Confocal spatial filtering for imaging with ballistic light in transillumination

The detection of ballistic and diffuse light in confocal imaging in transillumination is investigated. We find an optimum pinhole size for detection of ballistic and suppression of diffuse light. The limits of confocal imaging with ballistic light are primarily determined by sample parameters. Spherical aberration introduced by the sample is a major limiting factor for high resolution imaging. In the aberration free case and for sample and illumination characteristics which are typical for biomedical imaging, the limits of ballistic light detection in confocal imaging are close to the noise limits of standard detectors.