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Controlling Light with Optical Interference Coatings

Just a quick post on Dr. Mary Banning and Dr. Philip Baumeister, two pioneers in optical interference coatings. See Ref. 2 for a 50-year-old layman’s review on thin film optical coatings. See Ref. 3 for an excellent interview with Baumeister [Ref. 3].

“A recent communication from Brian O’Brien Jr. describes some of the activities at The Institute of Optics during World War II. “I did work for Dr. Mary Banning, as did several other undergraduates. I don’t remember just when she set up the evaporator lab but we did a lot of coating work during the war. This included multi-layer low-reflecting coatings, nickel neutral density filters, partial reflecting coatings, etc. I remember one job we did producing 50% coatings on 45/90 prisms for our entire fleet of submarine periscope cameras. These were actually not done by vacuum evaporation but by heat decomposition of titanium tetrachloride into titanium dioxide coating on glass.” “In 1947 Mary Banning wrote a classic paper explaining how to deposit multi-layer filters and how to control their thickness.” She also described the 1943 development of the polarizing beamsplitter in this paper as well.” [Ref. 1]

Dr. Mary Banning (1946)
A production coating chamber [Ref. 2].

“What do oil slicks, soap films, oyster shells and peacock feathers have in common? The familiar iridescent patterns of color reflected from all these surfaces are natural manifestations of the same phenomenon: optical interference in a thin layer. Although the principles of optical interference have been understood for more than a century, it has been only in the past few decades that this knowledge has been exploited for technological ends. The oldest, simplest and still the most common application of an optical interference film is as a single-layer anti­reflection coating, such as those used to reduce the reflectance of camera lenses.

In recent years more complicated optical interference coatings have been developed in which many layers of different materials are deposited on an optical surface. Stacks of such films are used not only as antireflection coatings but also as filters, polarizers, beam-dividers and highly reflecting mirrors. These coatings are indispensable components of not a few modern optical systems, such as lasers, color television cameras and infrared missile-guidance systems. This article explains the rudiments of optical interference and discusses in detail a number of current devices that make use of this phenomenon.” [Ref. 2, full article is excellent, link below]

Philip Baumeister

Barry Dame with Baumeister’s Big Berthe at University of Rochester, 1962 or later in the 1960’s.

References

[1] Carlos R. Stroud Jr, Editor, “A Jewel in the Crown,” Chap. 25, ISBN 978-1580461627.

[2] Philip Baumeister and Gerald Pincus, “Optical Interference Coatings,” Scientific American December 1970.

[3] Philip Baumeister Interview, Society of Vacuum Coaters.