Self-focusing Of Laser Radiation Research Articles

Self-focusing threshold of a beam of laser radiation in rubidium vapor

This paper describes the self-focusing of laser radiation in atomic rubidium vapor close to the 5S1/2–5P3/2 resonance transition (780 nm). The self-focusing threshold power is measured at various transverse beam sizes of the laser radiation at the input of a cell with rubidium vapor. An increase of the self-focusing threshold power was observed at small beam diameters of the laser radiation. The results of the measurements were compared with the data of theoretical studies.

Formation of filament structures of noble-metal nanoparticles in transparent dielectrics under the action of continuous laser radiation

The formation of filamentary structures (up to 5 mm in length and 5–90 mm thick) of gold and silver nanoparticles (NPs) was studied in porous Vycor glass and polymer material (crosslinked oligouretanmetakrilate) doped with appropriate organic and inorganic precursors of these metals (H[AuCl4] · 4H2O, AgNO3, Ag(hfac)COD) under the action of continuous laser radiation in the visible wavelength range of 5–100 mW power. The formation of such structures along the direction of a laser beam was observed both in the course of laser exposure and after it ended. The mechanism of self-assembling of filaments from metal NPs is rationalized by the photolysis of precursor molecules in the zone of irradiation, the release of metal atoms, and their assembly into NPs. The very process of particle assembly in the filaments are ordered by the effects of self-focusing of laser radiation on a micro lens arising in the matter and channeling it into a medium with a varying refractive index. The features of formation of filamentary structures in the matrices under laser irradiation with different wavelengths are discussed.

Strong self-focusing of axial symmetric laser beam due to quadratic nonlinearity

Strong self-focusing and defocusing of optical radiation with Gaussian spatial and temporal distribution due to cascading second harmonic generation without a significant change in the beam profile and the pulse shape for the fundamental wave under the condition of group velocity matching in the axial-symmetric case for a bulk medium is considered, and the maximum intensity of an optical beam increases in 70 times (or more) in comparison with the intensity of incident optical radiation. This result is obtained for pulse duration, which belongs to a time interval from microseconds to picoseconds, for which the dispersion of group velocity is negligible. Self-focusing of laser radiation allows the realization of the mode that is similar to Kerr-lens mode locking, but for laser systems generating the optical radiation with a duration from microseconds to picoseconds.

Study of Third- and Fifth-Order Nonlinear Optical Processes in Thin C[sub 60] Films

The nonlinear refraction in thin films of fullerene C60 (100 nm) is studied by the Z-and RZ-scan methods using the second harmonic of a picosecond Nd:YAG laser (λ = 532 nm, τ = 55 ps). The combined effect of n2 (self-focusing of laser radiation) and n4 (self-defocusing) is analyzed. Mechanisms responsible for the nonlinear refraction in films are discussed.

Self-focusing of laser radiation in cluster plasma

The self-focusing of laser radiation in plasma with ionized gaseous clusters is studied both analytically and numerically. An electrodynamic model is proposed for cluster plasma in a field of ultrashort laser pulse. The radiation self-action dynamics are studied using the equation for wave-field envelope with allowance for the electronic nonlinearity of the expanded plasma bunches and the group-velocity dispersion in a nanodispersive medium. It is shown that, for a laser power exceeding the self-focusing critical power, the wave-field self-compression occurs in a medium with dispersion of any type (normal, anomalous, or combined). Due to the strong dependence of the characteristic nonlinear field on the size of ionized cluster, the corresponding processes develop faster than in a homogeneous medium and give rise to the ultrashort pulses.

Optical properties of an “anomalous” droplet

The idea of using liquids to construct optical elements with controllable characteristics goes back to Newton, who suggested using the surface of mercury in a rotating container as a parabolic mirror. Such progress has now been made in this field that liquid metal telescopes with a mirror diameter of 4 m are now operating successfully. 1 In 1958, Block and Harwit 2 suggested using the thermocapillary-deformed free surface of a liquid as an optical element. The phenomenon of self-focusing of laser radiation observed when an incident beam is reflected from a thermocapillary deformed liquid layer was studied in Refs. 3‐6. Following the discovery of concentration-capillary convection induced by the thermal action of light in thin films of solutions of positively strain-active substances 1! in highly volatile solvents, it was suggested that the ‘‘anomalous’’ droplet 5 formed as a result of this effect could be used as a varifocal liquid lens. Bezuglyi 7 showed that a steady-state anomalous droplet could be achieved, and this was confirmed experimentally 8 using a mixture of acetone and a saturated solution of rhodamine G in water.

Nonlinear relativistic self-focusing of laser radiation in plasmas: Arbitrary intensity

A paraxial theory of relativistic self-focusing of a Gaussian laser beam in plasmas, when the nonlinear part of the effective dielectric constant is arbitrarily large, is presented. The plasma is taken to be homogeneous without any density fluctuations being necessary. The approach of Akhmanov et al. based on the WKB and paraxial ray approximations has been followed. It is seen that the saturating nature of nonlinearity leads to two values of critical power of the beam (Pcrl and Pcr2) for self-focusing. When the power of the beam P lies between the two critical values (i.e., Pcr1 < P < Pcr2), the medium behaves as an oscillatory waveguide; the beam first converges and then diverges, converges again, and so on. For P > Pcr2 the beam first diverges, then converges, then diverges, and so on. Because the relativistic mechanism is instantaneous, the theory is applicable to the understanding of selffocusing of laser pulses also.

Amplitude and polarization effects in self-focusing of laser radiation in media with spatial dispersion of nonlinearity

Amplitude and polarization effects in self-focusing of laser radiation in media with spatial dispersion of nonlinearity

Nonlinear scattering and self-focusing of laser radiation in an aerosol

Steady-state self-focusing of cw CO2 laser radiation was found to be possible in an aerosol consisting of metal particles. When the laser radiation intensity exceeded the self-focusing threshold the scattering ability of the aerosol particles fell strongly and the region of interaction with laser radiation became luminous.

Self-focusing of laser radiation in molecular gases

Self-focusing and self-defocusing of CO2 laser pulses of 1.6 to 80 nsec duration was observed in SF6 gas for several lines in the 10P branch. It was observed that self-focusing depends on the vibrational excitation of the molecules and on their distribution function. This new self-focusing mechanism may be useful for propagation of high-power laser radiation in the atmosphere.

Self-focusing of laser radiation in the case of a Fredericks transition

Self-focusing of laser radiation in the case of a Fredericks transition

Samofokusirovka lazernogo izlucheniya pri perekhode Frederiksa

Samofokusirovka lazernogo izlucheniya pri perekhode Frederiksa

Effect of spatial dispersion of nonlinearity on self-focusing of laser radiation in liquid crystals: Theory and numerical experiments

Effect of spatial dispersion of nonlinearity on self-focusing of laser radiation in liquid crystals: Theory and numerical experiments