Estimation of electron density and temperature of semiconductor surfaces excited by ultra-short laser pulses

A simple technique, based on the interference principle, to obtain simultaneously the instantaneous electron density and temperature of ultra-short laser-excited semiconductor surface plasma is proposed and demonstrated. The interference of the incident laser and the surface plasmons forms nano-ripples on the surface. From the observed nano-ripple period, one can easily retrieve the density and temperature information. As a demonstration of the technique, the electron density and temperature are obtained for various band gap semiconductor materials based on the experimentally observed nano-ripples using 800 and 400 nm light in various ambient media and incident angles. The electron density estimated varied in the range of 2 $n_{\mathrm{c} }$ –10 $n_{\mathrm{c}}$ and the corresponding electron temperature in the range 10 $^{4}$ –10 $^{5}$ K, depending on the material band gap, the incident laser intensity, the ambient medium, the angle of incidence, and the laser wavelength. The information of the electron density and temperature is useful for choosing laser parameters (like fluence, wavelength, angle of incidence, ambient medium) and target materials (different band gap semiconductors) for obtaining a better size controllability of the nanostructure production. The information can also help one in obtaining essential plasma parameter inputs in the quest for understanding ultra-fast melting or understanding the pre-plasma conditions created by the pre-pulse of ultra-high intensity laser pulses.