CN115541560A - Laser time-frequency transformation observation system and method based on hyperspectral imaging - Google Patents
Laser time-frequency transformation observation system and method based on hyperspectral imaging Download PDFInfo
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- G01N21/62—Systems in which the material investigated is excited whereby it emits light or causes a change in wavelength of the incident light
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Abstract
The invention provides a hyperspectral imaging-based laser time-frequency transformation observation system and a hyperspectral imaging-based laser time-frequency transformation observation method. The hyperspectral camera is adopted to replace the traditional CCD camera to perform optical imaging and spectral imaging on the instantaneous evolution state of the surface of the sample to be detected, the limited observation capability caused by the influence of the optical diffraction limit in the traditional optical pumping detection technology is made up, and the femtosecond laser is used for exciting the surface of the sample to be detected to perform real-time optical imaging and two-dimensional spectral imaging.
Description
Technical Field
The invention belongs to the technical field of ultrafast laser observation, and particularly relates to a laser time-frequency transformation observation system and method based on hyperspectral imaging.
Background
The femtosecond laser is used as a nonlinear, unbalanced and multi-scale ultrafast process, and relates to complex physical processes of energy deposition, transmission, phase change of a sample to be detected, removal and the like. Through experiments, an observation means with ultrafast time resolution is applied to reveal the interaction mechanism of the femtosecond laser and substances, and the method has important significance for the development of the field of femtosecond laser processing. At present, the observation means used for researching the interaction process of the femtosecond laser and the substance mainly has time resolution optical imaging technology, time resolution X-ray diffraction technology, time resolution electron diffraction technology, time resolution transient absorption spectrum and the like.
The basic idea of the pump detection technology is to utilize two pulse lasers with carefully designed time delay to study the transient evolution process, wherein one beam is used as pump light for exciting the transient process of a sample to be detected, and the other beam is used as detection light for observing an excitation region after certain time delay. At present, a pumping detection technology is used for researching the transient process of a sample to be detected processed by femtosecond laser, and light intensity and phase change of detection light under different detection time delays can be obtained through different signal acquisition modes mainly by means of signal receiving devices such as a CCD charge coupled device and a photodiode, so that the ultrafast evolution process of the transient property of the sample to be detected after laser action is analyzed. Due to the adoption of an optical imaging mode, the traditional femtosecond laser optical pumping detection technology can only observe the transient optical property change condition induced by the surface of a sample to be detected, the analysis of ultrafast dynamic information is mainly started from the aspects of reflectivity and image structure, the signal-to-noise ratio is low, the influence of background difference caused by fluctuation of laser output is large, the evolution content of observable plasmas, shock waves and phase change is limited, and the spatial resolution of detection is limited by the limit of optical diffraction, so that the dynamic information of nanoscale electrons and crystal lattices cannot be detected. The transient absorption spectrum detection technology derived from the pumping detection technology can only detect a single point of an excitation area of a sample to be detected so as to obtain a one-dimensional absorption spectrum, and the transient evolution process of the surface of the sample to be detected cannot be directly observed by combining a CCD (charge coupled device) due to weak optical signals, so that the propagation process of plasma eruption and shock wave on the surface of the sample to be detected cannot be observed, and the capability of observing ablation of the sample to be detected is limited.
The hyperspectral imaging technology organically combines the traditional two-dimensional imaging technology and the spectrum technology, is a fine technology capable of capturing and analyzing the spectrum point by point in a spatial area, and can detect substances which cannot be distinguished visually because unique spectrum 'features' on different spatial positions of a single object can be detected. The technology has the advantages of space identifiability, ultra-multiband, high spectral resolution, wide spectral range, spectrum combination and the like. The spectral imaging is mainly used for measuring reflected light after interaction of light and substances, and the imaging technology can obtain the instantaneous optical property change condition of the surface of a sample to be measured. Because the states of the surface under a plurality of time and space scales have different nonlinear non-equilibrium effects on the imaging light sources under different wavelengths after the sample is excited by the ultrafast laser, the two-dimensional spectrum technology for imaging under a plurality of wave bands can intuitively and comprehensively characterize the plasma characteristics carrying the sample element information and the energy transfer condition of the molecular excitation state, and acquire the kinetic information of the molecules. The hyperspectral imaging technology and the optical pumping detection technology are combined, and more physical and chemical information and morphological information of the surface of the sample to be detected under the ultrafast scale can be acquired, so that the femtosecond laser processing ultrafast dynamic process can be more comprehensively understood and explored.
Disclosure of Invention
Aiming at the defects in the prior art, the hyperspectral imaging-based laser time-frequency transformation observation system and the hyperspectral imaging-based laser time-frequency transformation observation method are provided by the invention, a hyperspectral camera is adopted to replace a traditional CCD camera to carry out optical imaging and spectrum imaging on the instantaneous evolution state of the surface of a sample to be detected, the limited observation capability caused by the influence of the optical diffraction limit in the traditional optical pumping detection technology is made up, and femtosecond laser is used for exciting the surface of the sample to be detected to carry out real-time optical imaging and two-dimensional spectrum imaging.
