Observation of an electronic plasma in picosecond laser annealing of silicon

Abstract

Changes of the optical reflectivity and transmission of Si during and after annealing with a 25-ps laser pulse at 532 nm are measured with 10-ps resolution. The reflectivity exhibits an initial minimum—which is attributed to the electron-hold plasma—followed by a jump to a value equal to the reflectivity of liquid Si. Below a well-defined threshold of (0.21±0.01) J/cm2 only the plasma effect is observed.