Photodeflection Spectroscopy of Magnetoactive Superlattices Irradiated by Bessel–Gaussian Light Beams*

Abstract

535.13The mechanism for the formation of photodefl ection signals in magnetoactive superlattices irradiated by polarized modes of Bessel-Gaussian light beams is studied. The feasibility of controlling the spatial distribution of the temperature distribution in test samples with subsequent thermo-optical excitation of photodefl ection signals is established. A method is proposed for nondestructive monitoring of the geometrical parameters of magnetoactive superlattices by means of laser photodefl ection spectroscopy.Introduction. Laser photodefl ection spectroscopy is widely used in research on solids [1-3]. It is distinguished by its universality, high sensitivity, and relative ease of making measurements [4,5]. In this paper, a photodefl ection method is used to study short-period two-layer magnetoactive superlattices formed by cubic crystals of bismuth germanate (Bi 12 GeO 20 ) and bismuth silicate (Bi 12 SiO 20 ). Polarized TE-and TH-modes of Bessel-Gaussian light beams (BGLB) are used to excite thermoelastic oscillations in the samples [6,7].Laser photodefl ection spectroscopy is based on the conversion of the energy absorbed from a light beam in the volume of a sample into a thermal fi eld which produces a refractive index gradient in the sample and the surrounding medium. The defl ection from the horizontal of a low-power probe laser beam as it passes through the region with a nonuniform refractive index yields information on the optical, dissipative, thermal, and other characteristics of the sample.Determination of the BGLB Energy Loss Rate and of the Defl ection Angles. Let an amplitude modulated Bessel light beam, e.g., with TE-polarization, be incident normally on a magnetically active superlattice (Fig. 1) consisting of cubic crystals such as bismuth germanate or bismuth silicate. In the long-wavelength approximation [8,9] a two-layer superlattice can be represented as a single-layer crystal with its optical axis perpendicular to the boundary of the layers, since the beam is normally incident on the sample. A two-layer magnetoactive superlattice is characterized [10] by uniaxial complex dielectric ε ij and induced optical activity G ij tensors. The corresponding principal values of these effective tensors are given by

On the theory of nonlinear photoacoustic signal generation during gas-microphone detection

“…We emphasize that when deriving a system of equations (4)− (6) The fact was taken into account that the degree of blackness of the sample A(T ) characterizes the optical properties of its surface and is not a function of its thickness. This is due to the appearance of terms with T 0s (0) and 0s (0, ω) in the right parts of the system of equations (4)−( 6), and then in equations (7) and (8).…”

“…Various options of the linear theory of laser generation of sound waves by one-and two-layer samples in a photoacoustic (PA) chamber, when the signal is recorded by a microphone technique, are proposed in [1][2][3][4]. Numerous theoretical and experimental studies have shown that the parameters of the PA signal are saturated with information about the physical quantities of condensed media, including nanosystems (see, for example, [5][6][7][8][9][10][11]). The main mechanism of excitation of acoustic waves in this case is thermal, due to the periodic change in the heat flux coming from the sample into the gas layer, the thermal acoustic piston model [1].…”