By Dr. Geoff Martin, Principal Systems Engineer, Raptor Photonics Ltd
CCD imaging sensors are used extensively in high-end imaging applications, enabling acquisition of quantitative images with both high (spatial) resolution and high sensitivity. Applications such as high content screening, genome sequencing, FRET / FRAP / TIRF, to name but a few, utilize the highest performance imaging devices available. Multi-mega pixel sensors are available with peak quantum efficiencies (QE) approaching 100% and a read noise floor of 2 electrons rms or less, presenting the user with an extremely sensitive imaging device. However there are some photon-starved applications, including bio-luminescence, astronomy and fluorescence microscopy, which require even these highly sensitive devices to be used with both long integration (exposure) times and high amounts of binning (on-chip charge summation) in order to obtain a detectable signal. For these type of applications the CCD sensor must be deep cooled in order to reduce the noise component associated with dark signal.