FIELD PROPERTIES OF MULTIPLE COHERENTLY COMBINED LASERS

The coherent combination of several single-mode lasers can produce a field similar to that of a mode-locked laser but with more flexibility. The field for a quasi-monochromatic wave is considered a complex coherence-separable random process. The ensemble mean and covariance are determined for the case of a temporally stabilized amplitude and a temporal phase that, with appropriate assumptions, is a stationary, Gaussian random process. Mean fields are used throughout as the signals of interest. The Huygens-Fresnel principle is used to investigate the field properties in the Fraunhofer region for two cases. The first case is N beams superimposed with optical axes coincident. Range measurement precision is found to be proportional to 1/(N3Δf)1/2, where Δf is the frequency difference between adjacent lasers. Velocity measurement precision is found to be proportional to (NΔf3)1/2. The second case is N beams in a linear array. The far-field result is a scanning beam that in certain cases can be steered. An array of about 1000 lasers is needed for reasonably low sidelobes. © 1979 Optical Society of America.