Silicon-based vacuum window for millimeter- and submillimeter-wave astrophysics.

Area of Science:

• Astrophysics
• Materials Science
• Optics

Background:

• Millimeter-wave astronomy requires specialized components for sensitive observations.
• Vacuum windows are critical for maintaining instrument integrity and performance in space-based or ground-based telescopes.

Purpose of the Study:

• To design, fabricate, and characterize a novel silicon-based vacuum window for millimeter-wave astrophysical applications.
• To evaluate the optical properties and suitability of the window for high-frequency astronomical instruments.

Main Methods:

• Fabrication of a silicon-based vacuum window with specific dimensions (124 mm diameter, 68 mm usable diameter, 4 mm thickness).
• Application of an anti-reflection coating using laser-ablated sub-wavelength structures (SWS).
• Characterization of optical properties, including transmittance and reflectance, across a fractional bandwidth of 67% centered at 300 GHz.

Main Results:

• The silicon vacuum window exhibits high average transmittance (99.6±3.5%) and low reflectance (1.3±1.4%).
• Optical performance agrees with modeling based on measured SWS shapes.
• Absorptive loss was below the detection limit of the measurement.
• The window was successfully integrated into the DESHIMA 2.0 instrument for year-long observations.

Conclusions:

• The developed silicon vacuum window meets the stringent requirements for millimeter-wave astrophysical applications.
• The use of laser-ablated SWS for anti-reflection coatings is effective for achieving high transmittance.
• The window's performance and successful integration demonstrate its viability for advanced astronomical instruments.