Correlation-induced spectral changes dependent upon spatiotemporal interference effects

A wave-front folded interferometer consisting of a Kosters prism and an image forming lens provides an excellent way to make a precision measurement of correlation-induced spectral changes. Experiments are successfully made by incorporating a primary spectral source of super-luminescent diodes. The diode emits a Gaussian-like spectrum. Theoretical background for the measurement is given in the framework of geometric optics. It is shown theoretically and experimentally that the spectral changes are induced by two causes: one is the complex degree of spectral coherence of the secondary source, and the other the time delay between the interfering optical waves. No spectral change takes place if the secondary source satisfies a spatially incoherent condition at particular optical frequency, whereas the spectrum changes most clearly if a spatially coherent condition is satisfied.