A laser time-frequency conversion observation system and method based on hyperspectral imaging

Abstract

The present invention provides a laser time-frequency conversion observation system and method based on hyperspectral imaging. The system includes an optical platform and a femtosecond laser, a pulse signal generator, a reflector, a beam splitter, a laser optical chopper, a white light crystal, a beam reduction and expansion subsystem, a beam homogenization and spot homogenization device, a focusing lens, an aperture, an optical power meter, an optical filter, an optical delay translation stage, a pulse shaping subsystem, a sample loading subsystem, a hyperspectral camera capture subsystem, and a computer control subsystem. The present invention uses a hyperspectral camera to replace a traditional CCD camera to perform optical and spectral imaging of the instantaneous evolution state of the surface of the sample to be measured, compensating for the limited observation capability of traditional optical pump-detection technology due to the optical diffraction limit, and performing real-time optical imaging and two-dimensional spectral imaging of the surface of the sample to be measured when excited by the femtosecond laser.

Description

Technical Field

[0001] The present invention belongs to the technical field of ultrafast laser observation, and in particular relates to a laser time-frequency conversion observation system and method based on hyperspectral imaging. Background Art

[0002] Femtosecond laser processing is a nonlinear, nonequilibrium, multi-scale ultrafast process involving complex physical processes such as energy deposition and transfer, as well as phase transitions and removal of the sample being measured. Experimental observations with ultrafast temporal resolution reveal the mechanisms of femtosecond laser-matter interactions, which is of great significance to the development of femtosecond laser processing. Currently, the main observational techniques used to study femtosecond laser-matter interactions include time-resolved optical imaging, time-resolved X-ray diffraction, time-resolved electron diffraction, and time-resolved transient absorption spectroscopy.

[0003] The basic concept of pump-probe technology is to study transient evolution processes using two pulsed laser beams with carefully designed time delays. One beam acts as the pump light to excite transient processes in the sample under test, while the other acts as the probe light to observe the excited region after a certain delay. Currently, pump-probe technology is used to study transient processes in femtosecond laser processing samples primarily with the help of signal receivers such as charge-coupled devices (CCDs) and photodiodes. By using different signal acquisition methods, the intensity and phase changes of the probe light at different detection delays can be obtained, thereby analyzing the ultrafast evolution of the transient properties of the sample after laser action. Due to its use of optical imaging, traditional femtosecond laser optical pump-probe technology can only observe transient optical property changes induced by the sample surface. Analysis of ultrafast dynamics primarily focuses on reflectivity and image structure, resulting in low signal-to-noise ratios and significant background variations caused by fluctuations in laser output. The observed plasma, shock wave, and phase transition evolution are limited, and due to the optical diffraction limit, the spatial resolution is insufficient to detect dynamic information of nanoscale electrons and lattices. The transient absorption spectroscopy detection technology derived from the pump-probe technology can only detect a single point in the excitation area of the sample to be tested to obtain a one-dimensional absorption spectrum. Moreover, due to the weak optical signal, it cannot be combined with the CCD to directly observe the transient evolution process of the surface of the sample to be tested. Therefore, it is impossible to observe the plasma eruption and shock wave propagation process on the surface of the sample to be tested, and the ability to observe the ablation of the sample to be tested is limited.

[0004] Hyperspectral imaging combines traditional two-dimensional imaging and spectroscopy techniques. It is a sophisticated technique that can capture and analyze spectra at each point within a spatial region. By detecting unique spectral "signatures" at different spatial locations within a single object, it can detect materials that are visually indistinguishable. This technique offers numerous advantages, including spatial identifiability, ultra-multi-band, high spectral resolution, a wide spectral range, and integrated spectra. Spectral imaging primarily measures reflected light after the interaction of light with matter. This imaging technique can reveal transient changes in the optical properties of the sample surface. Because the surface states of a sample at multiple temporal and spatial scales after ultrafast laser excitation exhibit distinct nonlinear, nonequilibrium effects on imaging light sources at different wavelengths, two-dimensional spectroscopy imaging at multiple wavelengths can intuitively and comprehensively characterize the plasma characteristics that carry elemental information about the sample, as well as the energy transfer of excited molecular states, thereby obtaining information about molecular dynamics. Combining hyperspectral imaging with optical pump-probe technology can provide additional physicochemical and morphological information about the sample surface at ultrafast scales, enabling a more comprehensive understanding and exploration of the ultrafast dynamics of femtosecond laser processing. Summary of the Invention

[0005] In response to the above-mentioned deficiencies in the prior art, the present invention provides a laser time-frequency conversion observation system and method based on hyperspectral imaging. The present invention uses a hyperspectral camera to replace the traditional CCD camera to perform optical imaging and spectral imaging of the instantaneous evolution state of the surface of the sample to be measured, thereby compensating for the limited observation capability caused by the influence of the optical diffraction limit in the traditional optical pump detection technology, and performing real-time optical imaging and two-dimensional spectral imaging of the surface of the sample to be measured by femtosecond laser excitation.

