CN111272298A

CN111272298A - Medium-and long-wave thermal infrared double-spectrum band non-refrigeration type imaging device and detection method thereof

Info

Publication number: CN111272298A
Application number: CN202010230128.2A
Authority: CN
Inventors: 朱晓晓; 朱嘉诚; 沈为民
Original assignee: Suzhou University
Current assignee: Suzhou University
Priority date: 2020-03-27
Filing date: 2020-03-27
Publication date: 2020-06-12

Abstract

The invention discloses a middle-and long-wave thermal infrared double-spectral band non-refrigeration type imaging device and a detection method thereof, which are mainly used for detecting high-temperature events, wherein the system comprises a first concave reflector, a convex reflector, a second concave reflector, an air slit, a concave spherical reflector, a convex spherical grating and a non-refrigeration detector; the convex spherical grating is a double blazed grating; the medium-long wave infrared light beam is parallelly incident on the first concave reflector, enters the air slit after being reflected by the first concave reflector, the convex reflector and the second concave reflector in sequence, then is converged to the convex spherical grating and is split after being reflected for the first time by the concave spherical reflector to obtain divergent light beams, the divergent light beams return to the concave spherical reflector and are reflected for the second time by the concave spherical reflector to be imaged on a focal plane, the uncooled detector is arranged on the focal plane, the spectrometer is compact in structure and low in cost, and target signals can be effectively extracted.

Description

Medium-and long-wave thermal infrared double-spectrum band non-refrigeration type imaging device and detection method thereof

Technical Field

The invention relates to the technical field of thermal infrared spectrum imaging, in particular to a medium-and long-wave thermal infrared double-spectral-band non-refrigeration type imaging device and a detection method thereof.

Background

The existing remote sensing systems for detecting high temperature events basically rely on sensors for measuring the surface temperature, the sensors are saturated at the temperature far lower than the highest combustion temperature of a fire, or the spatial resolution cannot meet the requirement of high temperature detection, and the sensors are mostly of refrigeration type and far less than non-refrigeration type systems in volume, weight and energy consumption.

The traditional dispersive imaging spectrometer mainly has the following structural forms: a plane grating C-T type, a convex grating Offner type, a concave grating Dyson type and the like. Compared with the C-T type, Dyson type and Offner type spectrometers of the planar grating, the spectrograph has the characteristics of small spectral surface bending and color distortion due to the concentric structure. However, in the Dyson type imaging spectrometer, the imaging quality is generally greatly influenced by temperature, and strict temperature control equipment is required to ensure that the imaging quality is stable. Offner type optical splitting devices are typical optical splitting devices based on convex gratings, developed from Offner relay systems. The Offner relay system was proposed by a.offner in 1973, which is a concentric total reflection type optical system, simple and compact in structure, capable of automatically eliminating distortion due to the characteristic of symmetry, and easy in optical processing. The Offner type light splitting device inherits the characteristics of small aberration, simple structure, compactness and the like of an Offner relay system, has the advantages of good imaging quality, large relative aperture, small spectral surface curvature and color distortion, easiness in adjustment and the like, and has low requirement on temperature control equipment.

Imaging spectrometers applied in the field of spatial optics generally have high requirements on the weight, volume, etc. of the instrument, and the excessive volume and weight can increase the manufacturing and emission costs of the instrument. Based on the characteristic that the double blazed gratings have high diffraction efficiency in a wide spectrum range, the medium-wavelength infrared and the long-wavelength infrared share the same diffraction order to replace the existing spectrometer system working in the double diffraction orders, so that the difficulty of eliminating the cascade spectrum is greatly reduced; these all put higher demands on the design of the mid-and-long-wave infrared imaging spectrometer, and require that it can overcome the serious stray radiation in the non-refrigeration environment and maintain good image quality in a larger spectral range.

