition image at this time is recorded. The second acquisition image includes the background signal. The first acquisition image and the second acquisition image are subtracted by the processor to obtain a filtered image. The filtered image includes the corresponding autocorrelation signal. The data software is used in the processor to identify and process the filtered image to obtain a clear envelope of the transverse second harmonic autocorrelation signal. Corresponding analysis is performed on the envelope of the transverse second harmonic autocorrelation signal, thereby obtaining the parameter information of the initial ultrashort optical pulse.

[0021] For better understanding and implementation, the present invention will be described in detail below with reference to the accompanying drawings. Description of the Drawings

[0022] Figure 1 It is a structural diagram of the ultrashort optical pulse transverse second harmonic generation measurement system for suppressing retroreflected light of the present invention.

[0023] Figure 2Schematic diagram of the collision of two counter-rotating circularly polarized light beams in the ultra-short optical pulse transverse second harmonic measurement system for suppressing retroreflected light of the present invention.

[0024] Figure 3 Curve graph of the corresponding transverse second harmonic signal when the polarization rotation angle changes at the coincidence point of the first incident light beam and the second incident light beam in the disordered nonlinear medium in the ultra-short optical pulse transverse second harmonic measurement system for suppressing retroreflected light of the present invention.

[0025] Figure 4 Transverse second harmonic image generated by the collision of the first incident light beam and the second incident light beam in the disordered nonlinear medium in the ultra-short optical pulse transverse second harmonic measurement system for suppressing retroreflected light of the present invention.

[0026] Figure 5 For Figure 4 Autocorrelation signal image after filtering the background of the second harmonic signal.

[0027] Figure 6 According to Figure 5 Fitting graph of the autocorrelation signal extracted from the transverse second harmonic image with the harmonic background filtered as described above. Detailed implementation manner

[0028] The applicant carefully analyzed the existing ultra-short optical pulse measurement methods using the transverse second harmonic effect and found that in the current transverse second harmonic measurement methods, the safety threats to front-end instruments such as femtosecond lasers are due to the existence of high-intensity retroreflected light in the collision optical path. Therefore, the applicant believes that it is necessary to suppress the retroreflected light in the system. However, the traditional method of suppressing retroreflected light is to use an optical isolator adapted to ultrafast lasers, which is relatively costly. Thus, the applicant believes that it is necessary to design a transverse second harmonic measurement system that can suppress retroreflected light in the optical path at a relatively low cost. By using a quarter-wave plate to generate two circularly polarized lights with opposite rotation directions and using these two circularly polarized lights to excite the transverse second harmonic autocorrelation signal; the applicant strictly proved its feasibility theoretically and actually tested the results of the two counter-rotating circularly polarized lights exciting the transverse second harmonic autocorrelation signal to prove that this design not only achieves the effect of suppressing retroreflected light in the system but also ensures the accuracy of the ultrafast laser pulse width measurement result.

[0029] Example 1

[0030] Based on this, please refer to Figure 1 The ultra-short optical pulse transverse second harmonic measurement system for suppressing retroreflected light of the present invention includes a laser generation unit 1, a focusing lens 2, a polarization beam splitter 3, a first wave plate 41, a second wave plate 42, a first mirror group, a second mirror group, a first aperture stop 61, a second aperture stop 62, a disordered nonlinear medium 7, and a measurement unit 8.

[0031] The laser generating unit 1 continuously emits an initial light beam containing the ultrashort pulse to be measured. The initial light beam is linearly polarized light, and its wavelength is preferably 800 nm. It can be understood that the ultrashort pulse to be measured can have various forms, including a single ultrashort laser pulse or an ultrashort laser pulse train, etc.

[0032] The focusing lens 2 is an ordinary convex lens, which is arranged in the propagation direction of the initial light beam to focus the initial light beam to form a focused light beam, so that the initial light beam is focused inside the disordered nonlinear medium 7 after passing through a series of devices.

