Scientists have developed the first efficient diamond Raman laser, using man-made diamonds to enhance their strength and effectiveness, and achieving a comparable efficiency to lasers built with other materials.
There is great potential for diamond lasers – as they are optimized to produce yellow laser light, they can be useful for medical techniques involved in ophthalmic surgery and in biodiagnostic systems, and can also be applied in defense technologies, as trace gas detectors and in the satellite mapping of greenhouse gases.
One of the most interesting physical and optical qualities of a diamond is the high Raman gain, which makes it a very practical laser material. The special properties of diamonds also means that these more powerful lasers can be optimized to produce other laser light colors currently unavailable to existing technologies.
Raman lasers in operation to date have used crystals of silicon, barium nitrate or metal tungstate to amplify light created by a pump laser. However, diamond has proved to have a higher optical gain and a greater thermal conductivity than these materials, which makes it ideal for high-power applications.
Published in the Optical Society (OSA) journal Optics Letters (doi: 10.1364/OL.34.002811), the researchers from Macquarie University and the Defence Science and Technology Organisation in Australia, started using diamond in their Raman lasers only recently, when it was discovered that the optical quality of this readily available synthetic material was good enough for the job.
Rich Mildren and Alexander Sabella had previously shown that it was possible to use synthetic diamond for lasers, although the laser efficiency was low, a lot lower than that of other standard Raman crystals. They then set about to investigate the possibilities of a diamond that could competing alongside standard materials and still demonstrate the efficiency levels needed by most practical applications.
Mildren, who for many years has been involved in laser and light source development and their optimization for applications, including for laser commercialization and medical device development, built the first diamond Raman laser in 2008. His current laser uses a 6.7 mm long diamond, achieving an efficiency of 63.5 percent, which is competitive with the 65% efficiency achieved by existing Raman lasers.
The studies were performed on high quality synthetic material that only became available recently, and they are now able to better understand the key properties of this material, such as absorption, optical damage and de-polarization that limit conversion efficiency.
As for the future, Mildren points out they are applying what they have learnt from other Raman laser materials, and “aim to next demonstrate output at non-visible wavelengths and to develop architectures that utilize diamond’s outstanding heat-spreading ability.”