Showing papers on "Filamentation published in 2009"
TL;DR: The experimental observation of curved plasma channels generated in air using femtosecond Airy beams, where the tightly confined main intensity feature of the axially nonsymmetric laser beam propagates along a bent trajectory, leaving a curved plasma channel behind.
Abstract: Plasma channel generation (or filamentation) using ultraintense laser pulses in dielectric media has a wide spectrum of applications, ranging from remote sensing to terahertz generation to lightning control. So far, laser filamentation has been triggered with the use of ultrafast pulses with axially symmetric spatial beam profiles, thereby generating straight filaments. We report the experimental observation of curved plasma channels generated in air using femtosecond Airy beams. In this unusual propagation regime, the tightly confined main intensity feature of the axially nonsymmetric laser beam propagates along a bent trajectory, leaving a curved plasma channel behind. Secondary channels bifurcate from the primary bent channel at several locations along the beam path. The broadband radiation emanating from different longitudinal sections of the curved filament propagates along angularly resolved trajectories.
746 citations
TL;DR: The state of the art of investigations on filamentation of a high-power femtosecond laser radiation in transparent media is reviewed in this article, where the physical picture of this phenomenon is presented and its relation to the fundamental concepts of nonlinear optics and practical applications is demonstrated.
Abstract: The state of the art of investigations on filamentation of a high-power femtosecond laser radiation in transparent media is reviewed. The physical picture of this phenomenon is presented and its relation to the fundamental concepts of nonlinear optics and practical applications is demonstrated. Experimental and theoretical methods are briefly considered and laser radiation parameters in the case of filamentation are given. The review can be of interest both for specialists and researches wanting to become familiar with a new, rapidly developing direction in laser physics.
258 citations
TL;DR: Experiments on the propagation of intense, femtosecond, self-bending Airy laser beams in water reveal the changing character of the laser-pulse evolution on propagation.
Abstract: We report experiments on the propagation of intense, femtosecond, self-bending Airy laser beams in water. The supercontinuum radiation generated along the curved beam path is angularly resolved in the far field. Spectral maps of this radiation reveal the changing character of the laser-pulse evolution on propagation.
184 citations
TL;DR: In this paper, a model including the main beam plasma instabilities is developed, and the full three-dimensional dielectric tensor is explained for a cold relativistic electron beam passing through a cold plasma, accounting for a guiding magnetic field, a return electronic current, and moving protons.
Abstract: Many competing linear instabilities are likely to occur in astrophysical settings, and it is important to assess which one grows faster for a given situation. An analytical model including the main beam plasma instabilities is developed. The full three-dimensional dielectric tensor is thus explained for a cold relativistic electron beam passing through a cold plasma, accounting for a guiding magnetic field, a return electronic current, and moving protons. Considering any orientations of the wave vector allows to retrieve the most unstable mode for any parameters set. An unified description of the filamentation (Weibel), two-stream, Buneman, Bell instabilities (and more) is thus provided, allowing for the exact determination of their hierarchy in terms of the system parameters. For relevance to both real situations and PIC simulations, the electron-to-proton mass ratio is treated as a parameter, and numerical calculations are conducted with two different values, namely 1/1836 and 1/100. In the system parameter phase space, the shape of the domains governed by each kind of instability is far from being trivial. For low-density beams, the ultra-magnetized regime tends to be governed by either the two-stream or the Buneman instabilities. For beam densities equaling the plasma one, up to four kinds of modes are likely to play a role, depending of the beam Lorentz factor. In some regions of the system parameters phase space, the dominant mode may vary with the electron-to-proton mass ratio. Application is made to solar flares, intergalactic streams, and relativistic shocks physics.
163 citations
TL;DR: In this article, the effect of femtosecond laser filamentation has on the refractive index of Nd:YAG ceramics, and which leads to the formation of waveguide lasers, has been studied by micro-spectroscopy imaging, beam propagation experiments and calculations.
