Ultrafast space-time light field measurement system and method

Abstract

The invention discloses an ultrafast space-time light field measurement system and method, and the method comprises the steps: carrying out the dispersion separation of an interference light field generated after the superposition of a to-be-measured laser pulse and a reference pulse, and carrying out the wavelength screening of the interference light field after the dispersion separation through a wavelength screening element, and obtaining a laser light field with a target wavelength, acquiring light field complex amplitude information corresponding to the laser light field of the target wavelength; and reconstructing according to the light field complex amplitude information to obtain a light field corresponding to the laser pulse to be measured. According to the system and the method disclosed by the invention, the delay between the signal light and the reference light in the measured laser pulse does not need to be regulated and controlled, and the ultrafast space-time light field can be reconstructed only by enabling the same-frequency components to interfere in the same spatial position to obtain the interference pattern of each frequency. The method provided by the invention has the characteristics of convenience in implementation, interference resistance, low background noise, low data volume, high measurement efficiency and high measurement result accuracy.

Description

Technical Field

[0001] The present invention relates to the field of optical measurement technology, and in particular to an ultrafast space-time optical field measurement system and method. Background Art

[0002] Fourier transform pulse control technology uses the 4f Fourier transform system to achieve fine control of femtosecond pulses and generate space-time structured light fields.

[0003] When measuring ultrafast space-time light fields, a measurement method with time resolution capability is needed to fully characterize the space-time light field. In the prior art, the interferometric measurement technology based on delayed scanning of signal light and reference light is usually used to reconstruct the ultrafast space-time light field by accumulating a large amount of delayed interference fringe data. However, this method requires the control of the delay between the signal light and the reference light, which is inefficient and the measurement results cannot meet the accuracy requirements.

[0004] Therefore, the prior art needs further improvement. Summary of the invention

[0005] In view of the deficiencies in the above-mentioned related technologies, the purpose of the present invention is to provide an ultrafast space-time light field measurement system and method, so as to overcome the defect that the ultrafast space-time light field measurement system and method in the prior art cannot meet the requirements of efficiently and accurately reconstructing the ultrafast space-time light field.

[0006] The technical solution adopted by the present invention to solve the technical problem is as follows:

[0007] In a first aspect, the present application provides an ultrafast spatiotemporal light field measurement system, which includes:

[0008] A diffraction element is used to perform dispersion separation on the interference light field generated by superposition of the laser pulse to be measured and the reference pulse;

[0009] A wavelength screening element is arranged on the optical path of the interference light field and is used to perform wavelength screening on the interference light field after dispersion separation to obtain a laser light field of a target wavelength;

[0010] The imaging element is arranged on the optical path of the laser light field of the target wavelength, and is used to obtain the light field complex amplitude information corresponding to the laser light field of the target wavelength, so that the light field reconstruction element reconstructs the light field corresponding to the laser pulse to be measured according to the light field complex amplitude information.

[0011] Optionally, a collimating element is further provided between the diffraction element and the wavelength screening element;

[0012] The collimating element is used to collimate the light of the interference light field received after dispersion separation, and output it to the wavelength screening element.

[0013] Optionally, the diffraction element is a grating, a metasurface grating or a liquid crystal grating; the collimating element is a cylindrical mirror, a metasurface cylindrical mirror, a liquid crystal cylindrical mirror; and the wavelength screening element is a slit, a metasurface slit or a liquid crystal slit grating.

[0014] Optionally, a first pulse beam splitting element is provided on the optical path of the interference light field and the laser light field of the target wavelength;

[0015] After the laser pulse to be measured and the reference pulse are superimposed, they pass through the first pulse beam splitting element and are transmitted to the diffraction element; and, after the laser light field of the target wavelength is transmitted from the wavelength screening element, it is incident on the first pulse beam splitting element, and after passing through the first pulse beam splitting element, it is input to the imaging element.

[0016] Optionally, the system further comprises a second pulse beam splitting element and a spectrometer;

[0017] The second pulse beam splitting element is located between the first pulse beam splitting element and the imaging element, and is used to receive the light beam output by the first pulse beam splitting element, and split the light beam into two parts, one part of the light beam is input to the imaging element, and the other part is input to the spectrometer;

[0018] The spectrometer is located at one side of the second pulse beam splitting element, and is used to receive the light beam split by the second pulse beam splitting element, and is used to detect the wavelength corresponding to the received light beam.

