Ultrafast spatiotemporal optical field measurement system and method

Abstract

The application discloses a kind of ultrafast space-time light field measurement system and method, the interference light field generated after superposition of to-be-measured laser pulse and reference pulse is dispersed, then wavelength screening element is used to the interference light field after dispersion wavelength screening, the laser light field of target wavelength is obtained, the light field complex amplitude information corresponding to the laser light field of target wavelength is acquired;According to the light field complex amplitude information, the light field corresponding to the to-be-measured laser pulse is reconstructed.The system and method disclosed by the application do not need to regulate and control the delay between signal light and reference light in the measured laser pulse, only need to make the same frequency component interfere in the same spatial position, obtain the interference pattern of each frequency, and the ultrafast space-time light field can be reconstructed.The method provided in the application has the characteristics of convenient implementation, anti-interference, low background noise, low data volume, high measurement efficiency and high measurement result accuracy.

Description

Technical Field

[0001] This invention relates to the field of optical measurement technology, and in particular to an ultrafast spatiotemporal optical field measurement system and method. Background Technology

[0002] Fourier transform pulse modulation technology uses a 4f Fourier transform system to achieve precise control of femtosecond pulses and generate a spatiotemporal structured light field.

[0003] When measuring ultrafast spatiotemporal optical fields, time-resolved measurement methods are needed to comprehensively characterize the spatiotemporal optical field. In existing technologies, interferometry techniques based on delayed scanning of signal and reference beams are commonly used to reconstruct the ultrafast spatiotemporal optical field by accumulating a large amount of delayed interference fringe data. However, this method requires control of the delay between the signal and reference beams, resulting in low efficiency and measurement results that cannot meet the accuracy requirements.

[0004] Therefore, existing technologies need further improvement. Summary of the Invention

[0005] In view of the shortcomings of the above-mentioned related technologies, the purpose of this invention is to provide an ultrafast spatiotemporal optical field measurement system and method, which overcomes the defects of existing ultrafast spatiotemporal optical field measurement systems and methods that cannot efficiently and accurately reconstruct ultrafast spatiotemporal optical fields.

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

[0007] In a first aspect, this application provides an ultrafast spatiotemporal optical field measurement system, comprising:

[0008] Diffraction elements are 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;

[0009] A wavelength filtering element is disposed in the optical path of the interference light field to filter the wavelength of the interference light field after dispersion separation, so as to obtain a laser light field with the target wavelength.

[0010] An imaging element is disposed in the optical path of the laser light field of the target wavelength, and is used to acquire the complex amplitude information of the light field corresponding to the laser light field of the target wavelength, so that the light field reconstruction element can reconstruct the light field corresponding to the laser pulse under test according to the complex amplitude information of the light field.

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

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

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

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

[0015] The laser pulse to be tested and the reference pulse are superimposed, and then passed through the first pulse beam splitter and transmitted to the diffraction element; and the laser light field of the target wavelength is transmitted from the wavelength selection element and then incident on the first pulse beam splitter, and after passing through the first pulse beam splitter, it is transmitted to the imaging element.

[0016] Optionally, the system further includes a second pulse beam splitter and a spectrometer;

[0017] The second pulse beam splitter is located between the first pulse beam splitter and the imaging element. It is used to receive the beam output by the first pulse beam splitter and split the beam into two parts. One part of the beam is input to the imaging element and the other part is input to the spectrometer.

[0018] The spectrometer is located on one side of the second pulse beam splitter and is used to receive the beam split by the second pulse beam splitter and to detect the wavelength corresponding to the received beam.

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

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

[0021] Optionally, both the first pulse beam splitter and the second pulse beam splitter are semi-reflective lenses.

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

[0023] Secondly, this application discloses an ultrafast spatiotemporal light field measurement method, which includes:

[0024] Dispersion separation is performed on the interference light field generated by the superposition of the laser pulse to be tested and the reference pulse;

[0025] Wavelength selection is performed on the interference light field after dispersion separation to obtain the laser light field of the target wavelength;

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

[0027] The optical field corresponding to the laser pulse under test is reconstructed based on the optical field complex amplitude information.

[0028] Optionally, the step of performing wavelength selection on the dispersion-separated interference light field to obtain the laser light field of the target wavelength specifically includes:

[0029] The position of the slit where the interference light field is incident is adjusted to select the laser light field of the target wavelength.

