Near-infrared nanospectroscopy using a low-noise supercontinuum source

Korbinian J Kaltenecker,Shreesha Rao D S,Peter Uhd Jepsen,Ole Bang,Enno Krauss,Edmund J R Kelleher,N Asger Mortensen,Lars Grüner-Nielsen,Christos Markos,Nicolas Stenger,Mattias Rasmussen,Bert Hecht,Henrik B Lassen

doi:10.1063/5.0050446

Abstract

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.

Highlights

Today’s silica fiber-based supercontinuum (SC) sources are ultra-broadband spatially coherent lasers covering several octaves from the visible (400 nm) to the near-infrared (NIR) (2400 nm) with a brightness that is over seven orders of magnitude higher than that of a Globar and even 2–3 orders of magnitude higher than that of a synchrotron.[1]
We demonstrate the leap in the performance of our newly developed low-noise SC source compared to existing commercial SC sources by spectroscopic imaging of surface plasmon polariton (SPP) waves propagating at the interface of extremely flat monocrystalline gold platelets
The outgoing and incoming SPPs interfere at the tip, and when scanning the tip along a line that is perpendicular to the edge [gray dashed line in both Figs. 2(a) and 2(b) but best seen in (b)], the scattered signal forms a field pattern that is similar to a standing wave with a fringe spacing of Λtl = λspp/2, where λspp is the SPP wavelength.[50]

Summary

Introduction

Today’s silica fiber-based supercontinuum (SC) sources are ultra-broadband spatially coherent lasers covering several octaves from the visible (400 nm) to the near-infrared (NIR) (2400 nm) with a brightness that is over seven orders of magnitude higher than that of a Globar and even 2–3 orders of magnitude higher than that of a synchrotron.[1] Using SC generation in gas-filled hollow-core fibers, the spectrum is being extended to the vacuum UV below 113 nm,[2] and using chalcogenide fibers, the spectrum is being pushed to the mid-IR above 13 μm.[3]. The SC source resembles an ultra-bright table-top synchrotron with a tremendous range of applications. The broadband and ultra-quiet nature of the SC source, together with interferometric measurement techniques, allows us to measure the experimental scitation.org/journal/app dispersion curve over the range 1.34–1.75 μm of the SPP waves.

Methods

Results

Conclusion