Abstract

Stimulated emission on the transitions, 5³S₁-4³P_J: 481.05, 472.22, 468.10 nm, 4³D-4³P_J:334.50, 330.27, 328.23 nm and 4¹D₂-4¹P₁ 636.24 nm is observed following pulsed laser excitation on 4¹S₀-4³P₁ resonance at 307.59 nm (peak intensity ~100 MW/cm²). To understand the mechanism we have performed the following experiments: excitation spectra of stimulated emission lines; side direction fluorescence (twenty-seven lines total, corresponding to triplet transitions from high-lying atomic states and two lines of zinc ion ZnII4p²P_J- 4s²S_1/2) and ion probe measurements; dependence of the stimulated emission intensity on Zn density and pump laser power; quenching of Zn4³P₁ by a small admixture of H₂ in Ar buffer gas; and energy transfer between 4¹D and 4⁴D states. The above experiments show the pump laser pulses efficiently photoionize the Zn vapor (1-photon resonance 3-photon ionization). Population of the upper levels result from two processes: (1) recombination of laser produced plasma and subsequent processes; (2) electron- impact collision. The energy defect of 4³P₁-5³S₁ 21 131 cm^-1 is approximately equal to an excess photoelectron energy of 21 1737 cm^-1 from 3- photon ionization. Depletion of the lower level 4³P₁ results from the collision quenching of this Zn atom with other atoms and especially with H₂ molecule: Zn(4³P₁) + H₂ - → ZnH(X²∑⁺) + H with a cross section ~20 Ų.

© 1991 Optical Society of America