A hyperspectral imaging device and method for detecting low-illumination targets

Abstract

The present application relates to a kind of for detecting low-illumination target hyperspectral imaging device, including front optical collimating system, acoustooptic modulation unit, light shield board, dispersion compensation unit, rear imaging group, photoelectric detection unit, computer control terminal.The present application also relates to a kind of for detecting low-illumination target hyperspectral imaging method, including the wavefront of measured target collimation, collimated target wavefront incidence acoustooptic tunable filter, focus formation with target information hyperspectral image, record and output different wavelength +1 level and-1 level diffraction light image, the process of obtaining higher intensity target image.The device of the present application uses equivalent balance method, so that incident light occurs twice acoustooptic interaction with ultrasonic wave in acoustooptic tunable filter, obtains wavelength same +1 level and-1 level two beams of light.The method of the present application can simultaneously utilize when target information is handled, energy utilization rate is improved by one time, and the two beams of light of output wavelength same can be simultaneously utilized.

Description

Technical Field

[0001] This invention belongs to the field of spectral imaging technology, specifically a hyperspectral imaging device and method for detecting low-light targets. Background Technology

[0002] The purpose of low-light image enhancement is to highlight useful features of an image while reducing or eliminating interfering information, making previously unclear or dimly lit images clearer or brighter. Low nighttime lighting, such as moonlight, firelight, and lamplight, creates complex ambient light, leading to a significant decrease in visible light and contrast, accompanied by substantial noise. Uneven lighting can also cause large differences in brightness between image areas. Many factors affect the brightness of low-light images, but for fields such as military, surveillance, and security, improving the brightness of low-light images is crucial.

[0003] In practical spectral imaging target detection, the reflected or radiated light from the target is transmitted through the atmosphere and then incident on the front mirror of the spectral imaging system. After passing through the beam splitter and the rear imaging unit, it is focused onto the detector target surface. The entire transmission process involves significant energy loss, including atmospheric scattering, reflection from the system's optical glass, and absorption, resulting in very limited energy at the detector target surface. The spectral resolution and energy transmittance of dispersive spectral systems are mutually constrained; increasingly higher spectral resolution is required, further limiting the target energy after passing through the slit. Although interferometric spectral imaging systems offer high throughput, the target energy at the detector target surface is still less than one-third of the initial target radiation.

[0004] Acousto-optic tunable filters are characterized by high throughput. When the incident light is polarized, the peak diffraction efficiency within the wavelength tuning range can exceed 80%. However, the diffraction efficiency at the front and back ends of the wavelength tuning range remains very low, almost less than 30%. In existing technologies, the incident light in the hyperspectral imaging system of the acousto-optic filter is polarized. That is, a polarization device with a polarization direction that can fully satisfy the acousto-optic interaction is added to the front end of the acousto-optic medium. In this way, the incident light wave, ultrasonic wave, and diffracted light wave in the acousto-optic medium will only undergo one acousto-optic interaction under the condition of momentum matching. The output of the acousto-optic medium is two beams of light: one is diffracted light, and the other is 0th order transmitted light.

[0005] Refractive index is a property of a medium for light. When a beam of light propagates within a crystal, the refractive index is a function of wavelength, and its value is the ratio of the speed of light in a vacuum to the speed of light in that medium. Due to the birefringence of acousto-optic media, when natural light is incident on the surface of an acousto-optic medium, two mutually orthogonal polarized beams are generated within the medium: the ordinary (o) beam and the extraordinary (e) beam. Traditional acousto-optic tunable filters can only satisfy the acousto-optic interaction between one of the incident beams (o or e) and the ultrasound. The other beam does not meet the momentum matching condition and therefore cannot interact with the ultrasound due to momentum mismatch. In other words, only one beam is filtered to form a narrowband output, and the detector only receives the diffracted light from one acousto-optic interaction; the remaining beam is blocked. In practical applications, this results in insufficient utilization of light energy and waste. Especially in low-light environments, traditional acousto-optic tunable filter hyperspectral imagers can cause blurred hyperspectral images, affecting target recognition results. In particular, when the diffraction efficiency of the tuned spectral band is low, the hyperspectral image becomes even more blurred and unclear. Summary of the Invention

[0006] To address the inherent technical problems of traditional acousto-optic tunable filter hyperspectral imagers and overcome the issue of insufficient energy utilization, this invention proposes a hyperspectral imaging device and method for detecting low-light targets in low-illuminance, low-light environments, based on acousto-optic modulation technology.

