Diffraction efficiency

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

Holographic polarization-separation elements.

Abstract: Volume holographic optical elements exhibit a property that we call bidiffringence, in which the diffraction efficiency of the element is strongly dependent on the polarization of the incident beam. Dualelement, volume holographic polarization separators utilizing bidiffringence can provide high extinction ratios, and they can provide greater angular separation of the polarized beams and greater flexibility in the beam-separation parameters than conventional birefringent elements. We designed and constructed holographic polarization separators using dichromated gelatin as the holographic medium. Experimental results are compared with the results predicted by the Kogelnik coupled wave theory.

High reflection mirrors for pulse compression gratings

Abstract: We report an experimental investigation of high reflection mirrors used to fabricate gratings for pulse compression application at the wavelength of 1.053microm. Two kinds of mirrors are studied: the mixed Metal MultiLayer Dielectric (MMLD) mirrors which combine a gold metal layer with some e-beam evaporated dielectric bilayers on the top and the standard e-beam evaporated MultiLayer Dielectric (MLD) mirrors. Various samples were manufactured, damage tested at a pulse duration of 500fs. Damage sites were subsequently observed by means of Nomarski microscopy and white light interferometer microscopy. The comparison of the results evidences that if MMLD design can offer damage performances rather similar to MLD design, it also exhibits lower stresses; being thus an optimal mirror substrate for a pulse compression grating operating under vacuum.

Analysis and synthesis of circular diffractive lens with local linear grating model and rigorous coupled-wave theory

Abstract: We describe a local linear grating model that permits estimation of the diffraction efficiency of high-numerical-aperture two-dimensional circular lenses with one-dimensional rigorous coupled-wave analysis. The model is self-consistent and is consistent with the scalar theory that results for low-numerical-aperture lenses. The accuracy of the model increases with the number of Fresnel zones of the lens. On the basis of this model we optimize the discrete phase profile of the lens for the maximum diffraction efficiency, using the random search method. The TE and the TM modes are optimized simultaneously. Their phase variations as functions of local grating periods are removed by cyclic shifts of the grating profiles, resulting in constructive summation at the focus and high diffraction efficiency.

Transmission grating spectroscopy and the Advanced X-Ray Astrophysics Facility

Abstract: The use of transmission gratings with grazing-incidence telescopes in celestial x-ray astronomy is reviewed. The basic properties of transmission grating spectrometers and the use of "phased" gratings to enhance the diffraction efficiency are outlined. Special attention is given to the AXAF high-energy transmission grating (HETG) being fabricated at MIT. The HETG operates over the range 0.4 to 8 keV, gives resolving powers of 100 to 1000, effective areas of 10 to 300 cm2, and a minimum detectable line flux of 1 to 10 x 10-6 photons cm-2 s-1. The instrument consists of a single array with two types of membrane-supported grating facets: medium-energy gratings (0.6-μm period, 0.5-μm-thick silver) mounted behind the outer three AXAF mirrors, and high-energy gratings (0.2-μm period, 1.0-μm-thick gold) mounted behind the inner three mirrors. The materials and thicknesses are selected to maximize efficiency throughout the energy band. The facets are fabricated at MIT using a process involving x-ray lithography. AXAF will also carry a low-energy transmission grating (LETG) supplied by the Laboratory for Space Research at Utrecht. It uses mesh-supported grating facets of 1.0-μm period and is optimized for operation down to 80 eV. Gratings are most effective for the study of point sources, but they also give moderate resolution spectra of slightly extended sources and can be used to map the spatial distribution of line-emitting regions.