Macroporous Silicon Ultraviolet Filters

Abstract

Many applications (such as solar blind non-line of sight communications, electrical spark imaging, photolithography, chemical and biological analysis) require optical filters to be used in the ultraviolet (λ < 400 nm), deep ultraviolet (λ < 300 nm), or even far ultraviolet (λ < 200 nm) wavelength ranges. The complexity in fabricating good performance filters for the deep and far UV range grows exponentially for established technologies since materials tend to become absorbant. No absorption-based filter material is known to have short-pass characteristics with a transparency range down to far UV. While a number of different absorption materials were suggested for band-pass deep UV solar blind filters [1–5], only dyedoped polymer filters [5] from Ofil Ltd. (Israel) have found reasonable commercial success and are currently used in certain demanding applications. It should be noted though that such filters offer generally poor transmission within the pass band (while providing very good levels of rejection) and suffer form quite poor environmental/thermal stability, insufficient for many applications.