An all-optical measurement method for measuring ultrafast electron dynamics in solids in situ

Abstract

The application discloses an all-optical measuring method for in-situ measuring electronic ultrafast dynamics in a solid. The application adopts probe light to generate high-order harmonics, pump light to excite a sample to initiate electronic non-equilibrium dynamics, and sets an optical pulse delay line on the light path of the pump light to control the relative delay of the pump light and the probe light, so that the normalized high-order harmonic spectral integral intensity of each order under different relative delays loaded with thermal electron cooling information is obtained, and the properties of the sample are analyzed; the whole process of the high-order harmonic generation is completed within a sub-optical cycle time scale, and the optical frequency comb can span an extremely wide energy range, and has the advantages of ultra-high time resolution and ultra-wide energy response; the application overcomes the harsh application scene limitation of the prior art measuring instrument; the application makes up for the narrow energy detectable range of the transient spectrum technology; and the application provides a tool for simultaneously meeting the low environmental restriction, high sensitivity, wide energy range and more economical and practical in-situ measurement of electronic ultrafast dynamics.

Description

TECHNICAL FIELD

[0001] The present application relates to ultrafast laser technology, in particular to a full-optical measurement method for in-situ measuring electron ultrafast dynamics in solid. BACKGROUND

[0002] As one of the basic existing forms of matter, the ultrafast non-equilibrium dynamics of electrons in solid (condensed state) under optical excitation determines many important properties of solid, including optics, electricity and magnetism, etc. Observing and studying the ultrafast non-equilibrium dynamics of electrons in solid provides a key platform for understanding and manipulating these properties.

[0003] Currently, the observation and study of the ultrafast non-equilibrium dynamics of electrons in solid are mainly based on two types of tools. The first type is to observe the outgoing electrons in the solid sample, and the representative platforms include photoemission electron microscopy (PEEM) and angle-resolved photoelectron spectroscopy (ARPES) based on photoelectric effect, etc. However, this detection method puts multiple strict requirements on the material quality (sample surface cleanliness, size, etc.), instrument vacuum degree (≤10 -10 mbar) and measurement environment (magnetic field, etc.), and at the same time, the expensive cost of the related instrument greatly limits its popularization and application. The second type studies the change of the absorption or reflectivity of the incident light by the solid sample, and the representative technology is transient spectroscopy technology, etc. However, the limited spectral width of the laser pulse limits the energy range of the measurement, and it is difficult to simultaneously measure the ultrafast dynamics of electrons in multiple energy ranges. In addition, the modulation degree of the ultrafast non-equilibrium dynamics of electrons in solid to the absorption and reflectivity of the incident light is generally less than 10 -3 orders of magnitude, which limits the detection accuracy of the instrument and the stability of the experimental platform.

[0004] For the above reasons, how to develop an in-situ measurement scheme of electron ultrafast dynamics that meets the requirements of low environmental constraints, high sensitivity, wide energy range and more economical at the same time has always been a very challenging problem. SUMMARY

[0005] In order to solve the above problem of observing the ultrafast non-equilibrium dynamics of electrons in solid under optical excitation, the present application provides a full-optical measurement method for in-situ measuring electron ultrafast dynamics in solid, which overcomes the strict application scenario limitations of measurement instruments including photoemission electron microscopy (PEEM) and angle-resolved photoelectron spectroscopy (ARPES); makes up for the deficiency of narrow energy detectable range of transient spectroscopy technology; and provides a tool for simultaneously meeting the requirements of low environmental constraints, high sensitivity, wide energy range and more economical in-situ measurement of electron ultrafast dynamics.

