The Gouy phase shift, the average phase lag of Fourier components of Hermite–Gaussian modes and their application to resonance conditions in optical cavities

An interpretation of the Gouy phase shift is proposed which relates the finite Gouy phase reduction of a Gaussian mode to the averaged phase retardation of the tilted waves in its Fourier spectrum compared to an on-axis plane wave. This provides a unified approach to resonance conditions in optical cavities with plane and curved mirrors. The possible relationship to pattern selection in nonlinear cavities is discussed.