A method and device for measuring the space-time structure of attosecond pulses

Abstract

The invention belongs to the technical field of ultrafast laser measurement, and specifically relates to a method and a device for measuring the spatiotemporal structure of an attosecond pulse, comprising: generating an attosecond pulse by driving light, introducing a perturbation light that propagates non-collinearly with the driving light to regulate the generation process of the attosecond pulse, scanning the relative delay between the perturbation light and the driving light to obtain a spatially resolved high-order harmonic spectrum, using a PCGPA algorithm to extract the spatial distribution of near-field harmonics and the spectral distribution on the far-field axis from a two-dimensional modulation diagram of the spatial distribution of the far-field high-order harmonic spectrum and a two-dimensional trace diagram of the spectrum of the attosecond pulse corresponding to the far-field axis, obtaining a spatiotemporally resolved far-field harmonic spectrum based on the spectral distribution on the far-field axis and the spatial distribution of the far-field harmonics obtained by spatial Fourier transform, obtaining a spatiotemporally resolved near-field harmonic spectrum by a spatial Fourier transform relationship, synthesizing a supercontinuum spectrum of near-field and far-field spatiotemporally resolved harmonic spectra to obtain an attosecond pulse, and thus realizing the measurement of the spatiotemporal structure of the attosecond pulse.

Description

Technical Field

[0001] The present invention belongs to the technical field of ultrafast laser measurement, and more specifically, relates to a method and a device for measuring the space-time structure of an attosecond pulse. Background Art

[0002] The radiation of high-order harmonics based on the interaction between strong femtosecond pulse lasers and atoms and molecules is an important way to generate attosecond pulse light sources. The extreme ultraviolet attosecond pulses generated by them have ultra-high time resolution, opening the door to observing ultrafast dynamics in atoms, molecules and solids. As a result, attosecond time-resolved electron ultrafast dynamics detection technologies such as attosecond photoelectron spectroscopy and attosecond transient absorption spectroscopy were born, bringing about technological innovation in the field of precision measurement. In order to develop new attosecond light sources and expand their application areas in ultrafast dynamics detection technology, it is crucial to obtain complete information about attosecond pulses. Completely defining attosecond pulses requires characterizing the amplitude and phase distribution of attosecond pulses in time and space. Therefore, accurately measuring the temporal and spatial distribution of attosecond pulses is of great significance for the generation and application of attosecond pulses.

[0003] The most widely used technology for measuring the timing of attosecond pulses is the frequency-resolved optical gating for completely reconstructing attosecond bursts (FROG-CRAB). The FROG-CRAB technology (Y. Mairesse, et al., Physical Review A 71(1), 1401(2005)) uses the photoelectron energy spectrum of atomic single-photon ionization to reconstruct the phase of attosecond pulses. This technology has the disadvantages of central momentum approximation and is limited to the intensity and bandwidth of the perturbation light that modulates the photoelectron energy spectrum. In order to overcome the shortcomings of the FROG-CRAB technology, researchers have developed the PROOF (Phase Retrieval by Omega Oscillation Filtering) technology (M. Chini, et al., Optics Express 18(12), 13006–13016(2010)) and the all-optical attosecond pulse diagnostic technology based on frequency-resolved optical gating (Zhen Yang, et al., 2011). al., Opt. Lett. 45, 567-570 (2020)). These attosecond pulse time characterization methods all rely on converting attosecond pulses into electron wave packets through the photoionization of atoms, thereby automatically averaging the spatial structure of attosecond pulses in the measurement. Considering that there may be significant spatiotemporal coupling in the process of high-order harmonic generation, in many cases, spatially averaged time measurements are insufficient. Although researchers have proposed some methods to measure attosecond spatial structure, such as the SWORD (the spectralwavefrontoptical reconstruction by diffraction) method (E. Frumker, et al., Opt. Lett. 34, 3026-3028 (2009)) and the LSI (lateral shearing interferometry) method (Dane R. Austin, et al., Opt. Lett. 36, 1746-1748 (2011)), these methods are not compatible with attosecond pulse time measurement.

[0004] The above-mentioned attosecond pulse time and space structure measurement schemes cannot measure the time and space domain structure of attosecond pulses. In 2013, Kim et al. demonstrated an all-optical in-situ scheme for characterizing attosecond pulses in the time and space domain (KT Kim, et al., Nat. Phys. 9, 159 (2013)). The perturbation light propagates non-collinearly with the driving light at a small deflection angle. When the delay between the perturbation light and the driving light changes, a spatial gating gate is established, which can simultaneously measure the time and space phase of the attosecond pulse. However, this scheme can only measure the group delay dispersion of the attosecond pulse in the frequency domain, and more complex phase information is often lost. Therefore, up to now, there is no simple and convenient method to accurately measure the time and space structure of attosecond pulses. Summary of the invention

[0005] In view of the defects of the prior art and the need for improvement, the present invention provides a method and a device for measuring the space-time structure of an attosecond pulse, which aims to accurately measure the space-time structure of an attosecond pulse.

[0006] To achieve the above object, according to one aspect of the present invention, a method for measuring the spatiotemporal structure of an attosecond pulse is provided, comprising:

[0007] Using driving light to act on the gas atoms to be measured to generate attosecond pulses; introducing a beam of perturbation light to perform spatiotemporal control on the generation process of the attosecond pulses; adjusting the time delay between the perturbation light and the driving light, and measuring and obtaining high-order harmonic spectra corresponding to multiple time delays;

[0008] Extracting the far-field distribution of each energy harmonic at each time delay from all the high-order harmonic spectra to form a two-dimensional modulation diagram of the spatial distribution corresponding to the energy harmonic; extracting the spatial complex amplitude distribution of the energy harmonic in the undisturbed near field from the two-dimensional modulation diagram of the spatial distribution corresponding to each energy harmonic and performing a spatial Fourier transform on it to obtain the spatial complex amplitude distribution of the energy harmonic in the undisturbed far field; extracting the spectrum distribution of a harmonic corresponding to a divergence angle at each time delay from all the high-order harmonic spectra to form a two-dimensional trajectory diagram of the far-field attosecond pulse spectrum corresponding to the divergence angle, and extracting the amplitude and phase distribution of the harmonic spectrum corresponding to the far-field divergence angle from the two-dimensional trajectory diagram of the far-field attosecond pulse spectrum;

[0009] Based on the spatial complex amplitude distribution of each energy harmonic in the undisturbed far field and the amplitude and phase distribution of the harmonic spectrum corresponding to the divergence angle, the intensity and phase of the far-field harmonics in time and space are determined to obtain a far-field harmonic spectrum with time and space resolution, and a far-field attosecond pulse is synthesized based on the far-field harmonic spectrum with time and space resolution.

