Scanning deflectometric profiler for measurement of transparent parallel plates

An angle-based deflectometric surface profiler has been improved for the measurement of transparent parallel plates. In the developed system, the unwanted beam reflected from the back surface of the transparent parallel plate is removed by ensuring that the beam is obliquely incident to the measurement surface; this is realized by using a modified pentamirror unit comprising two mirrors installed at a predetermined angle to one another. The surface profile measurement of a transparent parallel plate with a repeatability of less than ±0.7  nm was successfully achieved. A measurement accuracy of around 3 nm was reached by comparing the developed system with other scanning deflectometric profiler systems for the measurement of a silicon bar mirror with a length of 300 mm.