[0006] The full-optical measurement method for in-situ measuring electron ultrafast dynamics in solid of the present application comprises the following steps:

[0007] 1) a sample of solid material is set in a high harmonic generation cavity;

[0008] 2) a femtosecond laser with low photon energy is used as probe light, the photon energy of the probe light is lower than the energy range covered by the hot electron cooling to be detected, to ensure that the high harmonic photon energy generated by the probe light covers the energy range covered by the hot electron cooling to be detected, the probe light is focused onto the sample by a first focusing lens to generate high harmonics;

[0009] 3) a femtosecond laser with high photon energy is used as pump light, the photon energy of the pump light is greater than the energy range covered by the hot electron cooling to be detected, a light pulse delay line is arranged in the light path of the pump light, the pump light passes through the light pulse delay line and is focused onto the sample by a second focusing lens, by adjusting the light pulse delay line and the optical path of the pump light, the time when the pump light reaches the sample in the high harmonic generation cavity is accurately controlled to control the relative delay of the pump light and the probe light;

[0010] 4) the pump light injects hot electrons into the energy band of the sample that matches the photon energy of the pump light through optical excitation, triggering electron non-equilibrium dynamics, i.e. the hot electrons gradually cool down over time;

[0011] 5) when the hot electrons cool down to the energy band of the sample that can generate high harmonic emission, the hot electrons occupy the energy band of the high harmonic emission; electrons are fermions, and the states occupied by hot electrons cannot receive electrons for generating high harmonics, resulting in suppression of high harmonics matching these states; as the hot electrons cool down, the energy band states are sequentially occupied from high energy to low energy, and sequentially suppress different orders of high harmonics; when the energy of the hot electrons cools down to the energy band of the corresponding order of high harmonics, the suppression of the high harmonics of this order reaches the strongest, thereby loading the cooling information of the hot electrons in the high harmonics;

[0012] 6) the high harmonics are focused by a high harmonic focusing cavity and then enter a harmonic detection cavity, are received by an image acquisition device sealedly installed on the harmonic detection cavity, and are recorded by shooting to obtain a high harmonic spectrum, the high harmonic spectrum is composed of multiple orders of high harmonics, and is transmitted to a computer;

[0013] 7) setting a shutter in the light path of the pump light, the shutter being connected to the computer, at one relative delay, the computer controls the shutter to open, the image acquisition device takes a photo of the high harmonic spectrum with the pump light, the high harmonic in the high harmonic spectrum with the pump light is loaded with the cooling information of the hot electrons; then, the shutter is controlled to close, the image acquisition device takes a photo of the high harmonic spectrum without the pump light, the high harmonic in the high harmonic spectrum without the pump light is not loaded with the cooling information of the hot electrons; at the same relative delay, the high harmonic spectrum with the pump light and the high harmonic spectrum without the pump light constitute a group of measurements, the high harmonic spectrum with the pump light and the high harmonic spectrum without the pump light are integrated respectively for different orders, the integral intensity of the high harmonic spectrum with the pump light and the high harmonic spectrum without the pump light for each order is obtained, the two are taken as a ratio, the normalized high harmonic spectrum integral intensity of each order at one relative delay which is not affected by the fluctuation of the probe light and is loaded with the cooling information of the hot electrons is obtained, which reflects the characteristic influence of the electron non-equilibrium dynamics on the high harmonic;

[0014] 8) after completing a group of measurements at one relative delay, the computer accurately changes the relative delay of the pump light and the probe light by controlling the optical pulse delay line, and repeats the above step 7) multiple times, so as to obtain the normalized high harmonic spectrum integral intensity of each order at multiple relative delays;

[0015] 9) the computer analyzes the normalized high harmonic spectrum integral intensity of each order at each relative delay, taking the relative delay of the pump light and the probe light as the horizontal coordinate, and taking the normalized high harmonic integral spectrum intensity of each order as the vertical coordinate, to form a curve of the normalized high harmonic spectrum integral intensity of each order with the relative delay of the pump light and the probe light, the normalized high harmonic spectrum integral intensity of each order constitutes an independent curve, by observing the curve of the normalized high harmonic spectrum integral intensity of each order with the relative delay of the pump light and the probe light, the time when the suppression of the high harmonic spectrum integral intensity of each order reaches the extreme value is obtained, the cooling time of the hot electron energy is obtained, and thus the material properties of the sample are obtained.

[0016] In step 3), the optical pulse delay line comprises two plane mirrors and a nanometer one-dimensional displacement stage, the two plane mirrors are installed perpendicularly to each other on the nanometer one-dimensional displacement stage, the nanometer one-dimensional displacement stage is connected to the computer, and the computer adjusts the time when the pump light reaches the sample in the high harmonic generation cavity by controlling the change of the optical path of the pump light caused by the one-dimensional movement of the nanometer one-dimensional displacement stage.

