Ultrashort Laser Generated Warm Dense Matter - Transition from Solid to Plasma

Abstract

Materials under high intensity femtosecond laser irradiation yield extreme material conditions called warm dense matter (WDM) with thermal energy comparable with the Fermi energy and the ion-ion coupling parameter exceeding unity. The WDM state exists in a variety of processes ranging from laser micro machining to inertial confinement fusion experiments. The WDM exists as transient states including as nonthermal WDM in the first few hundred femtoseconds when the electron thermalization is important and as two temperature WDM with high electron temperature and relatively low ion temperature in the first few picoseconds. The WDM subsequently transits into the plasma state. We have used pump-probe techniques <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">1-5</sup> to study WDM produced by irradiating few ten's of nanometers thick free-standing metal foils with high intensity femtosecond laser pulses. In this talk I will focus on our studies using ultrafast optical Frequency Domain Interferometry to study the dissemble processes <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> and ultrafast electron diffraction technique to study the structural changes <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">1</sup> of the laser heated foils.