High-absorption optical stack for aluminum kinetic inductance detectors

Area of Science:

• Superconducting Devices
• Optical Engineering
• Materials Science

Background:

• Aluminum (Al) is a standard material for kinetic inductance detectors (KIDs) due to its micro-fabrication compatibility.
• Achieving high optical absorption in Al absorbers is difficult because Al reflects light strongly at optical wavelengths.
• Efficient light absorption is crucial for high-performance photon-counting and energy-resolving detectors.

Purpose of the Study:

• To design a high-absorption optical stack for Al-based KIDs.
• To overcome the challenge of high reflectivity in Al absorbers at optical wavelengths.
• To enable efficient photon detection in the optical to near-infrared (NIR) spectrum.

Main Methods:

• Embedding a thin Al film between an anti-reflection (AR) coating and a dielectric-based distributed Bragg reflector.
• Utilizing a transmission matrix model for calculating optical performance.
• Fabricating and measuring the optical properties of the designed stack.

Main Results:

• Achieved close-to-unity absorption (≈98.9%) at a specific wavelength (1518 nm) with the proposed optical stack.
• Experimental reflection and transmission measurements closely matched theoretical calculations.
• Demonstrated preliminary results of ≥70% absorption over a broader wavelength range (≈230 nm) using multilayer AR coatings.

Conclusions:

• The developed optical stack design significantly enhances light absorption in Al KIDs.
• This approach overcomes the inherent high reflectivity of aluminum at optical wavelengths.
• The design facilitates the development of highly efficient photon-counting and energy-resolving Al-based KIDs for optical and NIR applications.