Composite vacuum-tight window for simultaneous far-infrared and optical observations

Abstract

We analyse the optimization of windows which must transmit in the visible and in the far-infrared. The mechanical strength and the far-infrared transmission of available materials (mylar, TPX, quartz, sapphire, silica, diamond, plexiglass) are reviewed. We describe a composite window which is vacuum-tight and can withstand differential pressures of 1 bar. This window has permitted successful observations on the K.A.O. airborne telescope with transmission higher than 70% in the 50–200μ range.