ALMA MEMO NO. 412 68.5 to 118 GHz Measurements of Possible Infrared Filter Materials: Black Polyethylene, Zitex, and Grooved and Un-Grooved Fluorogold and HDPE

For the ALMA production test receivers at present being designed in the NRAO CDL, there is a need for infrared filters to reduce the thermal loading. One possibility is to use a plastic material which has reasonable absorption or scattering for the infrared wavelengths but low loss at the signal wavelengths. Black polyethylene (polyethylene with carbon filler) [1, 2], Zitex (expanded PTFE) [3], and Fluorogold (a glass-filled Teflon) [4] have been suggested as such materials. Measurements at 68.5-118 GHz with an HP8510 have been made on room temperature samples and multilayer filters (which were also measured at liquid nitrogen temperature). Measurements of grooved HDPE are also reported (which resolve an inconsistency in our earlier measurements [5]).