Development of nonimaging optics for particle counters

Abstract

A nonimaging optical system is developed for particle detec- tion in an optical particle counter (OPC) with a large measurement plane, the kind of OPC required to control particle contamination in clean pro- cess gases used in chip manufacture. The measurement plane must cover the whole cross section of the gas pipe to be able to detect each particle. In a conventional OPC with imaging detection optics, local de- pendence of the particle signal is caused by the inhomogeneity of light intensity in the measurement plane as well as by local dependence of the angle of the detected scattered light. However, most important is the local signal dependence caused by the imaging detection optics. Using nonimaging elements reduces local dependence of the scattered light signal which is caused by the imaging optics. The work carried out on nonimaging light concentrators for particle detection is described. We discuss the advantages of using light concentrators, summarize the op- tical theory of light concentration and investigate the optical characteris- tics of light concentrators. Through theoretical as well as experimental tests, we show that the local deviation is less than 625.6% for a homog- enous light intensity distribution in the measurement plane. © 2000 Society of Photo-Optical Instrumentation Engineers. (S0091-3286(00)01304-0)