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An Imaging Spectrometer using an Acousto-Optic Tunable Filter
Norwegian University of Science and Technology, Faculty of Information Technology, Mathematics and Electrical Engineering, Department of Engineering Cybernetics.
2012 (English)MasteroppgaveStudent thesis
Abstract [en]

Spectroscopy is a powerful tool for analysis in a wide range of scientific and industrial fields. Spectroscopic measurements obtain information about the interaction between matter and radiated energy. This information may be utilized for detection and classification of objects and substances. There is a wealth of different methods and technologies developed for different applications, from space- and air-borne remote sensing to medical sample analysis. In this report we present a spectral imaging system consisting of a digital camera with an acousto-optical tunable filter (AOTF) as the spectral band selective element. An evaluation of the properties of the imager is presented, and we investigate the feasibility of real-time spectral imaging video based on this system. A comparison with other spectral imaging technologies is made. Custom application software for camera control and image acquisition is presented. A special optical layout that minimizes the optical aberrations produced by the diffraction process in the AOTF is also presented. The system produce a stack of monochrome images at different wavelength bands forming an "image cube" containing a combination of spatial an spectral information. The system uses the visible part of the electromagnetic spectrum to collect spectral information at every point in an image plane. Our results show that the camera have good light sensitivity and a high signal-to-noise ratio, but that the image throughput and spatial resolution is not optimal for a high image rate. The AOTF is a highly flexible device with random access to wavelength bands and selectable band-pass shape. But the many configurable parameters of the system also complicates usage. Many parameters need to be calibrated, and we present some methods on this. A major challenge in an spectral imaging system is to get enough light through to the sensor, and we find that there is high loss of light caused by the diffraction process in the filter. It will be shown that the system is not suitable for real-time spectral video imaging because of the low frame rate. Suggestions for improvements are given.

Place, publisher, year, edition, pages
Institutt for teknisk kybernetikk , 2012. , 74 p.
Keyword [no]
ntnudaim:7056, MTTK teknisk kybernetikk
URN: urn:nbn:no:ntnu:diva-18781Local ID: ntnudaim:7056OAI: diva2:566260
Available from: 2012-11-08 Created: 2012-11-08

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