Probing optical resonances of silicon nanostructures using tunable-excitation Raman spectroscopy

• Published in: Optics express 2019-12, Vol.27 (26), p.38479-38492
• Main Authors: Matthiae, M, Nielsen, K E S, Larroche, A, Zhou, C, Kristensen, A, Raza, S
• Format: Article
• Language: English
• ISSN: 1094-4087; 1094-4087
• DOI: 10.1364/oe.385088

Optical materials with a high refractive index enable effective manipulation of light at the nanoscale through strong light confinement. However, the optical near field, which is mainly confined inside such high-index nanostructures, is difficult to probe with existing measurement techniques. Here, we exploit the connection between Raman scattering and the stored electric energy to detect resonance-induced near-field enhancements in silicon nanostructures. We introduce a Raman setup with a wavelength-tunable laser, which allows us to tune the Raman excitation wavelength and thereby identify Fabry-Pérot and Mie type resonances in silicon thin films and nanodisk arrays, respectively. We measure the optical near-field enhancement by comparing the Raman response on and off resonance. Our results show that tunable-excitation Raman spectroscopy can be used as a complimentary far-field technique to reflection measurements for nanoscale characterization and quality control. As proof-of-principle for the latter, we demonstrate that Raman spectroscopy captures fabrication imperfections in the silicon nanodisk arrays, enabling an all-optical quality control of metasurfaces.