A stronger absorption of pump/probe light is desirable for maximizing the sensitivity to enable accurate measurements of trace chemical elements. We introduce a new sensing technique built on light-sheet excitation of skew rays in a multimode fiber with an additional enhancement of localized surface plasmon resonance (LSPR) and its evanescent-field hotspots between gold nanospheres on the coated fiber. A skewed light-sheet (i.e., a thin plane of light) can exploit the optimum ray group, producing enhanced and uniform interactions between light and matter for higher absorption/sensitivity and higher power threshold. The heightened evanescent field couples to the localized surface plasmon resonant modes to attain even greater sensitivity. We compared this excitation method with the previously demonstrated light-sheet skew ray-based sensor without LSPR and observed an enhancement in normalized attenuation of pump light up to seven orders of magnitude for low-concentration rhodamine B. The improvement in the normalized detection limit is almost three orders of magnitude. This new sensing technique uses a functionalized fiber rather than pairing a passive fiber with added functional particles in the analyte, which offers better area-selectivity. The potentially low-cost chemical sensors can be used on a range of sensing mechanisms such as pump/probe light absorption.
Keywords: chemical sensor; light sheet; localized surface plasmon resonance; optical fiber; skew ray.