[0006] In order to achieve the above purpose, the technical solution adopted by the present invention is:

[0007] This solution provides a laser time-frequency conversion observation system based on hyperspectral imaging, including an optical platform and a femtosecond laser, a pulse signal generator, a reflector, a beam splitter, a laser optical chopper, a white light crystal, a beam shrinking and expanding subsystem, a beam homogenizing and spot homogenizing device, a focusing lens, an aperture, an optical power meter, an optical filter, an optical delay translation stage, a pulse shaping subsystem, a sample loading subsystem, a hyperspectral camera shooting subsystem, and a computer control subsystem arranged on the optical platform;

[0008] The computer control subsystem issues instructions to the pulse signal generator to stimulate the femtosecond laser to output high-energy femtosecond pulses, and uses a beam splitter to divide the high-energy femtosecond pulses into pump light and detection light. The laser path is collimated using an aperture to make it propagate in a straight line along a fixed direction. The pump light frequency is adjusted using a laser optical chopper, and the pump light is reflected by a reflector to adjust the direction of the pump light. It is focused on the excited sample to be tested in the sample loading subsystem with a set geometric relationship. The pump light energy of the sample to be tested is measured using an optical power meter, and the energy of the pump light is adjusted using an optical filter to obtain the required laser pulse energy. The detection light is then passed through a white light crystal, a beam shrinking and expanding subsystem, a beam homogenizer, and a spot homogenizer in sequence to output a detection white light with uniform light intensity distribution. The pulse shaping subsystem converts the incident laser into an output beam with a desired shape. After the optical delay translation stage outputs the detection light, the detection light with an adjustable time interval with the pump light is output, and the detection light is focused on the surface of the sample to be tested through an adjustable focusing lens for illumination. The computer control subsystem controls the sample loading subsystem to move in three mutually perpendicular directions, and moves the area to be excited of the sample to be tested to coincide with the focused spots of the pump light and the detection light. The hyperspectral camera shooting subsystem is used to shoot, amplify and record the kinetic signals after the femtosecond laser excites the surface of the sample to be tested, and collect image information of the spectral band. The computer control subsystem reads and processes the image information output by the hyperspectral camera shooting subsystem to obtain the two-dimensional spectral signal and two-dimensional imaging information of the sample to be tested.

[0009] The beneficial effects of the present invention are as follows: the present invention utilizes the femtosecond pulses output by a femtosecond laser to split into pump light and probe light. The pump light is focused onto the sample surface through a lens for excitation. The probe light is reflected by a time-delay mirror to detect changes in the surface of the sample to be tested caused by the pump light-induced excitation at different time lengths. The optical signal is received by a hyperspectral camera, and two-dimensional image information and two-dimensional spectral information are output through a computer. The present invention uses a hyperspectral camera to replace a traditional CCD camera to collect image information of hundreds of spectral bands of the instantaneous evolution state of the sample surface to be tested. The nonlinear effect causes the series of ultrafast instantaneous states of the sample surface to display different information under multiple spectral imaging. This allows the imaging spectroscopy system with spatial resolution to expand the target resolution capability from simple spectrum to spectral recognition combined with the target's geometric characteristics, thereby obtaining more information about the ultrafast plasma evolution and phase transition of the sample surface to be tested in different time and frequency domains.

[0010] Furthermore, the femtosecond laser includes a femtosecond pulse oscillator, a chirped pulse amplification subsystem and a laser control subsystem;

[0011] Femtosecond pulses are generated by a femtosecond pulse oscillator, and high-energy femtosecond pulses are obtained after amplification by a chirped pulse amplifier subsystem. The laser control subsystem is used to output the pulse signal synchronized with the femtosecond pulse to the pulse signal generator and computer control subsystem.

[0012] The beneficial effect of the above further scheme is: the present invention uses a chirped pulse amplification subsystem to obtain high-energy femtosecond pulses, which carry sufficiently high energy to excite the surface of materials under different ablation thresholds, produce an ablation effect on the surface, generate corresponding ablation signals, and facilitate the subsequent use of filters to adjust the femtosecond pulse energy.

[0013] Furthermore, the beam splitter is a non-polarizing beam splitter with a splitting ratio of 3:1.

[0014] The beneficial effect of the above further solution is that after passing through the beam splitter, the pump light obtains 3 / 4 of the energy, and the light intensity is sufficient to excite the material surface, and the detection light obtains 1 / 4 of the energy, and the light intensity is high enough to illuminate the material surface.

[0015] Still further, the optical delay translation stage includes a computer control subsystem of the translation stage and the translation stage;

[0016] The position of the translation stage is adjusted by the computer control subsystem of the translation stage to control the time interval between the detection light and the pump light reaching the sample to be measured.

[0017] The beneficial effect of the above further scheme is that the detection light is changed from a single wavelength of light to white light with uniform light intensity distribution at multiple wavelengths, and an optical path difference ranging from femtoseconds to nanoseconds can be generated between the pump light and the detection light. The detection light can reach the sample surface at different time intervals ranging from femtoseconds to nanoseconds after the pump light excites the sample, and illuminate the surface of the sample to be measured, so that the hyperspectral camera can capture optical signals at different time intervals ranging from femtoseconds to nanoseconds after the pump light excites the sample.

[0018] Furthermore, the hyperspectral camera shooting subsystem includes a hyperspectral camera and a computer;

[0019] A hyperspectral camera is used to detect the optical information intensity signal generated after the surface of the sample to be tested is excited by pump light, and a computer is used to collect and output the optical information intensity signal to obtain multi-region two-dimensional spectral signals and two-dimensional imaging information with spatial resolution capability.

[0020] The beneficial effect of the above further scheme is that due to the long exposure time of the hyperspectral camera, the computer controls the pulse signal generator to trigger the generation of femtosecond pulses after triggering the hyperspectral camera to open the shutter laser for a certain period of time by setting a control algorithm, thereby achieving accurate single exposure and image capture, recording the instantaneous optical information of the material surface, and outputting multi-dimensional spectral images through the computer.

