Differential laser absorption and thermal emission for remote identification of opaque surface coatings

We experimentally and theoretically studied the phenomenon of thermal emission from nonvolatile liquid surface coatings following heating with a pulsed CO2 laser. The effects of thermal diffusion across the liquid-air and liquid-substrate interfaces as well as the full absorption spectrum of the liquid are addressed theoretically. The differential temporal and intensity characteristics of the thermal emission signal from the heated surface coating, resulting from the differential heat deposition profile for on- and off-resonance excitation, are shown to be useful for the purposes of identifying different surface contaminants. The application of this technique to standoff thermal imaging of contaminated surfaces is discussed.