Abstract
The experimental and theoretical studies of the reflectivity oscillations of the probe beam from the single-crystal of bismuth excited by fs-laser pulses are presented. The reflectivity was measured by the pump-probe technique with the accuracy 10−5 and with time-resolution of 35 fs that allowed observing a novel feature - a sharp drop of the reflectivity below the initial value. The reflectivity then increased above the initial value, and then oscillates with the frequency of Als phonon in Bi in agreement with earlier findings [1]. Our analysis established the direct link between reflectivity oscillations and atomic vibrations through the electron-phonon coupling rate that is proportional to the phonon's amplitude. The major force driving atomic motion in a laser-excited solid is thermal force proportional to the temperature gradients. It was demonstrated that strain-dependent polarisation [2–4] is a lesser parts of the external field effect on a solid than the thermal force in opaque medium. The proposed theory explains all experimentally observed features of the transient reflectivity.
© 2007 IEEE
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