Abstract
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 $1/\sqrt{N}$, 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.
Highlights
Mirrorless lasing, where no resonant cavity is required for generating coherent, directional, laserlike emission, has attracted great attention in the past decade due to its significance in fundamental light-matter interaction research and potential application in remote atmospheric sensing and diagnostics of combustion and reacting flows [1,2]
Temporal profiles of the lasing pulses were measured for varying concentrations of atomic ox√ygen, 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
In order to further identify the nature of 845-nm lasing emission, i.e., whether the underlying mechanism of this lasing process is Amplified spontaneous emission (ASE) or SF, a crucial experiment is to measure the temporal dynamics of the lasing pulses with varying concentrations of the emitters
Summary
Mirrorless lasing, where no resonant cavity is required for generating coherent, directional, laserlike emission, has attracted great attention in the past decade due to its significance in fundamental light-matter interaction research and potential application in remote atmospheric sensing and diagnostics of combustion and reacting flows [1,2]. One approach is based on electron impact excitation of neutral nitrogen molecules driven by circularly polarized femtosecond laser pulses during filamentation, resulting in lasing emission at a wavelength of 337 nm [3,4,5,6,7,8,9,10]. Another approach employs resonant multiphoton excitation of atoms or molecules with deep-ultraviolet (UV) laser pulses [11,12,13,14,15,16,17,18,19,20,21,22,23,24,25].
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