CN107884339B - Adaptive laser spectrum suitable for deep space micro-area analysis and imaging method - Google Patents

Adaptive laser spectrum suitable for deep space micro-area analysis and imaging method Download PDF

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CN107884339B
CN107884339B CN201710950101.9A CN201710950101A CN107884339B CN 107884339 B CN107884339 B CN 107884339B CN 201710950101 A CN201710950101 A CN 201710950101A CN 107884339 B CN107884339 B CN 107884339B
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万雄
王泓鹏
袁汝俊
张铭
何强
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Shanghai Institute of Technical Physics of CAS
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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 discloses a self-adaptive laser spectrum and imaging method suitable for deep space micro-area analysis, which is realized on a self-adaptive laser spectrum and imaging detection system. The invention has the advantages that the invention provides a self-adaptive laser spectrum and imaging detection method, which can self-adaptively adjust the diameter of a focusing light spot during micro-area analysis; the regional average gray scale of the electronic eyepiece is used as the intensity of a scanning imaging point, and the requirements of self-focusing and wide-spectrum scanning imaging are met; the three-dimensional LIBS element analysis, the active laser Raman molecular analysis, the hyperspectral fluorescence and the visible wide-spectrum scanning imaging can be realized simultaneously, and various information is provided for the micro-area fine detection.

Description

Adaptive laser spectrum suitable for deep space micro-area analysis and imaging method
Technical Field
The invention relates to a substance detection method, in particular to a substance detection method adopting scanning laser-induced plasma LIBS, laser Raman imaging, laser-induced fluorescence imaging and laser illumination area array wide spectrum scanning imaging, which is suitable for substance detection in a deep space detection planet open environment and belongs to the field of planet in-situ detection.
Background
For future deep space exploration, higher requirements are put forward on a material component detection technology and a method, and the in-situ fine detection capability is the highest point of the technology aimed by the aerospace major countries. The fine detection requires a smaller laser focus point, the analyzed quality is very small, the elements and molecular species are richer, the quantification is more accurate, and the quantification is carried out under the monitoring of the extremely high spatial resolution imaging.
Laser-induced plasma spectroscopy (LIBS), laser Raman (Raman) and ultraviolet laser-induced fluorescence are important means for analyzing the composition of substances, wherein LIBS can analyze the composition elements of substances, laser Raman can analyze the molecular composition of substances, and ultraviolet laser-induced fluorescence can be used for imaging and analyzing some elements, especially rare earth elements. The LIBS and Raman substance analysis in deep space micro-area detection has higher application requirements than that of the conventional laser spectrum, and the main challenge and technical difficulty are that the mineral composition contained in the rock and soil of the test object is complex, and the particle size of the same mineral particle is extremely small. Therefore, when the micro-area analysis is carried out, the accurate micro-area analysis can be carried out on the mineral only when the laser focusing spot is required to be in the magnitude of 1 micron, the requirement on a microscopic light path is extremely high, the conventional Raman probe is influenced by a fiber transmission mode, and the focusing spot is influenced by laser mode degradation and a diffraction limit, so that the focusing spot is often larger than 5 microns and cannot meet the requirement; the integration of free light path, short wavelength laser, high magnification and high numerical aperture microscope objective is adopted to theoretically obtain extremely small focusing light spot, but because the depth of focus is extremely small, a proper self-focusing scheme for analyzing a three-dimensional structure in a micro-area analysis must be found, the size of the focusing light spot of each point is ensured to be consistent and consistent with a design value, and meanwhile, if the self-focusing time is long, the scanning imaging speed is influenced. Therefore, a simple and fast raman auto-focusing and wide-spectrum scanning imaging mode is required, and in addition, most optical components must be multiplexed for LIBS and raman detection in order to make the optical path of the system compact.
Aiming at the requirements of laser spectrum detection and imaging of the deep space micro-area, the invention provides a substance detection method adopting scanning LIBS, scanning laser Raman imaging, scanning laser induced fluorescence imaging and area array wide spectrum scanning imaging, which is suitable for micro-area substance detection in the open environment of the deep space detection planet and can obtain the three-dimensional appearance of the micro-area, and the corresponding atom and molecule distribution and rare earth fluorescent substance distribution.
Disclosure of Invention
The invention aims to provide a deep space micro-area self-adaptive laser spectrum and imaging detection method, which can accurately obtain the required constant focusing spot size, obtain the micro-area three-dimensional morphology of a detection object while LIBS and Raman fluorescence spectrum distribution detection are carried out, and meet the requirement of micro-area in-situ material analysis.
The invention provides a self-adaptive laser spectrum and imaging detection method which is realized on a self-adaptive laser spectrum and imaging detection system, wherein the system consists of a main controller, a spectrometer, an optical fiber, a three-dimensional motor driver, a three-dimensional precise electric platform, a digital pulse delay controller and an optical head;
the optical head consists of an LIBS laser, an LIBS cut-in total reflection mirror, a cut-in controller, an ultraviolet Raman laser, an ultraviolet interference optical filter, a secondary motor driver, a secondary linear electric platform, a low-power ultraviolet microscope objective, a dichroic mirror, a long working distance high-power ultraviolet microscope objective, a main motor driver, a main linear electric platform, an ultraviolet Rayleigh optical filter, a proportion beam splitter, a microscope objective, a tube lens and an electronic eyepiece; an imaging lens and an image sensor are arranged in the electronic microscope;
the pulsed LIBS laser beam emitted by the LIBS laser along the LIBS optical axis and the continuous laser emitted by the ultraviolet Raman laser along the main optical axis have the same initial beam diameter and the same minimum divergence angle; when the LIBS is in a non-LIBS working mode, the cut-in controller cuts in the LIBS to the total reflection mirror to cut out a main optical axis; when the laser is in an LIBS working mode, the cut-in controller cuts the LIBS cut-in total reflection mirror into the main optical axis, at the moment, the distance from the output port of the LIBS laser and the output port of the ultraviolet Raman laser to the LIBS cut-in total reflection mirror is equal, a pulse LIBS laser beam emitted by the LIBS laser along the LIBS optical axis enters the main optical axis to be transmitted after being cut into the total reflection mirror by the LIBS, a cylindrical near-collimation laser beam penetrates through the low-power ultraviolet microscope objective, a conical laser beam penetrates through the bicolor mirror to be focused to a detection target through the long working distance high-power ultraviolet microscope objective, an LIBS echo signal reversely penetrates through the long working distance high-power ultraviolet microscope objective along the main optical axis, the signal travels along the receiving optical axis after being reflected by the bicolor mirror, and is divided into two: one path of signal is reflected and travels along an imaging optical axis, and the signal is not used in an LIBS mode; after the other path of light passes through the proportional beam splitter, rayleigh scattering of the LIBS laser wavelength is filtered through an ultraviolet rayleigh filter, and then the light is focused to the incident end face of the optical fiber through a microscope objective and enters a spectrometer for analysis; the digital pulse delay controller is provided with two control ends which are respectively connected with an LIBS laser and an external trigger port of the spectrometer; the digital pulse delay controller is used for setting the working frequency of the LIBS laser and the time delay of the opening between the LIBS laser and the spectrometer;
