Abstract
A standoff method of detecting liquids on terrestrial and synthetic landscapes is presented. The interstitial liquid layers are identified through their unique molecular vibration modes in the 7.14–14.29-µm middle infrared (fingerprint) region of liberated thermal luminescence. Several seconds of 2.45-GHz beam exposure at 1.5 W cm-1 is sufficient for detecting polydimethyl siloxane lightly wetting the soil through its fundamental Si–CH3 and Si–O–Si stretching modes in the fingerprint region. A detection window of thermal opportunity opens as the surface attains maximum thermal gradient following irradiation by the microwave beam. The contaminant is revealed inside this window by means of a simple difference-spectrum measurement. Our goal is to reduce the time needed for optimum detection of the contaminant’s thermal spectrum to a subsecond exposure from a limited intensity beam.
© 1999 Optical Society of America
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