Methane ring laser with bidirectional optical pumping

Frequency pulling effects and competition of counterpropagating waves were demonstrated experimentally in a CH₃OH ring laser (λ = 118.8 μm) pumped bidirectionally by CO₂ laser radiation. Various lasing regimes were identified: they were characterized by independent existence of two counterpropagating waves, transfer of energy from one wave to another, and suppression of one of the waves. Frequency splitting of the counterpropagating waves of up to 190 kHz was achieved without using intracavity nonreciprocal elements. Dependences of the difference frequency on the power ratio of the counterpropagating pump waves, the CO₂ laser frequency, and the ring resonator eigenfrequency were explained using the model of formation of the gain band.