Direct imaging of nanophotonic cavity modes using Li ion microscope

Micrometer-scale photonic cavities with high quality factors (Q) enable on chip motion sensing with unparalleled precision and bandwidth. The optical mode shape is critical for the transducer performance, yet it is difficult to measure directly and noninvasively. Here we use a scanning lithium ion microscope to visualize the electric field energy density of a 10 um diameter, 245 nm thick, 60000 Q Si microdisk optical cavity and to identify the radial order of the mode. The technique utilizes a beam of Li ions as a high spatial resolution noncontact probe, minimally perturbing the measured cavity resonance.