[0030] Beneficial effects:

[0031] This embodiment discloses an ultrafast spatiotemporal optical field measurement system and method. It utilizes a diffraction element to perform dispersion separation on the interference optical field generated by the superposition of the laser pulse to be measured and a reference pulse. Then, a wavelength selection element is used to filter the wavelength of the dispersion-separated interference optical field to obtain the laser optical field of the target wavelength, acquiring the complex amplitude information of the optical field corresponding to the target wavelength laser optical field. The optical field corresponding to the laser pulse to be measured is reconstructed based on the complex amplitude information. The system and method disclosed in this embodiment do not require adjusting the delay between the signal light and the reference light in the laser pulse to be measured; they only need to ensure that components of the same frequency interfere at the same spatial position, and obtain the interference patterns of each frequency to reconstruct the ultrafast spatiotemporal optical field. The method provided in this application has the characteristics of convenient implementation, anti-interference, low background noise, low data volume, high measurement efficiency, and high measurement accuracy. Attached Figure Description

[0032] Figure 1 This is a schematic diagram of the ultrafast spatiotemporal optical field measurement system in this embodiment;

[0033] Figure 2 This is a schematic diagram of the ultrafast spatiotemporal optical field measurement system in this embodiment;

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

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

[0036] Figure 5 This is a diagram showing the light field intensity distribution of different frequencies of light 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 embodiment shows the light intensity distribution diagram of light intensity at a specific frequency by setting slits according to the spatial distribution of light at different frequencies to allow light of that frequency to pass through.

[0038] Figure 7This is a diagram showing the light field intensity distribution of different frequencies of light on the xy plane after the collimated light to be tested passes through the slit in this embodiment.

[0039] Figure 8 This is the light field recovery intensity map of the spatiotemporal ultrafast light field under test on the xt plane in this embodiment;

[0040] Figure 9 This is a flowchart of the steps of the ultrafast spatiotemporal optical field measurement method in this embodiment. Detailed Implementation

[0041] To make the objectives, technical solutions, and advantages of this application clearer, the following detailed description is provided in conjunction with the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the scope of this application.

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

[0043] In pulse modulation techniques, Fourier transform pulse modulation is commonly used. This technique, utilizing a 4f Fourier transform system, enables precise control of femtosecond pulses, thereby obtaining spatiotemporal structured light fields that meet various requirements. Ultrafast spatiotemporal light fields, exhibiting ultrafast time characteristics and high peak power, have important applications in the light-matter interaction of nonlinear optics. For example, spatiotemporal optical vortices (STOVs) can be considered a type of ultrafast spatiotemporal light field. Their phase singularity is located in the xt plane, carrying orbital angular momentum (OAM), exhibiting different light field dynamics. Because the STOV light field structure is embedded in the xt plane, its intensity distribution cannot be directly captured by imaging devices; imaging devices only obtain the time-averaged intensity distribution, making it difficult to fully reveal its dynamic characteristics. Therefore, time-resolved measurement methods are needed to comprehensively characterize spatiotemporal optical vortices.

[0044] Current methods for measuring ultrafast spatiotemporal optical fields typically employ interferometry techniques based on delayed scanning of the signal and reference beams. By accumulating a large amount of delayed interference fringe data, accurate reconstruction of the STOV three-dimensional distribution is achieved. However, this method not only has high hardware requirements, complex operation, and long reconstruction time, but also suffers from noise and system efficiency issues, affecting the contrast of the interference fringes and the accuracy of the phase data. Therefore, it may introduce additional noise and errors. Existing reconstruction methods need to address problems such as high hardware resource consumption, reconstruction time field, and interference from noise and system effects.

[0045] To address the aforementioned problems in the prior art, this embodiment provides an ultrafast spatiotemporal optical field measurement system and method. First, the interference optical field generated by the superposition of the laser pulse to be measured and the reference pulse is subjected to dispersion separation. Then, the wavelength of the dispersion-separated interference optical field is filtered to obtain the laser optical field of the target wavelength, and the complex amplitude information of the optical field corresponding to the target wavelength laser optical field is acquired. The optical field corresponding to the laser pulse to be measured is reconstructed based on the complex amplitude information. The system and method disclosed in this embodiment do not require adjusting the delay between the signal light and the reference light in the laser pulse to be measured. They only need to ensure that components of the same frequency interfere at the same spatial position and acquire the interference patterns of each frequency to reconstruct the ultrafast spatiotemporal optical field. Therefore, the method of this application is convenient to implement, highly efficient, and highly accurate.