laser beams emitted by the ultraviolet Raman laser along the main optical axis pass through the ultraviolet interference filter, so that frequency division harmonic interference of the ultraviolet laser emitted by the ultraviolet Raman laser can be filtered, and the signal-to-noise ratio of Raman signals excited by the ultraviolet Raman laser is higher; the formed cylindrical near-collimated laser beam passes through a low-power ultraviolet microscope objective to form a conical laser beam; the conical laser beam passes through the double-color lens and then reaches the entrance pupil of the long-working-distance high-power ultraviolet microscope objective, the diameter of the conical laser beam is larger than that of the entrance pupil at the position of the entrance pupil, and the more the distance between the low-power ultraviolet microscope objective and the long-working-distance high-power ultraviolet microscope objective is, the larger the diameter of the conical laser beam is, the weaker the laser energy passing through the long-working-distance high-power ultraviolet microscope objective is, and the smaller the focusing light spot is; therefore, by adjusting the distance between the low-power ultraviolet microscope objective and the long-working-distance high-power ultraviolet microscope objective, the laser energy passing through the long-working-distance high-power ultraviolet microscope objective is rejected from the size of a focused light spot, namely a large-energy large light spot and a small-energy small light spot; echo signals reversely pass through the long-working-distance high-power ultraviolet microscope objective along the main optical axis, travel along the receiving optical axis after being reflected by the double-color mirror, and are divided into two orthogonal paths after reaching the proportional beam splitter: one path of light is reflected and travels along an imaging optical axis, is focused between one time and two times of focal length of an imaging lens in the electronic eyepiece through the tube lens, and is converted into an amplified real image through the imaging lens to an image sensor; after the other path of light passes through the proportional beam splitter, rayleigh scattering of the wavelength of the ultraviolet Raman laser is filtered through an ultraviolet rayleigh filter, and then the rayleigh scattering is focused to the incident end face of the optical fiber through a microscope objective and enters a spectrometer for analysis; the low-power ultraviolet microscope objective is arranged on the secondary linear electric platform and can do one-dimensional precise translation along the main optical axis under the driving of a secondary motor driver; the long working distance high power ultraviolet microscope objective is arranged on the main linear electric platform and can do one-dimensional precise translation along the main optical axis under the drive of the main motor driver; the translation of the secondary linear electric platform is mainly used for changing the distance between the low-power ultraviolet microscope objective and the long-working-distance high-power ultraviolet microscope objective; the translation of the main linear electric platform is mainly used for accurately focusing the long-working-distance high-power ultraviolet microscope objective; the LIBS optical axis, the main optical axis, the imaging optical axis and the receiving optical axis are coplanar; the main optical axis is parallel to the imaging optical axis and is vertical to the LIBS optical axis and the receiving optical axis;
the optical head is arranged on a three-dimensional precise electric platform, and the three-dimensional precise electric platform can perform submicron three-dimensional precise motion under the driving of a three-dimensional motor driver;
the main controller can send control instructions to the switching-in controller, the digital pulse delay controller, the three-dimensional motor driver, the main motor driver, the secondary motor driver, the ultraviolet Raman laser, the image sensor and the spectrometer; the main controller also sets the exposure time of the spectrometer and can receive the output digital image of the image sensor and the output spectrum information of the spectrometer;
the invention provides a self-adaptive laser spectrum and imaging detection method, which comprises the following steps:
(1) prospective focal spot adaptive focus calibration
In the in-situ detection of deep space materials, different detection objects need Raman focal points with different scales, namely expected focal spots, for example, for minerals with uniform distribution, the expected focal spots with slightly large sizes can be adopted; for more varied minerals, the expected focal spot with extremely small size can be adopted to realize extremely fine micro-area analysis;
firstly, setting the diameter of an expected focal spot according to the basic properties of a detection object in a test region; placing a measuring reticle in a test area below a long-working-distance high-power ultraviolet microscope objective; uniform scribed lines are arranged on the measuring reticle;
the main controller controls to start the ultraviolet Raman laser, and an ultraviolet laser beam emitted by the ultraviolet Raman laser sequentially passes through the ultraviolet interference optical filter, the low-power ultraviolet microscope objective and the dichroic mirror, is illuminated and focused to the measurement reticle through the long-working-distance high-power ultraviolet microscope objective, and forms a real-time focal spot; the reflected light of the measuring reticle passes through the long-working-distance high-power ultraviolet microscope objective along the main optical axis in the reverse direction, is reflected by the dichroic mirror, is reflected by the proportional beam splitter, is focused by the tube lens, and is subjected to real-time microscopic imaging by the imaging lens to the image sensor;
the main controller receives the microscopic digital image output by the image sensor and performs real-time image processing; acquiring the excircle profile of the real-time focal spot by adopting an edge extraction algorithm, thereby determining an imaging region of the real-time focal spot and calculating the average gray value G of all pixels in the imaging region;
the main controller sends an instruction to the main motor driver to drive the main linear electric platform to move downwards by a step length; the main controller receives the microscopic digital image output by the image sensor, determines the imaging area of the real-time focal spot, calculates the average gray value G of all pixels in the imaging area, and compares whether the G value is increased or decreased: if the value of G is increased, it indicates that the downward motion is in a direction close to the focal point; if the value of G is decreased, it indicates that the upward movement is in a direction close to the focal point;
the main controller sends an instruction to the main motor driver to drive the main linear electric platform to move towards the direction close to the focal point, and simultaneously calculates the average gray value G of all pixels in the imaging area of the real-time focal spot in real time until the G value reaches the maximum value, and at the moment, the main controller is in a tight focusing state and sends an instruction to the main motor driver to stop moving;
in a tight focusing state, the main controller adopts an edge extraction algorithm to obtain the linear position of the scribed lines of the measuring reticle and the real-time focal spot excircle outline of the microscopic digital image output by the image sensor, and then calculates the number of pixels at the interval of adjacent scribed lines and the number of pixels of the real-time focal spot excircle outline diameter, so as to calculate the real-time focal spot diameter according to the distance of the scribed lines;
if the diameter of the real-time focal spot is larger than that of the expected focal spot, the main controller sends an instruction to the secondary motor driver to drive the secondary linear electric platform to move upwards, the distance between the low-power ultraviolet microscope objective and the long-working-distance high-power ultraviolet microscope objective is increased, the laser energy passing through the long-working-distance high-power ultraviolet microscope objective is weakened, the real-time focal spot is reduced until the diameter of the real-time focal spot is equal to that of the expected focal spot, and the main controller sends an instruction to the secondary motor driver to stop the movement of the secondary linear electric platform;
similarly, if the diameter of the real-time focal spot is smaller than that of the expected focal spot, the main controller sends an instruction to the secondary motor driver to drive the secondary linear electric platform to move downwards, the distance between the low-power ultraviolet microscope objective and the long-working-distance high-power ultraviolet microscope objective is reduced, the laser energy passing through the long-working-distance high-power ultraviolet microscope objective is increased, the real-time focal spot is increased until the diameter of the real-time focal spot is equal to that of the expected focal spot, and the main controller sends an instruction to the secondary motor driver to stop the movement of the secondary linear electric platform;
(2) single point tight focus of detection object
Removing the measuring reticle, and moving the self-adaptive Raman fluorescence imaging combination system into an actual test area, wherein the detection object is positioned below the optical head, and the distance from the long working distance to the high-power ultraviolet microscope objective is far larger than the focal length of the high-power ultraviolet microscope objective;
