Using two different empirical density profiles for the end region of a theta-pinch plasma, one with a maximum density on the axis (radiation-dispersing profile) the other with a pronounced axial minimum (radiation-trapping profile), the trajectory of the CO2 laser beam (10.6 μm) focused axially on such a plasma was studied numerically. This calculation is used to evaluate the optical influence of the plasma, since the maximum power density in the focal plane can be reduced by several orders of magnitude owing to the presence of the plasma. This influence can be substantial even for very subcritical electron densities (ne ≪ 1019 cm−3). In cases of large dispersion, the characteristics of a multifocal lens capable of producing perfect focusing are found, and it is shown that the solution is not unique. The radial distribution of the laser beam power density is also calculated and shows numerous irregularities and discontinuities due to the nonuniform beam dispersion.
© 1977 Optical Society of America
Original Manuscript: December 30, 1976
Published: July 1, 1977
Gilles Saint-Hilaire, "Numerical study of a CO2 laser beam focused on a theta-pinch plasma in the axial direction," Appl. Opt. 16, 1975-1981 (1977)