Description
Scintillator based time-of-flight systems may reach excellent time
resolution, by using fast scintillators and fast photomultipliers.
Examples are the large time-of-flight system constructed for the HARP
experiment at CERN PS (~150 ps intrinsic time resolution) or the most demanding time-of-flight system of the MICE experiment at RAL (~50 ps resolution). This level of timing resolutions puts demanding requirements on the calibration system for day by day time monitoring.
Diode-laser based systems may be realized by splitting a fast laser beam (FWHM~ 30 ps) to a fast photodiode, giving the START for the TDC system, and injecting the laser light into a system of fibers that transmit the pulse to the individual counters to be calibrated, giving the STOP signal. Due to the limited power of diode-laser systems (up to 1 W) extreme care must be put to minimize pulse power losses. The choice of the type of optical fiber to be used (multimode vs single-mode) is another critical issue.
Step-index multimode fibers has been chosen giving the best trade-off
between simplicity of use, input power loss minimization and timing properties of the system. A system based on optical switches, fused fiber splitters and a diode-laser will be described, together with laboratory tests to optimize the choice of components and characterize the complete timing performances.
Primary author
Maurizio Bonesini
(Universita & INFN, Milano-Bicocca (IT))
Co-authors
Antonio de Bari
(Universita' di Pavia)
Dr
Massimo Rossella
(INFN Pavia)
Roberto Bertoni
(Univ. + INFN)
