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.