Postfilament supercontinuum on 100  m path in air

Abstract

The pulses at 744 nm with the duration 90 fs, energy 6 mJ and weakly divergent wavefront propagated for more than 100 m and generated a filament followed by unprecedently long high intensity (≥ 1 TW/cm 2 ) light channel. Over a 20 m long sub-section of this channel the pulse energy is transferred continuously to the infrared wing, forming spectral humps that extend up to the wavelength of 850 nm. From 3D+time carrierresolved simulations of 100 m pulse propagation, we show that spectral humps indicate the formation of a train of fs pulses appearing at a predictable position in the propagation path.

Remote triggering of air-gap discharge by a femtosecond laser filament and postfilament at distances up to 80 m

“…Single "self-cleaned" hot spot surrounded by wide elliptical background was observed from 50 to 100 m, see Ref. 38 The high-voltage supply supported the direct voltage up to 10 kV, which dropped down during the discharge occurrence only and regained after the discharge current termination. When the voltage between the electrodes was higher than the self-breakdown one of ∼4.8 kV, the arc appeared independently of a laser shot, that is, even if we blocked the beam.…”

“…This beam was directed to the ∼100-m corridor inside the building using several highly reflective interference mirrors (the details are given in Ref. 38). The mirror system introduced a slight divergence to the laser beam (the focal length of the system was estimated as −50 m) thus increasing the distance of the beam collapse to 40-50 m. According to our previous analysis 38 , the single filament consisted in a short (about 0.3-m) region of high intensity located at z ∼ 50 m with plasma of density in excess of 10 16 cm −3 , followed by a long postfilament channel without plasma but an intensity in excess of 0.5 TW/cm 2 .…”

“…38). The mirror system introduced a slight divergence to the laser beam (the focal length of the system was estimated as −50 m) thus increasing the distance of the beam collapse to 40-50 m. According to our previous analysis 38 , the single filament consisted in a short (about 0.3-m) region of high intensity located at z ∼ 50 m with plasma of density in excess of 10 16 cm −3 , followed by a long postfilament channel without plasma but an intensity in excess of 0.5 TW/cm 2 . Single "self-cleaned" hot spot surrounded by wide elliptical background was observed from 50 to 100 m, see Ref.…”

“…The details about numerical grids required to capture finely the supercontinuum that diverges in the transverse domain and get delayed in time can be found in Ref. 38.…”

“…The central high-intensity part of the laser beam propagating in the discharge triggering zone is 1-2 mm in diameter and . The physical reason for this notably stable hot spot diameter is the nonlinear transformation of a femtosecond pulse in the postfilament 38,[45][46][47][48] . The peak power of a femtosecond pulse in the postfilament is about the critical power for self-focusing in air.…”