Preablation electron and lattice dynamics on the silicon surface excited by a femtosecond laser pulse
- Russian Academy of Sciences, Lebedev Physical Institute (Russian Federation)
- Russian Academy of Sciences, General Physics Institute (Russian Federation)
The study of the time-resolved optical reflection from the silicon surface excited by single femtosecond laser pulses below and near the melting threshold reveals fast (less than 10 ps) Auger recombination of a photogenerated electron–hole plasma with simultaneous energy transfer to the lattice. The acoustic relaxation of the excited surface layer indicates (according to reported data) a characteristic depth of 150 nm of the introduction of the laser radiation energy, which is related to direct linear laser radiation absorption in the photoexcited material due to a decrease in the energy bandgap. The surface temperature, which is probed at a time delay of about 100 ps from the reflection thermomodulation of probe radiation and the integrated continuous thermal emission from the surface, increases with the laser fluence and, thus, favors a nonlinear increase in the fluorescence of sublimated silicon atoms. The surface temperature estimated near the picosecond melting threshold demonstrates a substantial (20%) overheating of the material with respect to the equilibrium melting temperature. Above the melting threshold, the delay of formation of the material melt decreases rapidly (from several tens of picoseconds to several fractions of a picosecond) when the laser fluence and, correspondingly, the surface temperature increase. In the times of acoustic relaxation of the absorbing layer and even later, the time modulation of the optical reflectivity of the material demonstrates acoustic reverberations with an increasing period, which are related to the formation of melt nuclei in the material.
- OSTI ID:
- 22472008
- Journal Information:
- Journal of Experimental and Theoretical Physics, Vol. 121, Issue 5; Other Information: Copyright (c) 2015 Pleiades Publishing, Inc.; Country of input: International Atomic Energy Agency (IAEA); ISSN 1063-7761
- Country of Publication:
- United States
- Language:
- English
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