The ERIM Thermoplastic Optical Phase Recorder (TOPR) is a real-time, two-dimensional light modulator. The modulator employs electron beam writing on a deformable and reusable thermoplastic film. The varying thickness film causes phase modulation of a light beam in an optical processor. The data written into the plastic can be stored for periods from less than 0.5 sec to many months depending on the temperature at which the plastic is maintained. The time bandwidth product of the device is greater than 106 and its optical quality is suitable for optical data processing. Because of these features the TOPR, combined with an optical data processor, can offer advantages in size, cost, complexity, and processing speed relative to digital computers. Alternatively, the TOPR can be used in a hybrid optical-digital computer to provide preprocessing of data or a "quick-look" capability for digital data processing decisions. This paper describes characteristics of the TOPR and an application of the TOPR to processing of imagery from data recorded in a unique polar format. Introduction The purpose of this paper is to describe a real-time spatial light modulator and its use in a coherent optical computer in a practical application; synthetic aperture radar (SAR) data processing. In this modulator a scanning, intensity-modulated electron beam is used to deform a thin thermoplastic film. A large area light beam is passed through the film (or reflected from it) and the deformation image is impressed onto the light beam as a two-dimensionql phase modulation. This modulator was developed specifically for optical data processing', thus, it has good optical quality, large space-bandwidth product, near real-time response, and a reusable modulation medium. In the following we will discuss the modulator design, its specifications, and its performance in the SAR data processing application.