Ballistic and diffuse light detection in confocal and heterodyne imaging systems

Abstract

The detection of ballistic and diffuse light in confocal and heterodyne imaging systems in transillumination is studied experimentally and theoretically. We find an optimum pinhole size for ballistic light detection and diffuse light rejection for confocal imaging. The ratio of ballistic and diffuse light is found to be determined primarily by sample parameters and aberrations introduced by the sample. For sample and illumination characteristics that are typical for biomedical imaging, the limits of ballistic light detection in confocal imaging are close to the noise limits of standard detectors. Heterodyne detection with narrow-bandwidth light can extend these limits, depending on the spatial and the temporal coherence properties of the transmitted scattered light.