Abstract

Vibrational fluorescence has been observed previously from CN⁻ in KCl.¹ We have observed laser oscillation at 2054 cm⁻¹ from a purely vibrational transition of the CN⁻ molecule in KBr host crystals. A sample crystal, cooled to 1.7 K, was pumped on the 0 → 1 transition of CN⁻ at 2078.8 cm⁻¹ with a frequency-doubled CO₂ laser. In addition to 1 → 0 fluorescence, a series of lower-frequency lines has been observed. As in the similar system of CO in rare-gas matrices,² these have been identified as transitions between anharmonically shifted higher vibrational states, as well as isotope shifted states. In particular, the relative intensities of the 2 → 1 and 1 → 0 emission indicate the existence of a population inversion between the v = 2 and v = 1 levels, despite the fact that only the v = 1 level is populated by laser excitation. Exchange of vibrational energy (V–V transfer) between neighboring excited CN⁻ ions at large concentration is the mechanism that populates these additional states. Population inversion was confirmed by gain measurements using a tunable-diode laser, and laser oscillation was obtained when the sample faces were coated with gold films. This is the first reported observation of lasing on a purely vibrational transition in the solid state.

© 1984 Optical Society of America