[0007] The technical solution adopted by this invention to solve its technical problem is:

[0008] A hyperspectral imaging device for detecting low-light targets includes a front optical collimation system, an acousto-optic modulation unit, a light shield, a dispersion compensation unit, a rear imaging group, a photoelectric detection unit, and a computer control terminal.

[0009] The acousto-optic modulation unit includes an acousto-optic tunable filter and an acousto-optic tunable filter radio frequency driver. The dispersion compensation unit includes a first dispersion prism compensation unit and a second dispersion prism compensation unit. The rear imaging group includes a first rear imaging mirror group and a second rear imaging mirror group. The photoelectric detection unit includes a first detector and a second detector.

[0010] The incident light passes through a pre-optical collimation system and sequentially enters the acousto-optic modulation unit, dispersion compensation unit, post-imaging group, and photoelectric detection unit. A computer control terminal controls the dispersion compensation unit and the acousto-optic modulation unit, and collects information from the photoelectric detection unit. The light-blocking plate is located between the acousto-optic modulation unit and the dispersion compensation unit.

[0011] The RF driver of the acousto-optic tunable filter is connected to the computer control terminal.

[0012] The acousto-optic tunable filter receives the outgoing light from the pre-optical collimation system, generates +1st order diffracted light and -1st order diffracted light, which enter the acousto-optic modulation unit; it generates 0th order transmitted light, which enters the light shield.

[0013] The first dispersion prism compensation unit ensures that all +1 order diffracted light within the wavelength tuning range is output in parallel and enters the first rear imaging mirror group. The first detector receives the target information formed by the first rear imaging mirror group.

[0014] The second dispersion prism compensation unit ensures that all -1st order diffracted light within the wavelength tuning range is output in parallel and enters the second rear imaging mirror group. The second detector receives the target information formed by the second rear imaging mirror group.

[0015] In the aforementioned hyperspectral imaging device for detecting low-light targets, the +1 order diffraction light generated by the acousto-optic tunable filter passes sequentially through the first dispersive prism compensation unit and the first rear imaging mirror group, and is received by the first detector, forming a narrowband hyperspectral image with target information on the first detector.

[0016] The -1st order diffraction light generated by the acousto-optic tunable filter passes sequentially through the second dispersion prism compensation unit and the second rear imaging mirror group, and is received by the second detector, forming a narrowband hyperspectral image with target information on the second detector.

[0017] The zero-order transmitted light generated by the acousto-optic tunable filter is blocked by the light shield.

[0018] The aforementioned hyperspectral imaging device for detecting low-light targets comprises a first dispersion prism compensation unit that compensates for the +1st order diffraction drift caused by the dispersion of the broadband light source through the acousto-optic medium, allowing the light to enter the first rear imaging mirror group without drift. A second dispersion prism compensation unit compensates for the -1st order diffraction drift caused by the dispersion of the broadband light source through the acousto-optic medium, allowing the light to enter the second rear imaging mirror group without drift.

[0019] The aforementioned hyperspectral imaging device for detecting low-light targets uses a computer control terminal to control the ultrasonic wave value emitted by the radio frequency drive of the acousto-optic tunable filter, so that the acousto-optic tunable filter outputs +1st order diffraction light and -1st order diffraction light of different wavelengths.

[0020] The aforementioned hyperspectral imaging device for detecting low-light targets includes a dispersion compensation unit comprising a rotating stage, a first dispersion prism compensation unit and a second dispersion prism compensation unit mounted on the rotating stage, and a computer control terminal controlling the rotation of the rotating stage to ensure that the +1st order diffraction light and -1st order diffraction light at each driving frequency are output in parallel, thereby achieving zero drift in the first detector and the second detector.

[0021] A hyperspectral imaging method for detecting low-light targets includes the following steps:

[0022] Step 1: Establish the optical system of the hyperspectral imaging device. Place the target under test within the field of view of the optical system. The front optical collimation system compresses and collimates the reflected light, radiated light, or transmitted light of the target under test.

[0023] Step 2: The compressed and collimated target light is incident perpendicularly onto the acousto-optic tunable filter. The computer control terminal controls the acousto-optic tunable filter to emit ultrasonic waves via radio frequency drive. The emitted ultrasonic waves interact with the target light in the acousto-optic medium, satisfying the equivalence condition, and generate +1st order diffracted light, -1st order diffracted light, and 0th order transmitted light.

