Multimode Treatment of Misaligned CO₂ Waveguide Lasers

Abstract

We have developed and applied a multi-mode matrix resonator model of waveguide lasers, allowing for possible tilts and folds. Simpler one-mode or few-mode models do not accurately predict performance for practical resonators. Higher-order transverse mode effects can be very strong and perhaps surprising. We present here some recent theory-experiment comparisons for two similar r.f.-excited CO₂ waveguide laser designs with square bores. We conclude that excellent agreement with theory, including a much better grasp of line-hopping and hooting, can be gained if the waveguide dimensions are carefully controlled. We also demonstrate an important transverse-mode effect where the ordinary sense of ‘well aligned’ misleads: the laser gives more power when its mirror is tilted.