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Proceedings Paper

Optical fundamentals of an adaptive substance-on-surface chemical recognizer
Author(s): Richard Fauconier; Mandoye Ndoye; Webert Montlouis
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Paper Abstract

The objective is to identify the chemical composition of (isotropic and homogeneous) thin liquid and gel films on various surfaces by their infrared reflectance spectra. A bistatic optical sensing concept is proposed here in which a multi-wavelength laser source and a detector are physically displaced from each other. With the aid of the concept apparatus proposed, key optical variables can be measured in real time. The variables in question (substance thickness, refractive index, etc.) are those whose un-observability causes many types of monostatic sensor (in use today) to give ambiguous identifications. Knowledge of the aforementioned key optical variables would allow an adaptive signal-processing algorithm to make unambiguous identifications of the unknown chemicals by their infrared spectra, despite their variable presentations. The proposed bistatic sensor system consists of an optical transmitter and an optical receiver. The whole system can be mounted on a stable platform. Both the optical transmitter subsystem and the optical receiver subsystem contain auxiliary sensors to determine their relative spatial positions and orientations. For each subsystem, these auxiliary sensors include an orientation sensor, and rotational sensors for absolute angular position. A profilometer-and-machine-vision subsystem is also included. An important aspect of determining the necessary optical variables is an aperture that limits the interrogatory beams to a coherent pair, rejecting those resulting from successive multiple reflections. A set of equations is developed to characterize the propagation of a coherent pair of frequency-modulated thin beams through the system. It is also shown that frequency modulation can produce easily measurable beat frequencies for determination of sample thicknesses on the order of microns to millimeters. Also shown is how the apparatus’s polarization features allow it to measure the refractive index of any isotropic, homogeneous dielectric surface on which the unknown substance can sit. Concave, convex and flat supporting surfaces and menisci are discussed.

Paper Details

Date Published:
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Proc. SPIE 10433, Electro-Optical and Infrared Systems: Technology and Applications XIV, ; doi: 10.1117/12.2278579
Show Author Affiliations
Richard Fauconier, Precisyx, LLC (United States)
Mandoye Ndoye, Tuskegee Univ. (United States)
Webert Montlouis, Johns Hopkins Univ. (United States)


Published in SPIE Proceedings Vol. 10433:
Electro-Optical and Infrared Systems: Technology and Applications XIV
David A. Huckridge; Reinhard Ebert; Helge Bürsing, Editor(s)

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