A novel photodiode array for astronomical spectroscopy
Imaging arrays can be constructed from photodiode sensor elements using integrated circuit fabrication techniques. Such imaging arrays have proved to be useful in the field of observational astronomy, chiefly because of their linearity and good spectral response in the near infra red region. A photodiode array has been developed by the Plessey Co. Limited, in collaboration with the Royal Greenwich Observatory. This array incorporates certain novel techniques, including an "on-chip" charge amplifier on each element, and a multiplexing scheme that allows correlated double sampling and non-destructive readout. The array was originally designed to be used in an electron counting mode, installed in an electronographic tube. The Nuclear Instrumentation Group of Durham University has investigated the application of this array to direct optical imaging, in particular for astronomical spectroscopy. The characteristics of the array when used in the photon integration mode have been investigated, and measurements have been made of responsivity, thermal leakage, linearity, noise components, and other properties. A CAMAC based computer control system has been designed and constructed, and the required software developed, to operate the array as an observing instrument. The array has been used in observational tests at the Coudé spectrograph of the 30 inch telescope of the Royal Greenwich Observatory, and a quantity of spectral data has been obtained.