General configuration for using the longitudinal spatial coherence effect

The Fourier relation between the longitudinal degree of coherence and the radial intensity distribution of a light source can be demonstrated by two configurations of a low spatial-coherence interferometer. We propose a general configuration, which includes the two known types as special cases of the general design. Moreover, by adjusting the distance between the light source and the main lens of the interferometer we can apparently narrow the peak of coherence beyond its known limit. This result might have consequences on the resolution limits of the low spatial-coherence interferometer.