Search results for "Filter"
showing 10 items of 1019 documents
Real-time binary-amplitude phase-only filters.
2008
A real-time binary-amplitude phase-only filter (BAPOF) implemented in available phase-only modulators is presented. The BAPOF has an amplitude transmission equal to one only in a region of support, while the transmission is equal to zero in the complementary region. To implement zero transmission in a phase-only modulator we propose to add a linear phase to the region of support. In this way the correlation desired is obtained off axis. Computer simulations and experimental results obtained with this technique are given.
DarkFocus: numerical autofocusing in digital in-line holographic microscopy using variance of computational dark-field gradient
2020
Abstract We report on a novel computational technique for automatic numerical refocusing in digital in-line holographic microscopy. It is based on the adaptive filtering of the recorded on-axis hologram to eliminate its background term and extract interference intensity-component connected with light scattered on the sample (interference fringes). Numerical propagation of such filtered hologram yields the computationally generated dark-field imaging coming from the amplitude part of the complex field. We propose a simple measure in the form of the variance of the dark-field gradient, which attains its maximum value in the focal planes for all types of objects (phase, amplitude and mixed pha…
Multimodal reflectivity of CRIGF filters: First experimental observation and modelling
2015
International audience; Cavity Resonator Integrated Guided-mode Resonance Filter (CRIGF) are a new class of filtering reflectors whose selected wavelength and spectral width are independent of the angle of incidence unlike GMRF. These particular properties allow both compactness and a high angular acceptance. However, ours studies show that CRIGFs offer simultaneously spectral and modal filtering and we evidence high-spatial-order reflected modes. In this paper, we will present characterization of the spectral and spatial profile that demonstrates the existence of these high-order modes. In addition, we will present a model based on the physical understanding of implied phenomena to explain…
Design scheme for Mach–Zehnder interferometric coarse wavelength division multiplexing splitters and combiners
2006
I propose an analytical approach to design flattened wavelength splitters with cascaded Mach–Zehnder inter- ferometers when wavelength dependence of the directional couplers cannot be neglected. I start from a geo- metrical representation of the action of a doubly point-symmetrical filter, assuming no wavelength dependence of the couplers. Next I derive the analytical formulas behind its working principle and extend them to the wavelength-dependent case. I also show how the geometrical representation allows one to broaden the class of working structures. © 2006 Optical Society of America
The filter wheel and filters development for the X-IFU instruments onboard Athena
2016
Athena is the large mission selected by ESA in 2013 to investigate the science theme “Hot and Energetic Universe” and presently scheduled for launch in 2028. One of the two instruments located at the focus of the 12 m-long Athena telescope is the X-ray Integral Field Unit (X-IFU). This is an array of TES microcalorimeters that will be operated at temperatures of 50 mK in order to perform high resolution spectroscopy with an energy resolution down to 2.5 eV at energies < 7 keV. In order to cope with the large dynamical range of X-ray fluxes spanned by the celestial objects Athena will be observing, the X-IFU will be equipped with a filter wheel. This will allow the user to fine tune the i…
How does environmental variation translate into biological processes?
2001
Birth and death rates, as so many other biological processes, are usually not linearly related to environmental variation. Common examples of non-linear response forms include unimodal ‘‘optimum-type’’ responses and various saturating responses. These responses filter the signal coming from the environment to a corresponding biological process. We explored how different types of environmental signal may be transformed to a biological process. We were interested in the effect of the filter on modulation of (1) the variance of the signal, on (2) the variance-covariance structure between the signal and the filtered signal, and on (3) the match between the power spectra of the signal and the fi…
Compact dielectric reflective elements II Multichannel filter of closely spaced spectral bands
1994
The optical design of an interference wedge filter providing the simultaneous separation of a number of closely spaced spectral bands is studied. Multiple reflections of the incident collimated beam within the wedge are initiated, each of them characterized by a different angle of incidence and consequently by specific spectral parameters of the transmitted band. Model calculations based on the measured angular dependences of filter transmission parameters have been performed. The design is proposed for applications in optical communications (wavelength division demultiplexing), analytical spectroscopy (minipolychromators), color analysis, and similar areas.
The optical blocking filter for the ATHENA wide field imager: Ongoing activities towards the conceptual design
2015
ATHENA is the L2 mission selected by ESA to pursue the science theme "Hot and Energetic Universe" (launch scheduled in 2028). One of the key instruments of ATHENA is the Wide Field Imager (WFI) which will provide imaging in the 0.1-15 keV band over a 40'x40' large field of view, together with spectrally and time-resolved photon counting. The WFI camera, based on arrays of DEPFET active pixel sensors, is also sensitive to UV/Vis photons. Optically generated electron-hole pairs may degrade the spectral resolution as well as change the energy scale by introducing a signal offset. For this reason, the use of an X-ray transparent optical blocking filter is needed to allow the observation of all …
Status of the EPIC thin and medium filters on-board XMM-Newton after more than 10 years of operation II: analysis of in-flight data
2013
After more than ten years of operation of the EPIC camera on board the X-ray observatory XMM-Newton we have reviewed the status of its thin and medium filters by performing both analysis of data collected in-flight and laboratory measurements on on-ground back-up filters. We have investigated the status of the EPIC thin and medium filters by performing an analysis of the optical loading in the PN offset maps to gauge variations in the optical and UV transmission of the filters. We both investigated repeated observations of single optically bright targets and performed a statistical analysis of the extent of loading versus visual magnitude at different epochs. We report the results of these …
The on-board calibration system of the X-ray Imaging Polarimetry Explorer (XIPE)
2016
The calibration system for XIPE is aimed at providing a way to check and correct possible variations of performance of the Gas Pixel Detector during the three years of operation in orbit (plus two years of possible extended operation), while facilitating the observation of the celestial sources. This will be performed by using a filter wheel with a large heritage having a set of positions for the calibration and the observation systems. In particular, it will allow for correcting possible gain variation, for measuring the modulation factor using a polarized source, for removing non interesting bright sources in the field of view and for observing very bright celestial sources. The on-board …