Characterization of Optical Fast Transition-Edge Sensors With Optimized Fiber Coupling

Abstract

Energy resolution (Δ <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">E</i> ), recovery time (τ <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">eff</sub> ), and quantum efficiency ( <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">QE</i> ) are some of the most important single photon-counting detector parameters. New applications in the quantum optics field place extreme demand on detector performances that go beyond the capabilities of established single-photon detectors. Unfortunately, it is hard to reach best results for all these parameters at the same time. Concerning transition-edge sensors (TESs) as single photon detectors, Δ <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">E</i> and τ <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">eff</sub> are directly and inversely proportional to the transition temperature <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">T</i> <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">c</sub> , respectively. Moreover, the geometrical optical coupling between illuminating fiber and detector, the device material and the characteristics of the optical cavity or the antireflection coating, drastically influence the <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">QE</i> and in some cases also the Δ <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">E</i> . Previous TESs fabricated by Istituto Nazionale di Ricerca Metrologica were characterized by very high energy resolution (0.18 eV) but high τ <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">eff</sub> and low <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">QE</i> . In this work, we present a Ti/Au TES with higher <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">T</i> <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">c</sub> (300 mK) that, using the optical alignment system implemented by AIST, shows an optimization of these important parameters, energy resolution of 0.26 eV, recovery time of 186 ns, and a quantum efficiency of 50% without using any optical structure deposited on the detector.