Fiber-dispersive Raman spectrometer with single-photon sensitivity

Abstract

The two major challenges in Raman spectroscopy are the low intensity of spontaneous Raman scattering and often accompanying fluorescence. We overcome these two issues with a novel fiber-dispersive Raman spectrometer utilizing a superconducting nanowire single-photon detector (SNSPD). By exploiting chromatic dispersion in the fiber material, we temporally stretched Raman scattered light pulses and performed correlated measurements in the time domain, where the two emission processes, Raman scattering and fluorescence, can be effectively separated. The spectrometer greatly benefits from SNSPD metrics due to its broad spectral sensitivity (from UV to near-IR wavelength range) on a single-photon level and high temporal resolution (timing jitter) that outperform those of competing avalanche single-photon detectors. The spectral resolution achievable with a fiber-dispersive spectrometer for the best trade-off between its components is estimated to be as good as 2.6 - 10 cm−1 over the Stokes shifted range up to 4400 cm−1 with an excitation wavelength of 785 nm and 4.8 - 5.2 cm−1 covering the same range with an excitation wavelength of 532 nm.