<br/>Single-particle spectroscopy is a powerful tool for the investigation of the properties of nanomaterials because unsynchronized processes can be directly observed. However, the traditional reliance upon photoluminescence for single-particle measurements limits such investigations to systems where the target particle or molecule is emissive.<br/>Ultrahigh-Q optical microresonators offer a way of eliminating the need for emission by enabling additional sensitive means of interaction with individual particles. We present a new two-beam experimental geometry, where the goal is not detection of individual molecules, but the measurement of optical spectra and spectral dynamics of non-fluorescent molecules of interest. Our experiment relies on ultrahigh-Q toroidal optical microresonators as platforms for photothermal spectroscopy. Transitions are optically driven in the particle or molecule of interest, while the thermalization of the excitation energy is detected by the resonator.<br/>We will present two examples of applications of our new spectroscopy platform. First, we will show spectroscopy of individual gold nanoparticles that show strong interactions between the plasmonic resonance of the nanoparticle and the whispering gallery mode of the optical microresonator, resulting in substantial changes to the lineshape that are well-captured by theory. Second, we will show our method can be applied to non-emissive conductive polymer molecules to probe crystallinity and electronic structure at the single polymer level.

Optical microresonators as platforms for single-molecule spectroscopy

254th National Meeting (2017)

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