[0021] Furthermore, the hyperspectral camera is placed on the image plane of the hyperspectral camera shooting subsystem, a filter and a tube lens are provided in front of the hyperspectral camera, and a sample stage is provided on the object plane of the hyperspectral camera shooting subsystem.

[0022] The beneficial effect of the above further scheme is that the detection light is reflected by the delay mirror to detect the changes in the surface of the sample to be tested caused by the pump light induced excitation at different delay lengths. Its optical signal will be received by the hyperspectral camera and output high-resolution two-dimensional image information and two-dimensional spectral information through the computer.

[0023] Furthermore, the optical power meter, the sample carrier subsystem and the optical delay translation stage are all connected to the computer control subsystem.

[0024] The beneficial effect of the above further solution is that the electronic instruments and equipment in the experimental device are all linked and controlled by the computer, making the experimental operation simple, convenient and accurate.

[0025] The present invention provides a laser time-frequency conversion observation method based on hyperspectral imaging, comprising the following steps:

[0026] S1. Send instructions to the pulse signal generator to excite the femtosecond laser, and use the femtosecond laser to output high-energy 800nm femtosecond pulses, which are divided into pump light and probe light using a beam splitter;

[0027] S2, after being reflected by the reflector, the pump light is focused by a focusing lens onto the sample to be tested placed on the sample loading subsystem to excite the sample to be tested;

[0028] S3. Use a laser optical chopper to adjust the required pump light frequency, use an optical power meter to measure the pump light energy of the sample to be tested, and use an optical filter to adjust the energy of the pump light to obtain the required laser pulse energy;

[0029] S4. The detection light is passed through a white light crystal to output a detection white light pulse. The beam shrinking and expanding subsystems are used to make the spot size meet the incident aperture requirements of the focusing lens. The beam homogenization and spot homogenization devices are used to shape the detection white light pulse to output a stable detection white light with uniform light intensity distribution. The optical delay translation stage is used to output the detection light with an adjustable time interval with the pump light, and the detection light is focused on the surface of the sample to be tested through the focusing lens for illumination.

[0030] S5. Using the computer control subsystem, the sample loading subsystem is controlled to move in three mutually perpendicular directions, so that the area to be excited of the sample to be tested is moved to coincide with the focused spots of the pump light and the detection light;

[0031] S6. Using the hyperspectral camera shooting subsystem, the surface of the sample to be tested, which is illuminated by the detected detection light, is subjected to optical imaging and spectral imaging through the tube lens. The transient optical property information and spectral information of the excited surface of the sample to be tested are collected to obtain a two-dimensional spectral signal and two-dimensional imaging information of the sample to be tested.

[0032] The beneficial effects of the present invention are as follows: the present invention utilizes the femtosecond laser beam output by the laser to split into pump light and probe light. The pump light is focused onto the sample surface through a lens for excitation. The probe light is reflected by a time-delay mirror to detect changes in the surface of the sample to be tested caused by the pump light-induced excitation at different time lengths. The optical signal is received by a hyperspectral camera, and two-dimensional image information and two-dimensional spectral information are output through a computer. The present invention uses a hyperspectral camera to replace the traditional CCD camera to collect image information of hundreds of spectral bands of the instantaneous evolution state of the surface of the sample to be tested. The nonlinear effect causes the series of ultrafast instantaneous states of the sample surface to display different information under multiple spectral imaging. This allows the imaging spectroscopy system with spatial resolution to expand the resolution of the target from simple spectrum to spectral recognition combined with the target's geometric characteristics, thereby obtaining more information about the ultrafast plasma evolution and phase transition of the sample surface to be tested in different time and frequency domains.

[0033] Furthermore, the transient optical property information of the excited sample surface is obtained as follows:

[0034] Before the sample is pumped, a clean, unprocessed area is selected and illuminated with probe light. The optical properties at that moment are captured and recorded using a hyperspectral camera as a background image.

[0035] The optical information obtained after the sample to be tested is pumped and excited is recorded as the excitation image;

[0036] The background image and the excitation image are compared and cropped to obtain the transient optical properties of the surface of the excited sample under ultrafast scale.

[0037] The beneficial effect of this further approach is to combine hyperspectral imaging technology with optical pump-probe technology to obtain more physicochemical and morphological information on the material surface at ultrafast time scales. It also extracts two-dimensional spectral signals and two-dimensional image information on the material surface at ultrafast time scales after femtosecond pulse excitation, thereby providing a more comprehensive understanding and exploration of the ultrafast dynamics of femtosecond laser processing. In terms of testing methods, the triggering program for the laser and spectral camera is set by a pulse generator, enabling multiple and rapid imaging of the system, improving the system's data collection efficiency. BRIEF DESCRIPTION OF THE DRAWINGS

[0038] Figure 1 It is a flow chart of the method of the present invention.

[0039] Figure 2 3 is a structural diagram of an ultrafast laser time-frequency conversion observation method based on hyperspectral imaging technology according to an embodiment of the present invention.

[0040] Figure 3 1 is a schematic diagram of an optical path of an ultrafast laser time-frequency conversion observation method based on hyperspectral imaging technology according to an embodiment of the present invention.

[0041] Figure 4 3 is a schematic diagram of the use process of the ultrafast laser time-frequency conversion observation method based on hyperspectral imaging in this embodiment.

