Transfer of momentum and torque from a light beam to a liquid

Refraction or absorption of light results in the force and torque, i.e., transfer of momentum and angular momentum from light to the medium. In transversely inhomogeneous beams, the force per unit volume f may have curlf not equal 0 leading to flow or to nonthermal and nongravitational convection in liquids. The force and the torque in scattering systems are as strong as in absorbing materials and may allow one to carry out experiments avoiding thermal effects. Nonlinear optical response of liquid crystals due to this convection is discussed

POLICRYPS Composite Materials: Features and Applications

Physical chemistr

Tailoring symmetry groups using external alternate fields

Macroscopic systems with continuous symmetries subjected to oscillatory fields have phases and transitions that are qualitatively different from their equilibrium ones. Depending on the amplitude and frequency of the fields applied, Heisenberg ferromagnets can become XY or Ising-like -or, conversely, anisotropies can be compensated -thus changing the nature of the ordered phase and the topology of defects. The phenomena can be viewed as a dynamic form of "order by disorder".Comment: 4 pages, 2 figures finite dimension and selection mechanism clarifie

Observation of optical spatial solitons in a highly nonlocal medium

We report on the observation and quantitative assessment of self-trapped pulsating beams in a highly non-local nonlinear regime. The experiments were conducted in nematic liquid crystals and allow a meaningful comparison with the prediction of a scalar theory in the perturbative limit, while addressing the need for beyond-paraxial analytical treatments.Comment: 16 pages, 3 figure

Temporal instability due to competing spatial patterns in liquid crystals in the light field

We unveil the physical origin of the peculiar spatio-temporal instability phenomena observed in liquid crystals subject to the influence of a light wave of ordinary polarization. Our study shows that due to non-adiabatic propagation of a light beam in an anisotropic medium, the light polarization and, hence, the torque acting on the orientation of a nematic liquid crystal (NLC) is asymmetrically modulated over the NLC layer. The spatial pattern of the NLC reorientation that is formed across the NLC-layer under the influence of such a torque may become unstable in time due to competing interaction of symmetric and antisymmetric modes. The obtained results allow evaluation of the threshold intensity and the range of the light incidence angles where the longitudinal spatio-temporal instability is possible. © 1998 Elsevier Science B.V. All rights reserved

Applications Of Liquid Crystal Nonlinearities To Laser Instrumentation

Light waves can reorient liquid crystals (LC). The magnitude of this reorientation provides information about the main energetic characteristics of the laser beam. An intrinsic interferometric process provides precise all-optical method of orientation measurement. The temporal dynamics of the LC reorientation under the action of both continuous and pulsed radiation provides another method for determination of the light beam power, intensity and the beams size. The accuracy of measurements depends on the particular method of registration of the LC-orientation

Momentum and torque transfer from light to liquid crystal

Orientational nonlinearity such as momentum and torque transfer is demonstrated in dye-doped absorbing liquid crystals (LC) as a function of the light field. The light is considered as a flux of photons carrying momentum hk/2π and energy hv moving along the Poynting vector. The momentum is balanced when the energy in and out is exactly balanced for the transparent medium. However, the directions of the input and output photons make an angle with the perpendicular to the input/output facets. Therefore, a momentum arm a appears, resulting a torque T transferred from light to LC

Nonlinear Interaction Of Light With Transversely Moving Medium

Interaction of a light beam with matter reveals extreme sensitivity to transverse motions. Spatio-temporal delocalization of interaction and diffusive transport of light-induced perturbations is revealed through a new family of diffraction patterns. The response of the medium to the transverse motion of the light enhances near the second order phase transition point. The phenomenon has large application potential for the study of motions that are beyond the power of Doppler-effect-based methods, and suggests fundamental problems about critical processes with nonstationary influences. © 1996 The American Physical Society