Trapping and absorption of an axially directed CO2 laser beam by a theta-pinch plasma

A deuterium-filled θ pinch was axially irradiated in the first half-cycle by a CO2 laser to demonstrate the effects of beam trapping and absorption by a plasma. Peak electron densities were 5×1016 cm−3 and the nonirradiated axial temperature was about 1.3 eV. Detection of the laser radiation transmitted through the plasma showed that beam trapping occurred when the density profile had a minimum on axis, and the maximum laser-induced temperature increase of 2 eV occurred for irradiation at the time of maximum density, in agreement with inverse bremsstrahlung predictions. Furthermore, the plasma emission histories indicated that the column underwent a laser-induced elongation of up to twice its original length.