Self-focusing Behavior Research Articles

New beat length for writing periodic structures using Bessel beams

With the ultimate aim of exploiting the self-focusing behaviour to create periodic structures, we have investigated the behaviour of Bessel–Gauss beams in Kerr-like nonlinear media and have identified that a previously proposed nonlinear beat length is inaccurate with increasing power. By studying the behaviour of the beam we suggest a correction; providing a much better description of the beat length. This correction is tested against results from numerical simulations confirming the improved accuracy. Within the, scalar, nonparaxial limit we show that this modified beat length is valid for beam powers surpassing the paraxial self-focusing threshold. From this modified beat length equation, the appropriate experimental variables may be chosen to create accurate periodic structures by direct laser writing in a single exposure.

Individual difference influences on self-focused and other-focused counterproductive student behaviors

This paper extends previous research on counterproductive student behaviors by presenting an individual difference model of counterproductive student behaviors (CSBs) that includes four sets of antecedent variables: internal control variables; propensity variables; achievement striving; and severity perceptions of CSBs. Data from 276 undergraduate students shows that CSBs exhibit a two-factor solution (self-focused and other-focused CSBs), and that each of the four sets of antecedent variables explain unique variance in either self-focused CSBs or other-focused CSBs; with the influence of achievement striving being restricted to behaviors that harm the academic performance of students. The results are discussed in terms of their relationship with previous research on counterproductive behaviors and their implications for understanding of the broad domain of college student performance.

Multifocus Structures of Ultrashort Self-Focusing Laser Beam Observed in a Three-Photon Fluorescent Medium

Self-focusing effect and multifocus structures of an ultrashort (~160-fs) pulsed laser beam of ~1.3-mum wavelength are investigated in several organic liquids. The intensity-dependent self-focusing formation and multifocus structures of the infrared (IR) laser beam were directly observed in a three-photon active fluorescent dye solution cell, in which a high contrast image of the spatial structure of the self-focusing beam can be obtained due to the cubic dependence of the fluorescence intensity on the local IR laser intensity. By combining this dye solution cell with another cell filled with various transparent organic liquids, the contributions of these tested liquids to the observed self-focusing effect are elucidated. The numerical simulations for this type of self-focusing behavior are presented, based on the assumption that the major contribution to the observed self-focusing is the nonlinear refractive-index change of the solvent due to electronic-cloud distortion. The simulation results are in fairly good agreement with the experimental results.

Fabrication of Ag and Cu nanowires by a solid-state ionic method and investigation of their third-order nonlinear optical properties

Ag and Cu nanowires were separately fabricated in a direct current electric field using a solid-state ionic method, and characterized by scanning electron microscopy (SEM) and X-ray diffraction (XRD). Their optical nonlinearities induced by 8 ns laser pulses from a frequency-doubled, Nd:YAG laser at 532 nm, were investigated using the Z-scan technique. Experimental results indicate the metal nanowires have obvious positive refractive nonlinearities and reverse saturated absorption behaviors. The self-focusing behaviors of Ag and Cu nanowires can be attributed to Kerr-induced self-focusing of laser radiation, the nonlinear refractive indexes of Ag and Cu nanowires are n 2 = 1.7 × 10 − 11 esu and n 2 = 2.4 × 10 − 11 esu respectively, and the two-photon process of Ag and the one-photon process of Cu are responsible for the difference between Ag and Cu nanowires suspended in de-ionized water in nanosecond nonlinear absorptions.

Antecedents of Impression Management Use and Effectiveness in a Structured Interview†

The authors examine personality variables and interview format as potential antecedents of impression management (IM) behaviors in simulated selection interviews. The means by which these variables affect ratings of interview performance is also investigated. The altruism facet of agreeableness predicted defensive IM behaviors, the vulnerability facet of emotional stability predicted self- and other-focused behaviors, and interview format (behavior description vs. situational questions) predicted self-focused and defensive behaviors. Consistent with theory and research on situational strength, antecedent—IM relations were consistently weaker in a strong situation in which interviewees had an incentive to manage their impressions. There was also evidence that IM partially mediated the effects of personality and interview format on interview performance in the weak situation.

1-D Polymeric divalent metal m-ferrocenylbenzoates: Structures, NLO and electrochemical properties

