Accurate measurements of pressure-broadened linewidths in a transversely excited CO2discharge

A novel technique is used to measure He-dominated pressure-broadening coefficients in the 10μm band of CO
2
. Gain measurements in a pulsed transversely excited CO
2
discharge are made at line center using a CW CO
2
laser as a probe, and at a known offset frequency using a CW N
2
O laser. By measuring this gain ratio as a function of discharge pressure, we determine the linewidth with an accuracy of ∼ 2 percent. Linewidths are measured for nine different transitions in the 10 μm
P
-branch, and the
J
-dependence of the CO
2
-He pressure-broadening coefficient is determined and compared to theory. In addition, we examine the temperature dependence of the linewidth under conditions of constant number density and find that the linewidth increases as
T^{0.42 \pm 0.06}
. This agrees well with a recent theoretical prediction of T
^0.38
(R. T. Pack, "Pressure broadening of the dipole and Raman lines of CO
2
by He and Ar. Temperature dependence," J. Chem. Phys., vol. 70, pp. 3424-3433, 1979). To our knowledge, these experiments represent the first direct linewidth measurements in a transversely excited CO
2
discharge.