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Shift-free narrowband filters for the UV-B region

: Kaiser, N.; Uhlig, H.; Schallenberg, U.B.

France, C. ; Society of Photo-Optical Instrumentation Engineers -SPIE-, Bellingham/Wash.:
Developments in optical component coatings : Tagung 15-16 May 1996, Glasgow
Bellingham, Wash.: SPIE, 1996 (Europto series)
ISBN: 0-8194-2161-8
Conference "Developments in Optical Component Coatings" <1996, Glasgow>
Conference Paper
Fraunhofer IOF ()
Dünne optische Schicht; excimer laser optics; Excimer-Laser-Optik; fluoride thin films; Fluoridschicht; laser induced damage threshold; Laserzerstörschwelle; optical coating; optical thin films; oxide thin films; Oxidschicht; ultraviolet spectral region; ultravioletter Spektralbereich

Monitoring of stratospherical ozone depletion by filter rediometers calls for narrowband filters with outstanding parameters. At filter wavelengths down to 300 nm narrow bandwidth, high peak transmittance together with high out-of-band blocking especially at longer wavelength are demanded. Furthermore, filters have to be completely free of wavelength shift caused by humidity. Conventional interference filters suffer from such shift because of the water sorption of the evaporated layers. By using plasma ion assisted deposition (Advanced Plasma Source - APS, Leybold) of zirconia and silicia layers we succeeded in manufacturing blocked two-cavity filters with full width at half maximum (FWHM) of 1.7 nm and peak transmittance of 17 per cent at the center wavelength in the UV-B region. Outside the transmission band from UV to NIR (>= 1000 nm) optical density is at least 6. There was no decrease in wavelength of such filters (without hermetisation) by changing relative humidity from 100 per cent to 0 per cent. Corresponding conventional filters shifted 4.5 nm under the same conditions. The filter performance achieved allows use for the development of sensitive and specific instrumentation for environmental, climate, and meterological research.