the main controller controls and starts the ultraviolet Raman laser, an ultraviolet laser beam emitted by the ultraviolet Raman laser sequentially passes through an ultraviolet interference optical filter, a low-power ultraviolet microscope objective and a dichroic mirror, is defocused to the surface of a detection object through a long-working-distance high-power ultraviolet microscope objective, reflected light passes through the long-working-distance high-power ultraviolet microscope objective along a main optical axis in the reverse direction, is reflected by the dichroic mirror, is reflected by a proportional beam splitter, is focused through a tube lens, and is microimaged to an image sensor in real time through an imaging lens; the main controller receives the microscopic digital image output by the image sensor, and performs fast Fourier transform to extract a high-frequency component H of the microscopic digital image;
the main controller sends an instruction to a three-dimensional motor driver to drive an optical head on the three-dimensional precise electric platform to move downwards along the Z-axis, at the moment, the distance between a detected object and a long working distance high-power ultraviolet microscope objective is reduced, in the moving process, the main controller continuously carries out fast Fourier transform on a microscopic digital image output by an image sensor in real time, and continuously extracts a high-frequency component H of the microscopic digital image until the H reaches the maximum value, at the moment, laser is tightly focused to one point on the surface of the detected object, the size of a real-time focal spot is equal to that of an expected focal spot, and the laser is in a;
(3) raman fluorescence and imaging information acquisition
In this tight focus state, the master controller records the three-dimensional displacement of the three-dimensional precision motorized stage, setting it to the initial three-dimensional coordinates (x)1,y1,z1) (ii) a The main controller receives the microscopic digital image output by the image sensor, and the edge extraction algorithm is adopted to obtain the excircle outline of the real-time focal spot, so that the imaging area of the real-time focal spot is determined, and the average gray value g of all pixels in the imaging area is calculated1(ii) a Detecting Raman and fluorescence backscattering of a real-time focal spot position on the surface of an object, penetrating through a long working distance high-power ultraviolet microscope objective along a main optical axis, reflecting through a dichroic mirror, transmitting through a proportional beam splitter, filtering out Rayleigh scattering of the wavelength of an ultraviolet Raman laser through an ultraviolet Rayleigh filter, focusing to an incident end face of an optical fiber through the microscope objective, then entering a spectrometer, and outputting a spectrum signal to a main controller by the spectrometer for analysis; the main controller firstly extracts n discrete Raman spectral lines lambda of the spectral signal1，λ2，λ3，...，λnRecording the spectral line intensity I11，Ι12，Ι13，...，Ι1n(ii) a Then dividing the continuous fluorescence spectral line into m sections with equal spectral intervals; and recording the mean intensity J of the fluorescence spectrum of each segment11，J12，J13，...，J1m；
(4) Raman fluorescence imaging scanning micro-area analysis
The main controller determines A, B scanning points in the XY direction of the micro-area analysis and C, D scanning step length; the main controller sends an instruction to the three-dimensional motor driver to drive the optical head on the three-dimensional precise electric platform to perform S-shaped scanning on an XY plane, and then moves up and down along a Z axis for each point on the XY plane to execute the single-point tight focusing in the step (2);
for each scanning point i (i is more than or equal to 2 until i is equal to A multiplied by B), under the tight focusing state of the point, the main controller records the three-dimensional displacement of the three-dimensional precision electric platform and determines the three-dimensional coordinate (x) of the three-dimensional precision electric platformi,yi,zi) (ii) a The main controller receives the microscopic digital image output by the image sensor, and the edge extraction algorithm is adopted to obtain the excircle outline of the real-time focal spot, so that the imaging area of the real-time focal spot is determined, and the average gray value g of all pixels in the imaging area is calculatedi(ii) a The main controller records n discrete Raman spectral lines lambda1，λ2，λ3，...，λnSpectral line intensity Ii1，Ιi2，Ιi3，...，Ιin(ii) a And recording the average intensity J of the fluorescence spectrum of each section of the m sections of the fluorescence spectrumi1,Ji2,Ji3,...,Jim；
The main controller firstly integrates the three-dimensional coordinates of A multiplied by B scanning points and draws the three-dimensional geometric appearance of the surface of the detection object in the scanning area; then, g of each scanning point is integrated1,g2,...,gi,., obtaining a gray level image of the three-dimensional geometric shape of the surface of the detection object; then, the I of each scanning point is integrated11,I21,...,Ii1,., obtaining the wavelength of the surface of the detection object as lambda1Similarly, I of each scanning point is integrated12,I22,...,Ii2,., obtaining the wavelength of the surface of the detection object as lambda2Until the wavelength of the surface of the detected object is obtained as lambdan(ii) a raman image of; finally, the J of each scanning point is integrated11,J21,...,Ji1,., a first spectral fluorescence image of the surface of the detected object is obtained, and similarly, J of each scanning point is integrated12,J22,...,Ji2,., obtaining a fluorescence image of the second spectrum band of the surface of the detection object until obtaining a fluorescence image of the m spectrum band of the surface of the detection object;
(5) LIBS scanning micro-area analysis and information fusion
The main controller sends a command to the cut-in controller to cut the LIBS cut-in total reflection mirror into the main optical axis; the main controller sends out an instruction to set the exposure time of the spectrometer; the main controller sends an instruction to the digital pulse delay controller, and sets the working frequency of the LIBS laser and the time delay of the opening between the LIBS laser and the spectrometer;
the main controller sends an instruction to the three-dimensional motor driver to drive the optical head on the three-dimensional precise electric platform to perform scanning opposite to the step (4) according to the recorded three-dimensional coordinates of A multiplied by B scanning points, namely reverse S-shaped scanning, and reversely finishing the number A multiplied by B of the scanning points;
for each scanning point, performing LIBS detection with a single point of 1 second, receiving the output LIBS spectrum information of the spectrometer by the main controller, and qualitatively and quantitatively analyzing the element composition and content of the point according to the relation between the spectral line position and the intensity until the micro-area LIBS analysis of the whole A multiplied by B point is completed;
and (4) information fusion is carried out to complete the laser spectrum and imaging analysis of the micro-area, namely, the three-dimensional shape distribution of the micro-area, and the wide spectrum image of A multiplied by B scanning points, the ultraviolet laser Raman image of n wavelengths, the ultraviolet laser induced fluorescence hyperspectral image of m spectral bands and the element distribution image on the three-dimensional shape distribution are obtained.
The invention has the advantages that the invention provides a self-adaptive laser spectrum and imaging detection method, which can self-adaptively adjust the diameter of a focusing light spot during micro-area analysis; the regional average gray scale of the electronic eyepiece is used as the intensity of a scanning imaging point, and the requirements of self-focusing and wide-spectrum scanning imaging are met; the three-dimensional LIBS element analysis, the active laser Raman molecular analysis, the hyperspectral fluorescence and the visible wide-spectrum scanning imaging can be realized simultaneously, and various information is provided for the micro-area fine detection.
Drawings
FIG. 1 is a schematic diagram of the system of the present invention, in which: 1-three-dimensional motor drive; 2-an optical head; 3-ultraviolet Raman laser; 4-main optical axis; 5-ultraviolet interference filter; 6-secondary motor drive; 7-main controller; 8-low power ultraviolet microscope objective; 9-secondary linear electric platform; 10-imaging optic axis; 11-electronic eyepiece; 12-spectrometer; 13-an optical fiber; 14-microscope objective; 15-receive optical axis; 16-ultraviolet Rayleigh filter; 17-proportional beam splitter; 18-real time focal spot; 19-desired focal spot; 20-scribing; 21 — main motor drive; 22-primary linear electric platform; 23-detecting the object; 24-measuring reticle; 25-long working distance high power ultraviolet microscope objective; 26-entrance pupil; 27-dichroic mirror; 28-conical laser beam; 29-three dimensional precision electric platform; 30-cylindrical near collimated laser beam; 31-image sensor; 32-imaging lens; 33-tube lens; 34-LIBS cuts into the total reflection mirror; 35-LIBS laser beam; 36-cut-in controller; 37-LIBS optical axis; 38-LIBS laser; 39-digital pulse delay controller.
Note: LIBS, laser-induced spectroscopy, laser-induced breakdown spectroscopy.
