CN118464816A - Asynchronous wide-field ultrafast spectral microscopy imaging system and method - Google Patents

Abstract

The invention discloses an asynchronous wide-field ultrafast spectral microscopy imaging system and method. The system comprises an asynchronous wide-field femtosecond laser pumping detection subsystem and a time-space resolution spectral microscopy image reconstruction subsystem. The asynchronous wide-field femtosecond laser pumping detection subsystem is used to generate pump light and detection light with different time delays, and respectively focus the pump light and the detection light on the sample surface, and continuously sample the detection light image reflected by the sample at a fixed sampling frequency Fs, wherein Fs>2Fc, and Fc is the modulation frequency of the pump light; the time-space resolution spectral microscopy image reconstruction subsystem is used to obtain the grayscale value of the same pixel position of all detection light images under the same time delay to form a pixel grayscale array, and then calculate the amplitude and phase of each pixel position according to the pixel grayscale array of each pixel position under the same time delay, and reconstruct the amplitude and phase of all pixel positions under the same time delay according to the pixel position to obtain the microscopic spectrum under each time delay, and finally combine the microscopic spectra under all time delays to form a time-space resolution ultrafast spectral microscopy image sequence. The present invention not only reduces the cost of the hardware system, but also reduces the complexity of the image reconstruction algorithm, and has universal reference significance and application value.

Description

Asynchronous wide-field ultrafast spectral microscopy imaging system and method

Technical Field

The invention relates to optical microscopic imaging, and in particular to an asynchronous wide-field ultrafast spectral microscopic imaging system and method.

Background Art

Femtosecond laser pump detection is an important spectroscopic method for studying ultrafast photophysical processes. Due to its advantages of femtosecond time resolution, non-destructive and rapid detection, it has important application value in the detection and imaging of ultrafast processes such as carrier dynamics, thermal diffusion, coherent phonons, etc. in functional materials and devices such as semiconductors. It can not only measure important intrinsic physical parameters such as photogenerated carrier lifetime, mobility and thermal diffusion coefficient, but also realize device functional evaluation by monitoring processes such as ultrafast interface energy transfer.

In the early stage of femtosecond laser pump detection, the femtosecond laser pump pulse and the detection pulse were usually focused on the surface of the sample to be tested to form a micrometer diameter focal spot, and the phase-locked amplification method was used to realize sensitive detection of the intensity change of the detection pulse reflection signal at different times, so that the dynamic process of the photogenerated carriers (electrons, phonons, etc.) at the location of the focal spot (considered as a point) can be measured in time resolution. Furthermore, in order to realize the time-space resolution microscopic imaging of ultrafast spectroscopy, most people use spatial scanning or synchronous wide-field imaging. However, the spatial scanning method not only has high requirements on scanning accuracy, but also has a very slow imaging speed. Although the synchronous wide-field imaging method improves the imaging speed, it is technically necessary to accurately synchronize the optical chopping modulation and image acquisition, that is, the phase is the same and the image acquisition frequency is twice the chopping modulation frequency. A function generator needs to be used to apply synchronous triggering to the optical chopping modulation and image acquisition. This will not only increase the complexity of the hardware and spectral acquisition control system, but also cause the matching timing-dependent image differential reconstruction algorithm to occupy more computing resources, which seriously hinders the convenient and universal application of ultrafast spectral microscopic imaging technology.

Summary of the invention

In view of the problems existing in the existing synchronous wide-field ultrafast spectral microscopy imaging technology, the present invention provides a system and method that does not require synchronous triggering. The present invention also reduces the complexity of the hardware system, the spectral acquisition control system and the image reconstruction algorithm, and has universal reference significance and application value.

In order to achieve the above-mentioned object of the invention, the present invention provides an asynchronous wide-field ultrafast spectral microscopy imaging system, comprising:

An asynchronous wide-field femtosecond laser pump-probe subsystem is used to generate pump light and probe light with different time delays, and to focus the pump light on the sample surface and to form an expanded light spot on the sample surface after the probe light is pre-focused, and to continuously sample the probe light image reflected by the sample at a fixed sampling frequency Fs, where Fs>2Fc, and Fc is the modulation frequency of the pump light;

The time-space resolved spectral microscopy image reconstruction subsystem is used to obtain all detection light images under the same time delay of pump light and detection light, and to form a pixel grayscale array with the grayscale values of the same pixel position of all detection light images, and then calculate the amplitude and phase of each pixel position according to the pixel grayscale array of each pixel position under the same time delay, and combine the amplitude and phase of all pixel positions under the same time delay according to the pixel position to obtain the microscopic spectrum under each time delay, and finally combine the microscopic spectra under all time delays to form a time-space resolved ultrafast spectral microscopy image sequence.

