Showing papers on "Filamentation published in 1999"
TL;DR: In this paper, it was shown that a laser beam can be strongly compressed in a plasma by stimulated Raman backscattering in a time short compared to the time scale for filamentation instabilities to develop.
Abstract: Laser beams can be strongly compressed in a plasma by stimulated Raman backscattering in a time short compared to the time scale for filamentation instabilities to develop. Such a compression should make feasible multi-MJ multi-exawatt-laser pulses technologically challenging by other means. The compression efficiency can reach nearly $100%$ at the Langmuir wave breaking limit.
373 citations
TL;DR: In this article, the propagation of high-power short-pulse laser beams over considerable distances in air is studied both experimentally and via numerical simulations Filaments are formed after 5-10 m and their propagation over distances in excess of 200 m is reported for the first time.
Abstract: The propagation of high-power short-pulse laser beams over considerable distances in air is studied both experimentally and via numerical simulations Filaments are formed after 5–10 m and their propagation over distances in excess of 200 m is reported for the first time The lateral dimensions of the filaments are found to range from about 100 μm to a few millimeters in diameter The early values of plasma electron density have been inferred to be a few times 1016 cm−3 using longitudinal spectral interferometry For 500 fs pulses and a wavelength of 1053 nm, the energy in the filament can be quite high initially (∼8 mJ) and is found to stabilize at about 15–2 mJ, after about 35 m A simple model based on the nonlinear Schrodinger equation coupled to a multiphoton ionization law appears to describe several experimental results quite well
283 citations
TL;DR: Chlamydospore formation of the fungal pathogen Candida albicans was found to depend on the Efg1 protein, which regulates the yeast-hyphal transition, and filamentation ofefg1 cph1 double mutants in microaerophilic conditions suggests a novel EFG1p/Cph1p-independent filamentation pathway in C.Albicans.
Abstract: Chlamydospore formation of the fungal pathogen Candida albicans was found to depend on the Efg1 protein, which regulates the yeast-hyphal transition. Isogenic mutants lacking EFG1 or encoding T206A and T206E variants did not differentiate chlamydospores, while cek1 , cph1 , or tpk2 mutations had no effect. Furthermore, filamentation of efg1 cph1 double mutants in microaerophilic conditions suggests a novel Efg1p/Cph1p-independent filamentation pathway in C. albicans.
130 citations
TL;DR: In this article, the spontaneous filamentation of a dielectric barrier glow discharge plasma (Townsend, not streamer breakdown), i.e., an instability of the homogeneous state has been simulated and understood with the help of a self-consistent two-dimensional fluid model.
Abstract: The spontaneous filamentation of a dielectric barrier glow discharge plasma (Townsend, not streamer breakdown), i.e., an instability of the homogeneous state has been simulated and understood with the help of a self-consistent two-dimensional fluid model of the discharge. The formation of self-organized or solitary filaments observed experimentally and described in previous papers can be explained in terms of electron and ion transport coefficients only, without including gas heating, plasma chemistry or surface effects. The conditions favoring the plasma filamentation are discussed.
125 citations
TL;DR: In this paper, the filamentation of a plasma created by a dielectric barrier discharge in conditions of low pd products was investigated both experimentally and with a two-dimensional numerical discharge model.
Abstract: The filamentation of a plasma created by a dielectric barrier discharge in conditions of low pd products (i.e., Townsend breakdown and not streamer breakdown) is investigated both experimentally and with a two-dimensional numerical discharge model. Complex stationary and dynamical domains and filaments are observed experimentally. Some of the properties of these systems are reproduced by the model.
97 citations
TL;DR: P phenotypic comparison of various filamentation mutants illustrates that cell elongation and invasion/cell-cell adhesion during filamentation are separable processes controlled by the pseudohyphal transcriptional program.