[0010] Furthermore, it also includes:

[0011] An inverse spatial Fourier transform is performed on the spatial complex amplitude distribution of each energy harmonic in the spatially and temporally resolved far-field harmonic spectrum to obtain a spatially and temporally resolved near-field harmonic spectrum, and a near-field attosecond pulse is synthesized based on the spatially and temporally resolved near-field harmonic spectrum.

[0012] Further, the one divergence angle is a zero degree divergence angle.

[0013] Furthermore, the use of driving light to act on the gas atoms to be measured to generate attosecond pulses is specifically implemented as follows:

[0014] A two-color driving field is used to act on the gas atoms to be measured to generate attosecond pulses, and the relative phase of the two-color field is adjusted so that the measured high-order harmonic cutoff region spectrum becomes a smooth supercontinuum spectrum.

[0015] Furthermore, the PCGPA algorithm is used to extract the spatial complex amplitude distribution and the frequency spectrum distribution.

[0016] The present invention also provides a device for measuring the space-time structure of attosecond pulses, comprising:

[0017] A high-order harmonic generation and collection component is used to generate driving light and perturbation light; the driving light is used to act on the gas atoms to be measured to generate attosecond pulses; the perturbation light is used, and the perturbation light propagates non-collinearly with the driving light at a small deflection angle to perform spatiotemporal control on the generation process of the attosecond pulses; the time delay between the perturbation light and the driving light is adjusted, and the high-order harmonic spectra corresponding to multiple time delays are measured;

[0018] A calculation module is used to extract the far-field distribution of each energy harmonic at each time delay from all the high-order harmonic spectra to form a two-dimensional modulation diagram of the spatial distribution corresponding to the energy harmonic; extract the spatial complex amplitude distribution of the energy harmonic in the undisturbed near field from the two-dimensional modulation diagram of the spatial distribution corresponding to each energy harmonic and perform a spatial Fourier transform on it to obtain the spatial complex amplitude distribution of the energy harmonic in the undisturbed far field; extract the spectrum distribution of a harmonic corresponding to a divergence angle at each time delay from all the high-order harmonic spectra to form a two-dimensional trace diagram of the far-field attosecond pulse spectrum corresponding to the divergence angle, and extract the amplitude and phase of the harmonic spectrum corresponding to the far-field divergence angle from the two-dimensional trace diagram of the far-field attosecond pulse spectrum Distribution; based on the spatial complex amplitude distribution of each energy harmonic in the undisturbed far field and the amplitude and phase distribution of the harmonic spectrum corresponding to the divergence angle, since the relative amplitude and relative phase of the spatial complex amplitude of each energy harmonic in the far-field harmonic spectrum are determined, according to the amplitude and phase distribution of the harmonic spectrum corresponding to the divergence angle, the amplitude and phase of each energy harmonic complex amplitude corresponding to other divergence angles relative to the divergence angle are obtained, and the amplitudes and phases of the complex amplitudes of harmonics of different energy harmonics corresponding to different divergence angles are relative, so the intensity and phase of the far-field harmonics in time and space are determined, and a far-field harmonic spectrum with time and space resolution is obtained, and a far-field attosecond pulse is synthesized based on the far-field harmonic spectrum with time and space resolution.

[0019] Furthermore, the calculation module is also used for:

[0020] An inverse spatial Fourier transform is performed on the spatial complex amplitude distribution of each energy harmonic in the spatially and temporally resolved far-field harmonic spectrum to obtain a spatially and temporally resolved near-field harmonic spectrum, and a near-field attosecond pulse is synthesized based on the spatially and temporally resolved near-field harmonic spectrum.

[0021] Further, the one divergence angle is a zero degree divergence angle.

[0022] Furthermore, when the high-order harmonic generation and collection component uses the driving light to act on the gas atoms to be measured to generate attosecond pulses, it is specifically implemented as follows:

[0023] A two-color driving field is used to act on the gas atoms to be measured to generate attosecond pulses, and the relative phase of the two-color field is adjusted so that the measured high-order harmonic cutoff region spectrum becomes a smooth supercontinuum spectrum.

[0024] Furthermore, the calculation module specifically uses a PCGPA algorithm to extract the spatial complex amplitude distribution and the frequency spectrum distribution.

[0025] In general, the above technical solutions conceived by the present invention can achieve the following beneficial effects:

[0026] (1) The present invention is an all-optical measurement method for attosecond pulses. The all-optical method combines the advantages of in-situ measurement and avoids the errors in the attosecond pulse measurement results caused by the attosecond pulse propagation process. In addition, the measurement of the attosecond pulse frequency domain phase in the present invention is based on the PCGPA algorithm and does not rely on group delay dispersion. More complex phase information can be measured. Therefore, the present invention is a method for measuring the spatiotemporal structure of attosecond pulses with higher accuracy.

[0027] (2) The present invention regulates the generation process of attosecond pulses with a very weak perturbation field (one thousandth of the driving field strength). What is changed is the phase of the accumulation of the returning electrons in the free state during the high-order harmonic generation process, but the radiation intensity of the attosecond pulses will not be changed. This ensures that the present invention does not introduce additional errors in the measurement of attosecond pulses.

