Confocal Imaging Through Scattering Media with a Volume Holographic Filter

The use of a volume holographic filter as collector element in a confocal system imaging through scattering (turbid) material is described. We show that the penetration depth of the volume holographic system is de-coupled from the scatter noise discrimination properties, and is potentially more advantageous than the traditional confocal microscope. Since the volume-holographic filter is a matched-filter, the penetration depth is dependent on the mismatch of the refractive index of the sample being imaged relative to the recording conditions. We present a method to overcome this limitation based on using a pre-compensating index matching film during the recording of the volume hologram. An improvement of the penetration depth is shown experimentally.