Abstract: Several lines of evidence suggest that the morphogenetic transition from the yeast form to pseudohyphae in Saccharomyces cerevisiae may be regulated by the cyclin-dependent kinase (Cdk). To examine this hypothesis, we mutated all of the G1 cyclin genes in strains competent to form pseudohyphae. Interestingly, mutation of each G1 cyclin results in a different filamentation phenotype, varying from a significant defect in cln1/cln1 strains to enhancement of filament production in cln3/cln3 strains. cln1 cln2 double mutants are more defective in pseudohyphal development and haploid invasive growth than cln1 strains. FLO11 transcription, which correlates with the level of invasive growth, is low in cln1 cln2 mutants and high in grr1 cells (defective in proteolysis of Cln1,2), suggesting that Cln1,2/Cdks regulate the pseudohyphal transcriptional program. Epistasis analysis reveals that Cln1,2/Cdk and the filamentation MAP kinase pathway function in parallel in regulating filamentous and invasive growth. Cln1 and Cln2, but not Ste20 or Ste12, are responsible for most of the elevated FLO11 transcription in grr1 strains. Furthermore, phenotypic comparison of various filamentation mutants illustrates that cell elongation and invasion/cell-cell adhesion during filamentation are separable processes controlled by the pseudohyphal transcriptional program. Potential targets for G1 cyclin/Cdks during filamentous growth are discussed.
94 citations
01 Nov 1999
TL;DR: In this paper, the amplitude-equation formalism is used to study the transverse focusing or filamentation of weakly nonlinear Alfven waves propagating in a dispersive medium.
Abstract: Transverse focusing or filamentation of weakly nonlinear Alfven waves propagating in a dispersive medium is studied using an amplitude-equation formalism. Special attention is devoted to the small-β, regime, where kinetic effects are weak and Alfven-wave trains are unstable to convective filamentation. It is shown that, according to their initial duration, focusing wave packets can collapse in a finite distance or, conversely, the focusing can be arrested by the development of magnetosonic waves, which in both cases may lead to the formation of sharp acoustic fronts. This effect, which dominates the usual longitudinal steepening, provides an efficient mechanism to heat the plasma without requiring large-amplitude waves. It can significantly contribute to the acceleration of the solar wind.
56 citations
TL;DR: Using a scanning electron microscope, pleomorphism (notably filamentation) was seen when Escherichia coli was grown under starvation conditions for 14 d on microporous silicon wafers, titanium, glass and plastic discs.
Abstract: Using a scanning electron microscope, pleomorphism (notably filamentation) was seen when Escherichia coli was grown under starvation conditions for 14 d on microporous silicon wafers, titanium, glass and plastic discs. Under these conditions, the 'standard', rod shaped cell (1-3 microns) failed to separate after division and filaments developed, some as long as 50 microns, with many showing bulbous tips. Filamentation began to occur 5 d after the imposition of starvation conditions. Dumbbell shaped cells were also observed, although apparent 'Y' and 'V'-shaped cells proved to be artefacts, caused by overlapping rods. The implications of the appearance of pleomorphism in E. coli, when grown under starvation conditions, is discussed in relation to its pathogenicity and growth in the environment.
43 citations
TL;DR: It is demonstrated that the combined longitudinal instabilities, filamentation, and propagation effects may be controlled by suitable spatially structured delayed optical feedback allowing, in particular, the control of coherent regimes in originally temporally and spatially chaotic states.
Abstract: In large high-power broad-area lasers the spatiotemporal filamentation processes and instabilities occur macroscopic as well as on microscopic scales. Numerical simulations on the basis of Maxwell- Bloch equations for large longitudinally and transversely extended semiconductor lasers reveal the internal spatial and temporal processes, providing the relevant scales on which control for stabilization consequently has to occur. It is demonstrated that the combined longitudinal instabilities, filamentation, and propagation effects may be controlled by suitable spatially structured delayed optical feedback allowing, in particular, the control of coherent regimes in originally temporally and spatially chaotic states.
41 citations
TL;DR: In this paper, a unified treatment of electron parametric instabilities driven by ultraintense laser light in plasma is described, valid for any intensity, polarization, plasma density, and scattering geometry.
Abstract: A unified treatment of electron parametric instabilities driven by ultraintense laser light in plasma is described. It is valid for any intensity, polarization, plasma density, and scattering geometry. The method is applied to linearly polarized light in both underdense plasma and overdense plasma accessible by self-induced transparency. New options arise which are hybrids of stimulated Raman scattering, the two plasmon decay, the relativistic modulational and filamentation instabilities, and stimulated harmonic generation. There is vigorous growth over a wide range of wave numbers and harmonics.
34 citations
TL;DR: A partially and a highly antire ection coated broad area laser are operated in an external cavity Fourier-optical 4f set-up to experimentally investigate transverse mode selection.