Abstract: The effect that femtosecond laser filamentation has on the refractive index of Nd:YAG ceramics, and which leads to the formation of waveguide lasers, has been studied by micro-spectroscopy imaging, beam propagation experiments and calculations. From the analysis of the Nd3+ luminescence and Raman images, two main types of laser induced modifications have been found to contribute to the refractive-index change: (i) a lattice defect contribution localized along the self-focusing volume of the laser pulses, in which lattice damage causes a refractive-index decrease, and (ii) a lattice strain-field contribution around and inside the filaments, in which the pressure-driven variation of the inter-atomic distances causes refractive-index variations. Scanning near-field optical-transmission and end-coupling experiments, in combination with beam propagation calculations, have been used to quantitatively determine the corresponding contribution of each effect to the refractive-index field of double-filament waveguides. Results indicate that the strain-field induced refractive-index increment is the main mechanism leading to waveguiding, whereas the damage-induced refractive-index reduction at filaments leads to a stronger mode confinement.
147 citations
TL;DR: In this paper, a model including the main beam plasma instabilities is developed, and the full 3D dielectric tensor is explained for a cold relativistic electron beam passing through a cold plasma, accounting for a guiding magnetic field, a return electronic current and moving protons.
Abstract: Many competing linear instabilities are likely to occur in astrophysical settings, and it is important to assess which one grows faster for a given situation. An analytical model including the main beam plasma instabilities is developed. The full 3D dielectric tensor is thus explained for a cold relativistic electron beam passing through a cold plasma, accounting for a guiding magnetic field, a return electronic current and moving protons. Considering any orientations of the wave vector allows to retrieve the most unstable mode for any parameters set. An unified description of the Filamentation (Weibel), Two-Stream, Buneman, Bell instabilities (and more) is thus provided, allowing for the exact determination of their hierarchy in terms of the system parameters. For relevance to both real situations and PIC simulations, the electron-to-proton mass ratio is treated as a parameter, and numerical calculations are conducted with two different values, namely 1/1836 and 1/100. In the system parameters phase space, the shape of the domains governed by each kind of instability is far from being trivial. For low density beams, the ultra-magnetized regime tends to be governed by either the Two-Stream or the Buneman instabilities. For beam densities equalling the plasma one, up to four kinds of modes are likely to play a role, depending of the beam Lorentz factor. In some regions of the system parameters phase space, the dominant mode may vary with the electron-to-proton mass ratio. Application is made to Solar Flares, Intergalactic Streams and Relativistic shocks physics.
108 citations
TL;DR: In this paper, the Weibel-type instability has been extended to counterstreaming plasmas which have, in addition, intrinsic temperature anisotropies, and where any form of Weibel type instability can be excited.
Abstract: New arguments are given here in favor of Weibel-type instabilities as one of the most plausible sources of the cosmological magnetic field. The Weibel instability has recently been proposed as one of the secondary mechanisms of relaxation for the large interpenetrating formations of galactic and intergalactic plasma. Here, these investigations are extended to counterstreaming plasmas which have, in addition, intrinsic temperature anisotropies, and where any form of the Weibel-type instability can be excited. This can be a simple filamentation instability due to the relative motion of counterstreaming plasmas, or a Weibel-like instability when it is generated by an excess of transverse temperature with respect to the streaming direction. But it can also be a cumulative filamentation/Weibel instability when the plasma is hotter along the streaming direction. Such plasma systems are relevant for the relative motions of filaments and sheets of galaxies, and are expected to exist at large scales and any age of our Universe. For such counterstreaming plasmas with internal temperature anisotropies, any Weibel-type instability mentioned before can become the primary wave relaxation mechanism of the plasma anisotropy, because it develops easily faster than the principal competitor, which is the two-stream electrostatic instability. The estimations made here for typical parameters of intergalactic plasmas, provide micro-Gauss levels of the magnetic field of Weibel type, which are consistent with magnetic field values, 10–7-10–5 G, derived from Faraday rotation measure of the linearly polarized emission of galactic or extragalactic sources.