Detailed Description
The specific embodiment of the present invention is shown in fig. 1.
The self-adaptive laser spectrum and imaging detection method provided by the invention is realized on a self-adaptive laser spectrum and imaging detection system, and the system consists of a main controller 7, a spectrometer 12, an optical fiber 13, a three-dimensional motor driver 1, a three-dimensional precise electric platform 29, a digital pulse delay controller 39 and an optical head 2;
the optical head 2 consists of an LIBS laser 38, an LIBS cut-in total reflection mirror 34, a cut-in controller 36, an ultraviolet Raman laser 3, an ultraviolet interference optical filter 5, a secondary motor driver 6, a secondary linear electric platform 9, a low-power ultraviolet microscope objective 8, a dichroic mirror 27, a long working distance high-power ultraviolet microscope objective 25, a main motor driver 21, a main linear electric platform 22, an ultraviolet Rayleigh optical filter 16, a proportion beam splitter 17, a microscope objective 14, a tube lens 33 and an electronic eyepiece 11; an imaging lens 32 and an image sensor 31 are arranged in the electronic eyepiece 11;
the LIBS laser 38 (in this embodiment, a 355nm, repetition frequency 1-10Hz adjustable, pulse width 6ns, and pulse energy 20mJ semiconductor pump solid-state laser) emits a pulsed LIBS laser beam 35 along the LIBS optical axis 37, which has the same initial beam diameter and the same minimum divergence angle as the continuous laser light emitted by the uv raman laser 3 (in this embodiment, a 360nm, 50mW continuous laser) along the main optical axis 4; when in the non-LIBS mode of operation, the cut-in controller 36 cuts the LIBS into the total reflection mirror 34 and cuts out the primary optical axis 4; when the laser is in the LIBS working mode, the cut-in controller 36 cuts the LIBS cut-in total reflection mirror 34 into the main optical axis 4, at this time, the distance from the output port of the LIBS laser 38 and the ultraviolet raman laser 3 to the LIBS cut-in total reflection mirror 34 is equal, the pulse LIBS laser beam 35 emitted by the LIBS laser 38 along the LIBS optical axis 37 is totally reflected by the LIBS cut-in total reflection mirror 34, enters the main optical axis 4 to be transmitted, forms a cylindrical near-collimated laser beam 30, passes through the low-power ultraviolet microscope 8, forms a conical laser beam 28, passes through the dichroic mirror 27 (in this embodiment, the 355-plus 360nm high transmittance, the 220-plus 350, and the 364nm-900nm high reflectance), passes through the long working distance high-power ultraviolet microscope objective 25 (in this embodiment, the infinity composite flat field aberration-eliminating ultraviolet 100X microscope objective is used, the ultra-long working distance is 11mm) to focus on a detection target, the LIBS echo signal reversely passes through the long-power ultraviolet microscope objective 25 along the, the dichroic mirror 27 reflects and travels along the receiving optical axis 15, and after reaching the proportional splitter 17 (in this embodiment, a 9-to-1 proportional splitter, i.e., a transmission 9-to-a-1 splitter), it is divided into two orthogonal paths: one path travels along the imaging optical axis 10 by reflection, and the signal is not used in the LIBS mode; the other path of the light passes through a proportional beam splitter 17, passes through an ultraviolet Rayleigh filter 16 (in the embodiment, a band-stop Rayleigh filter with the wavelength of 355 and 360 nm), and then is focused to the incident end face of the optical fiber 13 through a microscope objective 14, and then enters the spectrometer 12 (the spectrometer in the embodiment is divided into two channels, wherein the first channel is 220 and 350nm, the optical resolution is 0.1nm, and the number of effective pixels is 1000; the detection spectral range of the second channel is 360 and 750nm, the optical resolution is 0.1nm, and the number of effective pixels is 2000; both channels in the LIBS mode are used, and only the second channel is used for Raman and fluorescence detection) to be analyzed; the digital pulse delay controller 39 has two control terminals, which are respectively connected to the LIBS laser 38 and the external trigger port of the spectrometer 12; a digital pulse delay controller 39 is used to set the operating frequency of the LIBS laser 38 and the delay between the turning on of the LIBS laser 38 and the spectrometer 12;
the laser beam emitted by the ultraviolet raman laser 3 along the main optical axis 4 passes through an ultraviolet interference filter 5 (the ultraviolet interference filter 5 is an ultraviolet narrow-band filter, in this embodiment, a band-pass filter with a bandwidth of 1nm and 360 nm), so that the frequency-division harmonic interference of the ultraviolet laser emitted by the ultraviolet raman laser 3 can be filtered, the signal-to-noise ratio of the raman signal excited by the laser is higher, and the formed cylindrical near-collimated laser beam 30 passes through the low-power ultraviolet microscope objective 8 to form a conical laser beam 28; after passing through the dichroic mirror 27, the conical laser beam 28 reaches the entrance pupil 26 of the long working distance high power ultraviolet microscope objective 25, at the position of the entrance pupil 26, the diameter of the conical laser beam 28 is larger than that of the entrance pupil 26, and because the cone angle of the conical laser beam 28 is a fixed value, the farther the distance between the low power ultraviolet microscope objective 8 and the long working distance high power ultraviolet microscope objective 25 is, the larger the diameter of the conical laser beam 28 is, the weaker the laser energy passes through the long working distance high power ultraviolet microscope objective 25, but the smaller the focused light spot is; therefore, by adjusting the distance between the low-power ultraviolet microscope objective 8 and the long-working-distance high-power ultraviolet microscope objective 25, the laser energy passing through the long-working-distance high-power ultraviolet microscope objective 25 and the size of a focused light spot are taken up or rejected, namely a large-energy large light spot and a small-energy small light spot; the echo signal reversely passes through the long-working-distance high-power ultraviolet microscope objective 25 along the main optical axis 4, the reflected beam of the dichroic mirror 27 travels along the receiving optical axis 15, and the reflected beam reaches the proportional beam splitter 17 (in this embodiment, the ratio of 9 to 1 is a ratio beam splitter, that is, the transmission is 9-1), and then the reflected beam is divided into two orthogonal paths: one path of light is reflected and travels along the imaging optical axis 10, is focused between one time and two times of focal length of the imaging lens 32 in the electronic eyepiece 11 through the tube lens 33, and is amplified into a real image through the imaging lens 32 to the image sensor 31 (in the embodiment, a black-and-white area array sensor is adopted, and the response wave band of the black-and-white area array sensor is 350 to 800 nanometers); after the other path of light passes through the proportional beam splitter 17, rayleigh scattering of the wavelength of the ultraviolet raman laser 3 is filtered through an ultraviolet rayleigh filter 16, and then is focused to the incident end face of the optical fiber 13 through a microscope objective 14, and then enters the spectrometer 12 for analysis; the low-power ultraviolet microscope objective 8 is arranged on a secondary linear electric platform 9 and can do one-dimensional precise translation along the main optical axis 4 under the driving of a secondary motor driver 6; the long working distance high power ultraviolet microscope objective 25 is arranged on the main linear electric platform 22 and can do one-dimensional precise translation along the main optical axis 4 under the driving of the main motor driver 21; the translation of the secondary linear electric platform 9 is mainly used for changing the distance between the low-power ultraviolet microscope objective 8 and the long-working-distance high-power ultraviolet microscope objective 25; the translation of the main linear electric platform 22 is mainly used for accurately focusing the long-working-distance high-power ultraviolet microscope objective 25; the LIBS optical axis 37, the main optical axis 4, the imaging optical axis 10 and the receiving optical axis 15 are coplanar; the main optical axis 4 is parallel to the imaging optical axis 10 and perpendicular to the LIBS optical axis 37 and the receiving optical axis 15;
