CN100427906C - Total Reflection Fourier Transform Imaging Spectrometer Using Fresnel Double Mirror - Google Patents

Abstract

A total reflection Fourier transform imaging spectrometer using Fresnel double-sided mirrors. The system consists of optical structure, focal plane detector and signal acquisition and processing system. The optical structure includes reflective front telescope, slit, reflective collimator, Fresnel double-sided reflector, reflective cylindrical mirror and other parts. The incident light is decomposed by the Fresnel double-sided reflector into two coherent beams with a certain intersection angle, which produces one-dimensional interference fringes on the surface of the focal plane detector; the other-dimensional grayscale image is focused and imaged by the cylindrical mirror. The two-dimensional focal plane detector can use any wavelength band from visible light to long-wave infrared (0.4-14μm). The signal acquisition and processing system can obtain the image and spectral distribution of each point on the slit. Push and broom along the direction perpendicular to the slit to obtain the target spectral image data cube. The device of the invention has wide spectral response band, large luminous flux, high signal-to-noise ratio and simple structure, and is especially suitable for the hyperspectral imaging field of aerospace remote sensing.

Description

Total Reflection Fourier Transform Imaging Spectrometer Using Fresnel Double Mirror

technical field

The invention relates to a total reflection Fourier transform imaging spectrometer, which belongs to the design technical category of the imaging spectrometer in the field of remote sensing technology; in particular, it relates to the optical system design of the space modulation interference type Fourier transform imaging spectrometer.

Background technique

Fourier Transform imaging spectrometer is also called imaging interferometer. Compared with the traditional dispersive imaging spectrometer, the Fourier transform imaging spectrometer has the characteristics of large input luminous flux and high spectral resolution, so it is especially suitable for hyperspectral imaging in the field of aerospace remote sensing. From the perspective of optical principles, Fourier transform imaging spectrometers can be divided into two categories: temporally modulated (Temporari1y Modulated) interferometric imaging spectrometers and spatially modulated (Spatially Modulated) interferometric imaging spectrometers. The former is represented by the Michelson Fourier transform imaging spectrometer that relies on moving mirror scanning; the typical representatives of the latter mainly include the Fourier transform imaging spectrometer using the Sagnac beam splitting structure or its variants, and the birefringent crystal beam splitting type. Polarization Interferometric Fourier Transform Imaging Spectrometer, etc. Documents [3], [4], [5] respectively introduced the spatially modulated Fourier transform imaging spectrometer using Sagnac beam-splitting interference components; Documents [6] and [7] respectively introduced the Spatial Modulation Fourier Transform Imaging Spectrometer. Note that the above-mentioned devices all use transflective beam splitters or transmissive beam splitters in their interference systems.

In terms of domestic patents, Chinese patents No.99115952[8] and No.99256131[9] respectively introduced the interference imaging spectrometer using the Sagnac beam splitting structure; No.01213109[10], No.01213108[11] and No. 99256129[12] respectively introduced the interference imaging spectrometer using polarization devices. The common feature of the above inventive devices is that they all contain transflective or transmissive optical components.

In terms of international patents, U.S. Patent US4523846[13] and US5777736[14] respectively introduced the interference imaging spectrometer using the Sagnac beam splitting structure, both of which include transflective or transmissive optical components; U.S. Patent US5260767[15] although A total reflection imaging spectrometer is introduced, but it uses a dispersion type spectroscopic structure, which does not belong to the type of Fourier transform imaging spectrometer.

