Pulsed-laser mode competition with a Na-colored intracavity flame

A mode competition effect is observed with a Na-colored H2-O2-Ar flame located inside the cavity of a pulsed tunable dye laser tuned near one of the D-lines. When the Na-concentration is sufficiently high, laser action in the dominant mode is temporarily suppressed and develops in an adjacent mode. Meantime, the saturation of the Na-vapor progresses and, ultimately, laser action in the dominant mode is restored. This explanation is supported by semiquantitative computer simulation.