Figure 3: Schematic of a WGM “hot cavity” anemometer.
From: Glass-on-Glass Fabrication of Bottle-Shaped Tunable Microlasers and their Applications
The excitation of the WGM is represented by the red arrows in the capillary wall. With sufficient absorption, the light in the WGM can locally heat the capillary. Fluid flowing through the capillary is represented by the green arrow. The flowing fluid removes the heat and shifts the WGMs to higher frequencies, represented by the movement of the transmission dip on the left of the figure.