[0024] Step 3: After the acousto-optic interaction, the +1st order diffracted light carrying the target's hyperspectral information passes through the first dispersive prism compensation unit and is focused onto the focal plane of the first detector by the first rear imaging mirror group. The -1st order diffracted light carrying the target's hyperspectral information passes through the second dispersive prism compensation unit and is focused onto the focal plane of the second detector by the second rear imaging mirror group.

[0025] Step 4: The first detector records the +1st order diffraction light containing the target hyperspectral information from Step 3 and stores it in the computer control terminal; the second detector records the -1st order diffraction light containing the target hyperspectral information from Step 5 and stores it in the computer control terminal.

[0026] Step 5: The computer control terminal changes the ultrasonic wave value emitted by the radio frequency drive of the acousto-optic tunable filter, and the acousto-optic tunable filter outputs +1 and -1 order diffraction light images of different wavelengths.

[0027] Step 6: The first detector and the second detector record the hyperspectral images of the +1 and -1 diffraction light of each different wavelength, respectively, and the computer control terminal acquires all narrowband wavelength hyperspectral images of the target wavefront.

[0028] Step 7: The computer control terminal performs data fusion processing on all narrowband wavelength hyperspectral images to obtain a target image with higher intensity.

[0029] In the hyperspectral imaging method described above for detecting low-light targets, the acute angle α of the first and second dispersion prism compensation units is determined by the performance of the acousto-optic tunable filter, and the calculation process is as follows:

[0030] The first step is to determine the diffraction angle.

[0031] For an acousto-optic tunable filter with a fixed incident angle, the diffraction angle can be determined based on the relationship between the incident angle and the o-ray and e-ray:

[0032]

[0033] In equation (1), θ1 is the incident angle of light, i.e., the angle between the incident light wave vector and the optical axis in the acousto-optic medium, θ2 is the diffraction angle, and n o n e σ represents the refractive index of the o-ray and e-ray, respectively, and σ is the optical rotation of the acousto-optic medium.

[0034] The second step is to calculate the separation angle.

[0035] Based on the diffraction angle θ1, determine the separation angle i1, which is the angle between the diffracted light and the normal to the acousto-optic medium. This is based on the following relationship:

[0036]

[0037] In equation (2), i0 is the incident angle of the diffracted light to the dispersion compensation prism, i1 is the angle between the diffracted light and the bottom edge of the dispersion compensation prism, i2 is the angle between the diffracted light and the hypotenuse of the dispersion compensation prism, i3 is the bottom angle of the dispersion compensation prism, and α is the fixed-focus acute angle of the dispersion compensation prism.

[0038] Therefore, we can obtain:

[0039] i1+α=i0 (3)

[0040] The third step is to determine the acute angle α of the dispersion-compensating prism.

[0041] According to the law of refraction

[0042] n0 sin i0=n1 sinα (4)

[0043] In equation (4), n0 is the air refractive index and n1 is the refractive index of the dispersion compensation prism.

[0044] Based on equations (2), (3), and (4), the relationship between the acute angle α of the dispersion-compensating prism and the diffracted light and the separation angle is as follows:

[0045] sin(i1+α)=n1 sinα (5)

[0046] α can be obtained from equation (5). Thus, the acute angle α of the dispersion-compensating prism can be obtained.

[0047] The hyperspectral imaging method for detecting low-light targets described above further includes step 7: using the o-light spectral image and the e-light spectral image to calculate the first two components S0 and S1 of the Stokes parameter.

[0048] The above-mentioned hyperspectral imaging method for detecting low-light targets further includes step 4, which involves calibrating each wavelength within the tuning range for precise tracking, and using a computer control terminal to control the first dispersion prism compensation unit and its precision rotating stage, so that the +1st order diffraction light and -1st order diffraction light at each driving frequency can be output in parallel, with no drift on the first detector and the second detector.

[0049] The beneficial effects of this invention are:

[0050] A hyperspectral imaging device for detecting low-light targets employs an equivalent balance method, which causes the incident light to undergo two simultaneous acousto-optic interactions with ultrasound within an acousto-optic tunable filter. Both acousto-optic interactions satisfy the momentum matching condition, thereby generating two beams of light with the same wavelength, a +1 order and a -1 order, at the output of the acousto-optic tunable filter.

[0051] A hyperspectral imaging method for detecting low-light targets can simultaneously satisfy the acousto-optic interaction of two orthogonally polarized beams within an acousto-optic medium using a single ultrasonic input, with the output wavelengths being the same.

