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 ${\text{[inverted lazy s]1.8×10}}^{17}\hspace{0.17em}{\mathrm{cm}}^{\text{−3}}$ with a rotational temperature of $\text{[inverted lazy s]400\hspace{0.17em}°}\mathrm{K}$ . This corresponds to a maximum 10.6‐μm optical storage density of $\text{[inverted lazy s]31\hspace{0.17em}}\mathrm{J/liter}$ and represents $\text{[inverted lazy s]17\%}$ of the electrical energy input to the discharge.