Journal of Applied Spectroscopy, Vol. 91, No. 1, March, 2024 (Russian Original Vol. 91, No. 1, January–February, 2024) REMOTE RECOGNITION OF MATERIALS USING LASER PHOTOTHERMAL RADIOMETRY P. I. Abramov, a E. V. Kuznetsov, a,b L. A. Skvortsov, a,b,* UDC 681.7.069.2; 543.52 and M. I. Skvortsova b 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 CO 2 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. Keywords: laser spectroscopy, photometric radiometry, laser radiometer, remote recognition of the material of an object. Introduction. The ability to recognize surrounding materials (plastic, glass, concrete) is important, both for people and for computer vision systems. Remote recognition of materials located at some distance is needed in the case where they are not distinguished visually, in particular, during sorting of a mixture of polymers during separation of polyethylene, polypropylene, polystyrene, polyvinyl chloride, and other plastics. Thus, remote recognition of materials can find application in the chemical industry, construction industry, and in automated lines for sorting of daily and industrial wastes [1]. The remote recognition of materials is no less important in searches for contamination and accumulation of waste on the earth's surface and in the oceans, and showing up as a result of environmental disasters [2]. Random dumps, fine debris, dangerous waste [3], and oil spills [4] can be detected and identified with the aid of remote recognition systems, and their hazard class can be identified, which can help eliminate causes of pollution, in cleaning surfaces, and in reworking waste. Remote recognition of materials can be both passive and active [5]. Passive range finding of materials is based on analysis of the spectral composition of the intrinsic (e.g., thermal) emission of an object or of sunlight reflected from it [6]. For active recognition additional external radiation sources are used. In most cases, these are lasers that, compared to the action of powerful lamp sources of light, provide a much larger detection range [7]. Much attention is paid to the problem of remote recognition of materials; there are two main approaches, one of which (passive) involves analysis of the temperature of an object and its dynamics with the aid of thermal vision methods [8–10], while the second (active) involves the creation and analysis of spectral portraits of light reflected from objects when they are irradiated with laser light [8, 11–14]. Each of these approaches has a limited application, so the development of new methods and technical means for remote recognition of different materials is of great current interest. For example, the creation of a spectral portrait of an object is limited by its surface, which prevents obtaining information on the volume properties of the material from which the object is made, especially if the surface of the material is protected from external effects by a paint and varnish layer. _____________________ * To whom correspondence should be addressed. a POLYUS Research Institute of M. F. Stelmakh Joint Stock Company, Moscow, Russia; b MIREA — Russian Technological University, Moscow, Russia; email: lskvortsov@gmail.com. Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 91, No. 1, pp. 134–140, January–February, 2024. Original article submitted June 3, 2023. 0021-9037/24/9101-0119 ©2024 Springer Science+Business Media, LLC 119 DOI 10.1007/s10812-024-01696-x