[0017] In step 6), the image acquisition device adopts a CCD camera.

[0018] In step 7), the opening time of the shutter is consistent with the exposure time of the image acquisition device in the harmonic detection cavity.

[0019] In step 8), the nanometer one-dimensional displacement stage in the optical pulse delay line has a microscale moving step, and the interval of the corresponding relative delay is 10 -14 seconds; the measurement group number of the normalized high-order harmonic spectral integral intensity is 100-1000 groups, and the corresponding relative delay scanning range is 10 -11 seconds.

[0020] Advantages of the present application:

[0021] The present application adopts probe light to generate high-order harmonics, pump light to excite sample to initiate electron non-equilibrium dynamics, and sets an optical pulse delay line in the light path of the pump light to control the relative delay of the pump light and the probe light, so as to obtain the normalized high-order harmonic spectral integral intensity loaded with hot electron cooling information, and analyze the properties of the sample material; the whole process of high-order harmonic generation is completed within the sub-optical cycle time scale, and the optical frequency comb composed of multiple high-order harmonics can span an extremely wide energy range, and the in-situ optical snapshot based on solid high-order harmonics naturally has the advantages of ultra-high time resolution and ultra-wide energy response; the application scene restrictions of the measuring instruments including photoemission electron microscope (PEEM) and angle-resolved photoelectron spectroscopy (ARPES) are overcome; the narrow energy detectable range of the transient spectrum technology is compensated; and a tool is provided for simultaneously meeting the low environmental restriction, high sensitivity, wide energy range and more economical and practical in-situ measurement of electron ultrafast dynamics. BRIEF DESCRIPTION OF DRAWINGS

[0022] Figure 1 A schematic diagram of an embodiment of the full-optical measuring device for in-situ measuring electron ultrafast dynamics in a solid according to the present application;

[0023] Figure 2 A band diagram of the full-optical measuring method for in-situ measuring electron ultrafast dynamics in a solid according to the present application;

[0024] Figure 3 A high-order harmonic curve with pump-probe delay obtained by an embodiment of the full-optical measuring method for in-situ measuring electron ultrafast dynamics in a solid according to the present application. DETAILED DESCRIPTION

[0025] The present application will be further described below by specific embodiments with reference to the accompanying drawings.

