Observation of harmonics in the visible and ultraviolet created in C$\mathrmO_2$-laser-produced plasmas

Experimental studies of inertially confined plasmas irradiated with CO2 laser intensities greater than 1015 W/cm2 at 10.6-μm wavelength reveal the generation of harmonic spectral components up to the 46th order (∼230 nm). These harmonics are of very short duration (<200 ps), have a polarization parallel to that of the incident 10.6-μm electric field, and exhibit a conversion efficiency approximately independent of the harmonic order up to a maximum order. The plasma-physics phenomena responsible for the high-harmonic emission are examined. The data and theory are consistent with the presence of self-focusing.