[0019] Optionally, the system further comprises: a reflective element;

[0020] The reflective element is located on the optical path of the laser light field of the target wavelength output by the wavelength screening element, and is used to reflect the light in the received laser light field of the target wavelength so that the reflected light passes through the collimating element and the diffraction element in sequence and is input into the first pulse beam splitting element.

[0021] Optionally, the first pulse beam splitting element and the second pulse beam splitting element are both half-reflecting and half-mirror elements.

[0022] Optionally, the imaging element is a color CCD camera, and the light field reconstruction element is a computer.

[0023] In a second aspect, the present application discloses a method for measuring ultrafast spatiotemporal light fields, which includes:

[0024] Perform dispersion separation on the interference light field generated by the superposition of the laser pulse to be measured and the reference pulse;

[0025] Perform wavelength screening on the interference light field after dispersion separation to obtain a laser light field of target wavelength;

[0026] Obtaining the complex amplitude information of the light field corresponding to the laser light field of the target wavelength;

[0027] The light field corresponding to the laser pulse to be measured is reconstructed according to the light field complex amplitude information.

[0028] Optionally, the step of performing wavelength screening on the interference light field after dispersion separation to obtain a laser light field of a target wavelength is specifically:

[0029] The slit position of the interference light field is adjusted to filter out the laser light field of the target wavelength.

[0030] Beneficial effects:

[0031] The present embodiment discloses an ultrafast space-time light field measurement system and method, which uses a diffraction element to perform dispersion separation on the interference light field generated by the superposition of the laser pulse to be measured and the reference pulse, and then uses a wavelength screening element to perform wavelength screening on the interference light field after dispersion separation to obtain a laser light field of a target wavelength, and obtain the light field complex amplitude information corresponding to the laser light field of the target wavelength; the light field corresponding to the laser pulse to be measured is reconstructed according to the light field complex amplitude information. The system and method disclosed in the present embodiment do not need to adjust the delay between the signal light and the reference light in the laser pulse to be measured, but only need to make the same-frequency components interfere at the same spatial position, obtain the interference pattern of each frequency, and then the ultrafast space-time light field can be reconstructed. The method provided in the present application has the characteristics of convenient implementation, anti-interference, low background noise, low data volume, high measurement efficiency and high accuracy of measurement results. BRIEF DESCRIPTION OF THE DRAWINGS

[0032] Figure 1 Schematic diagram of the structure of the ultrafast space-time light field measurement system of this embodiment;

[0033] Figure 2 This is a schematic diagram of the principle of the ultrafast space-time light field measurement system in this embodiment;

[0034] Figure 3 is a light field intensity distribution diagram of the first-order space-time optical vortex to be measured on the xt plane in this embodiment;

[0035] Figure 4 This is a light field intensity distribution diagram of light of different frequencies on the xy plane after the interference light field is dispersed by the grating in this embodiment;

[0036] Figure 5 This is a light field intensity distribution diagram of light of different frequencies on the xy plane after the interference light field dispersed by the grating in this embodiment is focused and collimated by the cylindrical lens;

[0037] Figure 6 This is a light intensity distribution diagram of setting slits according to the spatial distribution of light of different frequencies to allow light of a specific frequency to pass through in this embodiment;

[0038] Figure 7The light field intensity distribution diagram corresponding to the xy plane of light of different frequencies after the collimated light to be measured passes through the slit in this embodiment;

[0039] Figure 8 is a light field recovery intensity diagram of the space-time ultrafast light field to be measured on the xt plane in this embodiment;

[0040] Fig. 9 4 is a flow chart of the steps of the ultrafast space-time light field measurement method in this embodiment. DETAILED DESCRIPTION

[0041] In order to make the purpose, technical solution and advantages of the present application more clearly understood, the present application is further described in detail below in conjunction with the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain the present application and are not used to limit the present application.

[0042] Femtosecond lasers have unique advantages such as ultra-short spatial resolution, ultra-wide spectral bandwidth, and ultra-high peak power. They have not only become the core driving force in advanced manufacturing, precision measurement, optical communications and other precision fields, but have also promoted the development of basic and applied sciences such as physics, chemistry, and biomedicine. The ultrafast control technology of femtosecond pulses lies in the precise control of their phase, amplitude, polarization and other dimensions, thereby shaping femtosecond pulses of various shapes to meet the needs of scientific research and industry.

