Vladimir S. Pavelyev

Investigation of computer-generated diffractive beam shapers for flattening of single-modal CO 2 laser beams

A full cycle was realized of the photolithographic development and detailed testing of a diffractive optical element that transforms the diverging Gaussian beams of CO(2) lasers into a uniformly filled-in rectangle. The zone feature size of the beam shaper, the diffractive efficiency and accuracy, the focus depth, and the stability with respect to the size and the divergence of incident Gaussian beams are studied by computer modeling. Calculated flattop intensity distributions are presented in the same form of gray-level pictures and three-dimensional plots as the corresponding results measured by an IR camera.

Fibre sensors based on transverse mode selection

Use of diffractive optical elements (DOEs) in fibre sensors is very promising. This work is dedicated to the investigation of dependence of the transverse mode content in step-index fibres on the microbending value by means of diffractive optical elements. We describe the experimental set-up and methods of experimental data processing that afford precise measurements of mode power. The LP mode power dependencies on the fibre microbending value are obtained. The results obtained allow the designing of fibre sensors with advanced characteristics such as the dynamic range and accuracy.

Generation of Terahertz Surface Plasmon Polaritons Using Nondiffractive Bessel Beams with Orbital Angular Momentum.

Bessel vortex beams with topological charges of l=±1 and l=±2 were produced in the terahertz spectral range from a free electron laser Gaussian beam (λ=141  μm) transformed using silicon binary diffractive optical elements. The spatial characteristics of the beams were obtained using a microbolometer array. A radius to path length ratio of 1:100 was achieved for nondiffractive beams with the average power of 30 W. Surface plasmon polaritons (SPPs) on gold-zinc-sulphide-air interfaces were generated due to diffraction of vortex beams on a sample edge. A new effect, a dependence of the efficiency of SPP generation on the direction of the azimuthal component of incident-radiation Poynting vector, was revealed.

Novel continuously shaped diffractive optical elements enable high efficiency beam shaping

LIMOs unique production technology is capable to manufacture free form surfaces on monolithic arrays larger than 250 mm with high precision and reproducibility. Different kinds of intensity distributions with best uniformities or customized profiles have been achieved by using LIMOs refractive optical elements. Recently LIMO pushed the limits of this lens production technology and was able to manufacture first diffractive optical elements (DOEs) based on continuous reliefs profile. Beside for the illumination devices in lithography, DOEs find wide use in optical devices for other technological applications, such as optical communications, laser technologies and data processing. Classic lithographic technologies lead to quantized (step-like) profiles of diffractive micro-reliefs, which cause a decrease of DOEs diffractive efficiency. The newest development of LIMOs microlens fabrication technology allows us to make a step from free programmable microlens profiles to diffractive optical elements with high efficiency. Our first results of this approach are demonstrated in this paper. Diffractive beam splitters with continuous profile are fabricated and investigated. The results of profile measurements and intensity distribution of the diffractive beam splitters are given. The comparison between theoretical simulations and experimental results shows very good correlation.

Realization of binary radial diffractive optical elements by two-photon polymerization technique

Application of the two-photon polymerization (2PP) technique for the fabrication of submicron-size relief of radial binary diffractive optical elements (DOEs) is studied. Binary DOEs for the formation of special longitudinal intensity distribution (axial light segment) are realized. Interferometric investigations of the diffractive relief produced by the 2PP-technique and investigations of optical properties of the formed elements are presented. Results of computer simulations are in good agreement with the experimental observations.

Graded photonic quasicrystals

We introduce graded photonic quasicrystals and investigate properties of such structures on the example of a Luneburg lens based on a dodecagonal photonic quasicrystal. It is shown that the graded photonic quasicrystal lens has better focusing properties as compared with the graded photonic crystal lens in a frequency range suitable for experimental realization. The proposed graded photonic quasicrystals can be used in optical systems where compact and powerful focusing elements are required.

CVD diamond transmissive diffractive optics for CO2 lasers

Growing applications of CO2-lasers in many cases demand transmission optical elements (widows, lenses, etc.) which could reliably operate at high beam powers. In the present work we propose to produce CVD diamond transmissive diffractive optics. To realize this idea surface microstructuring by laser ablation was applied. Computer controlled selected area ablation of preliminary polished (plane) diamond plates with thickness of 0.3 mm was performed by scanning focused beam of KrF laser. As a test sample for radiation with (lambda) equals 10.6 micrometers a cylindrical lens with the aperture of 4 X 4 mm2 and focal length of 25 mm was produced. Numerical simulation of the lens was made for the fundamental mode TEM00. For tests of the diamond lens 20 W CO2 laser was used.

Application of the direct search in solving a problem of forming longitudinal distribution of intensity

This paper is devoted to the application of a well-known genetic algorithm for optimization of diffractive optical element forming pre-given axial intensity distribution. Computer simulation results and experimental research are presented.

Transverse mode multiplexing by diffractive optical elements

An increase in the data-carrying abilities of modern communication systems is a most important scientific and technical challenge, requiring further studies of the physical effects involved. The possibility to increase in the data-carrying abilities of optical communication systems by waveguide transverse modes multiplexing by diffractive optical elements (DOEs) is considered.

Optical elements for focusing of terahertz laser radiation in a given two-dimensional domain

Binary silicon-based diffractive optical element (DOE)—Gaussian-to-Square focuser (diameter of aperture is 30 mm) for the terahertz spectral range has been designed and characterized using terahertz radiation of the Novosibirsk Free Electron Laser (NovoFEL) at the wavelength of 141 μm. The preliminary experiments have demonstrated feasibility of application of binary silicon DOE for focusing of terahertz radiation into pre-given focal domain.