Self-focusing Of Light Research Articles

Fourier analysis of non-paraxial self-focusing

In this paper we deduce a vectorial non-paraxial equation describing the self-focusing of light in a homogeneous isotropic Kerr medium. The equation is derived via transformation to the spatial frequency domain, which clarifies the physical nature of the approximations made. We also present numerical solutions for a linearly polarized Gaussian input beam and discuss the dependence of the self-focusing length on beam width and input power.

Gravitational self-confinement of a photon beam

The mass of a photon beam, equivalent to its energy, forms a gravitational potential well (an induced waveguide) in vacuum and this leads to the appearance of a self-sustained photon jet in free space. A calculation of this effect, which is analogous to the familiar self-focusing of light in nonlinear material media, is made in the paraxial approximation.

Numerical simulations of induced spatial incoherence laser light self-focusing

The effect of induced spatial incoherence (ISI) on laser light self-focusing is investigated using a two-dimensional Eulerian hydrodynamic plasma simulation code. In homogeneous low-density plasmas (one-tenth of the critical density for radiation of wavelength λL=0.25 μm) it is found that ISI can effectively eliminate thermal and ponderomotive self-focusing for a wide range of intensities. In plasma containing an initial linear gradient in density, strong self-focusing occurs when the maximum intensity in the incident light I0 (where I0 represents the intensity that would be achieved for a perfectly coherent beam) is allowed to approach 1017 W cm−2. At lower intensities, I0∼1016 W cm−2, thermal self-focusing is eliminated and ponderomotive self-focusing is significantly reduced. The dwell time of the filamented light varies from the laser light coherence time to a few tens of picoseconds.

New Non-Reorientational Optical Nonlinear Effect in MBBA

Abstract A new effect producing self-focusing of light in a nematic MBBA film is reported. This effect produces a static diffraction pattern composed of circular rings which is different from the ones arising from self-focusing previously reported. The influence of the cell thickness, the optical intensity, and the wavelength is studied. Once the nematic is distorted by a laser beam, the effect produced in other light beam passing through the modified region is independent of its polarization. This isotropic behavior shows that a molecular reorientation has not been produced. The origin of this effect seems to be the same of that of the effect which produces a randomly oscillating diffraction pattern previously reported by our group. Some possible causes such as thermal indexing, convective instabilities and self-induced transparency are discussed.

Periodic density redistribution of parametrically excited spin waves in an antiferromagnet

A nonuniform distribution of the density of parametrically excited magnons is observed experimentally in an antiferromagnetic CsMnF3 sample. The nonuniform distribution occurs at a high pumping power when oscillations of the high frequency susceptibility occur. These oscillations were observed earlier and their nature was not clear. It is found that during the increase of the absorbed power on the occurrence of the oscillation, the spin wave condenses near the middle of the sample. The condensation occurs as a result of a nonlinear shift of the magnon spectrum and is similar to self-focusing of light in nonlinear media. The electromagnetic radiation of parametrically excited spin waves is studied. It is found that the periodic redistribution of the density exerts an additional restrictive effect on the amplitude of the parametrically excited magnons.

Orientational optical nonlinearity of liquid crystals

The orientational optical nonlinearity of the mesophases of liquid crystals (LCs) is attracting ever more attention, owing to the high values of the constants characterizing it, owing to the many interesting specific features that LCs introduce even into traditional nonlinear optical effects, and owing to the potentialities of studying the physical properties of LCs. This article presents the state of the theory and experiment of orientational interaction of light waves with LCs. Especial attention is paid to the physical mechanisms of interaction?the light-induced Freedericksz effect, recording of director gratings, and the action of surface light waves on the orientation of the director. Varied manifestations of the effects of orientational self-action and interaction of light waves are discussed: self-focusing of light, nonlinear optical activity, mutual focusing, stimulated light scattering, and wave-front conjugation. Optical nonlinearities specific for the mesophase of a liquid crystal and associated with absorption of light quanta are also discussed. They include photoconformational nonlinearity, thermal-orientational nonlinearity, and liquid-crystal light valves. Especial attention is paid to the methodological problem of deriving the Euler?Lagrange?Rayleigh variational equations and to the correct choice of the free energy for the system LC + electromagnetic field. Section 8 traces the history of the studies of orientational optical nonlinearity of LCs and reviews the studies whose results are not directly reflected in the main text, and also reviews the studies on practical applications of light-induced orientational effects.

Amplification of phase-conjugate plane waves by smallscale self-focusing of light in glass

Small-scale self-focusing of light in neodymium glass was investigated experimentally in the simplest case of an interaction between a high-intensity plane laser beam and a weak beam propagating at a small angle ? with respect to the former beam. By separating the beams in the far field and measuring their energies, an investigation was made of the dependence of the gain of the ? beam and the resultant phase-conjugate ? ? beam on the angle ? and on the energy density of the strong beam, including the saturated amplification regime. The experimental results are compared with the computer calculations. The feasibility of developing wavefront reversal systems utilizing the small-scale self-focusing mechanism is discussed.

Optical bistability based on self-focusing: An approximate analysis

Calculations are presented which describe approximately the behavior of optically bistable devices based on the self-focusing of light. A simple heuristic calculation and a more complicated calculation which incorporates saturation of the material nonlinearity are presented. Both give a good qualitative description of situations in which a single hysteresis loop is observed. More complicated types of behavior, some of which have been observed, are predicted by the calculations which incorporate saturation. The results provide useful guides for the design of such devices.

