Application of a synthetic extended source for interferometry

This paper presents the design of a synthetic extended source (SES) that reduces coherent noise in interferometric measurements. The SES uses a fully coherent source for data acquisition to preserve highcontrast interferograms. Multiple measurements are made while the point source is translated according to a prescribed trajectory. The average of the measurements has the effect of using a source with a distribution defined by the trajectory. Thus, the optical system uses a coherent point source, but the data combination synthesizes the behavior of an extended source. A parametric model to quantify measurement noise due to diffraction from small particles is developed and used to evaluate SES designs. Experimental results are shown that validate the modeling. An example of a practical working SES implemented in a custom SPSI interferometer is provided.