[0042] Among them, 1- femtosecond laser, 2- first beam splitter, 3- white light crystal, 4- beam reduction and expansion subsystem, 5- beam homogenization and spot homogenization device, 6- first reflector, 7- second reflector, 8- third reflector, 9- optical delay translation stage, 10- fourth reflector, 11- fifth reflector, 12- beam splitter, 13- first focusing lens, 14- sample to be tested, 15- second focusing lens, 16- sixth reflector, 17- optical chopper, 18- optical filter, 19- seventh reflector, 20- tube lens, 21- second filter, 22- hyperspectral camera, 23- computer control subsystem, 24- pulse signal generator. DETAILED DESCRIPTION

[0043] The specific embodiments of the present invention are described below to facilitate understanding of the present invention by those skilled in the art. However, it should be clear that the present invention is not limited to the scope of the specific embodiments. For those skilled in the art, as long as various changes are within the spirit and scope of the present invention as defined and determined by the appended claims, these changes are obvious, and all inventions and creations utilizing the concepts of the present invention are protected.

[0044] Example 1

[0045] The present invention provides a laser time-frequency conversion observation system based on hyperspectral imaging, comprising an optical platform and a femtosecond laser, a pulse signal generator, a reflector, a beam splitter, a laser optical chopper, a white light crystal, a beam shrinking and expanding subsystem, a beam homogenizing and spot homogenizing device, a focusing lens, an aperture, an optical power meter, an optical filter, an optical delay translation stage, a pulse shaping subsystem, a sample loading subsystem, a hyperspectral camera shooting subsystem, and a computer control subsystem arranged on the optical platform;

[0046] The computer control subsystem issues instructions to the pulse signal generator to stimulate the femtosecond laser to output high-energy femtosecond pulses, and the beam splitter is used to divide the high-energy femtosecond pulses into pump light and probe light, wherein the pump light is used to excite the sample to be tested, and the probe light is used to detect the changes in the surface optical properties of the sample to be tested after being excited by the pump light. The laser path is collimated using an aperture to make it propagate in a straight line along a fixed direction to prevent the light from being skewed. The pump light frequency is adjusted using a laser optical chopper, and the pump light is reflected by a reflector to adjust the direction of the pump light. It is focused on the excited sample to be tested in the sample loading subsystem with a set geometric relationship. The pump light energy of the sample to be tested is measured using an optical power meter, and the energy of the pump light is adjusted using an optical filter to obtain the required laser pulse energy. The probe light is sequentially passed through a white light crystal, a beam shrinking and expanding subsystem, and a beam homogenizer. After the light spot homogenization device, a detection white light with uniform light intensity distribution is output. The incident laser is converted into an output beam with the desired shape through the pulse shaping subsystem, thereby improving the detection quality and imaging quality. After the detection light is output by the optical delay translation stage, the detection light with an adjustable time interval with the pump light is output, and the detection light is focused on the surface of the sample to be tested through an adjustable focusing lens for illumination. The computer control subsystem is used to control the sample loading subsystem to move in three mutually perpendicular directions, and the area to be excited of the sample to be tested is moved to coincide with the focused light spots of the pump light and the detection light. The hyperspectral camera shooting subsystem is used to shoot, amplify and record the kinetic signal after the femtosecond laser excites the surface of the sample to be tested, and collect image information of the spectral band. The computer control subsystem is used to read and process the image information output by the hyperspectral camera shooting subsystem to obtain a two-dimensional spectral signal and two-dimensional imaging information of the sample to be tested. The femtosecond laser includes a femtosecond pulse oscillator, a chirped pulse amplification subsystem, and a laser control subsystem; the femtosecond pulse is generated by the femtosecond pulse oscillator, and a high-energy femtosecond pulse is obtained after amplification by the chirped pulse amplification subsystem. The high-energy femtosecond pulse carries a sufficiently strong photon energy to ablate the sample surface at different thresholds to generate a spectral signal, and facilitates the subsequent use of filters to adjust the femtosecond pulse energy. The laser control subsystem is used to output a pulse signal synchronized with the femtosecond pulse to the pulse signal generator and computer control subsystem. The beam splitter is a non-polarizing beam splitter with a splitting ratio of 3:1. The optical delay translation stage includes a computer control subsystem of the translation stage and a translation stage; the position of the translation stage is adjusted by the computer control subsystem of the translation stage to control the time interval between the detection light and the pump light arriving at the sample to be measured. The hyperspectral camera shooting subsystem includes a hyperspectral camera and a computer. The hyperspectral camera is used to detect the optical information intensity signal generated after the surface of the sample to be tested is excited by pump light, and the computer is used to collect and output the optical information intensity signal to obtain multi-region two-dimensional spectral signals and two-dimensional imaging information with spatial resolution capability.The hyperspectral camera is placed on the image plane of the hyperspectral camera capture subsystem. A filter and tube lens are also placed in front of the hyperspectral camera. A sample stage is placed on the object plane of the hyperspectral camera capture subsystem. The optical power meter, sample stage subsystem, and optical delay and translation stage are all connected to the computer control subsystem.