the optical head 2 is arranged on a three-dimensional precise electric platform 29, and the three-dimensional precise electric platform 29 can perform submicron three-dimensional precise motion under the driving of a three-dimensional motor driver 1;
the main controller 7 can send control instructions to the cut-in controller 36, the digital pulse delay controller 39, the three-dimensional motor driver 1, the main motor driver 21, the secondary motor driver 6, the ultraviolet Raman laser 3, the image sensor 31 and the spectrometer 12; the main controller 7 also sets the exposure time of the spectrometer 12, and can receive the output digital image of the image sensor 31 and the output spectrum information of the spectrometer 12;
the invention provides a self-adaptive laser spectrum and imaging detection method, which comprises the following steps:
(1) prospective focal spot adaptive focus calibration
In the deep space material in-situ detection, different scales of raman focal points, i.e. the expected focal points 19, are required for different detection objects 23, for example, for minerals distributed more uniformly, the expected focal points 19 with a slightly larger size can be adopted; for more varied minerals, the desired focal spot 19 can be used in extremely small sizes to achieve extremely fine domain analysis;
first, for the basic property of the detection object 23 according to the test region, the diameter of the expected focal spot 19 is set (in the present embodiment, for the olivine mineral, the diameter of the expected focal spot 19 is set to 1.7 μm); placing the measuring reticle 24 in a test area below a long-working-distance high-power ultraviolet microscope objective 25; the measurement reticle 24 has uniform scribe lines 20 (the measurement reticle used in this example has a scribe line pitch of 10 microns);
the main controller 7 controls the starting of the ultraviolet Raman laser 3, and an ultraviolet laser beam emitted by the ultraviolet Raman laser passes through the ultraviolet interference optical filter 5, the low-power ultraviolet microscope objective 8 and the dichroic mirror 27 in sequence, is illuminated and focused to the measurement reticle 24 through the long-working-distance high-power ultraviolet microscope objective 25, and forms a real-time focal spot 18; the reflected light of the measuring reticle 24 passes through the long working distance high power ultraviolet microscope objective 25 along the main optical axis 4 in the reverse direction, is reflected by the dichroic mirror 27, is reflected by the proportional beam splitter 17, is focused by the tube lens 33, and is subjected to real-time microscopic imaging by the imaging lens 32 to the image sensor 31;
the main controller 7 receives the microscopic digital image output by the image sensor 31 and performs real-time image processing; acquiring the outer circle contour of the real-time focal spot 18 by adopting an edge extraction algorithm, thereby determining an imaging region of the real-time focal spot 18 and calculating the average gray value G of all pixels in the imaging region;
the main controller 7 sends an instruction to the main motor driver 21 to drive the main linear electric platform 22 to move downwards by a step length; the main controller 7 receives the microscopic digital image output by the image sensor 31, determines the imaging area of the real-time focal spot 18, calculates the average gray value G of all pixels in the imaging area, and compares whether the G value is increased or decreased: if the value of G is increased, it indicates that the downward motion is in a direction close to the focal point; if the value of G is decreased, it indicates that the upward movement is in a direction close to the focal point;
the main controller 7 sends an instruction to the main motor driver 21 to drive the main linear electric platform 22 to move towards the direction close to the focal point, and simultaneously calculates the average gray value G of all pixels in the imaging area of the real-time focal spot 18 in real time until the G value reaches the maximum value, at this time, the main controller 7 is in a tight focusing state and sends an instruction to the main motor driver 21 to stop moving;
in a tightly focused state, the main controller 7 adopts an edge extraction algorithm to obtain the linear position of the scribed lines 20 of the measuring reticle 24 and the excircle contour of the real-time focal spot 18 from the microscopic digital image output by the image sensor 31, and then calculates the number of pixels at the interval between adjacent scribed lines 20 and the number of pixels of the excircle contour diameter of the real-time focal spot 18, so as to calculate the diameter of the real-time focal spot 18 according to the distance between the scribed lines 20;
if the diameter of the real-time focal spot 18 is larger than that of the expected focal spot 19, the main controller 7 sends an instruction to the secondary motor driver 6 to drive the secondary linear electric platform 9 to move upwards, the distance between the low-power ultraviolet microscope objective 8 and the long-working-distance high-power ultraviolet microscope objective 25 is increased, at the moment, the laser energy passing through the long-working-distance high-power ultraviolet microscope objective 25 is weakened, but the real-time focal spot 18 is reduced until the diameter of the real-time focal spot 18 is equal to that of the expected focal spot 19, and the main controller 7 sends an instruction to the secondary motor driver 6 to stop the movement of the secondary linear electric platform 9;
similarly, if the diameter of the real-time focal spot 18 is smaller than that of the expected focal spot 19, the main controller 7 sends an instruction to the secondary motor driver 6 to drive the secondary linear electric platform 9 to move downwards, so that the distance between the low-power ultraviolet microscope objective 8 and the long-working-distance high-power ultraviolet microscope objective 25 is reduced, the laser energy passing through the long-working-distance high-power ultraviolet microscope objective 25 is increased, the real-time focal spot 18 is increased until the diameter of the real-time focal spot 18 is equal to that of the expected focal spot 19, and the main controller 7 sends an instruction to the secondary motor driver 6 to stop the movement of the secondary linear electric platform 9;
(2) single point tight focus of detection object
The measuring reticle 24 is removed, the self-adaptive Raman fluorescence imaging combined system is moved into an actual test area, the detection object 23 is positioned below the optical head 2, and the distance from the long working distance to the high-power ultraviolet microscope objective 25 is far larger than the focal length of the high-power ultraviolet microscope objective;
the main controller 7 controls the starting of the ultraviolet Raman laser 3, an ultraviolet laser beam emitted by the ultraviolet Raman laser sequentially passes through the ultraviolet interference optical filter 5, the low-power ultraviolet microscope objective 8 and the dichroic mirror 27, is defocused to the surface of the detection object 23 through the long working distance high-power ultraviolet microscope objective 25, penetrates through the long working distance high-power ultraviolet microscope objective 25 along the main optical axis 4 in the reverse direction, is reflected by the dichroic mirror 27, is reflected by the proportional beam splitter 17, is focused through the tube lens 33, and is microimaged to the image sensor 31 in real time through the imaging lens 32; the main controller 7 receives the microscopic digital image output by the image sensor 31, and performs fast Fourier transform to extract a high-frequency component H of the microscopic digital image;