[0043] In the technology of pulse control, Fourier transform pulse control technology is usually used. This technology uses the 4f Fourier transform system to achieve fine control of femtosecond pulses, and then obtains space-time structure light fields that meet different needs. Among them, ultrafast space-time light fields have important applications in the interaction between light and matter in nonlinear optics because they show ultrafast time characteristics and high peak power. For example: Spatiotemporal Optical Vortices (STOV) can be regarded as an ultrafast space-time light field, whose phase singularity is located in the xt plane, carrying transverse orbital angular momentum (OAM), and showing different light field dynamic characteristics. Since the STOV light field structure is embedded in the xt plane, its light intensity distribution cannot be directly captured by imaging equipment. The imaging device only obtains the light intensity distribution after time averaging, so it is difficult to fully reveal its dynamic characteristics. Therefore, a measurement method with time resolution capability is required to fully characterize the space-time optical vortex.

[0044] At present, the method based on measuring ultrafast space-time light fields is usually based on the interferometric measurement technology of delayed scanning of signal light and reference light, which achieves accurate reconstruction of the three-dimensional distribution of STOV by accumulating a large amount of delayed interference fringe data. However, this method not only has high hardware requirements, complex operation, and long reconstruction time, but also has noise and system efficiency, which affects the contrast of interference fringes and the accuracy of phase data, and may introduce additional noise and errors. Therefore, the reconstruction method in the prior art needs to face the problems of large hardware resource consumption, reconstruction time field, noise and system effect interference.

[0045] In order to solve the above problems in the prior art, this embodiment provides an ultrafast space-time light field measurement system and method, firstly, the interference light field generated by the superposition of the laser pulse to be measured and the reference pulse is dispersed and separated, and then the interference light field after dispersion separation is wavelength screened to obtain the laser light field of the target wavelength, and the light field complex amplitude information corresponding to the laser light field of the target wavelength is obtained; the light field corresponding to the laser pulse to be measured is reconstructed according to the light field complex amplitude information. The system and method disclosed in this embodiment do not need to adjust the delay between the signal light and the reference light in the laser pulse to be measured, but only need to make the same frequency components interfere at the same spatial position, obtain the interference pattern of each frequency, and then the ultrafast space-time light field can be reconstructed. Therefore, the method of this application is easy to implement, efficient and accurate.

[0046] The following is a further description of an ultrafast space-time light field measurement system and method disclosed in this embodiment in conjunction with the accompanying drawings.

[0047] In a first aspect, the present application provides an ultrafast spatiotemporal light field measurement system, such as Figure 1 As shown, the measurement system includes:

[0048] The diffraction element 131 is used to perform dispersion separation on the interference light field generated by the superposition of the laser pulse to be measured and the reference pulse. In this embodiment, the light field formed by the laser pulse to be measured is the ultrafast spatiotemporal light field to be measured. The laser pulse to be measured and the reference pulse (without time delay) are combined and incident on the diffraction element. Due to the diffraction effect of the diffraction element, the light fields of different frequencies can be separated in space, thereby realizing the modulation of light of different frequencies. The diffraction element can be a diffraction optical element (DOE), a grating or a phase plate, etc.

[0049] In one implementation, the diffraction element is a grating, a metasurface grating or a liquid crystal grating. A grating is an optical device composed of a large number of parallel slits of equal width and spacing. These slits can be in the shape of notches or lenses, so that light diffracts and interferes when passing through. A metasurface grating is an optical element that combines metasurface technology with grating technology. The design of a metasurface grating is usually based on the combination of generalized Snell's law and grating equations, and the phase gradient of the required unit structure is obtained by calculation. Then, the appropriate unit structure is selected by dispersion control, and arranged according to a certain rule to form a metasurface grating. This design process gives the metasurface grating specific diffraction and reflection characteristics. A liquid crystal grating is an optical element that combines liquid crystal technology and grating technology. It uses the orientation change of liquid crystal under the action of an electric field or a magnetic field to control the propagation direction and polarization state of light. A liquid crystal grating is usually composed of two glass substrates, which are filled with liquid crystal molecules, and a conductive film is coated on the substrate to form an electrode. An alignment layer is then coated on the electrode to control the liquid crystal molecules to be arranged in a certain direction.