[0046] The following description, in conjunction with the accompanying drawings, further illustrates an ultrafast spatiotemporal optical field measurement system and method disclosed in this embodiment.

[0047] Firstly, this application provides an ultrafast spatiotemporal optical 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 tested and the reference pulse. In this embodiment, the light field formed by the laser pulse to be tested is the ultrafast spatiotemporal light field to be tested. The laser pulse to be tested and the reference pulse (without time delay) are combined and incident on the diffraction element. Due to the diffraction effect of the diffraction element, light fields of different frequencies can be separated in space, thereby achieving modulation of light of different frequencies. The diffraction element can be a diffractive 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 etched or lens-shaped, causing diffraction and interference phenomena as light passes through them. A metasurface grating is an optical element that combines metasurface technology and grating technology. The design of a metasurface grating is typically based on the simultaneous application of the generalized Snell's law and the grating equations, calculating the phase gradient of the desired unit structure. Then, a suitable unit structure is selected through dispersion modulation and arranged according to a certain pattern to form the 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 utilizes the orientation change of liquid crystals under the influence of an electric or magnetic field to control the propagation direction and polarization state of light. A liquid crystal grating typically consists of two glass substrates filled with liquid crystal molecules. A conductive film is coated on the substrates to form electrodes, and an alignment layer is then coated on the electrodes to control the alignment of the liquid crystal molecules in a certain direction.

[0050] Wavelength filtering element 133 is disposed in the optical path of the interference light field and is used to filter the wavelength of the interference light field after dispersion separation to obtain the laser light field of the target wavelength.

[0051] The wavelength filtering element is positioned behind the diffraction element to receive the light beam output by the diffraction element. Therefore, the wavelength filtering element is placed in the optical path of the interference light field output by the diffraction element to filter the wavelength of the light field after processing by the diffraction element, so as to obtain the laser light field of the target wavelength.

[0052] Specifically, a wavelength filtering element is an optical component used to separate light of a specific wavelength or wavelength range from polychromatic light. In specific implementations, the wavelength filtering element can be a filter, grating, tunable wavelength selector, prism, or slit. In one embodiment, to achieve the filtering of light of a specific wavelength in an interference light field, the wavelength filtering element uses a slit; by adjusting the position of the slit within the interference light field, the target wavelength light field is filtered. Furthermore, the slit can also be designed to be replaced by a metasurface or liquid crystal to achieve the wavelength filtering function.

[0053] Imaging element 17 is disposed in the optical path of the laser light field of the target wavelength, and is used to acquire the complex amplitude information of the light field corresponding to the laser light field of the target wavelength.

[0054] The laser light field of the target wavelength output by the wavelength selection element is sent to the imaging element. After being captured by the imaging element, the complex amplitude information of the corresponding laser light field is obtained. This imaging element is used to collect the complex amplitude information of the light field at a certain wavelength, so it needs to be able to detect the interference pattern and meet the resolution requirements. For example, a color CCD camera with 1920×1080 pixels and a resolution of 5-8µm can be used. In specific implementations, the resolution (size of a single pixel) is 7µm.

[0055] The optical field reconstruction element is used to reconstruct the optical field corresponding to the laser pulse under test based on the complex amplitude information of the optical field. Once the imaging element acquires the complex amplitude information of the optical field corresponding to the laser optical field of the target wavelength, it can reconstruct the ultrafast spatiotemporal optical field corresponding to the laser pulse under test based on the acquired complex amplitude information. Specifically, the interference complex amplitude information of all frequencies recorded by the imaging unit can be used to recover the ultrafast spatiotemporal optical field under test through an inverse Fourier transform from the frequency domain to the time domain.

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

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

[0058] The collimating element receives the light beam output from the diffraction element, collimates the received beam, and then inputs it to the wavelength selection element. This collimating element can be a cylindrical lens, a metasurface cylindrical mirror made using metasurface and lens technologies, or a liquid crystal cylindrical mirror made using liquid crystal and lens technologies. A liquid crystal cylindrical mirror typically consists of a liquid crystal layer and a cylindrical lens. The liquid crystal molecules in the liquid crystal layer can rotate under the influence of an electric field, thereby controlling the transmission and reflection of light. The cylindrical lens has a cylindrical surface that can focus incident light in a certain dimension and stretch the image. When light passes through the liquid crystal cylindrical mirror, the liquid crystal molecules rotate according to the change in the electric field, thereby changing the direction of light propagation. Simultaneously, the cylindrical lens focuses and stretches the light.