Furthermore, the asynchronous wide-field femtosecond laser pump detection subsystem specifically includes a femtosecond laser, a spectroscope, a time delay adjustment module, a frequency doubling crystal, a frequency adjustment module, a reflector assembly, a microscope objective, an eyepiece and a CMOS camera. The spectroscope is located behind the light output end of the femtosecond laser and is used to divide the output beam of the femtosecond laser into detection light and pump light. The reflector assembly is used to turn the propagation direction of the pump light, so that the pump light passes through the frequency doubling crystal and the frequency adjustment module in sequence to reach the light input end of the microscope objective. The frequency adjustment module is used to perform frequency modulation on the pump light with a frequency of Fc. The detection light reaches the light input end of the microscope objective via the time delay adjustment module. The sample is located at the focus of the microscope objective. The microscope objective is used to image the detection light reflected by the sample onto the camera through the eyepiece. The camera continuously samples at a fixed sampling frequency Fs to form a detection light image sequence.

Furthermore, the asynchronous wide-field femtosecond laser pumping detection subsystem also includes a first lens and a second lens, wherein the first lens and the second lens are located in the detection light path before the microscope objective lens, and are used to pre-focus the detection light beam.

Furthermore, the reflector assembly includes a first reflector, a second reflector and a third reflector sequentially arranged along a propagation path of the pump light, and the first reflector, the second reflector and the third reflector enable the pump light to finally reach a light input end of the microscope objective.

Furthermore, the time-space resolution spectral microscopy image reconstruction subsystem includes:

A pixel grayscale value acquisition module is used to acquire s detection light images taken at a specific time delay t, and extract the grayscale value of the same pixel position of each detection light image in the shooting order to form an array of pixel grayscale values _ai,j (t)={ _ai,j (t,1),…, _ai,j (t,s)}, where t=1,…,T; i=1,…,m; j=1,…,n, _ai,j (t,k) represents the grayscale value of the pixel position of the i-th row and j-th column of the k-th detection light image taken when the time delay is t, k=1,…,s, T is the measurement number of the time delay, and m and n are the number of pixels in the row and column of the detection light image;

The amplitude and phase calculation module is used to calculate the amplitude and phase according to the following formula:

Where A _i,j (t) is the pixel in the i-th row and j-th column of the uncorrected micro-spectral image, is the phase, |A _i,j (t)| is the amplitude;

The image reconstruction module is used to correct the uncorrected microscopic spectrum image according to the following formula and combine it according to the pixel position to obtain the microscopic spectrum at each time delay:

In the formula, is the pixel in the i-th row and j-th column of the microscopic spectrum under time delay t, A _i*,j* (t) is the selected reference pixel, and A ^* (t) is the microscopic spectrum under time delay t;

The time-space resolution micro-spectral image forming module is used to form a time-space resolution ultrafast spectral micro-image sequence A ^* ={A ^* (t)|t=1,…,T} from all micro-spectra under time delay.

Furthermore, the time delay adjustment module is a delay device placed on the displacement platform. The frequency adjustment module is a chopper.

The present invention also provides an asynchronous wide-field ultrafast spectral microscopy imaging method, comprising:

Step S1: Generate pump light and probe light with different time delays, focus the pump light on the sample surface, and form an enlarged light spot on the sample surface after the probe light is pre-focused, and continuously sample the probe light image reflected by the sample at a fixed sampling frequency Fs, where Fs>2Fc, and Fc is the modulation frequency of the pump light;

Step S2: Acquire all detection light images under the same time delay of pump light and detection light, and form a pixel grayscale array with the grayscale values of the same pixel position of all detection light images, and then calculate the amplitude and phase of each pixel position according to the pixel grayscale array of each pixel position under the same time delay, and combine the amplitude and phase of all pixel positions under the same time delay according to the pixel position to obtain the microscopic spectrum under each time delay, and finally combine the microscopic spectra under all time delays to form a time-space resolved ultrafast spectral microscopic image sequence.

