Diffraction efficiency

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

Diffractive phase elements based on two-dimensional artificial dielectrics

Abstract: We have designed, fabricated, and tested a blazed artificial dielectric transmission grating in fused quartz for use at the 633-nm wavelength. By locally varying the index, using fabricated two-dimensional arrays of dielectric cylinders, we can achieve a desired phase modulation to produce a diffractive phase element in one processing step. The effective index depends on the fill fraction of the cylinders.

The use of photoresist as a holographic recording medium.

Abstract: A technique is described for recording holograms and forming diffraction gratings in Shipley AZ1350 photoresist using the 4579-A output from an argon laser. A pre-exposure technique is described that not only reduces exposure times but increases the signal-to-noise ratio of the image. It is also shown that the effects of the variable characteristic of the resist can be alleviated by monitoring diffraction efficiency during development.

Aztec surface-relief volume diffractive structure

Abstract: Surface-relief diffractive optical elements made interferometrically typically are recorded with the off-axis technique, for which the fringe maxima lie on planes that are predominantly perpendicular to the recording surface and with an intensity variation that is sinusoidal. Such a structure can be readily replicated by mechanical means. Volume diffractive elements, on the other hand, which result from beams propagating in opposite directions, have fringe planes that are predominantly parallel to the surface and, as such, cannot be mechanically replicated. A new type of surface-relief diffractive structure called Aztec is discussed here; it combines features of both off-axis and volume recording geometries, with the result being a phase-quantized, or terraced, surface-relief pattern. The groove profile, instead of being sinusoidal, resembles a stepped pyramid. This structure has been replicated by metal mastering and molding into plastic in the same manner as conventional embossed surface-relief elements, but the diffraction characteristics are typical of volume phase reflective structures. Light of a given wavelength is resonantly diffracted from steps that are a half-wavelength apart and with a bandwidth that is inversely proportional to the number of steps. Color control has been achieved by overcoating the step structure with a clear dielectric that shifts the resonant wavelength to a new value, depending on the index of refraction of the dielectric. Information content is less for the single-layered, but stepped, Aztec structure than for the usual multilayered volume diffractive element. Deep Aztec stepped gratings have also been fabricated by optical lithography, using multiple-mask techniques.

Ultra-high resolution zone-doubled diffractive X-ray optics for the multi-keV regime.

Abstract: X-ray microscopy based on Fresnel zone plates is a powerful technique for sub-100 nm resolution imaging of biological and inorganic materials. Here, we report on the modeling, fabrication and characterization of zone-doubled Fresnel zone plates for the multi-keV regime (4―12 keV). We demonstrate unprecedented spatial resolution by resolving 15 nm lines and spaces in scanning transmission X-ray microscopy, and focusing diffraction efficiencies of 7.5% at 6.2 keV photon energy. These developments represent a significant step towards 10 nm spatial resolution for hard X-ray energies of up to 12 keV.

Simplified Spectropolarimetry Using Reactive Mesogen Polarization Gratings

Abstract: The measurement of complete polarimetric parameters for a broad spectrum of wavelengths is challenging because of the multi-dimensional nature of the data and the need to chromatically separate the light under test. As a result, current methods for spectropolarimetry and imaging polarimetry are limited because they tend to be complex and/or relatively slow. Here we experimentally demonstrate an approach to measure all four Stokes parameters using three polarization gratings and four simultaneous intensity measurements, with potential to dramatically impact the varied fields of air/space-borne remote sensing, target detection, biomedical imaging/diagnosis, and telecommunications. We have developed reactive mesogen polarization gratings using simple spin-casting and holography techniques, and used them to implement a potentially revolutionary detector capable of simultaneous measurement of full polarization information at many wavelengths with no moving or tunable elements. This polarimeter design not only enables measurements over a likely bandwidth of up to 70% of the center wavelength, it is also capable of measurements at relatively high speed (MHz or more) limited only by the choice of photo-detectors and processing power of the system. The polarization gratings themselves manifest nearly ideal behavior, including diffraction efficiencies of greater than 99%, strong polarization sensitivity of the first diffraction orders, very low incoherent scattering, and suitability for visible and infrared light. Due to its simple and compact design, simultaneous measurement process, and potential for preserving image registration, this spectropolarimeter should prove an attractive alternative to current polarization detection and imaging systems.