In order to achieve the above purpose, the invention adopts the technical scheme that:
the scheme provides a laser time-frequency transformation observation system based on hyperspectral imaging, which comprises an optical platform, a femtosecond laser, a pulse signal generator, a reflector, a beam splitter, a laser optical chopper, a white light crystal, a beam contraction and expansion subsystem, a light beam homogenization and facula homogenization device, a focusing lens, a diaphragm, an optical power meter, an optical filter, an optical delay translation platform, a pulse shaping subsystem, a sample loading subsystem, a hyperspectral camera shooting subsystem and a computer control subsystem, wherein the femtosecond laser, the pulse signal generator, the reflector, the beam splitter, the laser optical chopper, the white light crystal, the beam contraction and expansion subsystem, the light beam homogenization and facula homogenization device, the focusing lens, the diaphragm, the optical power meter, the optical filter, the optical delay translation platform, the pulse shaping subsystem, the sample loading subsystem, the hyperspectral camera shooting subsystem and the computer control subsystem are arranged on the optical platform;
the computer control subsystem sends an instruction to the pulse signal generator to excite the femtosecond laser to output high-energy femtosecond pulses, the beam splitter is used for dividing the high-energy femtosecond pulses into pump light and probe light, the diaphragm is used for collimating the laser path to enable the laser path to be linearly propagated along a fixed direction, the laser optical chopper is used for adjusting the frequency of the pump light, the reflector is used for reflecting the pump light to adjust the advancing direction of the pump light, focusing on the sample to be tested excited by the sample loading subsystem according to a set geometric relation, measuring the energy of the pump light of the sample to be tested by using an optical power meter, the energy of the pump light is adjusted by using the optical filter to obtain the required laser pulse energy, the detection light sequentially passes through the white light crystal, the beam shrinking and expanding subsystem, the light beam homogenizing device and the light spot homogenizing device to output detection white light with uniform light intensity distribution, the incident laser is converted into an output light beam with a required shape by the pulse shaping subsystem, and the detection light with adjustable time interval with the pumping light is output after the detection light is output by the optical delay translation stage, the method comprises the steps of focusing to the surface of a sample to be detected through an adjustable focusing lens for illumination, controlling a sample loading subsystem to move along three mutually perpendicular directions by using a computer control subsystem, moving a region to be excited of the sample to be detected to coincide with a pumping light and a detection light focusing spot, shooting, amplifying and recording a dynamic signal generated after the femtosecond laser excites the surface of the sample to be detected by using a hyperspectral camera shooting subsystem, collecting image information of a spectrum waveband, reading and processing the image information output by the hyperspectral camera shooting subsystem by using the computer control subsystem, and obtaining a two-dimensional spectrum signal and two-dimensional imaging information of the sample to be detected.
The invention has the beneficial effects that: the invention utilizes femtosecond pulse output by a femtosecond laser to split into pumping light and detection light, the pumping light is focused on the surface of a sample through a lens to be excited, the detection light is reflected by a delay reflector to detect the change generated by exciting the surface of the sample to be detected under the induction of the pumping light under different time lengths, the optical signal of the detection light is received by a hyperspectral camera, and two-dimensional image information and two-dimensional spectrum information are output through a computer. According to the invention, a hyperspectral camera is adopted to replace a traditional CCD camera to acquire image information of hundreds of spectral bands in a surface instantaneous evolution state of a sample to be detected, and a nonlinear effect enables a series of ultrafast instantaneous states of the surface of the sample to display different information under the imaging of a plurality of frequency spectrums, so that an imaging spectrum system with a space resolution capability expands the resolution capability of a target from a simple spectrum to spectrum recognition combined with the geometric characteristics of the target, thereby acquiring more information about the ultrafast plasma evolution and phase change of the surface of the sample to be detected in different time domains and frequency domains.
Further, the femtosecond laser comprises a femtosecond pulse oscillator, a chirped pulse amplification subsystem and a laser control subsystem;
the femtosecond pulse is generated by the femtosecond pulse oscillator, the high-energy femtosecond pulse is obtained after the femtosecond pulse is amplified by the chirped pulse amplification subsystem, and the pulse signal synchronized with the femtosecond pulse is output to the pulse signal generator and the computer control subsystem by utilizing the laser control subsystem.
The beneficial effects of the above further scheme are: the invention utilizes the chirped pulse amplification subsystem to obtain high-energy femtosecond pulses, the chirped pulse amplification subsystem carries enough energy to excite the surfaces of materials under different ablation thresholds, an ablation effect is generated on the surfaces of the materials, corresponding ablation signals are generated, and the energy of the femtosecond pulses can be conveniently adjusted by adopting an optical filter in the follow-up process.
Still further, the beam splitter is a non-polarizing beam splitter, and the splitting ratio is 3.
The beneficial effects of the above further scheme are: after passing through the beam splitter, the pump light obtains 3/4 of energy, the light intensity is enough to excite the surface of the material, the detection light obtains 1/4 of energy, and the light intensity is high enough to illuminate the surface of the material.
Still further, the optical time-delay translation stage comprises a translation stage computer control subsystem and a translation stage;
and the computer control subsystem of the translation stage is used for adjusting the position of the translation stage and controlling the time interval of the probe light and the pump light reaching the sample to be detected.
The beneficial effects of the further scheme are as follows: the detection light changes light with single wavelength into white light with multiple wavelengths and uniform light intensity distribution, optical path difference from femtosecond to nanosecond magnitude can be generated between the pumping light and the detection light, the detection light can reach the surface of a sample in different time intervals from femtosecond to nanosecond after the pumping light excites the sample, the surface of the sample to be detected is illuminated, and an optical signal in different time intervals from femtosecond to nanosecond after the pumping light excites the sample can be captured by the hyperspectral camera.
Still further, the hyperspectral camera shooting subsystem comprises a hyperspectral camera and a computer;
the hyperspectral camera is used for detecting optical information intensity signals generated after the surface of a sample to be detected is excited by pump light, and the computer is used for collecting and outputting the optical information intensity signals to obtain multi-region two-dimensional spectrum signals and two-dimensional imaging information with space resolution capability.
The beneficial effects of the further scheme are as follows: due to the long exposure time of the hyperspectral camera, the computer controls the pulse signal generator to trigger and generate femtosecond pulses after triggering the hyperspectral camera to open the shutter laser for a certain time by setting a control algorithm, so that accurate single exposure and image capture are realized, instantaneous optical information on the surface of a material is recorded, and data is output to a multidimensional spectral image through the computer.
