<title>Stable ultranarrow bandpass filters</title>

Abstract

A large format ultra-narrow bandpass filter for use in the visible through near IR which has improved transmission and environmental stability is discussed. The filter is composed of thin films of metal- oxide coating materials deposited at near bulk density using OCA's MicroPlasma coating process. The high packing factor of the coating results in nearly zero vacuum to air shift. The filter shows improved temperature stability due to the selection of coating materials with low coefficients of thermal expansion and temperature coefficients of refractive indices as compared to filters manufactured using conventional technologies. In addition, the materials also have very low optical absorption and scatter which leads to improved filter transmission. Experimental data is presented describing the spectral performance and humidity and temperature stability of multiple cavity filters with bandwidths of 10 angstroms or less which possess single piece (non-mosaic) clear apertures of up to 10 inches. The improved temperature stability can eliminate the need for active temperature controllers such as heating cells. Improved narrow band filters have several immediate applications as a method to improve signal-to-noise ratio of laser based optical systems for both military and commercial markets such as LIDAR, FTIR, and remote sensing.