Real-time 3-D holographic imaging using photorefractive media including multiple-quantum-well devices

We discuss a real-time coherence gated three-dimensional (3-D) imaging system, based on photorefractive holography with ultrashort pulses, which has been applied to imaging through turbid media with a view to developing biomedical instrumentation. Sub-100-μm depth-resolved images of 3-D objects embedded in a scattering medium have been obtained. Using a long integration time in rhodium-doped barium titanate (Rh:BaTiO₄), an image of a test chart has been obtained through 16 mean-free paths of scattering medium. Real-time depth-resolved imaging through 13 mean free paths of scattering medium has been demonstrated using a fast response time (<0.4 ms) photorefractive multiple quantum well device. This latter system can acquire depth-resolved images direct to video with no requirement for frame grabbing or signal processing. We discuss the tradeoffs and limitations of these photorefractive media for this application