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Strong photoacoustic oscillations in layered TlGaSe2 semiconductor

Periodic deflections of infrared probe are observed in TlGaSe2 after lateral excitation with optical pulse. The effect is explained by generation of photoacoustic dilatational wave, which propagates within the crystal. Low pulse fluence (0.01 mJ/cm2) is needed to induce such wave when the layer plane is excited. Acoustic wave is generated within a μm‐distance near the excited face, much shorter then the light penetration depth, 1/α, where α is the absorption coefficient. In the temperature range 105–120 K, where ferroelectric‐paraelectric phase transition occur in TlGaSe2, discontinuous changes of the longitudinal sound velocity have been detected. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)