Short-wave infrared spectral imaging device based on linear array sensor and imaging method

Abstract

The application discloses a kind of short-wave infrared spectrum imaging device and imaging method based on linear array sensor, including objective lens, slit, lens group, dispersive element, single-axis micro scanning mirror, linear array sensor and controller, one of lens group is located between slit and dispersive element, objective lens is imaged to slit and collimated after passing through lens, single-axis micro scanning mirror is deflected a certain angle in a certain range with the slit direction of slit as axis after light field, collimated through the last lens of lens group, so that after dispersion, light field is scanned and imaged on the image plane of linear array sensor along the dispersion direction, controller controls single-axis micro scanning mirror and linear array sensor, realize the acquisition of one-dimensional space and one-dimensional spectrum of the light field of the measured target in a deflection period, relative imaging device uniform speed moves measured target, realize the acquisition of another dimension space of the light field of the measured target, realize the spectral imaging device of built-in micro scanning+external linear scanning.

Description

Technical Field

[0001] The present application relates to the technical field of medium- and short-wave infrared spectral imaging, and specifically to a medium- and short-wave infrared spectral imaging device and imaging method based on a linear array sensor. Background Art

[0002] Shortwave infrared (SWIR, 0.9-2.5μm) and midwave infrared (MWIR, 3-5μm), as key windows in the infrared spectrum, have valuable applications in multiple fields due to their unique photophysical properties. SWIR's core capabilities stem from its absorption of molecular vibrational overtones. Industrial applications include wafer defect detection through silicon materials, plastic sorting via characteristic absorption of CH / OH bonds with >95% accuracy, and crop moisture monitoring in agriculture using the 1450 / 1940 nm moisture absorption peaks, with an accuracy of ±2%. MWIR, based on absorption of molecular fundamental frequency vibrations, excels in industrial high-temperature process monitoring, such as thermal imaging of equipment operating at 700-1500°C and detection of greenhouse gases like methane and CO2. Its 3.3 / 4.3μm absorption spectrum provides outstanding performance in overheating warnings for power equipment. In environmental monitoring, SWIR uses characteristic mineral reflectance spectra at 2.1-2.4μm for geological exploration. Combined with the MWIR's 4μm atmospheric window, it enables simultaneous surface mineral analysis and three-dimensional monitoring of atmospheric pollutants. However, short-wave and medium-wave spectral imaging face the bottleneck of high detector costs. SWIR relies on InGaAs sensors, and MWIR requires HgCdTe cooling devices, which are more expensive. This limits the application and popularity of medium- and short-wave infrared spectral imaging.

[0003] Existing medium- and short-wave infrared spectral imaging solutions are divided into two categories: push-broom and filters. Push-broom spectral imaging systems often use the relative movement of the conveyor belt and the camera as well as slit and grating imaging structures to achieve scanning imaging, which is suitable for industrial scenarios. However, medium- and short-wave area array sensors are required to achieve simultaneous spatial and spectral acquisition, which is expensive and difficult to popularize on a large scale in the industry. The filter solution captures images of multiple wavelength channels at one time by dividing the area array sensor and pre-placing filters of different wavelength channels, but is limited by low spatial resolution and insufficient number of spectral channels, and cannot achieve higher-precision detection. Currently, the vast majority of medium- and short-wave spectral cameras in the industry use a push-broom solution, which is mainly limited by the high price of sensors, limiting their large-scale application in industrial scenarios. Summary of the Invention

[0004] The present application provides a medium- and short-wave infrared spectral imaging device and imaging method based on a linear array sensor to solve the technical problems existing in the above-mentioned prior art.

