Showing papers on "Filamentation published in 2004"
TL;DR: In this article, a carrier-envelope offset (CEO) phase locked few-cycle pulses are generated using self-guiding of intense 43-fs, 0.84 mJ optical pulses during propagation in a transparent noble gas.
Abstract: Intense, well-controlled light pulses with only a few optical cycles start to play a crucial role in many fields of physics, such as attosecond science. We present an extremely simple and robust technique to generate such carrier-envelope offset (CEO) phase locked few-cycle pulses, relying on self-guiding of intense 43-fs, 0.84 mJ optical pulses during propagation in a transparent noble gas. We have demonstrated 5.7-fs, 0.38 mJ pulses with an excellent spatial beam profile and discuss the potential for much shorter pulses. Numerical simulations confirm that filamentation is the mechanism responsible for pulse shortening. The method is widely applicable and much less sensitive to experimental conditions such as beam alignment, input pulse duration or gas pressure as compared to gas-filled hollow fibers.
564 citations
TL;DR: In this article, the authors demonstrate remote elemental analysis at distances up to 90m, using a laser-induced breakdown spectroscopy scheme based on filamentation induced by the nonlinear propagation of unfocused ultrashort laser pulses.
Abstract: We demonstrate remote elemental analysis at distances up to 90m, using a laser-induced breakdown spectroscopy scheme based on filamentation induced by the nonlinear propagation of unfocused ultrashort laser pulses. A detailed signal analysis suggests that this technique, remote filament-induced breakdown spectroscopy, can be extended up to the kilometer range.
248 citations
TL;DR: In this paper, the authors report long-range self-channeling in air of multiterawatt femtosecond laser pulses with large negative initial chirps, and show that the peak intensity in the light channels is at least one order of magnitude lower than required for multiphoton ionization of air molecules.
Abstract: We report long-range self-channeling in air of multiterawatt femtosecond laser pulses with large negative initial chirps. The peak intensity in the light channels is at least one order of magnitude lower than required for multiphoton ionization of air molecules. A detailed comparison is made between experiments and realistic 3+1-dimensional numerical simulations. It reveals that the mechanism limiting the growth of intensity by filamentation is connected with broken revolution symmetry in the transverse diffraction plane.
198 citations
TL;DR: It is shown that it is possible to organize regular filamentation patterns in air by imposing either strong field gradients or phase distortions in the input-beam profile of an intense femtosecond laser pulse, and for the first time that a control of the transport of high intensities over long distances may be achieved by forcing this well ordered propagation regime.
Abstract: We show that it is possible to organize regular filamentation patterns in air by imposing either strong field gradients or phase distortions in the input-beam profile of an intense femtosecond laser pulse. A comparison between experiments and 3+1 dimensional numerical simulations confirms this concept and shows for the first time that a control of the transport of high intensities over long distances may be achieved by forcing this well ordered propagation regime. In this case, deterministic effects prevail in multiple femtosecond filamentation, and no transition to the optical turbulence regime is obtained [Mlejnek et al., Phys. Rev. Lett. 83, 2938 (1999)].
191 citations
TL;DR: This study investigates the linear stability of the system formed by an electron beam and its return plasma current within a general framework, namely, for any orientation of the wave vector k with respect to the beam and without any a priori assumption on the orientation ofThe electric field withrespect to k .
Abstract: We investigate the linear stability of the system formed by an electron beam and its return plasma current within a general framework, namely, for any orientation of the wave vector k with respect to the beam and without any a priori assumption on the orientation of the electric field with respect to k . We apply this formalism to three configurations: cold beam and cold plasma, cold beam and hot plasma, and cold relativistic beam and hot plasma. We proceed to the identification and systematic study of the two branches of the electromagnetic dispersion relation. One pertains to Weibel-like beam modes with transverse electric proper waves. The other one refers to electric proper waves belonging to the plane formed by k and the beam, it divides between Weibel-like beam modes and a branch sweeping from longitudinal two-stream modes to purely transverse filamentation modes. For this latter branch, we thoroughly investigate the intermediate regime between two-stream and filamentation instabilities for arbitrary wave vectors. When some plasma temperature is allowed for, the system exhibits a critical angle at which waves are unstable for every k . Besides, in the relativistic regime, the most unstable mode on this branch is reached for an oblique wave vector. This study is especially relevant to the fast ignition scenario as its generality could help clarify some confusing linear issues of present concern. This is a prerequisite towards more sophisticated nonlinear treatments.
