Abstract
Bicolour illumination by 1.54/0.77 μm 20 ns pulsed Er:glass laser beams leads to enhancement of the initial effective piezoelectric coefficients for Ag0.5Pb1.75GeS4 and Ag0.5Pb1.75GeS3Se crystals in a different way. The contribution of the photo-thermal effect did not exceed 4 %. The relaxation processes last up to 50 ms and are completely reversible with respect to piezoelectricity. The effect is reproducible even after more than 100 cycles of the photoinduced laser treatment. The use only of the mopnochromatic wavelengths 1.54 μm (0.77 μm) did not show sufficient enhancement of the effect, and the changes were commensurable with the background. The efficiency of the laser photoinduced treatment depends on the angle between the bicolour photoinducing beams, ratio of their intensities and their relaxation behaviour is a slightly different. However, at at 50 ms the photoinduced piezoelectric signal disappears for the both samples. It is crucial that laser polarizations of the photoinducing beams do not play important role.
Highlights
Bicolour illumination by 1.54/0.77 lm 20 ns pulsed Er:glass laser beams leads to enhancement of the initial effective piezoelectric coefficients for Ag0.5Pb1.75 GeS4 and Ag0.5Pb1.75GeS3Se crystals in a different way
A search of IR optically operated chalcogenide materials presents a promising direction of modern optoelectronics [1, 2]
In the Ref. [3] it was reported novel quaternary chalcogenide Ag0.5Pb1.75GeS4 and Ag0.5 Pb1.75GeSe4 crystals. These crystals possess non-centrosymmetric structure that indicates likely presence of effects described by third rank polar tensors (second harmonic generation (SHG), linear Pockels phenomenon, piezoelectricity etc.)
Summary
A search of IR optically operated chalcogenide materials presents a promising direction of modern optoelectronics [1, 2]. [3] it was reported novel quaternary chalcogenide Ag0.5Pb1.75GeS4 and Ag0.5 Pb1.75GeSe4 crystals These crystals possess non-centrosymmetric structure (space group I-43d) that indicates likely presence of effects described by third rank polar tensors (second harmonic generation (SHG), linear Pockels phenomenon, piezoelectricity etc.). Some roles here begin to play photothemal effect which is related to anharmonic phonons Such laser initiated dc-electric field may enhance the local charge density non-centrosymmetry defining efficiencies of the third rank polar tensors. As a consequence we have chosen a crystal which does not possesses substantial piezoelectric effect during excitation by one (monochromatic) laser beam wavelength (fundamental or doubled frequency) and which requires bicolour formation of additional internal dc-electric field aligning the particular crystalline dipoles. After interruption of the illumination the crystal is relaxed to its initial state These effects define the charge density acentricity. These effects are sensitive to the angles between the laser beams at different intensities
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