Still further, the hyperspectral camera is arranged in the image plane of the hyperspectral camera shooting subsystem, a filter and a tube lens are further arranged in front of the hyperspectral camera, and a sample objective table is arranged on the object plane of the hyperspectral camera shooting subsystem.
The beneficial effects of the further scheme are as follows: the detection light is reflected by the delay reflector to detect the change caused by the pumping light induced excitation of the surface of the sample to be detected under different delay time, the optical signal of the detection light is received by the hyperspectral camera, and high-resolution two-dimensional image information and two-dimensional spectrum information are output by a computer.
Still further, the optical power meter, the sample carrying subsystem and the optical time-delay translation stage are all connected with the computer control subsystem.
The beneficial effects of the above further scheme are: electronic instruments and equipment in the experimental device are subjected to linkage control by a computer, so that the experimental operation becomes simple, convenient and accurate.
The invention provides a laser time-frequency transformation observation method based on hyperspectral imaging, which comprises the following steps of:
s1, sending an instruction to a pulse signal generator, exciting a femtosecond laser, outputting a high-energy 800nm femtosecond pulse by using the femtosecond laser, and dividing the pulse into pumping light and detection light by using a beam splitter;
s2, after being reflected by the reflector, the pump light is gathered to a sample to be tested placed on the sample loading subsystem by using the focusing lens so as to excite the sample to be tested;
s3, adjusting the frequency of the required pump light by using a laser optical chopper, measuring the energy of the pump light of the sample to be measured by using an optical power meter, and adjusting the energy of the pump light by using an optical filter to obtain the required laser pulse energy;
s4, outputting detection white light pulses by the detection light through a white light crystal, enabling the size of light spots of the detection white light pulses to meet the requirement of an incident aperture of a focusing lens through a beam contracting and expanding subsystem, shaping the detection white light pulses by using a light beam homogenizing and light spot homogenizing device, outputting stable detection white light with uniform light intensity distribution, outputting detection light with adjustable time interval with pumping light by using an optical delay translation stage, and focusing the detection light on the surface of a sample to be detected through the focusing lens for illumination;
s5, controlling the sample loading subsystem to move along three mutually perpendicular directions by using the computer control subsystem, and moving a region to be excited of the sample to be detected to coincide with the pump light and the probe light focusing light spots;
s6, utilizing a hyperspectral camera shooting subsystem to perform optical imaging and spectral imaging on the surface of the sample to be detected, which is illuminated by the detected light, through a tube lens, and acquiring transient optical property information and spectral information of the surface of the excited sample to be detected to obtain a two-dimensional spectral signal and two-dimensional imaging information of the sample to be detected.
The invention has the beneficial effects that: the invention utilizes femtosecond laser output by a laser to split into pumping light and detection light, the pumping light is focused on the surface of a sample through a lens to be excited, the detection light is reflected by a time delay reflector to detect the change generated by exciting the surface of the sample to be detected under the induction of the pumping light under different time lengths, the optical signal of the detection light is received by a hyperspectral camera, and two-dimensional image information and two-dimensional spectrum information are output through a computer. According to the invention, a hyperspectral camera is adopted to replace a traditional CCD camera to acquire image information of hundreds of spectrum wave bands in a transient evolution state of the surface of a sample to be detected, and a nonlinear effect enables a series of ultrafast transient states of the surface of the sample to display different information under multiple spectrum imaging, so that an imaging spectrum system with spatial resolution capability expands the resolution capability of a target from a pure spectrum to spectrum identification combined with geometric characteristics of the target, thereby acquiring more information about ultrafast plasma evolution and phase change of the surface of the sample to be detected in different time domains and frequency domains.
Further, the obtaining of the transient optical property information of the surface of the excited sample to be measured is as follows:
before pumping excitation is carried out on a sample to be detected, a clean and unprocessed area is selected, and after being illuminated by detection light, the optical property at the moment is shot and recorded by a hyperspectral camera to be used as a background image;
recording optical information obtained after pumping excitation is carried out on a sample to be detected as an excitation image;
and comparing and cutting the background image and the excitation image to obtain the transient optical property of the surface of the excited sample to be detected under the ultrafast scale.
The beneficial effects of the further scheme are as follows: the hyperspectral imaging technology and the optical pumping detection technology are combined to obtain more physical and chemical information and morphological information of the material surface under the ultrafast scale, and two-dimensional spectral signals and two-dimensional image information of the material surface under the ultrafast time scale after being excited by femtosecond pulses are extracted, so that the femtosecond laser processing ultrafast dynamic process is more comprehensively understood and explored. In the testing method, the trigger programs of the laser and the spectrum camera are set through the pulse generator, so that multiple imaging and rapid imaging of the system are realized, and the data collection efficiency of the system is improved.
Drawings
FIG. 1 is a flow chart of the method of the present invention.
FIG. 2 is a schematic structural diagram of an ultrafast laser time-frequency transformation observation method based on a hyperspectral imaging technology according to an embodiment of the invention.
Fig. 3 is a schematic optical path diagram of an ultrafast laser time-frequency transformation observation method based on a hyperspectral imaging technology according to an embodiment of the invention.
Fig. 4 is a schematic diagram of a using process of the ultrafast laser time-frequency transformation observation method based on hyperspectral imaging in the embodiment.
