Gain and coherence effects induced by strong cw-laser coupling in potassium–rare-gas mixtures

Abstract

We describe theoretical and experimental investigations of steady-state gain without population inversion that can occur on the ${\mathit{D}}_{1}$ transition of potassium, upon strong cw-laser excitation of the ${\mathit{D}}_{2}$ transition. A Raman-driven four-level model, in which a noninverted population in the 4${\mathrm{}}^{2}$${\mathit{P}}_{1/2}$ level is established via collisional transfer from the 4${\mathrm{}}^{2}$${\mathit{P}}_{3/2}$ level, is in good qualitative agreement with a variety of experimental results. These results include, among other studies, an examination of the impact of coherence dephasing on the realizable gain, as well as measurements of atomic energy-level populations for a case of line-center pumping that clearly displays gain. The measured relative populations for this case are n(4${\mathit{P}}_{1/2}$)/${\mathit{n}}_{\mathrm{total}}$=0.098\ifmmode\pm\else\textpm\fi{}0.034 and n(4${\mathit{P}}_{3/2}$)/${\mathit{n}}_{\mathrm{total}}$=0.19\ifmmode\pm\else\textpm\fi{}0.08, where ${\mathit{n}}_{\mathrm{total}}$ is the total population. These measurements indicate that the probed level 4${\mathit{P}}_{1/2}$ population is not inverted with respect to the ground state. \textcopyright{} 1996 The American Physical Society.