Photon counting and fast photometry with L3 CCDs

The new L3 Technology CCDs from E2V allow detector read noise to be decoupled from readout speed. If operated at sufficiently high gain, the read noise drops to sub-electron levels and photon counting becomes possible. At ING we have incorporated CCD60, CCD87 and CCD97 L3 detectors into cryogenic cameras coupled to SDSU controllers for a variety of tests both in the lab and on-sky using the 4.2m William Herschel Telescope. These detectors have been operated in proportional and photon-counting mode using an in-house Linux based DAS. We have gained a number of insights into photon counting optimisation, how to cope with the effects of the L3 pipeline delay and the reduction of internal device-generated spurious charge. We have also discovered a statistical method for determining the gain of an L3 system from pulse height analysis of the individual photon events. Our on-sky test program has consisted to date of high frame rate photometry of the Crab Nebula Pulsar.