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Spectral Metal: Saving Time And Expense In The Manufacturing Process
January 30, 2009
•Technical Article: Spectral Metal: Saving Time And Expense In The Manufacturing Process
By ROBERT J. CRASE
For many years, metal reflectors have been used in optical systems. Early civilizations used polished silver plates to pipe light deep into their structures. With advances in both science and metalworking, metal reflectors were carefully shaped and used to collect light from a manmade source.
The optical material of choice to collect and reflect light was aluminum. Silver had a higher reflectivity but tarnished in a very short period of time. Aluminum was not as reflective, but it was relatively robust in the environment, which was an important consideration. Early in the 20th century, optical coating technology was used to apply a highly reflective coating to these metal reflectors, resulting in a great improvement in light output. Unfortunately, the metal would reflect all the wavelengths of light the source produced, creating an unwanted buildup of heat. The brightest light sources produced large amounts of heat and harmful ultraviolet (UV) rays that could damage elements in the system.
The solution to this challenge was the metal cold mirror (MCM). With the MCM, a layer of absorbing material is deposited onto the metal substrate, then the high reflective dielectric optical coating is deposited on top of the absorber.
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