Single-Particle Photothermal Microscopy Using On-Chip Silicon Nitride Microring Resonators.

Optical microresonators confine light in time and space, enabling high sensitivity for the detection of small thermal perturbations. We utilized these properties and investigated on-chip integrated silicon nitride microring resonators (MRRs) for single-particle photothermal microscopy. We calibrate the technique using individual nonphotoluminescent carbon nanotubes and determine values for absorption cross-section per atom that agree with literature values. Finite-element simulations are performed to track all relevant thermal gradients. The combination of experiment and simulation allows for discussion of the benefits and drawbacks of the planar MRR geometry for single-particle microscopy.