[0050] The wavelength screening element 133 is arranged on the optical path of the interference light field, and is used to perform wavelength screening on the interference light field after dispersion separation to obtain a laser light field of a target wavelength.

[0051] The wavelength screening element is arranged behind the diffraction element to receive the light beam output by the diffraction element. Therefore, the wavelength screening element is arranged on the optical path of the interference light field output by the diffraction element to perform wavelength screening on the light field processed by the diffraction element to obtain a laser light field of the target wavelength.

[0052] Specifically, the wavelength screening element is an optical element used to separate light of a specific wavelength or wavelength range from complex light. In a specific implementation, the wavelength screening element can be a filter, a grating, a tunable wavelength selector, a prism or a slit. In one embodiment, in order to achieve the screening of light of a specific wavelength in the interference light field, the wavelength screening element uses a slit, and the screening of the target wavelength light field is achieved by adjusting the position of the slit in the interference light field. Furthermore, the slit can also be designed to be replaced by a metasurface or a liquid crystal to achieve the function of wavelength screening.

[0053] The imaging element 17 is arranged on the optical path of the laser light field of the target wavelength, and is used to obtain the light field complex amplitude information corresponding to the laser light field of the target wavelength.

[0054] The laser light field of the target wavelength output by the wavelength screening element is output to the imaging element. After being captured by the imaging element, the light field complex amplitude information corresponding to the laser light field is obtained. The imaging element is used to collect the light field complex amplitude information of a certain wavelength, so it needs to be able to detect interference patterns and have a resolution that meets the requirements. For example, a color CCD camera with a pixel of 1920×1080 and a resolution of 5 to 8um is used. In specific implementation, the resolution (single pixel size) is 7um.

[0055] The light field reconstruction element is used to reconstruct the light field corresponding to the laser pulse to be measured according to the light field complex amplitude information. When the imaging element obtains the light field complex amplitude information corresponding to the laser light field of the target wavelength, the ultrafast space-time light field corresponding to the laser pulse to be measured can be reconstructed based on the obtained light field complex amplitude information. Specifically, the interference complex amplitude information of all frequencies recorded by the imaging unit can be used to restore the ultrafast space-time light field to be measured through an inverse Fourier transform from the frequency domain to the time domain.

[0056] Furthermore, combined with Figure 2 As shown, in order to obtain a more accurate wavelength screening effect, a collimating element 132 is further provided between the diffraction element 131 and the wavelength screening element 133 .

[0057] The collimating element is used to collimate the light of the interference light field received after dispersion separation, and output it to the wavelength screening element.

[0058] The collimating element receives the light beam output by the diffraction element, and after collimating the received light beam, it is input into the wavelength screening element. The collimating element can be a cylindrical lens, or a super-surface cylindrical mirror made by super-surface technology and lens technology, or a liquid crystal cylindrical mirror made by liquid crystal technology and lens technology. The liquid crystal cylindrical mirror is usually composed of a liquid crystal layer and a cylindrical lens. The liquid crystal molecules in the liquid crystal layer can rotate under the action of the electric field, thereby controlling the transmission and reflection of light. The cylindrical lens has a cylindrical surface that can make the incident light gather in a certain dimension and stretch the image. When light passes through the liquid crystal cylindrical mirror, the liquid crystal molecules will rotate according to the change of the electric field, thereby changing the propagation direction of the light. At the same time, the cylindrical lens will gather and stretch the light.

[0059] Furthermore, combined with Figure 1 As shown, a first pulse beam splitter element 15 is provided on the optical path of the interference light field and the laser light field of the target wavelength. After the laser pulse to be measured and the reference pulse are superimposed, they pass through the first pulse beam splitter element 15 and are transmitted to the diffraction element 131; and after the laser light field of the target wavelength is transmitted from the wavelength screening element 133, it is incident on the first pulse beam splitter element 15, and after passing through the first pulse beam splitter element 15, it is input to the imaging element 17.

[0060] In specific implementation, the first pulse beam splitting element adopts a half-reflecting half-mirror. Since the half-reflecting half-mirror can achieve 50% reflection and 50% transmission of the incident light energy, the light beam after the laser pulse to be measured and the reference pulse are superimposed can be split into two beams.

