1 December 1990 Window materials for high power gyrotron
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Proceedings Volume 1514, 15th International Conference on Infrared and Millimeter Waves; 15144V (1990) https://doi.org/10.1117/12.2301585
Event: 15th International Conference on Infrared and Millimeter Waves, 1990, Orlando, FL, United States
The absorption coefficient of most low absorbing materials increases almost linearly with increasing frequency. For ceramic boron nitride, this is opposite, the absorption decreases with increasing frequency atleast to about 600 GHz. Single crystal high resistivity silicon has the lowest absorption at room temperature in the entire millimeter wavelength region. Our new broadband continuous wave low temperature (76 K and 86 K) measurement on single crystal sapphire reveal that its absorption coefficient value is almost the same as its room temperature value around 90 GHz (0.05 Nepei/cm), then slowly increases to 0.07 Neper per cm at 290 GHz. The low tempertature absorption value then decreases to 0.015 Neper/cm at 450 GHz. Continuous broadband data on complex refractive index and complex dielectric permittivity at 4 kelvin will be available around the conference time. There is hardly any difference in its absorption value at 86 kelvin (compared to 76 kelvin). We do not see any advantage of using sapphire as a window material at 77 kelvin. Extra high resistivity silicon is by far the best window material as regards the absorption loss concerned.
© (1990) COPYRIGHT Society of Photo-Optical Instrumentation Engineers (SPIE). Downloading of the abstract is permitted for personal use only.
Mohammed Nurul Afsar, Mohammed Nurul Afsar, } "Window materials for high power gyrotron", Proc. SPIE 1514, 15th International Conference on Infrared and Millimeter Waves, 15144V (1 December 1990); doi: 10.1117/12.2301585; https://doi.org/10.1117/12.2301585

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