Spectral scale transformations of nonstationary optical fields

The notions of cross-spectral purity and spectral invariance of light impose specific structures for the field coherence. Such concepts were originally introduced for stationary light and recently extended to nonstationary fields. In this work, we establish general conditions for transforming scalar, pulsed, isodiffracting light beams produced, for instance, in usual spherical-mirror laser resonators, to nonstationary secondary sources that exhibit cross-spectral purity or spectral invariance. Further, we introduce hybrid refractive-diffractive imaging systems which perform the desired transformation accurately over a wide spectral range irrespective of the spatial coherence of the incident isodiffracting beam.