Experimental Investigation of Photoemitter Membrane Spatial Light Modulator Performance Limit

Abstract

A photoemitter membrane light modulator (PEMLM) is enhanced by adding a visible light photocathode to the basic structure [1]. The basic structure consists of four parts; a microchannel plate (MCP), a grid, a deformable membrane, and a transparent electrode as shown in Figure 1. Previously the input of the MCP was used as a photocathode to convert an ultraviolet (uv) image into an electron distribution. The MCP then amplifies this distribution by secondary emission, similar to a photomultiplier tube. At the output of the MCP the electron energies are low. The purpose of the grid that is added to the MCP output, is to control the electron energy. If the energy is low the electrons will be deposited onto the membrane. If they are high, excess secondary emission at the membrane will occur and electrons will be removed from the membrane. Thus, images are added or subtracted by changing the grid voltage. The rate at which these functions and other possible functions occur, is dependent upon the rate of electron generation by the MCP, up to the point of MCP saturation. This electron generation is the product of the light intensity and photocathode quantum efficiency. Using the MCP input as a photocathode requires a strong uv light because of a low quamtum efficiency (≃10-7), even at short wavelengths. To avoid the problems of working with uv, a cesium-antimony(Cs3Sb) photocathode for the PEMLM is being fabricated. This will allow the use of red light for a write beam. Previously, high frame rates were not achieved because of the limits of the light source. With the Cs3Sb photocathode frame rates should be increased to the MCP strip current limit.