TIME-RESOLVED HOLOGRAPHY

IN a conventional hologram, a photographic film records the interference pattern of monochromatic light, scattered from the object to be imaged, with a reference beam of unscattered light. Illumination of the developed film with a replica of the reference beam then creates a virtual image of the original object. Here we show how a molecular resonance can be used to record an interference pattern between light signals that arrive at different times, and with this technique create a hologram with time resolution. Using a timed reference pulse as a 'light shutter', we can record holographic images selectively, according to the time taken by light travelling from the object to the hologram. We use this method to image an object behind a semi-opaque screen, and indicate how a similar method could be used to inspect objects embedded in a dense scattering medium. Ultimately, this technique might be applied to the medical imaging of tumours.