Optical gain in rotationally excited nitrogen molecular ions

Ali Azarm, Paul Corkum, Pavel Polynkin

Research output: Contribution to journalArticlepeer-review

58 Scopus citations


We pump low-pressure nitrogen gas with ionizing femtosecond laser pulses at 1.5 μm wavelength. The resulting rotationally excited N2+ molecular ions generate directional, forward-propagating stimulated and isotropic spontaneous emissions at 428 nm wavelength. Through high-resolution spectroscopy of these emissions, we quantify rotational population distributions in the upper and lower emission levels. We show that these distributions are shifted with respect to each other, which has a strong influence on the transient optical gain in this system. Although we find that electronic population inversion exists in our particular experiment, we show that sufficient dissimilarity of rotational distributions in the upper and lower emission levels could, in principle, lead to gain without net electronic population inversion.

Original languageEnglish (US)
Article number051401
JournalPhysical Review A
Issue number5
StatePublished - Nov 7 2017

ASJC Scopus subject areas

  • Atomic and Molecular Physics, and Optics


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