[0005] The technical solution adopted by the present application to solve its technical problems is: a medium- and short-wave infrared spectral imaging device based on a linear array sensor, comprising: an objective lens, a slit, a lens group, a dispersion element, a uniaxial micro-scanning mirror, a linear array sensor, and a controller, wherein the objective lens, the slit, the dispersion element, and the uniaxial micro-scanning mirror are coaxially located on one side of the target to be measured, one lens of the lens group is located between the slit and the dispersion element, the objective lens images the target to be measured onto the slit and collimates it through the lens, and the uniaxial micro-scanning mirror deflects the light field within a certain range by a certain angle with the slit direction as the axis and then passes through the end of the lens group. A lens is used for collimation, so that the dispersed light field is scanned and imaged along the dispersion direction on the image plane of the linear array sensor; a controller is connected to the linear array sensor and the uniaxial micro-scanning mirror, and the controller controls the deflection angle of the uniaxial micro-scanning mirror and the timing synchronization with the linear array exposure acquisition of the linear array sensor, completing the acquisition of the one-dimensional space and one-dimensional spectrum of the target light field within one deflection cycle. The target is moved at a uniform speed relative to the imaging device, and the controller controls the linear array sensor and the uniaxial micro-scanning mirror to realize the acquisition of the other dimension of the target light field, thereby realizing a spectral imaging device with built-in micro-scanning + external line scanning.

[0006] This application uses medium- and short-wave infrared linear array sensors to replace the existing area array, reducing the overall cost by more than 50%. The micro-scanning structure is combined with the linear array sensor to complete built-in high-speed scanning through optical path rotation, realizing time-division multiplexing acquisition of the one-dimensional spectral space. The built-in scanning is achieved through single-axis rotation, which is easy to implement and has low device cost and complexity.

[0007] Preferably, the lens group includes a first lens and a second lens, the first lens is located between the slit and the dispersion element, and the second lens is located between the linear array sensor and the uniaxial micro-scanning mirror, transferring the real image on the imaging surface of the first lens and imaging it onto the imaging surface of the second lens.

[0008] Preferably, the lens group adopts a double cemented achromatic lens or a triplet lens group.

[0009] Preferably, the dispersion element decomposes light of different wavelengths into different directions, which is achieved by using an Abbe prism, a blazed grating or a holographic grating, and the uniaxial micro-scanning mirror deflects the incident light beam to different angles along the same plane, using a piezoelectrically driven galvanometer or a MEMS micro-galvanometer.

[0010] Preferably, the pixel size of the linear array sensor is positively correlated with the focal length of the second lens and the slit width of the slit, and the pixel size of the linear array sensor is negatively correlated with the focal length of the first lens. After the light passes through the dispersion element, the exit angle of the light with a central wavelength of zero field of view is at an angle α relative to the z-axis. The second lens is parallel to the plane of the linear array sensor and has an angle σ with the z-axis. The light with a central wavelength of zero field of view is imaged onto the photosensitive pixel area at the center of the linear array sensor through the second lens. The angle between the plane of the uniaxial micro-scanning mirror and the z-axis is β, and β is positively correlated with α and σ.

[0011] The present application also provides a medium- and short-wave infrared spectral imaging method based on a linear array sensor, which is implemented using the above-mentioned medium- and short-wave infrared spectral imaging device based on a linear array sensor, comprising:

[0012] Step 1: Obtain the target light field to be measured, image it onto the slit plane through the objective lens, and calculate the slit plane coordinates based on the target light field to be measured and the magnification of the objective lens;

[0013] Step 2: Constrain the light field passing direction of the slit, perform a wavelength-dependent shift based on the light field passing direction through a dispersive element, and calculate the coordinates after dispersion based on the light field passing direction and the slit plane coordinates;

[0014] Step 3: Adjust the relationship between the deflection angle of the uniaxial micro-scanning mirror, the light field offset, and the focal length of the last lens in the lens group according to imaging requirements. At any time, the light field offset is positively correlated with the focal length of the last lens in the lens group and the tangent value of the deflection angle.