The device comprises a 1-femtosecond laser, a 2-first beam splitter, a 3-white light crystal, a 4-beam shrinking and expanding subsystem, a 5-beam homogenizing and spot homogenizing device, a 6-first reflector, a 7-second reflector, an 8-third reflector, a 9-optical time-delay translation stage, a 10-fourth reflector, a 11-fifth reflector, a 12-beam splitter, a 13-first focusing lens, a 14-sample to be detected, a 15-second focusing lens, a 16-sixth reflector, a 17-optical chopper, an 18-optical filter, a 19-seventh reflector, a 20-tube lens, a 21-second filter, a 22-hyperspectral camera, a 23-computer control subsystem and a 24-pulse signal generator.
Detailed Description
The following description of the embodiments of the present invention is provided to facilitate the understanding of the present invention by those skilled in the art, but it should be understood that the present invention is not limited to the scope of the embodiments, and it will be apparent to those skilled in the art that various changes may be made without departing from the spirit and scope of the invention as defined and defined in the appended claims, and all matters produced by the invention using the inventive concept are protected.
Example 1
The invention provides a hyperspectral imaging-based laser time-frequency conversion observation system, which comprises an optical platform, 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 light beam homogenizing and facula homogenizing device, a focusing lens, a diaphragm, an optical power meter, an optical filter, an optical time-delay translation platform, a pulse shaping subsystem, a sample loading subsystem, a hyperspectral camera shooting subsystem and a computer control subsystem, wherein the femtosecond laser, the pulse signal generator, the reflector, the beam splitter, the laser optical chopper, the white light crystal, the beam shrinking and beam expanding subsystem, the light beam homogenizing and facula homogenizing device, the focusing lens, the diaphragm, the optical power meter, the optical filter, the optical time-delay translation platform, the pulse shaping subsystem, the sample loading subsystem, the hyperspectral camera shooting subsystem and the computer control subsystem are arranged on the optical platform;
the computer control subsystem sends an instruction to the pulse signal generator, the femtosecond laser is excited to output high-energy femtosecond pulses, the high-energy femtosecond pulses are divided into pump light and detection light by the beam splitter, wherein the pump light is used for exciting a sample to be detected, the detection light is used for detecting the change of the optical property of the surface of the sample to be detected after the excitation of the pump light, the laser path is collimated by the diaphragm to be transmitted linearly along a fixed direction to prevent the light from skewing, the frequency of the pump light is adjusted by the laser optical chopper, the advancing direction of the pump light is adjusted by reflecting the pump light by the reflector, the pump light is focused on the sample to be detected excited by the sample loading subsystem according to a set geometric relationship, the pump light energy of the sample to be detected is measured by the optical power meter, and the energy of the pump light is adjusted by the optical filter, acquiring required laser pulse energy, outputting detection white light with uniform light intensity distribution after the detection light sequentially passes through a white light crystal, a beam contracting and expanding subsystem, a light beam homogenizing device and a light spot homogenizing device, converting incident laser into output light beams with required shapes through a pulse shaping subsystem, improving detection quality and imaging quality, outputting detection light with adjustable time intervals with pumping light after the detection light is output by an optical delay translation stage, focusing the detection light to the surface of a sample to be detected through an adjustable focusing lens for illumination, controlling a sample loading subsystem to move along three mutually perpendicular directions by a computer control subsystem, moving a region to be excited of the sample to be detected to coincide with the pumping light and the detection light focusing spot, shooting, amplifying and recording a dynamic signal after the femtosecond laser excites the surface of the sample by a hyperspectral camera shooting subsystem, and acquiring image information of a spectrum waveband, and reading and processing the image information output by the hyperspectral camera shooting subsystem by using the computer control subsystem to obtain a two-dimensional spectrum signal and two-dimensional imaging information of the sample to be detected. The femtosecond laser comprises a femtosecond pulse oscillator, a chirped pulse amplification subsystem and a laser control subsystem; the femtosecond pulse is generated by the femtosecond pulse oscillator, the high-energy femtosecond pulse is obtained after amplification of the chirped pulse amplification subsystem, the high-energy femtosecond pulse carries sufficiently strong photon energy and can be ablated on the surfaces of samples with different thresholds so as to generate spectrum signals, the energy of the femtosecond pulse can be conveniently adjusted by adopting an optical filter in the follow-up process, and the pulse signals synchronized with the femtosecond pulse are output to the pulse signal generator and the computer control subsystem by utilizing the laser control subsystem. The beam splitter is a non-polarizing beam splitter, and the splitting ratio is 3. The optical time delay translation stage comprises a computer control subsystem of the translation stage and the translation stage; and the computer control subsystem of the translation stage is used for adjusting the position of the translation stage and controlling the time interval of the probe light and the pump light reaching the sample to be detected. The hyperspectral camera shooting subsystem comprises a hyperspectral camera and a computer; the hyperspectral camera is used for detecting optical information intensity signals generated after the surface of a sample to be detected is excited by pump light, and the computer is used for collecting and outputting the optical information intensity signals to obtain multi-region two-dimensional spectrum signals and two-dimensional imaging information with spatial resolution. The hyperspectral camera is arranged on an image plane of the hyperspectral camera shooting subsystem, a filter plate and a tube lens are further arranged in front of the hyperspectral camera, and a sample objective table is arranged on an object plane of the hyperspectral camera shooting subsystem. And the optical power meter, the sample carrying subsystem and the optical delay translation stage are all connected with the computer control subsystem.