[0033] The polarization beam splitter 3 can separate the linearly polarized light into mutually orthogonal p-polarization component and s-polarization component, and is arranged in the propagation direction of the focused light beam. Specifically, the p-polarization component in the transmitted focused light beam forms the first polarized light beam, and the s-polarization component in the reflected focused light beam forms the second polarized light beam. It can be understood that the separation directions of the p-polarization component and the s-polarization component of the incident light beam by the polarization beam splitter 3 can be interchanged, that is, the s-polarization component in the transmitted focused light beam forms the first polarized light beam, and the p-polarization component in the reflected focused light beam forms the second polarized light beam. At this time, other polarization-matching settings in the system are also interchanged synchronously.

[0034] Both the first wave plate 41 and the second wave plate 42 are quarter-wave plates, which can convert the incident linearly polarized light into circularly polarized light. Specifically, the first wave plate 41 is arranged in the propagation direction of the first polarized light beam to convert the first polarized light beam into a left-handed circularly polarized light to form a first converted light beam. The second wave plate 42 is arranged in the propagation direction of the second polarized light beam to convert the second polarized light beam into a right-handed circularly polarized light to form a second converted light beam. It can be understood that the first converted light beam is not limited to being left-handed circularly polarized light. When the linear polarization direction of the initial light beam is changed or the separation rule of the polarization beam splitter 3 is changed, the first converted light beam can also be right-handed circularly polarized light. At this time, the second converted light beam is left-handed circularly polarized light, as long as the first converted light beam and the second converted light beam are anti-rotating circularly polarized lights to each other. It can be understood that the second converted light beam will irradiate on the first wave plate 41 after passing through the disordered nonlinear medium 7, and the first wave plate 41 can also convert it into linearly polarized light, thus avoiding the influence of the return light in the optical path.

[0035] The first mirror group is arranged in the propagation direction of the first converted light beam to reflect the first converted light beam to change its propagation direction to form a first incident light beam, so as to be perpendicularly incident. The first mirror group includes a first mirror 511 and a second mirror 512, and the first mirror 511 is arranged between the second mirror 512 and the first wave plate 41.

[0036] The second mirror group is arranged in the propagation direction of the second converted light beam, and reflects the second converted light beam to change its propagation direction to form a second incident light beam, so as to be perpendicularly incident. The second mirror group includes a third mirror 521 and a fourth mirror 522, and the third mirror 521 is arranged between the fourth mirror 522 and the second wave plate 42.

[0037] The first aperture stop 61 is arranged between it and the first mirror group, and can change its own aperture size, so as to change the energy attenuation degree of the first incident light beam, and prevent the first incident light beam from having too high energy to damage the disordered nonlinear medium 7.

[0038] The second aperture stop 62 is arranged between it and the second mirror group, and can change its own aperture size, so as to change the energy attenuation degree of the second incident light beam, and prevent the second incident light beam from having too high energy to damage the disordered nonlinear medium 7.

[0039] The disordered nonlinear medium 7 is nanocrystalline glass, which is a composite material formed by embedding nonlinear nanocrystals in the glass. This material can generate transverse second harmonic waves under certain conditions. Specifically, the first incident light beam and the second incident light beam are perpendicularly transmitted through the surface of the disordered nonlinear medium 7 along opposite propagation directions, and the first incident light beam and the second incident light beam are strictly collinear inside the disordered nonlinear medium 7, generating transverse second harmonic waves and transverse second harmonic autocorrelation signals inside the disordered nonlinear medium 7, so as to form a detection light beam perpendicular to the propagation direction of the first incident light beam. It should be noted that the detection light beam generated by the transverse second harmonic effect of nanocrystalline glass exists in the entire cross section perpendicular to the propagation direction of the first incident light beam. In addition, it can be understood that using nanocrystalline glass as the disordered nonlinear medium 7 of the transverse second harmonic measurement system for suppressing retroreflected light of the present invention takes into account the cost and convenience of nanocrystalline glass, and it is not limited that only nanocrystalline glass can be used. Other materials that can generate transverse second harmonic waves can also meet the requirements, and those skilled in the art can make corresponding adjustments according to the actual situation.