89 citations
TL;DR: Simulations of filamentation during high power microwaves breakdown of near-atmospheric pressure gas are explained using a one-dimensional fluid model coupled to a theoretical wave-plasma model, which allows examination of many features not easily obtained experimentally.
Abstract: Recently reported observations of filamentation during high power microwaves breakdown of near-atmospheric pressure gas are explained using a one-dimensional fluid model coupled to a theoretical wave-plasma model. This self-consistent treatment allows for time-dependent effects, plasma growth and diffusion, and partial absorption and reflection of waves. Simulation results, consistent with experiments, show the evolution of the plasma filaments spaced less than one-quarter wavelength, the sequential discrete light emission propagating back toward the source, and the diffusion and decay of the plasma. The model allows examination of many features not easily obtained experimentally, including dependence on field strength and frequency, pressure, and gas composition, which influence the breakdown and emission properties, including the spacing and speed of propagation of the filaments.
86 citations
Book•
01 Jan 2009
TL;DR: In this article, the authors present a review of the history of self-focusing and self-trapping of optical beams, as well as some important papers from the past.
Abstract: Part I. Self-focusing in the Past: Review of Self-Focusing and Self-Trapped Filaments of Light.- Self-Focusing: Theory (Comments).- Optical Self-Focusing: Stationary Beams and Femtosecond Pulses.- Self-Focusing and Self-Trapping of Optical Beams.- Self-Focusing and Self-Channeling of Laser Radiation: History and Perspectives.- Multi-Focus Structure and Moving Nonlinear Foci - Adequate Model of Self-Focusing of Laser Beams.- Small-Scale Self-focusing.- Wave Collapse in Nonlinear Optics.- Super-Gaussian Beams for Suppression of Diffraction and Self-Focusing in High-Power Nd:Glass Laser Amplifiers.- Self-Action Effects, Pattern Formation and Nonlinear Dynamics in Atomic Vapors.- Diffraction and Interference in Supercontinuum Generation.- Reprints of Several Important Papers from the Past.- Part II. Self-focusing in the Present: Self-Trapping of Optical Beams: Spatial Solitons.- Self-Focusing of Femtosecond Pulses in Air and Condensed Matter: Simulations and Experiments.- Self-Organized Propagation of Femtosecond Laser Filamentation in Air.- The Physics of Intense Femtosecond Laser Filamentation.- Spatial and Temporal Dynamics of Self-focusing.- Some Comments on the History of Self-focusing Theory.- Nonlinear X Waves: Theory and Experiment.- On the Role of Conical Waves in Self-Focusing and Filamentation of fs Pulses.- Self-Focusing and Self-Defocusing of Femtosecond Pulses with Cascaded Quadratic Nonlinearities.- Effective Parameters of High-Power Laser Femtosecond Radiation at Self- focusing in Gas and Aerosol Media.- Diffraction-Induced High-Order Modes of the (2+1)-D Nonparaxial Nonlinear Schrodinger Equation.- Self-Focusing in Photorefractive Crystals.- Measurement of Nonlinear Susceptibilities Using Self-Action Effects (Including Z-scan).
81 citations
TL;DR: In this paper, a broad area quantum cascade laser (QCL) with ridge widths up to 400μm was studied with room temperature pulsed mode operation at an emission wavelength around 4.45μm, and the peak output power scales linearly with the ridge width.
Abstract: Broad area quantum cascade lasers (QCLs) are studied with ridge widths up to 400 μm, in room temperature pulsed mode operation at an emission wavelength around 4.45 μm. The peak output power scales linearly with the ridge width. A maximum total peak output power of 120 W is obtained from a single 400-μm-wide device with a cavity length of 3 mm. A stable far field emission characteristic is observed with dual lobes at ±38° for all tested devices, which suggests that these broad area QCLs are highly resistant to filamentation.
80 citations
TL;DR: In this article, the authors experimentally observed optical rogue wave statistics during high power femtosecond pulse filamentation in air and characterized wavelength-dependent intensity fluctuations across 300 nm broadband filament spectra generated by pulses with several times the critical power for filamentation.
