Microlens Hollow-Core Fiber Probes for Operando Raman Spectroscopy

Abstract

We introduce a flexible microscale all-fibre-optic Raman probe which can be embedded into devices to enable operando in-situ spectroscopy. The facile-constructed probe is composed of a nested anti-resonant nodeless hollow-core fibre combined with an integrated high refractive index barium titanate microlens. Pump laser 785 nm excitation and near-infrared collection are independently characterized, demonstrating an excitation spot of full-width-half-maximum 1.1 μm. Since this is much smaller than the effective collection area, it has the greatest influence on the collected Raman scattering. Our characterization scheme provides a suitable protocol for testing the efficacy of these fibre probes, using various combinations of fibre types and microspheres. Raman measurements on a SERS sample and a copper battery electrode demonstrate the viability of the fibre probe as an alternative to bulk optic Raman microscopes, giving comparable collection to a 10× objective, thus paving the way for operando Raman studies in applications such as lithium battery monitoring.