Whispering gallery microprobe opens up new opportunities for optical spectroscopy

Gentle–matter interplay is among the most elementary methods individuals observe the bodily world. Whereas reflection and refraction of sunshine reveal the morphology of matter, inelastic scattering of sunshine, like Raman scattering, encodes the molecular fingerprint of chemical bonds into the power shift of photons. Nonetheless, the potential for such interactions is vanishingly small.

Researchers have been creating particular mechanisms and buildings to reinforce Raman indicators over the previous many years. Floor-enhanced Raman spectroscopy, or SERS, represents some of the promising platforms of such efforts, the place metallic nanostructures are launched to considerably improve the electromagnetic subject close to the pattern floor and likewise tailor targets’ density of power states in favor of Raman scattering. However, whispering-gallery-mode (WGM) microresonators have emerged as frontrunners to reinforce light-matter interactions in purposes starting from sensing, spectroscopy, imaging, and so forth.

These sub-millimeter resonators might work as a reservoir of sunshine, accumulating mild and realizing a temporally enhanced optical subject. The mix of the 2 platforms is undoubtedly promising and intriguing, offering boosted light-matter interplay each spatially and temporally. Nonetheless, a scientific investigation and proof-of-concept demonstration was wanted.

In a latest paper revealed in Gentle: Science & Purposes, a staff of researchers led by Professor Lan Yang from Washington College in St. Louis introduced a novel Raman enhancing platform the place a WGM microprobe is mated with nano-plasmonic SERS buildings. Nano-plasmonic hotspots are coupled with WGMs by way of a phase-matched cavity-antenna coupling mechanism to maximise the spontaneous Raman scattering from numerous chemical and biochemical samples.

Two-orders-of-magnitude enhancement was reported on prime of the stand-along nano-plasmonic hotspots conventionally excited by a targeted free-space mild beam. The group additionally confirmed the compatibility of the microprobe to several types of SERS substrate, together with lithographically outlined nano-plasmonic hotspot array and business SERS substrate paper, demonstrating the flexibility of the novel platform.

Extra apparently, by mounting the probe onto a translation stage, a two-dimensional hyperspectral Raman imaging with sign enhancement was realized with solely sub-milliwatt continuous-wave pump energy. The reported outcomes opened the door to discover inelastic light-matter interplay enhancement with WGM-plasmonic hybrid resonance, and likewise introduced a flexible device for Raman-based materials evaluation and chemical imaging.

“This paper is a abstract of our group’s lengthy journey exploring the mix of WGM microresonators and nanoplasmonic SERS buildings. We discovered that as an alternative of merely serving as an optical pump excitation interface, WGMs type a hybrid mode with nano-plasmonic hotspots. As well as, as a result of guided-wave nature of WGMs, we noticed manifestation of the phase-matching situation, which is each proof of the hybrid resonance and likewise a big contributor to the Raman sign enhancement that may very well be leveraged,” the authors defined.

“In some methods, the WGM microprobe platform works equally to an atomic drive microscopy (AFM) tip. We additionally tried to display and consider the potential of this platform from an equipment growth viewpoint. This motivates our research of enhancing standard SERS and 2D scanned Raman imaging utilizing the microprobe configuration. With all the outcomes introduced, we're assured to say that this new method might unlock many alternatives for a greater and probably extra compact SERS take a look at platform,” the staff says.

“Most likely the over-simplified approach to perceive our work is: we developed a flexible and scannable contact lens to SERS samples,” concluded the researchers.