Ultrafast ellipsometric pump-probe diagnostic of liquid metal surface with chirped continuum probe pulses.

Abstract

We describe our ellipsometric pump-probe experiment to study materials at extreme conditions. To demonstrate the performance, liquid bismuth surface is pumped by intense 25 fs pulse and subsequent evolution of non-equilibrium bismuth plasma is probed by chirped continuum pulse. The shift in the origin-time at continuum spectral component is precisely corrected by comparing chirp behavior estimated from induced phase modulation (IPM) in fused silica to one from liquid bismuth reflectivity measurement. From IPM measurements, it was found that the time resolution of a chirped pulse depends on group delay dispersion at corresponding continuum spectral components. Moreover, due to explicit relation between time and frequency of a chirped probe pulse, pump induced rapid changes are projected onto different probe wavelengths. Using these properties, we investigated polarization dependent reflection dynamics of non-equilibrium bismuth plasma with sub-100 fs temporal resolution and a broader wavelength response. These ultrafast measurements will be useful to study exotic phase transitions at extreme states of matter.