Defocusing effects of a terawatt laser in an underdense plasma

The defocusing of a 1053 nm, 1-ps laser pulse focused in a cell filled with different noble gases has been studied in the 10 mbar to 1 bar pressure range. The focusing has been studied as a function of the gas pressure and of the incident laser power. The results clearly show that the beam tends to defocus as the incident power or the rare gas pressure are increased. The defocusing is interpreted as being due to the influence of the plasma refractive index: the radial profile of the electron distribution induces a minimum of the refractive index on the laser axis and consequently a refraction of the laser beam. The main and important consequence is that high laser intensities (1017 - 1018 W/cm2) and high electron densities (1019 - 1020 cm-3) cannot be achieved simultaneously with infrared laser radiation.© (1993) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.