Furthermore, the step S2 specifically includes:

Obtain s detection light images taken at a specific time delay t, and extract the grayscale value of the same pixel position of each detection light image in the shooting order to form an array of pixel grayscale values ai _,j (t)={ _ai,j (t,1),…, _ai,j (t,s)}, where t=1,…,T; i=1,…,m; j=1,…,n, _ai,j (t,k) represents the grayscale value of the pixel position of the i-th row and j-th column of the k-th detection light image taken when the time delay is t, k=1,…,s, T is the measurement number of the time delay, and m and n are the number of pixels in the rows and columns of the detection light image;

Calculate the magnitude and phase as follows:

Where A _i,j (t) is the pixel in the i-th row and j-th column of the uncorrected micro-spectral image, is the phase, |A _i,j (t)| is the amplitude;

The uncorrected microscopic spectrum image is corrected according to the following formula and combined according to the pixel position to obtain the microscopic spectrum at each time delay:

In the formula, is the pixel in the i-th row and j-th column of the microscopic spectrum under time delay t, A _i*,j* (t) is the selected reference pixel, and A ^* (t) is the microscopic spectrum under time delay t;

The microscopic spectra under all time delays are combined to form a temporally and spatially resolved ultrafast spectral microscopic image sequence A ^* ={A ^* (t)|t=1,…,T}.

Compared with the prior art, the present invention has the following beneficial effects: the present invention breaks through the technical bottleneck of the existing wide-field femtosecond laser micro-spectral imaging method, which requires synchronous triggering, and proposes an asynchronous wide-field ultrafast spectral micro-imaging system and method that does not require chopping modulation and image acquisition synchronization, thereby reducing the hardware system complexity and cost; and simplifies the algorithm for time-space resolution micro-spectral image reconstruction, thereby increasing the speed of time-space resolution ultrafast spectral imaging. The present invention will enable wide-field femtosecond laser micro-spectral imaging to obtain faster and more universal application scenarios.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG1 is a system block diagram of an asynchronous wide-field ultrafast spectral microscopy imaging system provided by an embodiment of the present invention;

FIG2 is a system block diagram of the asynchronous wide-field femtosecond laser pumping detection subsystem in FIG1;

FIG3 is a system block diagram of the time-space resolution spectral microscopy image reconstruction subsystem in FIG1 ;

FIG4 is a signal diagram of a pump pulse and a probe pulse;

FIG5 is a diagram showing the spatial distribution of the imaging results and the concentration of the extracted photogenerated carriers;

FIG. 6 is a graph showing the carrier diffusion coefficient of the two-dimensional semiconductor MoSe ₂ measured by the present invention.

DETAILED DESCRIPTION

The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

The embodiment of the present invention provides an asynchronous wide-field ultrafast spectral microscopy imaging system, as shown in FIG1 , comprising:

An asynchronous wide-field femtosecond laser pump-probe subsystem is used to generate pump light and probe light with different time delays, and to focus the pump light on the sample surface and to form an expanded light spot on the sample surface after the probe light is pre-focused, and to continuously sample the probe light image reflected by the sample at a fixed sampling frequency Fs, where Fs>2Fc, and Fc is the modulation frequency of the pump light;

The time-space resolved spectral microscopy image reconstruction subsystem is used to obtain all detection light images under the same time delay of pump light and detection light, and to form a pixel grayscale array with the grayscale values of the same pixel position of all detection light images, and then calculate the amplitude and phase of each pixel position according to the pixel grayscale array of each pixel position under the same time delay, and combine the amplitude and phase of all pixel positions under the same time delay according to the pixel position to obtain the microscopic spectrum under each time delay, and finally combine the microscopic spectra under all time delays to form a time-space resolved ultrafast spectral microscopy image sequence.

