The properties of opaque CsI photocathode

Cesium iodide (CsI) photocathode is widely used in various UV (ultraviolet) detecting devices because of its high quantum efficiency (QE) and good stability under short exposure to humid air. In this paper, the performance of the opaque CsI photocathode is studied, including imaging performance, influence of humidity on the quantum efficiency and the stability of the CsI photocathode under FUV irradiation. In the experiment, the input surface of the MCP was evenly divided into four parts. Different thicknesses of the CsI photocathode were deposited directly on the front surface of micro-channel plates (opaque photocathode). The response of different thicknesses and the stability of UV quantum efficiency of CsI photocathode under FUV illumination were studied by using UV monochromator. At the same time, the influence of humid air exposure on the quantum efficiency of CsI photocathode was tested. According to the experimental results, a FUV detector (vacuum tube) based on opaque CsI photocathode was fabricated and the quantum efficiency of the detector was tested. Absolute quantum efficiency of the FUV detector is over 15.5% at 121nm.