173 citations
TL;DR: The filamentation of femtosecond light pulses in air is numerically and experimentally investigated for beam powers reaching several TW and evolution of the filament patterns can be qualitatively reproduced by an averaged-in-time (2D+1)-dimensional model derived from the propagation equations for ultrashort pulses.
Abstract: The filamentation of femtosecond light pulses in air is numerically and experimentally investigated for beam powers reaching several TW. Beam propagation is shown to be driven by the interplay between intense, robust spikes created by the defects of the input beam and random nucleation of light cells. Evolution of the filament patterns can be qualitatively reproduced by an averaged-in-time $(2\mathrm{D}+1)$-dimensional model derived from the propagation equations for ultrashort pulses.
173 citations
TL;DR: It is shown that Tec1, a cofactor of Ste12 for the expression of filamentation genes, is rapidly degraded during pheromone response and Fus3 inhibits filamentous growth during mating by degrading Tec1.
143 citations
TL;DR: This Letter provides what is believed to be the first experimental evidence of suppression of the number of filaments for high-intensity laser pulses propagating in air by beam astigmatism and shows that the number, pattern, and spatial stability of the filaments can be controlled by varying the angle that a focusing lens makes with the axial direction of propagation.
Abstract: In this Letter we provide what is believed to be the first experimental evidence of suppression of the number of filaments for high-intensity laser pulses propagating in air by beam astigmatism. We also show that the number, pattern, and spatial stability of the filaments can be controlled by varying the angle that a focusing lens makes with the axial direction of propagation. This new methodology can be useful for applications involving atmospheric propagation, such as remote sensing.
123 citations
TL;DR: In this paper, the authors provided the first experimental evidence that multiple filamentation of ultrashort pulses can be induced by input beam ellipticity, which is called annular rings surrounding the central filament.
Abstract: We provide what is to our knowledge the first experimental evidence that multiple filamentation (MF) of ultrashort pulses can be induced by input beam ellipticity. Unlike noise-induced MF, which results in complete beam breakup, the MF pattern induced by small input beam ellipticity appears as a result of nucleation of annular rings surrounding the central filament. Moreover, our experiments show that input beam ellipticity can dominate the effect of noise (transverse modulational instability), giving rise to predictable and highly reproducible MF patterns. The results are explained with a theoretical model and simulations.
116 citations
TL;DR: Qualitative features in the evolution of the filament patterns are reproduced by the 2D reduced model, and these features are compared with space- and time-resolved numerical simulations.
Abstract: The filamentation of ultrashort pulses in air is investigated theoretically and experimentally. From the theoretical point of view, beam propagation is shown to be driven by the interplay between random nucleation of small-scale cells and relaxation to long waveguides. After a transient stage along which they vary in location and in amplitude, filaments triggered by an isotropic noise are confined into distinct clusters, called "optical pillars," whose evolution can be approximated by an averaged-in-time two-dimensional (2D) model derived from the standard propagation equations for ultrashort pulses. Results from this model are compared with space- and time-resolved numerical simulations. From the experimental point of view, similar clusters of filaments emerge from the defects of initial beam profiles delivered by the Teramobile laser facility. Qualitative features in the evolution of the filament patterns are reproduced by the 2D reduced model.
110 citations
TL;DR: Multilevel phase-type diffractive lenses were fabricated by translating a filament of a femtosecond laser pulse into three-dimensional space inside synthesized silica inside synthesised silica by use of a multi-level approximation to a kinoform lens.