[0052] A hyperspectral imaging method for detecting low-light targets can simultaneously utilize two beams of light with the same output wavelength during target information processing, theoretically doubling the energy utilization rate.

[0053] A hyperspectral imaging method for detecting low-light targets is proposed. Two beams of light with the same wavelength, +1 and -1, have orthogonal polarization directions. The target image can be polarized to obtain the first two components of Stokes, providing another technical approach for target recognition. Attached Figure Description

[0054] Figure 1 This is a schematic diagram of the hyperspectral imaging device of the present invention for detecting low-light targets;

[0055] Figure 2 This is a schematic diagram illustrating the principle that a single ultrasonic frequency can interact with both o-ray and e-ray simultaneously when the values ​​are in equilibrium.

[0056] Figure 3 It is the refractive index of the acousto-optic medium for o-rays and e-rays in the spectral range of 400nm to 800nm;

[0057] Figure 4 This is a schematic diagram of the optical path of a dispersion-compensating prism.

[0058] In the figure, 1. Front optical collimation system; 21. Acousto-optic tunable filter; 22. Acousto-optic tunable filter RF driver; 3. Light shield; 41. First dispersion prism compensation unit; 42. Second dispersion prism compensation unit; 51. First rear imaging mirror group; 52. Second rear imaging mirror group; 61. First detector; 62. Second detector; 7. Computer control terminal; 81. Indicates the change of incident angle with ultrasonic frequency when the incident light is e-ray; 82. Indicates the change of incident angle with ultrasonic frequency when the incident light is o-ray; 91. Refractive index of tellurium oxide crystal for e-ray in the 400nm~800nm ​​spectral range; 92. Refractive index of tellurium oxide crystal for o-ray in the 400nm~800nm ​​spectral range. Detailed Implementation

[0059] Example 1

[0060] like Figure 1 As shown, the hyperspectral imaging device for detecting low-light targets provided by the present invention consists of a front optical collimation system 1, an acousto-optic modulation unit, a light shield 3, a dispersion compensation unit, a rear imaging group, a photoelectric detection unit, and a computer control terminal 7.

[0061] The acousto-optic modulation unit is the core unit of this invention. It consists of an acousto-optic tunable filter 21 and an acousto-optic tunable filter radio frequency driver 22, wherein the acousto-optic tunable filter radio frequency driver 22 can emit radio frequency signals loaded on the acousto-optic tunable filter 21.

[0062] The dispersion compensation unit is composed of a first dispersion prism compensation unit 41 and a second dispersion prism compensation unit 42.

[0063] The rear imaging group consists of a first rear imaging lens group 51 and a second rear imaging lens group 51.

[0064] The photoelectric detection unit consists of a first detector 61 and a second detector 62.

[0065] The acousto-optic tunable filter 21 is disposed on the outgoing optical path of the front optical collimation system 1.

[0066] The incident light collimated by the pre-optical collimation system 1 and the ultrasonic waves emitted by the acousto-optic tunable filter RF driver 22 simultaneously interact with the e-light and o-light within the acousto-optic tunable filter 21, satisfying the momentum matching condition and undergoing equivalent equilibrium acousto-optic interaction, producing +1st order diffracted light, -1st order diffracted light, and 0th order transmitted light; different ultrasonic wave frequencies emitted by the acousto-optic tunable filter RF driver 22 correspond to different incident angles, thereby producing different equivalent equilibrium points.

[0067] The +1st order diffracted light passes sequentially through the first dispersion prism compensation unit 41 and the first rear imaging mirror group 51 before being received by the first detector 61 to form a narrowband hyperspectral image with target information.

[0068] The -1st order diffracted light passes sequentially through the second dispersion prism compensation unit 42 and the second rear imaging mirror group 52 before being received by the first detector 62 to form a narrowband hyperspectral image with target information.

[0069] The 0th order transmitted light is blocked by the shielding plate 3.

[0070] The first dispersion prism compensation unit 41 is specifically used to compensate for the drift of the +1st order diffracted light caused by the dispersion of the broadband light source through the acousto-optic medium, so that all +1st order diffracted light within the wavelength tuning range is output in parallel and can enter the first rear imaging mirror group 51 without drift. As a result, all the narrowband hyperspectral images received by the first detector 61 are imaged on the same position on the target surface, and there is no drift between the narrowband hyperspectral images.