To sum up, the Fourier transform imaging spectrometers so far have inevitably adopted transflective or transmissive beam splitting interference structures. In principle, there are many problems in the transflective or transmissive beam splitting interference structure. First, the spectral range is limited; the substrate material of the transflective beam splitter is selective to the light band; at the same time, the splitting ratio of the beam splitting film coated on the substrate surface is also related to the wavelength; as a result, it must be used in the imaging spectrometer Multiple beam-splitter plates with different spectral characteristics can complete the beam-splitting interference from visible light to infrared bands, thus increasing the complexity of the entire system structure. Second, the loss of light energy is large. The asymmetry of the transmission and reflection ratio of the beam splitter and the light loss existing on the surface and inside of the beam splitter will cause light energy loss. This problem is not conducive to hyperspectral imaging under low illumination . The third is the polarization problem. The beam splitting film causes the polarization of the two beams of light, resulting in a decrease in the degree of interference modulation, thereby reducing the signal-to-noise ratio of the acquired spectral image. Fourth, the nonlinear problem of optical path difference and fringe position. The transflective and transmissive interference structures adopt the principle of sub-amplitude interference, so a Fourier lens must be used in the interference optical path to make the optical path difference linear with the fringe position, which also increases the complexity of the system.

references

[1] Liao Ningfang, Interferometric Fourier Transform Imaging Spectral Bandwidth Image Processing System, National 863-13 Subject Project 2002AA135040 Research Report, 2004.

[2] Chu Jianjun, Research on Fourier Transform Imaging Spectroscopy Technology, Doctoral Dissertation of Beijing Institute of Technology, 2002.

[3] R.G.Sellar, J.B.Rafert, The effects of aberrations on spatially modulated Fourier transformspec-trometers.Opt.Engng., 1994, 33(16): 3087～3092.

[4] R.G.ellar, J.B.Rafert, Fourier transform imaging spectrometer with a single toroidal optic.Appl.Opt., 1995, 34(16): 2931～2933.

[5] J.B.Rafert, R.G.Sellar, J.H.Blatt, Monolithic Fourier transform imaging spectrometer.Appl.Opt., 1995, 34(31):7228～7230.

[6] P.D.Hammer, F.P.J.Valero, D.L.Peterson, An imaging interferometer for terrestrial remote sensing.Proc.SPIE, 1993, 1937: 244～255.

[7] W.H.Smith, P.D.Hammer, Digital array scanned interferometer: sensors and results. Appl. Opt., 1996, 35(16): 2902～2909.

[8] Xiang Libin, Zhao Baochang, Yang Jianfeng, Wang Wei, Yuan Xinjing, Gao Limin, Wang Zhonghou, Yuan Yan, high-sensitivity interference imaging spectroscopy device, Chinese patent: 99256131.

[9] Xiang Libin, Zhao Baochang, Yang Jianfeng, Yuan Xinjing, Gao Limin, Wang Zhonghou, Yuan Yan, Wang Wei, an interference imaging spectroscopy technology and its device, Chinese patent: 99115952.

[10] Zhang Chunmin, Xiang Libin, Zhao Baochang, Yang Jianfeng, ultra-small steady-state polarization interference imaging spectrometer, Chinese patent: 01213109.

[111 Zhang Chunmin, Steady-state large-field polarization interference imaging spectrometer, Chinese patent: 01213108.

[12] Xiang Libin, Yang Jianfeng, Ruan Ping, Zhang Chunmin, Wang Wei, Polarization Interferometric Imaging Spectrometer, Chinese Patent: 99256129.

[13]Integrated optics in an electrically scanned imaging Fourier transform spectrometer. Patent Number: US4523846.

[14]High Etendue Imaging Fourier Transform Spectrometer. Patent Number: US5777736.

[15]Compact all-reflective imaging spectrometer, Patent Number: US5260767

Contents of the invention

In order to overcome the problems existing in the transflective or transmissive beam-splitting interference structure of the existing Fourier transform imaging spectrometer, the present invention proposes a total reflection Fourier transform imaging spectrometer using Fresnel (Fresnel) double-sided mirrors as interference components . The Fresnel double-sided mirror is a classic wavefront interference device. Compared with other amplitude-divided interference devices, the Fresnel double-sided mirror has the characteristics of total reflection, so it can work in the wavelength band from visible light to thermal infrared scope. It is worth noting that the interference modulation degree of the Fresnel double-sided reflector has a certain relationship with the slit width, so in traditional non-imaging Fourier transform imaging spectrometers, such as Michelson interferometers, generally do not use phenanthrene The Niell double-sided mirror interference structure adopts the sub-amplitude interference structure. However, the imaging spectrometer involved in the present invention has higher requirements for spatial resolution, and a slit must be used to limit the instantaneous field of view (IFOV). Influenced by interference modulation.

