Angular momentum of photons and phase conjugation

Abstract

Using concept of an ideal phase-conjugating mirror we demonstrate that regardless to internal physical mechanism the phase-conjugation of singular laser beam is accompanied by excitation within mirror of internal waves which carry doubled angular momentum in order to match angular momentum conservation. For Brillouin hypersound wavefront-reversal mirror this means that each elementary optical vortex in a speckle pattern emits acoustical vortex wave with doubled topological charge. The exact spatial profiles of light intensity and intensity of hypersound in the vicinity of phase singularity are obtained. These spiral profiles have a form of a double helix which rotates with the speed of sound. The optoacoustic experiment is proposed for visualization of wavefront reversal of twisted optical beams and tunable twisted sound generation.The conservation of angular momentum (AM) J stems from isotropy of space [1]. In contrast to particles with nonzero rest mass m o , the decomposition of J for "spin" S and "orbital" L parts of photon's AM is referred to as ambiguous procedure [1,2]. The spin part S is related to polarization, i.e. time-dependent layout of electrical E and magnetic B fields of the "transverse" light wave. The orbital part (OAM) L is associated with helical staircase wavefront [2,3,4,5]. As a matter of fact a purely transverse light waves are abstraction because of a small but inevitable projections of E and B on direction of propagation, say Z-axis( fig.1). Indeed, the spin-orbital coupling of light occurs [6] due to vectorial interplay between longitudinal and transversal components of the fields E and B. The vectorial solutions of Maxwell's equations for propagation of a light spatially localized by a waveguide or emitted through finite aperture to free space give a strict relationship between longitudinal and transversal field components [7,8]. Nevertheless the approximate decomposition in the form J = S + L proved to be very fruitful for small curvatures of light wavefront, i.e. in paraxial wave approximation [2].The propagation of light in anisotropic medium changes the polarization and historically the spin of photon was observed firstly in Beth's experiment where

Spiral laser beams in inhomogeneous media

“…Among other quantum mechanical analogs, the minimum-uncertainty squeezed states for atoms and photons in a cavity are reviewed in [28]. (See also [6,10,19,29] and the references therein for extensions to nonlinear geometrical optics; an optoacoustic experiment is proposed in [30].) In summary, we present multiparameter solutions to homogeneous and inhomogeneous paraxial wave equations which may be of interest in adaptive optics of (partially) coherent beams propagating through an atmospheric turbulence [17,[31][32][33] and deserve an experimental observation.…”

Reflection and transmission of twisted light at phase conjugating interfaces

“…In the case of normal incidence, the azimuthal index of the reflected or the transmitted LG beam is increased and decreased by the cross-polarization coupling in the beam component of the incident beam [11][12][13]. In this contribution, we have study the propagation of twisted light in a multi layer dielectric medium containing interfaces that act as phase-conjugating mirrors (PCM) [14][15][16][17]. The problem for a single PCM has been addressed previously [14][15][16][17].…”

“…In this contribution, we have study the propagation of twisted light in a multi layer dielectric medium containing interfaces that act as phase-conjugating mirrors (PCM) [14][15][16][17]. The problem for a single PCM has been addressed previously [14][15][16][17].…”

Stimulated Brillouin scattering phase conjugation of light beams carrying orbit angular momentum (Invited Paper)

“…In order to conjugate the optical vortex, it is necessary to destroy the spatial structure of vortex beam in the SBS cell. It has been proposed that it is possible to use a transparent random phase plate for phase conjugation of a vortex beam due to the initiation of a high-fidelity phase-conjugation in the SBS cell [18] . However, until now, few detailed experimental results have been reported.…”

“…We obtain the SBS phase conjugation of a vortex beam with the help of an LSD and confirmed OAM conservation in the SBS PCM. The physical mechanism can be ascribed to the high phase-conjugating fidelity SBS and the acoustical vortex wave with a doubled TC generated by the speckle filed in the SBS medium [18] . Hence, although only the SBS phase conjugation of the vortex with a TC of 2 is investigated, similar results can be obtained for a vortex beam with other TC.…”