Filamentation Of Laser Pulses Research Articles

Dynamics of light structures during filamentation of femtosecond laser pulses in air

A model of single filamentation of a high-power ultrashort light pulse has been developed on the basis of evolutionary dependencies of phase and amplitude parameters of the light field found from the numerical solution of a nonlinear Schrodinger equation for air. A key role of aberration and diffraction effects during the formation of localized stable dynamic light structures near the propagation axis is shown. It is found that the angular divergence of the postfilamentation light channel decreases with an increase in the laser beam radius at a fixed peak pulse power and is saturated when the radius is greater than 1 mm.

Underwater acoustic wave generation by filamentation of terawatt ultrashort laser pulses.

Acoustic signals generated by filamentation of ultrashort terawatt laser pulses in water are characterized experimentally. Measurements reveal a strong influence of input pulse duration on the shape and intensity of the acoustic wave. Numerical simulations of the laser pulse nonlinear propagation and the subsequent water hydrodynamics and acoustic wave generation show that the strong acoustic emission is related to the mechanism of superfilamention in water. The elongated shape of the plasma volume where energy is deposited drives the far-field profile of the acoustic signal, which takes the form of a radially directed pressure wave with a single oscillation and a very broad spectrum.

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

Experimental and numerical studies of a temporal evolution of a light bullet formed in isotropic LiF by mid-IR femtosecond pulse (2600–3350 nm) of power, slightly exceeding the critical power for self-focusing, are presented. For the first time regular oscillations of the light bullet field peak amplitude during its propagation in a filament were registered by investigation of induced color centers in LiF. It was revealed that color centers in a single laser pulse filament have the strictly periodic structure with a length of separate sections about 30 μm, which increases with a laser pulse wavelength decreasing. It was shown that the origin of a light bullet modulation is a periodical change of the light field amplitude of a near single-cycle wave packet in a filament, due to a difference of the wave packet group velocity and the carrier wave phase velocity.

Periodic colour-centre structure formed under filamentation of mid-IR femtosecond laser radiation in a LiF crystal

A colour-centre structure formed in a LiF crystal under filamentation of a femtosecond mid-IR laser pulse with a power slightly exceeding the critical power for self-focusing has been experimentally and theoretically investigated. Strictly periodic oscillations have been detected for the first time for the density of the colour centres induced in an isotropic LiF crystal under filamentation of a laser beam with a wavelength tuned in the range from 2600 to . The structure period is found to be about . With an increase in the laser radiation wavelength, the period of the oscillations decreases and their amplitude increases. The maximum colour centre density, observed under filamentation of a beam, is related to the increased contribution of the direct generation of colour centres as a result of the absorption of an integer number of photons by the exciton band. It is numerically shown that the formation of a periodic colour-centre structure in LiF is due to the periodic change in the light field amplitude in the light bullet (1.5 optical periods long) formed under filamentation.

Microstructure of the multiple filamentation region of femtosecond laser radiation in a solid dielectric

Properties of multiple filamentation of gigawatt femtosecond laser pulses in optical glass are considered. The fine structure of the plasma region that is produced upon photoionization of quartz and accompanies light filaments are analyzed experimentally and in numerical simulation. The dependence of the number, position, and length of individual generations of plasma channels on the laser energy is studied for the first time. The role of pulse refocusing events in the plasma region formation is discussed.

Effect of geometrical focusing on femtosecond laser filamentation with low pressure

The influence of geometrical focusing on the filamentation of femtosecond laser pulses at various low pressures (<1 atm) in air has been numerically demonstrated. The main peculiarities, such as filamentation dynamics, spatial-temporal evolution and supercontinuum generation manipulated by external geometrical focusing in the low atmospheric pressure regime, are analyzed by numerically solving a spatial-temporal equation for femtosecond laser pulse propagation in air. The results show that those important characteristics are more sensitive to the focal length than the variation of atmospheric pressure. It indicates that suitable design of the focal length will result in further amplitude uniformity and a lack of temporal aberrations in the compressed pulse. This theoretical modelling of pulse shaping optimization is a step to realization of high-energy femtosecond pulse delivery from the Earth’s surface to altitudes of several kilometers up into the atmosphere.