As shown in FIG2 , the asynchronous wide-field femtosecond laser pump detection subsystem specifically includes a femtosecond laser, a beam splitter, a time delay adjustment module, a frequency doubling crystal, a frequency adjustment module, a reflector assembly, a microscope objective, an eyepiece, and a camera. The beam splitter is located behind the light output end of the femtosecond laser and is used to divide the output beam of the femtosecond laser into detection light and pump light. The reflector assembly is used to turn the propagation direction of the pump light so that the pump light passes through the frequency doubling crystal and the frequency adjustment module in sequence to reach the light input end of the microscope objective. The frequency adjustment module is used to perform frequency modulation on the pump light with a frequency of Fc. The detection light reaches the light input end of the microscope objective via the time delay adjustment module. The sample is located at the focus of the microscope objective. The microscope objective is used to image the detection light reflected by the sample onto the camera via the eyepiece. The camera continuously samples at a fixed sampling frequency Fs to form a detection light image sequence. The asynchronous wide-field femtosecond laser pump detection subsystem also includes a first lens and a second lens, which are located in the detection light path before the microscope objective lens and are used to pre-focus the detection light beam. The reflector assembly includes a first reflector, a second reflector and a third reflector arranged in sequence along the pump light propagation path, and the first reflector, the second reflector and the third reflector enable the pump light to finally reach the light input end of the microscope objective lens. The camera is an sCMOS camera. The time delay adjustment module is a delay device placed on a displacement platform. The frequency adjustment module is a chopper or other frequency modulation module.

The working principle of the asynchronous wide-field femtosecond laser pump-detection subsystem is as follows: first, a pump light pulse and a probe light pulse with an adjustable delay time relative to the pump light pulse are introduced. Among them, the pump pulse is a parallel light, which is modulated by the frequency (Fc) of the chopper to become an intermittent signal with a frequency of Fc, and is tightly focused on the surface of the sample to be tested through the microscope objective. After passing through the elongated lens pair, the probe light pulse becomes a slightly convergent light beam, which is pre-focused in front of the sample after being focused by the microscope objective, and then the expanded light spot after focusing covers a large area centered on the pump. The time delay between the pump light and the probe light reaching the sample can be adjusted, and ultrafast process detection on a time scale can be performed through different time delays. After reflection, the wide-field probe light reaching the sample surface is collected by the microscope objective, imaged to the CMOS camera through the eyepiece, and continuously collected into an image sequence at a frequency (Fs) using the CMOS camera.

In the femtosecond laser pump detection system, the time delay between the pump and detection pulses is t. Imaging under a certain time delay t requires continuous shooting of s image sequences. To obtain the ultrafast spectral image under this time delay, it is necessary to extract the signals of these s images to generate a complete time-space resolved ultrafast image. Therefore, as shown in Figure 3, the time-space resolved spectral microscopy image reconstruction subsystem includes:

A pixel grayscale value acquisition module is used to acquire s detection light images taken at a specific time delay t, and extract the grayscale value of the same pixel position of each detection light image in the shooting order to form an array of pixel grayscale values _ai,j (t) = { _ai,j (t,1), ..., _ai,j (t,s)}, where t = 1, ..., T; i = 1, ..., m; j = 1, ..., n, _ai,j (t,k) represents the grayscale value of the pixel position of the i-th row and j-th column of the k-th detection light image taken when the time delay is t, k = 1, ..., s, T is the measurement number of the time delay, and m and n are the number of row and column pixels of the detection light image;

The amplitude and phase calculation module is used to calculate the amplitude and phase according to the following formula:

Where A _i,j (t) is the pixel in the i-th row and j-th column of the uncorrected micro-spectral image, is the phase, |A _i,j (t)| is the amplitude;

The image reconstruction module is used to correct the uncorrected microscopic spectrum image according to the following formula and combine it according to the pixel position to obtain the microscopic spectrum at each time delay:

In the formula, is the pixel in the i-th row and j-th column of the microscopic spectrum under time delay t, A _i*,j* (t) is the selected reference pixel, and A ^* (t) is the microscopic spectrum under time delay t;

The time-space resolution micro-spectral image forming module is used to form a time-space resolution ultrafast spectral micro-image sequence A ^* ={A ^* (t)|t=1,…,T} from all micro-spectra under time delay.