[0059] Furthermore, combined Figure 1 As shown, a first pulse beam splitter 15 is provided in 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 15 and are transmitted to the diffraction element 131; and the laser light field of the target wavelength is transmitted from the wavelength selection element 133 and then incident on the first pulse beam splitter 15, and after passing through the first pulse beam splitter 15, it is transmitted to the imaging element 17.

[0060] In practice, the first pulse beam splitter uses a semi-reflective lens. Since a semi-reflective lens can achieve 50% reflection and 50% transmission of incident light energy, it can split the beam of the superimposed laser pulse and the reference pulse into two beams.

[0061] Furthermore, combined Figure 1 As shown, the system also includes a second pulse beam splitter 16 and a spectrometer 18; the second pulse beam splitter 16 is located between the first pulse beam splitter 15 and the imaging element 17, and is used to receive the beam output by the first pulse beam splitter 15 and split the beam into two parts, one part of which 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 splitter and is used to receive the beam split by the second pulse beam splitter and to detect the wavelength corresponding to the received beam. The wavelength information detected by the spectrometer corresponds to the wavelength information filtered by the wavelength filtering unit, and the wavelength information detected by the spectrometer is used to verify the wavelength information filtered by the wavelength filtering unit. At the same time, the target wavelength to be filtered in the wavelength filtering unit can also be adjusted by the wavelength detected by the spectrometer to obtain accurate measurement results of the ultrafast spatiotemporal optical field to be measured.

[0063] The system further includes a reflective element 14; the reflective element 14 is located on the optical path of the laser light field of the target wavelength output by the wavelength filtering element 133, and is used to reflect the light in the laser light field of the received 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 splitter 15.

[0064] In the measurement system disclosed in this embodiment, a reflective element reflects the light beam output from the wavelength selection element back to the collimating element and the diffraction element. After passing through the first pulse beam splitter and the second pulse beam splitter, the beam is received by the imaging unit. Both the first pulse beam splitter and the second pulse beam splitter are semi-reflective mirrors. The light, resulting from the superposition of the reference pulse and the measured laser pulse, is reflected by the first pulse beam splitter to the diffraction element. After dispersion separation by the diffraction element, it is transmitted to the collimation element. The collimation element collimates the received beam before it is input to the wavelength selection element. After passing through the wavelength selection element, the light field of the target wavelength is transmitted to the reflection element. Since the wavelength selection element, collimation element, and diffraction element are arranged sequentially in front of the reflection element, the light field of the target wavelength incident on the reflection element, after reflection, passes sequentially through the wavelength selection element, collimation element, and diffraction element before being input to the first pulse beam splitter. After transmission through the first pulse beam splitter, it is input to the second pulse beam splitter. The second pulse beam splitter splits the received beam into two beams, one of which is input to the imaging unit, where the complex amplitude information of the measured light field is received. The amplitude and phase spatiotemporal structure of the measured ultrafast light field are reconstructed through algorithms and data processing, thus achieving the reconstruction of the measured ultrafast spatiotemporal light field.

[0065] Combination Figure 2 The diagram shown is a schematic representation of the test system disclosed in this embodiment. Wherein, E(x,y,t) represents the ultrafast spatiotemporal optical field to be tested; Let E(x,y,t) be the light field after undergoing a one-dimensional Fourier transform (FT) from the time domain to the frequency domain, as shown in Equation (1-1).

[0066]

[0067] Where T is the total duration of the pulse.

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

[0069]

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

[0071] for The light field after two-dimensional filtering (2D filtering); for The light field after undergoing the two-dimensional inverse Fourier transform (2D iFT) is shown in equation (1-3).

[0072]

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

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

[0075]

[0076] Where Ω represents the total number of pulse frequencies after the Fourier Transform (FT).

[0077] Based on the above principle, it can be seen that when the interference information between the ultrafast spatiotemporal optical field under test and the reference light at all frequencies is collected, the optical field intensity map of the ultrafast spatiotemporal optical field under test on the xt plane can be recovered after the inverse Fourier transform from the frequency domain to the time domain, thus realizing the reconstruction of the ultrafast spatiotemporal optical field under test.