In this embodiment, the femtosecond laser outputs a high-energy 800nm femtosecond pulse, and the pulse is split into two beams of pulses by the beam splitter, which are respectively used as pump light and probe light. The pump light is focused by the lens onto a sample to be measured placed on the sample loading subsystem for exciting the sample to be measured. The optical power meter is used for measuring the energy of the pump light pulse for exciting the sample, and the optical filter is used for adjusting the energy of the pump light to obtain the laser pulse energy required in the experiment. Measuring the pump light energy of the sample to be measured by using an optical power meter; the transmitted light is changed into white light containing multiple wavelengths after passing through the white light crystal, the size of a laser spot is changed to a proper range by the beam contracting and expanding subsystem so as to conform to the incident aperture of a focusing lens in a subsequent light path, the optical delay translation table enables the pump light and the detection light to generate time delay from femtosecond magnitude to nanosecond magnitude, and the time delay is focused on the surface of a sample to be detected through an adjustable lens, so that the illumination effect is achieved. The hyperspectral camera shooting subsystem performs optical imaging and spectral imaging on the surface of the material illuminated by the detected light through the tube lens, collects transient optical property information and spectral information of the surface of the excited material, and outputs data after internal processing and calculation of the camera.
In this embodiment, both the reflector and the focusing lens can be manually adjusted, and the light beam advancing direction is adjusted by combining with the diaphragm, so that the light beam can be accurately focused on the to-be-excited region on the surface of the material.
In the embodiment, the femtosecond laser comprises a femtosecond pulse oscillator, a chirped pulse amplification subsystem and a laser control subsystem, wherein the femtosecond pulse oscillator generates femtosecond pulses, and the femtosecond pulses are amplified by the chirped pulse amplification subsystem to obtain high-energy femtosecond pulses; the laser control subsystem outputs a pulse signal synchronized with the femtosecond pulse to the pulse signal generator and the computer control subsystem, and is controlled by the computer control subsystem.
In this embodiment, the optical power meter, the laser optical chopper, the sample carrier system, and the optical delay translation stage are all electrically connected to the computer control subsystem. The computer control subsystem reads the real-time femtosecond pulse energy measured by the optical power meter; the objective table is controlled to move along three mutually vertical directions, and the area to be excited of the sample to be tested is moved to coincide with the pump and the probe light focusing light spot; the optical delay translation stage moves along one direction to generate time intervals of pump light and probe light required by the experiment.
In the embodiment, the hyperspectral camera shooting subsystem consists of a hyperspectral camera, a tube lens and a computer, and the computer controls the pulse signal generator to trigger and generate femtosecond pulses after triggering the hyperspectral camera to open the shutter laser for a certain time by setting a control algorithm due to the long exposure time of the hyperspectral camera, so that accurate single exposure and image capture are realized, instantaneous optical information on the surface of a material is recorded, and data output multi-dimensional spectral images are performed through the computer.
In this embodiment, because the exposure time of the hyperspectral camera is long, a certain time delay needs to be set between the triggering of the control pulse signal generator to generate the femtosecond pulse and the triggering of the hyperspectral camera to take a picture, the hyperspectral camera is triggered to take a picture first, and then the pulse signal generator is triggered after the certain exposure time is reached to excite the femtosecond pulse, so that the hyperspectral camera can take a picture of the change condition of the transient optical property.
As shown in fig. 2, there is provided a structure of a femtosecond pump detection system combined with a hyperspectral camera according to an embodiment of the present invention, including: femtosecond pulse emission, sample excitation, sample detection, light convergence and signal acquisition. The femtosecond pulse emission is used for emitting femtosecond pulse laser, and the femtosecond pulse laser is split by a beam splitter to respectively generate pump light and detection light; the sample excitation is used for converging the pump light on a to-be-excited region of the sample to be detected; the sample detection is used for converting the detection light into an optical signal which can be detected by the hyperspectral camera and focusing the optical signal to the light convergence part; the light converging part is used for superposing pump light and detection light in a region to be excited on the surface of the sample, wherein the pump light is used for exciting the sample to be detected, and the detection light is used for detecting the change of the optical property of the surface of the sample to be detected after the sample to be detected is excited by the pump light; and the signal acquisition part is used for acquiring the optical property intensity change generated on the surface of the sample to be detected due to the excitation of the pump light, completing the ultrafast dynamic data acquisition on the surface of the sample to be detected, and acquiring a transient optical image and a spectral image of the surface of the sample to be detected so as to obtain data combining the image with the spectrum space resolution capability and the spectrum.
In this embodiment, as shown in fig. 3, fig. 3 shows an optical path of a femtosecond pump detection system according to an embodiment of the present invention. The femtosecond laser 1 is controlled by the computer control subsystem 23 and the pulse signal generator 24 together to generate 800nm femtosecond laser pulses, which are transmitted through the first beam splitter 2 to form probe light and reflected to form pump light. The transmitted light is changed into white light containing multiple wavelengths after passing through the white light crystal 3, the laser spot size is changed to a proper range by the beam contracting and expanding subsystem 4 so as to conform to the incident aperture of a focusing lens in a subsequent light path, and then the white light passes through a light beam homogenizing and spot homogenizing device 5 so as to obtain light with uniform light intensity spatial distribution. The optical time delay translation stage 9 is composed of a first reflecting mirror 6, a second reflecting mirror 7, a third reflecting mirror 8, a fourth reflecting mirror 10 and an electric displacement stage. The pump light is reflected by the first reflecting mirror 6, then reflected by the seventh reflecting mirror 19 and the sixth reflecting mirror 16, focused by the second focusing lens 15 and then enters the surface of the sample 14 to be measured for excitation, the optical filter 18 can be used for adjusting the energy of the pump light, and the laser optical chopper 17 is used for adjusting the natural frequency of the pump light so as to obtain the pump light with the required pulse interval. The detection light passes through the optical delay translation stage 9 and then generates time delay with the pump light, and the detection light continues to pass through the fifth reflector 11, and is focused on a to-be-excited region of a to-be-detected sample 14 by the first focusing lens 13 after passing through the beam splitter 12. The computer control subsystem 23 controls the three-dimensional movement of the translation stage containing the sample 14 to be measured, and in combination with the two focusing lenses 13 and 15 mounted on the four-dimensional frame, adjusts so that the focusing spots of the pump light and the probe light on the surface of the sample coincide. After a transient optical signal generated by the surface of a sample to be detected and excited by pump light is illuminated by probe light, the transient optical signal is vertically reflected and reflected by the second beam splitter 12, the imaging quality is higher through the tube lens 20, scattered pump light with interference and plasma luminescence interference are filtered out through the second filter 21, and a final optical property signal is shot and recorded by the hyperspectral camera 22. The computer control subsystem 23 can simultaneously control the pulse signal generator 24, the optical time delay translation stage 9, the hyperspectral camera 22 and the object stage 14, so that all devices can work in a coordinated manner, wherein particularly under the synergistic action 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 start shooting of the hyperspectral camera 22, then the pulse signal generator 24 is controlled at a proper time to trigger the femtosecond laser 1 to output femtosecond pulses, meanwhile, the hyperspectral camera 22 can shoot, the optical time delay translation stage 8 can generate a series of optical time delays through movement, and finally, the hyperspectral camera collects, amplifies and outputs femtosecond-magnitude material surface transient two-dimensional optical images and femtosecond-magnitude spectrum images required by experiments, and therefore ultrafast dynamic information of the material surface in different frequency domains and time domains is extracted.