Abstract: Multilevel phase-type diffractive lenses were fabricated by translating a filament of a femtosecond laser pulse into three-dimensional space inside synthesized silica. The profile of the lenses was designed by use of a multilevel approximation to a kinoform lens. Two-level diffractive lenses with multiple layers along the optical axis provided a maximum efficiency of 37.6% at a wavelength of 632.8 nm. A four-level diffractive lens provided a maximum efficiency of 56.9%. The lenses fabricated with filamentation were free from birefringence.
01 Jan 2004
TL;DR: In this article, a carrier-envelope offset (CEO) phase locked few-cycle pulses are generated using self-guiding of intense 43-fs, 0.84 mJ opti- cal pulses during propagation in a transparent noble gas.
Abstract: Intense, well-controlled light pulses with only a few optical cycles start to play a crucial role in many fields of physics, such as attosecond science. We present an extremely simple and robust technique to generate such carrier-envelope offset (CEO) phase locked few-cycle pulses, relying on self-guiding of intense 43-fs, 0.84 mJ opti- cal pulses during propagation in a transparent noble gas. We have demonstrated 5.7-fs, 0.38 mJ pulses with an excellent spatial beam profile and discuss the potential for much shorter pulses. Numerical simulations confirm that filamentation is the mechan- ism responsible for pulse shortening. The method is widely applicable and much less sensitive to experimental conditions such as beam alignment, input pulse duration or gas pressure as compared to gas-filled hollow fibers.
TL;DR: Simple apertures such as slits and meshes inserted in the beam path of a powerful Ti:Sapphire laser pulse are suitable to produce stable 1-D and 2-D arrays of filaments in liquids to overcome the inherent beam irregularities which naturally give rise to random small-scale multiple filamentations.
Abstract: Simple apertures such as slits and meshes inserted in the beam path of a powerful Ti:Sapphire laser pulse are suitable to produce stable 1-D and 2-D arrays of filaments in liquids. The thus imposed intensity gradients and diffraction patterns can overcome the inherent beam irregularities which naturally give rise to random small-scale multiple filamentations. This method is visualized by means of two photon fluorescence imaging.
TL;DR: In this article, the propagation of ultra-short laser pulses in air under the influence of diffraction, group velocity dispersion, Kerr nonlinearity, stimulated Raman scattering, ionization, and plasma wakefield excitation is analyzed.
Abstract: Recent theoretical, computational, and experimental work carried out at the Naval Research Laboratory on the propagation of ultra-short laser pulses in air is presented. Fully time-dependent, three-dimensional, nonlinear equations describing the propagation of laser pulses in air under the influence of diffraction, group velocity dispersion,Kerr nonlinearity, stimulated Raman scattering,ionization, and plasma wakefield excitation are presented and analyzed. The propagation code, HELCAP [P. Sprangle, J. R. Penano, and B. Hafizi, Phys. Rev. E 66, 046418 (2002)], is used to simulate the propagation of laser pulses in air under the influence of the physical processes mentioned above. Simulations of laser filamentation together with experimental measurements are used to confirm that the filamentation process is dependent on pulse duration. An equilibrium configuration for optical and plasma filaments in air is derived and the dynamic guiding and spectral broadening of a laser pulse is modeled. The effect of atmospheric turbulence on nonlinear self-focusing is demonstrated. Simulations of a recent electromagnetic pulse (EMP) generation experiment are also presented and the efficiency of EMP generation is determined and found to be extremely small.
TL;DR: Observations are consistent with a laser-generated beam of relativistic electrons propagating through the target, which is subsequently fragmented by a Weibel-like instability in the low-density plasma at the rear.
Abstract: Filamented electron beams have been observed to be emitted from the rear of thin solid targets irradiated by a high-intensity short-pulse laser when there is low-density plasma present at the back of the target. These observations are consistent with a laser-generated beam of relativistic electrons propagating through the target, which is subsequently fragmented by a Weibel-like instability in the low-density plasma at the rear. These measurements are in agreement with particle-in-cell simulations and theory, since the filamentation instability is predicted to be dramatically enhanced when the electron beam density approaches that of the background plasma.