Abstract: A partially and a highly antireflection coated broad area laser are operated in an external cavity Fourier-optical 4f set-up to experimentally investigate transverse mode selection. The external cavity consists of a lens and a spatial frequency filter. Running freely the lasers show non-stationary filamentation. Placing the spatial filter unit directly onto the optical axis gives cw fundamental mode operation and a transverse shift of the spatial filter in the plane of the active region allows for selective excitation of higher order modes.
TL;DR: In this article, the authors present results of a two-dimensional hybrid simulation of the electromagnetic proton beam instability, showing that the oblique right-handed resonant modes play an important role in the structure of the quasi-parallel Earth's bow shock.
Abstract: We present results of a two-dimensional hybrid simulation of the electromagnetic proton beam instability. We show that for a case of cold and rather high density proton beam the oblique right-handed resonant modes play an important role. The interaction of these modes with the beam protons causes significant beam density fluctuations. At the nonlinear stage the oblique modes give rise to a beam filamentation. Beam filaments influence strongly the evolution of the instability. They create pulses of a strong magnetic field. These pulses share some properties of the magnetic pulsations (short, large-amplitude magnetic structures). We suppose that the oblique modes play an important role in the structure of the quasi-parallel Earth's bow shock.
TL;DR: In this paper, the safe reverse recovery limit for 3.3-kV Si power diodes using a novel optical experimental technique was measured for two temperatures at two temperatures with no temperature dependence and could not be reproduced in ordinary one-dimensional or two-dimensional (2D) device simulations.
Abstract: Measurements of the safe reverse recovery limit were performed for 3.3-kV Si power diodes using a novel optical experimental technique. In this experiment, influence of the junction termination is effectively eliminated by optical generation of a laterally-localized carrier plasma. The turn-off failures observed in measurements at two temperatures showed no temperature dependence and could not be reproduced in ordinary one-dimensional (1-D) or two-dimensional (2-D) device simulations. To simulate the stability of the current density toward current filamentation, two 1-D diodes with an area ratio 1:19 and a 10% difference in initial carrier plasma level, were simulated in parallel. This resulted in a strongly inhomogeneous current distribution, and a rapid reverse voltage fall resembling the measured turn-off failures. Inhomogeneous current distribution in these simulations appears as the current decay ceases due to impact ionization, in qualitative agreement with a current instability condition proposed by Wachutka [1991].
TL;DR: In this paper, a grating-coupled surface-emitting semiconductor laser was integrated with a focusing diffractive beamforming element, and a hyperbolic unstable resonator was used to introduce mode discrimination and suppress filamentation in a broad geometry.
Abstract: A grating-coupled surface-emitting semiconductor laser has been integrated with a focusing diffractive beamforming element. A hyperbolic unstable resonator is used to introduce mode discrimination and suppress filamentation in a broad geometry, resulting in a 200-/spl mu/m-wide coherent output. The light is focused 500 /spl mu/m above the laser surface to a spot size of 5/spl times/7 /spl mu/m. A remarkable beam stability is observed with very small spot size variation and beam-steering up to three times the threshold current under continuous operation.
TL;DR: A.A. Giulietti, A. A. Gizzi, and O. Schifano, 1 V. Biancalana, 1,4 C. Danson, 5 D. Azzopardi, E. Macchi, and E. Schofield, this article, reported that the performance of the Fisica Atomica e Molecolare (FOMC) project at the University of Pisa was poor.
Abstract: A. Giulietti, A. Macchi, E. Schifano, 1 V. Biancalana, 1,4 C. Danson, 5 D. Giulietti, L. A. Gizzi, and O. Willi Istituto di Fisica Atomica e Molecolare, CNR, Via del Giardino, 7, 56127 Pisa, Italy Scuola Normale Superiore, Pisa, Italy Istituto Nazionale Fisica della Materia, Sezione A, Universita ` di Pisa, Pisa, Italy Dipartimento di Fisica, Universita ` di Siena, Siena, Italy Central Laser Facility, Rutherford Appleton Laboratory, Chilton, United Kingdom Dipartimento di Fisica, Universita ` di Pisa, Pisa, Italy The Blackett Laboratory, Imperial College, London, United Kingdom ~Received 15 July 1998 !
TL;DR: In this paper, a method based on contour advection is introduced to quantify the formation of filament structures both equatorward and poleward of the subtropical barrier.