[0026] As Figure 1As shown, the all-optical measuring device for in-situ measuring ultrafast electron dynamics in solid of the present application comprises: probe light 1, pump light 2, first focusing lens F1, second focusing lens F2, plane mirror S, nanometer one-dimensional displacement table T, shutter R, high harmonic generation cavity A, harmonic focusing cavity B, harmonic detection cavity C, image acquisition device M and computer D; wherein the probe light 1 is focused by the first focusing lens F1 to the sample G located in the high harmonic generation cavity A; the pump light 2 is adjusted by the optical pulse delay line to adjust the optical path, and then is focused by the second focusing lens F2 and the shutter R to the sample G located in the high harmonic generation cavity A, the optical pulse delay line comprises two plane mirrors S which are installed perpendicularly on the nanometer one-dimensional displacement table T, and the nanometer one-dimensional displacement table T and the shutter R are connected to the computer respectively; the high harmonic generation cavity A, the harmonic focusing cavity B and the harmonic detection cavity C are all vacuum cavities with closed space inside; a plurality of windows are arranged on the side wall of the high harmonic generation cavity A at the height of the light path, one of the windows is selected as the probe light 1 incident window and one of the windows is selected as the pump light 2 incident window, the harmonic focusing cavity B is provided with one incident window and one exit window, and the harmonic detection cavity C is provided with one incident window; the exit window of the high harmonic generation cavity A is connected to the incident window of the harmonic focusing cavity B through a vacuum pipeline, the exit window of the harmonic focusing cavity B is connected to the incident window of the harmonic detection cavity C through a vacuum pipeline; the high harmonic generation cavity A is provided with a generation cavity molecular pump N, and the generation cavity molecular pump N is connected to a generation cavity mechanical pump O; the harmonic detection cavity C is provided with a detection cavity molecular pump P, and the detection cavity molecular pump P is connected to a detection cavity mechanical pump Q; a three-dimensional displacement table is arranged in the center of the high harmonic generation cavity A, and a five-dimensional displacement table E is arranged on the line connecting the incident window of the high harmonic generation cavity A and the three-dimensional displacement table, and the five-dimensional displacement table E is connected to the computer D; a sample holder is arranged on the five-dimensional displacement table E, and a sample G is placed on the sample holder, so that the sample can be translated, tilted and rotated in the plane of the sample; an optical mirror holder is arranged on the three-dimensional displacement table, an off-axis parabolic mirror H is arranged on the optical mirror holder, and the three-dimensional displacement table can adjust the position of the off-axis parabolic mirror H and adjust the tilt angle and in-plane rotation of the off-axis parabolic mirror H through the optical mirror holder; a first optical slit I is arranged between the off-axis parabolic mirror H and the exit window of the high harmonic generation cavity A; a toroidal mirror J is arranged in the harmonic focusing cavity B, and the toroidal mirror J is installed in a large-angle grazing incidence manner to enhance the reflection efficiency of high harmonics; a second optical slit K and a grating L are arranged in the harmonic detection cavity C in sequence along the light path propagation direction, a detection hole is arranged on the harmonic detection cavity C, an image acquisition device M is sealed and vacuumed on the harmonic detection cavity C through the detection hole, and the image acquisition device M is connected to the computer; the high harmonics pass through the first optical slit I, enter the harmonic focusing cavity B, are focused by the toroidal mirror J, enter the harmonic detection cavity C, pass through the second optical slit K and the grating L, and are received by the image acquisition device M. The image acquisition device adopts a CCD camera.The all-optical measuring device for in-situ measuring electron ultrafast dynamics in a solid adopted by the application is described in Chinese Patent Application CN112834039B.

[0027] High harmonic generation is an extreme optical up-conversion process in the interaction between laser and matter, through which high harmonic photons with several times the energy of input laser photons can be generated.

[0028] The yield of high harmonics is determined by the nonlinear current induced in the sample by the probe light, and the semiconductor Bloch equation gives the nonlinear current j(ω) in the sample as:

[0029]

[0030] where ω is the frequency of the probe light, E0 is the electric field strength of the probe light, A0 is the vector potential of the probe light, k is the momentum of the electron, T2 is the dephasing time, and S(k,t',t) is the classical action.

[0031] The phase part iφ of the above formula is:

[0032]

[0033] where ω is the frequency of the probe light, k is the momentum of the electron, T2 is the dephasing time, and S(k,t',t) is the classical action.

[0034] Only when the phase part of formula (1) (i.e. formula (2)) changes slowly, the integral part in formula (1) has a significant contribution, so there is:

[0035]

[0036]

[0037]

[0038] where ΔX c and ΔX v respectively represent the position change of the electron in the conduction band and the hole in the valence band under the driving of the light field, ε g is the band gap of the sample, k is the momentum of the electron, ω is the frequency of the probe light, and A0 is the vector potential of the probe light.

[0039] The above three formulas are used to describe the semi-classical model of the high harmonic generation process in a solid, and the generation process is as follows:

[0040] (1) Under the action of strong laser, the electron mainly tunnels to the upper energy band at the minimum band gap and its vicinity, for example, from the first energy band to the second energy band at k=0, and from the second energy band to the third energy band at k=π / a. As Figure 2The vertical upward real arrow on the left side of the middle indicates k = 0, π / a, where a is the lattice constant of the sample.

[0041] (2) The in-band dynamics driven by the laser is expressed as k(t) = k0 + A0(t) in the momentum space, where k0 represents the initial momentum of the electron in the crystal, and A0(t) represents the probe light vector potential. Through the repeated processes (1) and (2), the electron can enter a higher conduction band, as indicated by the curved real arrow along the energy band distribution on the left side of the figure.

