Spatio-temporal evolution scenarios of femtosecond laser pulse filamentation in fused silica

Abstract

We investigated the evolution of femtosecond laser pulses at different wavelengths corresponding to normal, zero, and anomalous regimes of group velocity dispersion (GVD) in fused silica. The laser pulse filamentation in different GVD regimes under the same similarity parameters was first considered. It was established numerically that the scenario of the pulse filamentation depends both on temporal factors, which are determined by pulse GVD and self phase modulation, and spatial factors associated with Kerr self focus ing and plasma defocusing. In presence of strong normal GVD the dispersive stretching causes, a pulse power decrease followed by lowering of the intensity in filament, electron density reduction in plasma channel, and suppressing of the refocusing. For zero GVD the multipeak regime of radiation propagation is realized in the filament as a result of recurring self focusings of powerful pulse tail, which was defocused in laser plasma. When GVD is anomalous a sequence of "light bullets" with duration about 10 fs forms in the filament. And the peak intensity in "light bullet" stays the same ≈ 5 × 10 13 W/cm 2 . In the regime of anomalous GVD power is transferred from the pulse edges to its center, where the repeated self focusings occur and form a "light bul let" sequence.

Light bullets from a femtosecond filament

“…The formation of a sequence of LBs along a filament in fused silica under conditions close to our experimental system was predicted in [25] based on a computer simulation of femtosecond laser pulse filamentation for different wavelengths. The slowly-evolving-wave approximation is used in numerical modeling [31].…”

“…The elongation of the filament was found under anomalous GVD, compared with the normal GVD of the condensed medium [24]. Numerical investigation into the formation of LB sequences during filamentation under anomalous GVD was carried out in [25]. The LBs sequence formation was confirmed experimentally by autocorrelation measurements [26][27][28].…”

Giantically blue-shifted visible light in femtosecond mid-IR filament in fluorides

“…For numerical simulations we used the nonlinear equation for pulse slowly varying envelope. Our model [26,27] includes diffraction, Kerr nonlinearity with stimulated Raman scattering (SRS), plasma nonlinearity, multiphoton absorption and linear attenuation, selfphase modulation (SPM), self-steepening, and full dispersion according to Sellmeier formula. In considered fluorides the GVD of Mid-IR pulses is anomalous as the second-order dispersion coefficient k 2 is negative.…”

Regular ‘breathing’ of a near-single-cycle light bullet in mid-IR filament

“…The evolution of an 1800-nm LB temporal-spatial structure in sapphire was investigated in [6]. One of the questions under the discussion concerns the LB propagation behavior in a nonlinear medium: either quasistationary [7] or recurrent [3][4][5]. In [7] a long glowing channel of a 1900 nm pulse filament is considered as a long-lived quasi-soliton, which does not change a shape over the distance of a several centimeters.…”