Observation of Gouy Phase Shift in a Mach-Zehnder Interferometer

Convergent beams travelling through their focus from minus infinity to plus infinity not only experience the accumulation of the phase corresponding to the traversed optical path length, but also accrue a constant p phase term, known as the Gouy phase shift, discovered by the scientist of the same name at the end of the nineteenth century. When such a beam interferes with a collimated one, the Gouy phase shift is revealed when the interference patterns generated on both sides of the focus are compared: the ring patterns are negatives of each other. This can be observed in a Mach-Zehnder.