Numerical optimization of integrating cavities for diffraction-limited millimeter-wave bolometer arrays

Area of Science:

• Astrophysics
• Optical Engineering
• Detector Physics

Background:

• Far-infrared to millimeter-wave bolometers are essential for astronomical observations.
• Integrating cavities enhance radiation absorption and minimize stray light in photometers.
• Future astronomical arrays will utilize hundreds of silicon nitride micromesh bolometers.

Purpose of the Study:

• To optimize integrating cavity designs for maximizing sensitivity in bolometer arrays.
• To investigate the electromagnetic fields within plane-parallel integrating cavities.
• To evaluate cavity performance for the Bolometer Array Camera (Bolocam) at 214 GHz.

Main Methods:

• Numerical simulations of electromagnetic fields in infinite plane-parallel integrating cavities.
• Modeling cavities with a solid reflecting backshort and feedhorn array block back surface.
• Comparison of simulation results with experimental data from a room-temperature model and Bolocam performance.

Main Results:

• Achieved monochromatic absorptions as high as 95% with less than 1% crosstalk.
• Identified optimal absorber impedances around 400 ohms/sq, with a broad maximum (150-700 ohms/sq).
• Determined that maximum absorption requires absorber diameters greater than or equal to 1.5 times the wavelength (λ).

Conclusions:

• The simulated integrating cavity design shows high absorption efficiency and low crosstalk.
• The findings provide critical parameters for optimizing bolometer cavity design for enhanced sensitivity.
• Good agreement between simulations and experimental data validates the modeling approach.