[0015] Step 4: Calculate the plane coordinates of the linear array sensor based on the magnification of the lens group imaging and the coordinates after dispersion;

[0016] Step 5: Integrate the light intensity of the exposure window at any moment based on the arrangement direction of the linear array sensor and the plane coordinates of the linear array sensor to obtain a function of the change of the object plane coordinates of the target to be measured over time;

[0017] Step 6: Calculate the micro-scanning period based on the single pixel size of the linear array sensor and the size of the target to be measured;

[0018] Step 7: In one micro-scanning cycle, N spectral channels corresponding to N wavelengths of the target to be measured are collected. Based on the relationship between the starting and ending deflection angles of the single-axis micro-scanning mirror, the relationship between the deflection angle and deflection period of the single-axis micro-scanning mirror, the exposure time of the linear array sensor, and the speed of the target to be measured is finally determined. The controller controls the deflection angle of the single-axis micro-scanning mirror and synchronizes the timing of the linear array exposure acquisition with the linear array sensor based on this relationship to achieve medium- and short-wave infrared spectral imaging.

[0019] Preferably, data is collected after a number of micro-scanning cycles to form a two-dimensional image data matrix, and the original hyperspectral data is restored after image reconstruction.

[0020] The substantial effects of this application are:

[0021] 1. This application uses medium- and short-wave infrared linear array sensors to replace existing area arrays, reducing overall costs by more than 50%. The micro-scanning structure is combined with the linear array sensor to complete built-in high-speed scanning through optical path rotation, realizing time-division multiplexing acquisition of the one-dimensional spectral space. The built-in scanning is achieved through single-axis rotation, which is easy to implement and has low device cost and complexity.

[0022] 2. This application combines built-in micro-scanning and external line scanning to scan simultaneously to achieve spatial spectral data collection of the entire format. The external line scanning method is simple and is generally achieved through the relative movement of the camera and the imaging target, such as a conveyor belt system. It is suitable for industrial conveyor belt scenarios and does not require the modification of existing production line equipment. It has strong versatility. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] Figure 1 Schematic diagram of the structure of the medium- and short-wave infrared spectral imaging device based on the linear array sensor of the first embodiment of the present application;

[0024] Figure 2 This is an imaging relationship diagram of the medium- and short-wave infrared spectrum imaging device based on the linear array sensor in Example 2 of the present application;

[0025] Figure 3 This is a schematic diagram of the deflection angle of the single-axis micro-scanning mirror and the timing synchronization with the linear array exposure acquisition of the linear array sensor in the medium- and short-wave infrared spectral imaging method based on the linear array sensor in the second embodiment of the present application;

[0026] Figure 4 This is a diagram of the simulation results of acquisition and reconstruction of the imaging device of the medium- and short-wave infrared spectral imaging method based on the linear array sensor in Example 2 of the present application. DETAILED DESCRIPTION

[0027] The technical solution of the present application is further described below through specific embodiments.

[0028] Example 1

[0029] A medium- and short-wave infrared spectral imaging device based on a linear array sensor, such as Figure 1As shown, it includes: an objective lens 1, a slit 2, a first lens 3, a dispersion element 4, a uniaxial micro-scanning mirror 5, a second lens 6, a linear array sensor 7 and a controller 8. The objective lens 1 realizes primary imaging and images the target to be measured onto the slit plane of the slit 2. It is followed by a lens group consisting of the first lens 3 and the second lens 6. A dispersion element 4 is placed in the middle of the lens group to disperse the image of the slit 2 in a direction perpendicular to the slit. The linear array sensor 7 is placed on the secondary imaging surface of the lens group, and the linear array direction is parallel to the slit. The uniaxial micro-scanning mirror 5 is in the middle of the lens group and is located after the dispersion element 4. It can deflect the light field by a fixed angle within a certain range with the slit direction as the axis, so that the light field after dispersion is scanned and imaged along the dispersion direction on the image plane of the linear array sensor 7, as shown in FIG. Figure 2 As shown, by controlling the deflection angle of the uniaxial micro-scanning mirror 5 and synchronizing the timing of the linear exposure acquisition of the linear array sensor 7 with the controller 8, both the one-dimensional spatial and one-dimensional spectral acquisition of the target light field can be completed within a single deflection cycle. By coordinating the uniform motion of the motion device carrying the target relative to the camera, the acquisition of the other spatial dimension of the target light field can be achieved, thus realizing a spectral imaging device combining internal micro-scanning and external line scanning.

