Abstract
We report on a systematic experimental study on the fluorescence spectra produced from a femtosecond laser filament in air under a high electric field. The electric field alone was strong enough to create corona discharge (CD). Fluorescence spectra from neutral and ionic air molecules were measured and compared with pure high-voltage CD and pure laser filamentation (FIL). Among them, high electric field assisted laser FIL produced nitrogen fluorescence more efficiently than either pure CD or pure FIL processes. The nonlinear enhancement of fluorescence from the interaction of the laser filament and corona discharging electric field resulted in a more efficient ionization along the laser filament zone, which was confirmed by the spectroscopic measurement of both ionization-induced fluorescence and plasma-scattered 800 nm laser pulses. This is believed to be the key precursor process for filament-guided discharge.
Highlights
Filamentation (FIL) induced by ultrashort intense laser pulses in air has attracted much scientific interest since it was first predicted theoretically in 1990[1] and first observed experimentally in 1995[2]
The fluorescence signal produced by the femtosecond laser filament with and without high-voltage corona discharge (CD) was collected by a pair of lenses and sent to a spectrometer coupled to a CCD camera
Laser-guided leader type of corona explored yet until recently, when we reported on a direct observation of laser-filament-guided CDs[37]
Summary
Filamentation (FIL) induced by ultrashort intense laser pulses in air has attracted much scientific interest since it was first predicted theoretically in 1990[1] and first observed experimentally in 1995[2]. During femtosecond laser FIL in air, many nonlinear effects occur simultaneously, such as intensity clamping, molecular alignment, harmonic generation, self-phase modulation and so on[3,4,5] These complex and interesting nonlinear phenomena accompanying femtosecond laser FIL lead to promising applications in different fields, such as remote sensing[6, 7], few-cycle pulse compression[8], atmospheric condensation and precipitation[9,10,11], secondary light source generation ranging from air lasing to terahertz emission[12,13,14,15,16,17,18], and triggering and guiding high-voltage discharge with possible applications in lightning control[19,20,21,22,23,24].
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