[0071] The second dispersion prism compensation unit 42 is specifically used to compensate for the -1st order diffraction light drift caused by the dispersion of the broadband light source through the acousto-optic medium, so that all -1st order diffraction light within the wavelength tuning range is output in parallel and can enter the first rear imaging mirror group 52 without drift. As a result, all the narrowband hyperspectral images received by the first detector 62 are imaged at the same position on the target surface, and there is no drift between the narrowband hyperspectral images.

[0072] The computer control terminal 7 changes the ultrasonic value emitted by the radio frequency driver 22 of the acousto-optic tunable filter, and the acousto-optic tunable filter 21 outputs +1 and -1 order diffraction light of different wavelengths; the computer control terminal 7 controls the first dispersion prism compensation unit 41 and the first dispersion prism compensation unit 42 to rotate and compensate for the drift of the diffraction light, so that the hyperspectral image is not blurred.

[0073] The computer control terminal 7 fuses the narrowband hyperspectral images received by the first detector 61 and the second detector 62 to obtain a narrowband hyperspectral image with stronger target information.

[0074] A hyperspectral imaging method for detecting low-light targets includes the following steps:

[0075] Step 1: Set up the above optical system and place the target under test within the system's field of view. The reflected light, radiated light, or transmitted light of the target under test will be compressed and collimated after passing through the pre-optical collimation system.

[0076] Step 2: The compressed and collimated target light is incident perpendicularly onto the acousto-optic tunable filter. The computer control terminal controls the radio frequency drive of the acousto-optic tunable filter to emit ultrasonic waves, so that the emitted ultrasonic waves can just meet the equivalence balance condition with the target light in the acousto-optic medium and interact with it, thereby generating +1st order diffracted light, -1st order diffracted light and 0th order transmitted light.

[0077] Step 3: After the acousto-optic interaction, the +1st order diffracted light carrying the target's hyperspectral information passes through the first dispersion-compensating prism unit and is then focused onto the focal plane of the first detector by the first rear imaging lens group. After the acousto-optic interaction, the -1st order diffracted light carrying the target's hyperspectral information passes through the second dispersion-compensating prism unit and is then focused onto the focal plane of the second detector by the second rear imaging lens group.

[0078] Step 4: The first detector records the +1st order diffraction light carrying the target hyperspectral information as described in Step 3 and stores it on the computer control terminal. The second detector records the -1st order diffraction light carrying the target hyperspectral information as described in Step 5 and stores it on the computer control terminal.

[0079] Step 5: Change the ultrasonic wave value emitted by the radio frequency drive of the acousto-optic tunable filter through the computer control terminal, and the acousto-optic tunable filter will output +1 and -1 order diffraction light images of different wavelengths.

[0080] Step 6: The first and second detectors record the hyperspectral images of the +1 and -1 diffraction light at each different wavelength, respectively, and the computer control terminal acquires all narrowband wavelength hyperspectral images of the target wavefront.

[0081] Step 7: By processing all the narrowband wavelength hyperspectral images on the computer control terminal in Step 6 through data fusion, a target image with higher intensity is obtained.

[0082] The following is in conjunction with the appendix Figure 1 - Appendix Figure 4 The specific workings of the present invention will be described in detail below.

[0083] like Figure 1 As shown, the radiated or reflected light from the target is collimated by the pre-optical collimation system 1 and then incident vertically onto the acousto-optic tunable filter 21, where it simultaneously undergoes two acousto-optic interactions with the ultrasonic waves emitted from the radio frequency drive 22 of the acousto-optic tunable filter.

[0084] To ensure that two simultaneous acousto-optic interactions can occur within the acousto-optic tunable filter 21, both interactions must satisfy a momentum matching condition. Specifically, an ultrasonic frequency emitted from the radio frequency driver 22 of the acousto-optic tunable filter must simultaneously interact with both the o-ray and e-ray generated by the crystal birefringence, satisfying an equal-value equilibrium condition. For example... Figure 2As shown, at a specific incident angle, there exists an equal equilibrium point. For this equal equilibrium point, each ultrasonic frequency value within the tuning range can simultaneously interact with both o-light and e-light, producing +1st order diffracted light with the same intensity, wavelength, and orthogonal polarization direction as -1st order diffracted light.

[0085] Different incident angles correspond to different equilibrium points, different equilibrium points correspond to different ultrasonic frequencies, and different ultrasonic frequencies correspond to different diffracted light wavelengths.

