Photoacoustic Diagnostics of Inhomogeneous Gyrotropic Materials with Internal Stress Using Bessel Light Beams

Abstract

This paper considers the investigation of photoacoustic transformation in naturally-gyrotropic and magnetoactive crystals, with internal stress under sound excitation in different modes by Bessel light beams (BLB). In the range of high modulation frequencies (Ω > 1 MHz), the dependence of the photoacoustic response amplitude on the radial coordinate ρ exhibits resonant phenomenon, which can be used to increase the resolution of photoacoustic spectroscopy for media with internal stresses.The expressions for amplitudes of photoacoustic signals in strained crystalline samples were obtained under different boundary conditions, taking into account the dependence of the thermoelastic coupling coefficient on the initial strain in the sample. It was showed that a resonant increase in the amplitude signal is related to the dependence on the geometric parameters of the sample-piezoelectric transducer system, the values of Murnagan constants, the mode composition of the Bessel light beam, and its amplitude modulation frequency.Keywords: photoacoustic spectroscopy, Bessel light beams, magnetoactive gyrotropic materials W pracy przedstawiono wyniki badań transformacji fotoakustycznej poprzez dźwięk generowany laserowymi wiązka-mi Bessela o różnych modach w kryształach naturalnie żyrotropowych i magnetoaktywnych, z wewnętrznymi naprężeniami. Stwierdzono, że w zakresie modulacji o wysokiej częstotliwości (Ω > 1 MHz), zależność amplitudy odpowiedzi fotoakustycznej od radialnej współrzędnej wykazuje efekt rezonansowy. Efekt ten może być wykorzystany do podwyższenia rozdzielczości spektroskopii fotoakustycznej w ośrodkach z wewnętrznymi naprężeniami.Otrzymano wyrażenia na amplitudy sygnałów fotoakustycznych w próbkach krystalicznych z wewnętrznymi naprężeniami, przy różnych warunkach brzegowych. Brano przy tym pod uwagę zależność współczynnika sprzężenia termoplastycznego od wewnętrznych naprężeń w próbce. Wykazano, że rezonansowy wzrost amplitudy sygnału jest zależny od geometrycznych parametrów układu próbka -przetwornik piezoelektryczny, wartości stałych Murnagana, modów wiązki Bessela i częstotliwości modulacji.

Identification of sources, propagation and structure vibrations affecting men in means of transport based on the example of automotive vehicles

“…Another example can be the photoacoustic transformation. In [141] the investigation of photoacoustic transformation in naturally-gyrotropic and magnetoactive crystals under internal stress by sound excitation in different modes by Bessel light beams was described.…”

Photoacoustic transformation of Bessel light beams in magnetoactive superlattices

“…yields an expression for the potential difference based on the Duhamel-Neumann relations [26,27] and the known technique [12, 28,], under the assumption that the open-circuit voltage V TE on the piezoelectric transducer is proportional to the difference in the displacement amplitudes U P of its boundaries; the latter are believed to be free: (15) Here, the factor (16) describes the purely acoustic properties of the absorbing superlattice-piezoelectric transducer system and the factor (17) is responsible for the dissipative, dielectric, thermophysical, and thermoelastic properties of the sample under study, as well as the BLB polarization and energy parameters.…”

“…One efficient method is based on the laser excitation of sound in the media under study [10,11]. As was shown in [12][13][14][15], the use of different polarization modes of Bessel light beams (BLBs) as sound-exciting radiation [16] is promising for this method, because these beams have a number of unique properties (for example, they are not diffracted when they propagate in space [17][18][19]). An important specific feature of BLBs is the occurrence of a radial energy flux, which compensates for the change in the light-beam transversality when screened the beam central region [20].…”