Abstract: We experimentally observed optical rogue wave statistics during high power femtosecond pulse filamentation in air. We characterized wavelength-dependent intensity fluctuations across 300 nm broadband filament spectra generated by pulses with several times the critical power for filamentation. We show how the statistics vary from a near-Gaussian distribution in the vicinity of the pump to a long tailed “L-shaped” distribution at the short wavelength and long wavelength edges. The results are interpreted in terms of pump noise transfer via self-phase modulation.
TL;DR: In this article, the authors showed that the clamped intensity along the propagation direction does not exceed 30% of the global intensity maximum for femtosecond pulse filamentation in atmospheric density gases.
Abstract: In the course of femtosecond pulse filamentation in atmospheric density gases, the peak intensity is always limited by optical-field-induced ionization. This intensity clamping phenomenon is universal in all the cases we studied, namely, single and multiple filament regimes with and without external focusing using pulses of up to subpetawatt level. Even in the tight focusing cases, the clamped intensity along the propagation direction does not exceed 30% of the global intensity maximum. The remarkable shot-to-shot stability of the clamped intensity (better than 1% of the maximum value) is revealed both experimentally and numerically in a single filament regime in air.
TL;DR: This work has experimentally demonstrated short lived plasma channels generated through filamentation of femtosecond laser pulses in air can be revived after several milliseconds by a delayed nanosecond pulse by focusing the nanose Cond laser with an axicon.
Abstract: Short lived plasma channels generated through filamentation of femtosecond laser pulses in air can be revived after several milliseconds by a delayed nanosecond pulse. Electrons initially ionized from oxygen molecules and subsequently captured by neutral oxygen molecules provide the long-lived reservoir of low affinity allowing this process. A Bessel-like nanosecond-duration laser beam can easily detach these weakly bound electrons and multiply them in an avalanche process. We have experimentally demonstrated such revivals over a channel length of 50 cm by focusing the nanosecond laser with an axicon.
TL;DR: In this article, a two-color laser-induced femtosecond filamentation was employed to generate high energy terahertz emission in air with high energy pump by controlling the pump pulse duration, more than four times enhancement was obtained when compared with a Fourier transform-limited pump.
Abstract: Two-color laser-induced femtosecond filamentation was employed to generate high energy terahertz emission in air with high energy pump. By controlling the pump pulse duration, more than four times enhancement in terahertz pulse energy has been obtained when compared with a Fourier transform-limited pump. Multiple filaments’ dynamics might be responsible for the terahertz enhancement. Superbroadband terahertz pulse with energy up to 2 μJ was generated using loose focusing condition, while the maximum terahertz pulse energy in the frequency range below 5.5 THz was around 60 nJ.
TL;DR: By chirping the pulses, the longitudinal range of the generated plasma channels can be extended relative to filaments generated by fully compressed, transform-limited femtosecond pulses, and there is a clear correlation between the extent of filamentation and the intensity of the on-axis emission by the femTosecond Bessel-Gauss beam.
Abstract: We report experimental results on ultrafast filamentation with temporally chirped femtosecond Bessel-Gauss beams. We find that by chirping the pulses, the longitudinal range of the generated plasma channels can be extended relative to filaments generated by fully compressed, transform-limited femtosecond pulses. We find a clear correlation between the extent of filamentation and the intensity of the on-axis emission by the femtosecond Bessel-Gauss beam. The on-axis emission is negligible for fully compressed pulses, but it can become quite substantial (up to 10% of the input pulse energy) when chirped pulses are used. Under certain conditions, the on-axis emission becomes sufficient for generating its own plasma channel thus resulting in extended filamentation. This effect may offer means of remote control over filament formation with femtosecond Bessel-Gauss beams. We identify a four-wave mixing process, enhancement of which is likely to result in a maximum of the on-axis emission, and derive a simple expression for estimating the duration of the chirped pulse that is required for such enhancement. Our estimations are in good agreement with the experiment.
