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Diamond takes the heat

27 Apr 2009

The heat-dissipating properties of diamond yield higher-power disk lasers.

UK researchers have demonstrated a disk-laser design that yields record output powers thanks to the incorporation of a diamond heat-spreader. The University of Strathclyde team hopes to commercialize the laser for applications ranging from pollution monitoring, high-brightness displays, medical imaging and materials processing (Optics Letters 34 782).

"We have demonstrated the highest continuous-wave output power reported to date from Nd:YVO4 and Nd:GdVO4 disk lasers using only one double-pump pass," Patricia Millar of the Strathclyde's Institute of Photonics, told optics.org. "Our lasers require fewer pump passes than those based on the more commonly used Yb:YAG disk lasers while removing constraints such as temperature sensitivity."

The key to the disk-laser architecture is the intracavity heat-spreader developed from single-crystal, low-birefringence diamond. The carefully designed synthetic diamond offers the same thermal management advantages as natural diamond, with similar insertion loss but significantly lower birefringence. This helps to reduce thermal effects and enhance power scalability, without introducing significant loss into the cavity.

In the set-up, the diamond heat-spreader is capillary-bonded to the gain medium (Nd:YVO4 and Nd:GdVO4) and results in an output power of 25.7 and 18.1 W respectively using only one double-pump pass. According to Millar, incorporating diamond heat-spreaders within a disk architecture can be applied to both doped-dielectric and semiconductor gain media.

"The intracavity use of diamond in doped-dielectric gain media enables the use of thin slices of material with stronger pump absorption, such as Nd:YVO4," she said. "Such materials are typically fragile and poor thermal conductors. Bonding to diamond helps to alleviate these problems by improving heat extraction, reducing thermal lensing, deformation and stress while simultaneously adding mechanical robustness."

Similarly, intracavity diamond heat-spreaders in semiconductor disk lasers permit an order-of-magnitude improvement in power-scaling across the red to mid-infrared spectral range. This, says Millar, is an important step toward high-wavelength engineerable laser technology.

The Strathclyde team is now working on optimizing the beam quality of the disk lasers. "We plan to explore the thermal properties of synthetic diamond within an integrated microchip laser configuration using both thin disks of doped-dielectric and semiconductor gain material," concluded Millar. "In doing so, we hope to demonstrate high power (>10 W) laser operation within a more compact laser cavity suitable for mobile applications."

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