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 the use of various plastic materials which have reasonable absorption or scattering for the infrared wavelengths but which have low loss at the signal wavelengths. One such material is HDPE, for which some sort of anti-reflection coating would be required, and because materials with the required refractive index are not available, anti-reflection grooves are a possibility. To investigate the practicality of such grooves, measurements have been made of un-grooved High Density Polyethylene (HDPE), and of samples with linear or concentric rectangular grooves and linear triangular grooves. At 75-110 GHz, measurements were made with an HP8510 and between 60 and 450 GHz with a low resolution FTS.
View a PDF version of ALMA Memo #347.Last modified: February 15, 2001
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