Abstract

The stability of the peak wavelength of narrowband filters is of great importance, particularly if band-pass filters with a full-width-at-half-maximum (FWHM) of below 10 nm are considered. For commercial reasons, a narrowband filter which does not need to be encapsulated is preferred and it was the goal of this study to investigate two different deposition technologies with respect to the stability of the peak wavelength. Our experimental setup consisted of a cryo-pumped, fully automatically (BPU 420) controlled BALZERS BAK 760 coater equipped with two electron-beam evaporators. For the ion-assisted deposition process (LAD) the ion beam of a 15cm Kaufman ion source was directed towards the substrate; the operation of the ion source was also controlled by the BPU 420. The substrate (usually a quartz plate) of diameter 100 mm was mounted in the center of a rotating substrate holder. The coating process was controlled by a transmission measurement through the rotating substrate using a BALZERS GSM 420 optical monitor (about 3 cm from the axis of rotation). The monitoring was done at the filter's central wavelength (546 nm) and the evaporation was stopped whenever the transmittance versus deposited thickness exhibited extrema. According to Ref. /1/, with this strategy an excellent error compensation is obtained assuming the errors are independent.

© 1992 Optical Society of America