Highly sensitive detection of nanoparticles with a self-referenced and self-heterodyned whispering-gallery Raman microlaser

Abstract

Optical whispering-gallery-mode resonators (WGMRs) have emerged as promising platforms for label-free detection of nano-objects. The ultimate sensitivity of WGMRs is determined by the strength of the light-matter interaction quantified by quality factor/mode volume, Q/V, and the resolution is determined by Q. To date, to improve sensitivity and precision of detection either WGMRs have been doped with rare-earth ions to compensate losses and increase Q or plasmonic resonances have been exploited for their superior field confinement and lower V. Here, we demonstrate, for the first time to our knowledge, enhanced detection of single-nanoparticleinduced mode splitting in a silica WGMR via Raman gain-assisted loss compensation and WGM Raman microlaser. In particular, the use of the Raman microlaser provides a dopant-free, self-referenced, and self-heterodyned scheme with a detection limit ultimately determined by the thermorefractive noise. Notably, we detected and counted individual nanoparticles with polarizabilities down to 3.82 × 10 −6 μm 3 by monitoring a heterodyne beatnote signal. This level of sensitivity is achieved without exploiting plasmonic effects, external references, or active stabilization and frequency locking. Single nanoparticles are detected one at a time; however, their characterization by size or polarizability requires ensemble measurements and statistical averaging. This dopant-free scheme retains the inherited biocompatibility of silica and could find widespread use for sensing in biological media. The Raman laser and operation band of the sensor can be tailored for the specific sensing environment and the properties of the targeted materials by changing the pump laser wavelength. This scheme also opens the possibility of using intrinsic Raman or parametric gain for loss compensation in other systems where dissipation hinders progress and limits applications.optical sensor | active microresonator | particle sensing T here is an increasing demand for new technologies to detect small molecules, nanoparticles, and airborne species (1-4). In the past decade we have witnessed a boost in the number of label-free detection techniques with varying levels of sensitivities. Techniques relying on electrical conductance (5), light scattering and interferometry (6-8), surface and localized plasmon resonance (9, 10), nanomechanical resonators (11,12), and optical resonances (13-17) have been demonstrated.Whispering-gallery-mode (WGM) microresonators with their high quality factor, Q, and small mode volume, V, are known to enhance light-matter interactions and have extraordinary sensitivities to changes and perturbations in their structure or proximity (18,19). They have been of great interest for sensing biomarkers, DNA, and medium-size proteins at low concentrations, as well as for detecting viruses and nanoparticles at single-particle resolution (19-31). A particle or molecule entering the mode volume of a resonator or binding onto its surface induces a net change in the polarizability of the resonator-...

Chiral modes and directional lasing at exceptional points

“…In addition to controlling the flow of light and laser emission in on-chip micro-and nanostructures, our findings have important implications in cavity quantum electrodynamics for the interaction between atoms/molecules and the cavity light. They may also enable high-performance sensors to detect nanoscale dielectric, plasmonic, and biological particles and aerosols (35)(36)(37)(38) and be useful for a variety of applications such as the generation of optical beams with a well-defined orbital angular momentum (39) and the topological protection in optical delay lines (9,10,40). …”

Electromagnetically induced transparency in optical microcavities

“…Most importantly, the optical microcavity systems allow for on-chip integration and room-temperature operation, and the resonant modes can be tuned to almost any wavelength range. With the rapid development of the micro/nano fabrication techniques, optical microcavities with ultrahigh quality factors (Q) and small mode volumes are widely studied [68][69][70], which have sought applications ranging from fundamental physics to applications, such as cavity quantum electrodynamics [71,72], nonlinear optics [73], low-threshold microlasing [74], and biosensing [75][76][77][78][79][80][81][82].…”

Loss-induced suppression and revival of lasing

“…3D). Finally, we tested the effect of the loss-induced recovery of the intracavity field intensity on Raman lasing in silica microtoroids (29,30). The threshold for Raman lasing scales as…”