The Fourier transform imaging spectrometer of the present invention has a total reflection light path structure. The whole device is composed of reflective front telescope, incident slit, reflective collimator, Fresnel double-sided mirror, reflective cylindrical mirror, focal plane detector and signal acquisition and processing system. The front telescope images the long-distance linear target on the incident slit, which is equivalent to imaging the long-distance one-dimensional linear target perpendicular to the push-broom direction on the incident slit of the interference system in the space remote sensing system. The collimating mirror projects the outgoing light from the incident slit to the surface of the Fresnel double-sided mirror in parallel; the surface of the Fresnel double-sided mirror is gold-plated to achieve wide-spectrum reflection characteristics from visible light to thermal infrared; after passing through the Fresnel double-sided mirror After reflection, the beam of light emitted from the slit is decomposed into two beams with a certain angle of intersection; the bus line of the cylindrical mirror and the intersection line of the Fresnel double-sided mirror are perpendicular to each other, so the one-dimensional grayscale of the slit can be The image is focused on the surface of the detector without hindering the two beams of light from the Fresnel double-sided mirror to produce another dimension of interference fringes on the surface of the detector. Using focal plane detectors with spectral response ranges of visible light and near-infrared (VIS&NIR, 0.4-1μm), short-wave infrared (SWIR, 1-5μm) and long-wave infrared (LWIR, 8-14μm), it is possible to realize from visible light to Interference fringe image signal acquisition in the infrared band. The signal acquisition and processing system is composed of a pre-processing circuit, a video image acquisition card, a microcomputer system, and input and output interfaces. The signal output by the focal plane detector is digitally collected and processed, and the Fourier transform from the air domain to the frequency domain is completed. Finally, Find the spectral distribution of the image at each point on the slit. A complete spectral image of a two-dimensional target image (ie, a spectral image data cube) can be generated by a push-broom process along a direction perpendicular to the slit.

The device of the invention has the characteristics of wide spectral range, large luminous flux, high image signal-to-noise ratio and simple optical structure, and is especially suitable for hyperspectral imaging systems in the field of aerospace remote sensing.

Description of drawings

Fig. 1 is a schematic diagram of the optical path structure of the total reflection Fourier transform imaging spectrometer of the present invention.

Fig. 2 is a schematic diagram of the generation principle of the Fresnel double-sided mirror interference pattern of the present invention.

Fig. 3 is a schematic diagram of the optical path principle of the Fresnel double-sided mirror, the cylindrical focusing mirror and the focal plane detector of the present invention.

Fig. 4 is the principle of the signal acquisition and processing system of the present invention.

Fig. 5 is a schematic diagram of the first embodiment.

Fig. 6 is a schematic diagram of the second embodiment.

The main structure in the figure is: 1-front telescope, 2-slit, 3-reflective collimator, 4-Fresnel double-sided mirror, 5-reflective cylindrical mirror, 6-focal plane detector, 7 -Signal acquisition and processing system.

Detailed ways

The Fourier transform imaging spectrometer described in the present invention is characterized in that a group of Fresnel double-sided mirrors are used as beam splitting interference components in the optical system, so as to realize the total reflection characteristic of the entire optical structure. The working principle of the present invention is described below with reference to FIG. 1 , FIG. 2 , FIG. 3 , FIG. 4 and FIG. 5 .

As shown in Fig. 1, device of the present invention is made of reflective front telescope 1, slit 2, reflective collimator mirror 3, Fresnel double-sided mirror 4, reflective cylindrical mirror 5, focal plane detector 6 and signal The collection and processing system consists of 7 components.