[0030] like Figure 3 As shown, the centers of all optical elements in the device are on the same optical axis, and the focal length of objective lens 1 is f obj , the zero field of view of the target in the y-axis direction is imaged onto the slit 2. The first lens 3 and the second lens 6 with focal lengths f1 and f2 form a generalized 4f system. The slit 2 plane is conjugate with the linear array sensor 7 plane. Here, the slit width w is defined s With the sensor pixel size d s Satisfaction: d s =f2w s / f1, the light passes through the dispersion element 4, and the exit angle of the zero-field-of-view central wavelength light relative to the z-axis is the exit angle. The second lens 6 is parallel to the plane of the linear array sensor 7 and the angle between the second lens 6 and the z-axis is σ. Then the central wavelength light passes through the second lens 6 and is imaged onto the photosensitive pixel area at the center of the linear array sensor 7. The angle between the plane of the uniaxial micro-scanning mirror 5 and the z-axis is β, β=(α+σ) / 2+π / 4.

[0031] Example 2

[0032] A medium- and short-wave infrared spectral imaging method based on a linear array sensor is implemented using the medium- and short-wave infrared spectral imaging device based on a linear array sensor of the first embodiment, comprising:

[0033] Step 1: Obtain the target light field S (x0, y0, λ) to be measured, and image it onto the slit plane of slit 2 through objective lens 1 with a magnification of M1. Calculate the slit plane coordinates based on the target light field to be measured and the magnification of objective lens 1: x1=M1x0, y1=M1y0.

[0034] Step 2: Constrain slit 2 to y1 = 0, allowing only the light field in the x1 direction to pass through. A wavelength-dependent lateral offset is introduced through dispersive element 4. The coordinates after dispersion are calculated based on the light field's direction of passage and the slit plane coordinates: x2 = x1, y2(λ) = y1 + γ(λ - λ0), where γ is the dispersion coefficient and λ0 is the reference wavelength.

[0035] Step 3: The deflection angle θ(t) of the uniaxial micro-scanning mirror 5 changes with time. According to the imaging relationship, the offset of the light field in the y-axis direction caused by the change in the deflection angle can be expressed as: Δy(t) = f2tan(θ(t)). The coordinate after dispersion can then be expressed as: y2'(λ, t) = y2(λ) + Δy(t).

[0036] Step 4: The secondary imaging process is to image the light field of the slit plane to the sensor plane. The imaging magnification of the lens group is M2. The plane coordinates of the linear array sensor 7 are: x s =M2x2,y s (λ,t)=M2y2'(λ,t).

[0037] Step 5: The line array sensors 7 are arranged along the x-direction and integrate the light intensity of the exposure window of time T: , where S(x s ,y s , λ) is the spectral radiation intensity of the sensor plane, T is the integration time, assuming that the motion device carries the target to be measured and moves along the y direction at a speed v, the object plane coordinates of the target to be measured change with time as follows: y0(t)=y0(0)+vt, and the final sensor signal can be expressed as:

[0038] ,in is the Dirac function, representing the point spread function (PSF) of the imaging device.

[0039] Step 6: The single pixel size of the linear array sensor 7 is d s , the object size of the target to be measured is d s / M1M2, defines the y-direction dimension d of the imaging device on the object plane s The time for scanning and imaging the length of / M1M (corresponding to the single pixel size of the linear array sensor 7) is a micro scanning cycle: T t =d s / M1M2v.

[0040] Step 7: In a micro scanning cycle T t Inner pair λ1, λ2...λ N The N spectral channels corresponding to the N wavelengths are collected. For the linear array sensor 7 for continuous exposure collection, the exposure time satisfies: Ts =T t / N. At the same time, we can know a micro scanning period T t The starting and ending deflection angles θ of the uniaxial micro-scanning mirror 5 are s and θ e satisfy: The deflection period of the uniaxial micro-scanning mirror 5 is equal to two micro-scanning periods, wherein the first micro-scanning period is the deflection period of the uniaxial micro-scanning mirror 5. s Deflection to θ e , complete the λ1 to λ N The scanning of the channel, the second micro scanning cycle uniaxial micro scanning mirror 5 is composed of θ e Deflection to θ s , complete the N The above formulas determine the relationship between the deflection angle, deflection period, exposure time of the linear array sensor 7, and the speed v of the motion device. Based on this relationship, the controller 8 controls the deflection angle of the uniaxial micro-scanning mirror 5 and synchronizes the timing of the linear array exposure acquisition with the linear array sensor 7 to achieve medium- and short-wave infrared spectral imaging.