In the thermal infrared imaging spectrometer reported in the existing literature, the large relative aperture, suitability for uncooled and medium-long wave infrared bands and working in the same diffraction order can not be met at the same time. See the literature "design of large-field-of-view small-F-number coaxial Offner structure thermal infrared spectrometer" ([ J ]. Infrared technology (7): 537) 541) and comparison of concentric long-wave infrared imaging spectrometers with different grating constants ([ J ]. Infrared and laser engineering, 2016,45(7): 148-. The convex grating Offner type imaging spectrometer in the document "Offner type athermal Medium wave Infrared imaging spectrometer design" ([ J ]. Infrared and laser engineering (11):95-101) only works in the Medium wave Infrared band. These hyperspectral imagers, which only work in the medium wave infrared or long wave infrared, cannot meet the increasingly wide application requirements of people. The Offner imaging spectrometer in the document 'middle/long wave infrared double diffraction order common path Offner imaging spectrometer' ([ J ] optical precision engineering, 2015(04): 965-.

In summary, the imaging spectrometer in the prior art is mainly of a refrigeration type, and has the technical problems that smooth and uniform grating diffraction efficiency cannot be realized in a wide spectral range, so that the imaging quality is poor, and the like. The refrigeration type imaging spectrometer reduces the radiation degree in a complete machine refrigeration or local refrigeration mode, so that the self heat radiation of the spectrometer is inhibited, but the cost is high and the quality is high due to the introduction of additional refrigeration equipment.

Disclosure of Invention

The invention aims to solve the technical problem of providing a middle-and long-wave thermal infrared double-spectrum-band non-refrigeration type imaging device and a detection method thereof, which are suitable for detecting high-temperature events, have compact structure, small spectral surface curvature and color distortion, large relative aperture, strong light collecting capacity of an imaging spectrometer, good imaging quality and non-refrigeration characteristic.

In order to solve the technical problem, the invention provides a middle-long wave thermal infrared double-spectral-band non-refrigeration type imaging device, which comprises a first concave reflector, a convex reflector, a second concave reflector, an air slit, a concave spherical reflector, a convex spherical grating and a non-refrigeration detector, wherein the first concave reflector is arranged on the upper surface of the first concave reflector;

the convex spherical grating is a double-blazed grating which can be blazed in a medium wave infrared band and a long wave infrared band respectively;

the concave spherical reflector and the convex spherical grating are coaxial, and the air slit and the uncooled detector deviate from the optical axis;

the medium-long wave infrared light beam is incident on the first concave reflector in parallel, enters an air slit after being reflected by the first concave reflector, the convex reflector and the second concave reflector in sequence, then is converged to the convex spherical grating and split after being reflected for the first time by the concave spherical reflector to obtain divergent light beams, the divergent light beams return to the concave spherical reflector and are reflected for the second time by the concave spherical reflector to be imaged on a focal plane, and the uncooled detector is arranged on the focal plane.

Preferably, the first concave mirror, the convex mirror, the second concave mirror, the concave spherical mirror and the convex spherical grating are made of the same material.

Preferably, the axial distance between the first and second concave mirrors is no more than 2 mm.

Preferably, the convex spherical grating is a linear groove engraved grating or a curved groove holographic grating.

Preferably, the F number of the imaging spectrometer system ranges from 1.5 to 10.

Preferably, the first concave reflecting mirror and the second concave reflecting mirror are quadratic aspherical surfaces.

Preferably, the ratio of the curvature radius of the concave spherical reflector to the curvature radius of the convex spherical grating is 1.8: 1-2.5: 1.

preferably, the axial distance between the air slit and the focal plane is not more than 5 mm.

Preferably, the imaging spectrometer is free of a central obscuration.

Preferably, the optical element further comprises a mechanical structure for fixing the optical element, wherein the optical element comprises a first concave mirror, a convex mirror, a second concave mirror, an air slit, a concave spherical mirror and a convex spherical grating, and the mechanical structure is made of the same material as the optical element.

Preferably, the surface of the mechanical structure is gold-plated.

