Investigating the Components of Signals Produced by the Pockels CCD Imaging Technique in CdZnTe

Abstract

Several groups have demonstrated the potential of the Pockels effect in Cadmium Zinc Telluride (CZT) as a means to detect ionizing radiation. Migrating charge carriers are believed to generate the signal detected via the Pockels effect due to the distortions they create within the electric field, however trapped space charge beneath the cathode has been regularly observed which suggests field changes away from the charge generation area. Consequently the Pockels signal amplitude contains a charge integrated, i.e. dose element. In this work, the effects of electric field collapse at the location of charge carrier generation are demonstrated. This opens the potential to apply the technique for imaging dose rate distributions. Charged coupled device (CCD) images representing the changes in electric field within the crystal were taken and the response to illumination from a collimated 1550 nm 4.5 mW IR laser and irradiation from 150 kVp X-rays measured. The data demonstrates that the signal acquired is a combination of both the local change in the electric field at the location where the carriers are being released/generated and an element caused by carriers becoming trapped, leading to electric field enhancement due to space charge near the cathode, and field reduction towards the anode.

Modulation of electrodes on the sensitivity of the Pockels effect

“…Pockels electro-optic effect has been widely used in detection, aviation, electric field research and other fields [1,2]. The electro-optical effect can be used to make electro-optical modulators [3], electro-optical opening lights [4], optical gates [5], optical communication equipment [6], laser Q switches [7], etc. Since the crystal refractive index changes regularly with the applied electric field, the design and manufacture of various measuring equipment, electro-optical modulation equipment and switchgear can be realized by establishing a relationship between the electric field to be measured and the electric field.…”