Transition edge sensors as single photon detectors

We have recently demonstrated wideband detection of individual photons from the mid infrared (IR), through the optical, and into the near ultraviolet (UV). We use thin film tungsten transition edge sensors about 20 mu m on a side to detect single photon events above a noise threshold of 0.3 eV (4 mu m wavelength), with an energy resolution of 0.12 eV FWHM (full width at ha lf maximum). The observed events have a risetime (falltime) of 0.5 mu s (30 mu s). In this paper we present a summary of recent calibration data and r esolution measurements as well as two proof-of-principle experiments to sho w the ability of TES detectors to extract both time and energy information from photons arriving at the detector during astronomical observations.