Coherent source transverse field profiles and far-field energy distribution

Northrop Grumman presents analysis of near-field electrical field distributions of coherent sources and the resultant far-field energy distributions. This work comparatively analyzes the effect of coherent mode content, transverse phase modulation at the source, and apertures at the source. Gaussian, top-hat, and high order Hermite-Gaussian mode distributions are propagated to the far-field and the intensity distribution is compared. Both phase and aperture transformations are applied to the source distributions and the resultant far-field distributions are compared. Using the Fraunhofer approximation and Parseval's theorem it is possible to provide an accurate intensity profile at ranges wherein the approximation is valid. Using this method various phase transformations at the aperture are analyzed with regard to their resultant far-field distribution. For an arbitrary given source energy with a Gaussian profile, the coherent source energy required to achieve a minimum intensity over a given area is determined for phase distributions at the source aperture. Assuming a desired intensity distribution in the far-field and Gaussian source, an adaptive-additive algorithm is employed to synthesize a phase transformation at the source to achieve the desired distribution. The far-field intensity distribution of this synthesized phase distribution applied to a Gaussian source is compared to the far-field produced by a non-phase transformed Gaussian source.