Resonance-enhanced, rare-gas-assisted femtosecond-laser electronic-excitation tagging in argon/nitrogen mixtures

Bidirectional Cascaded Superfluorescent Lasing in Air Enabled by Resonant Third Harmonic Photon Exchange from Nitrogen to Argon

Cavity-free lasing in atmospheric air has stimulated intense research toward a fundamental understanding of underlying physical mechanisms. In this Letter, we identify a new mechanism-a third-harmonic photon mediated resonant energy transfer pathway leading to population inversion in argon via an initial three-photon excitation of nitrogen molecules irradiated by intense 261 nm pulses-that enables bidirectional two-color cascaded lasing in atmospheric air. By making pump-probe measurements, we conclusively show that such cascaded lasing results from superfluorescence rather than amplified spontaneous emission. Such cascaded lasing with the capability of producing bidirectional multicolor coherent pulses opens additional possibilities for remote sensing applications.

OH planar laser-induced fluorescence imaging system using a kilohertz-rate 283 nm UV Ti:sapphire laser

A narrow linewidth Ti:sapphire laser is developed and characterized for the generation of an ultraviolet nanosecond laser pulses for the planar laser-induced fluorescence (PLIF) imaging of hydroxyl (OH). With a pump power of 11.4 W at 1 kHz, the Ti:sapphire laser produces 3.5 mJ at 849 nm with pulse duration of 17 ns and achieves a conversion efficiency of 28.2%. Accordingly, its third-harmonic generation outputs 0.56 mJ at 283 nm in BBO with type I phase match. An OH PLIF imaging system has been built; a 1 to 4 kHz fluorescent image of OH of a propane Bunsen burner has been captured based on this laser system.

Laser applications to chemical, security, and environmental analysis: introduction to the feature issue

This Applied Optics feature issue on laser applications to chemical, security, and environmental analysis (LACSEA) highlights papers presented at the LACSEA 2020 Seventeenth Topical Meeting sponsored by The Optical Society (OSA).

Temporal characterization of heating in femtosecond laser filamentation with planar Rayleigh scattering

Temporal and spatial evolution of temperature in femtosecond laser filamentation is investigated using planar Rayleigh scattering combined with optical flow algorithm, the corresponding mechanism is analyzed. The temperature increases sharply with a characteristic time of 4.53μs and reach a maximum value of 418 K within 1∼10μs, then decreases slowly to around 300 K with a characteristic time of 136μs. While the temperature first diffuses rapidly in the radial direction and then diffuses very slowly, an obvious step is observed around 2μs. The mechanism of heat transfer is the result of energy exchange between electron and heavy particles and heat conduction. Within 1 ns to 10μs, molecules obtain energy continuously due to collision with electrons, which is much larger than the energy loss due to thermal conduction, leading to rise of gas temperature and the high-speed movement of the filament edges. After 10μs, thermal conduction becomes the dominant factor, resulting gas temperature decreasing and slower movement of the filament edges.