Structuring Control Systems for Normalization of Optical Intensity with AVR Microcomputer : To Reduce the Spurious Signal on Photoreflectance

摘要

We describe microcomputer-based implementation of the PI-control system for normalization of the dc reflectance part from the photoreflectance data. Our technique uses a stepping-motor-driven variable neutral-density filter which keeps the dc component of the detecting signal constant by varying the light flux impinging into the specimen under test. This enabled extremely facile a-posteriori subtraction of the spurious component of the photoreflectance, which has been often problematic for the precise measurements. We optimized this feedback system through parameterization of the proportional and integral terms