An evanescent wave is a near-field standing wave whose intensity decays exponentially with distance from the boundary where it was formed. It carries no net energy flow in the direction of decay. In optics, these fields exist just outside the boundary of total internal reflection and are used in specialized microscopy and coupling light between waveguides.
Heard on the job
We can use the evanescent field to couple the pump light directly into the microresonator without touching it.