A generalized Gouy phase for focused, partially coherent wavefields and its implications for optical metrology

Abstract When a monochromatic wavefield is focused, its phase, compared to that of a non-diffracted spherical wave, undergoes a rapid π phase change. This effect bears the name of its discoverer, L.G. Gouy. In a partially coherent wavefield the phase is a random quantity and therefore, when such a field is focused, its Gouy phase is undefined. However, the phase of the correlation functions that characterize partially coherent fields, such as the cross-spectral density and the spectral degree of coherence, do have