"Feynman uses Dirac's notation to describe the quantum mechanics of stimulated emission... he applies that physics to... dye molecules... In this regard, Feynman could have predicted the existence of the tunable laser."

“The Dirac notation, though originally applied to the propagation of single particles, also applies to describing the propagation of ensembles of coherent, or indistinguishable, photons.”

“The most efficient and practical interpretation of quantum mechanics is... no interpretation at all.”

“Tunable Laser Optics at Google”

“All the indistinguishable photons illuminate the array of N slits, or grating, simultaneously. If only one photon propagates, at any given time, then that individual photon illuminates the whole array of N slits simultaneously.”

“Regardless of the prophetic value of Dirac’s description his was probably the first discussion... including a coherent beam of light. In other words, Dirac wrote the first chapter in laser optics.”

“The intimate relation between interference and diffraction has its origin in the interference equation itself.”