[0028] (3) The spatial phase and spectral phase of the attosecond pulse in the present invention are both extracted from the PCGPA algorithm. The spatial phase measurement and the frequency measurement phase are compatible both in theory and in experiment, thus ensuring the accuracy of the spatiotemporal measurement of the attosecond pulse in the present invention. BRIEF DESCRIPTION OF THE DRAWINGS

[0029] Figure 1 A flow chart of a method for measuring the spatiotemporal structure of attosecond pulses provided in an embodiment of the present invention;

[0030] Figure 2 Schematic diagram of high-order harmonic signals of Ar gas atoms driven by a two-color laser field synthesized by a 1300nm fundamental field and an 800nm ​​auxiliary field provided in an embodiment of the present invention; wherein (a) is a far-field spatially resolved harmonic spectrum driven by a two-color driving field synthesized by a 1300nm fundamental laser field and an 800nm ​​auxiliary laser field, and (b) is the intensity distribution of the harmonic spectrum on the central axis of (a);

[0031] Figure 3 Schematic diagram of attosecond pulse spatial measurement provided by an embodiment of the present invention; wherein, (a) is a two-dimensional modulation diagram of the far-field spatial distribution of the 35th-order harmonic of the dual-color driving field and the perturbation field at different delays, (b) is a two-dimensional modulation diagram of the far-field spatial distribution of the 35th-order harmonic obtained by reconstructing (a) using the PCGPA algorithm, (c) is the spatial intensity (solid line) and phase (dotted line) distribution of the undisturbed near-field 35th-order harmonic extracted by the algorithm, and (d) is the spatial intensity (solid line) and phase (dotted line) distribution of the undisturbed far-field 35th-order harmonic;

[0032] Figure 4Schematic diagram of attosecond pulse time measurement provided in an embodiment of the present invention; wherein (a) is a two-dimensional trace diagram of the attosecond pulse spectrum corresponding to the far-field axis, (b) is a two-dimensional trace diagram of the attosecond pulse spectrum obtained by reconstructing (a) using the PCGPA algorithm, and (c) is the intensity (solid line) and phase (dotted line) of the unperturbed far-field on-axis harmonic spectrum extracted using the algorithm;

[0033] Figure 5 Schematic diagram of the spatiotemporal measurement results of far-field and near-field attosecond pulses provided in an embodiment of the present invention; wherein (a) and (b) are respectively the intensity and phase distribution diagrams of the spatiotemporally resolved far-field harmonics reconstructed according to the measurement results; wherein (c) and (d) are respectively the intensity and phase distribution diagrams of the spatiotemporally resolved near-field harmonics reconstructed according to the measurement results;

[0034] Figure 6 The spatiotemporal distribution of attosecond pulses obtained from the supercontinuum spectrum (energy range of 33eV-47eV) of the near-field and far-field spatiotemporally resolved harmonic spectrum provided by the synthetic measurement of the embodiment of the present invention; wherein, (a) is the spatiotemporal distribution of the electric field amplitude of the far-field attosecond pulse, and the inner inset shows the spatiotemporal distribution of the corresponding attosecond pulse intensity; (b) is the intensity distribution of the attosecond pulse on the far-field axis in (a); (c) is the spatiotemporal distribution of the electric field amplitude of the near-field attosecond pulse, and the inner inset shows the spatiotemporal distribution of the corresponding attosecond pulse intensity; (d) is the attosecond pulse intensity distribution on the near-field axis in (c);

[0035] Figure 7 A schematic diagram of the system structure for measuring the spatiotemporal structure of attosecond pulses provided in an embodiment of the present invention;

[0036] In all drawings, the same reference numerals are used to denote the same elements or structures, wherein:

[0037] 1 is a pump-detection device, 11 is a laser, 121 is a first beam splitter, 122 is a second beam splitter, 123 is a third beam splitter, 13 is an optical parametric amplifier, 14 is a dichroic mirror, 151 is a first half-wave plate, 152 is a second half-wave plate, 16 is a wire grid polarizer, 17 is a wedge mirror pair, 18 is a delay line, 191 is a first reflector group, 192 is a second reflector group, 193 is a third reflector group, 194 is a fourth reflector, 2 is a focusing device, 3 is a gas chamber, 31 is a gas nozzle, 41 is an entrance slit, 42 is a flat-field grating, 43 is a microchannel plate, 44 is a CCD detector, and 5 is a control device. DETAILED DESCRIPTION

[0038] In order to make the purpose, technical solutions and advantages of the present invention more clearly understood, the present invention is further described in detail below in conjunction with the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not intended to limit the present invention. In addition, the technical features involved in the various embodiments of the present invention described below can be combined with each other as long as they do not conflict with each other.

[0039] Before explaining the technical solution of the present invention in detail, the following brief introduction to the relevant technical terms is given:

[0040] Near field: In the present invention, the near field refers to the position where the photo-driven gas atoms radiate high-order harmonics. The spatial coordinates of the near field are one-dimensional and are represented by y.

[0041] Far field: In the present invention, far field refers to the position where we detect high-order harmonics. At this time, the spatial coordinate is also one-dimensional and is expressed by the divergence angle.

[0042] On-axis: The on-axis of the near field refers to the spatial coordinate y=0 position, and the on-axis of the far field is the spatial position where the far field divergence angle is 0.