the main controller 7 sends an instruction to the three-dimensional motor driver 1 to drive the optical head 2 on the three-dimensional precise electric platform 29 to move downwards along the Z axis, at the moment, the distance between the detection object 23 and the long working distance high-power ultraviolet microscope objective 25 is reduced, during the movement process, the main controller 7 continuously carries out fast Fourier transform on the microscope digital image output by the image sensor 31 in real time, and continuously extracts the high-frequency component H of the microscope digital image until the H reaches the maximum value, at the moment, the laser is tightly focused to one point on the surface of the detection object 23, the size of the real-time focal spot 18 is equal to that of the expected focal spot 19, and the real-time focal;
(3) raman fluorescence and imaging information acquisition
In this tightly focused state, the main controller 7 records the three-dimensional displacement amount of the three-dimensional precision motorized stage 29, and sets it as an initial three-dimensional coordinate (x)1,y1,z1) (ii) a The main controller 7 receives the microscopic digital image output by the image sensor 31, and acquires the outer circle contour of the real-time focal spot 18 by adopting an edge extraction algorithm, so as to determine the imaging area of the real-time focal spot 18 and calculate the average gray value g of all pixels in the imaging area1(ii) a The Raman and fluorescence backscattering of the real-time focal spot 18 position on the surface of the detection object 23 passes through a long-working-distance high-power ultraviolet microscope objective 25 along a main optical axis 4, is reflected by a dichroic mirror 27, penetrates through a proportional beam splitter 17, is filtered by an ultraviolet Rayleigh filter 16 to remove Rayleigh scattering of the wavelength of an ultraviolet Raman laser 3, is focused to the incident end face of an optical fiber 13 through a microscope objective 14, and then enters a spectrometer 12, and the spectrometer 12 outputs a spectrum signal to a main controller 7 for analysis; the main controller 7 first extracts n (n-3 in this embodiment) discrete raman lines λ of the spectral signal1，λ2，λ3，...，λnRecording the spectral line intensity I11，Ι12，Ι13，...，Ι1n(ii) a Then dividing the continuous fluorescence line into m sections with equal spectral intervals (m is 300 in the embodiment); and recording the mean intensity J of the fluorescence spectrum of each segment11，J12，J13，...，J1m；
(4) Raman fluorescence imaging scanning micro-area analysis
The main controller 7 determines A, B scanning points in XY direction of micro-area analysis and C, D scanning step length; the main controller 7 sends an instruction to the three-dimensional motor driver 1 to drive the optical head 2 on the three-dimensional precise electric platform 29 to perform S-shaped scanning on the XY plane (namely, after scanning to A points along the X axis according to a scanning step C, the Y axis is moved forward by a step D, then A points are scanned reversely along the X axis, then the Y axis is moved forward by a step D, then A points are scanned forward along the X axis, then the Y axis is moved forward by a step D, then A points are scanned reversely along the X axis until the preset scanning area size is completed, the total scanning point number is A multiplied by B, namely AxB), and each point on the XY plane is moved up and down along the Z axis to execute single-point tight focusing of the step (2);
for each scanning point i (i is more than or equal to 2 until i is equal to A multiplied by B), under the state of tight focusing of the point, the main controller 7 records the three-dimensional displacement of the three-dimensional precision electric platform 29 and determines the three-dimensional coordinate (x) thereofi,yi,zi) (ii) a The main controller 7 receives the microscopic digital image output by the image sensor 31, and acquires the outer circle contour of the real-time focal spot 18 by adopting an edge extraction algorithm, so as to determine the imaging area of the real-time focal spot 18 and calculate the average gray value g of all pixels in the imaging areai(ii) a The main controller 7 records n discrete raman spectral lines lambda1，λ2，λ3，...，λnSpectral line intensity Ii1，Ιi2，Ιi3，...，Ιin(ii) a And recording the average intensity J of the fluorescence spectrum of each section of the m sections of the fluorescence spectrumi1,Ji2,Ji3,...,Jim；
The main controller 7 firstly integrates the three-dimensional coordinates of A multiplied by B scanning points and draws the three-dimensional geometric shape of the surface of the detection object 23 in the scanning area; then, g of each scanning point is integrated1,g2,...,gi,., obtaining a gray scale image (in this embodiment, a wide spectrum image with a response wave band of 350 to 800 nanometers) of the three-dimensional geometric topography of the surface of the detection object 23; then, the I of each scanning point is integrated11,I21,...,Ii1,., obtaining the wavelength lambda of the surface of the detection object 231Similarly, I of each scanning point is integrated12,I22,...,Ii2,., obtaining the wavelength lambda of the surface of the detection object 232Until the wavelength of the surface of the detection object 23 is obtained as lambdan(ii) a raman image of; finally, the J of each scanning point is integrated11,J21,...,Ji1,., a first spectral fluorescence image of the surface of the object 23 is obtained, and similarly, J of each scanning point is integrated12,J22,...,Ji2,., obtaining a fluorescence image of the second spectral band of the surface of the detection object 23, until obtaining a fluorescence image of the m spectral band of the surface of the detection object 23;
(5) LIBS scanning micro-area analysis and information fusion
The main controller 7 sends a command to the cut-in controller 36 to cut the LIBS cut-in total reflection mirror 34 into the main optical axis 4; the main controller 7 issues an instruction to set the exposure time (1 millisecond in this embodiment) of the spectrometer 12; the main controller 7 sends a command to the digital pulse delay controller 39 to set the operating frequency of the LIBS laser 38 (3 hz in this embodiment) and the delay between the activation of the LIBS laser 38 and the spectrometer 12 (10 μ s in this embodiment);
the main controller 7 sends an instruction to the three-dimensional motor driver 1 to drive the optical head 2 on the three-dimensional precise electric platform 29 to perform scanning opposite to the step (4) according to the recorded three-dimensional coordinates of A × B scanning points, namely reverse S-shaped scanning, and reversely complete the A × B scanning points;
for each scanning point, performing LIBS detection with a single point of 1 second, receiving LIBS spectrum information output by the spectrometer 12 by the main controller 7 (in this embodiment, 3 LIBS spectra obtained in 1 second are averaged and then analyzed), and qualitatively and quantitatively analyzing element composition and content of the point according to a relation between spectral line positions and intensities until the micro-area LIBS analysis of the whole axb point is completed;
and (4) information fusion is carried out to complete the laser spectrum and imaging analysis of the micro-area, namely, the three-dimensional shape distribution of the micro-area, and the wide spectrum image of A multiplied by B scanning points, the ultraviolet laser Raman image of n wavelengths, the ultraviolet laser induced fluorescence hyperspectral image of m spectral bands and the element distribution image on the three-dimensional shape distribution are obtained.

