Construction progress in the photon counting detector for the European Laser Timing experiment

We are presenting a progress in a construction and indoor tests of the photon counting detector for the European Laser Timing (ELT) experiment. ELT is an optical link prepared in the frame of the ESA mission "Atomic Clock Ensemble in Space" (ACES). The objective of this laser time transfer is the synchronization of the ground based clocks and the clock on board the space station with precision of the order of units of picoseconds and the accuracy of 50 ps. The requirements put on the detector package are quite high — temperature stability of the delay better than 20 ps peak to peak within one satellite orbit, operation within a broad temperature, absolute calibration of the photon to electrical signal delay with precision 25 ps and others.