[0043] In order to achieve high-precision spatiotemporal measurement of attosecond pulses, in an embodiment of the present invention, a method for all-optical measurement of the spatiotemporal distribution of attosecond pulses is provided, such as Figure 1 As shown, the following steps are included:

[0044] S1. Use driving light to act on the gas atoms to be measured to generate attosecond pulses; introduce a beam of perturbation light to perform spatiotemporal control on the generation process of attosecond pulses; adjust the time delay between the perturbation light and the driving light, and measure the high-order harmonic spectra corresponding to multiple time delays;

[0045] S2. Extract the far-field distribution of each energy harmonic at each time delay from all high-order harmonic spectra to form a two-dimensional modulation diagram of the spatial distribution corresponding to the energy harmonic; extract the spatial complex amplitude distribution of the energy harmonic in the undisturbed near field from the two-dimensional modulation diagram of the spatial distribution corresponding to each energy harmonic and perform a spatial Fourier transform on it to obtain the spatial complex amplitude distribution of the energy harmonic in the undisturbed far field; extract the spectrum distribution of a harmonic corresponding to a divergence angle at each time delay from all high-order harmonic spectra to form a two-dimensional trace diagram of the far-field attosecond pulse spectrum corresponding to the divergence angle, and extract the amplitude and phase distribution of the harmonic spectrum corresponding to the far-field divergence angle from the two-dimensional trace diagram of the far-field attosecond pulse spectrum;

[0046] S3. Based on the spatial complex amplitude distribution of each energy harmonic in the undisturbed far field and the amplitude and phase distribution of the harmonic spectrum corresponding to the above divergence angle, since the relative amplitude and relative phase of the spatial complex amplitude of each energy harmonic in the far-field harmonic spectrum are determined, the amplitude and phase of each energy harmonic complex amplitude corresponding to the divergence angle at other divergence angles are obtained according to the amplitude and phase distribution of the harmonic spectrum corresponding to the divergence angle. The amplitude and phase of the harmonic complex amplitudes of different energy harmonics corresponding to different divergence angles are relative, so the intensity and phase of the far-field harmonics in time and space are determined to obtain a far-field harmonic spectrum with time and space resolution, and synthesize a far-field attosecond pulse based on the far-field harmonic spectrum with time and space resolution. Perform an inverse spatial Fourier transform on the spatial complex amplitude distribution of each energy harmonic in the far-field harmonic spectrum with time and space resolution to obtain a near-field harmonic spectrum with time and space resolution, and synthesize a near-field attosecond pulse based on the near-field harmonic spectrum with time and space resolution, thereby measuring the time and space structure of the attosecond pulse.

[0047] Specifically, in S1, a two-color driving field is used to act on the gas atoms to be measured to generate attosecond pulses, and the relative phase of the two-color field is adjusted so that the generated high-order harmonic cutoff region spectrum is a smooth supercontinuum spectrum.

[0048] In this embodiment, the gas atoms to be measured are argon (Ar) atoms; in other embodiments of the present invention, the gas to be measured may also be any other gas atoms, and the measurement process is similar to that of Ar atoms.

[0049] As an optional implementation, in this example, the dual-color driving field is synthesized by a 1300nm basic laser field and an 800nm ​​auxiliary laser field.

[0050] like Figure 2 As shown, (a) and (b) respectively represent the far-field spatially resolved high-order harmonic spectrum and the on-axis high-order harmonic spectrum generated by Ar gas atoms driven by a dual-color driving field.

[0051] In addition, a beam of perturbation light is introduced into S1. The perturbation light propagates non-collinearly with the driving light at a small deflection angle, and the generation process of attosecond pulses is controlled in time and space, which is manifested in the modulation of the spatial distribution and spectral distribution of the measured high-order harmonic spectrum.

[0052] In an optional implementation, in this embodiment, the angle between the non-collinear propagation of the perturbation light and the driving light is 15 mrad.

[0053] In an optional implementation, the far-field spatial divergence angle corresponding to the two-dimensional trajectory diagram of the far-field attosecond pulse spectrum selected in S2 is 0.

[0054] Specifically, the high-order harmonic spectrum obtained in S2 based on S1 can extract the spatial distribution two-dimensional modulation diagram of the far-field distribution of different energy harmonics that changes with time delay. The PCGPA algorithm is used to extract the spatial complex amplitude distribution of the undisturbed near field from the spatial distribution two-dimensional modulation diagram of the far field. The spatial complex amplitude distribution of each energy harmonic in the undisturbed near field is subjected to a spatial Fourier transform to obtain the spatial complex amplitude distribution of the far-field harmonics.

[0055] In this example, the principle of spatial measurement of harmonics is as follows:

[0056] Perturbing light in space changes the wavefront of higher harmonics in the near field, thereby changing the far-field spatial distribution of the harmonic spectrum. By scanning the time delay between the perturbing light and the driving light, the spatial modulation in the far-field distribution of the harmonics can be observed. In this example, the laser beam has a lateral spatial distribution in the (x, y) plane perpendicular to the propagation direction z. Since an entrance slit along the y direction is used, only the y-axis component of the harmonic signal is measured. Based on the strong field approximation theory, the spatial modulation caused by perturbing light can be expressed as:

[0057]

[0058] where y is the spatial coordinate of the near field, θ is the divergence angle of the far field harmonics, and τ and are the time delay between the driving light and the perturbation light and the intersection angle of non-collinear focusing, k ω is the wave number of the harmonic with frequency ω, and c is the speed of light. far (ω,θ,τ) is the complex amplitude of the far-field harmonic with frequency ω and divergence angle θ with time delay τ, E near (ω,θ,τ) is the complex amplitude of the harmonic of frequency ω and spatial position y in the near field with time delay τ. It is a spatial gate caused by disturbed light. In this example, the phase matching condition generated by high-order harmonics only considers the effect of short orbits. The PCGPA algorithm is used to extract the spatial complex amplitude distribution and spatial gate of the unperturbed near field from the two-dimensional modulation diagram of the spatial distribution of each energy harmonic.

[0059] like Figure 3 As shown, Figure 3 (a) and (b) respectively represent the two-dimensional modulation diagrams of the far-field spatial distribution of the 35th harmonic measured by the experiment and reconstructed by the PCGPA algorithm. Figure 3 (c) shows the spatial intensity distribution (solid line) and phase distribution (dotted line) of the undisturbed near-field 35th-order harmonic reconstructed by the algorithm. The spatial Fourier transform of the obtained near-field harmonic complex amplitude can be used to obtain the undisturbed far-field 35th-order harmonic spatial distribution. Figure 3(d) shows the spatial intensity distribution (solid line) and phase distribution (dotted line) of the far field of the 35th-order harmonic, where the spatial Fourier transform formula is as follows:

[0060]

[0061] Where E far (ω,θ) is the complex amplitude of the harmonic with frequency ω and divergence angle θ in the far field, E near (ω,θ) is the complex amplitude of the harmonic with frequency ω and spatial position y in the near field. The spatial distribution of the harmonics in the near field and the far field is obtained through the above operation.