Abstract: A method based on contour advection is introduced that aims to quantify the formation of filaments both equatorward and poleward of the subtropical barrier. It is applied to diagnosed potential vorticity fields for every day of January and February in 1997 and 1998. An isosurface of modified potential vorticity is found to represent the region of largest isentropic gradients of potential vorticity and is hence assumed as the tropopause. Tropopause-penetrating structures (“filaments”) forming in contour-advected potential vorticity fields are identified, and statistics of the abundance of such structures are derived. Filamentation as measured by this method exhibits a large temporal variability on the scale of days to weeks. For example, tropospheric cutoff systems developing in the wake of Rossby wave breaking events cause strong filamentation to occur in the lowermost stratosphere. The timescales governing filamentation are a function of altitude, reflecting the differing types and amplitudes of waves inducing filamentation at different isentropic levels. Zonal asymmetries arise as Rossby waves favorably break near the end of the North Atlantic storm track. A difference in the intensities of filamentation in January and February of 1997 and 1998 suggests that the relatively low values of ozone in the lowermost stratosphere observed in 1997 are related to increased filamentation-induced stratosphere-troposphere exchange, compared to 1998. For example, around 30% more filaments are found in the hemispheric and bimonthly mean at the 330 K isentropic surface in January and February of 1997 than during the same months of 1998. Single events can represent most of the filamentation occurring in a month, and hence interannual variability in the frequency of filamentation can be considerable.
TL;DR: In this paper, a quasiparaxial approximation to the wave equation was proposed to analyze the propagation and stability of laser pulses in plasmas, and coupled envelope-power equations including finite pulse length effects, as well as nonlinearities, were derived and analyzed.
Abstract: Laser pulse propagation can be strongly influenced by nonlinearity effects (relativistic and/or atomic electrons), ionization processes, and finite pulse length effects. In this paper these processes are included in the analysis of the propagation and stability of intense laser pulses in plasmas. An envelope equation, which includes ionization and nonlinear effects, is derived and the spot size is found to be unstable to an ionization–modulation instability. Introducing a quasiparaxial approximation to the wave equation, a pair of coupled envelope-power equations including finite pulse length effects, as well as nonlinearities, is derived and analyzed. In addition, short laser pulses propagating in plasma channels are found to undergo an envelope modulation that is always damped in the front and initially grows in the back of the pulse. Finite pulse length effects are also shown to modify nonlinear focusing processes. Finally, it is shown that, in a partially stripped plasma, the bound electrons can significantly alter the stability of laser pulses. In the presence of both free and bound electrons, an atomic modulation instability develops that can have a growth rate substantially higher than either the conventional relativistic modulational instability or the forward Raman instability. The filamentation instability is shown to be enhanced by bound electrons while the backward Raman instability is unaffected. An example of laser wakefield acceleration to electron energies greater than 2.5 GeV in a plasma channel is described.
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TL;DR: In this article, the stability and dynamics of higher-order solitary waves in quadratic media were investigated and the existence of two qualitatively different behaviors were shown. And for positive phase mismatch the rings break up into filaments which move radially to initial ring, forming a single oscillating filament.
Abstract: We investigate stability and dynamics of higher-order solitary waves in quadratic media, which have a central peak and one or more surrounding rings. We show existence of two qualitatively different behaviours. For positive phase mismatch the rings break up into filaments which move radially to initial ring. For sufficient negative mismatches rings are found to coalesce with central peak, forming a single oscillating filament.
TL;DR: In this article, a model of filamentation in azimuthal direction for cylindrical microwave discharges is presented, which is driven by particle diffusion, caused by electron pressure gradients.
Abstract: A model of filamentation in azimuthal direction for cylindrical microwave discharges is presented. Instability is shown to be driven by particle diffusion, caused by electron pressure gradients. A "window" for the azimuthal mode numbers, where the azimuthally asymmetric modes are unstable, is shown to open if the electron density in the discharge is sufficiently high. The presented model is in reasonable agreement with experimental observations of filamentation in surface-wave-sustained discharges.
TL;DR: The kinetic theory of the stationary and nonstationary thermal filamentation instability in fully ionized plasmas is presented in this paper, where the collisionless transport limit is modeled by new transport coefficients corresponding to the convective heat flux and the temperature anisotropy.
