Self-guided Propagation Research Articles

Clustered gases as a medium for efficient plasma waveguide generation

Clustered gas jets are shown to be an efficient means for plasma waveguide generation, for both femtosecond and picosecond generation pulses. These waveguides enable significantly lower on-axis plasma density (less than 10(18) cm(-3)) than in conventional hydrodynamic plasma waveguides generated in unclustered gases. Using femtosecond pump pulses, self-guided propagation and strong absorption (more than 70%) are used to produce long centimetre scale channels in an argon cluster jet, and a subsequent intense pulse is coupled into the guide with 50% efficiency and guided at above 10(17)W cm(-2) intensity over 40 Rayleigh lengths. We also demonstrate efficient generation of waveguides using 100 ps axicon-generated Bessel-beam pump pulses. Despite the expected sub-picosecond cluster disassembly time, we observe long pulse absorption efficiencies up to a maximum of 35%. Simulations show that in the far leading edge of the long laser pulse, the volume of heated clusters evolves to a locally uniform and cool plasma already near ionization saturation, which is then efficiently heated by the remainder of the pulse.

Observation of Spontaneous Self-Channeling of Light in Air below the Collapse Threshold

We report the observation of the self-guided propagation of 120 fs, 0.56 mJ infrared radiation in air for distances greater than 1 m. In contrast with the known case of filamentation, in the present experiment the laser power is lower than the collapse threshold. Therefore the counterbalance between Kerr self-focusing and ionization induced defocusing as the stabilizing mechanism is ruled out. Instead, we find evidence of a process in which the transversal beam distribution reshapes into a form similar to a Townes soliton, with the particularity of a very high stability. We include numerical support for this conclusion.

High-order harmonic generation by chirped and self-guided femtosecond laser pulses. I. Spatial and spectral analysis

For the analysis of high-order harmonics generated in a long gas jet by intense chirped femtosecond laser pulses, calculations of the laser propagation and harmonic generation were performed in terms of a nonadiabatic three-dimensional model. The self-guided propagation, observed at the conditions of bright harmonic generation, was confirmed by the model calculations. When using negatively chirped pulses, the calculated distribution of the harmonic field is spatially and spectrally confined, being generated on axis with a narrow spectral profile. The positively chirped pulses generate broad spectral distribution on axis, and narrow off axis, but in the latter case with a large emission angle. The estimation of harmonic beam divergence agreed well with experimentally measured data, showing the lowest divergence at the conditions of the brightest harmonic generation. Spectral, temporal, and spatial modifications of the propagated laser pulse are found to influence decisively the single-atom response and ultimately the harmonic field, providing a coherent picture of harmonic generation.

Filament-induced remote surface ablation for long range laser-induced breakdown spectroscopy operation

We demonstrate laser induced ablation and plasma line emission from a metallic target at distances up to 180 m from the laser, using filaments (self-guided propagation structures ∼ 100 μm in diameter and ∼ 5 × 10 13 W/cm 2 in intensity) appearing as femtosecond and terawatt laser pulses propagating in air. The remarkable property of filaments to propagate over a long distance independently of the diffraction limit opens the frontier to long range operation of the laser-induced breakdown spectroscopy technique. We call this special configuration of remote laser-induced breakdown spectroscopy “remote filament-induced breakdown spectroscopy”. Our results show main features of filament-induced ablation on the surface of a metallic sample and associated plasma emission. Our experimental data allow us to estimate requirements for the detection system needed for kilometer-range remote filament-induced breakdown spectroscopy experiment.

Enhanced harmonic conversion efficiency in the self-guided propagation of femtosecond ultraviolet laser pulses in argon

Harmonic generation during the self-guided propagation of femtosecond ultraviolet (UV) laser pulses (248-nm, 450-fs) in argon is investigated. The third (82.7-nm) and fifth (49.6-nm) harmonics are generated in the UV filament. The energy-conversion efficiencies for the harmonics are found to be at least two orders of magnitude higher than those reported in the literature for similar gas pressures. The enhancement is attributed to the quasi-phase matching of the harmonics due to the self-guiding of the driving pulse.

Ray-tracing simulation of ionization-free filamentation

A new ray-tracing scheme is proposed to simulate the non-linear propagation of ultra-short pulses. The results are in good agreement with experimental data and numerical solving of the non-linear Schrodinger equation in both the self-focusing and the filamentation regions. In particular, they indicate a major contribution of the ‘photon bath’ in the self-guided propagation of ultra-short pulses. The model suggests that a pure-Kerr self-guiding mode can allow filamentation without ionization.

Self-guided propagation of femtosecond light pulses in water: erratum

Self-guided propagation of femtosecond light pulses in water: erratum

Experimental and theoretical analyses of a correlation between pump-pulse propagation and harmonic yield in a long-interaction medium

We performed experimental and theoretical analyses of a correlation between pump pulse propagation and harmonic yield in Ar and Xe, in a long static gas cell, at high pumping energies, for loose focusing geometry, using 35-fs pulses from a Ti:sapphire laser. Axial and transverse profiles of the plasma column were measured under several experimental conditions with the aim of characterizing the pulse propagation. From the plasma fluorescence profiles observed, it was found that self-guided propagation of the pump pulse in Xe resulted in the channel formation. A three-dimensional nonadiabatic propagation model was used to calculate the field configuration in the interaction region and to explain the channel formation. A model developed to calculate the transverse plasma profiles can adequately reproduce the experimental data and confirm the channel formation. Correlated measurements of harmonics generation reveal that channel formation greatly enhances the harmonic yield as harmonics propagate under phase-matched conditions.