[0062] In addition, specifically, S2 extracts the corresponding two-dimensional trace diagram of the attosecond pulse spectrum on the far-field axis based on the high-order harmonic spectrum obtained in S1, and the amplitude and phase distribution of the harmonic spectrum on the far-field axis can be extracted from the two-dimensional trace diagram of the attosecond pulse spectrum through the PCGPA algorithm.

[0063] In this example, the principle of the time measurement of harmonics is as follows:

[0064] For time measurement, the perturbation electric field will change the trajectory of photoelectrons in the free state, that is, regulate the generation process of attosecond pulses. Finally, the phase of electron accumulation in the free state changes, resulting in time domain modulation of the high-order harmonic generation process. Considering that the perturbation field intensity is too weak to generate photoelectrons alone; based on the above assumptions, the electric dipole moment of high-order harmonic radiation can be written as

[0065] d(t,τ)=d0(t)e -iσ(t,τ) +cc (3)

[0066] Where d0(t) represents the dipole moment without perturbation and σ(t,τ) is the additional phase caused by the perturbation pulse. The harmonic spectrum is then obtained by:

[0067] S(ω,τ)=ω 4 |∫d(t,τ)e iωt dt| 2 (4)

[0068] Equation (4) shows that the weak perturbation pulse introduces a temporal phase gate in the harmonic generation, which will lead to frequency modulation in the harmonic spectrum.

[0069] Recalculating formula (3), we can get:

[0070]

[0071] Equation (5) is also equivalent to the equation used in the FORG technique. The PCGPA algorithm is used to extract the unperturbed dipole moment d0(t) from the two-dimensional trace of the attosecond pulse spectrum. The reconstructed unperturbed dipole moment d0(t) is Fourier transformed to obtain the spectral amplitude and phase of the harmonics, thus realizing the time measurement of the harmonics on the far-field axis.

[0072] like Figure 4 As shown, Figure 4 (a) and (b) are two-dimensional trace diagrams of the harmonic spectrum on the far-field axis measured by the experimental measurement and reconstructed by the PCGPA algorithm, respectively. Figure 4 (c) shows the spectral intensity (solid line) and phase (dotted line) of the undisturbed harmonics on the axis in the far field reconstructed according to the algorithm.

[0073] Specifically, in S3, the amplitude and phase distribution of the spectrum of the far-field on-axis harmonics obtained in the aforementioned S2 and the spatial complex amplitude distribution of the harmonics are combined, so that the intensity and phase distribution of the far-field harmonics can be completely determined in time and space, and a far-field harmonic spectrum with time and space resolution can be obtained; an inverse spatial Fourier transform is performed on the far-field spatial complex amplitude of each energy harmonic in the measured time-space resolved far-field harmonic spectrum, so that a near-field harmonic spectrum with time and space resolution can be obtained, and a supercontinuum spectrum is selected from the time-space resolved near-field and far-field harmonic spectra to synthesize attosecond pulses, thereby completing the time-space measurement of attosecond pulses.

[0074] Figure 5 The final measured spatially and temporally resolved far-field and near-field harmonic intensities are shown ( Figure 5 (a) and (c)) and phase ( Figure 5 The distribution of (b) and (d)).

[0075] according to Figure 5 Based on the results of the spatiotemporal measurement of far-field harmonics and near-field harmonics, the supercontinuum spectrum (33eV-47eV) of the near- and far-field harmonic spectra is selected to synthesize attosecond pulses to realize the spatiotemporal measurement of attosecond pulses. Figure 6 (a) shows the temporal and spatial distribution of the electric field amplitude of the far-field attosecond pulse, and the inset depicts the temporal and spatial distribution of the corresponding attosecond pulse intensity. Figure 6 As shown in (b), the on-axis attosecond pulse width is 270as. Figure 6 (c) shows the spatiotemporal distribution of the electric field amplitude of the near-field attosecond pulse, and the inset depicts the spatiotemporal distribution of the attosecond pulse intensity. Figure 6 As shown in (d), the pulse width of the attosecond pulse on the near-field axis is 243as, completing the measurement of the spatiotemporal structure of the attosecond pulse.

[0076] In summary, this embodiment generates a single attosecond pulse through the dual-color field gating gate technology, introduces another perturbation light beam that propagates non-collinearly with the driving light at a smaller deflection angle, and the perturbation light will regulate the generation process of the attosecond pulse. The relative delay between the perturbation light and the driving light is scanned to obtain a spatially resolved high-order harmonic spectrum, and further, a two-dimensional modulation diagram of the spatial distribution of the far-field high-order harmonic spectrum and a two-dimensional trace diagram of the spectrum of the corresponding attosecond pulse on the far-field axis can be extracted; using an algorithm similar to the FROG technology, the perturbation field is regarded as a spatial gate, and the spatial complex amplitude distribution of the undisturbed near-field harmonics is extracted using the spatially resolved PCGPA algorithm. The spatial complex amplitude distribution of each energy harmonic in the undisturbed near-field can be spatially Fourier transformed. The spatial complex amplitude distribution of far-field harmonics is obtained; the amplitude and phase distribution of the harmonic spectrum on the far-field axis can be extracted from the two-dimensional trajectory diagram of the attosecond pulse spectrum corresponding to the far-field axis using the frequency-resolved PCGPA algorithm; the amplitude and phase distribution of the harmonics on the far-field axis in the frequency domain and the spatial complex amplitude distribution of the far-field harmonics are connected, the intensity and phase of the far-field harmonics can be completely determined in time and space, thereby completing the measurement of the spatiotemporal structure of the far-field harmonics; the spatiotemporal structure of the near-field harmonics can be obtained by performing an inverse spatial Fourier transform on the far-field spatial complex amplitude of each reconstructed energy harmonic, and the supercontinuum spectrum is selected in the reconstructed spatiotemporally resolved near-field and far-field harmonic spectra to synthesize attosecond pulses, thereby completing the spatiotemporal measurement of attosecond pulses.