[0086] By calibrating the relationship between each incident angle, ultrasonic frequency value, and wavelength value, the full-spectrum isopleth point can be obtained. In practical use, only the ultrasonic frequency value needs to be input to obtain the wavelength values ​​of the +1st and -1st order diffracted light.

[0087] Under the condition of equal equilibrium:

[0088] The 0th order transmitted light output from the acousto-optic tunable filter 21 is cut off by the shielding plate 3.

[0089] The +1st order diffracted light output from the acousto-optic tunable filter 21 passes sequentially through the first dispersion compensation prism 41 and the second rear imaging mirror group 51 before being received by the first detector 61.

[0090] The -1st order diffracted light output from the acousto-optic tunable filter 22 passes sequentially through the second dispersion compensation prism 42 and the second rear imaging mirror group 52 before being received by the second detector 62.

[0091] The acousto-optic birefringent medium within the acousto-optic tunable filter exhibits birefringence properties, possessing different refractive indices for different wavelengths of light, such as... Figure 3 As shown, the refractive index of tellurium oxide crystal for o-ray and e-ray in the 400-800nm ​​range is illustrated. At the same wavelength, the refractive indices of o-ray and e-ray are different. That is, when the acousto-optic tunable filter 21 is tuned across the entire broadband wavelength range, the refractive indices of the output +1st and -1st order diffracted lights differ due to wavelength changes. This results in the diffraction angles of the +1st and -1st order diffracted lights inside and outside the medium not being constant, but rather exhibiting a drift within a certain range. This drift is caused by chromatic aberration, causing the detector image to drift with wavelength changes. This diffraction drift caused by chromatic aberration degrades image quality, which is detrimental to subsequent image analysis. To compensate for this diffraction drift caused by chromatic aberration, a first dispersion compensation prism 41 and a second dispersion compensation prism 42 are inserted into the +1st and -1st order diffracted light paths, respectively, to ensure that the output light is parallel.

[0092] The acute angle value α of the first dispersion compensation prism 41 and the second dispersion compensation prism 42 is determined by the performance of the acousto-optic tunable filter 21, such as... Figure 4 As shown, the calculation method is as follows:

[0093] (1) The incident angle of the light in the acousto-optic tunable filter 21 is constant, and the diffraction angle can be calculated based on the relationship between the incident angle and the o-ray and e-ray:

[0094]

[0095] In equation (1), θ1 is the angle between the incident light wave vector and the optical axis in the acousto-optic medium (light incident angle), θ2 is the diffraction angle, and n o n e σ represents the refractive index of the o-ray and e-ray, respectively, and σ is the optical rotation of the acousto-optic medium.

[0096] (2) The angle (separation angle) i1 between the diffracted light and the normal of the acousto-optic medium can be calculated from the diffraction angle θ1. Figure 4 The following relationship exists:

[0097]

[0098] In equation (2), i0 is the incident angle of the diffracted light to the dispersion compensation prism, i1 is the angle between the diffracted light and the bottom edge of the dispersion compensation prism, i2 is the angle between the diffracted light and the hypotenuse of the dispersion compensation prism, i3 is the bottom angle of the dispersion compensation prism, and α is the fixed-focus acute angle of the dispersion compensation prism.

[0099] Therefore, we can obtain:

[0100] i1+α=i0 (3)

[0101] (3) According to the law of refraction:

[0102] n0 sin i0=n1 sinα (4)

[0103] n0 is the refractive index of air, and n1 is the refractive index of the dispersion-compensating prism.

[0104] Based on equations (2), (3) and (4), the relationship between the acute angle α of the dispersion compensation prism and the diffracted light and the separation angle can be obtained, and then α can be obtained.

[0105] sin(i1+α)=n1 sinα (5)

[0106] The shape of the dispersion compensation prism can then be obtained.

[0107] (4) The acute angle α of the dispersion compensation prism obtained by the above method is only for one specific angle and cannot satisfy every diffraction wavelength in the wide spectrum range. Therefore, the dispersion compensation prism is installed on a precision rotating stage to form the first dispersion prism compensation unit 41 and the first dispersion prism compensation unit 42. By calibrating each wavelength in the tuning range, precise tracking is implemented. The computer control terminal 7 controls the precision rotating stage of the first dispersion prism compensation unit 41 and the first dispersion prism compensation unit 42 so that the +1st order diffraction light and the -1st order diffraction light at each driving frequency can be output in parallel, with no drift on the first detector 61 and the second detector 62.

