Spatial heterodyne spectroscopy for long-wave infrared identifies an ozone line near 1133 cm-1 (about 8.8 μm) as a suitable target line, the Doppler shifts of which are used to retrieve stratosphere wind and ozone concentration. The basic principle of Spatial Heterodyne Spectroscopy (SHS) is elaborated. Theoretical analyses for the optical parameters of spatial heterodyne spectroscopy are deduced. The optical system is designed to work at 160 K and to maximize the field of view (FOV). The optical design and simulation is carried on to fulfill the requirement. The principle prototype was built and a frequency-stable laser was used to conduct the experiment. Result shows that the designed interferometer can meet the requirement of spectral resolution (0.1 cm-1 ) and that the spatial frequency of fringe pattern is consistent with the theoretical value at normal temperature and pressure.
Doppler asymmetric spatial heterodyne spectroscopy (DASH) is a new technology for measuring upper atmospheric winds by observing the Doppler shift of atmospheric emission lines from a satellite using a limb viewing geometry. The real-fringe DASH interferometer is a modification of conventional DASH interferometer; it keeps the advantages of the conventional one. Moreover, this interferometer will not need exit optics to image the superposed fringes onto the detector; it will be more compact and lightweight, making it suitable for space-based platforms. We describe the concept of the new interferometer and present the exact expression of spatial frequency and phase of the interferogram. We also describe design and simulation of a real-fringe DASH interferometer for observation of the O [1D] 630nm emission. The simulation results agree with the theory.
A novel dual-band static Fourier transform imaging spectrometer was designed, which was the spatio-temporally modulated imaging Fourier transform spectrometer based on Sagnac interferometer. The approach represented a simplification and mass reduction over the traditional approach. It could obtain two-dimensional spatial images and one dimensional spectral image in two bands simultaneously. The two bands was separated through a dichroic prism and imaging in two detectors. one band was the visible and near infrared band, with the spectral range 400nm-1000nm and spectral resolution 187.5 wave numbers; the other was the short wave infrared band, with the spectral range 1000nm- 2500nm and spectral resolution 150 wave numbers. To reduce the size of the Interferometer, a high aperture compression ratio telescope system was designed before. The optical aperture was compressed to 1/10, and the volume of interferometer was reduced to 1/1000. For the convenience of engineering implementation, the telescope was composed of two no-aberration object lens: fore-lens and Collimating lens. The two band imaging spectrometers shared the primary lens and the second lens of the fore-lens and use their own collimating lens, interferometers and Fourier transform lens. The collimating lens and the Fourier transform lens of each spectrometer could be designed to the same structural style and parameters. The both spectrometers had a focal length of 1000mm, F number of 5, FOV(field of view) of 1°. Moreover, both image qualities were close to the diffraction limit, the distortion was less than 2%. The advantage of the instrument was that dual band spectral image could be acquired at the same time and the interferometer was miniaturized extremely in the case of unchanged technical indicators.
Due to the manufacturing technique, some kinds of CCD, such as the back illuminated CCD, have the problem of spectral response nonuniformity. The near infrared light passing through the substrate and gates and is reflected back into the substrate for a second pass resulting in increased response. For the Fourier transform imaging spectrometer, it adds stripe pattern error to the interferogram and distorts the reconstructed spectrum. The nonuniform response is wavelength dependent due to changes in reflectivity of metal and the cavity formed by silicon and metal with transparent dielectric, so it adds difficulty to the correction of the error of the reconstructed spectrum.
In order to reduce the error of the reconstructed spectrum, in this paper, a calibration method and a correction method to correct the error caused by the CCD spectral response nonuniformity was developed, basing on analysis of the property of the CCD spectral response nonuniformity. Firstly, a calibrated monochromater was used to measure the CCD spectral response nonuniformity and the property and affect of the CCD spectral response nonuniformity were analyzed. Method to correct the error of the reconstructed spectrum caused by the stripe pattern error was developed. Secondly, to calibrate the CCD spectral response nonuniformity, the spectral response coefficient and the spatial response nonuniformity coefficient was measured and computed. Finally, we took data with a Fourier transform imaging spectrometer, and got the correction results of the reconstructed spectrums. The results showed that the distortion of recovered spectrum was evidently reduced and the effect of the calibration and correction method was proved.
Image Intensified CCD (ICCD) camera is widely used in the field of low-light-level image detection. The crucial part of
ICCD, coupling component, which realizes the image transmitting between the image intensifier and detector, affects the
final performance of the ICCD camera significantly. There are two means of coupling: relay lens and optical fiber taper
(OFT). OFT has the merits of small volume and relatively high coupling efficiency, therefore it is commonly used in the
portable devices or applications with less precision demands. However, relay lens turns out to be a better solution other
than OFT for the applications with no volume and weight restrictions, since it provides higher resolution, perfect image
plane uniformity and manufacture flexibility. In this paper, we discuss a methodology of high performance relay lens
design and based on the method a solid design is proposed. There are three major merits of the lens design. Firstly, the
lens has large object space numerical aperture and thus the coupling efficiency reaches 5% at the magnification of 0.25.
Secondly, the lens is telecentric in both sides of object space and image space, this feature guarantees uniform light
collection over the field of view and uniform light receiving on the detector plane. Finally, the design can be
conveniently optimized to meet the needs of different type of image intensifier. Moreover, the paper presents a prototype
ICCD camera and a series of imaging experiment as well. The experiment results prove the validity of the foregoing
analysis and optical design.
Spatial heterodyne spectrometers have been used in multiple scientific studies since their invention and early
development. Broadband spatial heterodyne spectrometers also have the advantages of large etendue, high spectral
resolving powers, and high data collection rates as traditional spatial heterodyne spectrometer. Basic theory, design and
performance parameters, breadboard experiment for a broadband, high-resolution spatial heterodyne spectrometer are
reported. The experimental spatial heterodyne spectrometer achieves a design resolution 0.39cm-1. Firstly, it is
demonstrated that broadband spatial heterodyne spectrometer have the advantages of wide spectral coverage and high
spectral resolving power simultaneously; secondly, the effects of optical defects on the system are discussed; thirdly,
Two dimension interference data procession also is mentioned.
The principle of a shooting positions measurement system with laser illumination is introduced. A narrow band-pass filter is
used to suppress background radiation except the laser band for detecting small, high-speed, dark objects. The maximal angle
of the entrance ray is limited in the case of using the narrow band-pass filter, so different designs of optical systems with a
wide field of view are discussed. The result of telecentric objective with 54° field of view and a relative aperture 1/2 is given.
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