Adaptive coherent energy beam formation using iterative phase conjugation

Abstract

A method for iterative phase conjugation adaptive reduction of phase aberration effects upon the time delays necessary for formation of a beam of coherent energy focused within non-homogeneous medium at a selected range R from, and at an angle .theta. with respect to the normal to, the surface of an array of a plurality N of transducers, each for providing a portion of the energy of the beam when excited and for converting energy reflected thereto to a signal therefrom, first bounces from a large collection of scatterers, contained in a portion of the medium to be investigated, a probe beam for that beam angle .theta.. The received signals from each of the (N-1) pairs of adjacent transducers are cross-correlated to drive a like number of phase conjugation correction signals, which are then arithmetically operated upon to provide a time correction for the time delay associated with each probe beam transducer, for that range R and angle .theta.. The time correction for each transducer then modifies each of at least one iteration of excitation to, and return signal received from, the media portion. A plurality of iterations, with each excitation made with the most recent corrected delays values, better focuses the interrogating beam, until, after a selected number of iterations, actual imaging data can be obtained with minimal phase aberrations.