Institute of Physics

... AV Ilyenkov, AI Khiznyak, LV Kreminskaya, MS Soskin, MV Vasnetsov Institute of Physics, National Academy of Sciences of Ukraine, Prospect Nauki 46, 252650 Kiev 22, Ukraine (E-mail:SOSKIN@oqe.ip.kiev.ua) ... I beam 2 ~plitter Ben$ / --t I He-Cd la~er attenuator negative /1"t~ ...

ABSTRACT SiO20 crystals in the diffusion regime. We find unusually high cross-talk for two gratings with close spatial frequencies at wavelengths 488 and 476nm. The results indicate that the density of free charge carriers does not directly follow light modulation at low spatial frequencies.

ABSTRACT Recently significant crosstalk has been observed in a multibeam experiment in which gratings were previously thought to be independent. In this letter, it is shown that the crosstalk is due to a coherent nonlinear combination of the primary gratings, which causes additional peaks to occur in the diffraction pattern and changes the diffraction efficiency of the primary gratings explaining the apparent crosstalk. It is shown that the effect can be derived from the band transport model when all the terms in the expression for the generation of charge carriers are retained. Results are presented for a configuration consisting of a reference beam and two object beams and show experimental results that confirm the model. © 1995 American Institute of Physics.

Light beams with optical vortices (OVs) are of inter-est because of their unusual properties and possible applications to the manipulation of microobjects [1]. The OV structure is determined by the phase circulation about the vortex axis, on which the phase is indefinite while the ...

ABSTRACT We have performed experiments to establish the origin of phase defects in a phase-conjugate cavity composed of a curved mirror of high reflectivity and a phase-conjugating mirror based on four-wave mixing in photorefractive BaTiO3 pumped by counterpropagating Ar laser beams. An intracavity diaphragm was used to change the Fresnel number, thus providing the observation of different transverse structures in the output plane of the photorefractive oscillator.

ABSTRACT We present an elaborated holographic technique for synthesis of optical beams possessing optical vortices with fractional topological charge. The technique is based on the production of sub-harmonic diffraction orders. The diffraction orders corresponding to the fundamental period have embedded vortices with integer topological charge and sub-harmonic diffraction orders have optical vortices with fractional topological charge. An analytical approach for charge-1/2 optical-vortex beam structure description is presented.

ABSTRACT We present an analytical investigation of the influence of the periodic motion of a light source (a monochromatic Gaussian beam) on its frequency spectrum. The radiation of a source that travels along an elliptical path (or vibrates along straight line) possesses a discrete spectrum with frequency components shifted by nΩ with respect to the optical frequency, where n is an integer and Ω is the frequency of the periodic motion of the source. We show that the nth-order harmonic spectrum component contains n anisotropic optical vortices arranged symmetrically along the direction of the big axis of the ellipse. In the case of linear vibration of the source edge dislocations appear instead of vortices. During wave propagation in free space the vortices come closer to each other and finally join into one central n-charged optical vortex in the far field.

It is shown that the resolving power of dichromated gelatin (DG) volume phase gratings is limited most significantly by changes in layer parameters occurring under processing during development. The recording characteristics of holographic grazing-incidence gratings are examined, and factors leading to the appearance of optical defects in DG holographic gratings are investigated. Inhomogeneous transverse deformations of the layer are shown to produce grating defects (period variations and formation of the lens effect), i.e., to lead to a deterioration of resolving power. Recommendations on eliminating these defects and enhancing the resolving power are presented.

A new treatment of the well-known Sommerfeld solution of the problem of plane-wave diffraction from a perfectly conducting half-plane is reported. We show, in both theory and experiment, that the diffraction field (E-polarization) can be represented as a superposition of real physically existing waves, in contrast to geometrical and boundary waves postulated in Sommerfeld's representation. Our representation includes two pairs of wave components: one pair propagates along the direction of the incident wave, and the other in a mirror-reflected direction. Each wave pair consists of a plane-wave component with an amplitude half that of the incident wave and a nearly plane-wave component with an infinitely extended edge dislocation. On the basis of the proposed interpretation, all features of the half-plane diffraction are explained.

The influence of the periodic motion of a monochromatic light source on the observed spectrum of its radiation in the far-field and near-field zones is considered. The appearance of components shifted in frequency (harmonics of the oscillation frequency of the source) is demonstrated. The spatial structure of harmonics is investigated, and the presence of optical vortices in these harmonics is shown.