Broadband ultraviolet CO₂⁺ lasing and its coherent control

Coherent ultraviolet light source provides applications in both fundamental research and industrial applications. Here we demonstrate an ultraviolet lasing ranging from 300 nm to 450 nm from CO₂⁺ driven by carrier-envelope-offset phase (CEP) stabilized near-single-cycle light pulses. The lasing is assigned to the transitions from the first excited to the ground cationic state and is self-seeded by the self-phase modulation and the third harmonic generation in the laser-induced filament. Our study provides direct evidence on the population inversion in molecules by strong-field ionization. The observed ultraviolet supercontinuum is extremely sensitive to the CEP of the driving laser, which allows us to measure and tag the CEP on a single-shot basis when switching off the CEP stabilization. Our study offers a general approach for the generation and control of broadband ultraviolet lasing from molecular ions by strong short laser pulses.