[0078] The following description uses a spatiotemporal optical vortex (STOV) as the ultrafast spatiotemporal optical field to be tested, a diffraction element as a grating, a collimation element as a cylindrical mirror, a wavelength selection element as a slit, and an imaging element as a CCD camera to further illustrate the testing method disclosed in this invention.

[0079] Combination Figure 3 As shown, a first-order STOV (E(x,y,t), E(x,y,ω)) is combined with a reference pulse and then fed into a first pulse beam splitter. The beam is reflected by the first pulse beam splitter to a grating. The grating performs dispersion separation on the interference field after the STOV and reference pulse are combined, causing light of different frequencies in the interference field to be spatially separated (in the X direction), forming a dispersion-separated interference field. The modulation of different frequencies ω is shown in equation (1-5):

[0080]

[0081] Where β is the dispersion coefficient of the grating; ω0 is the center frequency of the incident pulse. In practical 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 light frequencies (ω0+Δω, ω0, ω0-Δω) after passing through the grating. Figure 4 Figure (a) shows the light field intensity distribution of light with frequency ω0-Δω after passing through the grating. Figure 4 Figure (b) shows the light field intensity distribution of light with frequency ω0 after passing through the grating. Figure 4 Figure (c) shows the light field intensity distribution of light with frequency ω0+Δω after passing through the grating. The spatially dispersed light, after passing through the cylindrical lens, is then focused and collimated in the x-direction. As shown in modulation formula (1-6).

[0083]

[0084] Where F is the focal length of the cylindrical lens. Cylindrical lenses are used to collimate spatially dispersed spectra, and their focal lengths are typically between 150mm and 300mm. For example... Figure 5 The images shown are the light field patterns of three different frequencies of light ω0+Δω, ω0, and ω0-Δω after passing through a cylindrical lens. Figure 5 Figure (a) shows the pattern of the light field after light with frequency ω0-Δω passes through a cylindrical lens. Figure 5 Figure (b) shows the pattern of the light field after light with frequency ω0 passes through a cylindrical lens. Figure 5 Figure (c) shows the pattern of the light field after light with frequency ω0+Δω passes through a cylindrical lens. Figure 6 The figures shown are light intensity distribution diagrams for allowing light of a specific frequency to pass through slits set according to the spatial distribution of light of different frequencies. Figure 6 Figure (a) shows the light intensity distribution through the slit, which is set according to the spatial distribution of light with frequency ω0-Δω. Figure 6 Figure (b) shows the light intensity distribution through the slit, which is set according to the spatial distribution of light at frequency ω0. Figure 6 Figure (c) shows the light intensity distribution through the slit set according to the spatial distribution of light with frequency ω0+Δω. According to the Fourier transform translation theorem, the frequency shift of the spatial frequency domain is calculated. The position of the slit for different frequencies of light is shown in Equation (1-7), and the pulse modulation of the slit is shown in Equation (1-8).

[0085]

[0086]

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

[0088] In practice, the slit width is less than 1 mm, and the wavelength of the filtered light is changed by altering the slit's position. Ideally, a specific slit should only allow a single frequency of light field to pass through. However, in reality, because the frequencies of ultrafast spatiotemporal light fields are not discrete but continuously distributed, the light passing through a specific slit will be interfered with by light of other frequencies. For example... Figure 7 The image shows the light field intensity distribution of three different frequencies of light after passing through the slit. Finally, the spectrum reflected by the reflecting element (mirror) passes sequentially through the cylindrical lens. The grating, the first pulse beam splitter, and the second pulse beam splitter, along with the corresponding wavelengths monitored by the spectrometer and the interference complex amplitude information of all frequencies recorded by the imaging unit, allow for the subsequent recovery of the measured ultrafast spatiotemporal optical field (E″(x,y,t)) through a frequency-domain to time-domain inverse Fourier transform. The recovered first-order STOV is as follows: Figure 8 As shown.