TL;DR: It is shown that the effects of electron-electron collisions and thermal spread lower the growth rate of the relativistic Weibel instability, which is essential for transport of homogeneous electron beam produced by the interaction of high power laser pulses with plasma.
Abstract: I theoretically found eigenmodes and growth rates of relativistic current filamentation instability in collisional regimes, deriving a generalized dispersion relation from self-consistent beam-Maxwell equations. For symmetrically counterstreaming, fully relativistic electron currents, the collisional coupling between electrons and ions creates the unstable modes of growing oscillation and wave, which stand out for long-wavelength perturbations. In the stronger collisional regime, the growing oscillatory mode tends to be dominant for all wavelengths. In the collisionless limit, those modes vanish, while maintaining another purely growing mode that exactly coincides with a standard relativistic Weibel mode. It is also shown that the effects of electron-electron collisions and thermal spread lower the growth rate of the relativistic Weibel instability. The present mechanisms of filamentation dynamics are essential for transport of homogeneous electron beam produced by the interaction of high power laser pulses with plasma.
TL;DR: In this paper, the interplay between self-focusing and filamentation of the laser pulses is analyzed for a broad range of focusing conditions, and it is shown that even in the case of very tight focusing, filamentation is observed as evidenced by the scanning electron microscope (SEM) pictures.
TL;DR: In this paper, a comparative study of numerical simulations and experiments on the spatiotemporal dynamics and emission characteristics of quantum-well and quantum-dot lasers of identical structure is presented.
Abstract: We present a comparative study of numerical simulations and experiments on the spatiotemporal dynamics and emission characteristics of quantum-well and quantum-dot lasers of identical structure. They show that, in the quantum-dot laser, the strong localization of carrier inversion and the small amplitude-phase coupling enable a significant improvement of beam quality compared to quantum-well lasers of identical geometry. Near-field profiles and beam quality (M-2) parameters calculated on the basis of time-dependent effective Maxwell-Bloch equations into which the physical properties of the active media are included via space-dependent material parameters, effective time constants, and matrix elements are fully confirmed by experimental measurements. Together they indicate that, in the quantum-dot laser, the strong localization of carrier inversion and the small amplitude-phase coupling enable a significant improvement of beam quality compared with quantum-well lasers of identical geometry. (C) 2004 American Institute of Physics.
TL;DR: In this article, the authors derived equations for nonlinearly interacting intense laser pulses and an electron-positron plasma, taking into account the combined action of the relativistic particle mass increase and the plasma density profile modification.
TL;DR: In this article, the behavior of time-periodic three-dimensional incompressible flows modelled by 3D volume-preserving maps in the presence of a leakage is studied.
Abstract: We study the behavior of time-periodic three-dimensional incompressible flows modelled by three-dimensional volume-preserving maps in the presence of a leakage. The distribution of residence times, and the chaotic saddle together with its stable and unstable invariant manifolds are described and characterized. They shed light on typical filamentation of chaotic flows whose local stable and unstable manifolds are always of different character (plane or line). We point out that leaking is a useful method which sheds light on typical filamentation of chaotic flows. In particular, the topology depends on the number of local expanding directions, and is the same in the leaked system as in the closed flow.
TL;DR: In this article, the authors monitored the space-time transformation of a 150-fs pulse undergoing self-focusing and filamentation in water, by means of the nonlinear gating technique.
Abstract: We have monitored the space-time transformation of a 150-fs pulse undergoing self-focusing and filamentation in water, by means of the nonlinear gating technique. We have observed that pulse splitting and subsequent recombination apply to axial temporal intensity only, whereas the space-integrated pulse profile preserves its original shape.
TL;DR: In this article, the authors investigated the transverse modulational instability in undoped nematic liquid crystals and observed the one-dimensional development of transverse patterns eventually leading to beam breakup, filamentation, and spatial solitons.