Three 1-D metal–organic polymers containing m-ferrocenylbenzoate components: {[Pb(μ 2-η 2-OOCH 4C 6Fc) 2] · (CH 3OH) 2} n ( 1), [Zn(OOCH 4C 6Fc) 2(bpe)] n ( 2) and [Mn(η 2-OOCH 4C 6Fc) 2(4,4′-bpy)] n ( 3) were synthesized and structurally characterized. In polymer 1, each m-FcC 6H 4COO − anion adopts a tridentate fashion, bridging the central Pb(II) ions to form a 1-D chain. Polymers 2 and 3 give similar zigzag chain structures. Their third-order NLO properties were investigated with 532 nm laser pulses of 8 ns duration by Z-scan experiment in DMF solution. All of the polymers exhibit good NLO refractive properties with self-focusing behaviors. The third-order NLO refractive indexes n 2 are 2.44 × 10 −11 esu for 1, 2.33 × 10 −11 esu for 2, and 2.10 × 10 −11 esu for 3, respectively. Through quantum chemistry calculations, we conclude that the nonlinear refractive behaviors of the three polymers mainly come of the ferrocenyl units and organic adjuvant ligands; Mn(II) ions and Pb(II) ions have also some influence on NLO properties. The solution-state differential pulse voltammetrys indicate that the half-wave potential of the ferrocenyl moiety in 3 has slightly higher value than those of 1 and 2. This may be because the HOMO orbitals in 1 and 2 are located in the m-FcC 6H 4COO − groups, while in 3 the HOMO orbital is located in the m-FcC 6H 4COO − and Mn(II)groups, the charge transitions of the metal cores may play an important role in the change of the Fe(II)/Fe(III) oxidation potential of 3, so the Fe(II) centers of 1 and 2 are more easily oxidized to Fe(III) centers than that of 3.

Self‐Assembly of Interpenetrating Coordination Nets Formed from Interpenetrating Cationic and Anionic Three‐Dimensional Diamondoid Cluster Coordination Polymers

Tetrathiometalates [WS4]2− are the nodal building blocks in a new kind of heterometallic interpenetrating three-dimensional cluster coordination polymer (see picture) that has interesting nonlinear optical properties. The polymer exhibits optical self-focusing behavior and reverse saturable absorption effects.

Numerical simulation of the propagation of a single laser pulse in a photorefractive medium

Abstract The paper presents a numerical study of the self-focusing time behaviour of a ns single laser pulse propagating in a biased photorefractive sillenite crystal. Assuming particular hypotheses in the case of short pulse illumination, a nonlinear partial differential equation linking the refraction index and the beam intensity has been derived from a mono-dimensional Kukhtarev band transport model. The numerical resolution of this equation has been coupled to the simulation of the propagation of a beam in a nonlinear medium using a Beam Propagation Method. We thus simulate the self-focusing phenomena of a single laser pulse on the nanosecond time-scale. These calculations let us describe the output beam profile evolution during the laser pulse and study theoretically the influence of different parameters on self-focusing such as the applied electric field, the beam intensity and waist. A successful comparison to previous experimental measurements is reported.

Relativistic nonlinearity and wave-guide propagation of rippled laser beam in plasma

In the present paper we have investigated the self-focusing behaviour of radially symmetrical rippled Gaussian laser beam propagating in a plasma. Considering the nonlinearity to arise from relativistic phenomena and following the approach of Akhmanov et al, which is based on the WKB and paraxial-ray approximation, the self-focusing behaviour has been investigated in some detail. The effect of the position and width of the ripple on the self-focusing of laser beam has been studied for arbitrary large magnitude of nonlinearity. Results indicate that the medium behaves as an oscillatory wave-guide. The self-focusing is found to depend on the position parameter of ripple as well as on the beam width. Values of critical power has been calculated for different values of the position parameter of ripple. Effects of axially and radially inhomogeneous plasma on self-focusing behaviour have been investigated and presented here.

Dynamics of single-wall carbon nanotube synthesis by laser vaporization

The key spatial and temporal scales for single-wall carbon nanotube (SWNT) synthesis by laser vaporization at high temperatures are investigated with laser-induced luminescence imaging and spectroscopy. Graphite/(Ni, Co) targets are ablated under typical synthesis conditions with a Nd:YAG laser at 1000 °C in a 2-in. quartz tube reactor in flowing 500-Torr Ar. The plume of ejected material is followed for several seconds after ablation using combined imaging and spectroscopy of Co atoms, C2 and C3 molecules, and clusters. The ablation plume expands in stages during the first 200 μs after ablation and displays a self-focusing behavior. Interaction of the plume with the background gas forms a vortex ring which segregates and confines the vaporized material within a ∼1-cm3 volume for several seconds. Using time-resolved spectroscopy and spectroscopic imaging, the time for conversion of atomic and molecular species to clusters was measured for both carbon (200 μs) and cobalt (2 ms) at 1000 °C. This rapid conversion of carbon to nanoparticles, combined with transmission electron microscopy analysis of the collected deposits, indicate that nanotube growth occurs over several seconds in a plume of mixed nanoparticles. By adjusting the time spent by the plume within the high-temperature zone using these in situ diagnostics, single-walled nanotubes of controlled (∼100 nm) length were grown and the first estimate of a growth rate on single laser shots (0.2 μm/s) was obtained.

Experimental study of the self-focusing process temporal behavior in photorefractive Bi12TiO20

A systematic experimental study of the photorefractive self-focusing process in Bi12TiO20 is conducted and its results are successfully compared to previous and new theoretical work.

A New Cognitive Treatment for Social Phobia: A Single-Case Study

A recent cognitive model of social phobia which pays particular attention to the maintenance of the disorder is outlined. Within this model self-focused attention, safety behaviors, and selective retrieval strategies interact to prevent social phobics from disconfirming their negative beliefs about the way they appear to others. The model suggests specific clinical interventions which target each of the maintaining factors and which also address key interpersonal assumptions particular to this disorder. The successful 12-session cognitive application of this model to a 30-year-old woman with a 13-year history of the problem is described.