Optical bistability in nematic films utilizing self-focusing of light

Optical bistable operation in the transmission characteristics of a nematic liquid crystal film is observed. The mechanism for the bistability is the self-focusing of light via optically induced molecular reorientations. The process occurs at very modest cw input laser power on the order of 0.3 W (intensity of ∼500 W/cm2) in a 60-μm-thick sample.

Erratum: Theory of optically induced molecular reorientations and quantitative experiments on wave mixing and the self-focusing of light

Erratum: Theory of optically induced molecular reorientations and quantitative experiments on wave mixing and the self-focusing of light

Theory of optically induced molecular reorientations and quantitative experiments on wave mixing and the self-focusing of light

We present a theoretical treatment of optical-field-induced molecular reorientations and quantitative experimental verifications of the associated nonlinear-optical processes in the nematic phase of liquid crystals. Explicit analytic expressions are obtained in the small-angle linearized approximation of the Euler-Lagrange equation describing the molecular reorientation. It is found that optical-field strengths much lower than the so-called optical Freedericksz transition threshold can create substantial molecular reorientations and generate easily observable nonlinear-optical effects such as self-focusing and degenerate four-wave mixings. The theoretically predicted dependences on the scattering geometry, the optical intensities, and the nematic thicknesses are in excellent agreement with experimental data. The relative contribution of thermal effect is also determined.

Role of thermal self-focusing in optical breakdown of transparent dielectrics by nanosecond pulse fields

A theoretical analysis is made of the influence of self-focusing of light on the optical breakdown of transparent materials by focused beams. Special attention is paid to the influence of thermal self-focusing. It is shown that this effect is not usually the dominant mechanism of beam contraction in optical breakdown experiments. This is because, in contrast to the instantaneous Kerr mechanism, the diffraction in thermal self-focusing can compensate the nonlinear refraction; in some cases, thermal diffusion may also be important. The methods for experimental determination of the dominant self-focusing mechanism in optical breakdown are analyzed. It is pointed out that, in many cases, the necessary information can be obtained from measurements of the dependence of the breakdown threshold on the focal length of a lens.

Investigation of the self-focusing of light scattered in the stimulated Raman effect at different excitation levels

An investigation was made of the dependence of the self-focusing of the light scattered in the stimulated Raman effect on the power of the pulse of the first Stokes component. The investigation was carried out on substances with different values of the Kerr constant: These substances included liquid nitrogen, calcite, carbon disulfide, and nitrobenzene. It was found that the self-focusing of the scattered light was always observed, even if the exciting radiation was not self-focused. The distributions of the self-focusing points near the front and rear ends of a sample were similar, if the scattering layer was thin and the power density of the exciting radiation was low. An increase in the power density of the first Stokes component resulted in an increase of the self-focusing points and a reduction in their diameter. The maximum power density at the self-focusing points was a constant characteristic of a given substance.

Investigation of the focusing action of media with residual stresses

An experimental study was made of glass plates which exhibited a focusing action after illumination with a CO laser beam. Focusing of helium–neon laser radiation by these plates gave rise to a spatial structure similar to that observed in the thermal self-focusing of light. When the region illuminated with the CO2 laser was greater than the cross section of the helium-neon laser beam, the divergence and the transverse dimensions of the beam decreased without affecting the mode structure.

Explanation of Limiting Diameters of the Self-Focusing of Light

For incident laser giant pulses the high conversion of laser light into Raman light limits the size of the beam diameter in liquid toluene, benzene, and in mixtures of benzene and C${\mathrm{S}}_{2}$. Computer calculations are in agreement with the experimental results.

Transient self-focusing of light

The aberration-free approximation is used in a theoretical analysis of self -focusing of wave beams in a medium of permittivity It is shown that two effects appear under transient self-focusing conditions: 1) filaments undergoing gradual constriction form behind a nonlinear focus in a medium with e = e(t); 2) large frequency shifts result from transverse compression of a self-focusing channel when a beam collapses in a medium with a noninstantaneous nonlinearity of the aforementioned type or with an instantaneous nonlinearity of the e = e0(1 + e' |E|2) type.

Explanation of limiting diameters of the self-focusing of light

Explanation of limiting diameters of the self-focusing of light

Self-Focusing of Laser Light and Stimulated Scattering Processes in Transparent and Absorbing Liquids: 1. Self-Focusing

Abstract The spatial and temporal development of self-focusing of light pulses is investigated. The beam diameter in CS2 and molten para-di-chlorobenzene decreases with increasing incident laser power to small values in good agreement with theory. The strong influence of beam divergence, non-linearity of refractive index, and absorption on self-focusing action is found to agree well with numerical calculations. It is shown that both backward stimulated Brillouin and Raman scattering terminate the self-focusing process.

Aberrational thermal self-focusing of light

Aberrational thermal self-focusing of light

Self-Focusing of Light by Potassium Vapor

Raman-shifted ruby-laser light on the high-frequency side of the $^{2}P_{\frac{3}{2}}$ resonance line (7665 \AA{}) of potassium was self-focused by a dilute potassium gas.