Chaotic cavity key to high-quality laser images

A new semiconductor laser developed at Yale University is claimed to have the potential to improve the imaging quality of next generation high-tech microscopes, laser projectors, holographs and biomedical imagery. 

Based on a chaotic cavity laser, the technology is said to combine the brightness of traditional lasers with the lower image corruption of light emitting diodes (LEDs). The new laser is described in a paper in Proceedings of the National Academy of Sciences.

In a statement, co-author A. Douglas Stone, the Carl A. Morse Professor and chair of applied physics, and professor of physics said: ‘This chaotic cavity laser is a great example of basic research ultimately leading to a potentially important invention for the social good.

‘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 of those problems – dubbed ‘speckle’ – is a random, grainy pattern caused by high spatial coherence that can corrupt the formation of images when traditional lasers are used. A way to avoid such distortion is by using LED light sources, which are often not bright enough for high-speed imaging.

The new, electrically pumped semiconductor laser is said to offer a different approach by producing an intense emission with low spatial coherence.

‘For full-field imaging, the speckle contrast should be less than ~4 per cent to avoid any disturbance for human inspection,’ said Hui Cao, professor of applied physics and of physics, who is the paper’s corresponding author. ‘As we showed in the paper, the standard edge-emitting laser produced speckle contrast of ~50 per cent, while our laser has the speckle contrast of three per cent. So our new laser has completely eliminated the issue of coherent artefact for full-field imaging.’

Co-author Michael A. Choma, assistant professor of diagnostic radiology, paediatrics, and biomedical engineering, said laser speckle is a major barrier 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,’ Choma said. ‘It also is exciting to think about the new kinds of clinical diagnostics we can develop.’