[0089] In practical implementation, after the imaging element (e.g., a color CCD camera) acquires the complex amplitude information, it needs to reconstruct the acquired complex amplitude information to obtain the reconstructed complex amplitude information. Then, based on the reconstructed complex amplitude information, the ultrafast spatiotemporal optical field is reconstructed. First, the color CCD camera detects and records the interference fringes, and transmits the recorded interference fringes to the optical field reconstruction element (e.g., a computer system). The optical field reconstruction element performs a Fourier transform on the acquired interference fringes to obtain the spectral distribution of the interference fringes. Through frequency domain filtering, the zero-order spectral component and the first-order spectral component are separated. An inverse Fourier transform is performed on the first-order spectral component to obtain the phase distribution of the wavefront of the laser pulse to be measured and the amplitude modulation function of the interference fringes. An inverse Fourier transform is performed on the zero-order spectral component to obtain the background light intensity of the interference fringes. Combining the combined amplitude modulation function of the laser and the background light intensity, the amplitude distribution of the laser to be measured is calculated. Finally, the ultrafast spatiotemporal optical 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 rather achieves the detection of ultrafast spatiotemporal optical fields by acquiring interference fringe data at various frequencies. Compared with traditional measurement methods, this method does not require adjusting the delay between the signal light and the reference light. It only needs to use the synergistic effect of the grating and the cylindrical mirror to make the components of the same frequency interfere at the same spatial position. By adjusting the position of the slit and capturing the interference patterns of various frequencies with the imaging device, the ultrafast spatiotemporal optical field can be reconstructed. The measurement method designed in this application aims to provide a more efficient and accurate measurement means for the study of spatiotemporal structured optical fields.

[0091] Based on the aforementioned measurement system, this embodiment also provides an ultrafast spatiotemporal optical field measurement method, such as... Figure 9 As shown, the measurement method includes:

[0092] Step S1: Perform dispersion separation on the interference light field generated by the superposition of the laser pulse to be tested and the reference pulse.

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

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

[0095] Combination Figure 1 As shown, the scanning and filtering system 13, composed of a grating, a cylindrical lens, and a slit, filters the wavelength of the interference light field to obtain the laser light field of the target wavelength. The target wavelength is set to correspond to the center wavelength of the laser pulse corresponding to the ultrafast spatiotemporal light field to be measured.

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

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

[0098] Step S4: Reconstruct the optical field corresponding to the laser pulse to be tested based on the optical field complex amplitude information.

[0099] Furthermore, the step of performing wavelength selection on the dispersion-separated interference light field to obtain the laser light field of the target wavelength specifically includes:

[0100] The position of the slit where the interference light field is incident is adjusted to select the laser light field of the target wavelength.

[0101] When reconstructing the ultrafast spatiotemporal optical field corresponding to the laser pulse under test based on the complex amplitude information of the optical field, MATLAB is generally used to reconstruct the optical field based on the complex amplitude information of the optical field.

[0102] Specifically, the steps for reconstructing the ultrafast spatiotemporal optical field based on the complex amplitude information of the optical field include: obtaining time-resolved measurement information based on the complex amplitude distribution of the optical field to obtain the optical field information of the laser pulse under test at different time points; and then constructing the ultrafast spatiotemporal optical field corresponding to the laser pulse under test based on the time-resolved measurement information. This ultrafast spatiotemporal optical field will contain information such as the light intensity and phase of the laser pulse at different time points and spatial locations.

[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. The incident ultrafast spatiotemporal light field can be recovered by the complex amplitude information of the light field at 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 references to terms such as "one embodiment," "some embodiments," "example," "specific example," or "some examples," etc., indicate that a specific feature, structure, material, or characteristic described in connection with that embodiment or example is included in at least one embodiment or example of this application. In this specification, the illustrative expressions of the above terms do not necessarily refer to the same embodiment or example. Furthermore, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in one or more embodiments or examples. Moreover, without contradiction, those skilled in the art can combine and integrate the different embodiments or examples described in this specification, as well as the features of different embodiments or examples.

[0105] The embodiments described above are merely illustrative of several implementation methods of this application, and while the descriptions are relatively specific and detailed, they should not be construed as limiting the scope of the invention patent. It should be noted that those skilled in the art can make various modifications and improvements without departing from the concept of this application, and these all fall within the protection scope of this application. Therefore, the protection scope of this patent application should be determined by the appended claims.

