Tracing Evolution of Angle-Wavelength Spectrum along the 40-m Postfilament in Corridor Air

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.

Nonlinear Propagation and Filamentation on 100 Meter Air Path of Femtosecond Beam Partitioned by Wire Mesh

“…In this section, we discuss in details the possibility to control the location of the ∼1 TW/cm 2 zone including the filament and the postfilament channel along the propagation path by insertion of the meshes with different cells into the beam at the laser system output. We identify this zone by the minimal beam diameter and the low divergence of laser radiation [43], the high-voltage discharge triggering [44], and the emission of the infrared supercontinuum with the strongly modulated spectrum [43,45]. None of the three diagnostics methods can identify the presence of the laser plasma nor quantify the intensity of the pulse.…”

“…The luminescence was projected to a CCD camera by an objective lens. Technical details on measurement techniques used can be found in [45].…”

“…Indeed, the pioneering experiments on femtosecond laser filamentation in air [1][2][3] were carried out using ∼800 nm pulses with the peak power P less than ∼200 GW and provided researchers with the detailed information on the beam distribution [1,3] and conical emission in the visible part of the spectrum [2,42]. In our recent experiments on the 100 m path [43][44][45], the ∼60 GW pulse formed ∼30 cm plasma filament followed by ∼40 m postfilament [22,46,47] with the intensity higher than ∼1 TW/cm 2 . Such high intensity is sufficient to enhance the infrared spectral wing [43] and to trigger high-voltage discharge [44].…”