Optical amplification and gain dynamics of cavity-free lasing of argon pumped by ultraviolet femtosecond pulses

Argon gas excited by resonant femtosecond ultraviolet pulses gives rise to cavity-free lasing emission in the near-infrared (NIR) range. Here we reported on a pump-probe study of the optical gain of this lasing phenomenon. With the injection of an external seeding pulse, the forward signal was significantly enhanced, confirming the existence of optical gain. The temporal dynamics of the optical gain were characterized by a time-resolved measurement. It was found that the optical gain decays on a time scale of similar to 10 ps and it does not present a significant dependence on the gas pressures. Moreover, the intensity of the forward NIR emission signal shows a linear dependence on the gas pressure. These features suggest that the nature of this forward MR radiation is amplified spontaneous emission, not superradiance when multiple-photon resonant excitation is involved. (C) 2022 Optica Publishing Group under the terms of the Optica Open Access Publishing Agreement