[0061] Furthermore, combined with Figure 1 As shown, the system also includes a second pulse beam splitting element 16 and a spectrometer 18; the second pulse beam splitting element 16 is located between the first pulse beam splitting element 15 and the imaging element 17, and is used to receive the light beam output by the first pulse beam splitting element 15, and split the light beam into two parts, one part of the light beam is input to the imaging element 17, and the other part is input to the spectrometer 18.

[0062] The spectrometer is located on one side of the second pulse beam splitting element, and is used to receive the light beam split by the second pulse beam splitting element, and is used to detect the wavelength corresponding to the received light beam. The wavelength information detected by the spectrometer corresponds to the wavelength information screened by the wavelength screening unit, and the wavelength information detected by the spectrometer is used to verify the wavelength information screened by the wavelength screening unit. At the same time, the target wavelength to be screened in the wavelength screening unit can also be adjusted by the wavelength detected by the spectrometer, so as to obtain accurate measurement results of the ultrafast space-time light field to be measured.

[0063] The system also includes: a reflecting element 14; the reflecting element 14 is located on the optical path of the laser light field of the target wavelength output by the wavelength screening element 133, and is used to reflect the light in the received laser light field of the target wavelength, so that the reflected light passes through the collimating element 132 and the diffraction element 131 in sequence and is input to the first pulse beam splitting element 15.

[0064] In the measurement system disclosed in this embodiment, the light beam output from the wavelength screening element is reflected back to the collimating element and the diffraction element by the reflecting element, and is received by the imaging unit after passing through the first pulse beam splitting element and the second pulse beam splitting element. The first pulse beam splitting element and the second pulse beam splitting element are both half-reflecting and half-mirror elements. The light after the reference light pulse and the measured laser pulse are superimposed is reflected by the first pulse beam splitter element to the diffraction element, and after dispersion separation by the diffraction element, it is transmitted to the collimation element. After the collimation element collimates the received light beam, it is input to the wavelength screening element. After passing through the wavelength screening element, the light field of the target wavelength is transmitted to the reflection element. Since the wavelength screening element, the collimation element and the diffraction element are arranged in sequence in front of the reflection element, the light field of the target wavelength incident on the reflection element is reflected by the reflection element, and then passes through the wavelength screening unit, the collimation element and the diffraction element in sequence, and then input to the first pulse beam splitter element, and then transmitted through the first pulse beam splitter element to the second pulse beam splitter element. The second pulse beam splitter element divides the received light beam into two beams, one of which is input to the imaging unit, and the imaging unit receives the complex amplitude information of the measured light field. The amplitude and phase space-time structure of the measured space-time ultrafast light field is reconstructed through algorithms and data processing to achieve reconstruction of the measured ultrafast space-time light field.

[0065] Combination Figure 2 FIG. 1 is a schematic diagram of the principle of the test system disclosed in this embodiment. Wherein, E(x, y, t) is the ultrafast spatiotemporal light field to be tested; It is the light field after E(x, y, t) is transformed from time domain to frequency domain through one-dimensional Fourier transform (FT), as shown in formula (1-1).

[0066]

[0067] Where T is the total time the pulse exists.

[0068] for The light field after the spatial two-dimensional Fourier transform (Two dimensional Fourier transform, 2D FT) is shown in formula (1-2).

[0069]

[0070] Wherein, X is the length range of the incident light field, and Y is the width range of the incident light field.

[0071] for Light field after two-dimensional filtering (2DFiltering); for The light field after spatial two-dimensional inverse Fourier transform (2D iFT) is shown in formula (1-3).

[0072]

[0073] Among them, KX is the light field length range after 2D FT, and KY is the light field width range after 2D FT.

[0074] E″(x,y,t) is The final restored light field after the frequency domain to time domain one-dimensional inverse Fourier transform (iFT) is shown in formula (1-4).

[0075]

[0076] Where Ω is the total pulse frequency after FT.

[0077] From the above principle, it can be concluded that when the interference information between the ultrafast space-time light field to be measured and the reference light is collected at all frequencies, the light field intensity diagram of the ultrafast space-time light field to be measured on the xt plane can be restored through an inverse Fourier transform from the frequency domain to the time domain, thereby realizing the reconstruction of the ultrafast space-time light field to be measured.

[0078] The following further illustrates the test method disclosed in the present invention by taking spatiotemporal optical vortices (STOV) as the ultrafast spatiotemporal light field to be tested, the diffraction element as a grating, the collimation element as a cylindrical mirror, the wavelength screening element as a slit, and the imaging element as a CCD camera.

