Abstract
Raman spectroscopy reveals chemically specific information and provides label-free insight into the molecular world. However, the signals are intrinsically weak and call for enhancement techniques. Here, we demonstrate Purcell enhancement of Raman scattering in a tunable high-finesse microcavity, and utilize it for molecular diagnostics by combined Raman and absorption imaging. Studying individual single-wall carbon nanotubes, we identify crucial structural parameters such as nanotube radius, electronic structure and extinction cross-section. We observe a 320-times enhanced Raman scattering spectral density and an effective Purcell factor of 6.2, together with a collection efficiency of 60%. Potential for significantly higher enhancement, quantitative signals, inherent spectral filtering and absence of intrinsic background in cavity-vacuum stimulated Raman scattering render the technique a promising tool for molecular imaging. Furthermore, cavity-enhanced Raman transitions involving localized excitons could potentially be used for gaining quantum control over nanomechanical motion and open a route for molecular cavity optomechanics.
Highlights
Raman spectroscopy reveals chemically specific information and provides label-free insight into the molecular world
Due to the need for microscopic mode volumes, Purcell enhancement of Raman signals has only been observed in monolithic systems with limited spatial control or spectral tunability like microdroplets[5,7], photonic crystal cavities[8] and Fabry–Perot microcavities[6,9,10,11,12,13]
We demonstrate cavity-enhanced Raman imaging to study individual single-walled carbon nanotubes (CNTs), a material with widespread applications in fields as diverse as electronics[15], photonics[16], nanomechanics[17] and quantum optics[18,19]
Summary
Raman spectroscopy reveals chemically specific information and provides label-free insight into the molecular world. Due to the need for microscopic mode volumes, Purcell enhancement of Raman signals has only been observed in monolithic systems with limited spatial control or spectral tunability like microdroplets[5,7], photonic crystal cavities[8] and Fabry–Perot microcavities[6,9,10,11,12,13]. This has restricted the spectral coverage and impeded spatially resolved measurements so far, and only large ensembles of molecules have been studied. Our approach allows to simultaneously probe the vibrational spectrum and the optical properties of a wide range of samples with enhanced sensitivity
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