LASER OPTOGALVANIC SPECTROSCOPY OF Fe-Ar HOLLOW CATHODE LAMP IN WAVELENGTH REGION 605-740nm

Abstract

Two photon optogalvanic trasitions in Ar glow discharge with Nd-YAG laser pumped tunable dye laser excitation in the frequency range $16515-13520 cm^{-1}$ has been studied using linearly and circularly polarization radiation. The metastable $4s[3/2]^{0}2$ level accounts for more than half of the 38 two photon resonant transitions whereas 10 of them originate in $4s[3/2]^{O}1$ four in $4s^{\prime}[1/2]^{O}0$ and only two in $4s^{\prime}[1/2]^{O}1$ level. The intensities of two photon optogalvanic transitions are very sensitive to changes in the incident laser power which is not the case with one photon transitions. Intensity ratios for circular to linear polarization for two photon transitions $6s^{\prime}[1/2]^{O}1 \leftarrow 4s[3/2]^{O}2 6s^{\prime}[1/2]^{O}0 \leftarrow 4s[3/2]^{O}2$ and $5d[1/2]^{O}1 \leftarrow 4s[3/2]^{O}2 5d[1/2]^{O}0 \leftarrow 4s[3/2]^{O}2$ are quite different from other two photon transitions. This has been explained as due to near one photon resonance of $4p^{\prime}[3/2]1$ level for the first pair and $4p^{\prime}[1/2]1$ for the second pair of transitions.