In this embodiment, the femtosecond laser is a titanium sapphire femtosecond laser from spectral Physics (Spectra Physics) of the united states, and the maximum power of the laser is 3.5W, the center wavelength is 800nm, and the pulse width is 35fs. The reflectivity of the time delay can reach 16ns at most.
The specific detection steps are as follows: (1) A sample to be detected is not placed, and the hyperspectral camera receives optical signals of the surface of the detection light illuminating material and uses the optical signals as reference signals and background; (2) The computer controls the hyperspectral camera to start exposure, the output frequency of the optical chopper is set, and then the pulse signal generator controls the laser to generate a beam of femtosecond laser pulses; (3) The pump light outputs light with natural frequency after passing through the chopper, and the probe light outputs illumination white light with uniform light intensity distribution through the white light crystal, the beam contracting and expanding subsystem and the light beam homogenizing and light spot homogenizing device; (4) The movement of the optical translation stage enables the pump light and the probe light to generate certain time delay, the hyperspectral camera quickly excites the pump light and shoots optical information of a material surface area illuminated by the probe light, the optical translation stage continuously moves to generate more time delay, and the hyperspectral camera continuously shoots related optical information; (5) Comparing the shooting information under each detection delay with the reference signal, and cutting off a background image to obtain optical information corresponding to each detection delay and spectral information under the illumination of detection light with different wavelengths; (6) By rotating the control filter and repeating the steps, ultrafast kinetic information of the surface of the material excited by the pump light under different energies can be obtained.
In this embodiment, a translation platform for placing the sample is three-dimensional piezoelectricity translation platform, and the displacement precision of its three dimensions can reach 1nm, is enough to guarantee the required precision of experiment to sample space removal, need strictly guarantee in the experiment that the coupling well between pumping objective, the detection objective and the sample to make hyperspectral camera can carry out accurate formation of image to the excitation information on material surface. After data obtained by experimental measurement is processed by a computer, a series of femtosecond-nanosecond-magnitude optical property change rules can be obtained, the resolving power of the material is expanded from a pure spectrum to spectrum recognition combined with the geometric characteristics of a target, and more multi-frequency transient evolution information under different time domain ultrafast dynamics is obtained, for example, the absorption mechanism of laser energy can be revealed by researching plasma excitation and analyzing the time-space evolution rule of plasma free electron density; by researching the propagation of the plasma and the shock wave and the radiation process of the plasma, the evolution rules of different types/components of the plasma and the shock wave/stress wave are analyzed, the laser energy deposition rule can be explored, the surface transformation process under the microscale can be analyzed, and the phase change process of the material can be finally disclosed. On the basis, the interaction process of the laser and the material can be regulated and controlled by further optimizing the laser processing conditions, such as adopting femtosecond laser space-time shaping, so that the final processing appearance and property of the material can be effectively regulated and controlled, and the processing quality, precision, efficiency and consistency are improved.
In the embodiment, the pulse triggering of the femtosecond laser is controlled by a computer and a pulse signal generator, the optical delay translation stage controls the time delay interval between the pump light and the detection light, the optical filter controls the energy of the pump light, and the spatial image information and the multiband two-dimensional spectrum information which evolve along with time under the excitation of different energies on the surface of the measured sample are obtained by scanning the interval between the pump light and the detection light and combining the data obtained by a hyperspectral camera shooting system for processing.
Example 2
As shown in FIG. 1, the invention provides a laser time-frequency transformation observation method based on hyperspectral imaging, which is implemented by the following steps:
s1, sending an instruction to a pulse signal generator, exciting a femtosecond laser, outputting a high-energy 800nm femtosecond pulse by using the femtosecond laser, and dividing the pulse into pumping light and detection light by using a beam splitter;
s2, after being reflected by the reflector, the pump light is gathered to a sample to be tested placed on the sample loading subsystem by using the focusing lens so as to excite the sample to be tested;
s3, adjusting the frequency of the required pump light by using a laser optical chopper, measuring the energy of the pump light of the sample to be measured by using an optical power meter, and adjusting the energy of the pump light by using an optical filter to obtain the required laser pulse energy;
s4, outputting detection white light pulses by the detection light through a white light crystal, enabling the size of light spots of the detection white light pulses to meet the requirement of an incident aperture of a focusing lens through a beam contracting and expanding subsystem, shaping the detection white light pulses by using a light beam homogenizing and light spot homogenizing device, outputting stable detection white light with uniform light intensity distribution, outputting detection light with adjustable time interval with pumping light by using an optical delay translation stage, and focusing the detection light on the surface of a sample to be detected through the focusing lens for illumination;
s5, controlling the sample loading subsystem to move along three mutually perpendicular directions by using the computer control subsystem, and moving a region to be excited of the sample to be detected to coincide with the pump light and the probe light focusing light spot;
s6, utilizing a hyperspectral camera shooting subsystem to perform optical imaging and spectral imaging on the surface of the sample to be detected, which is illuminated by the detected light, through a tube lens, and acquiring transient optical property information and spectral information of the surface of the excited sample to be detected to obtain a two-dimensional spectral signal and two-dimensional imaging information of the sample to be detected.
