Microdifferential holography.

A novel coherent imaging method analogous to electronic differential amplification is described and analyzed. The method is well suited to highlighting local changes in the optical properties of a dynamic object whose more prominent details are largely static. The object may be examined either in transmitted light or in reflected light. The method discriminates between changes that result from substructural reorganization of object details too fine to be imaged as resolved structures and changes that result from the microdisplacement of optically resolved structures. Substructural reorganization is signaled by changes in the amplitude of the transmitted or reflected light, whereas ordinary displacement is displayed in the usual way through a change in phase. The method is capable of detecting displacements as small as several milliwavelengths. Images of contractile activity in muscle are presented that illustrate the method's sensitivity and analytic power.