Self-guided propagation of femtosecond light pulses in water.

We report experimental evidence of self-guided propagation of femtosecond laser pulses in water. A light filament induced by 170-fs, 527-nm pulses has a diameter of 60 microm (at the 1/e2 level) and persists over a distance of 20 mm. The filamentary mode is sustained over a wide range of input power, and the energy excess is converted into conical emission. In the time domain, the pulse trapped in a filamentary mode experiences a number of splittings occurring in the early stage of filament formation.

Generation of high-order harmonics in a self-guided beam

Generation of high-order harmonics in Xe was studied in a static cell at high pump energies, 5 m focal length, and up to 14 cm interaction lengths. Self-guided propagation of the pulse was observed experimentally and confirmed by a three-dimensional model. Phase-matched generation was demonstrated in the self-guided beam, and the high energy and low divergence of the harmonic radiation were explained. Harmonic field calculations, in good agreement with experimental results, allow for the explanation of the higher-order harmonic generation dynamics in the self-guided region.

Propagation dynamics of femtosecond laser pulses in argon

The propagation dynamics of intense femtosecond laser pulses in argon have been investigated theoretically and the results are compared with experimental data. It was found that in the initial stage the pulse propagates with the focal point moving ahead of the original one. The central beam of the trailing part experiences defocusing owing to ionization by the leading part and then regains self-focusing provided by power from the outer part. On propagating further, a quasistable balance is established between self-focusing and defocusing due to ionization-induced nonlinearity and diffraction, causing the beam to propagate in a self-guided mode. Furthermore, it was shown that the front of the split pulse decays faster, while the trailing edge experiences self-focusing and self-defocusing until a self-guided propagation mode is achieved. Multiple pulse splitting and shortening as a result of the dynamics near the focal point were also observed.

Self-guided propagation of ultrashort IR laser pulses in fused silica.

We report self-guided propagation of ultrashort IR laser pulses in fused silica over several Rayleigh lengths. Self-guiding is accompanied by pulse splitting and time compression. Numerical simulations involving pulse self-focusing, temporal dispersion, and multiphoton ionization are found to be in good agreement with the experimental results. They show that a quasidynamic equilibrium between multiphoton ionization and self-focusing drives the filamentation process, while temporal dispersion plays a negligible role.

Femtosecond laser-guided electric discharge in air.

The filament due to the self-guided propagation of an infrared femtosecond laser pulse in atmospheric-pressure air is used to trigger and guide an electric discharge. The long low density plasma channel due to the filament is first heated by the Joule effect during an initial transient plasma stage. The heated channel of recombined gas then hydrodynamically expands radially. The onset of a discharge starts when the density depression on axis reaches the threshold discharge value. This model is supported by detailed experimental and numerical analysis.

Femtosecond and picosecond ultraviolet laser filaments in air: experiments and simulations

We report a study of the long-range self-guided propagation of intense femtosecond and picosecond UV laser pulses in air. Measurements of the laser beam profile along the propagation axis together with the ionization rate, the pulse temporal profile and power spectrum provide a comprehensive image of the UV filamentation process and its characteristics. Self-guiding is shown to subsist in both fs and ps cases, with a robust filament propagating over several meters in air. Stable filamentation is accompanied by an important restructuring of the pulse temporal profile. Complementary numerical simulations, using a three-dimension propagation code, are compared to the experimental results. The simulations reproduce most experimental observations, allowing for a better understanding of the phenomena involved in this unique propagation mode.

Stable self-guided propagation of two optical harmonics coupled by a microwave or a terahertz wave

We propose a new scheme for self-trapping of (2+1)-dimensional optical beams: parametric interaction between self-guided waves of optical and microwave (or terahertz) frequencies, which relies on the combination of optical rectification and the electro-optic effect in a bulk noncentrosymmetric medium. We show that, in spite of strong domination of quasi-cubic terms, quadratic nonlinearity provides an effective stabilization mechanism to prevent collapse in a large range of parameters where three-wave solitons exist.

Anomalous long-range propagation of femtosecond laser pulses through air:?moving focus or pulse self-guiding?

Self-guided propagation of femtosecond laser pulses is studied for a converging-beam configuration. Channeling of the pulse energy through various gases is observed over distances well beyond the lens focal point, a fact that cannot be explained by the moving-focus model. The results are in good agreement with three-dimensional numerical simulations.

Observation of the self-guided propagation of a dark and bright spatial soliton pair in a focusing nonlinear medium

Experimental results are presented showing the simultaneous propagation of a dark and bright spatial solitary waves of different colors (1064 and 532 nm) in a homogeneous Kerr medium of the focusing type, owing to cross-phase modulation. They correspond to a soliton pair, already proposed as a particular analytical solution of the two coupled wave equations. The intensity ratio between the two beams at which solitary propagation occurs is close to the theoretical value, and the observed phenomena are consistent with numerical simulations of the experiment.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>