Measuring the coherence function of continuous-wave lasers by a photorefractive grating method.

We demonstrate a simple, adjustment-insensitive technique for measuring the temporal coherence function of cw multimode and monomode semiconductor lasers, using two-beam coupling in photorefractive InP and CdTe crystals. The emission spectra of the diodes are measured independently. The coherence functions are also calculated from these spectra and agree with the photorefractive measurements. Coupling of two partially coherent waves in low-speed photorefractive media is described theoretically. The range of the experimental parameters in which the method of coherence measurement is correct is given.