Developing metal coated mesh filters for mid-infrared astronomy

摘要

A metal mesh filter is appropriate to a band-pass filter for astronomy in the long mid-infrared between 25 and 40 μm,where most of optical materials are opaque. The mesh filter does not require transparent dielectric materials unlikeinterference filters because the transmission characteristics bare determined by surface plasmon-polariton (SPP)resonances excited on a metal surface with a periodic structure. In this study, we have developed the mesh filtersoptimized to atmospheric windows at 31.8 and 37.5 μm accessible from the Chajnantor site of 5,640 m altitude. First,mesh filters made of a gold film of 2 μm thickness have been fabricated. Four identical film-type filters are stackedincoherently to suppress leakages at stop-bands. The transmissions of the stacked filters have been measured to be 0.8 atthe peaks and below 1 x 10sup-3/sup at the stop-bands at 4 K. The ground-based mid-infrared camera MAX38 has been equippedwith the stacked filters and successfully obtained diffraction-limited stellar images at the Chajnantor site. The film-typemesh filter does not have sufficient mechanical strength for a larger aperture and for use in space. We have developedmesh filters with higher strength by applying the membrane technology for x-ray optics. The membrane-type mesh filteris made of SiC and coated with a thin gold layer. The optical performance of the mesh filter is independent of internalmaterials in principle because the SPP resonances are excited only on the metal surface. The fabricated membrane-typemesh filter has been confirmed to provide comparable optical performance to the film-type mesh filter.© (2012) COPYRIGHT Society of Photo-Optical Instrumentation Engineers (SPIE). Downloading of the abstract is permitted for personal use only.