[0040] The measurement unit 8 is arranged in the propagation direction of the detection light beam, receives the detection light beam, measures the spatial intensity distribution of the transverse second harmonic autocorrelation signal therein, and performs image analysis to obtain the parameter information of the initial ultrashort light pulse. Please refer to Figure 2 , when two counter-rotating circularly polarized light beams with the same frequency propagate in opposite directions, observing along the propagation direction of one of the light beams, it can be seen that at a certain point where the two light beams spatially coincide, the rotating electric vectors of the two will always maintain a fixed angle. Similarly, there is a rotation angle that linearly changes with the spatial position at the coincidence point of the first incident light beam and the second incident light beam inside the disordered nonlinear medium 7, and the rotation angle is determined by the meeting position of the two light beams; Please refer to Figure 3 ,Figure 3 The spatial intensity envelope of the transverse second harmonic autocorrelation signal and the variation of the spatial intensity with the rotation angle in the amplification curve are shown: when the rotation angle is 0 / 180°, the electric vectors of the first incident beam and the second incident beam will generate a peak of the transverse second harmonic autocorrelation signal at this position inside the disordered nonlinear medium 7. With the change of the spatial position, the relative angle between the two optical electric vectors also changes rapidly, resulting in a synchronous rapid oscillation of the intensity of the excited autocorrelation signal. However, the change frequency of the autocorrelation signal intensity is equivalent to the spatial frequency of the incident light, and the modulation effect generated will be averaged by the detector, without affecting the measurement and its accuracy of the transverse second harmonic autocorrelation signal.

[0041] Example 2

[0042] In this embodiment 2, compared with embodiment 1, at least one translation stage (not shown in the figure) is added. Through the translation stage, the first mirror group or the second mirror group can be moved, so that the coincidence position of the first incident beam and the second incident beam inside the disordered nonlinear medium 7 is moved, realizing fine adjustment of the excitation position of the disordered nonlinear medium 7. Specifically, translation stages are arranged at the first mirror 511 and the second mirror 512, and the translation stages are controlled to move the first mirror 511 and the second mirror 512 to change the optical path of the first converted beam, so that the coincidence position of the first incident beam and the second incident beam inside the disordered nonlinear medium 7 moves along the collinear direction of the first incident beam and the second incident beam. In addition, another translation stage can be arranged at the third mirror 521, and the translation stage is controlled to move the first mirror 511 and the third mirror 521, so that the coincidence position of the first incident beam and the second incident beam inside the disordered nonlinear medium 7 moves along the direction perpendicular to the collinear direction of the first incident beam and the second incident beam. The remaining structures are exactly the same as those in embodiment 1 and will not be described in detail here.

[0043] In order to further ensure the accuracy of the measurement of the transverse second harmonic of the ultrashort optical pulse transverse second harmonic measurement system for suppressing retroreflected light of the present invention, the applicant uses the measurement unit 8 to obtain the optical image after the collision of the first incident beam and the second incident beam, and analyzes the transverse second harmonic to fit the transverse second harmonic autocorrelation signal function, so as to confirm the accuracy of the measurement.

[0044] Specifically, the measurement unit 8 includes an imaging and amplification system, a CCD, and a processor. The imaging and amplification system collects the transverse second harmonic and the corresponding autocorrelation signal generated inside the disordered nonlinear medium 7 and performs amplification processing on them. The amplified signal image is recorded by the CCD located at the image plane. The processor is connected to the CCD, and the signal image is displayed in real time on the processor window. The processor analyzes to obtain the parameter information of the initial ultrashort optical pulse.