TL;DR: Calculations with subcycle precision of laser-driven filamentation in argon show that the laser peak intensity can exceed the clamping intensity by a factor of 3 during recurring spikes which can last over several centimeters of propagation.
Abstract: We present calculations with subcycle precision of laser-driven filamentation in argon which show that the laser peak intensity can exceed the clamping intensity by a factor of 3 during recurring spikes which can last over several centimeters of propagation. The high intensity occurs during a few-femtosecond subpulse in the trailing edge of the main pulse and gives rise to isolated 500 attosecond, 2 pJ pulses which can be extracted from the filament. We also show that the high harmonic radiation emerging from the filament is an excellent diagnostic of the intensity spikes.
TL;DR: Third-harmonic generation during filamentation of IR femtosecond laser pulses in air experiences strong spatial reshaping and conversion enhancement when a thin plasma string created by another femTosecond pulse is introduced perpendicularly to the filament's path.
Abstract: The process of third-harmonic generation during the filamentation of intense IR femtosecond laser pulses in air is investigated experimentally. It is shown that the introduction of a thin plasma string created by another femtosecond pulse, perpendicularly to the filament's path, dramatically reshapes the third-harmonic beam into a Bessel-like far-field distribution, while at the same time significantly enhances, up to 250 times, its conversion efficiency.
TL;DR: This work proposes to exploit a self-focusing effect in the atmosphere to assist delivering powerful laser beams and demonstrates that when the self -focusing length is comparable with the atmosphere height, the catastrophic self- focusing can be greatly suppressed and a smooth compression of the whole beam is possible.
Abstract: We propose to exploit a self-focusing effect in the atmosphere to assist delivering powerful laser beams from orbit to the ground. We demonstrate through numerical modeling that when the self-focusing length is comparable with the atmosphere height the spot size on the ground can be reduced well below the diffraction limits without beam quality degradation. The density variation suppresses beam filamentation and provides the self-focusing of the beam as a whole. The use of light self-focusing in the atmosphere can greatly relax the requirements for the orbital optics and ground receivers.
TL;DR: The filamentation process and the produced plasma strings are tailored and an important terahertz pulse shortening is found for plasma strings with uniform electron density.
Abstract: We study the generation of intense terahertz pulses produced by two-color laser pulse filamentation in air. We tailor the filamentation process and the produced plasma strings and study how the generated terahertz field is modified. An important terahertz pulse shortening is found for plasma strings with uniform electron density.
TL;DR: In this paper, the creation of volume plasma density gratings in air by temporally overlapped high-intensity IR femtosecond laser pulses is demonstrated experimentally, and diffraction properties of various probe beams are recovered including its thickness and refractive index modulation, as well as its decay dynamics.
Abstract: The creation of volume plasma density gratings in air by temporally overlapped high-intensity IR femtosecond laser pulses is demonstrated experimentally. Through the diffraction of various probe beams the plasma grating properties are recovered including its thickness and refractive index modulation, as well as its decay dynamics. The diffraction properties of these plasma photonic devices suggest that they can be used in applications involving high intensity lasers, such as filamentation, where no physical objects can be placed in the path of the laser beams.
TL;DR: In this article, an experimentally and theoretically investigated approach for the generation of ultrashort ultraviolet (uv) pulses by using nonlinear frequency conversion through filamentation was proposed. But the results indicated that the pressure dependence of the conversion efficiency cannot be explained by a one-dimensional model.
Abstract: Generation of ultrashort ultraviolet (uv) pulses by using nonlinear frequency conversion through filamentation was experimentally and theoretically investigated. By gently focusing second harmonic and fundamental Ti:sapphire laser pulses into gases, ultrashort uv pulses were efficiently generated by four-wave mixing processes through filamentation. The pressure dependence of the conversion efficiency cannot be explained by a one-dimensional model, but calculation of multicolor filament by a three-dimensional model was successful. The simulation result indicates a broad scalability of the scheme for frequency conversion of ultrashort pulses. The generated two-color uv pulses (200 and 260 nm) were successfully compressed down to $\ensuremath{\sim}15\text{ }\text{fs}$.
