A necessary and sufficient non-negative definiteness condition for the cross-spectral density (CSD) is provided. It is also shown that any genuine CSD can be expanded in terms of the so-called pseudo-modes of the source, understood as coherent contributions, not orthogonal to one another, that, superposed in an uncorrelated way, give rise to the CSD. Their evaluation is analyzed by means of an illustrative example.
© 2009 Optical Society of America
Coherence and Statistical Optics
Original Manuscript: February 10, 2009
Manuscript Accepted: March 31, 2009
Published: April 24, 2009
R. Martínez-Herrero, P. M. Mejías, and F. Gori, "Genuine cross-spectral densities and pseudo-modal expansions," Opt. Lett. 34, 1399-1401 (2009)