Atomic line filter
Atomic line filters work via the absorption or resonance lines of atomic vapors. The three major types of atomic line filters are absorption-re-emission ALFs, Faraday filters and Voigt filters. They are used regularly in Laser Imaging Detection and Ranging and are being studied for potential use in laser communication systems.
About Atomic line filter in brief
Atomic line filters work via the absorption or resonance lines of atomic vapors. The three major types of atomic line filters are absorption-re-emission ALFs, Faraday filters and Voigt filters. Atomic line filters can be considered the optical equivalent of lock-in amplifiers. They are used regularly in Laser Imaging Detection and Ranging and are being studied for their potential use in laser communication systems. The exact parameters of any filter may be tuned to a specific value by computers due to the extreme complexity of the systems.atomic line filters operate in the visible and infrared regions of the electromagnetic spectrum. If photomultiplier tubes are used, then the active ALFs would have the advantage over passive filters over the long-lived PMT tubes. In a PMT filter, the output frequency of the filter must be shifted in order for the passive device to operate. This means that passive filters are rarely able to work with infrared light, because the outputfrequency would be impractically low. In such a case, such filters would have to be used over the passive ALF tubes, which would be much higher in sensitivity than the passive filters used in the PMT case. The most effective passive filters would be PMT filters, which have a maximum sensitivity over PMF tubes of up to 100,000 times higher than the active filters used for LIDAR. The maximum sensitivity of an active ALF would be over 1,500 times that of a passive filter, which means that the passive filter would have a much higher sensitivity over the active filter.
This advantage would be the result of energy conservation, simply because of the lower energy conservation of PMTs. The first atomic line filter was the infrared quantum counter, designed in the 1950s by Nicolaas Bloembergen. It was a quantum mechanical amplifier theorized by Joseph Weber to detect infrared radiation with very little noise. The media of these devices were crystals with transition metal ion impurities, absorbing low-energy light and re-emitting it in thevisible range. By the 1970s, atomic vapor quantum counters were used in atomic vapor quantum counters for detection of infrared electromagnetic radiation, as they were found to be superior to the metallic salts and crystals that had been used. The principles hitherto employed in infrared amplification were put together into a passive sodium ALF. This design and those that immediately followed it were primitive and suffered from low quantum efficiency and slow response time. As this was the original design for ALF, many references use only the designation “atomic line filter” to describe specifically the absorption-Re-Emission construction. In 1977, Gelbwachs, Klein and Wessel created the first active atomic line Filter, which was called a Faraday filter. Faraday filters are significantly sturdier and may be six times cheaper at around US$15,000 per unit. Compared to etalons, another high-end optical filter, they are significantly more powerful than ALFs.