Claims (1)

1. A self-adaptive laser spectrum and imaging method suitable for deep space micro-area analysis is realized on a self-adaptive laser spectrum and imaging detection system, wherein the system consists of a main controller (7), a spectrometer (12), an optical fiber (13), a three-dimensional motor driver (1), a three-dimensional precise electric platform (29), a digital pulse delay controller (39) and an optical head (2); the optical head (2) consists of an LIBS laser (38), an LIBS cut-in total reflection mirror (34), a cut-in controller (36), an ultraviolet Raman laser (3), an ultraviolet interference filter (5), a secondary motor driver (6), a secondary linear electric platform (9), a low-power ultraviolet microscope objective (8), a dichroic mirror (27), a long-working-distance high-power ultraviolet microscope objective (25), a main motor driver (21), a main linear electric platform (22), an ultraviolet Rayleigh filter (16), a proportion beam splitter (17), a microscope objective (14), a tube lens (33) and an electronic eyepiece (11); an imaging lens (32) and an image sensor (31) are arranged in the electronic eyepiece (11);
the pulsed LIBS laser beam (35) emitted by the LIBS laser (38) along the LIBS optical axis (37) and the continuous laser emitted by the ultraviolet Raman laser (3) along the main optical axis (4) have the same initial beam diameter and the same minimum divergence angle; when in the non-LIBS working mode, the cut-in controller (36) cuts the LIBS into the total reflection mirror (34) and cuts out the main optical axis (4); when the laser is in an LIBS working mode, the cut-in controller (36) cuts the LIBS cut-in total reflection mirror (34) into the main optical axis (4), at the moment, the distance from the output ports of the LIBS laser (38) and the ultraviolet Raman laser (3) to the LIBS cut-in total reflection mirror (34) is equal, after a pulse LIBS laser beam (35) emitted by the LIBS laser (38) along the LIBS optical axis (37) is cut into the total reflection mirror (34) through the LIBS for total reflection, enters a main optical axis (4) for transmission, forms a cylindrical near-collimation laser beam (30) which passes through a low-power ultraviolet microscope objective (8), forms a conical laser beam (28) which passes through a dichroic mirror (27), the LIBS echo signal reversely passes through the long working distance high-power ultraviolet microscope objective (25) along the main optical axis (4) and travels along the receiving optical axis (15) after being reflected by the dichroic mirror (27), and is divided into two orthogonal paths after reaching the proportional beam splitter (17): one path of the signal travels along an imaging optical axis (10) through reflection, and the signal is not used in an LIBS mode; the other path of light passes through the proportional beam splitter (17), then passes through an ultraviolet Rayleigh filter (16) to filter out Rayleigh scattering of the LIBS laser (38) wavelength, then passes through a microscope objective (14) to be focused to the incident end face of the optical fiber (13), and then enters the spectrometer (12) for analysis; the digital pulse delay controller (39) is provided with two control ends which are respectively connected with an LIBS laser (38) and an external trigger port of the spectrometer (12); the digital pulse delay controller (39) is used for setting the working frequency of the LIBS laser (38) and the time delay of the opening between the LIBS laser (38) and the spectrometer (12);
laser beams emitted by the ultraviolet Raman laser (3) along the main optical axis (4) pass through the ultraviolet interference filter (5), so that frequency division harmonic interference of the ultraviolet laser emitted by the ultraviolet Raman laser (3) can be filtered, and the signal-to-noise ratio of Raman signals excited by the ultraviolet Raman laser is higher; the formed cylindrical near-collimation laser beam (30) passes through a low-power ultraviolet microscope objective (8) to form a conical laser beam (28); the conical laser beam (28) passes through the dichroic mirror (27) and then reaches an entrance pupil (26) of the long-working-distance high-power ultraviolet microscope objective (25), the diameter of the conical laser beam (28) is larger than that of the entrance pupil (26) at the position of the entrance pupil (26), and the farther the distance between the low-power ultraviolet microscope objective (8) and the long-working-distance high-power ultraviolet microscope objective (25) is, the larger the diameter of the conical laser beam (28) is than that of the entrance pupil (26) because the cone angle of the conical laser beam (28) is a fixed value, the weaker the laser energy passing through the long-working-distance high-power ultraviolet microscope objective (25) is, and the smaller the focused light spot is; therefore, by adjusting the distance between the low-power ultraviolet microscope objective (8) and the long-working-distance high-power ultraviolet microscope objective (25), the selection is made between the laser energy passing through the long-working-distance high-power ultraviolet microscope objective (25) and the size of a focused light spot, namely a large-energy large light spot and a small-energy small light spot; echo signals reversely pass through a long working distance high-power ultraviolet microscope objective (25) along a main optical axis (4), and travel along a receiving optical axis (15) after being reflected by a dichroic mirror (27) and reach a proportional beam splitter (17) and then are divided into two orthogonal paths: one path of light is reflected and travels along an imaging optical axis (10), is focused between one time and two times of focal length of an imaging lens (32) in the electronic eyepiece (11) through a tube lens (33), and is amplified to form a real image to an image sensor (31) through the imaging lens (32); the other path of light passes through the proportional beam splitter (17), then passes through an ultraviolet Rayleigh filter (16) to filter Rayleigh scattering of the wavelength of the ultraviolet Raman laser (3), and then is focused to the incident end face of the optical fiber (13) through a microscope objective (14), and then enters a spectrometer (12) for analysis; the low-power ultraviolet microscope objective (8) is arranged on a secondary linear electric platform (9) and can do one-dimensional precise translation along the main optical axis (4) under the driving of a secondary motor driver (6); the long working distance high power ultraviolet microscope objective (25) is arranged on the main linear electric platform (22) and can do one-dimensional precise translation along the main optical axis (4) under the drive of the main motor driver (21); the translation of the secondary linear electric platform (9) is mainly used for changing the distance between the low-power ultraviolet microscope objective (8) and the long-working-distance high-power ultraviolet microscope objective (25); the translation of the main linear electric platform (22) is mainly used for accurately focusing the long-working-distance high-power ultraviolet microscope objective (25); the LIBS optical axis (37), the main optical axis (4), the imaging optical axis (10) and the receiving optical axis (15) are coplanar; the main optical axis (4) is parallel to the imaging optical axis (10) and is vertical to the LIBS optical axis (37) and the receiving optical axis (15);
the optical head (2) is arranged on a three-dimensional precise electric platform (29), and the three-dimensional precise electric platform (29) can do submicron three-dimensional precise motion under the driving of a three-dimensional motor driver (1);
the main controller (7) can send control instructions to the switching-in controller (36), the digital pulse delay controller (39), the three-dimensional motor driver (1), the main motor driver (21), the secondary motor driver (6), the ultraviolet Raman laser (3), the image sensor (31) and the spectrometer (12); the main controller (7) also sets the exposure time of the spectrometer (12), and can receive the output digital image of the image sensor (31) and the output spectrum information of the spectrometer (12);
the method is characterized in that the self-adaptive laser spectrum and imaging method comprises the following steps:
1) prospective focal spot adaptive focus calibration
In the in-situ detection of deep space materials, Raman focusing points with different scales are needed for different detection objects, namely expected focal spots;
firstly, setting the diameter of an expected focal spot according to the basic properties of a detection object in a test region; placing a measuring reticle in a test area below a long-working-distance high-power ultraviolet microscope objective; uniform scribed lines are arranged on the measuring reticle;
the main controller controls to start the ultraviolet Raman laser, and an ultraviolet laser beam emitted by the ultraviolet Raman laser sequentially passes through the ultraviolet interference optical filter, the low-power ultraviolet microscope objective and the dichroic mirror, is illuminated and focused to the measurement reticle through the long-working-distance high-power ultraviolet microscope objective, and forms a real-time focal spot; the reflected light of the measuring reticle passes through the long-working-distance high-power ultraviolet microscope objective along the main optical axis in the reverse direction, is reflected by the dichroic mirror, is reflected by the proportional beam splitter, is focused by the tube lens, and is subjected to real-time microscopic imaging by the imaging lens to the image sensor;
the main controller receives the microscopic digital image output by the image sensor and performs real-time image processing; acquiring the excircle profile of the real-time focal spot by adopting an edge extraction algorithm, thereby determining an imaging region of the real-time focal spot and calculating the average gray value G of all pixels in the imaging region;
the main controller sends an instruction to the main motor driver to drive the main linear electric platform to move downwards by a step length; the main controller receives the microscopic digital image output by the image sensor, determines the imaging area of the real-time focal spot, calculates the average gray value G of all pixels in the imaging area, and compares whether the G value is increased or decreased: if the value of G is increased, it indicates that the downward motion is in a direction close to the focal point; if the value of G is decreased, it indicates that the upward movement is in a direction close to the focal point;
