​Lake Shore Far IR band pass filters specified for NASA’s FORCAST instrument on the SOFIA Airborne Telescope
Lake Shore Band Pass Filters for NASA FORCAST Instrument on SOFIA Telescope

Lake Shore Cryotronics today announced that researchers at Cornell University’s Department of Space Science have successfully tested a series of metal-mesh, band pass filters and will fly them in the FORCAST instrument aboard the SOFIA science center. Dr. Terry Herter is FORCAST’s Principle Investigator and Dr. Joe Adams is the Project Scientist who has led the testing and evaluation of the filters. Dr. Adams commented, “After multiple thermal cycling down to 4 K, these far-infrared filters have met our requirements for transmission and image quality.” Dr. Adams further added, “We utilize Lake Shore’s filters on account of their high transmission and higher reliability during thermal cycling when compared to competing far-infrared filter technologies.”

Employing frequency selective surface technology, the filters are designed with patterned, cross-shaped, and other resonant opening geometries that allow the transmission of light at specific wavelengths. Multiple 25 mm diameter filters have been supplied to Cornell with center wavelengths (CWLs) of 24.4, 33.4, and 38.8 µm. 

They have CWL transmissions up to 85%, CWL tolerance of ±0.1 µm, and out-of-band transmission down to 0.5%. The filters exhibit excellent thermal properties with stable and repeatable performance down to 4 K. Their 1 mm thickness enables entry into existing filter wheels, cryostats, and compact optical instruments. 

FORCAST (Faint Object infraRed CAmera for the Sofia Telescope) is a mid/far infrared camera for the SOFIA airborne observatory. It is a two-channel camera with selectable filters for imaging in the 4-8, 16–25, and 25-40 µm regions and is intended to provide multicolor imaging of the galactic center, Vega-like dust clouds, and star formations in our galaxy, normal spiral galaxies and active galaxies. For more information on SOFIA, see http://www.nasa.gov/mission_pages/SOFIA/