Experimental and theoretical study of absorption of femtosecond laser pulses in interaction with solid copper targets

The reflectivity of near-infrared 150 fs laser pulses from copper targets has been measured in the intensity range of 6x10(11)-1.6x10(14) W cm(-2), showing a drop in reflectivity versus intensity as the target is heated. A simple semianalytical model of femtosecond electron heating and resultant optical absorption is developed to describe the time dependent and integral reflectivity covering the range from cold metal response to hot plasma response. The model is in good agreement with experimental ultrafast reflectivity measurements over the intensity range studied.