Focusing limits of a terawatt laser in an underdense plasma

Abstract

The focusing of an intense 1053-nm, 1-ps laser pulse in an argon gas vapor has been studied. Experimental results are reported for different gas pressures and incident laser powers. In this paper we show that defocusing can occur and that it is sensitive both to the incident laser power and to the argon gas pressure in the experimental chamber. It is suggested that such a phenomenon is due to the refractive index of the plasma created by optical-field-induced ionization of the gas in the leading edge of the laser pulse. We show that it is not possible to obtain simultaneously a high focused intensity (>1017 W/cm2) and a high electron density (>1019 cm−3).