Preferably, the light source further comprises a reflective light shield which is a Stavroudis type light shield and is positioned in the object space of the first concave reflecting mirror to suppress stray light outside the field of view.

The invention also discloses a detection method of the medium-wave and long-wave thermal infrared double-spectrum band non-refrigeration type imaging device, wherein a shutter is arranged at the air slit, and the detection method comprises the following steps:

s1, closing the shutter, and acquiring a first dark measurement signal X by the uncooled detector_ijt0。

S2, opening the shutter, and acquiring a bright measurement signal X by the uncooled detector_ijt1。

S3, closing the shutter again and obtaining a second dark measurement signal X_ijt2；

S4, measuring X by the first dark_ijt0And a second dark measurement X_ijt2Performing time linear interpolation to calculate brightness measurement X_ijt1Containing noise signals and measuring the noise signals from bright X_ijt1Subtracting to obtain a target signal, the target signal

The hyperspectral imager has the beneficial effects that:

1. the off-axis three-mirror telescope system is provided with the first concave reflector, the convex reflector and the second concave reflector, avoids introducing chromatic aberration through the off-axis three-mirror telescope system, and is good in imaging quality.

2. The invention adopts the design of medium-long wave infrared common optical path, realizes the structure simplification, and based on the double blazed grating, the medium-long wave infrared common same diffraction order replaces the existing wide spectrum system working in the double diffraction order, thereby greatly reducing the difficulty of eliminating the cascade spectrum.

3. The invention adopts a total reflection type structure, is less influenced by temperature, does not need to introduce other refrigeration equipment, and has low cost and small quality.

4. The invention adopts the light splitting device based on the Offner type concentric structure, has compact structure, small spectral surface bending and color distortion, greatly improves the relative aperture of the imaging spectrometer, has strong light collecting capacity of the imaging spectrometer, high signal-to-noise ratio, small noise of the shot spectral image and high contrast.

5. The air slit and the uncooled detector deviate from the optical axis, so that the imaging spectrometer is free of center blocking.

6. The imaging spectrometer provided by the invention has a wide spectrum range, relates to a wider application field, and can acquire more remote sensing information.

The detection method of the long-wave thermal infrared double-spectrum-band non-refrigeration type imaging device has the beneficial effects that: the self thermal radiation noise of the optical system is deducted, the effective detection of the target signal is realized, and the great problem of the application of the existing uncooled thermal infrared optical system is solved.

Drawings

FIG. 1 is a front view of the optical path of a spectrometer of the present invention;

FIG. 2 is a top view of the optical path at the 0.7 field of view of the spectrometer of the present invention;

FIG. 3 is a graph of the MTF curve for the center wavelength of the optical system of the present invention;

FIG. 4 is a light trace plot of the center wavelength of the optical system of the present invention;

FIG. 5 is a plot of energy concentration within a single pixel for the center wavelength of the optical system of the present invention;

FIG. 6 is a graph of the illumination of the detection surface of the uncooled detector with the shutter closed in the detection method of the present invention;

FIG. 7 is a diagram of the illuminance of the detection surface of the uncooled detector with the shutter open in the detection method of the present invention;

FIG. 8 is a diagram illustrating a final calculation result of a target signal according to the present invention.

The reference numbers in the figures illustrate: 1. parallel light rays; 2. a first concave mirror; 3. a convex reflector; 4. a second concave reflector; 5. an air slit; 6. a concave spherical reflector; 7. convex spherical grating; 8. a focal plane; 9. an optical axis.

Detailed Description

The present invention is further described below in conjunction with the following figures and specific examples so that those skilled in the art may better understand the present invention and practice it, but the examples are not intended to limit the present invention.