[0042] (3) When each electron undergoes an inter-band transition to the initial energy band, a high-order harmonic photon is emitted. The photon energy is given by the energy difference Δε between the energy band where the electron is located and the initial energy band. The time-domain interference of the light emission limits the energy difference Δε to be an integer multiple of the incident laser photon energy, which forms a series of discrete regions on the conduction band, near which the conduction band electrons emit harmonic photons of corresponding energy. As shown in the figure, the three dashed lines from right to left correspond to the n, n+1 and n+2 order harmonics. Figure 2 The vertical dashed arrow on the left side of the middle indicates k = 0, π / a, where a is the lattice constant of the sample.

[0043] The in-situ measurement method for measuring ultrafast dynamics of electrons in a solid according to the embodiment of the present application, comprising the following steps:

[0044] 1) A single-layer graphene is used as a sample of a solid material and is arranged in a high-order harmonic generation cavity;

[0045] 2) A femtosecond laser with low photon energy is used as a probe light, the frequency of the probe light is ω probe = 0.47 fs -1 , the wavelength is 4000 nm, the photon energy of the probe light is lower than the energy range covered by the hot electron cooling to be detected, i.e. lower than the lowest energy of the hot monomer cooling, so as to ensure that the high-order harmonic photon energy generated by the probe light covers the energy range 0.5-3 eV covered by the hot electron cooling to be detected, and the probe light is focused onto the sample by a first focusing lens to generate high-order harmonics;

[0046] 3) A femtosecond laser with high photon energy is used as a pump light, the frequency of the pump light is ω pump = 4.7 fs -1 , the wavelength is 400 nm, the photon energy of the pump light is greater than the energy range covered by the hot electron cooling to be detected, i.e. higher than the highest energy of the hot monomer cooling, an optical pulse delay line is arranged on the light path of the pump light, the pump light passes through the optical pulse delay line and is focused onto the sample by a second focusing lens, the optical pulse delay line is adjusted to adjust the optical path of the pump light, and the time when the pump light reaches the sample in the high-order harmonic generation cavity is accurately controlled to control the relative delay of the pump light and the probe light;

[0047] 4) Pumping light injects hot electrons into the states of the energy band of the sample that match the photon energy of the pumping light by photo-excitation, and then induces electron non-equilibrium dynamics, i.e. the hot electrons gradually cool down over time, as shown in Figure 2 ; Figure 2 In the process of photo-excitation by the pumping light, as shown in Figure 2 , the hot electrons are injected into the states corresponding to the energy of the energy band, as indicated by the vertical upward dotted arrow in the figure, and the cooling process of the hot electrons along the energy band is as shown by the downward arrow on the right side of the figure; in order to more clearly show the process, the process of high harmonic generation and the cooling process of the hot electrons injected by the pumping light are respectively drawn in the left and right parts of the figure in Figure 2 ; Figure 2

[0048] 5) When the hot electrons cool down to the states of the energy band of the sample that can generate high harmonic emission, the hot electrons occupy the states of the energy band of the high harmonic emission; since the electrons are fermions, the states that have been occupied by the hot electrons cannot receive electrons for generating high harmonics, resulting in the suppression of the high harmonics that match these states; as the hot electrons cool down, the states of the energy band are sequentially occupied from high energy to low energy, and sequentially generate suppression to different orders of high harmonics; when the energy of the hot electrons cools down to the states of the energy band of the corresponding order of high harmonics, the suppression to the high harmonics of this order reaches the strongest; the high harmonics are loaded with the cooling information of the hot electrons;

[0049] 6) The high harmonics loaded with the cooling information of the hot electrons are focused by the high harmonic focusing cavity to the harmonic detection cavity, received by the image acquisition device mounted on the harmonic detection cavity through the detection hole, and the high harmonic spectrum is obtained by shooting and recording, and the high harmonic spectrum is composed of multiple orders of high harmonics, and is transmitted to the computer;

