Inspection of Large Area and Large Volume Optics by Raster Scanning

Scattered light is a problem in many optical systems. Increasingly, scatter is becoming recognized as the real issue with component specifications written in terms of the BSDF (bidirectional scatter distribution function) instead of the often less appropriate surface finish parameters (rms roughness, etc)[1,2]. Additionally, the presence of light scatter from a local area, on an otherwise uniform optic, indicates the presence of a defect or a contamination site. Unfortunately, complete sample coverage by full angle BSDF inspection is often impractical due to time and cost limitations imposed by sample size and/or sample numbers. For these situations a raster scanning technique which rapidly covers the required area may be the best solution. Raster data provides valuable insights into sample non-uniformity caused by production processes and contamination.