In this embodiment, the obtaining of the transient optical property information of the surface of the excited sample to be measured is as follows:
before pumping excitation is carried out on a sample to be detected, a clean and unprocessed area is selected, and after being illuminated by detection light, the optical property at the moment is shot and recorded by a hyperspectral camera to be used as a background image;
recording optical information obtained after pumping excitation is carried out on a sample to be detected as an excitation image;
and comparing and cutting the background image and the excitation image to obtain the transient optical property of the surface of the excited sample to be detected under the ultrafast scale.
As shown in fig. 4, the following describes in detail the use process of the ultrafast laser time-frequency transformation observation method based on the hyperspectral imaging technology according to the embodiment of the present invention:
1. adjusting and collimating the light path of the whole device to ensure the accurate transmission of laser beams in the whole optical system, and placing a sample on an electric displacement table;
2. initializing each instrument, setting the value of a pulse signal generator, setting parameters of a spectrum camera by a computer control subsystem, and resetting the positions of an electric displacement table and a time delay translation table to zero;
3. setting parameters of the electric translation stage and the delay translation stage through the computer control subsystem, determining the moving step length, the initial position and the final position of the electric translation stage and the delay translation stage, and setting the storage of a spectrum camera acquisition system;
4. a pumping excitation attempt is carried out on a sample by moving a delay translation stage, a spectrum camera is adopted to collect two-dimensional image information, so that pumping light and detection light are ensured to reach the surface of the sample simultaneously, and a delay zero point is set at the moment;
5. the time delay translation stage moves by one step length to generate time delay of pump light and detection light, because the exposure time of the spectrum camera is longer, a spectrum camera shooting system is started firstly, when a period of time reaches a camera shooting point, a laser is triggered by a pulse signal generator to generate laser, the pump light excites the surface of a sample, the detection light illuminates the surface of the sample, and meanwhile, the spectrum camera acquires two-dimensional image information and two-dimensional spectrum information under the time delay;
6. the spectrum camera amplifies, processes and calculates the collected related information to obtain series transient spectrum data and corresponding two-dimensional image information in the time domain, and stores and outputs the transient spectrum data and the corresponding two-dimensional image information;
7. judging whether the time delay translation stage moves to the set final time delay or not, and if so, finishing signal acquisition; if not, the electric displacement table and the delay translation table move by one step, and 5 and 6 are repeated to continue the test.
The invention utilizes femtosecond laser output by a laser to split into pumping light and detection light, the pumping light is focused on the surface of a sample through a lens to be excited, the detection light is reflected by a time delay reflector to detect the change generated by exciting the surface of the sample to be detected under the induction of the pumping light under different time lengths, the optical signal of the detection light is received by a hyperspectral camera, and two-dimensional image information and two-dimensional spectrum information are output through a computer. According to the invention, a hyperspectral camera is adopted to replace a traditional CCD camera to acquire image information of hundreds of spectrum wave bands in a transient evolution state of the surface of a sample to be detected, and a nonlinear effect enables a series of ultrafast transient states of the surface of the sample to display different information under multiple spectrum imaging, so that an imaging spectrum system with spatial resolution capability expands the resolution capability of a target from a pure spectrum to spectrum identification combined with geometric characteristics of the target, thereby acquiring more information about ultrafast plasma evolution and phase change of the surface of the sample to be detected in different time domains and frequency domains.
The present invention is not limited to the above-described embodiments, and any obvious improvements, substitutions or modifications can be made by those skilled in the art without departing from the spirit of the present invention.
Claims (9)
1. A laser time-frequency transformation observation system based on hyperspectral imaging is characterized by comprising an optical platform, 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 light beam homogenizing and facula homogenizing device, a focusing lens, a diaphragm, an optical power meter, an optical filter, an optical time-delay translation stage, a pulse shaping subsystem, a sample loading subsystem, a hyperspectral camera shooting subsystem and a computer control subsystem, wherein the femtosecond laser, the pulse signal generator, the reflector, the beam splitter, the laser optical chopper, the white light crystal, the beam shrinking and beam expanding subsystem, the light beam homogenizing and facula homogenizing device, the focusing lens, the diaphragm, the optical power meter, the optical filter, the optical time-delay translation stage, the pulse shaping subsystem, the sample loading subsystem, the hyperspectral camera shooting subsystem and the computer control subsystem are arranged on the optical platform;
the computer control subsystem sends an instruction to the pulse signal generator to excite the femtosecond laser to output high-energy femtosecond pulses, the beam splitter is used for dividing the high-energy femtosecond pulses into pump light and probe light, the diaphragm is used for collimating the laser path to enable the laser path to be linearly propagated along a fixed direction, the laser optical chopper is used for adjusting the frequency of the pump light, the reflector is used for reflecting the pump light to adjust the advancing direction of the pump light, focusing on the sample to be tested excited by the sample loading subsystem according to a set geometric relation, measuring the energy of the pump light of the sample to be tested by using an optical power meter, the energy of the pump light is adjusted by using an optical filter to obtain the required laser pulse energy, the detection light sequentially passes through a white light crystal, a beam contraction and expansion subsystem, a light beam homogenizing device and a light spot homogenizing device to output detection white light with uniform light intensity distribution, the pulse shaping subsystem converts the incident laser into an output beam with a required shape, the optical delay translation stage outputs probe light, the time interval between the probe light and the pump light is adjustable, the method comprises the steps of focusing to the surface of a sample to be detected through an adjustable focusing lens for illumination, controlling a sample loading subsystem to move along three mutually perpendicular directions by using a computer control subsystem, moving a region to be excited of the sample to be detected to coincide with a pumping light and a detection light focusing spot, shooting, amplifying and recording a dynamic signal generated after the femtosecond laser excites the surface of the sample to be detected by using a hyperspectral camera shooting subsystem, collecting image information of a spectrum waveband, reading and processing the image information output by the hyperspectral camera shooting subsystem by using the computer control subsystem, and obtaining a two-dimensional spectrum signal and two-dimensional imaging information of the sample to be detected.