[0079] Combination Figure 3 As shown in FIG. 1 , after the first-order STOV (E(x, y, t), E(x, y, ω)) is combined with the reference pulse, it is transmitted to the first pulse beam splitter element, and is reflected to the grating by the first pulse beam splitter element. The grating performs dispersion separation on the interference light field after the STOV and the reference pulse are combined, so that the light of different frequencies in the interference light field is separated in space (set as the X direction), forming an interference light field after dispersion separation. The modulation of different frequencies ω is shown in formula (1-5):

[0080]

[0081] Wherein, β is the dispersion coefficient of the grating; ω0 is the central frequency of the incident pulse. In a specific implementation, the grating constant can be 600 lines / mm to 1800 lines / mm.

[0082] Figure 4 The figure shows the light field intensity distribution of three selected lights of different frequencies (ω0+Δω, ω0, ω0-Δω) after passing through the grating, where: Figure 4 Figure (a) shows the intensity distribution of the light field after the light with a frequency of ω0-Δω passes through the grating. Figure 4 Figure (b) shows the intensity distribution of the light field after the light with frequency ω0 passes through the grating. Figure 4 Figure (c) shows the intensity distribution of the light field after the light with frequency ω0+Δω passes through the grating. After the spatial dispersion, the light passes through the cylindrical lens and is focused and collimated in the x direction. As shown in the modulation formula (1-6).

[0083]

[0084] Where F is the focal length of the cylindrical lens. The cylindrical lens is used to collimate the spatially dispersed spectrum, and the focal length is generally 150mm to 300mm. Figure 5 The following are the patterns of three different frequency lights ω0+Δω, ω0, ω0-Δω passing through the cylindrical lens light field, where: Figure 5 Figure (a) shows the pattern of the light field of the cylindrical lens with a frequency of ω0-Δω. Figure 5 Figure (b) shows the pattern of the light field of the light with a frequency of ω0 passing through the cylindrical lens. Figure 5 Figure (c) shows the pattern of the light field of light with a frequency of ω0+Δω passing through a cylindrical lens. Figure 6 The following are the light intensity distribution diagrams of setting slits according to the spatial distribution of light of different frequencies to allow light of a specific frequency to pass through, where: Figure 6 Figure (a) shows the intensity distribution of light passing through the slit set according to the spatial distribution of light with a frequency of ω0-Δω. Figure 6 Figure (b) shows the intensity distribution of light passing through the slit set according to the spatial distribution of light with a frequency of ω0. Figure 6 Figure (c) shows the intensity distribution of light passing through the slit set according to the spatial distribution of light with a frequency of ω0+Δω. According to the Fourier transform translation theorem, the frequency shift in the spatial frequency domain is calculated. The position of the slit for light of different frequencies is shown in formula (1-7), and the pulse modulation of the slit is shown in formula (1-8).

[0085]

[0086]

[0087] Among them, G τ is the gate function.

[0088] In specific implementation, the slit width is less than 1 mm, and the wavelength of the screened light is changed by changing the slit position. Ideally, a specific slit only allows a single frequency of light to pass through, but in practice, since the frequency of the ultrafast space-time light field is not discrete but continuously distributed, the light passing through a specific slit will be interfered by light of other frequencies. Figure 7 The figure shows the intensity distribution of the light field of three different frequency lights after passing through the slit. Finally, the spectrum reflected by the reflective element (reflector) passes through the cylindrical lens in turn. The grating, the first pulse beam splitter and the second pulse beam splitter are used to monitor the corresponding wavelength through a spectrometer, and the interference complex amplitude information of all frequencies is recorded by an imaging unit. The ultrafast space-time light field (E″(x, y, t)) to be measured can be restored by inverse Fourier transform from frequency domain to time domain. The restored first-order STOV is as follows: Figure 8 shown.