[0047] In this embodiment, a femtosecond laser outputs high-energy 800nm femtosecond pulses, which are split into two beams by a beam splitter, serving as pump light and probe light respectively. The pump light is focused by a lens onto the sample to be tested, which is placed on the sample loading subsystem, to excite the sample to be tested. An optical power meter is used to measure the energy of the pump light pulses that excite the sample, and a filter is used to adjust the energy of the pump light to obtain the laser pulse energy required in the experiment. The pump light energy of the sample to be tested is measured using an optical power meter; the transmitted light is converted into white light containing multiple wavelengths after passing through a white light crystal, and the beam shrinking and expanding subsystems change the laser spot size to an appropriate range to match the incident aperture of the focusing lens in the subsequent optical path. The optical delay translation stage will cause the pump light and probe light to produce a delay ranging from femtoseconds to nanoseconds, and focus on the surface of the sample to be tested through an adjustable lens to provide illumination. The hyperspectral camera shooting subsystem will perform optical imaging and spectral imaging on the surface of the material illuminated by the detection light through the tube lens, collect the transient optical property information and spectral information of the surface of the excited material, and output the data after internal processing and calculation in the camera.

[0048] In this embodiment, both the reflector and the focusing lens can be manually adjusted, and the direction of the light beam can be adjusted in combination with the aperture so as to accurately focus on the area to be excited on the surface of the material.

[0049] In this embodiment, the femtosecond laser includes a femtosecond pulse oscillator, a chirped pulse amplification subsystem and a laser control subsystem. The femtosecond pulse oscillator generates femtosecond pulses, which are amplified by the chirped pulse amplification system to obtain high-energy femtosecond pulses; the laser control subsystem outputs a pulse signal synchronized with the femtosecond pulse to a pulse signal generator and a computer control subsystem, and is controlled by the computer control subsystem at the same time.

[0050] In this embodiment, the optical power meter, laser optical chopper, sample stage, and optical delay translation stage are all electrically connected to a computer control subsystem. The computer control subsystem reads the real-time femtosecond pulse energy measured by the optical power meter and controls the stage's movement in three mutually perpendicular directions, moving the sample's excitation region to coincide with the focused spots of the pump and probe beams. The optical delay translation stage also moves in one direction to generate the time interval between the pump and probe beams required for the experiment.

[0051] In this embodiment, the hyperspectral camera shooting subsystem consists of a hyperspectral camera, a tube lens, and a computer. Due to the long exposure time of the hyperspectral camera, the computer sets a control algorithm to control the pulse signal generator to trigger the generation of femtosecond pulses after triggering the hyperspectral camera to open the shutter laser for a certain period of time, thereby achieving precise single exposure and image capture, recording the instantaneous optical information of the material surface, and outputting a multi-dimensional spectral image through the computer.

[0052] In this embodiment, since the exposure time of the hyperspectral camera is relatively long, the computer control subsystem needs to set a certain time delay between controlling the pulse signal generator to trigger the generation of femtosecond pulses and triggering the hyperspectral camera to take pictures. The hyperspectral camera is first triggered to take pictures, and then the pulse signal generator is triggered after a certain exposure time is reached to stimulate the femtosecond pulses so that the hyperspectral camera can capture the changes in transient optical properties.

[0053] like Figure 2 As shown, the structure of a femtosecond pump-probe system combined with a hyperspectral camera according to one embodiment of the present invention is provided, comprising: femtosecond pulse emission, sample excitation, sample detection, light convergence, and signal acquisition. The femtosecond pulse emission is used to emit femtosecond pulse laser light, which is split by a beam splitter to generate pump light and probe light, respectively; the sample excitation is used to converge the pump light onto the area to be excited on the sample to be tested; the sample detection is used to convert the probe light into an optical signal that can be detected by the hyperspectral camera and focus it onto the light convergence part; the light convergence part is used to overlap the pump light and probe light in the area to be excited on the sample surface, wherein the pump light is used to excite the sample to be tested, and the probe light is used to detect changes in the surface optical properties of the sample to be tested after being excited by the pump light; the signal acquisition part is used to collect the changes in the optical property intensity of the sample to be tested caused by the pump light excitation, complete the ultrafast dynamics data acquisition of the sample surface to be tested, obtain the transient optical image and spectral image of the sample surface to be tested, and thus obtain data combining images and spectra with spectral spatial resolution capability.

[0054] In this embodiment, Figure 3 As shown, Figure 3The figure shows the optical path of a femtosecond pump-probe system according to one embodiment of the present invention. The femtosecond laser 1 is controlled by a computer control subsystem 23 and a pulse signal generator 24 to generate 800nm femtosecond laser pulses. After passing through a first beam splitter 2, the transmitted light forms the probe light, and the reflected light forms the pump light. The transmitted light passes through a white light crystal 3 and becomes white light containing multiple wavelengths. The beam reduction and expansion subsystem 4 changes the laser spot size to an appropriate range to match the incident aperture of the focusing lens in the subsequent optical path. The white light then passes through a beam homogenizer and spot homogenizer 5 to obtain light with uniform spatial intensity distribution. The optical delay translation stage 9 is composed of a first reflector 6, a second reflector 7, a third reflector 8, a fourth reflector 10, and a motorized translation stage. The pump light is reflected by the first reflector 6, then by the seventh reflector 19 and the sixth reflector 16. It is focused by the second focusing lens 15 and incident on the surface of the sample 14 to be tested for excitation. The optical filter 18 is used to adjust the energy of the pump light, and the laser optical chopper 17 is used to adjust the natural frequency of the pump light to obtain the desired pulse interval. The probe light passes through the optical delay stage 9, where it is time-delayed with the pump light. The probe light then passes through the fifth reflector 11 and the beam splitter 12 before being focused by the first focusing lens 13 onto the area to be excited on the sample 14 to be tested. The computer control subsystem 23 controls the three-dimensional movement of the stage carrying the sample 14. In conjunction with the two focusing lenses 13 and 15 mounted on the four-dimensional mirror frame, the computer control subsystem 23 adjusts the focused spots of the pump light and probe light on the sample surface to overlap. The transient optical signal generated by the pump light excitation on the surface of the sample to be tested is illuminated by the detection light, vertically reflected and reflected by the second beam splitter 12, and passes through the tube lens 20 to improve the imaging quality. The second filter 21 filters out the interfering scattered pump light and plasma luminescence interference, and the final optical property signal is captured and recorded by the hyperspectral camera 22. The computer control subsystem 23 can simultaneously control the pulse signal generator 24, the optical delay translation stage 9, the hyperspectral camera 22 and the stage 14, so that each device can work in coordination, especially the synergy between the pulse signal generator 24 and the hyperspectral camera 22. The long exposure time of the hyperspectral camera 22 requires the computer control subsystem to first start the shooting of the hyperspectral camera 22, and then control the pulse signal generator 24 to trigger the femtosecond laser 1 to output femtosecond pulses at the appropriate time so that the hyperspectral camera 22 can shoot. The optical delay translation stage 8 can generate a series of optical delays by moving, and finally the hyperspectral camera collects, amplifies and outputs the transient two-dimensional optical images and spectral images of the material surface in the femtosecond to nanosecond range required for the experiment, thereby extracting the ultrafast dynamic information of the material surface in different frequency domains and time domains.

