A pump-probe investigation of laser-droplet plasma dynamics

The temporal character of the plasma formed by the irradiation of micron-sized argon and krypton droplets with intense 100-ps laser pulses is investigated using a pump-probe scheme. The evolution of the droplet plasma is assessed by monitoring delay-dependent x-ray and extreme ultraviolet (EUV) emission, and by imaging frequency-doubled probe light scattered from the interaction region. Depending on the spectral region of interest, the type of emission, and the droplet characteristics, the effective plasma lifetime can extend from a few hundred picoseconds to as long as several nanoseconds. Knowledge of the droplet plasma lifetime is important in optimizing the efficiency of this laser plasma as an EUV or x-ray source. (C) 2001 American Institute of Physics.