Inhibition of multi-filamentation of high-power laser beams (original) (raw)

Spatiotemporal Rogue Events in Optical Multiple Filamentation

2013

The transient appearance of bright spots in the beam profile of optical filaments formed in xenon is experimentally investigated. Fluence profiles are recorded with high-speed optical cameras at the kilohertz repetition rate of the laser source. A statistical analysis reveals a thresholdlike appearance of heavy-tailed fluence distributions together with the transition from single to multiple filamentation. The multifilament scenario exhibits near-exponential probability density functions, with extreme events exceeding the significant wave height by more than a factor of 10. The extreme events are isolated in space and in time. The macroscopic origin of these experimentally observed heavy-tail statistics is shown to be local refractive index variations inside the nonlinear medium, induced by multiphoton absorption and subsequent plasma thermalization. Microscopically, mergers between filament strings appear to play a decisive role in the observed rogue wave statistics.

Filamentation and supercontinuum generation by singular beams in self-focusing nonlinear media

Journal of Optics-nouvelle Revue D Optique, 2011

We study numerically and experimentally the propagation of pulsed singular beams, including dark crosses and optical vortices, in self-focusing nonlinear media, resulting in filamentation and supercontinuum generation. Our results show that the singular beams survive the process of modulation instability and appear well preserved in both the near and far field.

Dynamics of femtosecond filamentation from saturation of self-focusing laser pulses

Physical Review A, 2003

We study the effect of Two-Photon Absorption (TPA) nonlinear losses on Gaussian pulses, with power that exceeds the critical power for self-focusing, propagating in bulk kerr media. Experiments performed in fused silica and silicon highlight a spontaneous reshaping of the input pulse into a pulsed Bessel beam. A filament is formed in which sub-diffractive propagation is sustained by the Bessel-nature of the pulse.

Multiple filamentation induced by input-beam ellipticity

Optics Letters, 2004

The standard explanation for multiple filamentation (MF) of intense laser beams has been that it is initiated by input beam noise (modulational instability). In this study we provide the first experimental evidence that MF can also be induced by input beam ellipticity. Unlike noise-induced beam breakup, the MF pattern induced by ellipticity is reproducible shot to shot. Moreover, our experiments show that ellipticity can dominate the effect of noise, thus providing the first experimental methodology for controlling the MF pattern of noisy beams. The results are explained using a theoretical model and simulations. PACS numbers: 260.5950, 190.5530 The propagation of high-power ultrashort pulses through the atmosphere is currently one of the most active areas of research in nonlinear optics, with potential applications such as remote sensing of the atmosphere and lightning control . In experiments, narrow filaments of typical width of 100µm have been observed to propagate over distances of hundreds of meters, i.e., over many Rayleigh lengths. The stability of a single filament over such long distances is nowadays known to be the result of the dynamic balance between the focusing Kerr nonlinearity, diffraction and the defocusing effect of plasma formation due to multiphoton ionization. The initial stage of propagation during which filaments are formed, however, is much less understood. In particular, since in these experiments the laser power is many times the critical power for self-focusing, a single input beam typically breaks-up into several long and narrow filaments, a phenomenon known as multiple filamentation (MF). Since MF involves a complete breakup of the beam cylindrical symmetry, it has to be initiated by a symmetry-breaking mechanism. The standard explanation for MF in the Literature has been that it is initiated by input beam noise [2], see also Ref.

Spatiotemporal rogue events in femtosecond filamentation

Physical Review A, 2011

We present experimental and numerical investigations of optical extreme (rogue) event statistics recorded in the regime of femtosecond pulse filamentation in water. In the spectral domain, the extreme events manifest themselves as either large or small extremes of the spectral intensity, justified by right-or left-tailed statistical distributions, respectively. In the time domain, the observed extreme events are associated with pulse splitting and energy redistribution in space and therefore are exquisitely linked to three-dimensional, spatiotemporal dynamics and formation of the X waves.

Multifilamentation of powerful optical pulses in silica

2010

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.

Supplementary Material: Rogue Waves in Optical Filaments

2013

For further elucidation of the processes driving rogue dynamics in multiple filamentation, we conducted a series of numerical simulations of the transverse fluence profiles F (x, y) = |E(x, y, t)| 2 dt emerging during propagation along the coordinate z. For this purpose, we numerically solve the Nonlinear Schrödinger Equation

Asymptotic pulse shapes in filamentary propagation of intense femtosecond pulses

Laser Physics, 2009

Self-compression of intense ultrashort laser pulses inside a self-guided filament is discussed. The filament self-guiding mechanism requires a balance between diffraction, plasma self-defocusing and Kerr-type self-focusing, which gives rise to asymptotic intensity profiles on axis of the filament. The asymptotic solutions appear as the dominant pulse shaping mechanism in the leading part of the pulse, causing a pinch of the photon density close to zero delay, which substantiates as pulse compression. The simple analytical model is backed up by numerical simulations, confirming the prevalence of spatial coupling mechanisms and explaining the emerging inhomogeneous spatial structure. Numerical simulations confirm that only spatial effects alone may already give rise to filament formation. Consequently, self-compression is explained by a dynamic balance between two optical nonlinearities, giving rise to soliton-like pulse formation inside the filament.