Referring to fig. 1, the invention discloses a middle-and long-wave thermal infrared double-spectrum non-refrigeration type imaging device, which comprises a first concave reflector 2, a convex reflector 3, a second concave reflector 4, an air slit 5, a concave spherical reflector 6, a convex spherical grating 7 and a non-refrigeration detector. The convex spherical grating 7 is a double blazed grating which can blaze respectively in the medium wave infrared band and the long wave infrared band. Therefore, the diffraction light of the double blazed gratings in the same order is utilized in the medium wave infrared band and the long wave infrared band, the diffraction efficiency is excellent and uniform in the medium wave infrared range and the long wave infrared range, and the defect of uneven distribution of the diffraction efficiency of the traditional gratings is overcome.

The invention also comprises a mechanical structural part for fixing the optical element, wherein the optical element comprises a first concave reflector, a convex reflector, a second concave reflector, an air slit, a concave spherical reflector and a convex spherical grating, and the mechanical structural part and the optical element are made of the same material, namely the same material of an optical structure and a mechanical structure, such as aluminum. Therefore, the heat-insulation material has the characteristics of light weight and easiness in processing, can avoid thermal deformation caused by thermal expansion difference of a mechanical element and an optical element, and meets the non-refrigeration requirement.

The concave spherical reflector 6 and the convex spherical grating 7 are coaxial, and the air slit 5 and the uncooled detector are deviated from the optical axis 9.

The medium-long wave infrared light beam is incident on the first concave reflector 2 in parallel, then enters the air slit 5 after being reflected by the first concave reflector 2, the convex reflector 3 and the second concave reflector 4 in sequence, then converges to the convex spherical grating 7 and splits light after being reflected for the first time by the concave spherical reflector 6 to obtain divergent light beams, the divergent light beams return to the concave spherical reflector 6 and are reflected for the second time by the concave spherical reflector 6 to be imaged on a focal plane 8, and the uncooled detector is arranged on the focal plane 8. The medium-wavelength infrared light beam incident on the first concave reflecting mirror is parallel light incident from infinity.

Wherein, the central wavelength imaging light beam is incident to the central position of the convex spherical grating, and the included angle between the plane where the incident light beam and the diffracted light beam of the convex spherical grating are positioned and the main section of the convex spherical grating is α, and 0 degree is more than α and less than 180 degrees.

The first concave reflector 2, the convex reflector 3, the second concave reflector 4, the concave spherical reflector 6 and the convex spherical grating 7 are made of the same material and can be made of aluminum.

In the present invention, the axial distance between the first concave mirror 2 and the second concave mirror 3 does not exceed 2 mm. The convex spherical grating 7 is a linear groove etching grating or a curved groove holographic grating. The F number range of the imaging spectrometer system is 1.5-10.

The first concave mirror 2 and the second concave mirror 3 are quadratic aspherical surfaces. The ratio of the curvature radius of the concave spherical reflector to the curvature radius of the convex spherical grating is 1.8: 1-2.5: 1.

the axial distance between the air slit 5 and the focal plane 8 does not exceed 5 mm. The imaging spectrometer has no central obscuration.

In one embodiment, the medium-and long-wave thermal infrared double-spectrum band non-refrigeration type imaging device has the following relevant indexes:

spectral range: 3.5-14 μm;

system F number: 2;

length of slit: 17.38 mm;

spectral resolution: 200 nm;

pixel size of the uncooled detector: 34 μm.times.34 μm.

See table 1 for specific optical parameters of each optical element in this example. In the table, "surface" indicates each optical surface code; "radius of curvature" means the size of the radius of each optical surface; "Material" means the material used for the optical element; "distance" means the lateral distance from the vertex of the optical surface to the vertex of the next optical surface; the groove density of the convex spherical grating 7 is 1.34 Lp/mm.

TABLE 1

Referring to fig. 2, a top view of the optical path at 0.7 field of view of the middle-and long-wave thermal infrared dual-band uncooled imaging apparatus provided in this embodiment is shown. The whole spectroscopic assembly, including the air slit and the focal plane, of the infrared spectrometer is symmetrical about the optical axis 9. The imaging magnification of the imaging spectrometer in the space dimension is 1:1, and the length of the space dimension of the focal plane is equal to the length of the air slit; the axial distance between the air slit and the focal plane is not more than 5mm, and the axial distance between the concave reflector and the concave reflector 4 is not more than 2 mm.