Multiple Filamentation of Laser Pulses in a Glass

Results are presented of experiments on investigation of the spatial characteristics of multi-filamentation region of giga- and terawatt pulses of a Ti:sapphire laser in a glass. Dependences are obtained of the coordinate of the beginning of filamentation region, number of filaments, their distribution along the laser beam axis, and length of filaments on the pulse power. It is shown that with increasing radiation power, the number of filaments in the multi-filamentation region decreases, whereas the filament diameter has a quasiconstant value for all powers realized in the experiments. It is shown that as a certain power of the laser pulse with Gauss energy density distribution is reached, the filamentation region acquires the shape of a hollow cone with apex directed toward the radiation source.

Microstructure of the multiple-filamentation zone formed by femtosecond laser radiation in a solid dielectric

The regularities of multiple filamentation of gigawatt femtosecond laser pulses in a solid dielectric (optical glass) have been considered. The fine spatial structure of the plasma region that is formed under glass photoionisation and accompanies the formation of light filaments is analysed experimentally and by means of numerical simulation. The dependence of the number, position, and extension of individual ‘generations’ of plasma channels on the laser pulse energy has been investigated for the first time. It is found that the distribution of the number of plasma channels over the length of a dielectric sample has a maximum, the position of which correlates well with the position of the nonlinear focus of the light beam as a whole; at the same time, the average channel length decreases with increasing pulse power, whereas the number of successive channel ‘generations’, on the contrary, increases.

Multiple filamentation of femtosecond laser pulses

The formation of fluorescent channels with color centers in LiF crystals under the action of the multiple filamentation of femtosecond laser pulses is studied experimentally and theoretically for pulse powers around four orders of magnitude higher than the critical self-focusing value.

Динамика световых структур при филаментации фемтосекундных лазерных импульсов в воздухе

Динамика световых структур при филаментации фемтосекундных лазерных импульсов в воздухе

Numerical simulations of ultrashort laser pulse multifilamentation in fused silica: plasma channels statistics

The regime of multiple filamentation of gigawatt-power femtosecond laser pulses in fused silica bars is theoretically investigated. Numerical simulations are used to analyze the fine spatial structure of the plasma region formed due to photoionization of silica and accompanying pulse filamentation. The dependence of the number, spatial position, and length of different generations of plasma channels on the energy and focusing conditions of the optical pulse is studied. The role of pulse sequential refocusing in the formation of the plasma region is discussed.

Role of coherent resonant nonlinear processes in the ultrashort KrF laser pulse propagation and filamentation in air

Recent experiments on multiple filamentation of sub-picosecond terawatt-level KrF laser pulse in air and multi-photon ionization of air revealed an extremely low electron density in filaments, which is out of the conventional filamentation model considering Kerr self-focusing and plasma de-focusing. We propose here the coherent resonant scattering and ionization processes at the pulse durations significantly less than the polarization relaxation time to be possible explanation of the observed filamentation peculiarities. Namely, we argue that the plasma production results from the resonance enhanced (2+1)-photon ionization of the oxygen molecules through the two-photon excitation of the 3s metastable Rydberg state. Coherent Raman self-scattering at rotational transitions of nitrogen molecules provides self-induced focusing of the ultrashort UV laser pulse and filament formation.

Dispersion of a Femtosecond Wave Packet Focused by an Axicon. A Scaling Parameter

We investigate the propagation of a femtosecond wave packet focused by an axicon in the linear medium. We introduce a scaling parameter for the problem of the Bessel–Gaussian beam formation in the femtosecond light. This parameter is based on a multiplicative representation for spatiotemporal distribution of the light-field complex amplitude. In this approach, the systematic error for estimating the wave-packet energetic parameters is determined. The approximate method presented can be used for analyzing a femtosecond laser-pulse filamentation under axicon focusing.

Quasi-steady-state air plasma channel produced by a femtosecond laser pulse sequence.

