Laser gain characterization of near-atmospheric CO2:N2:He glows in a planar electrode geometry

Abstract

Temporally and spatially resolved gain measurements are reported for near-atmospheric CO2:N2:He glow discharges in a contoured planar electrode configuration. When suitably preionized by rows of electrically stressed dielectric interfaces, the entire interelectrode volume is filled with a uniform glow discharge for large ranges of capacitor energy, voltage, and gas pressure. The 10.59-μm gain reaches a peak value of 2.8% cm−1 in 2 μsec, and decays exponentially with a 20-μsec time constant in near-optimum laser mixtures of 60 Torr CO2, 180 Torr N2, and 60 Torr He. Peak gain is uniform over the transverse dimensions to within 5%. Mathematical expressions are developed which relate the small-signal gain to the P and R branch rotational quantum numbers in a linear fashion. This analysis shows that for optimized laser conditions the 00°1–10°0 population inversion is [inverted lazy s]1.8×1017 cm−3 with a rotational temperature of [inverted lazy s]400 °K. This corresponds to a maximum 10.6-μm optical storage density of [inverted lazy s]31 J/liter and represents [inverted lazy s]17% of the electrical energy input to the discharge.