Identification of Chemical Compounds by the Reflected Spectra in the Range of 5.3–12.8 μm Using a Tunable Quantum Cascade Laser

We have considered the technique and experimental laboratory setup that allow the recording of the specular and diffuse reflectance spectra of the infrared radiation of substances in solid and liquid aggregate states on various surfaces. A quantum cascade laser, tunable in the wavelength range of 5.3–12.8 μm with a spectral resolution of 2 cm–1 and an average power of 15 mW, was used as a probing radiation source. The experimental setup made it possible to record the spectra of the diffusely reflected radiation of the substances. Methods for the identification of substances based on the scattered radiation spectra are proposed. It is shown that the use of the Kramers–Kronig integral transform increases the degree of selectivity of the spectra and, as a consequence, the reliability of identification.