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Anti-reflection coated vacuum window for the Primordial Inflation Polarization ExploreR (PIPER) balloon-borne
Rahul Datta1, David T Chuss2, Joseph Eimer1
1Department of Physics and Astronomy, Johns Hopkins University, 3701 San Martin Drive, Baltimore, Maryland 21218, USA.
The Review of Scientific Instruments
|April 6, 2021
Summary
The Primordial Inflation Polarization ExploreR (PIPER) instrument uses a novel anti-reflection coating and indium seal on its fused-silica window to minimize reflections and prevent helium leaks, crucial for cosmic microwave background polarization measurements.
Area of Science:
- Cosmology
- Astrophysics
- Optical Engineering
Background:
- Measuring cosmic microwave background (CMB) polarization requires high sensitivity and control over systematic effects.
- Dielectric optical elements in polarimetric instruments must minimize reflective losses and imaging artifacts.
- The Primordial Inflation Polarization ExploreR (PIPER) is a balloon-borne instrument for CMB polarization and dust foreground characterization.
Purpose of the Study:
- To detail the design and testing of a specialized fused-silica vacuum window for the PIPER instrument.
- To present the anti-reflection (AR) coating procedure and optical measurements.
- To describe the indium vacuum sealing process and its integrity for superfluid helium containment.
Main Methods:
- A fused-silica window was AR coated with polytetrafluoroethylene to reduce interface reflections to <1%.
- Room temperature optical measurements were performed to characterize the window's performance.
- An indium seal was employed to prevent superfluid helium leaks into the cryostat.
Main Results:
- The AR coating significantly reduced reflections compared to an uncoated window.
- Optical measurements confirmed the effectiveness of the AR coating.
- The indium seal demonstrated integrity against superfluid helium leaks.
Conclusions:
- The developed AR-coated window and indium seal effectively address critical optical and cryogenic challenges for the PIPER instrument.
- These components are essential for achieving the high sensitivity and reliability needed for CMB polarization measurements.
- The successful implementation supports PIPER's mission to study the early universe and astrophysical foregrounds.
