Gaseous saturable absorbers for the helios CO2laser system

Saturable absorbers are widely used to suppress parasitic oscillations in large-aperture, high-power CO
2
fusion-laser systems. We report experimental results on SF
6
-based gaseous saturable absorbers used for parasitic suppression in the eight-beam, 10 kJ Helios fusion-laser system. The gas mix effectively quenches self-lasing in the 9 and 10 μm branches of the CO
2
laser spectrum while simultaneously allowing high transmission of subnanosecond multiwavelength pulses for target-irradiation experiments. The gas isolator now in use consists of SF
6
and the additional fluorocarbons: 1, 1-difluoroethane (FC-152a); dichlorodifluoromethane (FC-12); chloropentafluoroethane (FC-115); 1,1-dichloro 2, 2-difluoroethylene (FC-1112a); chlorotrifluoroethylene (FC- 1113); and perfluorocyclobutane (FC-C318). The saturation of the mix was studied as a function of incident fluence, pressure, cell length, and incident wavelength. Experimental results are presented on the saturation properties of pure SF
6
and FC-152a and compared with the saturation behavior of CO
2
at 400°C.