H- LASER PHOTODETACHMENT AT 1064, 532, AND 355 NM IN PLASMA

The fundamental frequency (1064 nm), the second harmonic (532 nm), and the third harmonic (355 nm) of a Nd yttrium aluminum garnet laser have been used to investigate the influence of the energies of photodetached electrons upon the determination of the H− density and the H− drift velocity in a hydrogen plasma, where the electron density and temperature range from 1010 cm−3 to 1011 cm−3 and from 0.5 to 3 eV, respectively, with the n−/ne ratio less than 2%. From the δIp−Vp characteristics, where δIp is the photodetachment current and Vp is the probe voltage, it is found that there is no dependence of the energies of photodetached electrons on the photon energies. The effective temperature of photodetached electrons Teff is close, within 40%, to that of background electrons. As a result the H− density and the H− drift velocity are not affected by photon energies.