THICK OPTICAL FILMS FOR USE AS INTERFERENCE FILTERS

The design, manufacture and use of optically transparent films with th icknesses exceeding the coherence length of the incident light is disc ussed. An analysis of the reflection and transmission of spatially and temporally incoherent light by transparent thick films is presented u sing both classical and quantum mechanical arguments. The analysis dem onstrates that, contrary to frequently stated assertions, films with t hicknesses greatly exceeding the coherence length of the incident ligh t can be used to construct optical interference filters. The results o f experiments are presented which confirm this conclusion. Finally, a discussion of the design, construction and use of interference filters made from thick optical films is presented. Designs specifically suit ed to eye and sensor protection from laser radiation are emphasized. T he manufacture of a prototype thick-film optical filter, useful for ey e and sensor protection against the radiation from several lasers, is reported. (C) 1998 Elsevier Science S.A.