Abstract: Transverse modulational instability is investigated in undoped nematic liquid crystals, a highly nonlocal material system encompassing a reorientational nonlinear response. Using an elliptic Gaussian excitation, we observe the one-dimensional development of transverse patterns eventually leading to beam breakup, filamentation, and spatial solitons, both in the cases of spatially coherent and partially incoherent excitations.
TL;DR: This study investigates the frequencies, conditions, and characteristics of a filamentous P. aeruginosa at single cell and single chromosome resolutions and shows that filamentous cells (elongated rods) contain multiple copies of the cell's chromosome.
Abstract: Pseudomonas aeruginosa is a leading opportunistic pathogen in human infections, and it is renowned for its intrinsic resistance to structurally and functionally unrelated antibiotics. Filamentation induced by antibiotics appears to trigger bacteria to depart from a normal growth phase and enter a stationary growth phase. As antibiotic concentrations decline below a therapeutic range, filamentous bacteria begin to divide normally, leading to a more rapid regrowth of the bacteria. Furthermore, filamentous bacteria are associated with an increase in endotoxin release. Moreover, the immune system of a patient needs to cope with uncharacteristic filamentous bacteria. Thus, it is biologically and clinically significant to study and understand bacterial filamentation. In this study, we investigate the frequencies, conditions, and characteristics of a filamentous P. aeruginosa at single cell and single chromosome resolutions. Our results show that filamentous cells (elongated rods) contain multiple copies of the cell's chromosome. It appears that the unsuccessful segregation of replicated chromosomes in an individual cell accompanies the formation of undivided filamentous cells. The quantity of chromosomes and the length of the filamentous wild-type cells increase as the chloramphenicol concentration increases to 50 and 250 microg/mL, suggesting that chloramphenicol induces the filamentation. Filamentation in three strains of P. aeruginosa depends on the expression level of efflux pump (MexAB-OprM) and the minimum inhibitory concentration of chloramphenicol. This study also opens up the new possibility of real-time monitoring of modes of actions of antibiotics in live cells with both temporal and spatial resolution.
TL;DR: To segregate functions of Bmh1p that are required for optimal growth and the different filamentation pathways in C. albicans, site-directed nucleotide substitutions were made in the C.Albicans BMH1 gene to allow the identification of 14-3-3 target interactions and correlate the individual functions of H1p to cellular processes involved in pathogenesis.
Abstract: The opportunistic fungal pathogen Candida albicans has the ability to exploit diverse host environments and can either reside commensally or cause disease. In order to adapt to its new environment it must respond to new physical conditions, nutrient sources, and the host immune response. This requires the co-regulation of multiple signalling networks. The 14-3-3 family of proteins is highly conserved in all eukaryotic species. These proteins regulate signalling pathways involved in cell survival, the cell cycle, and differentiation, and effect their functions via interactions with phosphorylated serines/threonines. In C. albicans there is only one 14-3-3 protein, Bmh1p, and it is required for vegetative growth and optimal filamentation. In order to dissect separate functions of Bmh1p in C. albicans, site-directed nucleotide substitutions were made in the C. albicans BMH1 gene based on studies in other species. Putative temperature-sensitive, ligand-binding and dimerization mutants were constructed. In addition two mutant strains identified through random mutagenesis were analysed. All five mutant strains demonstrated varying defects in growth and filamentation. This paper begins to segregate functions of Bmh1p that are required for optimal growth and the different filamentation pathways. These mutant strains will allow the identification of 14-3-3 target interactions and correlate the individual functions of Bmh1p to cellular processes involved in pathogenesis.
TL;DR: In this paper, backscattered fluorescence from nitrogen molecules from filaments induced by intense, ultrafast Ti:sapphire laser pulses increases exponentially with an increase in the length of the filament.
Abstract: Backscattered fluorescence from nitrogen molecules from filaments induced by intense, ultrafast Ti:sapphire laser pulses increases exponentially with an increase in the length of the filament. This shows that the fluorescence undergoes amplified spontaneous emission along the filament direction, a finding that could have applications in lightning discharge control and remote sensing.
