Chris writes: "A holographic imaging system gives the first visual "fly-through" of living tumors just under the skin. David Nolte and colleagues from Purdue University, US, have developed an optical imaging system that allows clinicians to "fly-through" near-surface tumors in real time. In the scheme, a laser fires 100 fs probe pulses into the skin. The pulses weakly reflect from varying depths below the surface and are compared to a coherent reference pulse which, thanks to a time-of-flight measurement, originates from a known depth. A hologram then rejects unwanted, incoherent light leaving only the useful, image-bearing signal. Only a fraction of a nanowatt of optical power is required to write the hologram. A joystick controlling the depth of the reference pulse allows the clinician to explore the tumor. For example, to probe deeper into the tumor, the clinician simply pushes the joystick forward. The reflected pulses are then compared to this new reference and new depth information is written onto the hologram."