Abstract
The densities of critical points of phase (extrema and saddles), which play an important role in the theory of phase singularities (wave dislocations) in two dimensions, are calculated in isotropic plane wave superpositions. Critical points and dislocations are put on an equal footing as zeros of the two-dimensional current (Poynting vector), and the results, depending only on the second and fourth moments of the wave spectrum (distribution of wavenumbers), are related to the corresponding dislocation density. Explicit results for several spectra are derived, discussed and related to previous results.