Referring to fig. 3, an MTF curve of the center wavelength of the optical system of this embodiment is shown. As can be seen from FIG. 3, the MTF value of the spectrometer at the detector Nyquist frequency of 14.7Lp/mm is greater than 0.56, the diffraction limit is approached, and the imaging quality is excellent.

Referring to FIG. 4, a trace point diagram of the central wavelength of the optical system of this embodiment is shown. The black circles in the figure represent the airy disk size, and it can be seen from the figure that the dot patterns at different fields of view of each wavelength of the structure can be almost concentrated within the airy disk, and are close to the diffraction limit.

Referring to fig. 5, the energy concentration curve in a single pixel of the center wavelength of the optical system shown in this embodiment can be seen to be greater than 72% in the single pixel of the uncooled detector.

The principle of the invention is as follows: the optical splitting device based on the Offner concentric structure is compact in structure, small in spectral surface bending and color distortion, and capable of greatly improving the relative aperture of the imaging spectrometer; a total reflection type telescopic system is adopted, chromatic aberration and secondary spectrum are avoided, and image quality is good; based on the double blazed gratings, the medium-wave infrared and the long-wave infrared share the same diffraction order to replace the existing wide spectrum system working in the double diffraction orders, so that the difficulty of eliminating the cascade spectrum is greatly reduced; the imaging spectrometer has stable image quality in a large temperature range by adopting a total reflection type system structure made of the same material; the optical and mechanical elements are preferably made of aluminum, so that the optical and mechanical element has the characteristics of light weight and easiness in processing, and can avoid thermal deformation caused by thermal expansion difference of a mechanical element and an optical element; the method is suitable for the field of hyperspectral remote sensing with medium-wave and long-wave infrared, large relative caliber and non-refrigeration requirements.

And plating gold on the surface of the mechanical structural part. The gold plating effect, the gold film has high reflectivity in the thermal infrared band, and the reflectivity stability of the gold film under the severe environment is good, so the emissivity is small, and the heat radiation generated by the structural component is small.

The invention also comprises a reflective light shield which is a Stavroudis type light shield and is positioned in the object space of the first concave reflecting mirror to inhibit stray light outside the field of view.

The invention also discloses a detection method of the middle-and long-wave thermal infrared double-spectral band non-refrigeration type imaging device, based on the non-refrigeration hyperspectral imager, a shutter is arranged at the air slit, and the detection method comprises the following steps:

s1, closing the shutter, and acquiring a first dark measurement signal by the uncooled detector

S2, opening the shutter, and acquiring bright measurement signals by the uncooled detector

S3, closing the shutter again and obtaining a second dark measurement signal

S4, measuring the first dark

And a second dark measurement

Performing time linear interpolation to calculate brightness measurement

Containing noise signals and measuring the noise signals from the light

Subtracting to obtain a target signal, the target signal

By adopting the detection method, the self thermal radiation noise of the system can be deducted, the effective detection of the target signal is realized, and the great problem of the application of the existing uncooled thermal infrared optical system is solved.

Referring to fig. 6, it is a diagram showing the illuminance of the detection surface of the uncooled detector when the shutter is closed in the detection method of the present invention. The target signal is 500K, and as can be seen from the figure, the 500K target signal is submerged in the self-heat radiation noise in the 300K environment.

Fig. 7 is a diagram of the illuminance of the detection surface of the uncooled detector when the shutter is opened in the detection method of the present invention, and it can be seen from the diagram that the background noise is severe.

Fig. 8 is a schematic diagram of the final calculation result of the target signal of the present invention, and it can be seen from the diagram that the target signal can be successfully obtained.

Compared with the prior art, the invention has the characteristics that:

1. the imaging spectrometer provided by the invention has a wide spectrum range, relates to a wider application field, and can acquire more remote sensing information.

