Whispering-gallery wave

Whispering-gallery waves were first explained for the case of St Paul's Cathedral circa 1878[3] by Lord Rayleigh, who revised a previous misconception[4][5] that whispers could be heard across the dome but not at any intermediate position.

He explained the phenomenon of travelling whispers with a series of specularly reflected sound rays making up chords of the circular gallery.

[1] Many other monuments have been shown[8] to exhibit whispering-gallery waves, such as the Gol Gumbaz in Bijapur and the Temple of Heaven in Beijing.

[26] The light waves are guided around almost perfectly by total internal reflection, leading to Q factors in excess of 1010 being achieved.

[28] Optical modes in a whispering gallery resonator experience some loss due to a mechanism similar to quantum tunneling, even in theoretically ideal conditions.

[48] Galleries simultaneously containing both acoustic and optical whispering-gallery waves have also been made,[49] exhibiting very strong mode coupling and coherent effects.

Snapshot of an acoustic whispering-gallery mode calculated at a frequency of 69 Hz in an enclosed cylinder of air of the same diameter (33.7 m) [ 1 ] as the whispering gallery in St Paul's Cathedral. Red and blue represent higher and lower air pressures, respectively, and the distortions in the grid lines show the displacements. In the case of the waves travelling one way round the gallery, the air particles move in elliptical trajectories. [ 2 ]
Optical whispering-gallery modes in a glass sphere of diameter 300 μm experimentally imaged with a fluorescence technique. The tip of an angle-cut optical fiber , visible on the right, excites the modes in the red region of the optical spectrum. [ 16 ]