APPLIED PHYSICS Obtaining information on the internal makeup of living tissue has generally been the domain of x-ray imaging techniques. However, it has recently been found that light at far-infrared wavelengths, whose low energy avoids the harmful effects of ionizing x-rays, can also penetrate biological tissue without being appreciably absorbed. Collecting and analyzing this scattered light is the basis of optical coherence tomography. Using photorefractive quantum wells, which essentially work as a dynamic holographic image plate for the storage of the scattered light interference pattern, Yu et al. demonstrate the ability to take three-dimensional non-invasive slices of tumour spheroids. Without the need for post-processing, this nondestructive imaging technique may prove a useful window through which to visualize the dynamical internal working of living biological tissue. — ISO Appl. Phys. Lett. 83 , 575 (2003).