The embodiment of the present invention further provides an asynchronous wide-field ultrafast spectral microscopy imaging method, comprising:

Step S1: Generate pump light and probe light with different time delays, focus the pump light on the sample surface, and form an enlarged light spot on the sample surface after the probe light is pre-focused, and continuously sample the probe light image reflected by the sample at a fixed sampling frequency Fs, where Fs>2Fc, and Fc is the modulation frequency of the pump light;

Step S2: used to obtain all detection light images under the same time delay of pump light and detection light, and form a pixel grayscale array with the grayscale values of the same pixel position of all detection light images, and then calculate the amplitude and phase of each pixel position according to the pixel grayscale array of each pixel position under the same time delay, and combine the amplitude and phase of all pixel positions under the same time delay according to the pixel position to obtain the microscopic spectrum under each time delay, and finally combine the microscopic spectra under all time delays to form a time-space resolved ultrafast spectral microscopic image sequence.

Wherein, the step S2 specifically includes:

Obtain s detection light images taken at a specific time delay t, and extract the grayscale value of the same pixel position of each detection light image in the shooting order to form a pixel grayscale array ai _,j (t)={ _ai,j (t,1),…, _ai,j (t,s)}, t=1,…,T, i=1,…,m, j=1,…,n, ai _,j (t,k) represents the grayscale value of the pixel position of the i-th row and j-th column of the k-th detection light image taken when the time delay is t, k=1,…,s, T is the number of time delays, m and n are the row and column pixel sizes of the detection light image, and s is the number of detection light images;

Calculate the magnitude and phase as follows:

Where A _i,j (t) is the pixel in the i-th row and j-th column of the uncorrected micro-spectral image, is the phase, |A _i,j (t)| is the amplitude;

The uncorrected microscopic spectrum image is corrected according to the following formula and combined according to the pixel position to obtain the microscopic spectrum at each time delay:

In the formula, is the pixel in the i-th row and j-th column of the microscopic spectrum under time delay t, A _i*,j* (t) is the selected reference pixel, and A ^* (t) is the microscopic spectrum under time delay t;

The microscopic spectra under all time delays are combined to form a temporally and spatially resolved ultrafast spectral microscopic image sequence A ^* ={A ^* (t)|t=1,…,T}.

The following is an experiment using a specific example. In the experiment, the femtosecond laser is a titanium sapphire femtosecond laser with a repetition frequency of 80MHz (pulse width of about 100fs) and an output wavelength of 800nm; a microscope objective with a numerical aperture of 0.4 is used; an optical chopper modulates the pump laser, and the chopping frequency is about Fc=4Hz; an sCMOS camera is used to collect data, and the acquisition frequency is Fs=24Hz. The sample is a multilayer _MoSe2 nanofilm sample. The purpose of the experiment is to image the carrier diffusion process of the sample, so that its carrier mobility, an electronic parameter, can be measured by optical methods. First, a multilayer _MoSe2 sample is prepared on an optical glass substrate by mechanical peeling, and its micro-area optical absorption spectrum is measured. The exciton resonance peak is about 800nm wavelength. A 400nm femtosecond laser is selected as the pump pulse, and an 800nm femtosecond laser is used as the detection pulse, as shown in Figure 4. Keep the pump pulse parallel to the microscope objective, focus on the multilayer MoSe ₂ surface, and use an optical chopper to modulate the pump light at 4Hz (Fc=4Hz), and adjust the power of the pump pulse to about 150uW. After the detection pulse passes through the elongated first lens and second lens, it is in a convergent state. The convergent detection pulse enters the microscope objective, and after pre-focusing in front of the sample, the expanded light spot is irradiated on the sample. The microscope objective collects the reflected detection pulse, and after filtering out stray light through a long-pass filter, it is imaged on the CMOS camera through the eyepiece. Select the imaging area on the CMOS camera, control the sampling frequency to 24Hz (Fs=24Hz), and collect 2000 images (s=2000) at a single time t. After further optimization of the collimation, focusing and other conditions of the pump and detection lasers and the position of the eyepiece, the signal is optimized. At this time, time scanning is performed to collect a series of image sequences corresponding to different ultrafast times (t). At each time delay t, the obtained s=2000 images are combined in the shooting order to form a time sequence, and then the 4Hz chopping frequency of the image sequence is extracted to reconstruct the time-space resolved ultrafast spectral microscopy image sequence. Since _MoSe2 is an isotropic material, the grayscale value of a row of pixels can be taken out to form a two-dimensional Gaussian distribution map. The time-space resolved microscopic spectrum at 0ps is shown in Figure 5(a), and the standard deviation σ of the fitted Gaussian ^distribution is shown in Figure 5(b). The image of ^σ2 and time delay t is shown in Figure 6. Using linear curve fitting ^σ2 (t)= _σ02 +2Dt, the carrier diffusion coefficient D= ^2.43cm2 /s is obtained, and then from the Einstein relationship Further calculations revealed that the carrier mobility at 293K was μ=96.07 cm ² ·V ^-1 ·s ^-1 .

