Diffraction efficiency

About: Diffraction efficiency is a research topic. Over the lifetime, 10320 publications have been published within this topic receiving 158298 citations.

Super-smooth x-ray reflection grating fabrication

Abstract: Blazed, grazing incidence x-ray reflection gratings are an important component of modern high resolution spectrometers and related x-ray optics. These have traditionally been fabricated by diamond scribing in a ruling engine, or more recently by interferometric lithography followed by ion etching. These traditional methods result in gratings which suffer from a number of deficiencies, including high surface roughness and poor control of the groove profile. These deficiencies lead to poor diffraction efficiency and high levels of scattered light. We have developed a novel fabrication method for fabricating blazed x-ray reflection gratings which utilizes silicon wafers that are cut 0.7° off of the (111) plane. In solutions such as potassium hydroxide (KOH), silicon is etched in 〈111〉 directions orders of magnitude slower than in other directions, resulting in extremely smooth {111} facets. The gratings are patterned using interferometric lithography with 351.1 nm wavelength and transferred into the substrat...

Generalized Space-Time-Periodic Diffraction Gratings: Theory and Applications

Abstract: Unlike a conventional diffraction grating, a space-time-periodic (STP) grating produces spatial diffraction orders, each of which is formed by an infinite set of temporal diffraction orders. STP gratings offer enhanced functionalities and exotic characteristics, such as asymmetric diffraction patterns, nonreciprocal and asymmetric transmission and reflection, and an enhanced diffraction efficiency. Here a rigorous, general theory of diffraction by STP gratings is formulated, and a particular practical application in wireless communication is proposed: an inventive multiple-access communication system, featuring full duplex operation and high data-transmission rate.

In situ optical control and stabilization of the curing process of holographic gratings with a nematic film-polymer-slice sequence structure

Abstract: We report on the realization of what we believe to be a new holographic setup for the fabrication of polymer liquid-crystal polymer-slice diffraction gratings, which utilizes an optical-feedback-driven nanopositioning technique. We have increased the stability of the interference pattern by means of a simple piezomirror used in a feedback configuration to keep constant the phase of the interferometer. The feedback system is driven by a proportional, integral, derivative control software, and the stability degree is controlled by the reference signal coming from a standard test grating. A preliminary experimental characterization indicates that good control and stabilization of parasitic fluctuations of the interference pattern are obtained.

Analysis of the kinetics of diffraction efficiency during the holographic grating recording in azobenzene functionalized polymers.

Abstract: The laser-assisted holographic grating recording process in films of azobenzene functionalized polymers is usually studied by observation of the efficiency of light scattering on a developing in time diffraction grating. Various possible mechanisms contributing to grating formation as well as the bulk or surface origin (bulk refractive index and/or relief grating) of light scattering make the analysis of kinetics of grating recording, from the light scattering data only, difficult and ambiguous. To fully explain experimentally observed various and complex (frequently nonexponential) kinetics of the first-order light diffraction intensity, we considered a simple single-exponential growth of the two phase gratings in the same polymer film. In modeling we assumed that the bulk refractive index grating Deltan(t) and the surface relief grating Deltad(t) differ considerably in their growth rates and we allowed for a nonstationary phase shift Deltaphi(t) between them which was experimentally observed during the recording process. The origin of the nonstationary phase shift is a result of a slow shift of interference pattern due to delicate symmetry breaking in illumination conditions (e.g., difference in beam intensities and deviation of exact symmetrical beam incidence angles on the sample). Changing only such parameters as stationary amplitudes of refractive index and relief gratings for a span of phase shifts (0-pi) between them, we obtained a series of kinetic responses which we discuss and interpret. The various examples of temporal evolution of diffraction efficiency for the same grating formation kinetics, modeled in our work, supply evidence that great care must be taken to properly interpret the experimental results.

In dark analysis of PVA/AA materials at very low spatial frequencies: phase modulation evolution and diffusion estimation

Abstract: Molecular diffusion effects have been widely studied inside photopolymers for holographic applications. Recently some works have focused on low spatial frequencies to evaluate in real time the monomer diffusion effects. Assuming a Fermi-Dirac function-based profile, we have fitted the diffracted intensities, reflected and transmitted (up to the 8th order), to obtain the phase and surface profile of the recorded gratings. We have studied the influence of diffusion in polyvinyl-alcohol/acrylamide for the range of spatial frequencies between 2 lines/mm and 6 lines/mm. We have demonstrated the influence of the spatial frequency on the magnitude and sign of the material volume variations. We also studied in dark the evolution of the grating shape. We show that it is possible to achieve diffractive gratings with diffraction efficiency in the first order near 35% if the in dark evolution is taken into account. Furthermore we present a method to calculate the monomer diffusivity in photopolymers. The differential equation is deduced and solved, and experimental average value is obtained (D=1.1·10−8 cm2s−1).