We measure the temperature dependent resistance of a niobium nitride (NbN) from room temperature to 4 K. The increasing resistance with decreasing temperature can be explained by tunneling of...Show moreWe measure the temperature dependent resistance of a niobium nitride (NbN) from room temperature to 4 K. The increasing resistance with decreasing temperature can be explained by tunneling of electrons between grain boundaries. Once the detector is in the superconducting regime single photon counts can be registered. We find an optimal setting of the trigger level of 0.2 V to register detection events while minimizing the influence of amplifier noise. From the measured voltage pulses we estimate a kinetic inductance of 200 nH for our devices. We explore the regime of high photon energies by plotting the count rate vs optical power on a double logarithmic scale. For photons with 500 nm wavelength the highest initial slope is equal to 2.6, indicating that detector tomography with 3 photon events realistic. Unfortunately, higher slopes are not observed and makes looking into detection events with more than 10 eV total energy difficult if not impossibleShow less
We study superconductivity and photon detection in a NbN nanobridge of 150 nm width and 4 nm thickness. Superconductivity is observed below Tc = 8.4K. The measured critical current as a function of...Show moreWe study superconductivity and photon detection in a NbN nanobridge of 150 nm width and 4 nm thickness. Superconductivity is observed below Tc = 8.4K. The measured critical current as a function of temperature shows a slow decrease up to 7.9 K and more rapid decrease between 7.9 K and 8.4K. Light counts are only observed below T = 8.4K and dark counts below 7.85K. We characterize the detector by measuring the count rate as a function of polarization and average power to explore a multi-photon polarization dependence. We find a large difference in the response curves of the detector that cannot be explained by a change in the absorption efficiency h. Unfortunately, at the moment of writing the origin of the effect is inconclusive and is at least partly caused by a shift in the position of the focused laser beam on the sample when rotating a l/2 plate to change the polarizationShow less