[0055] In this embodiment, the femtosecond laser is a titanium sapphire femtosecond laser produced by Spectra Physics, USA, with a maximum power of 3.5W, a central wavelength of 800nm, a pulse width of 35fs, and a time delay reflectivity of up to 16ns.

[0056] The specific detection steps are as follows: (1) Without placing the sample to be tested, the hyperspectral camera receives the optical signal of the surface of the material illuminated by the detection light as a reference signal and background; (2) The computer controls the hyperspectral camera to start exposure, sets the output frequency of the optical chopper, and then the pulse signal generator controls the laser to generate a beam of femtosecond laser pulses; (3) The pump light outputs the light of the inherent frequency after passing through the chopper, and the detection light outputs the illumination white light with uniform light intensity distribution through the white light crystal, the beam shrinking and expanding subsystem, and the beam homogenization and spot homogenization device; (4) The movement of the optical translation stage makes the pump light A certain delay is generated with the detection light, and the hyperspectral camera quickly captures the optical information of the material surface area after the pump light excitation and the detection light illumination. The optical translation stage continues to move to generate more delays, and the hyperspectral camera continues to capture the relevant optical information; (5) The captured information under each detection delay is compared with the reference signal, and after cutting off the background image, the corresponding optical information under each delay and the spectral information under the illumination of different wavelengths of detection light are obtained; (6) By rotating the control filter and repeating the above steps, the ultrafast dynamic information of the material surface excited by pump light at different energies can be obtained.

[0057] In this embodiment, the translation stage used to place the sample is a three-dimensional piezoelectric translation stage with a displacement accuracy of 1 nm in three dimensions, sufficient to meet the experimental precision requirements for sample spatial movement. During the experiment, strict coupling between the pump and detection lenses and the sample is required to enable the hyperspectral camera to accurately image the excitation information on the material surface. Computer processing of the experimentally measured data reveals a series of optical property changes ranging from femtoseconds to nanoseconds. This expands the material resolution from simple spectral analysis to spectral identification combined with target geometric characteristics, and provides more multi-frequency transient evolution information under ultrafast dynamics in different time domains. For example, by studying plasma excitation and analyzing the spatiotemporal evolution of plasma free electron density, the absorption mechanism of laser energy can be revealed. By studying plasma and shock wave propagation and plasma radiation processes, and analyzing the evolution of different plasma types / compositions and shock waves / stress waves, the patterns of laser energy deposition can be explored, surface transformation processes at the microscopic scale can be analyzed, and ultimately, material phase transitions can be revealed. On this basis, by further optimizing the laser processing conditions, such as adopting femtosecond laser spatiotemporal shaping, the interaction process between laser and material can be regulated, thereby achieving effective control of the final processing morphology and properties of the material, and improving the processing quality, precision, efficiency and consistency.

[0058] In this embodiment, the present invention controls the pulse triggering of the femtosecond laser through a computer and a pulse signal generator, controls the time delay interval between the pump light and the probe light through an optical delay stage, and controls the energy of the pump light through a filter. By scanning the interval between the pump light and the probe light and processing the data obtained in combination with the hyperspectral camera shooting system, spatial image information and multi-band two-dimensional spectral information of the measured sample surface evolving over time under different energy excitations are obtained.

[0059] Example 2

[0060] like Figure 1 As shown, the present invention provides a laser time-frequency conversion observation method based on hyperspectral imaging, and its implementation method is as follows:

[0061] S1. Send instructions to the pulse signal generator to excite the femtosecond laser, and use the femtosecond laser to output high-energy 800nm femtosecond pulses, which are divided into pump light and probe light using a beam splitter;

[0062] S2, after being reflected by the reflector, the pump light is focused by a focusing lens onto the sample to be tested placed on the sample loading subsystem to excite the sample to be tested;

[0063] S3. Use a laser optical chopper to adjust the required pump light frequency, use an optical power meter to measure the pump light energy of the sample to be tested, and use an optical filter to adjust the energy of the pump light to obtain the required laser pulse energy;

[0064] S4. The detection light is passed through a white light crystal to output a detection white light pulse. The beam shrinking and expanding subsystems are used to make the spot size meet the incident aperture requirements of the focusing lens. The beam homogenization and spot homogenization devices are used to shape the detection white light pulse to output a stable detection white light with uniform light intensity distribution. The optical delay translation stage is used to output the detection light with an adjustable time interval with the pump light, and the detection light is focused on the surface of the sample to be tested through the focusing lens for illumination.

