Collisional and Radiative Relaxation of Selected States in Neon I and Argon II

A treatment of transient monochromatic perturbations for the determination of fast relaxation times in gas spectra is presented. In a corresponding experiment, the radiative lifetimes of the $3s_2$ and $2p_4$ states of neon I were determined by direct perturbation of these levels with nanosecond bursts of intense 6328-Å monochromatic radiation ($\approx 50$ ${\mathrm{W}/\mathrm{c}\mathrm{m}}^2$). The effective inelastic-destruction cross sections of these states for collisions with neutral helium atoms were also evaluated. The respective radiative lifetimes and cross sections obtained are 54.0 ± 4 nsec, (1.49 ± 0.2) × ${10}^{-15\mathrm{}}$ ${\mathrm{cm}}^2$ and 15.9 ± 0.7 nsec, (0.72 ± 0.3) × ${10}^{-15\mathrm{}}$ ${\mathrm{cm}}^2$. A value of 9.4 ± 0.6 nsec was determined for the radiative lifetime of the argon II $4p{}_{}{}^2{}_{}{}^{}D_{\frac{5}{2}}^{}{}_{}{}^{}$ level from direct perturbation of this level with picosecond mode-locked pulses at 4880 Å. The relatively intense optical pulses were generated by acousto-optically diffracting a part of the circulating radiation from within He-Ne and argon ion-laser cavities. The method provides significant improvements in resolution for optically initiated direct lifetime measurements in gas spectra.