Physicist David Nolte can peer into the body using nothing but ordinary light. To the eye, skin appears opaque because it scatters almost all incoming light. But roughly one time in a million, a particle of light naturally travels into the skin and back out without scattering. Nolte and his colleagues at Purdue University in Indiana can focus in on those purely reflected photons, revealing an image of what lies beneath.

Nolte recently demonstrated his technique on a rat tumor. He split an infrared laser beam in two. One part shone directly into the tumor; the other part served as a reference beam. The small amount of unscattered laser light that reflected out of the tissue was collected by an electrified film, producing a holographic pattern that created a perfect picture when recombined with the reference beam. By moving a mirror, Nolte imaged different tissue depths and then created a three-dimensional view of the rat's tumor.

In the future, Nolte's holographic imaging technique could lessen the need for surgical biopsies and could greatly speed up tumor analysis. "A thorough sectioning under a microscope takes many weeks, but I can optically section one in a matter of seconds," he says.