Rotational Coherence Encoded in an “Air-Laser” Spectrum of Nitrogen Molecular Ions in an Intense Laser Field

Abstract

When exposed to intense infrared laser pulses of femtosecond duration, molecules such as N${}_{2}$, CO${}_{2}$, and H${}_{2}$O not only become ionized but can also produce lasers as a result of simultaneous population inversion. Scientists look deep into this ``air lasing'' phenomenon in N${}_{2}$ gas and uncover both quantum coherence in the rotational wave packets of the lasing molecular ions and its footprint in the air-laser spectrum.