[0045] Please refer toFigure 4 , Figure 4 shows the optical image after the collision of the first incident light beam and the second incident light beam. At this time, the processor records that the first acquisition image when the autocorrelation signal can be observed is "autocorrelation signal + background". It can be seen that the brightness at the position where the transverse second harmonic autocorrelation signal is generated is the most obvious. Subsequently, the translation stage is adjusted to move the autocorrelation signal out of the lens of the CCD, and the second acquisition image at this time is recorded as "background"; please refer to Figure 5 , Figure 5 shows the image of the transverse second harmonic and the corresponding autocorrelation signal in the optical image after the collision of the first incident light beam and the second incident light beam. By subtracting the first acquisition image and the second acquisition image through the processor, the background signal is cancelled at this time, and only the Figure 5 filtered image shown in is left, which contains the corresponding autocorrelation signal. The data software is used in the processor to identify and process the filtered image to obtain a clear envelope of the transverse second harmonic autocorrelation signal; the envelope of the transverse second harmonic autocorrelation signal is analyzed accordingly to obtain the parameter information of the initial ultrashort optical pulse.

[0046] Please refer to Figure 6 , Figure 6 shows the transverse second harmonic function fitted according to the transverse second harmonic image after filtering the harmonic background. It can be seen that the peak of the fitted transverse second harmonic is single and obvious, which proves that the ultrashort optical pulse transverse second harmonic measurement system for suppressing retroreflected light of the present invention can ensure the measurement accuracy of the transverse second harmonic autocorrelation signal.

[0047] The ultrashort optical pulse transverse second harmonic measurement system for suppressing retroreflected light of the present invention generates two circularly polarized light beams with opposite rotation directions by using a quarter-wave plate, and uses these two circularly polarized light beams to excite the transverse second harmonic autocorrelation signal, and analyzes it to obtain the parameter information of the initial ultrashort optical pulse, which not only realizes the retroreflected light suppression effect of the system at low cost, but also ensures the accuracy of the measurement result of the ultrafast laser pulse width.

[0048] The above-described embodiments only represent several implementation manners of the present invention, and their descriptions are relatively specific and detailed, but they should not be construed as limiting the scope of the invention patent. It should be noted that for those of ordinary skill in the art, without departing from the concept of the present invention, several modifications and improvements can still be made, and the present invention also intends to include these modifications and deformations.

Claims

1. An ultrashort optical pulse transverse second harmonic generation device for suppressing retroreflected light, characterized in that: Including the following components arranged in the direction of the ultra-short pulsed beam to be measured: A polarization beam splitter that transmits the first polarization component of the ultra-short pulsed beam to be measured to form a first polarized beam and reflects the second polarization component of the ultra-short pulsed beam to be measured to form a second polarized beam; wherein, the first polarization component and the second polarization component are orthogonal to each other; A first wave plate that converts the first polarized beam into a first circularly polarized light with a first sense of rotation to form a first converted beam; A second wave plate that converts the second polarized beam into a second circularly polarized light with a second sense of rotation to form a second converted beam; wherein, the first sense of rotation and the second sense of rotation are opposite to each other; A first mirror group that changes the propagation direction of the first converted beam to form a first incident beam; A second mirror group that changes the propagation direction of the second converted beam to form a second incident beam; A disordered nonlinear medium, where the first incident beam and the second incident beam are incident perpendicular to the surface of the disordered nonlinear medium; wherein, the first incident beam and the second incident beam generate transverse second harmonics and corresponding transverse second harmonic autocorrelation signals inside the disordered nonlinear medium.

2. The device for suppressing retroreflected light of an ultrashort optical pulse with transverse second harmonic according to claim 1, characterized in that: Both the first wave plate and the second wave plate are quarter-wave plates, which respectively convert the two linearly polarized light beams from the polarization beam splitter into circularly polarized light and restore the circularly polarized light returned after passing through the disordered nonlinear medium to linearly polarized light in the original polarization state.

