Field-induced gain in homonuclear diatomic molecules

This paper explores the possibility of inducing useful gain on the variation-rotation bands of homonuclear diatomic molecules by immersion in an electric field. General expressions are set up and two cases in particular are examined, both enhanced by motional line narrowing. A partial inversion in the gas phase favors the O branch of light molecules and the gain at breakdown scales as the square of density; for hydrogen approximately 1 percent/cm should arise at 30 Amagat. Cryogenic liquids require a complete inversion and are predicted to have strong polarised Q-branch gain. Comparison with collision-induced data reveals that the field-induced effect is much stronger.