Conclusions

The electron multiplying CCDs developed by E2V Technologies represent a major advance in high frame-rate, low light-level imaging (also presumably those developed by Texas Instruments, although at present there is less practical experience with these devices in the Institute of Astronomy). Numerical simulations indicate that these devices could be operated as a two-dimensional array of photon counting detectors with high quantum efficiencies. At high light levels where coincidence losses become significant, the output can be treated in an analogue fashion just like a conventional CCD. This flexibility gives the devices enormous dynamic range, ideal for the Lucky Exposures method. Bright reference stars could be recorded without the limitation of coincidence losses, while in another part of the field individual photons from a faint object could be counted individually with high Quantum efficiency.

Observational data taken using electron-multiplying CCDs in a custom-built camera was found to be generally consistent with a simple theoretical model for the electron-multiplying CCD architecture. There was evidence for poor charge transfer efficiency at low signal level under some operating conditions and this may impact some of the astronomical observations. The statistical properties of some sample data taken from an observing run suggest that the best approach to analysing the data presented in the following chapter is to treat the output of the CCD like an analogue signal.