A Fabry-Perot Scanning Spectrometer for Standoff Chemical Detection
This development program built a computer controlled
infrared Fabry-Perot scanning spectrometer system for enhanced standoff
chemical detection. The target specifications for the system are
operation over the 8μm to 12μm spectral region with a free spectral
range of 400cm-1 and resolution of 8cm-1. A successfully developed
system will directly support the Army’s Chemical Imaging Program, which
has been identified as a far-term need in the DoD Joint Detection
Program Strategy as defined by the Joint Panel for Chemical and
Biological Defense.
The Fabry-Perot Scanning Spectrometer system is effectively an
imaging system (e.g. a camera, represented by the lens and FPA) with a
narrowband wavelength filter placed in front of it. The narrowband
filter is a Fabry-Perot Interferometer (FPI), which uses two
highly-reflecting, parallel plates to pass only light that is at the
resonance condition, λ = 2d (1st order). Each plate separation
generates a two-dimensional image at a wavelength with spectral extent
given by the FWHM of the transmission response (e.g. a hyperspectral
slice). The figure shows how the system can be used to detect chemical
agent clouds. Two images are collected at wavelengths on and off the
agent’s absorption band which are then subtracted to eliminate the
background and obtain the spatial location of the chemical agent cloud.
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