Fluorescence Correlation Spectroscopy with Visible-Wavelength Superconducting Nanowire Single-Photon Detector

We present the fluorescence correlation spectroscopy (FCS) using superconducting nanowire single-photon detectors (SSPDs) which is after-pulse free unlike the avalanche photodiode (APD). Multimode-fiber-coupled SSPDs with high system detection efficiency for visible wavelengths were developed and implemented in the FCS system. We performed FCS measurements for Rhodamine 6G as fluorescent samples, and demonstrated that autocorrelation functions obtained by the SSPDs showed an after-pulse-free curve in the short correlation time region of sub microseconds where the afterpulse effect was dominant using the APD. Also for the longer correlation time region over microseconds, the SSPD revealed the triplet component of Rhodamine 6G, which is obscured by the APD due to after-pulse effect. The obtained results clearly indicate the advantage of SSPDs for the FCS system.