Generation of extended plasma channels in air using femtosecond Bessel beams

College of Optical Sciences, The University of Arizona, Tucson, Arizona 85721, USA.
Optics Express (Impact Factor: 3.49). 10/2008; 16(20):15733-40. DOI: 10.1364/OE.16.015733
Source: PubMed


Extending the longitudinal range of plasma channels created by ultrashort laser pulses in atmosphere is important in practical applications of laser-induced plasma such as remote spectroscopy and lightning control. Weakly focused femtosecond Gaussian beams that are commonly used for generating plasma channels offer only a limited control of filamentation. Increasing the pulse energy in this case typically results in creation of multiple filaments and does not appreciably extend the longitudinal range of filamentation. Bessel beams with their extended linear foci intuitively appear to be better suited for generation of long plasma channels. We report experimental results on creating extended filaments in air using femtosecond Bessel beams. By probing the linear plasma density along the filament, we show that apertured Bessel beams produce stable single plasma channels that span the entire extent of the linear focus of the beam. We further show that by temporally chirping the pulse, the plasma channel can be longitudinally shifted beyond the linear-focus zone, an important effect that may potentially offer additional means of controlling filament formation.

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    ABSTRACT: We report experimental results on ultrafast filamentation with temporally chirped femtosecond Bessel-Gauss beams. We find that by chirping the pulses, the longitudinal range of the generated plasma channels can be extended relative to filaments generated by fully compressed, transform-limited femtosecond pulses. We find a clear correlation between the extent of filamentation and the intensity of the on-axis emission by the femtosecond Bessel-Gauss beam. The on-axis emission is negligible for fully compressed pulses, but it can become quite substantial (up to 10% of the input pulse energy) when chirped pulses are used. Under certain conditions, the on-axis emission becomes sufficient for generating its own plasma channel thus resulting in extended filamentation. This effect may offer means of remote control over filament formation with femtosecond Bessel-Gauss beams.We identify a four-wave mixing process, enhancement of which is likely to result in a maximum of the on-axis emission, and derive a simple expression for estimating the duration of the chirped pulse that is required for such enhancement. Our estimations are in good agreement with the experiment.
    Preview · Article · Feb 2009 · Optics Express
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    ABSTRACT: The formation of long stationary filaments resulting in uniform high density plasma strings in air using short pulse UV laser Bessel beams is shown. The length and the electron density of the plasma strings can be easily tuned by adjusting the conical Bessel wavefront angle. It is shown that in this regime the length of the plasma string can be extended over meter-long scales without any compromise in the string uniformity or any temporal evolution of the filamented laser pulse. (C) 2009 Optical Society of America
    Full-text · Article · Apr 2009 · Optics Express
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    ABSTRACT: Plasma channel generation (or filamentation) using ultraintense laser pulses in dielectric media has a wide spectrum of applications, ranging from remote sensing to terahertz generation to lightning control. So far, laser filamentation has been triggered with the use of ultrafast pulses with axially symmetric spatial beam profiles, thereby generating straight filaments. We report the experimental observation of curved plasma channels generated in air using femtosecond Airy beams. In this unusual propagation regime, the tightly confined main intensity feature of the axially nonsymmetric laser beam propagates along a bent trajectory, leaving a curved plasma channel behind. Secondary channels bifurcate from the primary bent channel at several locations along the beam path. The broadband radiation emanating from different longitudinal sections of the curved filament propagates along angularly resolved trajectories.
    No preview · Article · May 2009 · Science
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