The front telescope 1 images the long-distance linear object on the incident slit 2, which is equivalent to imaging the long-distance ground linear target perpendicular to the push-broom direction on the incident slit of the interference system in the space remote sensing system superior. After the slit 2, the reflective collimator 3 projects the light emitted from the slit to the surface of the Fresnel double-sided mirror 4; after being reflected by the Fresnel double-sided mirror 4, a beam of light emitted from the slit 2 is decomposed It is two beams of light that form a certain angle with each other; the two beams of light are then focused by the reflective cylindrical mirror 5 and then projected onto the surface of the focal plane detector 6, and simultaneously form a one-dimensional interference fringe distribution and another One-dimensional grayscale image distribution. Wherein, the intersecting lines of the busbars of the reflective cylindrical mirror 5 and the Fresnel double-sided mirror 4 are perpendicular to each other; the direction of the interference fringes is parallel to the busbars of the reflective cylindrical mirror 5 . The focal plane detector 6 adopts a sensing device with a wide spectral response to realize signal acquisition of a wide spectral band. The signal acquisition and processing system 7 is composed of a pre-processing circuit, a video image acquisition card, a microcomputer system, and input and output interfaces, etc., and converts the video image signal of the focal plane detector into a digital image signal, and implements the Fourier transform from the air domain to the frequency domain. Transformation, the spectral distribution of the one-dimensional target image distributed along the direction of the slit can be obtained. The spectral distribution of another dimensional target image can be generated by a push-broom process, and the push-broom direction is perpendicular to the slit direction.

The interference principle of the Fresnel double-sided mirror 4 is shown in FIG. 2 . There is a small intersection angle θ between the two plane mirrors S ₁ and S ₂ in the Fresnel double-sided mirror, and the intersection line of the two mirrors is perpendicular to the drawing surface and passes through point O. Consider the ideal situation, assuming that the very thin incident slit is located at L in the figure, that is, the exit at L is an ideal spherical wave, and assuming that the two mirrors are ideal planes, then the light emitted by point L passes through the two mirrors After that, two separate virtual images L ₁ and L ₂ are formed, which are a pair of coherent virtual light sources. The two images are located on a circle with 0 as the center and 0L as the radius. The arc L ₁ L ₂ is equal to 2θ. According to the theory of wave optics, the light wave from point L passes through mirrors S ₁ and S ₂ to obtain two series of spherical waves, whose centers are L ₁ and L ₂ respectively. The two series of spherical waves partially overlap, and the interference of the two beams of spherical waves is produced in this overlapping portion. Interferograms can be collected on any plane BB placed within the interferometric region.

Since the device of the present invention adopts the principle of collimating mirror and sub-wavefront interference in the interference optical path, the relationship between the optical path difference ΔL generated on the focal plane and the interference fringe position ξ is ΔL=2ξsinθ, where 0 is Fresnel double The intersection angle of the mirror, so the optical path difference has a linear relationship with the position of the interference fringe.

The interference fringe width Δx produced by the device of the present invention on the surface of the focal plane detector is calculated by the following formula:

$\mathrm{<span\; class="notranslate">\; \&Delta;x</span>}<span\; class="notranslate">\; =</span>\frac{\mathrm{<span\; class="notranslate">\; \&lambda;</span>}}{\mathrm{<span\; class="notranslate">\; 2</span>}\mathrm{<span\; class="notranslate">\; sin</span>}\mathrm{<span\; class="notranslate">\; \&theta;</span>}}<span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 1</span>}<span\; class="notranslate">\; )</span>$

Where λ is the wavelength of light, and θ is the intersection angle of the Fresnel double-sided mirror. It can be known from formula (1) that the larger the intersection angle of the Fresnel double-sided mirror, the denser the interference fringes, and the higher the resolution requirement of the detector.