[0050] 7) A shutter is arranged on the light path of the pumping light, the shutter is connected to the computer, under a relative delay, the shutter is controlled to be opened, the image acquisition device shoots and records the high harmonic spectrum of the pumping light, and the high harmonics in the high harmonic spectrum of the pumping light are loaded with the cooling information of the hot electrons; then, the shutter is controlled to be closed, and the image acquisition device shoots and records the high harmonic spectrum without the pumping light, and the high harmonics in the high harmonic spectrum without the pumping light are not loaded with the cooling information of the hot electrons; under the same relative delay, the high harmonic spectrum with the pumping light and the high harmonic spectrum without the pumping light constitute a group of measurements, the high harmonic spectrum with the pumping light and the high harmonic spectrum without the pumping light are integrated for different orders respectively, the integrated intensities of the high harmonic spectrum with the pumping light and the high harmonic spectrum without the pumping light of each order are obtained, a ratio of the two is obtained, and the normalized high harmonic spectrum integrated intensity of each order is obtained, which is not affected by the fluctuation of the detection light, and reflects the characteristic influence of electron non-equilibrium dynamics on high harmonics.​

[0051] 8) After the completion of one relative delay, control the nanometer one-dimensional displacement platform T to move to the next position, the moving step length is determined according to the measurement time accuracy, the one-dimensional displacement platform T moves 150 nm, which corresponds to the relative time delay change of 1 fs (1 fs = 10 -15 s) of the laser pulse, by controlling the optical pulse delay line to accurately change the relative delay of the pump light and the probe light, a group of measurements is obtained at the new relative delay, and the above step 7) is repeated one thousand times, so that the normalized high-order harmonic spectral integral intensity at 1000 relative delays is obtained;

[0052] 9) The computer analyzes the normalized high-order harmonic spectral integral intensity at each relative delay, takes the relative delay of the pump light and the probe light as the horizontal coordinate, and takes the normalized high-order harmonic spectral integral intensity as the vertical coordinate to form a curve of the normalized high-order harmonic spectral integral intensity with the relative delay of the pump light and the probe light, and each order of the normalized high-order harmonic spectral integral intensity forms an independent curve, as shown in Figure 3 The time when the suppression of each order of the normalized high-order harmonic spectral integral intensity reaches the extreme value (denoted as t n , where the subscript n is the order of the high-order harmonic) is obtained by observing the curve of each order of the normalized high-order harmonic spectral integral intensity with the relative delay of the pump light and the probe light, and t n represents the meaning that the energy of the hot electrons injected by the pump light is cooled from ω pump to nω probe , and needs to undergo t n , denoted as (ω pump , nω probe , t n ), since the probe light can generate multiple orders of high-order harmonics, n can take positive integers, and multiple sets of (ω pump , nω probe , t n ) are combined to allow the cooling process of the hot electrons to be represented in a wider energy range (covering all regions with energy equal to nω probe , where n takes positive integers, and the maximum value of n satisfies n max ω probe ≤ω pump ), so as to obtain the material properties of the sample, and further to make applications according to the material properties of the sample.

[0053] Finally, it is to be understood that the embodiments are for purposes of illustration only and that various changes and modifications can be made by those skilled in the art without departing from the scope of the application as disclosed in the specification and appended claims. Therefore, the scope of the application is not to be limited to the embodiments disclosed but is to be accorded the full scope permissible by the appended claims.

