Wikipedia:Today's featured article/September 2, 2006

A potassium Faraday filter

An atomic line filter is an advanced optical filter, specifically a narrow band-pass filter, used in the physical sciences for filtering electromagnetic radiation with precision, accuracy, and minimal signal strength loss. The three major types of atomic line filters are absorption-re-emission, Faraday filters and Voigt filters. Atomic line filters take advantage of the narrow lines of absorption or resonance in a metallic vapor and manipulate a specific frequency of light past a series of filters that block all other light. Atomic line filters are used in scientific applications requiring the effective detection of laser light that would otherwise be obscured by broadband EMF sources, such as daylight. They are used regularly in LIDAR and are being studied for their potential use in laser communication systems. Atomic line filters are superior to conventional dielectric optical filters such as interference filters and Lyot filters, but their greater complexity makes them practical only in background-limited detection, where a weak signal is detected while suppressing a strong background. (more...)

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