Extending single-photon optimized superconducting transition edge sensors beyond the single-photon counting regime

We illuminate a photon-number-resolving transition edge sensor with strong pulses of light containing up to 6.7 million photons (0.85 pJ per pulse). These bright pulses heat the sensor far beyond its transition edge into the normal resistance regime. We show that the sensor operates from the single-photon-counting regime to picowatt levels of light and that the detection noise is below shot-noise for up to 1000 photons.