Among different approaches to generate mirrorless lasing, resonant multiphoton pumping of gas constituents by deep-UV laser pulses exhibits so far the highest efficiency and produces measurable lasing energies, but the underlying mechanism was not yet fully settled. Here, we report lasing generation from atomic oxygen in a methane-air flame via femtosecond two-photon excitation. Temporal profiles of the lasing pulses were measured for varying concentrations of atomic oxygen, which shows that the peak intensity and time delay of the lasing pulse approximately scales as N and 1/N, respectively, where N represents the concentration. These scaling laws match well with the prediction of oscillatory superfluorescence (SF), indicating that the lasing we observed is essentially SF rather than amplified spontaneous emission. In addition, the quantum-beating effect was also observed in the time-resolved lasing pulse. A theoretical simulation based on nonadiabatic Maxwell-Bloch equations well reproduces the experimental observations of the temporal dynamics of the lasing pulses. These results on fundamentals should be beneficial for the better design and applications of lasing-based techniques.
Bibliografisk informationFunding Information:
This research work was sponsored by the National Science Foundation for Young Scientists of China (Grant No. 12004147), the Knut and Alice Wallenberg Foundation (COCALD KAW2019.0084), the European Research Council (ERC Advanced Grant TUCLA 669466), the Swedish Research Council (VR), and the Swedish Foundation for Strategic Research (SSF, ITM17-0309). This work was also partially supported by the Fundamental Research Funds for the Central Universities. L.Y. acknowledged the support from the Program for Professor of Special Appointment (Eastern Scholar) at Shanghai Institutions of Higher Learning.
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- Atom- och molekylfysik och optik