Thermal Laser Excitation by Mixing in a Highly Convective Flow

Abstract

Population inversion has been generated through the mixing of CO2 or N2O into a supersonic N2 flow, vibrationally excited by thermal means. Gain at 10.6μ, corresponding to the 001 → 100 transition in CO2, equal to 0.8%/cm has been measured in this medium. Using an optical cavity, oriented transverse to the flow, up to 60-W cw laser power at 10.6μ from CO2 was extracted from a 5-cm length by 1.2-cm2 cross-section active volume. When N2O was substituted for CO2 in the mixing region, cw laser emission was demonstrated at 10.8μ, corresponding to the 001 → 100 transition in N2O.

Thermal blooming in gases

“…In the rotational case, the value is 0.0027 J/cm s . It is to be noted that the power densities required for vibrational saturation are within the realm of current fast-flow devices [11], while that required for rotational saturation can be obtained in Q-switched operation [12].…”

Gasdynamic problems for optically inverse media

“…The experimental check [6][7][8] has proved the feasibility of rapid supersonic flow mixing of the working mixture components. However, these mixing schemes and parameters obtained are far from being optimum, hence, the efficiency of these laser systems has appeared to be relatively low.…”

“…However, these mixing schemes and parameters obtained are far from being optimum, hence, the efficiency of these laser systems has appeared to be relatively low. In [8] the value of small-signal optical gain per unit length was only about g ~ 0.8 m-1, and the output power in the active medium, 6 cm' in volume, was only -60 W, which corresponds to specific laser energy, i.e. to the output power referred to the gas flow rate, of the order of 13-14 J/g.…”

“…In the A-variant, gas mixing occurs in the formed supersonic cocurrent flows. This mixing scheme has been employed in [8,17,[19][20][23][24][25]. The lower part in figure 5A shows that with flow mixing, an additional expansion can be caused by the finite thickness of the nozzle cut.…”

“…This injection variant (the upper part of Fig. 5B) has been employed in the first constructions of MGDLs [8]. However, considerable stagnation and temperature recovery in this mixing scheme makes it impossible to obtain high population inversion characteristics of working media.…”