[0065] S5. Using the computer control subsystem, the sample loading subsystem is controlled to move in three mutually perpendicular directions, so that the area to be excited of the sample to be tested is moved to coincide with the focused spots of the pump light and the detection light;

[0066] S6. Using the hyperspectral camera shooting subsystem, the surface of the sample to be tested, which is illuminated by the detected detection light, is subjected to optical imaging and spectral imaging through the tube lens. The transient optical property information and spectral information of the excited surface of the sample to be tested are collected to obtain a two-dimensional spectral signal and two-dimensional imaging information of the sample to be tested.

[0067] In this embodiment, the transient optical property information of the excited sample surface is obtained as follows:

[0068] Before the sample is pumped, a clean, unprocessed area is selected and illuminated with probe light. The optical properties at that moment are captured and recorded using a hyperspectral camera as a background image.

[0069] The optical information obtained after the sample to be tested is pumped and excited is recorded as the excitation image;

[0070] The background image and the excitation image are compared and cropped to obtain the transient optical properties of the surface of the excited sample under ultrafast scale.

[0071] like Figure 4 As shown, the following describes in detail the use of the ultrafast laser time-frequency conversion observation method based on hyperspectral imaging technology of the present invention through specific embodiments:

[0072] 1. Adjust and align the optical path of the entire device to ensure the accurate propagation of the laser beam in the entire optical system, and place the sample on the electric translation stage;

[0073] 2. Initialize each instrument, set the value of the pulse signal generator, set the parameters of the spectral camera by the computer control subsystem, and reset the position of the electric translation stage and the time-delay translation stage;

[0074] 3. Set the parameters of the electric translation stage and the time-delay translation stage through the computer control subsystem, determine the moving step size, starting position and final position of the two, and set the storage of the spectral camera acquisition system;

[0075] 4. Perform pump excitation attempts on the sample by moving the time-delay translation stage and use a spectral camera to capture two-dimensional image information to ensure that the pump light and probe light reach the sample surface at the same time. This is set as the delay zero point.

[0076] 5. The time-delay translation stage moves one step to generate a time delay of the pump light and the probe light. Since the exposure time of the spectral camera is relatively long, the spectral camera shooting system is started first. When the camera shooting point is reached after a period of time, the laser is triggered by the pulse signal generator to generate laser light. The pump light will excite the sample surface, and the probe light will illuminate the sample surface. At the same time, the spectral camera collects the two-dimensional image information and two-dimensional spectrum information under this delay.

[0077] 6. The spectral camera amplifies, processes and calculates the collected relevant information to obtain a series of transient spectral data and corresponding two-dimensional image information in the time domain, and saves and outputs them;

[0078] 7. Determine whether the delay translation stage has moved to the set final delay. If so, end signal acquisition; if not, both the electric translation stage and the delay translation stage move one step, and repeat 5 and 6 to continue testing.

[0079] The present invention uses a femtosecond laser beam split from a laser to form pump light and probe light. The pump light is focused onto the sample surface through a lens for excitation. The probe light is reflected by a time-delay mirror to detect changes in the sample surface caused by the pump light-induced excitation at different durations. The optical signal is received by a hyperspectral camera, and a computer outputs two-dimensional image information and two-dimensional spectral information. The present invention uses a hyperspectral camera to replace a traditional CCD camera to capture image information of hundreds of spectral bands of the instantaneous evolution state of the sample surface. The nonlinear effect causes the series of ultrafast instantaneous states of the sample surface to display different information under multiple spectral imaging. This allows the imaging spectroscopy system with spatial resolution to expand the target resolution capability from simple spectral analysis to spectral recognition combined with the target's geometric characteristics, thereby obtaining more information about the ultrafast plasma evolution and phase transitions of the sample surface in different time and frequency domains.

[0080] The embodiments described are preferred implementations of the present invention, but the present invention is not limited to the above implementations. Any obvious improvements, substitutions or modifications that can be made by those skilled in the art without departing from the essence of the present invention are within the scope of protection of the present invention.

