| Popis: |
We describe a method for imaging of opaque objects embedded in highly scattering media, such as human tissue. The method is based on electronic holography, in which a hologram is formed on the surface of a CCD camera, the hologram is read into a computer, and the reconstruction is carried out digitally. The illumination is a train of 150-fs pulses. The scattering medium is assumed to be unstable, so that the speckle on the transmitted light changes, i.e., becomes uncorrelated, after a short time, such as ~30ms. The hologram is made during this very short exposure time, using only the first arriving portion of the light transmitted by the scattering medium, since the first arriving light is scattered least and therefore should form the best image. A key element of the technique is that many holograms are made in rapid succession, at time intervals that exceed the speckle correlation time, so that the images from successive holograms have uncorrelated speckle. We then average over many (so far up to seventy-five) holograms, thus averaging out the speckle as well as other noise, resulting in an image vastly better than the image from a single hologram. Experimental results are shown. |
