With random lasers, Yale researchers fight random noise, improve imaging

Light emerges from a random laser. (Image byBrandon Redding, Yale)

Using "random lasers" as a source of illumination in medical imaging equipment could improve both processing time and the clarity of the final images, according to new research by Yale University scientists.

Imaging systems currently rely on a variety of light sources -- specialty light bulbs, light-emitting diodes (LEDs), and traditional lasers. But systems using traditional lasers, the brightest of these light sources, often yield undesirable visual byproducts that mar the final picture. One common byproduct, speckle, looks something like a snowfall pattern.

The Yale researchers have engineered a special type of laser called a random laser -- which generates and emits light differently from traditional lasers -- to serve the same function without giving off speckle or other visual blight. They report their results online April 29 Photonics.

"Our work is innovative and significant because we show that random lasers are much brighter than LEDs and light bulbs and also generate speckle-free images," said Michael A. Choma, an assistant professor of diagnostic radiology, pediatrics, and biomedical engineering at Yale. He is one of the study’s principal investigators.

Hui Cao, a professor of applied physics and physics at Yale, is the other principal investigator. Brandon Redding, a postdoctoral associate in applied physics, is the lead author.

A traditional laser emits a single intense beam of light, known as a spatial mode. Photons from that single beam can be scattered by a sample under observation, resulting in random grainy background noise -- speckle -- on top of the desired image.

One way of mitigating the noise is to use many different spatial modes, such as the light emitted by a LED or light bulb. Unfortunately, these light sources are dim compared with lasers.

But random lasers offer the best of both worlds, according to the Yale researchers. They are bright, like lasers, while also having many modes, like a light bulb, so they generate speckle-free images. That is, random lasers are something akin to a light bulb with the intensity of a laser.