Abstract: The kinetic theory of the stationary and nonstationary thermal filamentation instability in fully ionized plasmas is presented. The collisionless transport limit is modeled by new transport coefficients corresponding to the convective heat flux and the temperature anisotropy. It is shown, in particular, that these effects decrease the instability growth rates by about a factor of 2, in conditions typical of current experiments. These two effects, combined with the collisional absorption of the light energy by the plasma electrons, lead to a thermal growth rate comparable to the one due to the ponderomotive drive. The comparison of the results obtained in this work with the principal results established in the literature, is also presented.
01 Jan 1999
TL;DR: In this article, different asymptotic equations are derived to describe wave filamentation, depending on the level of dispersion with respect to the nonlinearity, and the amount of dissipated energy that results from the wave collapse when damping processes are retained.
Abstract: Alfven wave filamentation is an important instability as it can lead to wave collapse and thus to the formation of small scales. Different asymptotic equations are here derived to describe this phenomenon. They apply in different regimes, depending on the level of the dispersion with respect to the nonlinearity. The (scalar) nonlinear Schrodinger equation, valid when the wave is strongly dispersive, allows the study of the influence of the coupling to magneto-sonic waves on the development of the instability. This equation generalizes to a vector nonlinear Schrodinger equation when the dispersion is decreased. The amount of dissipated energy that results from the wave collapse when damping processes are retained, is also estimated in these two cases. When the dispersion is weak and comparable to the effects of the nonlinearities, a reductive perturbation expansion can be used to derive long-wave equations that generalize the DNLS equations and also contain the reduced MHD for the dynamics in the plane transverse to the propagation.
06 Aug 1999
TL;DR: In this paper, all-optical schemes for controlling complex delay-induced and spatio-temporal dynamics in multi-stripe and broad-area semiconductor lasers are presented.
Abstract: All-optical schemes for controlling complex delay-induced and spatio-temporal dynamics in multi-stripe and broad-area semiconductor lasers are presented. The underlying control-principle is based on continuous delayed optical feedback. Its influence on the general spatiotemporal dynamics of semiconductor lasers is discussed. The delayed feedback control principle allows successful control of delay-induced chaotic behavior as well as the dynamic optical filamentation in broad-area and multi-stripe lasers. The suppression of spatiotemporal instabilities in semiconductor laser arrays is achieved by selectively stabilizing relevant transverse optical modes. The relevant values of delay-times and delay-phase are obtained from a nonlinear eigenmode analysis based on a complex extension of the Karhunen-Loeve decomposition. Thereby a destructive interference condition in the higher-order transverse modes conveying the instabilities is achieved. The stabilization technique is demonstrated on multi-stripe laser arrays. In high-power broad-area lasers the spatiotemporal filamentation processes occur on both macroscopic and microscopic scales. Numerical simulations on the basis of Maxwell-Bloch equations for spatially extended semiconductor lasers reveal the internal spatial and temporal scales on which control consequently has to occur. It is demonstrated that the combined filamentation and propagation effects may be controlled by suitable spatially structured delayed optical feedback allowing, in particular, the control of coherent regimes in originally temporally and spatially chaotic states.
TL;DR: In this paper, a model for the scaling of strongly driven stimulated Brillouin and Raman scattering was proposed, which postulates an intensity-dependent correlation length associated with spatial incoherence due to filamentation and stimulated forward scattering.
Abstract: An improved understanding of strongly driven laser-plasma coupling is important for optimal use of the National Ignition Facility (NIF) for both inertial fusion and for a variety of advanced applications. Such applications range from high-energy x-ray sources and high-temperature hohlraums to fast ignition and laser radiography. We discuss a novel model for the scaling of strongly driven stimulated Brillouin and Raman scattering. This model postulates an intensity-dependent correlation length associated with spatial incoherence due to filamentation and stimulated forward scattering. We first describe the model and then relate it to a variety of experiments. Particular attention is paid to high-temperature hohlraum experiments, which exhibit low to modest stimulated Brillouin scattering even though this instability is strongly driven. We also briefly discuss the strongly nonlinear interaction physics for efficient generation of high-energy electrons either by irradiating a large plasma with near quarter-critical density or by irradiating overdense targets with ultra-intense laser light.
TL;DR: In this paper, the authors show that the tendency of a laser beam to break into a filamentary structure in passing through a nonlinear optical medium can be largely suppressed by proper tailoring of the vacuum field that interacts with the laser beam.
