Abstract
Postfilamentation channel resulting from filamentation of freely propagating 744-nm, 5-mJ, 110-fs pulse in the corridor air is examined experimentally and in simulations. The longitudinal extension of postfilament was determined to be 55–95 m from the compressor output. Using single-shot angle-wavelength spectra measurements, we observed a series of red-shifted maxima in the spectrum, localized on the beam axis with the divergence below 0.5 mrad. In the range 55–70 m, the number of maxima and their red-shift increase with the distance reaching 1 μm, while the pulse duration measured by the autocorrelation technique is approximately constant. Further on, for distances larger than 70 m and up to 95 m, the propagation is characterized by the suppressed beam divergence and unchanged pulse spectrum. The pulse duration increases due to the normal air dispersion.
Highlights
Nonlinear propagation of a collimated high-power ultrashort laser pulse in ambient air [1] results in the beam collapse [2,3] and filamentation [4,5,6]
We experimentally studied the postfilament of the femtosecond pulse
We traced the angle-wavelength spectrum evolution in postfilament obtained without external focusing on the 100-meter-long path in air
Summary
Nonlinear propagation of a collimated high-power ultrashort laser pulse in ambient air [1] results in the beam collapse [2,3] and filamentation [4,5,6]. The laser radiation localizes into single or multiple filaments due to the dynamic equilibrium between Kerr self-focusing and defocusing in the self-induced plasma [7,8,9,10,11,12]. The filament in air produced by Ti:sapphire laser pulses is characterized by the key parameters such as the clamped intensity of about 100 TW/cm2 [30,31,32], plasma density of 1016 –1017 cm−3 [33,34] and diameter of ∼100 μm [4,35]. By the filament we mean spatio-temporally localized light structure accompanied by plasma channel. The light channel induced by the same femtosecond pulse can be much longer than the plasma channel and it can reach tens to hundreds of meters [36,37,38]. More than fifteen-meter uninterrupted light channels formed by sub-terawatt ultraviolet pulse were reported in [39]
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