The theoretical spectral resolution limit of the present invention (that is, the minimum resolvable wavenumber difference δv) mainly depends on the geometric parameters of the optical system and the characteristics of the detector. The calculation formula is:

$\mathrm{<span\; class="notranslate">\; \&delta;v</span>}<span\; class="notranslate">\; =</span>\frac{\mathrm{<span\; class="notranslate">\; 1</span>}}{\mathrm{<span\; class="notranslate">\; 2</span>}{\mathrm{<span\; class="notranslate">\; \&xi;</span>}}_{\mathrm{<span\; class="notranslate">\; m</span>}}\mathrm{<span\; class="notranslate">\; sin</span>}\mathrm{<span\; class="notranslate">\; \&theta;</span>}}<span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 2</span>}<span\; class="notranslate">\; )</span>$

Where ξ _M is the maximum width of the detector, and 2ξ _M sinθ is the maximum optical path difference obtained by the interference system. It can be known from (2) that the larger the total width of the focal plane detector, the higher the spectral resolution.

According to (1) formula also can deduce the cut-off wavelength computing formula of detectable spectrum of the present invention:

λ _cut-off = 4dsinθ(3)

Where d is the CCD unit size.

It can be known from (3) that a detector with a high pixel density helps to expand the detectable wavelength range of the system.

The principle of the signal acquisition and processing system 7 of the present invention is shown in FIG. 4 . The composite video signal collected by the focal plane detector 6 includes the one-dimensional grayscale image information of the slit and the one-dimensional interference fringe information. Under the control of the CPU, after the input signal is processed by the pre-processing circuit and A/D conversion, stored in memory. The system processes the saved signal, completes the Fourier transform from the space domain to the frequency domain, obtains the spectral distribution of the image at each point on the slit and saves the result for further application. The CPU can also perform push-broom synchronous sampling on the entire system, so that the system can obtain a complete target spectral image data cube.

In the present invention, the spectral distribution B (v) is obtained by the Fourier transform of the interference fringe distribution I (ξ), that is:

B(v)=FT{I(ξ)}(4)

In the computer, one-dimensional discrete Fourier transform algorithm can be used to calculate (4) formula, the method is as follows:

Set in the direction perpendicular to the interference fringe, the data sequence of the intensity distribution of the interference fringe can be obtained:

I(ξ), ξ=0, 1, 2...N-1

Then the Fourier transform formula of I (ξ) is:

$\mathrm{<span\; class="notranslate">\; B</span>}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 0</span>}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; =</span>\frac{\mathrm{<span\; class="notranslate">\; 1</span>}}{\sqrt{\mathrm{<span\; class="notranslate">\; N</span>}}}\underset{\mathrm{<span\; class="notranslate">\; \&xi;</span>}<span\; class="notranslate">\; =</span>\mathrm{<span\; class="notranslate">\; 0</span>}}{\overset{\mathrm{<span\; class="notranslate">\; N</span>}<span\; class="notranslate">\; -</span>\mathrm{<span\; class="notranslate">\; 1</span>}}{\mathrm{<span\; class="notranslate">\; \&Sigma;</span>}}}\mathrm{<span\; class="notranslate">\; I</span>}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; \&xi;</span>}<span\; class="notranslate">\; )</span>$

$\mathrm{<span\; class="notranslate">\; B</span>}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; v</span>}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; =</span>\sqrt{\frac{\mathrm{<span\; class="notranslate">\; 2</span>}}{\mathrm{<span\; class="notranslate">\; N</span>}}}\underset{\mathrm{<span\; class="notranslate">\; no</span>}<span\; class="notranslate">\; =</span>\mathrm{<span\; class="notranslate">\; 0</span>}}{\overset{\mathrm{<span\; class="notranslate">\; N</span>}<span\; class="notranslate">\; -</span>\mathrm{<span\; class="notranslate">\; 1</span>}}{\mathrm{<span\; class="notranslate">\; \&Sigma;</span>}}}\mathrm{<span\; class="notranslate">\; I</span>}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; \&xi;</span>}<span\; class="notranslate">\; )</span>\mathrm{<span\; class="notranslate">\; cos</span>}\frac{<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 2</span>}\mathrm{<span\; class="notranslate">\; \&xi;</span>}<span\; class="notranslate">\; +</span>\mathrm{<span\; class="notranslate">\; 1</span>}<span\; class="notranslate">\; )</span>\mathrm{<span\; class="notranslate">\; v\&pi;</span>}}{\mathrm{<span\; class="notranslate">\; 2</span>}\mathrm{<span\; class="notranslate">\; N</span>}}<span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 5</span>}<span\; class="notranslate">\; )</span>$

v=1, 2, 3, . . . N-1

ξ=0, 1, 2, 3...N-1

At present, the above calculation can be completed by commercialized Fast Fourier Transform (FFT) software.

