Remote Recognition of Materials Using Laser Photothermal Radiometry

The feasibility of recognizing opaque materials in remote objects using pulsed laser photothermal radiometry with prolonged pulsed exposure is examined. Theoretical calculations are given of the range of recognition of materials with laser activation of their surfaces. The computational results indicate a significant influence of thermal parameters on recognition range. It is shown experimentally that there is a reduction in the range by roughly an order of magnitude if the material of the search object has a large thermal inertia (metals) compared to a material with a low thermal inertia (polycarbonate, rubber), which provides a sufficient probability for their difference. Here a condition of strong surface absorption must hold at the laser wavelength. In the case of synthetic polymer products these conditions are met to the greatest extent by a CO₂ laser. The effect of wind load on the temperature of a laser spot on the object is one of the key conditions in this method. A way of reducing this effect to a minimum or even eliminating it nearly completely is proposed. Issues related to the feasibility of increasing the recognition range are discussed.