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Harvard scientists develop ‘plug and play’ laser

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Raman injection laser represents several key innovations

Engineers and applied physicists have demonstrated the feasibility of a new type of plug-in laser that could lay the groundwork for wide-ranging security applications.
Their Raman injection laser, described in the most recent issue of the journal Nature, combines the advantages of nonlinear optical devices and semiconductor injection lasers with a compact “plug and play” design.

“While our paper merely demonstrates proof of concept, one day it may lead to the sort of security experts dream of having: a portable device that you could use to detect things like weapons or explosives simply by shining an invisible light to see what someone might be hiding,” says Federico Capasso, Robert L. Wallace Professor of Applied Physics and Vinton Hayes Senior Research Fellow in Electrical Engineering in Harvard University’s Division of Engineering and Applied Sciences. “The work also represents an important advance in quantum design since we are now able to engineer, from the bottom-up, a new Raman material and laser, and tailor its property for a given application.”

While Raman lasers have been used for a long time, they have generally required a large and powerful pump to compensate for the beam’s weakening as it propagates through a material. In their work, Capasso and his colleagues were able to combine the pump and the material itself in a single device.

Conventional Raman lasers depend on a fundamental phenomenon in physics called the Raman effect: the change in the frequency of monochromatic light, such as that found in a laser, when it passes through a substance. When light from an intense laser beam, known as the “pump,” deflects off the molecules of certain materials, some of the incident photons lose part of their energy. As a result, a secondary laser beam, with a frequency shifted from that of the first, emerges from the material.

By combining the power source and the Raman material together, literally creating a laser-within-a-laser, the team has created the first current-driven Raman laser. The current generates an internal laser beam within a material, which, in turn, generates the Raman laser radiation. Because the pump laser is now self-generated, the device is highly efficient, reducing the standard decline that happens when an external power source is used.