Search results for "efficiency"
showing 10 items of 1430 documents
Analysis of acousto-optic tunable filter performance for imaging applications
2010
Acousto-optic tunable filters (AOTFs) can be used as spec- tral filters in multispectral imaging applications. Acousto-optic crystals diffract a single wavelength from a broadband light beam, depending on the applied radio frequency signal. However, experimental measurements show that the actual performance is far from the expected behavior. We present an experimental characterization of several commercial off-the- shelf AOTFs for the implementation of multispectral imaging instruments. The diffraction performance of three bare crystals is compared, while a fourth AOTF crystal is mounted on the optical path of a multispectral im- ager to evaluate its performance. The experiments show that t…
Enhanced diffraction of light in GaAs microcavities
1995
We theoretically analyze the diffraction of light by gratings that are photogenerated in Fabry–Perot microcavities. The coupled-wave theory of volume gratings is combined with appropriate boundary conditions to yield expressions for the diffraction efficiency. Multiple round trips within the cavity are seen to increase the effective grating thickness and therefore the efficiency. Numerical calculations specific to GaAs microcavities show that the diffraction efficiency can be enhanced by more than 2 orders of magnitude at the resonant wavelengths.
Dispersion-compensated Lau-like processor
2004
We present a diffractive lens-based optical assembly with which to achieve high-contrast Lau-like interferential fringes with totally incoherent illumination.
White-light-modified Talbot array illuminator with a variable density of light spots.
2008
A flexible array illuminator, comprising only two conventional optical elements, with a variable density of bright white-light spots is presented. The key to our method is to obtain with a single diffractive lens an achromatic version of different fractional Talbot images, produced by free-space propagation, of the amplitude distribution at the back focal plane of a periodic refractive microlens array under a broadband point-source illumination. Some experimental results of our optical procedure are also shown.
Fractal zone plates with variable lacunarity.
2009
Fractal zone plates (FZPs), i.e., zone plates with fractal structure, have been recently introduced in optics. These zone plates are distinguished by the fractal focusing structure they provide along the optical axis. In this paper we study the effects on this axial response of an important descriptor of fractals: the lacunarity. It is shown that this parameter drastically affects the profile of the irradiance response along the optical axis. In spite of this fact, the axial behavior always has the self-similarity characteristics of the FZP itself.
Fabrication of Diffractive Optics: Surface Reliefs and Artificial Dielectrics
1997
After a period of fundamental theoretical research, the field of diffractive optics is now reaching a time of assessment, when we can define the useful limits of each design procedure. Selecting a suitable procedure derives from a compromise between several factors, including design time, desired optical efficiency, and precision. A major consideration in finding such a compromise has been, and still is today, the availability of technologies which can realize the design by generating the diffracting structure with assigned tolerances.
Elemental distribution and structural characterization of GaN/InGaN core-shell single nanowires by Hard X-ray synchrotron nanoprobes
2019
Improvements in the spatial resolution of synchrotron-based X-ray probes have reached the nano-scale and they, nowadays, constitute a powerful platform for the study of semiconductor nanostructures and nanodevices that provides high sensitivity without destroying the material. Three complementary hard X-ray synchrotron techniques at the nanoscale have been applied to the study of individual nanowires (NWs) containing non-polar GaN/InGaN multi-quantum-wells. The trace elemental sensitivity of X-ray fluorescence allows one to determine the In concentration of the quantum wells and their inhomogeneities along the NW. It is also possible to rule out any contamination from the gold nanoparticle …
Multifractal zone plates
2010
We present multifractal zone plates (MFZPs) as what is to our knowledge a new family of diffractive lenses whose structure is based on the combination of fractal zone plates (FZPs) of different orders. The typical result is a composite of two FZPs with the central one having a first-order focal length f surrounded by outer zones with a third-order focal length f. The focusing properties of different members of this family are examined and compared with conventional composite Fresnel zone plates. It is shown that MFZPs improve the axial resolution and also give better performance under polychromatic illumination.
Polarization holograms and diffraction anisotropy in amorphous chalcogenides
2004
Polarization hologram recording based on the effect of photoinduced anisotropy (PA) is reviewed, focusing on amorphous chalcogenides (ACh). Possible PA mechanisms in ACh are considered. Polarization holographic grating recording in amorphous As?S?Se (a-As?S?Se) films is experimentally studied and analysed in comparison with scalar recording. It is holographically established that linearly polarized 632.8 nm light produces photoinduced anisotropy and the chalcogen related D+, D? centre reorientation and generation mechanism is proposed. It is used to explain the observed peculiarities of polarization (vector) recording in comparison with scalar recording based on photoinduced structural chan…
Totally incoherent optical processing operations with achromatic diffraction-based setups
2000
We report on a novel family of totally incoherent, chromatic-dispersion compensated hybrid (refractive-diffractive) lens setups for implementing, in the Fraunhofer or in the Fresnel diffraction region, different achromatic diffraction-based processing operations.