Design and construction of a hyper-spectral imager for 400~950 nm and design of an Offner hyper-spectral imager for 900~1700 nm

Abstract

Spectroscopy itself is a very useful tool for examining and inspecting the spectral properties or fingerprints of objects thus can be made use of for object identification and recognition. Hyper-spectral imagers form not only the spectral fingerprints but also the actual projections just as human eyes see(even in the bands other than visible range, false coloring navigates us to a totally different world of view). This combination of spectral and spatial information is peculiarly brilliant when we want to distinguish objects with the same appearance but of different material compositions. Therefore, its use is comprehensive in various areas such as forestry, geology, agriculture, medicine, security, manufacturing, colorimetry, oceanography, ecology and others. In this paper, I introduce spectrometer designs in VNIR(400~950 nm) and SWIR(900~1700 nm) bands. In both bands, the design starts from system specification of hyper-spectral imagers. The specification of a CCD camera influences FOV, FFOV, F/# and they are interrelated with the width and length of a slit, which is placed at the entrance of the imaging spectrometer. The VNIR band design uses a detector which pitch is 10 . It comprises a 10 slit, off-the-shelf lenses(front, collimation and focusing lens) that are easy to get and also a conventional plane reflective grating. Optimization of the system was conducted by following guiding equations: grating equation, spectral range, focal length and so on. The VNIR band experiment did not terminate at the design level but has actually been progressed to building and testing the instrument. Its spectral resolution was calculated to be 2.1 nm and images taken by the instrument are given as well. The SWIR band took the form of an Offner type intended to employ its inherent benefits. In this band, the design was primarily specified on the methodology and the procedure. It first starts as the form with the best performance in MTF then by increasing the off axis ...