[0077] The present embodiment is an all-optical measurement method for attosecond pulses. The all-optical method combines the advantages of in-situ measurement to avoid the errors caused by attosecond pulses in the propagation process. In addition, the measurement of the frequency domain phase of attosecond pulses in the present embodiment does not rely on group delay dispersion and can measure more complex phase information. Therefore, the present embodiment is a method for measuring the spatiotemporal structure of attosecond pulses with higher accuracy.

[0078] Embodiment 2

[0079] A device for measuring the space-time structure of an attosecond pulse, comprising:

[0080] A high-order harmonic generation and collection component is used to generate driving light and perturbation light; the driving light is used to act on the gas atoms to be measured to generate attosecond pulses; the perturbation light is used to perform spatiotemporal control of the attosecond pulse generation process; the time delay between the perturbation light and the driving light is adjusted, and the high-order harmonic spectra corresponding to multiple time delays are measured;

[0081] A calculation module is used to extract the far-field distribution of each energy harmonic at each time delay from all high-order harmonic spectra to form a two-dimensional modulation diagram of the spatial distribution corresponding to the energy harmonic; extract the spatial complex amplitude distribution of the energy harmonic in the undisturbed near field from the two-dimensional modulation diagram of the spatial distribution corresponding to each energy harmonic and perform spatial Fourier transform on it to obtain the spatial complex amplitude distribution of the energy harmonic in the undisturbed far field; extract the spectrum distribution of a harmonic corresponding to a divergence angle at each time delay from all high-order harmonic spectra to form a two-dimensional trace diagram of the far-field attosecond pulse spectrum corresponding to the divergence angle, and extract the amplitude and phase distribution of the harmonic spectrum corresponding to the far-field divergence angle from the two-dimensional trace diagram of the far-field attosecond pulse spectrum; based on the spatial complex amplitude distribution of each energy harmonic in the undisturbed far field and the amplitude and phase distribution of the harmonic spectrum corresponding to the divergence angle, determine the intensity and phase of the far-field harmonic in time and space, obtain a far-field harmonic spectrum with time and space resolution, and synthesize a far-field attosecond pulse based on the far-field harmonic spectrum with time and space resolution. The spatial complex amplitude distribution of each energy harmonic in the spatially resolved far-field harmonic spectrum is subjected to an inverse spatial Fourier transform to obtain a spatially resolved near-field harmonic spectrum, and a near-field attosecond pulse is synthesized based on the spatially resolved near-field harmonic spectrum, thereby measuring the spatial-temporal structure of the attosecond pulse.

[0082] Specific implementation methods, such as Figure 7 As shown, it includes: a pump-detection device 1, a focusing device 2, a gas chamber 3, an X-ray spectrometer 4 and a control device 5; the control device 5 is connected to the X-ray spectrometer 4.

[0083] The pump-detection device 1 is used to generate coherent dual-color driving light and perturbation light with adjustable time delay, and make the generated dual-color driving light and perturbation light successively emerge in parallel along the emergent light path;

[0084] The focusing device 2 is used to make the two-color driving light and the perturbation light emitted by the pump-detection device act on the gas atoms to be measured in the gas chamber first and then, the two-color driving light acts on the gas molecules to be measured to generate attosecond pulses, and the perturbation light then regulates the generation process of the attosecond pulses; optionally, in this embodiment, the focusing device 2 is specifically a concave reflector;

[0085] The focusing device 2 is also used to focus the two-color driving light and the perturbation light emitted by the pump-detection device 1 non-collinearly at an angle of 15 mrad on the gas atoms to be measured in the gas chamber 3;

[0086] The gas chamber 3 is used to contain the gas molecules to be measured. The gas chamber 3 is provided with a gas nozzle 31 to maintain the background pressure of the gas. The relative position of the gas nozzle in the gas chamber and the laser focus after passing through the focusing device can also be adjusted to optimize the short orbit phase matching condition for generating high-order harmonics at this time, and the single attosecond pulse generation efficiency is high.

[0087] The X-ray spectrometer 4 is used to measure the spatially resolved high-order harmonic spectrum generated by the gas atoms to be measured under the action of the two-color driving light and the perturbation light.

[0088] The control device 5 includes a measuring module and a calculating module;

[0089] The measurement module is connected to the X-ray spectrometer 4, and the high-order harmonic spectrum corresponding to the time delay between the current two-color driving light and the perturbation light is obtained through the X-ray spectrometer; further, the two-dimensional spatial distribution diagram of the far-field harmonics modulated with the delay and the two-dimensional trace diagram of the attosecond pulse spectrum corresponding to the far-field axis can be extracted;

[0090] The calculation module is used to extract the undisturbed near-field harmonic spatial complex amplitude distribution from the two-dimensional modulation diagram of the spatial distribution of the far-field harmonics modulated with the delay obtained by the measurement module using the spatially resolved PCGPA algorithm, and perform spatial Fourier transform on the near-field harmonic spatial complex amplitude distribution to obtain the far-field harmonic spatial complex amplitude distribution; and is used to extract the amplitude and phase distribution of the harmonic spectrum on the far-field axis from the two-dimensional spectrum diagram of the attosecond pulse corresponding to the far-field axis obtained by the measurement module using the frequency-resolved PCGPA algorithm;

[0091] The calculation module is also used to connect the spatial complex amplitude distribution of the far-field harmonics and the amplitude and phase distribution of the harmonic spectrum on the far-field axis to obtain the time-space resolved far-field harmonics, thereby completing the time-space measurement of the far-field harmonics, and perform an inverse spatial Fourier transform on the obtained time-space resolved far-field harmonic complex amplitudes to obtain time-space resolved near-field harmonics, and select supercontinuum spectra from the reconstructed time-space resolved near-field and far-field harmonic spectra to synthesize attosecond pulses, thereby completing the time-space measurement of attosecond pulses.