3. The ultra-short optical pulse transverse second harmonic generation device for suppressing retroreflected light according to claim 2, wherein: The first mirror group includes a first mirror and a second mirror, and the first mirror is arranged between the second mirror and the first wave plate; the second mirror group includes a third mirror and a fourth mirror, and the third mirror is arranged between the fourth mirror and the second wave plate.

4. The device for suppressing retroreflected light of an ultrashort optical pulse for transverse second harmonic generation according to claim 3, characterized in that: It further includes at least one translation stage, which is arranged at the first mirror and the second mirror, and controls the translation stage to move the first mirror and the second mirror to change the optical path of the first converted beam, so that the coincidence position of the first incident beam and the second incident beam inside the disordered nonlinear medium moves along the collinear direction of the first incident beam and the second incident beam.

5. The device for suppressing retroreflected light of an ultrashort optical pulse for transverse second harmonic according to claim 3, wherein: It further includes at least one translation stage, which is arranged at the first mirror and the third mirror, and controls the translation stage to move the first mirror and the third mirror, so that the coincidence position of the first incident beam and the second incident beam inside the disordered nonlinear medium moves along the direction perpendicular to the collinearity of the first incident beam and the second incident beam.

6. The ultra-short optical pulse transverse second harmonic generation device for suppressing retroreflected light according to any one of claims 3 to 5, characterized in that: It further includes a first aperture stop and a second aperture stop. The first aperture stop is arranged between the disordered nonlinear medium and the first mirror group to change the energy attenuation degree of the first incident beam, and the second aperture stop is arranged between the disordered nonlinear medium and the second mirror group to change the energy attenuation degree of the second incident beam.

7. The device for suppressing retroreflected light and generating a transverse second harmonic of an ultrashort optical pulse according to claim 6, wherein: It further includes a focusing lens, which is arranged between the laser generating unit and the polarization beam splitter to focus the initial beam so that the initial beam is focused inside the disordered nonlinear medium.

8. An ultrashort optical pulse transverse second harmonic measurement system for suppressing retroreflected light, characterized in that: An apparatus and a measurement unit for suppressing retroreflected light of an ultrashort optical pulse as described in claims 1-7, wherein the measurement unit receives the transverse second harmonic wave and the corresponding transverse second harmonic wave autocorrelation signal, measures the spatial intensity distribution of the transverse second harmonic wave autocorrelation signal therein and performs image analysis to obtain parameter information of the initial ultrashort optical pulse.

9. The ultra-short optical pulse transverse second harmonic measurement system for suppressing retroreflected light according to claim 8, characterized in that: The measurement unit includes an imaging amplification system, a CCD and a processor; the imaging amplification system collects the transverse second harmonic wave and the corresponding autocorrelation signal generated inside the disordered nonlinear medium and performs amplification processing on them; the CCD records the amplified signal image; the processor is connected to the CCD, and the signal image is displayed in real time on the window of the processor and the parameter information of the initial ultrashort optical pulse is analyzed and obtained.

10. The ultra-short optical pulse transverse second harmonic measurement system for suppressing retroreflected light according to claim 9, wherein: The parameter information of the initial ultrashort optical pulse is processed and analyzed in the following manner: the first acquisition image when the autocorrelation signal can be observed is recorded by the CCD, and the first acquisition image includes the autocorrelation signal and the background signal; the translation stage is adjusted to move the autocorrelation signal outside the lens of the CCD, and the second acquisition image at this time is recorded, and the second acquisition image includes the background signal; the processor subtracts the first acquisition image from the second acquisition image to obtain a filtered image, and the filtered image includes the corresponding autocorrelation signal; the data software is used in the processor to identify and process the filtered image to obtain a clear envelope of the transverse second harmonic wave autocorrelation signal; the envelope of the transverse second harmonic wave autocorrelation signal is analyzed accordingly to obtain the parameter information of the initial ultrashort optical pulse.

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