Multi-pulse fitting of Transition Edge Sensor signals from a near-infrared continuous-wave source

TL;DR

This paper introduces a novel multi-pulse fitting method for TES signals that improves timing and photon-number resolution in high-flux, low signal-to-noise scenarios, enabling better analysis of near-infrared photons.

Contribution

It presents a new approach combining a two-level discriminator and heuristic model fitting to accurately assign detection times to overlapping TES signals.

Findings

Effective detection time assignment for overlapping signals

Improved photon-number resolution in high-flux conditions

Successful measurement of second-order time correlation

Abstract

Transition-edge sensors (TES) are photon-number resolving calorimetric spectrometers with near unit efficiency. Their recovery time, which is on the order of microseconds, limits the number resolving ability and timing accuracy in high photon-flux conditions. This is usually addressed by pulsing the light source or discarding overlapping signals, thereby limiting its applicability. We present an approach to assign detection times to overlapping detection events in the regime of low signal-to-noise ratio, as in the case of TES detection of near-infrared radiation. We use a two-level discriminator, inherently robust against noise, to coarsely locate pulses in time, and timestamp individual photoevents by fitting to a heuristic model. As an example, we measure the second-order time correlation of a coherent source in a single spatial mode using a single TES detector.