Random Lasers Used to Combat Random Noise, Improve Imaging

Employing “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.

Imaging systems presently rely on a range of light sources--specialty light bulbs, light-emitting diodes (LED), and conventional lasers. However, systems employing traditional lasers, the brightest of these light sources, frequently yield undesirable visual byproducts that blemish the completed image. One common byproduct, speckle, looks something like a snowfall pattern.

The Yale University (New Haven, CT, USA) researchers have modified a special kind 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 reported their findings online April 29, 2012, in the journal Nature 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 Dr. Michael A. Choma, an assistant professor of diagnostic radiology, pediatrics, and biomedical engineering at Yale, and one of the study’s lead investigators. Dr. 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. Regrettably, these light sources are dim compared with lasers. However, random lasers provide the best of both worlds, according to the Yale researchers. They are bright, similar to lasers, while also having many modes, like a light bulb, so they generate speckle-free images. Random lasers are analogous to a light bulb with the intensity of a laser. “Our random lasers combine the advantages of lasers and the white light sources, and may be used for a wide range of imaging and projection applications,” said Dr. Cao.

The light emitted by random lasers could also enable faster image generation. This would help researchers and clinicians better catch fast-moving physiologic phenomena--the movements of embryo hearts, possibly, or blood flow patterns in the eye--as well as broad bands of tissue in less time than needed by current technologies. “Your light source really defines the boundaries of what you can do--how fast you can image,” said Dr. Choma. “And you always want to go faster.”

Moreover, random lasers could have applications in consumer electronics, according to the researchers-- for example, in digital light projection systems. Within medical imaging, the introduction of random lasers could lead to improved microscopy and endoscopy, the investigators reported. The scientists have built a prototype random laser for use in imaging applications and are refining it.

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