The correlation function between two speckle patterns produced by different
incident waves is studied by means of stochastic approaches. The angular-f
requency memory effect, which includes the angular memory effect as a speci
al case, is discussed, and the concept of the conjugate memory effect is in
troduced, which implies the interference of a complex-conjugate pair of sca
ttering processes in the intensity. (C) 1999 Optical Society of America [S0
740-3232(99)01106-0].