Abstract

We present the first observation of triplet infrared absorption over a 1.13-1.17-μm range to the ${\text{Li}}_2{}^3{\text{E}}_u^{+}{-}^3{\text{E}}_g^{+}$ transition, an estimation of the absorption coefficient, which is ~1.5 m^-1 in view of the vapor column length of 0.6 m at 1080°C, an investigation into the possibility of achieving triplet laser oscillation. The triplet absorption spectrum of lithium dimer peaks near 1.154μm with a bandwidth of ~ 500 Å, but intense absorption on the shorter wavelength side to the peak is also obvious. According to Konowalow’s calculations for the electronic transition dipole moment functions, there should be a maximum dipole moment for the ${}^3{\Sigma }_g^{+}{\to }^3{\Sigma }_u^{+}$ transition at the Li internuclear separation of 6.5 a.u., which corresponds to the vibrational level v' = 2 of triplet state ${}^3{\Sigma }_g^{+}$. Our results are in excellent agreement with Konowalow’s prediction. The Li lower energy level belongs to a repulsive electronic state $\left(X^3{\Sigma }_u^{+}\right)$. The absorption transition that occurred might be from somewhere near the turning point of this repulsive curve. To observe an efficient triplet absorption, as described above, higher buffer gas pressure (200 Torr) and higher heat-pipe oven temperature (1100°C) are important. In the same experiment we have identified a new UV absorption band centered at 3900 Å.

© 1986 Optical Society of America