Claims

1. An ultrafast spatiotemporal optical field measurement system, characterized in that, include: Diffraction elements are 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; A wavelength filtering element is disposed in the optical path of the interference light field to filter the wavelength of the interference light field after dispersion separation, so as to obtain a laser light field with the target wavelength. An imaging element is disposed in the optical path of the laser light field at the target wavelength, and is used to acquire the complex amplitude information of the laser light field corresponding to the target wavelength, so that the optical field reconstruction element can reconstruct the light field corresponding to the laser pulse under test based on the complex amplitude information of the laser light field. The diffraction element is a metasurface grating or a liquid crystal grating; A first pulse beam splitter element is provided in the optical path of the interference optical field and the laser optical field of the target wavelength; The laser pulse to be tested and the reference pulse are superimposed and then transmitted to the diffraction element through the first pulse beam splitter. 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 splitter element, and after passing through the first pulse beam splitter element, it is transmitted to the imaging element; the imaging element records the interference complex amplitude information of all frequencies, and recovers the ultrafast spatiotemporal light field to be measured through the inverse Fourier transform from the frequency domain to the time domain. The system also includes: a reflective element; The reflective element is located in the optical path of the laser light field of the target wavelength output by the wavelength selection element, and is used to reflect the light in the laser light field of the received target wavelength so that the reflected light passes through the collimating element and the diffraction element in sequence and is input to the first pulse beam splitter. The system also includes a second pulse beam splitter and a spectrometer; The second pulse beam splitter is located between the first pulse beam splitter and the imaging element. It is used to receive the beam output by the first pulse beam splitter and split the beam into two parts. One part of the beam is input to the imaging element and the other part is input to the spectrometer. The spectrometer is located on one side of the second pulse beam splitter and is used to receive the beam split by the second pulse beam splitter and to detect the wavelength corresponding to the received beam. First, an imaging element is used to detect and record the interference fringes. The recorded interference fringes are then transmitted to an optical field reconstruction element. The optical field reconstruction element performs a Fourier transform on the acquired interference fringes to obtain the spectral distribution of the interference fringes. Through frequency domain filtering, the zero-order spectral component and the first-order spectral component are separated. An inverse Fourier transform is performed on the first-order spectral component to obtain the phase distribution of the wavefront of the laser pulse to be tested and the amplitude modulation function of the interference fringes. An inverse Fourier transform is performed on the zero-order spectral component to obtain the background light intensity of the interference fringes. Combining the amplitude modulation function of the laser and the background light intensity, the amplitude distribution of the laser to be tested is calculated. Finally, the ultrafast spatiotemporal optical field to be tested is reconstructed based on the amplitude distribution of the laser to be tested.

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

3. The ultrafast spatiotemporal light field measurement system of claim 2, wherein, The collimating element is a cylindrical mirror, a metasurface cylindrical mirror, or a liquid crystal cylindrical mirror; the wavelength filtering element is a slit, a metasurface slit, or a liquid crystal slit grating.

4. The ultrafast spatiotemporal light field measurement system of claim 1, wherein, Both the first pulse beam splitter and the second pulse beam splitter are semi-reflective lenses.

5. The ultrafast spatiotemporal light field measurement system of claim 1, wherein, The imaging element is a color CCD camera, and the light field reconstruction element is a computer.

6. A method of ultrafast spatiotemporal light field measurement, comprising: The ultrafast spatiotemporal optical field measurement method, applied to the ultrafast spatiotemporal optical field measurement system as described in any one of claims 1-5, comprises: Dispersion separation is performed on the interference light field generated by the superposition of the laser pulse to be tested and the reference pulse; Wavelength selection is performed on the interference light field after dispersion separation to obtain the laser light field of the target wavelength; Obtain the complex amplitude information of the laser field corresponding to the target wavelength; The optical field corresponding to the laser pulse under test is reconstructed based on the optical field complex amplitude information. The diffraction element is a metasurface grating or a liquid crystal grating; A first pulse beam splitter element is provided in the optical path of the interference optical field and the laser optical field of the target wavelength; The laser pulse to be tested and the reference pulse are superimposed, and then passed through the first pulse beam splitter and transmitted to the diffraction element; and the laser light field of the target wavelength is transmitted from the wavelength selection element and then incident on the first pulse beam splitter, and after passing through the first pulse beam splitter, it is transmitted to the imaging element; the imaging element records the interference complex amplitude information of all frequencies, and recovers the ultrafast spatiotemporal light field to be tested through the inverse Fourier transform from the frequency domain to the time domain.

7. The ultrafast spatiotemporal light field measurement method of claim 6, wherein, The specific steps for performing wavelength selection on the dispersion-separated interference light field to obtain the laser light field of the target wavelength are as follows: The position of the slit where the interference light field is incident is adjusted to select the laser light field of the target wavelength.

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