Low-retardance fused-quartz window for real-time optical applications in ultrahigh vacuum

Abstract

We describe a low-strain, Suprasil quartz window assembly for ultrahigh vacuum applications that require high transmittance and/or low retardance over a wide spectral range. The assembly mounts on a 2 (3)/(4) in. Conflat flange. The window can be heated externally to 400 °C to remove typical molecular-beam-epitaxy growth deposits, thereby eliminating a major source of inaccuracy in optical pyrometry and allowing high-light fluences to be transmitted with minimal attenuation. Retardations at 459 nm (2.5 eV) of four unmounted Bellcore windows ranged from 0.05° to 0.3° while retardations of properly mounted windows were <0.5°. These retardations could be reduced an order of magnitude by applying small counterstresses, thereby allowing highly accurate real-time growth data to be obtained by polarization-sensitive optical techniques such as reflectance-difference spectroscopy or spectroellipsometry.