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MM: Metall- und Materialphysik

MM 44: Mechanical Properties II

MM 44.1: Vortrag

Freitag, 31. März 2006, 11:00–11:15, IFW A

Bolometric detection of strain solitons in Sapphire, Si and GaAs — •Anthony Kent and Nicola Stanton — School of Physics and Astronomy, University of Nottingham, Nottingham, NG7 2RD, UK.

We show that superconducting bolometers possess sufficient temporal resolution to detect strain soliton pulses propagating over mm distances in c-axis Sapphire and [001] Si and GaAs crystals. Using imaging techniques we show that the soliton pulses propagate as a narrow collimated beam. Strain pulses of up to 1% amplitude were generated by absorption of 100 fs light pulses from a Ti:Sapphire regenerative amplifier in a Cr-film deposited on the crystal surface. As these travel in the crystal, the combined effects of nonlinearity and dispersion results in the formation of a train of strain solitons. We use superconducting Aluminium bolometers to detect the pulses reaching the back surface of the crystal (opposite the Cr film). When the fluence of the laser pulse exceeds a certain threshold value, a sharp pulse arrives just ahead of the leading edge of the longitudinal phonon heat pulse. The speed of the sharp pulse is slightly faster than the normal speed of sound, as predicted for soliton propagation. The advantage of bolometers is that they can be used for high-resolution phonon imaging. Using this technique we find the solitons propagate as a collimated wavefront over cm distances in Sapphire and Si, but only mm in GaAs due to strong scattering.