Optical breakdown at 10.6 μ wavelength near the boundary of a plasma layer in argon

An experimental study was made of the interaction of pulsed laser radiation at 10.6 μ wavelength with a plasma layer in argon. The plasma parameters were determined spectroscopically. In the unperturbed state its temperature was 1.4×10⁴ °K, its electron density 3×10¹⁷cm^–3 and its pressure 3 atm. It was established that under the influence of the laser radiation an observable plasma perturbation takes place at power densities exceeding 5×10⁵ W/cm². At power densities ~10⁷ W/cm² there appears a heated zone whose geometry is determined by the beam caustic and the absorption coefficient of the plasma. At higher power densities breakdown occurs in the cold gas near the plasma boundary. The breakdown pattern is similar to that observed in the interaction of radiation with a solid target.