TL;DR: In this paper, a ray-tracing scheme is proposed to simulate the non-linear propagation of ultra-short pulses, and the results are in good agreement with experimental data and numerical solving of the nonlinear Schrodinger equation in both the self-focusing and the filamentation regions.
Abstract: 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.
TL;DR: In this article, the growth of a Gaussian perturbation on a uniform plane wave front of an Alfven wave has been investigated and the effect of the nonlinear coupling between the main AW and the perturbations has been studied.
Abstract: This paper presents an investigation of the growth of a Gaussian perturbation on a uniform plane wave front of an Alfven wave (AW). The effect of the nonlinear coupling between the main AW and the perturbation has been studied. The dynamical equation for the field of the perturbation has been established and its semianalytical solution has been obtained in low (β≪me/mi) and high (β≫me/mi) β cases (β≪1). The critical field of the perturbation has been evaluated for the given size of the perturbation for its filamentation process (hot spot formation). Nonlinear evolution of the perturbation into filamentary structures and its dependence on various parameters of the solar wind and corona has been investigated in detail.
TL;DR: In this paper, the nonlinear propagation of laser beams, smoothed by spatial and temporal bandwidth, near the critical density surface of direct-drive inertial confinement fusion targets has been modeled.
Abstract: The nonlinear propagation of laser beams, smoothed by spatial and temporal bandwidth, near the critical density surface of direct-drive inertial confinement fusion targets has been modeled. The interplay between filamentation and forward and backward stimulated Brillouin scattering (SBS) is described in the presence of light reflected from the critical density surface and high absorption of light near the critical density. The spectrum of backscattered light develops a red shift due to SBS, which can be seeded by the reflection of light from the critical surface. The intensity of backscattered light decreases moderately as the bandwidth of smoothing by spectral dispersion is increased.
09 Dec 2004
TL;DR: In this paper, the authors measured the thresholds of self-focusing and filamentation on the shape of index modifications for the waveguides written perpendicularly under a very tight focusing, together with the observed pulse refocusing.
Abstract: The interaction of focused femtosecond laser pulses at 810 nm and 1 kHz repetition rate with bulk fused silica is studied. Ultra-short pulse-induced optical breakdown (OB) and filamentation (FL) are two electronic excitation mechanisms leading to photo-structural modifications (e.g. uniform refractive index change) based on plasma formation inside transparent materials. Beyond a certain input power associated with the focusing geometry, the localized OB plasma formed around the geometrical focus can lead to structural damage characterized by a void-like morphology with a non-uniform high index contrast, while the modifications caused by plasma generation in the FL process usually give rise to a moderate index change. However, the formation of multiple filaments at certain higher powers using long focal lengths might be a drawback for waveguide applications. In this work, the thresholds of FL and its associated supercontinuum (SC), OB, and structural damage are measured as a function of focusing geometry. Consequently, various tracks were written and characterized in terms of writing geometry (parallel or perpendicular), focusing condition, pulse energy, and translation speed. In the parallel configuration, waveguides with a circular core of 3-6 m, and index change as large as 5 x 10-3 were achieved. Furthermore, the influence of self-focusing and filamentation on the shape of index modifications for the waveguides written perpendicularly under a very tight focusing, together with the observed pulse refocusing are also investigated.
TL;DR: In this paper, the authors investigated the growing interaction of a rippled laser beam with an electron plasma wave leading to enhanced Raman scattering and derived an expression for scattered power and the effect of externally applied magnetic field on the enhancement of scattered power.
Abstract: In the laser–plasma interaction experiments, self-focusing and filamentation affect quite a large number of other parametric processes including stimulated scattering processes. Nonlinearity considered in the present problem is the collisional type. The coupling between the main beam, ripple, and excited electron plasma wave is strong. Authors have investigated the growing interaction of a rippled laser beam with an electron plasma wave leading to enhanced Raman scattering. An expression for scattered power is derived and the effect of the externally applied magnetic field on the enhancement of scattered power is observed. From computational results, it is observed that the effect of increased intensity of the main beam leads to suppression of power associated with the Raman scattered wave.