Reflectivity experiments with 60 femtosecond laser pulses

The reflectivity of solid silicon and aluminium targets has been measured at a fixed angle of incidence as a function of focused intensity for 60 fs pulses of 750 nm laser tight. It was found that, even for intensities in excess of 10(15) W cm(-2) there was no observable change in reflectivity from the low intensity value. This is taken to indicate that there is no formation of a high density gaseous plasma during the laser pulse. However, examination of the silicon target shows significant damage spots that indicate that melting and possibly gaseous plasma formation do occur after the pulse.