| Summary: | The advent of intense femtosecond lasers has created the exciting possibility of accessing
regimes of extreme high pressure using a relatively small laser system. This
stems from the lack of significant hydrodynamic expansion during the process of laser
deposition in a solid via skin-depth absorption, which leads to extremely high energy
densities in the irradiated sample. After the short-pulse laser energy has been absorbed,
the laser-heated material begins to be released which drives a shock wave into the sample.
However, unlike previous long-pulse laser driven shock waves, the shock wave driven by
a intense short-pulse laser rapidly decays as it propagates through the sample. Before
adopting such a shock wave as a new approach in the study of high density plasmas, its
unique characteristics must be understood.
A one-dimensional hydrodynamic code which is coupled to an electromagnetic wave
solver is used to elucidate the basic properties of shock waves generated by intense femtosecond
lasers. Using a unique experimental scheme, the electrical conductivity of silicon
in the dense, plasma state can also be studied. Calculations were performed in which a
shock wave was driven. into a silcion sample by a pump laser with a wavelength of 400
nm, pulse length of 120 fs (FWHM) and irradiances ranging from 10¹⁴ — 10¹⁵W/cm²,
while rear-side optical measurements were made by a 800 nm, 120 fs probe laser.
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