[0089] In the specific implementation, after the imaging element (such as a color CCD camera) acquires the complex amplitude information, it is necessary to reconstruct the collected complex amplitude information to obtain the reconstructed complex amplitude information, and then reconstruct the ultrafast space-time light field based on the reconstructed complex amplitude information. First, the interference fringes are detected by a color CCD camera, and the interference fringes are recorded, and the recorded interference fringes are transmitted to the light field reconstruction element (such as a computer system), and the light field reconstruction element performs Fourier transform on the acquired interference fringes to obtain the spectrum distribution of the interference fringes. Through frequency domain filtering, the zero-order spectrum component and the first-order spectrum component are separated. The first-order spectrum component is Fourier inverse transformed to obtain the phase distribution of the laser pulse wavefront to be measured and the amplitude modulation function of the interference fringes. The zero-order spectrum component is Fourier inverse transformed to obtain the background light intensity of the interference fringes, and the amplitude distribution of the laser to be measured is calculated based on the combined amplitude modulation function of the laser and the background light intensity. Finally, the ultrafast space-time light field to be measured is reconstructed based on the amplitude distribution of the laser to be measured.

[0090] The measurement method provided in this embodiment does not start from the delay time, but realizes the detection of ultrafast space-time light field by collecting interference fringe data of each frequency. Compared with the traditional measurement method, this measurement method does not need to adjust the delay between the signal light and the reference light. It only needs to make the same frequency components interfere at the same spatial position through the synergy of the grating and the cylindrical reflector, and adjust the slit position to capture the interference pattern of each frequency in the imaging device, so as to reconstruct the ultrafast space-time light field. The measurement method designed in this application aims to provide a more efficient and accurate measurement method for the study of space-time structure light field.

[0091] Based on the above-mentioned measurement system, this embodiment further provides an ultrafast spatiotemporal light field measurement method. Fig. 9 As shown, the measuring method comprises:

[0092] Step S1, performing dispersion separation on the interference light field generated by superposition of the laser pulse to be measured and the reference pulse.

[0093] Combination Figure 1 As shown, a diffraction element (eg, a grating) is used to achieve dispersion separation of the interference light field generated by superposition of the laser pulse to be measured and the reference pulse.

[0094] Step S2: performing wavelength screening on the interference light field after dispersion separation to obtain a laser light field of a target wavelength.

[0095] Combination Figure 1 As shown, the scanning screening system 13 composed of grating, cylindrical lens and slit can screen the wavelength of the interference light field to obtain the laser light field of the target wavelength. The setting of the target wavelength corresponds to the central wavelength of the laser pulse corresponding to the ultrafast spatiotemporal light field to be measured.

[0096] Step S3: Obtaining light field complex amplitude information corresponding to the laser light field of the target wavelength.

[0097] The light output by the laser light field of the target wavelength can be detected and received by a color CCD camera to obtain the light field complex amplitude information corresponding to the laser light field.

[0098] Step S4: reconstructing the light field corresponding to the laser pulse to be measured according to the light field complex amplitude information.

[0099] Furthermore, the step of performing wavelength screening on the interference light field after dispersion separation to obtain a laser light field of a target wavelength is specifically as follows:

[0100] The slit position of the interference light field is adjusted to filter out the laser light field of the target wavelength.

[0101] When the ultrafast spatiotemporal light field corresponding to the laser pulse to be measured is reconstructed based on the complex amplitude information of the light field, MATLAB is generally used to reconstruct the light field based on the complex amplitude information of the light field.

[0102] Specifically, the steps of reconstructing the ultrafast space-time light field based on the complex amplitude information of the light field include: obtaining time-resolved measurement information based on the complex amplitude distribution of the light field to obtain the light field information of the laser pulse to be measured at different time points, and then constructing the ultrafast space-time light field corresponding to the laser pulse to be measured based on the time-resolved measurement information. The ultrafast space-time light field will contain information such as the light intensity and phase of the laser pulse at different time points and spatial positions.

[0103] The method and system provided in this embodiment only need to adjust the position of the slit and change the spectrum of the transmitted light field, so as to restore the incident ultrafast space-time light field through the complex amplitude information of the light fields of each frequency collected by the imaging unit. Therefore, it is not only convenient to implement, efficient, and anti-interference, but also can obtain accurate measurement results.

[0104] In the description of this specification, the description with reference to the terms "one embodiment", "some embodiments", "example", "specific example", or "some examples" etc. means that the specific features, structures, materials or characteristics described in conjunction with the embodiment or example are included in at least one embodiment or example of the present application. In this specification, the schematic representations of the above terms do not necessarily refer to the same embodiment or example. Moreover, the specific features, structures, materials or characteristics described may be combined in any one or N embodiments or examples in a suitable manner. In addition, those skilled in the art may combine and combine the different embodiments or examples described in this specification and the features of the different embodiments or examples, without contradiction.

