Calibration prototype for the EUDET HCAL
  The electronics producing a few nanoseconds long LED pulses tuneable in the amplitude and the optical system distributing the LED light to scintillators by a single optical fibre are described. The properties of the LED pulses are controlled by a computer connected via a CANbus to the controller on the board. We produced a prototype with 6 LED pulse drivers placed on a 4-layer PCB with dimension 250 x 147 mm2. The pulse width is constant and 3 ns long. Its amplitude can be tuned from zero to 1.2 A. The pulse frequency can be set in the range up to 100 kHz. The LED light is distributed by a 1 mm diameter optical fibre. On the length of 2 m the fibre has every 30 mm a notch which flashes light with homogeneity of \pm20%. The system is foreseen for calibration of silicon photomultipliers embedded in scintillation tiles. 
J. Cvach, M. Janata, J. Kvasnicka, D. Lednicky, I. Polak, J. Smolik,   J. Zalesak (Institute of Physics of the ASCR, Prague,...
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