It should be noted that the terms "first", "second", etc. in the specification and claims of the present invention and the above-mentioned drawings are used to distinguish different objects rather than to describe a specific order. The reference to "embodiment" in this article means that the specific features, structures or characteristics described in conjunction with the embodiment may be included in at least one embodiment of the present invention. The appearance of this phrase in various places in the specification does not necessarily refer to the same embodiment, nor is it an independent or alternative embodiment that is mutually exclusive with other embodiments. It is explicitly and implicitly understood by those skilled in the art that the embodiments described herein may be combined with other embodiments.

Claims (10)

1. An asynchronous wide-field ultrafast spectral microscopy imaging system, comprising: An asynchronous wide-field femtosecond laser pump-probe subsystem is used to generate pump light and probe light with different time delays, wherein the pump light is focused on the sample surface, and the probe light is pre-focused on the sample surface to form an enlarged light spot, and the probe light image reflected by the sample is continuously sampled at a fixed sampling frequency Fs, wherein Fs>2Fc, and Fc is the modulation frequency of the pump light; The time-space resolved spectral microscopy image reconstruction subsystem is used to obtain all detection light images under the same time delay of pump light and detection light, and to form a pixel grayscale array with the grayscale values of the same pixel position of all detection light images, and then calculate the amplitude and phase of each pixel position according to the pixel grayscale array of each pixel position under the same time delay, and combine the amplitude and phase of all pixel positions under the same time delay according to the pixel position to obtain the microscopic spectrum under each time delay, and finally combine the microscopic spectra under all time delays to form a time-space resolved ultrafast spectral microscopy image sequence. 2. The asynchronous wide-field ultrafast spectral microscopy imaging system according to claim 1 is characterized in that the asynchronous wide-field femtosecond laser pump detection subsystem specifically includes a femtosecond laser, a beam splitter, a time delay adjustment module, a frequency doubling crystal, a frequency adjustment module, a reflector assembly, a microscope objective, an eyepiece and a camera, wherein the beam splitter is located behind the light output end of the femtosecond laser, and is used to divide the output beam of the femtosecond laser into detection light and pump light, and the reflector assembly is used to turn the propagation direction of the pump light, so that the pump light passes through the frequency doubling crystal and the frequency adjustment module in sequence to reach the light input end of the microscope objective, and the frequency adjustment module is used to perform frequency modulation on the pump light with a frequency of Fc, and the detection light reaches the light input end of the microscope objective through the time delay adjustment module, and the sample is located at the focus of the microscope objective, and the microscope objective is used to image the detection light reflected by the sample onto the camera through the eyepiece, and the camera continuously samples at a fixed sampling frequency Fs to form a detection light image sequence. 3. The asynchronous wide-field ultrafast spectral microscopy imaging system according to claim 2 is characterized in that the asynchronous wide-field femtosecond laser pumping detection subsystem also includes a first lens and a second lens, and the first lens and the second lens are located in the detection light path before the microscope objective lens, and are used to pre-focus the detection light beam. 4. The asynchronous wide-field ultrafast spectral microscopy imaging system according to claim 2 is characterized in that the reflector assembly includes a first reflector, a second reflector and a third reflector arranged in sequence along the propagation path of the pump light, and the first reflector, the second reflector and the third reflector enable the pump light to finally reach the light input end of the microscope objective. 