A depth-resolved imaging system is described for recording three dimensional images of objects embedded in diffuse media. Time-gated holographic imaging, employing rhodium- doped barium titanate as the recording medium, is used to obtain whole-field depth-resolved two dimensional images. Infra-red radiation has been used which corresponds to the medical imaging window, as well as blue radiation which may be suitable for undersea imaging.
We present results for real-time holographic imaging in the medical imaging window (approximately 650 to 1000 nm) using photorefractive media. By recording holograms of a USAF test chart using a Ti:sapphire laser, we have selected the coherent)mostly ballistic) light and formed an image through a scattering medium which simulates biological tissue. The advantage of this approach is that a 2D image may be acquired in 'real time', i.e. without scanning. This will permit electronic signal processing and averaging, which may be used to reduce the deleterious effects of speckle. If the holograom is written with ultrashort pulses, then time-gated imaging is possible. This may be used to provide depth information by recording the 'time of flight' of the image light. We have recorded such holograms with picosecond pulses and present time-gated image data.