Diamond Raman Laser Paves the Way to Improved Laser Surgery

At a pulse repetition rate of 5 kHz, the Raman laser generated 1.2 W output with a conversion efficiency of 63.5%, a slope efficiency of 75%, and a pulse peak instantaneous conversion efficiency of 85% that is competitive with the 65% efficiency achieved by current Raman lasers, which typically use crystals made of silicon, barium nitrate, or metal tungstate to amplify light created by a Q-switched pump lasers. Compared to these materials, diamond has a higher optical gain (91%), as well as a greater thermal conductivity, making it ideal for high-power applications, ranging from defense technologies and trace gas detectors to medical devices and satellite mapping of greenhouse gases.

The artificial diamond crystals are grown using an industrial process known as chemical vapor deposition, allowing the synthesis of crystals with a lower birefringence, which makes them less likely to split apart an incoming beam of light. Future diamond crystals could also be made to generate a wider variety of wavelengths of light, each of which has its own applications - from ultraviolet light at 225 nanometers to far-infrared light at 100 microns. The device is currently optimized to produce yellow laser light useful for medical applications such as eye surgery, and other applications should be possible with different optimization schemes. The study was published in the September 2009 issue of Optics Letters.

"Diamond is quite a bizarre material with unique and extreme properties; single crystal diamond is very new on the scene as an optical and laser material," said lead author Richard Mildren, Ph.D. "The material is now good enough to start moving into applications that are of real practical interest.”

The Raman laser is a byproduct of Raman scattering, discovered in 1928 by Nobel laureate Chandrasekhara Venkata Raman and Kariamanickam Srinivasa Krishnan in liquids, and independently by Grigory Landsberg and Leonid Mandelshtam in crystals. When light hits a substance, it causes its atoms to vibrate sympathetically; the collision of photons with the substance causes some of the photons to gain or lose energy, resulting in a secondary light of a different wavelength. A Raman laser takes this secondary light and amplifies it by reflecting it and pumping energy into the system to emit a coherent laser beam.

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Macqaurie University
Australian Defence Science and Technology Organisation