A long air plasma channel can be formed by filamentation of intense femtosecond laser pulses. However, the lifetime of the plasma channel produced by a single femtosecond laser pulse is too short (only a few nanoseconds) for many potential applications based on the conductivity of the plasma channel. Therefore, prolonging the lifetime of the plasma channel is one of the key challenges in the research of femtosecond laser filamentation. In this study, a unique femtosecond laser source was developed to produce a high-quality femtosecond laser pulse sequence with an interval of 2.9 ns and a uniformly distributed single-pulse energy. The metre scale quasi-steady-state plasma channel with a 60–80 ns lifetime was formed by such pulse sequences in air. The simulation study for filamentation of dual femtosecond pulses indicated that the plasma channel left by the previous pulse was weakly affected the filamentation of the next pulse in sequence under our experimental conditions.

Remote electrical arc suppression by laser filamentation

We investigate the interaction of narrow plasma channels formed in the filamentation of ultrashort laser pulses, with a DC high voltage. The laser filaments prevent electrical arcs by triggering corona that neutralize the high-voltage electrodes. This phenomenon, that relies on the electric field modulation and free electron release around the filament, opens new prospects to lightning and over-voltage mitigation.

Guiding supersonic projectiles using optically generated air density channels

We investigate the feasibility of using optically generated channels of reduced air density to provide trajectory correction (guiding) for a supersonic projectile. It is shown that the projectile experiences a force perpendicular to its direction of motion as one side of the projectile passes through a channel of reduced air density. A single channel of reduced air density can be generated by the energy deposited from filamentation of an intense laser pulse. We propose changing the laser pulse energy from shot-to-shot to build longer effective channels. Current femtosecond laser systems with multi-millijoule pulses could provide trajectory correction of several meters on 5 km trajectories for sub-kilogram projectiles traveling at Mach 3.

Spatial coherence of a Raman wake excited inside a uniform filament

We present results of an investigation of the spatial-temporal structure of the delayed Kerr nonlinearity excited during filamentation of a femtosecond laser pulse inside a crystalline target. It is found that the pulse splitting, which is an inherent property of the filamentation process, constrains the length of the spatial coherence of the Raman wake wave which follows the pump pulse. Each subpulse induces lattice vibrations, which interfere either constructively or destructively depending on the delay between the subpulses. This results in abrupt ``switching'' of the phase of the wake wave along and across the filament volume. For the same reason, the maximal amplitude of the Raman response is observed not at the point of the maximal laser intensity and electron concentration\char22{}it is shifted forward to the end of the filament. This effect should be observed if the period of Raman oscillations is close to the duration of the pump pulse.

Filamentation of terawatt laser pulses along hundred-meter atmospheric paths

Results of the experimental study of filamentation of terawatt femtosecond pulses of a Ti:Sapphire laser along an atmospheric path 106 m long using different spatial focusing and pulse power are presented. The control of filamentation region position and length by means of changing the initial laser beam focusing is shown to be highly effective. Dependencies are derived of filamentation region position and length on the initial degree of focusing, pulse power, and the number of filaments along the filamentation region. The obtained data on the filamentation region length and the number of filaments are compared with the results of our previous experiments and data from other authors.

Control of the domain of multiple filamentation of terawatt laser pulses along a hundred-meter air path

We report the results of experiments and numerical simulation for multiple filamentation of terawatt femtosecond pulses of a Ti : sapphire laser on a long air path under varied initial spatial focusing and laser output power. Highly efficient control of the position and length of the filamentation domain is realised by varying the initial focusing of the laser beam, which provides the movement of the filamentation domain along the entire optical path. The unimodal character of the distribution of the number of plasma channels formed by the laser beam along the optical path is revealed and a correlation of the coordinates corresponding to the maximal number of plasma channels and to the nonlinear focus of the beam as a whole is established.

Multiple filamentation of collimated Ti:Sapphire laser beams in water

The results of experimental studies of femtosecond laser pulse filamentation in water are described. The dependencies of the number of filaments, spectrum width, distance of nonlinear focusing, and diameter of filamentation zone on the laser pulse power are measured. Existence of a segment on the scale of relative power is marked out, where the number of filaments increases dramatically.