Proof of concept of fiber dispersed Raman spectroscopy using superconducting nanowire single-photon detectors.

Due to its high molecular specificity, Raman spectroscopy is a well-established analytical tool. Usually the inelastically scattered Raman light is spectrally dispersed by a spectrometer. Here, we present an alternative method, using an optical fiber as dispersive element. As the group velocity within the fiber is wavelength-dependent, different Raman bands arrive at different times at the detector. In combination with time-correlated single-photon counting, Raman spectra can be measured in the time domain. As detector we implemented a Superconducting Nanowire Single-Photon Detector (SNSPD), which possesses a timing accuracy of about 20 ps. Within this contribution we show first results of Raman spectra measured in the time domain using gradient index fibers of varying length.

Design, realization, and characteristics of a transition edge bolometer for sub-millimeter wave astronomy.

The large array bolometer camera is scheduled to succeed its semiconducting predecessor at the Atacama pathfinder experiment. It shall be an array of 300 transition edge sensors operated at a temperature of about 0.25 K, provided by a (3)He evaporation cooler and a pulse tube refrigerator. The instrument will be read out by a superconducting quantum interference device time domain multiplexer. The design and realization of a suitable detector for this instrument is described. Based on sensitivity demands derived from the background limit, the thermal and electrical designs for a spider-web bolometer are deduced. The theoretical predictions are compared to experimental results. The pixel design yields a background-limited performance for background loads corresponding to blackbody sources between 77 K and 300 K and a partially effective anti-aliasing filter for the intended multiplexed readout.

Superconducting single-photon counting system for optical experiments requiring time-resolution in the picosecond range.

We have developed a cryogenic measurement system for single-photon counting, which can be used in optical experiments requiring high time resolution in the picosecond range. The system utilizes niobium nitride superconducting nanowire single-photon detectors which are integrated in a time-correlated single-photon counting (TCSPC) setup. In this work, we describe details of the mechanical design, the electrical setup, and the cryogenic optical components. The performance of the complete system in TCSPC mode is tentatively benchmarked using 140 fs long laser pulses at a repetition frequency of 75 MHz. Due to the high temporal stability of these pulses, the measured time resolution of 35 ps (FWHM) is limited by the timing jitter of the measurement system. The result was cross-checked in a Coherent Anti-stokes Raman Scattering (CARS) setup, where scattered pulses from a ß-barium borate crystal have been detected with the same time resolution.