Nondestructive, contrast enhanced imaging of biological tissues using photorefractive recycling

Summary form only given. Many biological samples are nearly transparent. In order to observe the structure of such tissues and cells in a microscope, either the samples must be stained, or optical processing techniques are required to enhance the image. In many cases image processing is preferable because, unlike staining of the sample, it allows observation without killing or disturbing the tissues under study. One well established technique that enhances the contrast of phase objects is high pass filtering. In this method, the background illumination is removed thereby enhancing the contrast of the image. A disadvantage of this technique is that most of the energy in the illuminating beam is discarded. It therefore yields weak images, especially at low power levels that must not be exceeded when imaging living tissues. Recently our group has demonstrated a technique to amplify filtered images by recycling the energy rejected by the filter. The technique is ideal for biomedical imaging because it produces a strong high-contrast image with only weak nondestructive illumination of the sample itself. We apply this technique with good results to different biological samples.