January 20, 2015

New semiconductor laser could revolutionize science imagery

John Hopton for - Your Universe Online

Scientists at Yale have created a new semiconductor laser which could significantly enhance image production. The development could mean major improvements in several areas of science and medicine.

Yale’s Jim Shelton says that such a discovery “has been the focus of intense experimentation and research in recent years,” and the new laser technology is seen as a triumph of nuts and bolts research leading to a hugely beneficial product. It is the result of collaboration between several Yale labs and departments, with scientists in applied physics, electrical and biomedical engineering, and diagnostic radiology all involved.

Success in the search for better light sources for high-speed, full-field imaging applications will have an impact in areas such as high-tech microscopes, laser projectors, photo lithography, holography, and biomedical imaging.

This technology isn't necessarily new

Semiconductor lasers are the most widely used of all lasers. They are cheap and compact and as such are common in everyday life, including supermarket barcode scanning, as well as in science and medicine. The new product is based on a chaotic cavity laser, which co-author A. Douglas Stone, the Carl A. Morse Professor and chair of applied physics and professor of physics, explained, “is a great example of basic research ultimately leading to a potentially important invention for the social good.”

He added: “All of the foundational work was primarily motivated by a desire to understand certain classes of lasers--random and chaotic--with no known applications. Eventually, with input from other disciplines, we discovered that these lasers are uniquely suited for a wide class of problems in imaging and microscopy.”

One such problem is known as “speckle.”  This is “a random, grainy pattern, caused by high spatial coherence that can corrupt the formation of images when traditional lasers are used.” One solution is to use LEDs (light emitting diodes), but they are not bright enough for high-speed imaging.

What the new laser does differently

The new semiconductor laser combines the brightness of traditional lasers with the lower image corruption of light emitting diodes (LEDs) to produce an intense emission, but with low spatial coherence.

“For full-field imaging, the speckle contrast should be less than 4 percent to avoid any disturbance for human inspection,” explains Hui Cao, professor of applied physics and of physics, the paper's corresponding author. “As we showed in the paper, the standard edge-emitting laser produced speckle contrast of 50 percent, while our laser has the speckle contrast of 3 percent. So our new laser has completely eliminated the issue of coherent artifact for full-field imaging.”

Co-author Michael A. Choma, assistant professor of diagnostic radiology, pediatrics, and biomedical engineering, says that laser speckle has been a major stumbling block in the development of certain classes of clinical diagnostics that use light. “It is tremendously rewarding to work with a team of colleagues to develop speckle-free lasers,” he added. "It also is exciting to think about the new kinds of clinical diagnostics we can develop."

The new laser is described in a paper in the Jan. 19 online edition of the Proceedings of the National Academy of Sciences.


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