Whispering gallery mode

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Whispering gallery modes (WGMs) occur at particular resonant wavelengths of light confined to a cylindrical or spherical volume with an index of refraction greater than that surrounding it. At these wavelengths, the light undergoes total internal reflection at the volume surface and becomes trapped within the volume for timescales of the order of nanoseconds. WGMs are named after the whispering gallery at St. Paul's Cathedral in London. The light is concentrated near the circumference of the particle and can be assigned a mode number and a mode order. The mode number, n, tells us the number of wavelengths around the circumference of the particle, and the mode order, l, the number of maxima in the radial dependence of the electromagnetic field within the volume. Specifically, for a cylinder, we can describe the system using the azimuthal mode number, m, the radial maxima, n, and the axial surface minima, p. These values can be predicted through manipulation of Maxwell's equations.