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 /spl mu/m on a side to detect single photon events above a noise threshold of 0.3 eV (4 /spl mu/m wavelength), with an energy resolution of 0.12 eV FWHM (full width at half maximum). The observed events have a risetime (falltime) of 0.5 /spl mu/s (30 /spl mu/s). In this paper we present a summary of recent calibration data and resolution measurements as well as two proof-of-principle experiments to show the ability of TES detectors to extract both time and energy information from photons arriving at the detector during astronomical observations.