Abstract: We show that the tendency of a laser beam to break into a filamentary structure in passing through a nonlinear optical medium can be largely suppressed by proper tailoring of the vacuum field that interacts with the laser beam
TL;DR: In this article, the authors investigate the nasence of current filaments in thin-film n-GaAs samples with two concentric circular contacts (Corbino disks) and show that for a constant applied voltage in the regime of low-temperature impurity breakdown, a radially symmetric impact ionization front breaks up into streamers forming pre-filaments.
Abstract: We report on theoretical investigations of the nasence of current filaments in thin film n-GaAs samples with two concentric circular contacts (Corbino disks). For a constant applied voltage in the regime of low-temperature impurity breakdown, a radially symmetric impact ionization front breaks up into streamers forming pre-filaments, among which a winner-takes-all dynamics sets in due to global coupling. On sweeping the external bias we find the spontaneous appearance of multiple stable filaments and hysteresis. In a perpendicular magnetic field the filaments are bent due to the Lorentz force.
TL;DR: In this article, the results of two-dimensional Particle-in-Cell simulations of plasma cloud collisions are presented, where the initial configuration is assumed to have the slab form and the second configuration has a form of the cylindrical. And in both cases, the counterstreaming motion of the plasmas is unstable with respect to the electromagnetic mode excitation with the developing of the hollow structures in the electron density distribution.
Abstract: We present the results of two dimensional PIC (Particle-in-Cell) simulations of plasma cloud collisions We investigate two different types of the plasma configuration: in the first one the initial configuration is assumed to have the slab form and the second configuration has a form of the cylindrical In both cases we found that the counterstreaming motion of the plasmas is unstable with respect to the electromagnetic mode excitation with the developing of the hollow structures in the electron density distribution, the formation of the electric current filaments and the merging of the filaments and quasistatic magnetic field generation
08 Nov 1999
TL;DR: In this article, the main difficulty associated with high brightness is that, because of COD, high power requires a large aperture, which results in high order transverse modes, filamentation and spatio-temporal instabilities, all of which degrade spatial coherence and therefore brightness.
Abstract: High brightness semiconductor lasers have many applications. The main difficulty associated with high brightness is that, because of COD, high power requires a large aperture. Large apertures result in high order transverse modes, filamentation and spatio-temporal instabilities, all of which degrade spatial coherence and therefore brightness.
DOI•
01 Jan 1999
TL;DR: A submitted manuscript is the version of the article upon submission and before peer-review as mentioned in this paper, while a published version is the final layout of the paper including the volume, issue and page numbers.
Abstract: • A submitted manuscript is the version of the article upon submission and before peer-review. There can be important differences between the submitted version and the official published version of record. People interested in the research are advised to contact the author for the final version of the publication, or visit the DOI to the publisher's website. • The final author version and the galley proof are versions of the publication after peer review. • The final published version features the final layout of the paper including the volume, issue and page numbers.
TL;DR: In this paper, the growth rates of filamentation instabilities in a light ion beam-plasma system with an external magnetic field were obtained using a particle-in-cell (PIC) method.
24 May 1999
TL;DR: In this article, a Fourier-optical set-up within the external cavity of a commercially available broad-area laser diode to select certain transverse modes is investigated experimentally.
Abstract: A Fourier-optical set-up within the external cavity of a commercially available broad-area laser diode to select certain transverse modes is investigated experimentally. The external cavity consists of a lens and a spatial frequency filter, the latter consisting of a reflecting slit (perpendicular to the active layer) surrounded by a darkened background. This is a Fourier-optical 4f set-up (2f plus reflection). The laser employed first is a partially antireflection coated 0.25 W 655 nm AlGaInP broad area laser. The free running laser shows non-stationary filamentation. Placing the slit directly onto the optical axis gives cw fundamental mode operation and a transverse shift of the spatial filter allows for selective excitation of higher order modes at low pump currents. Next, a highly antireflection coated 1.2 W 811 nm AlGaAs broad area laser is utilized in the 4f set-up. Selective excitation of higher order modes is achieved at high pump currents. Another approach to support fundamental mode operation uses a 2f set-up (1f plus reflection) consisting of a concave mirror at a distance f away from the laser facet. Here, the laser facet with its active region dimensions is the spatial filter. Also, the feasibility of autocatalytic mode coupling for reduction of unstable filamentation of broad-area lasers is examined experimentally.