[0092] Preferably, the X-ray spectrometer 4 comprises: an entrance slit 41, a flat-focus field grating 42, a microchannel plate 43 and a CCD detector 44. The entrance slit 41 is 0.2 mm wide and 15 mm high, and is used to intercept high-order harmonic signals in the y direction.

[0093] The flat-focus field grating 42 is placed behind the entrance slit and has an angle with the high-order harmonic light beam. The high-order harmonics of different frequency components are incident on the flat-focus field grating through the slit, and the high-order harmonics of different frequency components can be separated in space through reflection and diffraction of the grating; the microchannel plate 43 with a fluorescent screen is placed behind the flat-focus field grating to enhance the received high-order harmonic signals; the CCD detector 44 is placed behind the microchannel plate to collect the frequency-resolved high-order harmonic signals after the microchannel plate gain.

[0094] Preferably, the pump-probe device 1 comprises:

[0095] The laser 11 is used to generate 800nm ​​femtosecond laser pulses.

[0096] The first beam splitter 121 is arranged on the output light path of the laser, and is used to split the laser beam generated by the laser, wherein the transmitted laser beam is used to generate the basic driving field, and the reflected laser beam is used to generate the auxiliary driving field and the perturbation field.

[0097] An optical parametric amplifier 13 (i.e., TOPAS), which is arranged on the transmission light path of the first beam splitter, is used to pump the 800nm ​​femtosecond pulse to generate a 1300nm femtosecond pulse, which serves as the basic driving field of the dual-color driving field;

[0098] The second beam splitter 122 is arranged on the reflection light path of the first beam splitter. The laser beam transmitted through the second beam splitter is used to generate an 800nm ​​auxiliary driving field, and the laser beam reflected through the second beam splitter is used to generate an 800nm ​​perturbation laser field.

[0099] The dichroic mirror 14 is disposed at the intersection of the propagation paths of the 1300nm basic driving light and the 800nm ​​auxiliary driving light, and is used to combine the basic driving light and the auxiliary driving light into a two-color driving field.

[0100] The third beam splitter 123 is disposed at the intersection of the propagation paths of the two-color driving light and the perturbation light, and is used to adjust the propagation directions of the two-color driving light and the perturbation light so that the two-color driving light and the perturbation light are propagated to the reflector in sequence.

[0101] The first half-wave plate 151 is arranged on the propagation light path of the perturbation light and is used to adjust the energy of the perturbation light;

[0102] The second half-wave plate 152 is arranged on the propagation light path of the 800nm ​​auxiliary driving light and is used to adjust the energy of the 800nm ​​auxiliary driving light;

[0103] The wire grid polarizer 16 is arranged on the propagation light path after the perturbation light and the two-color driven light beam are combined to make the polarizations of the three beams the same.

[0104] The wedge mirror pair 17 is arranged on the propagation optical path of the perturbation light and is used to adjust the relative delay between the perturbation light and the two-color driving light;

[0105] The delay line 18 is arranged on the propagation optical path of the 800nm ​​driving light and is used to adjust the relative phase of the two-color driving field.

[0106] Preferably, the pump-detection device further includes: a first reflector group 191, a second reflector group 192, a third reflector group 193, and a fourth reflector 194. The first reflector group 191 is arranged on the propagation optical path of the 1300nm driving light, and is used to adjust the propagation direction of the 1300nm driving light; the second reflector group 192 is arranged on the propagation optical path of the 800nm ​​driving light, and is used to adjust the propagation direction of the 800nm ​​driving light; the third reflector group 193 is arranged on the propagation optical path of the 800nm ​​driving light, and is used to adjust the propagation direction of the 800nm ​​driving light; the fourth reflector 194 is used to reflect the two-color driving light and the perturbation light to the focusing device.

[0107] In this embodiment, the specific implementation of each module in the control device can refer to the description in the above method embodiment, which will not be repeated here.

[0108] The present invention can generate a single attosecond pulse through a dual-color field gate technology, introduce another perturbation pulse that propagates non-collinearly with the driving light at a smaller deflection angle, and the perturbation light will regulate the generation process of the attosecond pulse. The relative delay between the perturbation light and the driving light is scanned to obtain a spatially resolved high-order harmonic spectrum, and further extract a two-dimensional modulation diagram of the spatial distribution of the far-field high-order harmonic spectrum and a two-dimensional trace diagram of the spectrum of the attosecond pulse corresponding to the far-field axis; using an algorithm similar to the FROG technology, the perturbation field is regarded as a spatial gate, and the spatial complex amplitude distribution of the unperturbed near field is extracted using a spatially resolved PCGPA algorithm, and the spatial complex amplitude distribution of each energy harmonic in the unperturbed near field is subjected to a spatial Fourier transform to obtain The spatial complex amplitude distribution of far-field harmonics; the frequency-resolved PCGPA algorithm can be used to extract the amplitude and phase distribution of the harmonic spectrum on the far-field axis from the corresponding two-dimensional trajectory diagram of the attosecond pulse spectrum on the far-field axis; the frequency-domain amplitude and phase distribution of the harmonics on the far-field axis and the spatial complex amplitude distribution of the far-field harmonics are connected to fully determine the intensity and phase of the far-field harmonics in time and space, thereby completing the measurement of the spatiotemporal structure of the far-field harmonics; the spatiotemporal structure of the near-field harmonics can be obtained by performing an inverse spatial Fourier transform on the far-field spatial complex amplitude of each reconstructed energy harmonic, and the supercontinuum spectrum is selected from the reconstructed spatiotemporally resolved near-field and far-field harmonic spectra to synthesize attosecond pulses, thereby completing the spatiotemporal measurement of attosecond pulses.

[0109] The present invention is an all-optical measurement method for attosecond pulses. The all-optical method combines the advantages of in-situ measurement and avoids the errors caused by the attosecond pulse measurement results during the propagation process. In addition, the measurement of the attosecond pulse frequency domain phase in the present invention does not rely on group delay dispersion and can measure more complex phase information. Therefore, the present invention is a method for measuring the spatiotemporal structure of attosecond pulses with higher accuracy.