[0041] In addition, this application proposes a synchronization mechanism for triggering and collecting the single-axis micro-scanning mirror 5 and the imaging device. Assuming that the imaging device uses the rising edge of the voltage to trigger the exposure and collection, and the single-axis micro-scanning mirror 5 uses a piezoelectric vibrating mirror to control the light deflection angle, the timing synchronization relationship between the single-axis micro-scanning mirror 5 drive signal and the imaging device trigger signal is as follows: Figure 3 As shown. The single-axis micro-scanning mirror 5 adopts a valley voltage of v s , the peak voltage is v e , with a period of 2T t The triangle wave is used as the driving signal. When the voltage is v s When the single-axis micro-scanning mirror 5 has an angle deflection value θ s , when the voltage is v e When the single-axis micro-scanning mirror 5 is deflected to θ e The imaging device trigger signal adopts a period of T t Rectangular wave, using the rising edge to trigger exposure acquisition.

[0042] Furthermore, this application proposes a mathematical model for reconstructing a spectral image from images collected by a medium- and short-wave infrared spectral imaging device based on a linear array sensor. Given that the number of pixels of the linear array sensor 7 is m×1 and the number of spectral channels collected is c, the data obtained after collecting n micro-scanning cycles can be written in a matrix form: , then the reconstructed spectral image data can be defined as the matrix , where the position of each element in the matrix is:

[0043] , then when j is an even number: , when j is an odd number: ,This embodiment simulates the proposed imaging device and reconstruction process, and the simulation results are shown in Figure 4 The simulation used the Indian Pines[4] hyperspectral data, and intercepted 171 channel data from 900-2500nm as the simulation input, as shown in Figure 4 As shown in the figure, the data collected by the linear array sensor 7 is accumulated and converted into two-dimensional image data. After image reconstruction, the original hyperspectral data is restored.

[0044] The embodiment described above is only a preferred solution of the present application and does not limit the present application in any form. There are other variations and modifications without exceeding the technical solution described in the claims.

Claims

1. A medium- and short-wave infrared spectrum imaging device based on a linear array sensor, characterized in that: include: Objective lens (1), slit (2), lens group, dispersion element (4), single-axis micro-scanning mirror (5), linear array sensor (7) and controller (8), The objective lens (1), the slit (2), the dispersion element (4) and the uniaxial micro-scanning mirror (5) are coaxially located on one side of the target to be measured, one of the lenses of the lens group is located between the slit (2) and the dispersion element (4), the objective lens (1) images the target to be measured onto the slit (2) and collimates it through the lens, and the uniaxial micro-scanning mirror (5) deflects the light field by a certain angle within a certain range with the slit direction of the slit (2) as the axis and collimates it through the last lens of the lens group, so that the dispersed light field is scanned and imaged along the dispersion direction on the image plane of the linear array sensor (7); The controller (8) is connected to the linear array sensor (7) and the uniaxial micro-scanning mirror (5). The controller (8) controls the deflection angle of the uniaxial micro-scanning mirror (5) and the timing synchronization of the linear array exposure acquisition of the linear array sensor (7). The acquisition of the one-dimensional space and the one-dimensional spectrum of the light field of the target to be measured is completed within one deflection cycle. The target to be measured is moved at a uniform speed relative to the imaging device. The controller (8) controls the linear array sensor (7) and the uniaxial micro-scanning mirror (5) to realize the acquisition of the other dimensional space of the light field of the target to be measured, thereby realizing a spectral imaging device with built-in micro-scanning and external line scanning.

2. The medium- and short-wave infrared spectrum imaging device based on a linear array sensor according to claim 1, characterized in that: The lens group includes a first lens (3) and a second lens (6), wherein the first lens (3) is located between the slit (2) and the dispersion element (4), and the second lens (6) is located between the linear array sensor (7) and the uniaxial micro-scanning mirror (5), and transmits the real image on the imaging surface of the first lens (3) and forms an image on the imaging surface of the second lens (6).

