Modeling of lasing in coils with stable resonators

A model is developed describing the power extraction in COILs with stable resonators when a large number of transverse Hermite-Gaussian eigenmodes oscillate. The extraction efficiency, mode intensities and intensity distribution along the flow depend only on two parameters. The first is the ratio γ0 of the residence time of the gas in the resonator to the O₂(¹Δ) energy extraction time and the second is the ratio of the threshold to the small signal gain. The efficiency is maximum for γo → ∞, and decreases very fast as YQ decreases. It is found that for a range of parameters corresponding to the highest efficiencies the intensity distribution along the flow is nonuniform and has two peaks near the resonator inlet and exit. In this case only the highest order modes totally filling the resonator cross section oscillate (the so-called, experimentally observed “sugar scooping” bimodal intensity distribution). For the range of parameters corresponding to smaller efficiencies the intensity is uniform. In this case all the modes participate in lasing; however, the intensities of the high order modes are larger than those of the low order. The present model is compared with the plane mirrors Fabry-Perot resonator model and with the constant intraresonator intensity and rooftop models of COILs with stable resonators. The extraction efficiency calculated using the last two models is very close to that estimated from our model. However, the intensity distribution can not be calculated correctly using the Fabry-Perot, the constant intraresonator intensity or the rooftop model.