Claims

1. A laser time-frequency conversion observation system based on hyperspectral imaging, characterized in that: It includes an optical platform and a femtosecond laser, a pulse signal generator, a reflector, a beam splitter, a laser optical chopper, a white light crystal, a beam shrinking and expanding subsystem, a beam homogenizing and spot homogenizing device, a focusing lens, an aperture, an optical power meter, an optical filter, an optical delay translation stage, a pulse shaping subsystem, a sample loading subsystem, a hyperspectral camera shooting subsystem, and a computer control subsystem arranged on the optical platform; The computer control subsystem issues instructions to the pulse signal generator to stimulate the femtosecond laser to output high-energy femtosecond pulses, and uses a beam splitter to divide the high-energy femtosecond pulses into pump light and detection light. The laser path is collimated using an aperture to make it propagate in a straight line along a fixed direction. The pump light frequency is adjusted using a laser optical chopper, and the pump light is reflected by a reflector to adjust the direction of the pump light. It is focused on the excited sample to be tested in the sample loading subsystem with a set geometric relationship. The pump light energy of the sample to be tested is measured using an optical power meter, and the energy of the pump light is adjusted using an optical filter to obtain the required laser pulse energy. The detection light is then passed through a white light crystal, a beam shrinking and expanding subsystem, a beam homogenizer, and a spot homogenizer in sequence to output a detection white light with uniform light intensity distribution. The pulse shaping subsystem converts the incident laser into an output beam with a desired shape. After the optical delay translation stage outputs the detection light, the detection light with an adjustable time interval with the pump light is output, and the detection light is focused on the surface of the sample to be tested through an adjustable focusing lens for illumination. The computer control subsystem controls the sample loading subsystem to move in three mutually perpendicular directions, and moves the area to be excited of the sample to be tested to coincide with the focused spots of the pump light and the detection light. The hyperspectral camera shooting subsystem is used to shoot, amplify and record the kinetic signals after the femtosecond laser excites the surface of the sample to be tested, and collect image information of the spectral band. The computer control subsystem reads and processes the image information output by the hyperspectral camera shooting subsystem to obtain the two-dimensional spectral signal and two-dimensional imaging information of the sample to be tested.

2. The laser time-frequency conversion observation system based on hyperspectral imaging according to claim 1 is characterized in that: The femtosecond laser includes a femtosecond pulse oscillator, a chirped pulse amplification subsystem and a laser control subsystem; Femtosecond pulses are generated by a femtosecond pulse oscillator, and high-energy femtosecond pulses are obtained after amplification by a chirped pulse amplifier subsystem. The laser control subsystem is used to output the pulse signal synchronized with the femtosecond pulse to the pulse signal generator and computer control subsystem.

3. The laser time-frequency conversion observation system based on hyperspectral imaging according to claim 2 is characterized in that: The beam splitter is a non-polarizing beam splitter with a splitting ratio of 3:

1.

4. The laser time-frequency conversion observation system based on hyperspectral imaging according to claim 3 is characterized in that: The optical delay translation stage includes a computer control subsystem of the translation stage and the translation stage; The position of the translation stage is adjusted by the computer control subsystem of the translation stage to control the time interval between the detection light and the pump light reaching the sample to be measured.

5. The laser time-frequency conversion observation system based on hyperspectral imaging according to claim 4 is characterized in that: The hyperspectral camera shooting subsystem includes a hyperspectral camera and a computer; A hyperspectral camera is used to detect the optical information intensity signal generated after the surface of the sample to be tested is excited by pump light, and a computer is used to collect and output the optical information intensity signal to obtain multi-region two-dimensional spectral signals and two-dimensional imaging information with spatial resolution capability.

6. The laser time-frequency conversion observation system based on hyperspectral imaging according to claim 5, characterized in that: The hyperspectral camera is placed on the image plane of the hyperspectral camera shooting subsystem. A filter and a tube lens are provided in front of the hyperspectral camera, and a sample stage is provided on the object plane of the hyperspectral camera shooting subsystem.

7. The laser time-frequency conversion observation system based on hyperspectral imaging according to claim 6, characterized in that: The optical power meter, the sample carrier subsystem and the optical delay translation stage are all connected to the computer control subsystem.

8. The observation method of the laser time-frequency conversion observation system based on hyperspectral imaging according to any one of claims 1 to 7, characterized in that: The following steps are involved: S1. Send instructions to the pulse signal generator to excite the femtosecond laser, and use the femtosecond laser to output high-energy 800nm femtosecond pulses, which are divided into pump light and probe light using a beam splitter; S2, after being reflected by the reflector, the pump light is focused by a focusing lens onto the sample to be tested placed on the sample loading subsystem to excite the sample to be tested; S3. Use a laser optical chopper to adjust the required pump light frequency, use an optical power meter to measure the pump light energy of the sample to be tested, and use an optical filter to adjust the energy of the pump light to obtain the required laser pulse energy; S4. The detection light is passed through a white light crystal to output a detection white light pulse. The beam shrinking and expanding subsystems are used to make the spot size meet the incident aperture requirements of the focusing lens. The beam homogenization and spot homogenization devices are used to shape the detection white light pulse to output a stable detection white light with uniform light intensity distribution. The optical delay translation stage is used to output the detection light with an adjustable time interval with the pump light, and the detection light is focused on the surface of the sample to be tested through the focusing lens for illumination. S5. Using the computer control subsystem, the sample loading subsystem is controlled to move in three mutually perpendicular directions, so that the area to be excited of the sample to be tested is moved to coincide with the focused spots of the pump light and the detection light; S6. Using the hyperspectral camera shooting subsystem, the surface of the sample to be tested, which is illuminated by the detected detection light, is subjected to optical imaging and spectral imaging through the tube lens. The transient optical property information and spectral information of the excited surface of the sample to be tested are collected to obtain a two-dimensional spectral signal and two-dimensional imaging information of the sample to be tested.

9. The laser time-frequency conversion observation method based on hyperspectral imaging according to claim 8, characterized in that: The transient optical property information of the excited sample surface is obtained as follows: Before the sample is pumped, a clean, unprocessed area is selected and illuminated with probe light. The optical properties at that moment are captured and recorded using a hyperspectral camera as a background image. The optical information obtained after the sample to be tested is pumped and excited is recorded as the excitation image; The background image and the excitation image are compared and cropped to obtain the transient optical properties of the surface of the excited sample under ultrafast scale.

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