<title>Exposure-Induced Charge Distribution Effects On The Modulation Transfer Function (MTF) Of Electrooptic Spatial Light Modulators</title>

Abstract

The theoretical resolution of an electrooptic spatial light modulator [such as the Pockels Readout Optical Modulator (PROM)] is a function of the electrostatic field distribution arising from stored point charges located within the active electrooptic crystal layer. The Fourier transform of the voltage distribution (which can be directly related to the modulation transfer function) is expressed as a function of the charge location within the electrooptic crystal. In addition, the resultant analytic expression contains the dielectric constants of the blocking layers and electrooptic crystal, and the thicknesses of the three layers. This formulation allows the effects of charge trapping within the bulk of the electrooptic crystal to be modeled. In particular, the low spatial frequency response decreases linearly and the high spatial frequency response decreases exponentially with the distance of the point charge from the dielectric blocking layer/electrooptic crystal interface. Thus the overall sensitivity and resolution are degraded strongly by charge storage in the bulk away from the interface. Utilizing superposition, this formulation can be readily extended to accommodate arbitrary charge distributions arising from different exposure parameters. The spatial frequency response of the PROM is calculated for both analytic (exponential hole/gaussian electron) and iterative (exposure-induced charge transport) continuous charge distributions. The limiting form of the high spatial frequency response is shown to be independent of the particular distribution of volume charge. The implications of these results for device design and operation are discussed.