Abstract

The spectrum of light emitted by a partially coherent source depends on the degree of spectral coherence across the source. Wolf¹ has shown that, if the degree of spectral coherence at the source satisfies a certain scaling law, the normalized spectrum of light is the same throughout the far zone and is equal to the normalized spectrum at the source. If the spectral coherence function does not satisfy the scaling law, the spectrum of the emitted radiation detected some distance away from the source is generally different from that measured at the source. Recently Bocko et al.² have observed frequency shifts of the spectrum detected in the far field of two appropriately correlated acoustical sources. We describe experiments in which frequency shifts of the optical spectrum detected in the far field of a planar secondary source are observed. In the experiments we use a Fourier achromat to generate a secondary source with a degree of spectral coherence that is independent of wavelength and, therefore, does not satisfy the scaling law. The spectrum detected in the far field of the source is found to depend on the spectrum at the source, the degree of spectral coherence at the source, and the location of the observation point.

© 1987 Optical Society of America