2. The hyperspectral imaging-based laser time-frequency transformation observation system according to claim 1, wherein the femtosecond laser comprises a femtosecond pulse oscillator, a chirped pulse amplification subsystem and a laser control subsystem;
the femtosecond pulse is generated by the femtosecond pulse oscillator, the high-energy femtosecond pulse is obtained after the femtosecond pulse is amplified by the chirped pulse amplification subsystem, and the pulse signal synchronous with the femtosecond pulse is output to the pulse signal generator and the computer control subsystem by the laser control subsystem.
3. The laser time-frequency transformation observation system based on hyperspectral imaging according to claim 2, wherein the beam splitter is a non-polarizing beam splitter, and the splitting ratio is 3.
4. The hyperspectral imaging based laser time-frequency transform observation system according to claim 3 is characterized in that the optical time-delay translation stage comprises a translation stage and a computer control subsystem of the translation stage;
and the computer control subsystem of the translation stage is used for adjusting the position of the translation stage and controlling the time interval between the detection light and the pump light reaching the sample to be detected.
5. The hyperspectral imaging based laser time-frequency transformation observation system according to claim 4 is characterized in that the hyperspectral camera shooting subsystem comprises a hyperspectral camera and a computer;
the hyperspectral camera is used for detecting optical information intensity signals generated after the surface of a sample to be detected is excited by pump light, and the computer is used for collecting and outputting the optical information intensity signals to obtain multi-region two-dimensional spectrum signals and two-dimensional imaging information with space resolution capability.
6. The hyperspectral imaging-based laser time-frequency transformation observation system according to claim 5 is characterized in that the hyperspectral camera is placed in an image plane of the hyperspectral camera shooting subsystem, a filter and a tube lens are further arranged in front of the hyperspectral camera, and a sample stage is arranged on an object plane of the hyperspectral camera shooting subsystem.
7. The hyperspectral imaging-based laser time-frequency transformation observation system according to claim 6 is characterized in that the optical power meter, the sample carrying subsystem and the optical time-delay translation stage are all connected with the computer control subsystem.
8. The observation method of the laser time-frequency transformation observation system based on the hyperspectral imaging according to any one of claims 1 to 7 is characterized by comprising the following steps:
s1, sending an instruction to a pulse signal generator, exciting a femtosecond laser, outputting a high-energy 800nm femtosecond pulse by using the femtosecond laser, and dividing the pulse into pumping light and detection light by using a beam splitter;
s2, after being reflected by the reflector, the pump light is gathered to a sample to be tested placed on the sample loading subsystem by using the focusing lens so as to excite the sample to be tested;
s3, adjusting the frequency of the required pump light by using a laser optical chopper, measuring the energy of the pump light of the sample to be measured by using an optical power meter, and adjusting the energy of the pump light by using an optical filter to obtain the required laser pulse energy;
s4, outputting detection white light pulses by the detection light through a white light crystal, enabling the size of light spots of the detection white light pulses to meet the requirement of an incident aperture of a focusing lens through a beam contracting and expanding subsystem, shaping the detection white light pulses by using a light beam homogenizing and light spot homogenizing device, outputting stable detection white light with uniform light intensity distribution, outputting detection light with adjustable time interval with pumping light by using an optical delay translation stage, and focusing the detection light on the surface of a sample to be detected through the focusing lens for illumination;
s5, controlling the sample loading subsystem to move along three mutually perpendicular directions by using the computer control subsystem, and moving a region to be excited of the sample to be detected to coincide with the pump light and the probe light focusing light spot;
s6, utilizing a hyperspectral camera shooting subsystem to perform optical imaging and spectral imaging on the surface of the sample to be detected, which is illuminated by the detected light, through a tube lens, and acquiring transient optical property information and spectral information of the surface of the excited sample to be detected to obtain a two-dimensional spectral signal and two-dimensional imaging information of the sample to be detected.
9. The hyperspectral imaging-based laser time-frequency transform observation method according to claim 8 is characterized in that the acquisition of the transient optical property information of the surface of the excited sample to be measured is as follows:
before pumping excitation is carried out on a sample to be detected, a clean and unprocessed area is selected, and after being illuminated by detection light, the optical property at the moment is shot and recorded by a hyperspectral camera to be used as a background image;
recording optical information obtained after pumping excitation is carried out on a sample to be detected as an excitation image;
and comparing and cutting the background image and the excitation image to obtain the transient optical property of the surface of the excited sample to be detected at the ultrafast scale.
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| CN116879208B (en) * | 2023-09-08 | 2023-11-28 | 星元极光(苏州)光电科技有限公司 | Transient absorption spectrum measuring method and device |
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