[0108] By fusing the o-ray and e-ray spectral images received by the first detector 61 and the second detector 62, a hyperspectral image of the target enhancement effect is obtained. If measurements are performed in a low-light environment, this invention can effectively improve the intensity of the target being measured, solving the problem of target information loss due to low illumination.

[0109] In addition, the o-light spectral image and e-light spectral image obtained by this invention are two images with orthogonal polarization. Therefore, it is also very convenient to calculate the first two components S0 and S1 of the Stokes parameter, which can obtain useful information about the target from the perspective of polarization target identification.

Claims

1. A hyperspectral imaging device for detecting low-light targets, characterized in that, It includes a front optical collimation system (1), an acousto-optic modulation unit, an optical shield (3), a dispersion compensation unit, a rear imaging group, a photoelectric detection unit, and a computer control terminal (7); The acousto-optic modulation unit includes an acousto-optic tunable filter (21) and an acousto-optic tunable filter radio frequency driver (22); The dispersion compensation unit includes a first dispersion prism compensation unit (41) and a second dispersion prism compensation unit (42); The rear imaging group includes a first rear imaging mirror group (51) and a second rear imaging mirror group (52); the photoelectric detection unit includes a first detector (61) and a second detector (62); The incident light passes through the pre-optical collimation system (1) and enters the acousto-optic modulation unit, dispersion compensation unit, post-imaging group, and photoelectric detection unit in sequence. The computer control terminal (7) controls the dispersion compensation unit and the acousto-optic modulation unit and collects information from the photoelectric detection unit. The light shield (3) is located between the acousto-optic modulation unit and the dispersion compensation unit. The acousto-optic tunable filter radio frequency driver (22) is connected to the computer control terminal (7); The acousto-optic tunable filter (21) receives the outgoing light from the front optical collimation system (1), generates +1st order diffraction light and -1st order diffraction light, which enter the acousto-optic modulation unit; it generates 0th order transmitted light, which enters the light shield (3). The first dispersion prism compensation unit (41) makes all +1 order diffraction light within the wavelength tuning range output in parallel and enter the first rear imaging mirror group (51). The first detector (61) receives the target information formed by the first rear imaging mirror group (51). The second dispersion prism compensation unit (42) makes all -1st order diffracted light within the wavelength tuning range output in parallel and enter the second rear imaging mirror group (52). The second detector (62) receives the target information formed by the second rear imaging mirror group (52).

2. The hyperspectral imaging device for detecting low-light targets according to claim 1, characterized in that, The +1 order diffraction light generated by the acousto-optic tunable filter (21) passes sequentially through the first dispersive prism compensation unit (41) and the first rear imaging mirror group (51), and is received by the first detector (61), forming a narrowband hyperspectral image with target information on the first detector (61). The -1st order diffraction light generated by the acousto-optic tunable filter (21) passes sequentially through the second dispersion prism compensation unit (42) and the second rear imaging mirror group (52), and is received by the second detector (62), forming a narrowband hyperspectral image with target information on the second detector (62). The zero-order transmitted light generated by the acousto-optic tunable filter (21) is blocked by the light shield (3).

3. The hyperspectral imaging device for detecting low-light targets according to claim 2, characterized in that, The first dispersion prism compensation unit (41) compensates for the +1st order diffraction light drift caused by the dispersion of the broadband light source through the acousto-optic medium, and enters the first rear imaging lens group (51) without drift; the second dispersion prism compensation unit (42) compensates for the -1st order diffraction light drift caused by the dispersion of the broadband light source through the acousto-optic medium, and enters the second rear imaging lens group (52) without drift.

4. The hyperspectral imaging device for detecting low-light targets according to claim 1, characterized in that, The computer control terminal (7) controls the ultrasonic wave value emitted by the radio frequency driver (22) of the acousto-optic tunable filter, so that the acousto-optic tunable filter (21) outputs +1 order diffraction light and -1 order diffraction light of different wavelengths.

5. The hyperspectral imaging device for detecting low-light targets according to claim 4, characterized in that, The dispersion compensation unit includes a rotating stage. The first dispersion prism compensation unit (41) and the second dispersion prism compensation unit (42) are both installed on the rotating stage. The computer control terminal (7) controls the rotating stage to rotate, so that the +1 order diffraction light and -1 order diffraction light at each driving frequency are output in parallel, so that the first detector (61) and the second detector (62) have no drift.

