Multifilamentation of powerful optical pulses in silica

Abstract

The multiple filamentation of powerful light pulses in fused silica is numerically investigated for central wavelengths at 355 nm and 1550 nm. We consider different values for beam waist and pulse duration and compare the numerical results with behaviors expected from the plane-wave modulational instability theory. Before the nonlinear focus, the spatiotemporal intensity patterns can be explained in the framework of this theory. Once the clamping intensity is reached, for long input pulse durations (∼1 ps), the ionization front defocuses all trailing components within a collective dynamic, and a spatial replenishment scenario takes place upon further propagation. Short pulses (∼50 fs) undergo similar ionization fronts, before an optically turbulent regime sets in. We observe moderate changes in the total temporal extent of ultraviolet pulses and in the corresponding spectra. In contrast, infrared pulses may undergo strong temporal compression and important spectral broadening. For short input pulses, anomalous dispersion and self-steepening push all pulse components to the trailing edge, where many small-scaled filaments are nucleated. In the leading part of the pulse, different spatial landscapes, e.g., broad ring patterns, may survive and follow their own propagation dynamics.

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

“…For the fil amentation under these conditions it was shown that the pulse may decay into a quasi periodic sequence of pulses of a few optical periods duration. Comparative analysis of the spatiotemporal stability and multiple filamentation in fused silica for laser pulses at wave lengths that lie in the normal (λ 0 = 355 nm) and anom alous (λ 0 = 1550 nm) GVD regions was made in [38]. The scenarios of spatiotemporal evolution for pulses at these wavelengths were investigated numerically for several values of pulse duration, beam radius, and pulse peak power.…”

Ultrafast supercontinuum generation in bulk condensed media

“…The intensity distributions of multiple filaments emerge in the form of regular or irregular patterns, that are governed by the input beam size, symmetry and smoothness (see, e.g. [140][141][142]). Although the multifilamentation regime creates an illusion of energy scaling of SC, each individual filament is subject to a combined effect of the intensity clamping [60] and the dispersion landscape of the material [61,62], hence no additional spectral broadening with increasing the input power is achieved.…”

Regularizing Aperiodic Cycles of Resonant Radiation in Filament Light Bullets

“…In a similar way, in our filament, the pulse maintains several temporal slices with sufficient optical power to induce aperiodic recurrent focusing or refocusing events according to the dynamic spatial replenishment model [51] (in contrast to existing periodic solutions mentioned above). As individual time slices refocus, they propagate quasistationary along a distance of some millimeters and are temporally compressed and shifted towards the trailing pulse edge due to the interplay of self-steepening and anomalous dispersion [44]. Every time the corresponding spectral broadening exhibits an overlap to a phase-matched component, a pronounced emission of resonant radiation takes place [ Fig.…”

“…According to Ref. [44], curves of constant exponential MI gain in the ðk ⊥ ; ωÞ plane are defined by…”

“…where E ω denotes the analytic signal of the electric field EðtÞ in the frequency domain, the free electron currentĴ is governed by the Drude model and a rate equation for the instantaneous electron density according to the widely used tunnel ionization model of Ammosov, Delone, and Krainov [43] for crystals, g is the fractional contribution of the Raman delayed nonlinearity, ∘ denotes the convolution integral, h R ðtÞ is the Raman kernel, and βðωÞ ¼ ωn 0 ðωÞ=c is the propagation constant related to the refractive index n 0 ðωÞ of bulk fused silica [44]. For the numerical solution of Eq.…”