3. The medium- and short-wave infrared spectrum imaging device based on a linear array sensor according to claim 1, characterized in that: The lens group adopts a double cemented achromatic lens or a triplet lens group.

4. The medium- and short-wave infrared spectrum imaging device based on a linear array sensor according to claim 1, characterized in that: The dispersion element (4) decomposes light of different wavelengths into different directions, which is achieved by using an Abbe prism, a blazed grating or a holographic grating.

5. The medium- and short-wave infrared spectrum imaging device based on a linear array sensor according to claim 1, characterized in that: The single-axis micro-scanning mirror (5) deflects the incident light beam to different angles along the same plane, and adopts a piezoelectrically driven galvanometer or a MEMS micro-galvanometer.

6. The medium- and short-wave infrared spectrum imaging device based on a linear array sensor according to claim 2, characterized in that: The pixel size of the linear array sensor is positively correlated with the focal length of the second lens (6) and the slit width of the slit (2), and the pixel size of the linear array sensor is negatively correlated with the focal length of the first lens (3).

7. The medium- and short-wave infrared spectrum imaging device based on a linear array sensor according to claim 6, characterized in that: After the light passes through the dispersion element (4), the angle of the zero-field-of-view central wavelength light relative to the z-axis is α, the angle between the second lens (6) and the linear array sensor (7) and the z-axis is σ, the zero-field-of-view central wavelength light passes through the second lens (6) and is imaged to the photosensitive pixel area at the center of the linear array sensor (7), and the angle between the plane of the uniaxial micro-scanning mirror (5) and the z-axis is β, which is positively correlated with α and σ.

8. A medium- and short-wave infrared spectral imaging method based on a linear array sensor, implemented using the medium- and short-wave infrared spectral imaging device based on a linear array sensor according to any one of claims 1 to 7, characterized in that: include: Step 1: obtaining the target light field to be measured, imaging it to the slit plane of the slit (2) through the objective lens (1), and calculating the slit plane coordinates based on the target light field to be measured and the magnification of the objective lens (1); Step 2: constraining the light field passing direction of the slit (2), performing a wavelength-dependent shift based on the light field passing direction through the dispersive element (4), and calculating the coordinates after dispersion based on the light field passing direction and the slit plane coordinates; Step 3: According to the imaging requirements, the relationship between the deflection angle of the single-axis micro-scanning mirror (5), the light field offset, and the focal length of the last lens of the lens group is adjusted. At any moment, the light field offset is positively correlated with the focal length of the last lens of the lens group and the tangent value of the deflection angle. Step 4: Calculate the plane coordinates of the linear array sensor (7) based on the magnification of the lens group imaging and the coordinates after dispersion; Step 5: Based on the arrangement direction of the linear array sensor (7) and the plane coordinates of the linear array sensor (7), the light intensity of the exposure window at any moment is integrated to obtain a function of the object plane coordinates of the target to be measured varying with time; Step 6: Calculate the micro-scanning period according to the single pixel size of the linear array sensor (7) and the size of the target to be measured; Step 7: In one micro-scanning cycle, N spectral channels corresponding to N wavelengths of the target to be measured are collected. Based on the relationship between the starting and ending deflection angles of the single-axis micro-scanning mirror (5), the relationship between the deflection angle and deflection period of the single-axis micro-scanning mirror (5), the exposure time of the linear array sensor (7) and the speed of the target to be measured is finally determined. The controller (8) controls the deflection angle of the single-axis micro-scanning mirror (5) and the timing synchronization of the linear array exposure collection of the linear array sensor (7) according to the relationship, thereby realizing medium and short-wave infrared spectral imaging.

9. The medium- and short-wave infrared spectral imaging method based on a linear array sensor according to claim 8, characterized in that: After collecting several micro-scanning cycles, the data is obtained to form a two-dimensional image data matrix. After image reconstruction, the original hyperspectral data is restored.

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