2. The imaging spectrometer provided by the invention does not need to introduce other refrigeration equipment, and has small volume and low cost.

3. The optical system has high spectral resolution, few total optical elements, compact structure and light weight and is suitable for the field of space remote sensing.

4. The double blazed gratings are adopted, and the middle-wavelength infrared and the long-wavelength infrared share the light splitting mode of the same diffraction order, so that the difficulty of eliminating the cascade spectrum is greatly reduced.

5. And a total reflection structure is adopted, chromatic aberration and secondary spectrum are avoided, and imaging quality is good.

6. Optical and mechanical elements are made of aluminum, the used materials are optimized for the thermal expansion coefficient, the deformation of the optical surface of the system due to material difference is avoided, the image quality can be kept stable in a large temperature range, the non-refrigeration characteristic is realized, the system is light, and the production and development cost is reduced.

7. The relative aperture is large, the light collecting capacity of the imaging spectrometer is strong, the signal to noise ratio is high, the noise of the shot spectrum image is small, and the contrast is high.

The above-mentioned embodiments are merely preferred embodiments for fully illustrating the present invention, and the scope of the present invention is not limited thereto. The equivalent substitution or change made by the technical personnel in the technical field on the basis of the invention is all within the protection scope of the invention. The protection scope of the invention is subject to the claims.

Claims

1. A middle-and long-wave thermal infrared double-spectral-band non-refrigeration type imaging device is characterized by comprising a first concave reflector, a convex reflector, a second concave reflector, an air slit, a concave spherical reflector, a convex spherical grating and a non-refrigeration detector;

the medium-long wave infrared light beam is incident on the first concave reflector in parallel, then enters an air slit after being reflected by the first concave reflector, the convex reflector and the second concave reflector in sequence, then converges to the convex spherical grating and splits the light after being reflected by the concave spherical reflector for the first time to obtain divergent light beams, the divergent light beams return to the concave spherical reflector and are reflected by the concave spherical reflector for the second time to be imaged on a focal plane, and the uncooled detector is arranged on the focal plane.

2. The mid-and long-wavelength thermal infrared bispectral uncooled imaging apparatus according to claim 1, wherein the first concave mirror, the convex mirror, the second concave mirror, the concave spherical mirror and the convex spherical grating are of the same material.

3. The mid-to long-wavelength thermal infrared bispectral uncooled imaging apparatus according to claim 1, wherein the convex spherical grating is a straight-line groove-scribed grating or a curved-groove holographic grating.

4. The medium and long wave thermal infrared double band non-refrigeration type imaging device according to claim 1, wherein the F number of the imaging spectrometer system is 1.5-10.

5. The mid-and long-wavelength thermal infrared bispectral uncooled imaging apparatus according to claim 1, wherein the first concave mirror and the second concave mirror are quadratic aspheres.

6. The mid-to-long wavelength thermal infrared dual band non-refrigerated imaging apparatus of claim 1 wherein the imaging spectrometer is free of center obscuration.

7. The mid-and long-wavelength thermal infrared bispectral uncooled imaging apparatus according to claim 1, further comprising a mechanical structure that secures the optical elements, the optical elements comprising the first concave mirror, the convex mirror, the second concave mirror, the air slit, the concave spherical mirror, and the convex spherical grating, the mechanical structure being of the same material as the optical elements.

8. The mid-and long-wavelength thermal infrared dual band non-refrigerated imaging apparatus of claim 1 wherein the surface of the mechanical structure is gold plated.

9. The medium and long wavelength thermal infrared bispectral uncooled imaging apparatus of claim 1, further comprising a reflection type light shield, the reflection type light shield being a Stavroudis type light shield, the reflection type light shield being positioned in the object space of the first concave mirror to suppress stray light outside the field of view.

10. A detection method of a middle-and long-wave thermal infrared double-band non-refrigeration type imaging device, based on the non-refrigeration type imaging device as claimed in any one of claims 1 to 9, wherein a shutter is installed at the air slit, the detection method comprising the steps of: