Laminate polyethylene window development for large aperture millimeter receivers

TL;DR

This paper presents a novel, stronger, and thinner vacuum window made from woven High Modulus Polyethylene (HMPE) for large aperture millimeter telescopes, enhancing sensitivity for Cosmic Microwave Background B-mode polarization experiments.

Contribution

Development of a new laminated HMPE vacuum window using a specialized autoclave, improving mechanical strength and optical performance for large cryogenic telescopes.

Findings

Successfully fabricated full-scale laminate windows

Demonstrated improved mechanical strength over HDPE

Achieved acceptable optical transmission properties

Abstract

New experiments that target the B-mode polarization signals in the Cosmic Microwave Background require more sensitivity, more detectors, and thus larger-aperture millimeter-wavelength telescopes, than previous experiments. These larger apertures require ever larger vacuum windows to house cryogenic optics. Scaling up conventional vacuum windows, such as those made of High Density Polyethylene (HDPE), require a corresponding increase in the thickness of the window material to handle the extra force from the atmospheric pressure. Thicker windows cause more transmission loss at ambient temperatures, increasing optical loading and decreasing sensitivity. We have developed the use of woven High Modulus Polyethylene (HMPE), a material 100 times stronger than HDPE, to manufacture stronger, thinner windows using a pressurized hot lamination process. We discuss the development of a specialty autoclave for generating thin laminate vacuum windows and the optical and mechanical characterization of full scale science grade windows, with the goal of developing a new window suitable for BICEP Array cryostats and for future CMB applications.