[0105] The above-mentioned embodiments only express several implementation methods of the present application, and the descriptions thereof are relatively specific and detailed, but they cannot be understood as limiting the scope of the invention patent. It should be pointed out that, for a person of ordinary skill in the art, several variations and improvements can be made without departing from the concept of the present application, and these all belong to the protection scope of the present application. Therefore, the protection scope of the patent of the present application shall be subject to the attached claims.

Claims

1. An ultrafast spatiotemporal light field measurement system, characterized in that: include: A diffraction element is used to perform dispersion separation on the interference light field generated by superposition of the laser pulse to be measured and the reference pulse; A wavelength screening element is arranged on the optical path of the interference light field and is used to perform wavelength screening on the interference light field after dispersion separation to obtain a laser light field of a target wavelength; The imaging element is arranged on the optical path of the laser light field of the target wavelength, and is used to obtain the light field complex amplitude information corresponding to the laser light field of the target wavelength, so that the light field reconstruction element reconstructs the light field corresponding to the laser pulse to be measured according to the light field complex amplitude information.

2. The ultrafast spatiotemporal light field measurement system according to claim 1, characterized in that: A collimating element is also provided between the diffraction element and the wavelength screening element; The collimating element is used to collimate the light of the interference light field received after dispersion separation, and output it to the wavelength screening element.

3. The ultrafast spatiotemporal light field measurement system according to claim 2, characterized in that: The diffraction element is a grating, a super-surface grating or a liquid crystal grating; the collimating element is a cylindrical mirror, a super-surface cylindrical mirror, a liquid crystal cylindrical mirror; the wavelength screening element is a slit, a super-surface slit or a liquid crystal slit grating.

4. The ultrafast spatiotemporal light field measurement system according to claim 1, characterized in that: A first pulse beam splitting element is provided on the optical path of the interference light field and the laser light field of the target wavelength; After the laser pulse to be measured and the reference pulse are superimposed, they pass through the first pulse beam splitting element and are transmitted to the diffraction element; Furthermore, after the laser light field of the target wavelength is transmitted from the wavelength screening element, it is incident on the first pulse beam splitting element, and after passing through the first pulse beam splitting element, it is input to the imaging element.

5. The ultrafast spatiotemporal light field measurement system according to claim 4, characterized in that: The system also includes a second pulse beam splitting element and a spectrometer; The second pulse beam splitting element is located between the first pulse beam splitting element and the imaging element, and is used to receive the light beam output by the first pulse beam splitting element, and split the light beam into two parts, one part of the light beam is input to the imaging element, and the other part is input to the spectrometer; The spectrometer is located at one side of the second pulse beam splitting element, and is used to receive the light beam split by the second pulse beam splitting element, and is used to detect the wavelength corresponding to the received light beam.

6. The ultrafast spatiotemporal light field measurement system according to claim 4 or 5, characterized in that: The system further comprises: a reflective element; The reflective element is located on the optical path of the laser light field of the target wavelength output by the wavelength screening element, and is used to reflect the light in the received laser light field of the target wavelength so that the reflected light passes through the collimating element and the diffraction element in sequence and is input into the first pulse beam splitting element.

7. The ultrafast spatiotemporal light field measurement system according to claim 5, characterized in that: The first pulse beam splitting element and the second pulse beam splitting element are both half-reflecting and half-mirror elements.

8. The ultrafast spatiotemporal light field measurement system according to claim 1, characterized in that: The imaging element is a color CCD camera, and the light field reconstruction element is a computer.

9. A method for measuring ultrafast space-time light field, characterized in that: include: Perform dispersion separation on the interference light field generated by the superposition of the laser pulse to be measured and the reference pulse; Perform wavelength screening on the interference light field after dispersion separation to obtain a laser light field of target wavelength; Obtaining the complex amplitude information of the light field corresponding to the laser light field of the target wavelength; The light field corresponding to the laser pulse to be measured is reconstructed according to the light field complex amplitude information.

10. The ultrafast spatiotemporal light field measurement method according to claim 9, characterized in that: The step of performing wavelength screening on the interference light field after dispersion separation to obtain the laser light field of target wavelength is specifically as follows: The slit position of the interference light field is adjusted to filter out the laser light field of the target wavelength.

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