Self-trapped bidirectional waveguides in a saturable photorefractive medium

We introduce a time-dependent model for the generation of joint solitary waveguides by counter-propagating light beams in a photorefractive crystal. Depending on initial conditions, beams form stable steady-state structures or display periodic and irregular temporal dynamics. The steady-state solutions are non-uniform in the direction of propagation and represent a general class of self-trapped waveguides, including counterpropagating spatial vector solitons as a particular case.Comment: 4 pages, 5 figure

Effective and flexible modeling approach to investigate various 3D Talbot carpets from a spatial finite mask

We present an effective modeling approach for a fast calculation of the Talbot carpet from an initially 2-dimensional mask pattern. The introduced numerical algorithm is based on a modified angular-spectrum method, in which it is possible to consider the border effects of the Talbot region from a mask with a finite aperture. The Bluestein’s fast Fourier transform (FFT) algorithm is applied to speed up the calculation. This approach allows as well to decouple the sampling points in the real space and the spatial frequency domain so that both parameters can be chosen independently. As a result an extended three-dimensional Talbot-carpet can be calculated with a minimized number of numerical steps and computation time, but still with high accuracy. The algorithm was applied to various 2-dimensional mask patterns and illumination setups. The influence of specific mask patterns to the resulting field intensity distribution is discussed

Modelling adapted to manufacturing aspects of holographic grating structures

The diffraction efficiencies of modified sinusoidal and blazed gratings are investigated in the high spatial frequency regime by rigorous numerical methods and are compared to experimentally manufactured gratings. The introduced modifications take actual technological induced variations of the profile geometries, such as specific corner rounding, into account. The high spatial frequency regime (resonance regime) is characterized by a local grating period, g, to wavelength, λ, ratio of 0.7 ≤ g/λ ≤ 4 and shows an important relevance for applications in spectroscopy and diffractive imaging. The investigations are carried out for both reflection on metallic surfaces and transmission of dielectric structures over a broad range of grating periods and incidence angles. It was found that near the grating resonance, the more simply producible sine gratings can compete in diffraction efficiency with sawtooth structures. Additionally, for certain application conditions, holographically modified sine structures achieve higher efficiencies than the ideal sine profile. It is also shown that holographical sinusoidal-like profiles measured by AFM can be fitted to a super-Gaussian shape, which is then used to inversely reconstruct the structure profiles from efficiency data

Efficiency-achromatized reflective dispersion grating by a double-blaze configuration: Theoretical conditions for optimal material selection

Blazed gratings are key components both for imaging and for spectrally analyzing optical systems. However, the blazing effect is very sensitive towards wavelength variations. Double-blazed gratings overcome this disadvantage but have been investigated up to now only for transmission geometries. Here we present a systematical theoretical analysis of the diffraction efficiency of double-blazed gratings in the reflection geometry. We find appropriate conditions for a systematical material selection to achieve efficiency-achromatized blazed gratings, based on fundamental dispersion parameters such as the Abbe’s number and relative partial dispersion of the materials. We discuss how to keep the profile heights as shallow as possible. Therefore, appropriate material combinations which are suitable for spectral blazed gratings have to be found

Beam bending in photorefractive conjugators

Strong bending of laser beams in photorefractive conjugators is explained using the grating action method and Fermat's principle. A bent bidirectional optical path in the crystal consists of a finite number of kinks formed at the double-phase conjugate interaction regions, and straight segments in between. The device in operation strives to minimize the optical path length and maximize the coupling between beams