Whispering-gallery wave Whispering-gallery wave Whispering-gallery waves, or whispering-gallery modes, are a type of wave that can travel around a concave surface. Originally discovered for sound waves in the whispering gallery of St Paul’s Cathedral, they can exist for light and for other waves, with important applications in nondestructive testing, lasing, cooling and sensing, as well as in astronomy. Whispering-gallery waves were first explained for the case of St Paul's Cathedral circa 1878 by Lord Rayleigh, who revised a previous misconception that whispers could be heard across the dome but not at any intermediate position. He explained the phenomenon of travelling whispers with
Whispering-gallery wave acoustic diffraction (lateral wave spreading) are then completely compensated. Whispering-gallery waves exist for light waves. They have been produced in microscopic glass spheres or toruses, for example, with applications in lasing, optomechanical cooling, frequency comb generation and sensing. The light waves are almost perfectly guided round by optical total internal reflection, leading to Q factors in excess of 10 being achieved. This is far greater than the best values, about 10, that can be similarly obtained in acoustics. Optical modes in a whispering gallery resonator are inherently lossy due to a mechanism similar to quantum tunneling. As a result, light