TL;DR: In this article, the propagation of focused femtosecond laser pulses with supercritical peak powers in air has been investigated by the methods of optical visualization, profilometry and calorimetry.
Abstract: The propagation of focused femtosecond laser pulses with supercritical peak powers in air has been investigated by the methods of optical visualization, profilometry, and calorimetry. Laser pulses with supercritical powers create a bundle of submillimeter filaments with a diameter of about 5 µm ahead of the lens focus; the maximum number of filaments in the beam cross section and their length increase linearly and sublinearly, respectively, with the radiation peak power. The optical visualization and calorimetry indicate that the plasma channels of filaments are optical contrast (a plasma density of 1018–1019 cm−3), ensuring the refraction of laser radiation incident on them.
TL;DR: In this article, the authors demonstrate the generation of supercontinuum with controllable cutoff extension in ultraviolet spectral region through femtosecond filamentation in parallel aligned molecules, which results in a self-cleaned beam profile by attracting almost all the energy into a single core.
Abstract: We demonstrate the generation of supercontinuum with controllable cutoff extension in ultraviolet spectral region through femtosecond filamentation in parallel aligned ${\text{CO}}_{2}$ molecules. The additional cross-focusing effect from the quantum wake of impulsive molecular alignment and the subsequently enhanced self-phase-modulation as well as self-steepening and space-time focusing play important roles for the observed supercontinuum generation, which also result in a self-cleaned beam profile by attracting almost all the energy into a single core.
TL;DR: In this article, a femtosecond laser probe pulse can be readily controlled by properly matching it to the quantum revivals of pre-aligned molecules prepared through impulsive rotational Raman excitation with an advancing ultrashort pump pulse.
Abstract: We show that the filamentation dynamics of a femtosecond laser probe pulse can be readily controlled by properly matching it to the quantum revivals of pre-aligned molecules prepared through impulsive rotational Raman excitation with an advancing ultrashort pump pulse. Several features of the filamentation process including supercontinuum generation, the length of the plasma channel generated in the wake of the filament, the associated secondary radiations and the multiple filamentation pattern are all easily modified by tuning the cross phase modulation induced by the field-free revivals of molecular alignment, through the delay between the pump and the probe pulses. We show that molecular alignment can also be used to generate conical waves with extremely short intensity spike called shocked X-waves and to further tune the frequency of a few-cycle laser pulse in the wake of a self-guided intense filament.
TL;DR: It is demonstrated for the first time that input polarisation control inducing one single filamentation is a very robust technique to accurately control the filamentation dynamics enhancing throughput energy of the supercontinuum generation up to 1.2 millijoule.
Abstract: We demonstrate for the first time that input polarisation control inducing one single filamentation is a very robust technique to accurately control the filamentation dynamics enhancing throughput energy of the supercontinuum generation up to 1.2 millijoule. Reaching the above-millijoule regime opens the way to post-compression of multi-terawatt laser pulses.
TL;DR: Numerical solutions under parameters close to the fast ignition scenario (FIS) show that the CFI growth rate can be enhanced by 2 orders of magnitude instead of being suppressed in the dense region, which is potentially significant for the target heating in the FIS.
Abstract: The collisional effects on the current-filamentation instability (CFI) and the two-stream instability (TSI), which appear as a relativistic intense electron beam penetrating into a cold dense plasma, are investigated. It is shown that the growth rate of the CFI mode is first attenuated and then enhanced by the collisional effects as the density ratio of the background plasma to the beam increases. Meanwhile, the maximum CFI growth rate is shifted to the long-wavelength region due to both the bulk plasma density increase and the collisional effects, resulting in larger filaments formation. On the other hand, collisional effects mainly attenuate the TSI and finally stabilize it. Numerical solutions under parameters close to the fast ignition scenario (FIS) are given, which show that the CFI growth rate can be enhanced by 2 orders of magnitude instead of being suppressed in the dense region. Therefore, the CFI-induced electron filaments formation and the resultant kinetic anomalous heating are potentially significant for the target heating in the FIS.
