Search results for "Diode"
showing 10 items of 469 documents
Red-green flicker resolution as a function of heterochromatic luminous modulation.
1993
Critical fusion frequencies have been evaluated in heterochromatic red-green flicker as a function of red-green luminous modulation defined by mL = (R-G)/(R+G)%, at five different mean luminance levels, two test sizes (2 degrees and 5 degrees) and square wave stimuli. The extreme values mL = +/- 100 correspond to ordinary light-dark flicker (red or green); mL = 0 corresponds to pure chromatic flicker, and any other values correspond to simultaneous luminous and chromatic flicker. To implement the stimuli we have developed a new stimuli generator (AVICO, colour vision analyser) using bicolour LEDs as the light source and electronic control of the luminances and frequencies. The results for a…
Compact dielectric reflective elements I Half-sphere concentrators of radially emitted light
1994
Optical designs of aspheric internally reflective concentrators of divergent light emitted within a spatial angle of 2n sr are proposed and discussed. Four types of solid transparent element are considered: the divergence angle reducer, the small-spot illuminator, the point focuser, and the collimator. The output beam aperture in all cases is comparable with the light-source external dimensions. Expressions describing the profiles of beam-transforming surfaces and results from experiments with model devices are presented.
X-ray and gamma-ray astronomy with NTD germanium-based microcalorimeters
2002
We report on the performance of our NTD-Ge microcalorimeters. To date, the spectral resolution for x-ray and gamma-ray lines from radioactive sources and laboratory plasmas is 4.8 eV in the entire 1 - 6 keV band and 52 eV at 60 keV. Technical details responsible for this performance are presented as well as an innovative electro-thermal approach for enhancing count-rate capability.
Characterization of Al-Schottky CdTe detectors
2011
In the last decades, great efforts are being devoted to the development of CdTe detectors for high resolution X-ray and gamma ray spectroscopy. Recently, new rectifying contacts based on aluminum (Al) are very appealing in the development of CdTe detectors with low leakage currents and anode pixellization. In this work, we report on preliminary results of electrical and spectroscopic investigations on Schottky CdTe diode detectors (4.1 × 4.1 × 0.75 and 4.1 × 4.1 × 2 mm3) with Au/Ti/Al/CdTe/Pt electrode configuration. The detectors are characterized by very low leakage currents even at room temperature (26 pA at 25 °C under a bias voltage of −100 V for the 2 mm thick detector). Polarization …
All-optical fiber-based amplitude jitter magnifier
2010
International audience; We describe the concept of an all-fibered device that enables the optical magnification of the amplitude jitter of low-fluctuation pulse trains, facilitating the measurement of the statistical properties by usual photodiodes and electronic equipments. Taking advantage of a highly nonlinear fiber with anomalous dispersion followed by central optical bandpass filtering, we experimentally demonstrate an amplification of small-scale fluctuations by a factor 10.
Arbitrary Waveform Generator Based on All-Incoherent Pulse Shaping
2006
An all-incoherent technique for the generation of arbitrary electromagnetic intensity profiles is presented. It is based on spectral filtering of a broadband continuous-wave light source so that the filtered spectral density function (SDF) becomes the user-defined waveform. After large temporal modulation and subsequent distortion in a first-order dispersive medium, the incoherent mapping of the filtered SDF to the time domain occurs. Finally, optical-to-electrical conversion in a fast photodiode allows the optical intensity to be mapped into the electrical domain
Stimulated Emission in InGaN/GaN Multiple Quantum Wells with Different Indium Content
2005
1. IntroductionLight-emitting and laser diodes for the green to near-UV region are basedon quantum structures with the InGaN active region [1]. The indium contentin the wells is a technological parameter that provides a straightforward accessfor the change in the color of the light-emitting device. However, the redshift ofthe emission peak with increase in indium content is caused not only by a simplealloying, but also by carrier localization due to difierence in In and Ga atomic
Preliminary radiation hardness tests of single photon Si detectors
2010
Single photon Si detectors were fabricated by STMicroelectronics and fully characterized in standard operation conditions and after irradiations. Both single cells and arrays, of dimensions ranging from 5x5 up to 64x64, were electrically tested. The devices operation was studied as a function of the temperature from -25 degrees C to 65 degrees C varying the voltage over breakdown, from 5% up to 20% of the breakdown voltage before and after irradiation using both light ions, 10 MeV B ions to doses in the range 3x10(7)-5x10(10) cm(-2), and X-rays irradiations in the range 0.5-20 krad(Si). Optical characterization was performed using a laser at 659 nm and opportunely chosen filters to vary the…
Shadowing of the operating mode by sidebands in gyrotrons with diode-type electron guns
2021
In gyrotrons operating in high-order modes, during the startup process, the shadowing of the operating mode by two sidebands may take place. By “shadowing,” we mean the situation when, during the voltage rise, one of the parasitic modes is excited first, and this excitation prevents the excitation of the desired mode. Then, the oscillations of the first parasitic mode, whose frequency is higher than the frequency of the desired operating mode, can be replaced by excitation of the second parasitic mode, whose frequency is lower than the operating one. As a result, the desired mode remains in the “shadow” of these parasitic modes and is never excited. This paper describes such effect in gyrot…
A two-dimensional liquid-filled ionization chamber array prototype for small-field verification: characterization and first clinical tests.
2012
In this work we present the design, characterization and first clinical tests of an in-house developed two-dimensional liquid-filled ionization chamber prototype for the verification of small radiotherapy fields and treatments containing such small fields as in radiosurgery, which consists of 2 mm × 2 mm pixels arranged on a 16×8 rectangular grid. The ionization medium is isooctane. The characterization of the device included the study of depth, field-size and dose-rate dependences, which are sufficiently moderate for a good operation at therapy radiation levels. However, the detector presents an important anisotropic response, up to ≃ 12% for front versus near-lateral incidence, which can …