Spatial coherence measurements of quasi-monochromatic thermal light using double-exposure specklegrams

Abstract A new method to measure the degree of spatial coherence of partially coherent quasi-monochromatic thermal light is proposed by using double-exposure specklegrams. The method is shown to be basically equivalent to the conventional two-beam interference method based on Young's experiments in which a pair of apertures (pinholes or slits) are used. Since the new method corresponds to the Young's experiments in case of apertures with a very small size, it has the significant advantage that it is applicable to a light field with low-level intensity. In addition, fabrication of specklegrams used in the present method is made in a simple way.