Continuous-Wave Laser Action on Vibrational-Rotational Transitions of CO2

Abstract

We have obtained cw laser action on a number of rotational transitions of the ${{\ensuremath{\Sigma}}_{u}}^{+}\ensuremath{-}{{\ensuremath{\Sigma}}_{g}}^{+}$ vibrational band of C${\mathrm{O}}_{2}$ around 10.4 and 9.4\ensuremath{\mu}. The laser wavelengths are identified as the $P$-branch rotational transitions from $P(12)$ to $P(38)$ for the 00\ifmmode^\circ\else\textdegree\fi{}1-10\ifmmode^\circ\else\textdegree\fi{}0 band and from $P(22)$ to $P(34)$ for the 00\ifmmode^\circ\else\textdegree\fi{}1-02\ifmmode^\circ\else\textdegree\fi{}0 band. Strongest laser transition occurs at 10.6324\ensuremath{\mu} (vacuum). A cw power output of about 1 mW has been measured. All these laser transitions can also be made to oscillate under pulsed discharge conditions with a small increase in the peak laser power output. No $R$-branch transitions have been seen to oscillate either under cw or pulsed discharge conditions. The wavelength measurements are in reasonable agreement with earlier measurement of the bands in absorption, but there are slight differences. These are ascribed to possible pressure-dependent frequency shift effects. A study has been made of the time dependence of the laser output under pulsed excitation, and some conclusions about possible excitation processes are given. Theoretical interpretation given earlier for laser action on vibrational-rotational transitions is discussed in a generalized form. The theory is applicable to both the linear polyatomic molecules and the diatomic molecules.