Rotational diffusion measurements using polarization-dependent fluorescence correlation spectroscopy based on superconducting nanowire single-photon detector.

Conventional polarization-dependent fluorescence correlation spectroscopy (pol-FCS) requires two sets of photon detectors to eliminate after-pulse noises (dual-channel pol-FCS; DC-pol-FCS) in the sub-microsecond range. In this study, we successfully realized pol-FCS using a visible-wavelength superconductive nanowire single-photon detector (single-channel pol-FCS; SC-pol-FCS). The detector used is free of after-pulse noises and thus eliminates the need for dual channels in pol-FCS. Further, the optics in the SC-pol-FCS system are easier to adjust than those in the conventional system. Consequently, we obtained higher signal-to-noise ratios compared with conventional DC-pol-FCS systems. Thus, SC-pol-FCS is a potentially useful system for obtaining pol-FCS measurements, and can facilitate improved rotational diffusion studies.