Mutual coherence in time-varying radiation fields and interferometric frequency discrimination.
The theory of partially coherent light is extended to cover time-varying fields observed by a detector with time constant T. The response of an interferometric optical discriminator is examined. The system uses a two-beam interferometer with transit time difference taur. The curves presented show discriminator response to step-function optical frequency shifts as a function of tau/T. They point to two conclusions, valid for tau/T > 10(-1): (i) initial and final states, and exponential detector response, neglecting mutual coherence theory, fail to explain dynamic behavior; (ii) multiple-fringe step-function frequency shifts are stretched over a period tau, permitting fringe counting.
Rapier
J L
JL