Abstract
The ICARUS T600 LAr TPC is the far detector of the Short Baseline Program at FNAL. As it will have to work at shallow depth in the Booster Neutrino Beam, a large cosmic rays background (∼ 11 kHz) will be present. To reduce it, precise timing information is needed from the new light detection system, based on 360 large area photomultipliers. For precise time measurements a calibration system based on a fast laser diode and a system based on one optical switch, several 01 × 1 fused fiber splitters, ultra-high vacuum optical feedthroughs and multimode optical patchcords up to 20 m long, to distribute the laser pulses to each single PMT, was designed. The time evolution of the PMTs' gain/timing and possibly their initial calibrations at a time t0 will be done by using this system. The expected time resolution of this calibration system will be around 100 ps. The laboratory tests needed to set up the system are reported.