Strong photoacoustic pulses generated in TlGaSe2 layered crystals

Periodic deflections of infrared probe beam in TlGaSe2 crystal after its lateral excitation by laser pulse with photon energy near the band gap are observed. Such deflections arise from travelling of the acoustic pulse within sample which, in turn, is produced by optical pump pulse through photoacoustic effect. The photoacoustic pulse is generated within thin region near the crystal excited face, much shorter then the light penetration depth. In the case of volume excitation photoacoustic pulse is also generated in the region near back face as well. Tentative explanation of the generation mechanism is discussed