In the calculation result of the present invention, adopt following method to the wavelength position calibration of spectral data:

According to the optical path difference ΔL of the device of the present invention and the linear relationship ΔL=2ξsinθ of the position coordinates ξ of the interference fringes at the focal plane, it can be known that for any monochromatic light of a given wavelength, the spacing of the interference fringes produced at the focal plane is equal; therefore According to the space invariance of Fourier transform, after Fourier transform, the scale of the frequency domain space is also linear, that is, in the spectral data sequence of the calculation result, the wave value is proportional to the data sequence number. Assuming that in the calculation result, the spectral data sequence is:

x ₁ , x ₂ , x ₃ , ... x _n

Their corresponding wavenumber sequences are:

v ₁ , v ₂ , v ₃ , ... v _n

Then there is the following proportional relationship:

$\frac{{\mathrm{<span\; class="notranslate">\; v</span>}}_{\mathrm{<span\; class="notranslate">\; 1</span>}}<span\; class="notranslate">\; -</span>{\mathrm{<span\; class="notranslate">\; v</span>}}_{\mathrm{<span\; class="notranslate">\; 2</span>}}}{{\mathrm{<span\; class="notranslate">\; x</span>}}_{\mathrm{<span\; class="notranslate">\; 1</span>}}<span\; class="notranslate">\; -</span>{\mathrm{<span\; class="notranslate">\; x</span>}}_{\mathrm{<span\; class="notranslate">\; 2</span>}}}<span\; class="notranslate">\; =</span>\frac{{\mathrm{<span\; class="notranslate">\; v</span>}}_{\mathrm{<span\; class="notranslate">\; 3</span>}}<span\; class="notranslate">\; -</span>{\mathrm{<span\; class="notranslate">\; v</span>}}_{\mathrm{<span\; class="notranslate">\; 2</span>}}}{{\mathrm{<span\; class="notranslate">\; x</span>}}_{\mathrm{<span\; class="notranslate">\; 3</span>}}<span\; class="notranslate">\; -</span>{\mathrm{<span\; class="notranslate">\; x</span>}}_{\mathrm{<span\; class="notranslate">\; 2</span>}}}<span\; class="notranslate">\; =</span>\mathrm{<span\; class="notranslate">\; \&Lambda;</span>}\frac{{\mathrm{<span\; class="notranslate">\; v</span>}}_{\mathrm{<span\; class="notranslate">\; no</span>}}<span\; class="notranslate">\; -</span>{\mathrm{<span\; class="notranslate">\; v</span>}}_{\mathrm{<span\; class="notranslate">\; no</span>}<span\; class="notranslate">\; -</span>\mathrm{<span\; class="notranslate">\; 1</span>}}}{{\mathrm{<span\; class="notranslate">\; x</span>}}_{\mathrm{<span\; class="notranslate">\; no</span>}}<span\; class="notranslate">\; -</span>{\mathrm{<span\; class="notranslate">\; x</span>}}_{\mathrm{<span\; class="notranslate">\; no</span>}<span\; class="notranslate">\; -</span>\mathrm{<span\; class="notranslate">\; 1</span>}}}<span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 6</span>}<span\; class="notranslate">\; )</span>$

Therefore, in wavelength calibration, if the starting position of the wavenumber is known, it is only necessary to determine the spectral line position of one of the known wavelength rays, and then the wavenumber positions of other rays can be determined according to equation (6). If the wavenumber positions of the two spectral lines are determined, the wavenumber positions of the entire band can be calibrated according to formula (6) without the zero position of the wavenumber.

