Temporal coherence of laser fields analyzed by heterodyne interferometry

For partially coherent fields, where the coherence time may be quite large, a new method is described to obtain the coherence function and other statistical properties. Coherence lengths of over 100m were measured, and it was deduced that microphonic noise is the dominant source of incoherence in laser fields. It is also found experimentally that seemingly uncorrelated fields may have a strong phase relationship.