Direct illumination calibration of telescopes at the quantum precision limit

The electronic response of a telescope under direct illumination by a point-like light source is based on photon counting. With the data obtained using the SNDICE light source and the Megacam camera on the CFHT telescope, we show that the ultimate precision is only limited by the photon statistical fluctuation, which is below 1 ppm. A key feature of the analysis is the incorporation of diffuse light that interferes with specularly reflected light in the transmission model to explain the observed diffraction patterns. The effect of diffuse light, usually hidden conveniently in the Strehl ratio for an object at infinity, is characterized with a precision of 10 ppm. In particular, the spatial frequency representation provides some strong physical constraints and a practical monitoring of the roughness of various optical surfaces.Comment: accepted for publication in Astronomy & Astrophysic

Test of Skydice CLAP electronics

This report describes the test of the CLAP readout electronics done for the commisioning the Skydice instrument. The CLAP hardware consists of a) the Cooled Large Area Photodiode (Hamamatsu S3477), b) a FE_box containing the frontend electronic board and the CLAP, c) a BE-box containing the backend electronic board, d) a PC readout of the BE-box through a USB interface. The tests reported here concern a prototype version of the CLAP electronics delivered in July 2011. A final version of both FE and BE boards are expected for end of october 2011

Analysis of Purity Probes H1 Liquid Argon Calorimeter

The sensitivity of our liquid argon purity measurement -around 0.03%- leads us to refine the tools used classically in this field. First we introduce an analytical form describing the spectrum of a 207Bi source for different values of purity and ionisation chamber gap. Second we analyse a surprising new effect: the variation of the ionisation yield of this source with the liquid argon temperature. Third we use our data to refine the charge collection models which relate electron recombination and attachment cross-sections to the electrical field

Digital Image Processing for SNDICE

We shall report here the methods developped for the analysis of diffractive ring features in Megacam images produced by SNDICE light source in a position fixed relatively to the telescope. The basic hypothesis, knowing the great stability of SNDICE illumination (10-4), is that they are due to small angle scattering of light transmitted through the CFH telescope on small defects lying on the optical surfaces either on the primary mirror or inside the camera (including correction lens, image stabilisation unit, filter, cryostat window or CCD surface)

Direct illumination LED calibration for telescope photometry

Accepted by Nuclear Inst. and Methods in Physics Research, A NIMAA calibration method for telescope photometry, based on the direct illumination of a telescope with a calibrated light source regrouping multiple LEDs, is proposed. Its purpose is to calibrate the instrument response. The main emphasis of the proposed method is the traceability of the calibration process and a continuous monitoring of the instrument in order to maintain a 0.2% accuracy over a period of years. Its specificity is to map finely the response of the telescope and its camera as a function of all light ray parameters. This feature is essential to implement a computer model of the instrument representing the variation of the overall light collection efficiency of each pixel for various filter configurations. We report on hardware developments done for SNDICE, the first application of this direct illumination calibration system which will be installed in Canada France Hawaii telescope (CFHT) for its leading supernova experiment (SNLS)

Spectral calibration of SNDICE

SNDICE primary goal was to provide a photometric calibration of the CFH telescope in order to supplement its astronomic calibration based on reference stars. In particular it is intended to uniformize the response of the telescope over the very large field of the Megacam instrument and over well defined segments of the optical spectrum corresponding more or less to the filter set used for the SNLS experiment. The study of spectral features ofthe LED sources used by SNDICE came in this perpective mainly as a way to quantify second order corrections taking into account the shape of the spectral distribution around its central wavelength value. The spectrophotometric bench presented here did not need to have a precision better than a few percent for this task and consequently it is just an adaptation of our photometric bench presented elsewhere. It could be roughly described, as its photometric counterpart, as a «direct illumination LED calibration

L0 Project: Monitoring H1 Triggers with SpaCal

We have built a VME module using H1’s ADC and BaBar TDC interfaced to H1’s 29K processor. It is used to monitor SpaCal trigger, energy sums and trigger elements, by reading up to 130Kevents/s. The timing resolution is found to be surprisingly good ( »1ns) for energy sum signals. The performances under various beam conditions are shown, including a first study of the “hotspot” counters designed as a veto against e-beam background

Optoelectronic tests for SNDICE

We have gathered in this report the results of the tests involving only the SNDICE light source and one of the detectors used in SNDICE benches in a fixed position. In short in these tests one varies the led and the photodiode parameters (current, voltage and temperature). The underlying subject is the overall emission model of LEDs and the optimisation of their electronic control (the spectral distribution model was detailed in LPNHE 2009-01). The test of the CLAP and its asic electronics belongs to this ‘optoelectronic’ type but it has been already the subject of a particular report (LPNHE 2007-04). These tests involving only the electronics -mainly noise measurements-, including dark currents, can be done in the electronic lab where electromagnetic interferences can be controled, but when they involve light propagation they are better done on the optical benches where respective positions and vibrations are better controled

Testing Megacam with SNDICE (revised 2013)

We have gathered in this report the studies of the Megacam images produced by the SNDICE led light source. Other reports are dedicated of the study of this light source using a spectrophotometric test bench equipped with two large area photodiode detectors. A first report[1] was issued in year 2010. More data was taken in 2010 and 2011 and many issues were clarified and presented in Augustin Guyonnet thesis[2]. This paper is an update of both