6. A hyperspectral imaging method for detecting low-light targets, using the hyperspectral imaging apparatus for detecting low-light targets according to any one of claims 1 to 5, characterized in that, Includes the following steps: Step 1: Establish the optical system of the hyperspectral imaging device. Place the target under test within the field of view of the optical system. The front optical collimation system (1) compresses and collimates the reflected light, radiated light or transmitted light of the target under test. Step 2: The collimated target light is perpendicularly incident on the acousto-optic tunable filter (21). The computer control terminal (7) controls the acousto-optic tunable filter (21) to emit ultrasonic waves via radio frequency. The emitted ultrasonic waves interact with the target light in the acousto-optic medium to meet the equal value balance condition and generate +1 order diffraction light, -1 order diffraction light and 0 order transmission light. Step 3: After the acousto-optic interaction, the +1 order diffraction light of the target hyperspectral information passes through the first dispersive prism compensation unit (41) and is focused by the first rear imaging mirror group (51) onto the focal plane of the first detector (61). The -1st order diffraction light carrying the target hyperspectral information passes through the second dispersion prism compensation unit (42) and is focused by the second rear imaging mirror group (52) onto the focal plane of the second detector (62); Step 4: The first detector (61) records the +1st order diffraction light with target hyperspectral information in step 3 and stores it in the computer control terminal (7); the second detector (62) records the -1st order diffraction light with target hyperspectral information in step 5 and stores it in the computer control terminal (7). Step 5: The computer control terminal (7) changes the ultrasonic wave value emitted by the radio frequency drive (22) of the acousto-optic tunable filter, and the acousto-optic tunable filter (21) outputs +1 and -1 order diffraction light images of different wavelengths. Step 6: The first detector (61) and the second detector (62) record the hyperspectral images of the +1 and -1 diffraction light of each different wavelength, respectively, and the computer control terminal (7) acquires all narrowband wavelength hyperspectral images of the target wavefront. Step 7: The computer control terminal (7) performs data fusion processing on all narrowband wavelength hyperspectral images to obtain a target image with higher intensity.

7. The hyperspectral imaging method for detecting low-light targets according to claim 6, characterized in that, The acute angle value α of the first dispersion prism compensation unit (41) and the second dispersion prism compensation unit (42) is determined by the performance of the acousto-optic tunable filter (21), and the calculation process is as follows: The first step is to determine the diffraction angle: The incident angle of the light in the acousto-optic tunable filter (21) is constant. The diffraction angle is obtained based on the relationship between the incident angle and the o-ray and e-ray: In formula (1), θ1 is an optical incidence angle, i.e. an included angle between an optical wave vector of the light incident on the acousto-optic medium and an optical axis, θ2 is a diffraction angle, n o , n e are refractive indexes of o light and e light respectively, and σ is an optical rotation rate of the acousto-optic medium. The second step is to calculate the separation angle: Based on the diffraction angle θ1, determine the separation angle i1, which is the angle between the diffracted light and the normal to the acousto-optic medium; according to the following relationship: In equation (2), i0 is the incident angle of the diffracted light to the dispersion compensation prism, i1 is the angle between the diffracted light and the bottom edge of the dispersion compensation prism, i2 is the angle between the diffracted light and the hypotenuse of the dispersion compensation prism, i3 is the bottom angle of the dispersion compensation prism, and α is the fixed-focus acute angle of the dispersion compensation prism. Therefore, we can obtain: i1+α=i0 (3) The third step is to determine the acute angle α of the dispersion-compensating prism: According to the law of refraction n0sinα = n1sinα (4) In equation (4), n0 is the air refractive index and n1 is the refractive index of the dispersion compensation prism; Based on equations (2), (3), and (4), the relationship between the acute angle α of the dispersion-compensating prism and the diffracted light and the separation angle is as follows: sin(i1+α)=n1sinα (5) α can be obtained from equation (5); thus, the acute angle α of the dispersion compensation prism can be obtained.

8. The hyperspectral imaging method for detecting low-light targets according to claim 6 or 7, characterized in that, Step 7 also includes: using the o-light spectral image and the e-light spectral image, calculating the first two components S0 and S1 of the Stokes parameter.

9. The hyperspectral imaging method for detecting low-light targets according to claim 8, characterized in that, Step 4 also includes calibrating each wavelength within the tuning range to perform precise tracking. The computer control terminal (7) controls the precision rotating stage of the first dispersion prism compensation unit (41) and the first dispersion prism compensation unit (42) so that the +1st order diffraction light and the -1st order diffraction light at each driving frequency can be output in parallel, with no drift on the first detector (61) and the second detector (62).

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