Claims

1. An all-optical measurement method for measuring ultrafast electron dynamics in a solid in-situ, characterized in that, The full-optical measurement method comprises the following steps: 1) a sample of solid material is arranged in a high harmonic generation cavity; 2) a femtosecond laser with low photon energy is used as probe light, the photon energy of the probe light is lower than the energy range covered by the hot electron to be detected, so as to ensure that the high harmonic photon energy generated by the probe light covers the energy range covered by the hot electron to be detected, the probe light is focused on the sample by a first focusing lens to generate high harmonics; 3) a femtosecond laser with high photon energy is used as pump light, the photon energy of the pump light is greater than the energy range covered by the hot electron to be detected, a light pulse delay line is arranged on the light path of the pump light, the pump light passes through the light pulse delay line and is focused on the sample by a second focusing lens, the light path of the pump light is adjusted by adjusting the light pulse delay line, so as to accurately control the time when the pump light reaches the sample in the high harmonic generation cavity, so as to control the relative delay of the pump light and the probe light; 4) the pump light injects hot electrons into the energy band state of the sample which matches the photon energy of the pump light through optical excitation, and initiates electron non-equilibrium dynamics, that is, the hot electrons gradually cool down over time; 5) when the hot electrons cool down to the energy band state of the sample which can generate high harmonic emission, the hot electrons occupy the energy band state of the high harmonic emission; the electron is a fermion, and the state occupied by the hot electron cannot receive the electron for generating high harmonics, resulting in the suppression of the high harmonics matched with these states; as the hot electrons cool down, the energy band states are sequentially occupied from high energy to low energy, and sequentially suppress different orders of high harmonics; when the energy of the hot electrons cools down to the energy band state of the corresponding order of high harmonics, the suppression of the high harmonics of this order reaches the strongest, so that the cooling information of the hot electrons is loaded in the high harmonics; 6) the high harmonics are focused by a high harmonic focusing cavity and then enter a harmonic detection cavity, are received by an image acquisition device sealedly mounted on the harmonic detection cavity, and are photographed and recorded to obtain a high harmonic spectrum, the high harmonic spectrum is composed of multiple orders of high harmonics, and is transmitted to a computer; 7) a shutter is arranged on the light path of the pump light, the shutter is connected to the computer, at one relative delay, the computer controls the shutter to open, the image acquisition device photographs and records the high harmonic spectrum of the pump light, the high harmonic spectrum of the pump light with the pump light loads the cooling information of the hot electrons; then, the shutter is controlled to close, and the image acquisition device photographs and records the high harmonic spectrum without the pump light, the high harmonic spectrum without the pump light does not load the cooling information of the hot electrons; the high harmonic spectrum with the pump light and the high harmonic spectrum without the pump light at the same relative delay constitute a group of measurements, the high harmonic spectrum with the pump light and the high harmonic spectrum without the pump light are integrated respectively for different orders, the integral intensities of the high harmonic spectrum with the pump light and the high harmonic spectrum without the pump light for each order are obtained, a ratio of the two is obtained, the normalized high harmonic spectrum integral intensity of each order at one relative delay which is loaded with the cooling information of the hot electrons and is not affected by the fluctuation of the probe light is obtained, and reflects the characteristic influence of electron non-equilibrium dynamics on high harmonics. 8) after a set of measurements at one relative delay is completed, the computer precisely changes the relative delay between the pump light and the probe light by controlling the optical pulse delay line, and repeats step 7) multiple times to obtain the normalized high-order harmonic spectral integrated intensity of each order at multiple relative delays; 9) the computer analyzes the normalized high-order harmonic spectral integrated intensity of each order at each relative delay, and constructs a curve of the normalized high-order harmonic spectral integrated intensity of each order versus the relative delay between the pump light and the probe light, taking the relative delay between the pump light and the probe light as the horizontal coordinate and the normalized high-order harmonic spectral integrated intensity of each order as the vertical coordinate, each order of the normalized high-order harmonic spectral integrated intensity constitutes an independent curve, by observing the curve of the normalized high-order harmonic spectral integrated intensity of each order versus the relative delay between the pump light and the probe light, the time at which the suppression of the high-order harmonic spectral integrated intensity of each order reaches an extreme value is obtained, the cooling time of the hot electron energy is obtained, and thus the material properties of the sample are obtained.

2. The all-optical measurement method according to claim 1, characterized in that, In step 3), the optical pulse delay line comprises two plane mirrors and a nanometer-level one-dimensional displacement stage, the two plane mirrors are installed perpendicularly to each other on the nanometer-level one-dimensional displacement stage, the nanometer-level one-dimensional displacement stage is connected to the computer, and the computer adjusts the time for the pump light to reach the sample in the high-order harmonic generation cavity by controlling the change in the optical path of the pump light caused by the one-dimensional movement of the nanometer-level one-dimensional displacement stage.

3. The all-optical measurement method according to claim 1, wherein In step 7), the time for the shutter to open is consistent with the exposure time of the image acquisition device in the harmonic detection cavity.

4. The all-optical measurement method of claim 1, wherein, In step 8), the moving step of the nanometer one-dimensional displacement stage in the optical pulse delay line is in the order of microns, and the interval of the corresponding relative delay is in the order of 10 -14 seconds.

5. The all-optical measurement method of claim 1, wherein, In step 8), the measurement group number of the normalized each order high harmonic spectrum integral intensity is 100-1000 groups, and the corresponding relative delay scanning range is 10 -11 second order.

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