Near-infrared nanospectroscopy using a low-noise supercontinuum source

K. J. Kaltenecker, S. Rao D. S., M. Rasmussen, H. B. Lassen, E. J. R. Kelleher, E. Krauss, B. Hecht, N. A. Mortensen, L. Grüner-Nielsen, C. Markos, O. Bang, N. Stenger and P. U. Jepsen

APL Photonics 6, 066106 (2021)
Unlocking the true potential of optical spectroscopy on the nanoscale requires development of stable and low-noise laser sources. Here, we have developed a low-noise supercontinuum (SC) source based on an all-normal dispersion fiber pumped by a femtosecond fiber laser and demonstrate high resolution, spectrally resolved near-field measurements in the near-infrared (NIR) region. Specifically, we explore the reduced-noise requirements for aperture-less scattering-type scanning near-field optical microscopy (s-SNOM), including inherent pulse-to-pulse fluctuation of the SC. We use our SC light source to demonstrate the first NIR, spectrally resolved s-SNOM measurement, a situation where state-of-the-art commercial SC sources are too noisy to be useful. We map the propagation of surface plasmon polariton (SPP) waves on monocrystalline gold platelets in the wavelength region of 1.34–1.75 μm in a single measurement, thereby characterizing experimentally the dispersion curve of the SPP in the NIR. Our results represent a technological breakthrough that has the potential to enable a wide range of new applications of low-noise SC sources in near-field studies.