Raman-gain induced loss-compensation in whispering-gallery-microresonators and single-nanoparticle detection with whispering-gallery Raman-microlasers

摘要

Recently optical whispering-gallery-mode resonators (WGMRs) have emerged aspromising platforms to achieve label-free detection of nanoscale objects and toreach single molecule sensitivity. The ultimate detection performance of WGMRsare limited by energy dissipation in the material they are fabricated from. Upto date, to improve detection limit, either rare-earth ions are doped into theWGMR to compensate losses or plasmonic resonances are exploited for theirsuperior field confinement. Here, we demonstrate, for the first time, enhanceddetection of single-nanoparticle induced mode-splitting in a silica WGMR viaRaman-gain assisted loss-compensation and WGM Raman lasing. Notably, wedetected and counted individual dielectric nanoparticles down to a record lowradius of 10 nm by monitoring a beatnote signal generated when split Ramanlasing lines are heterodyne-mixed at a photodetector. This dopant-free schemeretains the inherited biocompatibility of silica, and could find widespread usefor sensing in biological media. It also opens the possibility of usingintrinsic Raman or parametric gain in other systems, where dissipation hindersthe progress of the field and limits applications.