Implementation example:

In Embodiment 1 shown in FIG. 5 , the device of the present invention samples a short-distance linear light source (mercury lamp) target to calibrate the spectral line position of the system. Among them, the wavelengths of the two main spectral lines of the light source are 4358nm (22946cm ^-1 ) and 5461nm (18312cm ^-1 ) respectively; the front telescope 1 uses a single off-axis parabolic reflector with a focal length of 250mm, an effective aperture of φ60mm, and an off-axis distance of 30mm , has very good imaging quality in the paraxial region: the slit 2 is located near the focal point of the front telescope 1, so the image of the measured object is formed on the incident surface of the slit. The reflective collimator 3 also adopts an off-axis parabolic reflector identical to the front telescope 1, and its object focus coincides with the image plane position of the front telescope 1, that is, coincides with the image plane position of the slit 2; the slit The outgoing light of 2 is collimated and becomes a parallel beam and projected to the central area of Fresnel double-sided mirror 4 at a certain angle. The reflective cylindrical mirror 5 adopts an off-axis parabolic cylindrical mirror with a focal length of 40mm, an effective aperture of 50×50mm, and an off-axis distance of 30mm; the focal plane detector adopts a silicon CCD array (1/2 inch, 768×586 pixel), responds in the visible light and near-infrared bands (0.4-1.0μm). The image acquisition card is an ordinary video image acquisition card with a quantization precision of 8 bits, which is connected to the computer through the PCI bus. The signal processing system uses visual programming technology to complete functions such as image acquisition, noise processing, FFT transformation, and data storage.

Assuming that the slit width is 0.1mm, the corresponding instantaneous field of view is:

IFOV=0.1/250=0.004rad=4mrad.

Assuming that the intersection angle of the Fresnel double-sided mirror is 0.5°, and the effective width 2ξ _M of the interference beam received by the photosensitive surface of the CCD is 7.68mm, then the spectral (wavenumber) resolution limit limited by the optical system is:

At the same time, if the CCD unit size d is 9 μm, the detectable cut-off wavelength limited by the optical system is:

λ _cut-off ＝4dsinθ＝4×9000×sin0.5°≈314nm

In Embodiment 2 shown in FIG. 6 , the device of the present invention samples a one-dimensional black and white strip target to obtain a spectral image data cube. Among them, the measured target is illuminated by ordinary tungsten-halogen lamps, so it has continuous spectral signals in the visible light and near-infrared bands; the strip direction is perpendicular to the slit direction; the parameters of the optical system and focal plane detector are exactly the same as those in Figure 5. In addition, the device shown in Figure 6 can also sample infrared band targets. At this time, the strip target is changed to an isothermal strip infrared radiation target source, and the focal plane detector is changed to an infrared focal plane detector. For example, in the 1-5μm band, use a cooled PtSi-CCD array (512×512 pixels); white). Also assume that the intersection angle of the Fresnel double-sided mirror is 0.5°, and the single pixel size of the PtSi-CCD array is 30 μm, then the cut-off wavelength of the detectable spectrum of the system is:

λ _cut-off ＝4×30×sin0.5°≈1.04μm.

Claims (1)

1. a total reflection type Fourier transform imaging spectrometer that adopts Fresnel double-mirror comprises optical texture, focus planardetector (6) and signal acquiring processing system (7); It is characterized in that: in its optical texture, adopt one group of two-sided catoptron of Fresnel (4) to constitute optical interference structure; Fresnel double mirror (4) is by two plane mirror s with certain angle theta ₁, s ₂Form; Optical texture also comprises a cover reflective preposition telescope (1), slit (2), reflective collimating mirror (3), reflective cylindrical mirror (5); Slit (2) is positioned on the focal plane of preposition telescope (1), and the focus in object space of reflective collimating mirror (3) overlaps with the image planes position of slit (2); Fresnel double mirror (4) is positioned at reflective collimating mirror (3) afterwards; Be provided with reflective cylindrical mirror (5), focus planardetector (6) and signal acquiring processing system (7) behind the Fresnel double mirror (4); Reflective cylindrical mirror (5) bus intersection and the slit (2) with Fresnel double mirror (4) two mirrors respectively is vertical.

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