Abstract

The first observation is reported of a stimulated emission at 0.75–0.81 μm for the high-lying $F^{\prime }{\Sigma }_g^{+}—B^{\prime }{\Pi }_4$ transition and a new cascade radiation at 1.14–1.18 μm for the $F^{\prime }{\Sigma }_g^{+}\to 2^{\prime }{\Sigma }_4^{+}—2^{\prime }{\Sigma }_g^{+}$ transition in sodium vapor, two-photon resonantly pumped by an excimer laser–dye laser (rhodamine 6G) tunable over a 570–615-nm range. The lasing at 0.75–0.81 μm is recorded in Na₂ at 500 °C and buffer argon pressures of 0.5, 5, and 100 Torr, respectively. At higher pressures the operating temperature range at which laser action can occur is very limited. A comparison of the theoretically calculated datum-Derslands table, the Franck-Condon factors, and experimental results—two-pump photon energy and observed lasing wave-length—shows that a kinetic channel should be as follows: the sodium dimers at the ground state are pumped to the vibrational level v = 15 for the high-lying excited state $F^{\prime }{\Sigma }_g^{+}$ through the vibrational level v = 24 for the intermediate state $F^{\prime }{\Sigma }_4^{+}$ and then $F^{\prime }{\Sigma }_g^{+}\to B^{\prime }{\Pi }_4$ stimulated emission at 0.75–0.81 μm occurred. In the same two-photon pumping conditions for the $F^{\prime }{\Sigma }_g^{+}$ state the second emission band was observed at 1.14–1.18 μm, which is characterized by the vapor temperature condition, originating in our opinion, from the final process of the cascade transition $F^{\prime }{\Sigma }_g^{+}—2^{\prime }{\Sigma }_4^{+}—2^{\prime }{\Sigma }_g^{+}$.

© 1986 Optical Society of America