Self-focusing in photorefractive BaTiO3 crystal under external DC electric field

Experimental observations of 1D and 2D self-focusing in a BaTiO3 crystal under externally DC applied electric field are reported. Stationary self-focusing behaviour can be obtained with and without additional uniform illumination.

Electromagnetic Beam Breakup: Multiple Filaments, Single Beam Equilibria, and Radiation.

In the framework of the nonlinear Schr\"odinger equation, the radiation aspect of self-focusing in two transverse dimensions appears to be (together with self-trapped propagation) an essential part of any self-focusing process. The final beamlets created in multiple filamentation are shown to be very close to canonical solitonlike solutions. This fact is used to establish an upper bound on the amount of radiation emitted. From this a parameter is defined which proves to be useful to characterize the self-focusing behavior as a function of the initial conditions.

Evolution of spatial optical solitons in biased photorefractive media under steady state conditions

The dynamical evolution of bright spatial solitons in biased photorefractive crystals is investigated under steady-state conditions. Our numerical study indicates that these optical solitons are stable against small perturbations whereas optical beams that significantly differ from soliton solutions tend to experience larger cycles of compression and expansion. The influence of loss in a typical photorefractive material like SBN:60 is studied in detail. The effect of the external bias field on the self-focusing behavior of optical beams is discussed and the interaction forces among optical solitons are also investigated.

Simulation of strong nonlinear effects in optical waveguides

Nonlinear optical channel waveguides are modeled. It is demonstrated that a saturable nonlinear permittivity model is essential mathematically when strong nonlinear effects are simulated, so that the nonlinear wave equation possesses realistic solutions. Several precautionary factors in the numerical simulation of self-focusing behavior are addressed. For example, care must be exercised when the threshold power is calculated for some nonlinear structure exhibiting an abrupt all-optical switching phenomenon.

Self-focusing instability and chaotic behavior of nonlinear optical waves guided by dielectric slab structures

The propagation of nonlinear optical waves guided by a nonlinear thin film bounded by two linear claddings is examined numerically. Numerical results for the propagation constant versus the propagation axis indicate that for higher-order modes the transition from periodic behavior to chaos through period doubling is observed as the guided-wave power increases, whereas for the fundamental mode an extremely stable self-focusing propagation is possible.

Self-focusing and filamentation of laser light in high Z plasmas

Self-focusing and filamentation of short wavelength laser light in high Z plasmas of interest to laser fusion are discussed. It is found that self-focusing behavior is very dependent on the details of the characteristics of the laser beam, the plasma conditions, and the energy transport processes. Laser light absorption and self-focusing are strongly competitive processes. At. 0.26 μm wavelength the collisional absorption is often so great that there is no intensity amplification of the beam despite the fact that strong self-focusing is present. Wide variations are found in laser light penetration, affected by several factors. Diverging optics reduce the likelihood of self-focusing. Large scale length density gradients have little effect on focusing behavior. The self-focusing behavior is very dependent on beam shape. Large scale hot spots can have a significant effect on whole beam self-focusing early in the pulse. The behavior of small scale hot spots can be qualitatively different than the standard picture. The calculations indicate that small scale hot spots do not achieve a steady state in some cases. Sound waves cause chaotic interactions among neighboring hot spots. It is found that sub-beam size structures are also generated when nonlocal thermodynamic equilibrium (non-LTE) radiation and atomic physics are used in the calculations. The nature of the heat flux and thermoelectric magnetic field generation are examined with a kinetic model. Stimulated Raman backscattering levels in self-focused light are significantly reduced for short wavelengths and high Z plasmas Landau damping plays an important role in determining the Raman levels. Implications for suprathermal electron production, symmetric illumination, x-ray conversion efficiency, and laser light absorption are discussed.

Physical attractiveness, self-awareness, and mirror-gazing behavior

In a field study, 86 students (37 males and 49 females) were observed as they walked past a section of reflecting glass that served as a mirror. The amount of time spent by each subject in gazing at his or her own image was recorded. The physical attractiveness of each participant was rated by experimental observers, and subjects filled out a questionnaire that assessed the degree to which they ordinarily engage in self-focused behavior. For both males and females, time spent in mirror gazing was positively correlated with physical attractiveness. Mirror gazing and self-focusing were unrelated, although self-focusing was positively correlated with attractiveness.

Self-focusing in a plasma due to ponderomotive forces and relativistic effects

The propagation of intense laser pulses in a plasma is discussed in terms of a constant shape, paraxial ray approximation. Self-focusing due to ponderomotive forces and relativistic effects is investigated. It is found that the stationary self-focusing behaviour of each mechanism treated separately is similar, with several orders of magnitude difference in critical power. In stationary self-focusing due to the combined mechanisms, complete saturation of ponderomotive self-focusing prevents the occurrence of relativistic effects. Self-focusing lengths and minimum radii are given for a large range of beam powers. A characteristic focal spot radius is found which depends only on the plasma density.