Omega Optical Inc. manufactures its 3rd Millenium filters using proprietary Alpha technology to produce steep cut-on and cut-off slopes. The steep slopes allow precise location of cut-on and cut-off points, close placement of transmission and rejection regions, and higher attenuation between the passband and the rejection bands. The substrates are composed of highly purified silica and use soft dielectric coatings without constraining polymers. The company says the filters' hermetic physical assembly eliminates the need for optical epoxies, resulting in lower autofluorescence and improved transmitted wavefront and heat tolerance. The hermetically sealed filter ring provides a barrier against air and moisture for environmental stability.