Development of techniques to characterize electron-bombarded charge-coupled devices

Abstract

Electron Bombarded Charge Coupled Devices (EBCCDs) are a new hybrid image intensifier tube device that allows photoelectrons to be directly detected by a CCD placed as the tube anode. These devices have many significant advantages over traditional image intensified systems, due to their lower noise figure, high intra-scene dynamic range, and high signal to noise ratio. EBCCDs are not subject to some of the deleterious effects that plague traditional intensifiers including veiling glare, "chicken wire" patterns, and ion scintillation. Currently, there is not a standardized set of characterization methods used to measure the performance of these hybrid devices. Furthermore, the normal method of measuring device gain as a ratio of output current (measured as current through the anode substrate) to input current (as measured through the photocathode) does not apply to EBCCDs. This dissertation presents several new methods that have been developed to characterize in situ EBCCD tubes. The new characterization methods that have been developed are: (1) How to measure the actual gain of an EBCCD when operated as a CCD (normal operating mode), (2) How to measure the mean and variance of a single electron pulse height distribution when only multiple electron pulse height distribution data is available, (3) How to measure the spatially varying probability of secondary electron capture by the CCD potential wells, (4) How to measure the thickness of an aluminum overcoat using only optical measurements, (5) How to measure the gain variation due to aluminum thickness variations. These methods have been designed to enable characterization of the EBCCD even after it has been mounted in a camera. This will allow both tube and camera manufacturers to measure performance in a production setting. These new methods were employed, along with other standard measurement techniques, to characterize a commercially available EBCCD (Hamamatsu N7220) controlled by a camera designed by the author. Several figures of merit were measured as a function of accelerating potential including the gain, device signal to noise ratio, detective quantum efficiency, and noise figure. The tube MTF, radiometric sensitivity, aluminum thickness, dynamic range, and probability of secondary electron detection were also measured.