An imaging spectrometer (IS) can get continuous spectrum and acquire the image of the observed object, and it is used widely in the fields of remote sensing, industrial inspecting, etc. A compact imaging spectrometer system based on computed-tomography principle by using a special designed binary phase grating is described in this paper. The computed tomography imaging spectrometer (CTIS) records the projection data of different direction at the same time. The data cube of the object is acquired by reconstruction of the projection data. The instrument can record both spectral and spatial information of a dynamic scene. As only a 2-D binary phase grating is used as splitter and disperser, there are no moving parts, the system of CTIS becomes very compact. As the key component, the characteristics of grating are important to system stability and accuracy of reconstruction. In our work, the grating is designed and fabricated, and the whole system is set up. The configuration of the system is presented and the method of the spectral and spatial calibration is introduced. The mapping matrix of system is established by the results of calibration. The real object such as a colorful doll or a cluster of flower is imaged by the CTIS. The data cube of the real object is reconstructed by the EM algorithm. The size of the image of the object is about 200*200pixel, and the spectral range is from 410nm to 700nm. The spectral resolution is 10nm which depends on the step of spectral calibration. The accuracy of reconstruction and SNR is analyzed. The experimental results are presented, and the work is proven to be encouraging.
The multi-spectal or hyper-spectral imager provides three dimensional description for spatial and spectral intensity distribution of objective scenes and it can be a powerful tool for remote sensing in much application. There are several approaches to collection three dimensional data cube of image, and most of them require a scanning mechanism. Therefore those methods are difficult to record both spectral and spatial information of a dynamic scene such as a missile in flight, changing rapidly red tide, and so forth. Computed Tomography Imaging Spectrometer (CTIS) is a new branch application of computed tomography technology. The CTISs with different type configuration have been reported by a few of author. Two main types of CTISs are proposed. One is to use the two dimension gratings like Dammann gratings, the two 1-D gratings placed in orthogonal way, or three 1-D gratings separated by 60 degree. Due to its temporally and spatially non-scanning technique, this type is capable of capturing the flash events and can be used for instantaneous spectral imaging. The main problem of these CTISs is that the diffractive efficiencies are not only depended on the various wavelength but also on the different diffractive orders. That will effect the reconstruction algorithm and its results. These problems lead to reduce the signal to noise and dynamic range of spectral imaging system. The other is to take the approaches such as rotational spectro-tomography, or grating combined with a rotational direct-view prism. The advantages of these approaches are a)high throughput and b)easy to obtain more uniform data of different projection, but its disadvantage is obvious that the moving parts must be adopted. In our work, a principle and configuration of CTIS is indicated, and especially, a novel hybrid diffractive-refractive element is proposed, which is a combination of an array of optical prisms and one dimension holographic gratings. It can provide the uniformity of performance of projection data in different directions. As a result of high throughput and non-scanning parts, it can collect transient spectral imaging. Furthermore this grating is easily fabricated relatively. The capability enables it to be a prospect of applications in variety of application fields. This type of CTIS with the novel hybrid diffractive-refractive element is designed.
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