the main controller sends an instruction to the main motor driver to drive the main linear electric platform to move towards the direction close to the focal point, and simultaneously calculates the average gray value G of all pixels in the imaging area of the real-time focal spot in real time until the G value reaches the maximum value, and at the moment, the main controller is in a tight focusing state and sends an instruction to the main motor driver to stop moving;
in a tight focusing state, the main controller adopts an edge extraction algorithm to obtain the linear position of the scribed lines of the measuring reticle and the real-time focal spot excircle outline of the microscopic digital image output by the image sensor, and then calculates the number of pixels at the interval of adjacent scribed lines and the number of pixels of the real-time focal spot excircle outline diameter, so as to calculate the real-time focal spot diameter according to the distance of the scribed lines;
if the diameter of the real-time focal spot is larger than that of the expected focal spot, the main controller sends an instruction to the secondary motor driver to drive the secondary linear electric platform to move upwards, the distance between the low-power ultraviolet microscope objective and the long-working-distance high-power ultraviolet microscope objective is increased, the laser energy passing through the long-working-distance high-power ultraviolet microscope objective is weakened, the real-time focal spot is reduced until the diameter of the real-time focal spot is equal to that of the expected focal spot, and the main controller sends an instruction to the secondary motor driver to stop the movement of the secondary linear electric platform;
if the diameter of the real-time focal spot is smaller than that of the expected focal spot, the main controller sends an instruction to the secondary motor driver to drive the secondary linear electric platform to move downwards, the distance between the low-power ultraviolet microscope objective and the long-working-distance high-power ultraviolet microscope objective is reduced, the laser energy passing through the long-working-distance high-power ultraviolet microscope objective is increased, the real-time focal spot is increased until the diameter of the real-time focal spot is equal to that of the expected focal spot, and the main controller sends an instruction to the secondary motor driver to stop the movement of the secondary linear electric platform;
2) single point tight focus of detection object
Removing the measuring reticle, and moving the self-adaptive Raman fluorescence imaging combination system into an actual test area, wherein the detection object is positioned below the optical head, and the distance from the long working distance to the high-power ultraviolet microscope objective is far larger than the focal length of the high-power ultraviolet microscope objective;
the main controller controls and starts the ultraviolet Raman laser, an ultraviolet laser beam emitted by the ultraviolet Raman laser sequentially passes through an ultraviolet interference optical filter, a low-power ultraviolet microscope objective and a dichroic mirror, is defocused to the surface of a detection object through a long-working-distance high-power ultraviolet microscope objective, reflected light passes through the long-working-distance high-power ultraviolet microscope objective along a main optical axis in the reverse direction, is reflected by the dichroic mirror, is reflected by a proportional beam splitter, is focused through a tube lens, and is microimaged to an image sensor in real time through an imaging lens; the main controller receives the microscopic digital image output by the image sensor, and performs fast Fourier transform to extract a high-frequency component H of the microscopic digital image;
the main controller sends an instruction to a three-dimensional motor driver to drive an optical head on the three-dimensional precise electric platform to move downwards along the Z-axis, at the moment, the distance between a detected object and a long working distance high-power ultraviolet microscope objective is reduced, in the moving process, the main controller continuously carries out fast Fourier transform on a microscopic digital image output by an image sensor in real time, and continuously extracts a high-frequency component H of the microscopic digital image until the H reaches the maximum value, at the moment, laser is tightly focused to one point on the surface of the detected object, the size of a real-time focal spot is equal to that of an expected focal spot, and the laser is in a;
3) raman fluorescence and imaging information acquisition
In this tight focus state, the master controller records the three-dimensional displacement of the three-dimensional precision motorized stage, setting it to the initial three-dimensional coordinates (x)1,y1,z1) (ii) a The main controller receives the microscopic digital image output by the image sensor, and the edge extraction algorithm is adopted to obtain the excircle outline of the real-time focal spot, so that the imaging area of the real-time focal spot is determined, and the average gray value g of all pixels in the imaging area is calculated1(ii) a Detecting Raman and fluorescence backscattering of a real-time focal spot position on the surface of an object, penetrating through a long working distance high-power ultraviolet microscope objective along a main optical axis, reflecting through a dichroic mirror, transmitting through a proportional beam splitter, filtering out Rayleigh scattering of the wavelength of an ultraviolet Raman laser through an ultraviolet Rayleigh filter, focusing to an incident end face of an optical fiber through the microscope objective, then entering a spectrometer, and outputting a spectrum signal to a main controller by the spectrometer for analysis; the main controller firstly extracts n discrete Raman spectral lines lambda of the spectral signal1，λ2，λ3，...，λnRecording the spectral line intensity I11，Ι12，Ι13，...，Ι1n(ii) a Then dividing the continuous fluorescence spectral line into m sections with equal spectral intervals; and recording the mean intensity J of the fluorescence spectrum of each segment11，J12，J13，...，J1m；
4) Raman fluorescence imaging scanning micro-area analysis
The main controller determines A, B scanning points in the XY direction of the micro-area analysis and C, D scanning step length; the main controller sends an instruction to the three-dimensional motor driver to drive the optical head on the three-dimensional precise electric platform to perform S-shaped scanning on an XY plane, and then moves up and down along a Z axis for each point on the XY plane to execute single-point tight focusing in the step 2);
for each scanning point i, i is more than or equal to 2 until i is equal to A multiplied by B, and under the tight focusing state of the point, the main controller records the three-dimensional displacement of the three-dimensional precision electric platform and determines the three-dimensional coordinate (x) of the three-dimensional precision electric platformi,yi,zi) (ii) a The main controller receives the microscopic digital image output by the image sensor, and the edge extraction algorithm is adopted to obtain the excircle outline of the real-time focal spot, so that the imaging area of the real-time focal spot is determined, and the average gray value g of all pixels in the imaging area is calculatedi(ii) a The main controller records n discrete Raman spectral lines lambda1，λ2，λ3，...，λnSpectral line intensity Ii1，Ιi2，Ιi3，...，Ιin(ii) a And recording the average intensity J of the fluorescence spectrum of each section of the m sections of the fluorescence spectrumi1,Ji2,Ji3,...,Jim；
The main controller firstly integrates the three-dimensional coordinates of A multiplied by B scanning points and draws the three-dimensional geometric appearance of the surface of the detection object in the scanning area; then, g of each scanning point is integrated1,g2,...,gi,., obtaining a gray level image of the three-dimensional geometric shape of the surface of the detection object; then, the I of each scanning point is integrated11,I21,...,Ii1,., obtaining the wavelength of the surface of the detection object as lambda1Raman image of (2), integrating I of each scanning point12,I22,...,Ii2,., obtaining the wavelength of the surface of the detection object as lambda2Until the wavelength of the surface of the detected object is obtained as lambdan(ii) a raman image of; finally, the J of each scanning point is integrated11,J21,...,Ji1,., obtaining a fluorescence image of the first spectrum of the surface of the detected object, and integrating J of each scanning point12,J22,...,Ji2,., obtaining a fluorescence image of the second spectrum band of the surface of the detection object until obtaining a fluorescence image of the m spectrum band of the surface of the detection object;
5) LIBS scanning micro-area analysis and information fusion
The main controller sends a command to the cut-in controller to cut the LIBS cut-in total reflection mirror into the main optical axis; the main controller sends out an instruction to set the exposure time of the spectrometer; the main controller sends an instruction to the digital pulse delay controller, and sets the working frequency of the LIBS laser and the time delay of the opening between the LIBS laser and the spectrometer;
the main controller sends an instruction to the three-dimensional motor driver to drive the optical head on the three-dimensional precise electric platform to perform scanning opposite to the step 4) according to the recorded three-dimensional coordinates of A multiplied by B scanning points, namely reverse S-shaped scanning, and reversely finishing the number A multiplied by B of the scanning points;
for each scanning point, performing LIBS detection with a single point of 1 second, receiving the output LIBS spectrum information of the spectrometer by the main controller, and qualitatively and quantitatively analyzing the element composition and content of the point according to the relation between the spectral line position and the intensity until the micro-area LIBS analysis of the whole A multiplied by B point is completed;
and 4) information fusion is carried out with the step 4) to complete the laser spectrum and imaging analysis of the micro-area, namely, the three-dimensional shape distribution of the micro-area, the wide spectrum image of A multiplied by B scanning points on the three-dimensional shape distribution, the ultraviolet laser Raman image of n wavelengths, the ultraviolet laser induced fluorescence hyperspectral image of m spectral bands and the element distribution image are obtained.
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