5. The asynchronous wide-field ultrafast spectral microscopy imaging system according to claim 1, characterized in that the spatiotemporal resolution spectral microscopy image reconstruction subsystem comprises: A pixel grayscale value acquisition module is used to acquire s detection light images taken at a specific time delay t, and extract the grayscale value of the same pixel position of each detection light image in the shooting order to form an array of pixel grayscale values _ai,j (t)={ _ai,j (t,1),…, _ai,j (t,s)}, where t=1,…,T; i=1,…,m; j=1,…,n, _ai,j (t,k) represents the grayscale value of the pixel position of the i-th row and j-th column of the k-th detection light image taken when the time delay is t, k=1,…,s, T is the measurement number of the time delay, and m and n are the number of pixels in the row and column of the detection light image; The amplitude and phase calculation module is used to calculate the amplitude and phase according to the following formula: Where A _i,j (t) is the pixel in the i-th row and j-th column of the uncorrected micro-spectral image, is the phase, |A _i,j (T)| is the amplitude; The image reconstruction module is used to correct the uncorrected microscopic spectrum image according to the following formula and combine it according to the pixel position to obtain the microscopic spectrum at each time delay: In the formula, is the pixel in the i-th row and j-th column of the microscopic spectrum under time delay t, A _i*,j* (t) is the selected reference pixel, and A ^* (t) is the microscopic spectrum under time delay t; The time-space resolution micro-spectral image forming module is used to form a time-space resolution ultrafast spectral micro-image sequence A ^* ={A ^* (t)|t=1,…,T} from all micro-spectra under time delay. 6 . The asynchronous wide-field ultrafast spectral microscopy imaging system according to claim 2 , wherein the camera is a CMOS camera. 7. The asynchronous wide-field ultrafast spectral microscopy imaging system according to claim 2, characterized in that the time delay adjustment module is a delay device placed on a displacement platform. 8 . The asynchronous wide-field ultrafast spectral microscopy imaging system according to claim 2 , wherein the frequency adjustment module is a chopper. 9. An asynchronous wide-field ultrafast spectral microscopy imaging method, characterized by comprising: Step S1: Generate pump light and probe light with different time delays, and focus the pump light on the sample surface while the probe light is pre-focused on the sample surface to form an enlarged light spot, and continuously sample the probe light image reflected by the sample at a fixed sampling frequency Fs, where Fs>2Fc, and Fc is the modulation frequency of the pump light; Step S2: used to obtain all detection light images under the same time delay of pump light and detection light, and form a pixel grayscale array with the grayscale values of the same pixel position of all detection light images, and then calculate the amplitude and phase of each pixel position according to the pixel grayscale array of each pixel position under the same time delay, and combine the amplitude and phase of all pixel positions under the same time delay according to the pixel position to obtain the microscopic spectrum under each time delay, and finally combine the microscopic spectra under all time delays to form a time-space resolved ultrafast spectral microscopic image sequence. 10. The asynchronous wide-field ultrafast spectral microscopy imaging method according to claim 9, wherein step S2 specifically comprises: Obtain s detection light images taken at a specific time delay t, and extract the grayscale value of the same pixel position of each detection light image in the shooting order to form an array of pixel grayscale values ai _,j (t)={ _ai,j (t,1),…, _ai,j (t,s)}, where t=1,…,T; i=1,…,m; j=1,…,n, _ai,j (t,k) represents the grayscale value of the pixel position of the i-th row and j-th column of the k-th detection light image taken when the time delay is t, k=1,…,s, T is the measurement number of the time delay, and m and n are the number of pixels in the rows and columns of the detection light image; Calculate the magnitude and phase as follows: Where A _i,j (t) is the pixel in the i-th row and j-th column of the uncorrected micro-spectral image, is the phase, |A _i,j (t)| is the amplitude; The uncorrected microscopic spectrum image is corrected according to the following formula and combined according to the pixel position to obtain the microscopic spectrum at each time delay: In the formula, is the pixel in the i-th row and j-th column of the microscopic spectrum under time delay t, A _i*,j* (t) is the selected reference pixel, and A ^* (t) is the microscopic spectrum under time delay t; The microscopic spectra under all time delays are combined to form a spatiotemporally resolved microscopic spectral image A ^* ={A ^* (t)|t=1,…,T}.