TL;DR: In this article, a simple interference model is proposed for conical emission frequency-angular spectrum formation during the filamentation of femtosecond laser pulses in a nonlinear dispersive medium.
Abstract: A simple interference model is proposed for conical emission frequency-angular spectrum formation during the filamentation of femtosecond laser pulse in a nonlinear dispersive medium. The model allows to obtain analytical expressions for frequency-angular distributions of the supercontinuum spectral components of pulses at different wavelengths in media with arbitrary material dispersion law. The model reproduces the supercontinuum frequency-angular spectrum transformation for the case of laser pulse splitting into several subpulses and for multiple refocusing of the light field in filament. Frequency-angular spectra analytically calculated from the proposed interference model are in good agreement with the results of numerical simulations performed for the filamentation of femtosecond laser pulses in fused silica.
TL;DR: In this paper, a systematic study as a function of incident power enables us to extract quantitative information on laser intensity within the condensed medium, the electron density and the six-photon absorption cross section.
Abstract: Filamentation occurs within a 1.5 cm-long crystal of BaF2 during the propagation of intense, ultrashort (40 fs) pulses of 800 nm light; a systematic study as a function of incident power enables us to extract quantitative information on laser intensity within the condensed medium, the electron density and the six-photon absorption cross section. At low incident power, a single filament is formed within the crystal; two or more filaments are observed along the direction transverse to laser propagation at higher incident powers. Further, due to fluorescence from six-photon absorption (6PA), we are able to map the intensity variation in the focusing–refocusing cycles along the direction of laser propagation. At still higher incident powers, we observe splitting of multiple filaments. By measuring the radius (Lmin ) of single filament inside BaF2, we obtain estimates of peak intensities (Imax ) and electron densities (ρmax ) to be 3.26×1013 W cm−2 and 2.81×1019 cm−3, respectively. Use of these values enables us to deduce that the 6PA cross-section in BaF2 is 0.33×10−70 cm12 W−6 s−1.
TL;DR: The terahertz radiation produced by a 2-color femtosecond laser scheme strongly saturates and develops an oscillatory behavior with increasing power of the driving femtosescond laser pulses, explained by the formation of a plasma channel due to filamentation.
Abstract: The terahertz radiation produced by a 2-color femtosecond laser scheme strongly saturates and develops an oscillatory behavior with increasing power of the driving femtosecond laser pulses. This is explained by the formation of a plasma channel due to filamentation. Due to dispersion inside the filament and the Gouy phase shift, the phase difference between the 800 nm and 400 nm pulses varies along this plasma emitter. As a result, the local THz radiations generated along the filament interfere destructively or constructively, which manifests itself in the form of Maker fringes.
TL;DR: The supercontinuum generation through femtosecond filamentation is studied by using the quantum wake of the prealigned diatomic molecules of O(2) and N(2), where significant ultraviolet extension of the generatedsupercontinuum is attributed to the additional cross-focusing effect around parallel revival of molecular alignment and the consequent self-steepening as well as space-time focusing effect.
Abstract: We study the supercontinuum generation through femtosecond filamentation by using the quantum wake of the prealigned diatomic molecules of O2 and N2, where significant ultraviolet extension of the generated supercontinuum is attributed to the additional cross-focusing effect around parallel revival of molecular alignment and the consequent self-steepening as well as space-time focusing effect. Due to the discrepancy of the polarizabilities between O2 and N2 molecules, the spectral ultraviolet extension of the generated supercontinuum is more noticeable in molecular O2 than that in N2, and an extended supercontinuum spectrum from 370 to 900 nm is observed in O2 of 2 atm. The detailed dependence of the generated supercontinuum on the pump intensity for molecular alignment and gas pressure of O2 and N2 molecules are performed.