An optical transition-edge sensor with high energy resolution

TL;DR

This paper reports a high-energy-resolution optical transition-edge sensor (TES) using a Au/Ti bilayer, achieving 67 meV FWHM at 0.8 eV, with analysis of noise sources and comparison to typical TES performance.

Contribution

The study demonstrates a novel Au/Ti bilayer TES with significantly improved energy resolution at cryogenic temperatures for optical photon detection.

Findings

Achieved 67 meV FWHM energy resolution at 0.8 eV

Lowered Tc to 115 mK to enhance resolution

Identified excess Johnson noise as a limiting factor

Abstract

Optical transition-edge sensors have shown energy resolution for resolving the number of incident photons at the telecommunication wavelength. Higher energy resolution is required for biological imaging and microscope spectroscopy. In this paper, we report on a Au/Ti (10/20 nm) bilayer TES that showed high energy resolution. This was achieved by lowering the critical temperature Tc to 115 mK and the resultant energy resolution was 67 meV full width at half maximum (FWHM) at 0.8 eV. When Tc was lowered to 115 mK, the theoretical resolution would scaled up to 30 meV FWHM, considering that the typical energy resolution of optical TESs is 150 meV and Tc is 300 mK. To investigate the gap between the theoretical expectation (30 meV) and the measured value (67 meV), we measured its complex impedance and current noise. We found excess Johnson noise in the TES and an excess Johnson term M was 1.5 at a bias point where the resistance was 10% of normal resistance. For reference, the TES was compared with a TES showing typical energy resolution (156 meV FWHM). We will discuss what improved the energy resolution and what might have been the limiting factor on it.