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UBC Theses and Dissertations

Shock waves generated by intense femtosecond lasers Ao, Tommy


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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