Photometric testing apparatus using shaped diffuser and light beam having a spatially ill-defined energy distribution

摘要

A testing apparatus for making photometric measurements of transmission and reflectance of large parts uses a light beam having a spatially ill- defined energy distribution. A detector for receiving the light beam has a spatial variation in its sensitivity over its sensing area. A diffuser is provided which is disposed in the light beam for intercepting the light beam before it strikes the detector. The diffuser is formed of a white-like plastic and has a thickness which decreases progressively towards the outer edges of the same to compensate for the fall-off in sensitivity of the detector to rays closer to the outer margins of the diffuser or away from the center of the diffuser. The diffuser is formed in two portions in which a portion of the diffuser is in substantially closer proximity to the detector than the other portion to minimize the directional sensitivity of the detector.PP The apparatus uses an invisible beam which is aimed by a coaxial visible beam. Measurements of transmission and reflectance are made in quick succession by moving the sample on a carriage and using a movable mirror assembly. The invisible beam is aimed separately for each of the two measurements.