[0110] It will be easily understood by those skilled in the art that the above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions and improvements made within the spirit and principles of the present invention should be included in the protection scope of the present invention.

Claims

1. A method for measuring the spatiotemporal structure of attosecond pulses, characterized in that: include: Using driving light to act on the gas atoms to be measured to generate attosecond pulses; introducing a beam of perturbation light to perform spatiotemporal control on the generation process of the attosecond pulses; Adjusting the time delay between the perturbation light and the driving light, and measuring and obtaining high-order harmonic spectra corresponding to a plurality of time delays; Extracting the far-field distribution of each energy harmonic at each time delay from all the high-order harmonic spectra to form a two-dimensional modulation diagram of the spatial distribution corresponding to the energy harmonic; extracting the spatial complex amplitude distribution of the energy harmonic in the undisturbed near field from the two-dimensional modulation diagram of the spatial distribution corresponding to each energy harmonic and performing a spatial Fourier transform on it to obtain the spatial complex amplitude distribution of the energy harmonic in the undisturbed far field; extracting the spectrum distribution of a harmonic corresponding to a divergence angle at each time delay from all the high-order harmonic spectra to form a two-dimensional trajectory diagram of the far-field attosecond pulse spectrum corresponding to the divergence angle, and extracting the amplitude and phase distribution of the harmonic spectrum corresponding to the far-field divergence angle from the two-dimensional trajectory diagram of the far-field attosecond pulse spectrum; Based on the spatial complex amplitude distribution of each energy harmonic in the undisturbed far field and the amplitude and phase distribution of the harmonic spectrum corresponding to the divergence angle, the intensity and phase distribution of the far-field harmonics in time and space are determined to obtain a far-field harmonic spectrum with time and space resolution, and a far-field attosecond pulse is synthesized based on the far-field harmonic spectrum with time and space resolution.

2. The method for measuring the space-time structure of attosecond pulses according to claim 1, characterized in that: Also includes: An inverse spatial Fourier transform is performed on the spatial complex amplitude distribution of each energy harmonic in the spatially and temporally resolved far-field harmonic spectrum to obtain a spatially and temporally resolved near-field harmonic spectrum, and a near-field attosecond pulse is synthesized based on the spatially and temporally resolved near-field harmonic spectrum.

3. The method for measuring the space-time structure of attosecond pulses according to claim 1, characterized in that: The one divergence angle is a zero degree divergence angle.

4. The method for measuring the spatiotemporal structure of attosecond pulses according to claim 1, characterized in that: The method of using driving light to act on the gas atoms to be measured to generate attosecond pulses is specifically implemented as follows: A two-color driving field is used to act on the gas atoms to be measured to generate attosecond pulses, and the relative phase of the two-color field is adjusted so that the measured high-order harmonic cutoff region spectrum becomes a smooth supercontinuum spectrum.

5. The method for measuring the space-time structure of attosecond pulses according to claim 1, characterized in that: The PCGPA algorithm is used to extract the spatial complex amplitude distribution and the frequency spectrum distribution.

6. A device for measuring the spatiotemporal structure of attosecond pulses, characterized in that: include: High-order harmonic generation and collection components for generating driving light and perturbation light; The driving light is used to act on the gas atoms to be measured to generate attosecond pulses; Using perturbation light to perform spatiotemporal control on the generation process of the attosecond pulse; Adjusting the time delay between the perturbation light and the driving light, and measuring and obtaining high-order harmonic spectra corresponding to a plurality of time delays; A calculation module is used to extract the far-field distribution of each energy harmonic at each time delay from all the high-order harmonic spectra to form a two-dimensional modulation diagram of the spatial distribution corresponding to the energy harmonic; extract the spatial complex amplitude distribution of the energy harmonic in the undisturbed near field from the two-dimensional modulation diagram of the spatial distribution corresponding to each energy harmonic and perform spatial Fourier transform on it to obtain the spatial complex amplitude distribution of the energy harmonic in the undisturbed far field; extract the spectrum distribution of a harmonic corresponding to a divergence angle at each time delay from all the high-order harmonic spectra to form a two-dimensional trace diagram of the far-field attosecond pulse spectrum corresponding to the divergence angle, and extract the amplitude and phase distribution of the harmonic spectrum corresponding to the far-field divergence angle from the two-dimensional trace diagram of the far-field attosecond pulse spectrum; based on the spatial complex amplitude distribution of each energy harmonic in the undisturbed far field and the amplitude and phase distribution of the harmonic spectrum corresponding to the divergence angle, determine the intensity and phase distribution of the far-field harmonic in time and space, obtain a far-field harmonic spectrum with time and space resolution, and synthesize a far-field attosecond pulse based on the far-field harmonic spectrum with time and space resolution.

7. The device for measuring the space-time structure of attosecond pulses according to claim 6, characterized in that: The calculation module is also used for: An inverse spatial Fourier transform is performed on the spatial complex amplitude distribution of each energy harmonic in the spatially and temporally resolved far-field harmonic spectrum to obtain a spatially and temporally resolved near-field harmonic spectrum, and a near-field attosecond pulse is synthesized based on the spatially and temporally resolved near-field harmonic spectrum.

8. The device for measuring the space-time structure of attosecond pulses according to claim 6, characterized in that: The one divergence angle is a zero degree divergence angle.

9. The device for measuring the space-time structure of attosecond pulses according to claim 6, characterized in that: When the high-order harmonic generation and collection component uses driving light to act on the gas atoms to be measured to generate attosecond pulses, the specific implementation is as follows: A two-color driving field is used to act on the gas atoms to be measured to generate attosecond pulses, and the relative phase of the two-color field is adjusted so that the measured high-order harmonic cutoff region spectrum becomes a smooth supercontinuum spectrum.

10. The device for measuring the space-time structure of attosecond pulses according to claim 6, characterized in that: The calculation module specifically uses the PCGPA algorithm to extract the spatial complex amplitude distribution and the frequency spectrum distribution.

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