Improvements in ALMA Band 10 Optics: Influence of IR Filters and Solutions

Infrared (IR) filters and cryostat window in the Atacama large millimeter/submillimeter array (ALMA) cryostat were found to greatly degrade the optical performance of ALMA band 10 optics. This degradation has its origin in the reflection the beam suffers when going through the filters and window. The cause and mechanism of this degradation were identified using THz-TDS and simple analysis techniques and a simple solution was found. The proposed solution is based on corrugated horns with chamfered rims and Terahertz absorber paint applied around the horns. This solution proves efficient in keeping the original optical performance when the optics is used in real operation at cryogenic temperature.