Photon number and timing resolution of a near-infrared continuous-wave source with a transition-edge sensor

Transition-edge sensors (TES) are calorimetric spectrometers that have near unit e(sic)ciency and are photon-number resolving. A recovery time on the order of microseconds, however, limits the number resolving ability and timing accuracy in high photon-flux conditions. This can be addressed by pulsing the light source or discarding overlapping signals, thereby limiting its applicability. A method that works for stationary light sources uses the di rectangle erentiated TES signal to determine the detection time of overlapping signals and to count photons [1]. However, the low signal-to-noise ratio of TES response when detecting near-infrared photons complicates the direct estimation of their detection times by this method. Here, we present an alternative approach where we use a discriminator inherently robust against noise to coarsely locate pulses in time, the integral of the identified signal regions to count photons, and a separate fit to determine the exact detection instant.