Forced airflow efficiently cools high-power beam-combining VBGs
Volume Bragg gratings (VBGs), which are recorded as refractive-index variations in photothermorefractive (PTR) glass, can be used for high-power, high-spectral-density laser beam combining. However, the high powers cause heating of the VBG, as well as the copper holder for the VBG, leading to thermal deformation of the VBG, reduced efficiency, and beam degradation. Minimizing these effects requires careful mechanical and heat-flow design.
To model such a system, which requires the ability to model heat flow, airflow, and geometry, researchers at the College of Optics and Photonics (CREOL; Orlando, FL) and OptiGrate (Oviedo, FL) turned to multiphysics software produced by COMSOL (Burlington, MA). The model was created to closely imitate the characteristics of VBG experimental setups at CREOL. In the case of a freestanding VBG, four experimental laser-beam powers of 4.5, 6.7, 8.9, and 11 kW were modeled; in the case of a VBG placed between two glass plates (with airflow between them), beam powers of 4.5, 6.1, 6.7, 8.9, and 11 kW were used. Airflows varying between 0 and 121 m/s were also included in the model. The simulation results matched experimental temperatures of both systems with sufficient precision, and provided extra information that the experiments could not provide. Results showed that forced-air cooling of a VBG works well, especially with the addition of the glass plates. Contact Sergiy Kaim at [email protected].
John Wallace | Senior Technical Editor (1998-2022)
John Wallace was with Laser Focus World for nearly 25 years, retiring in late June 2022. He obtained a bachelor's degree in mechanical engineering and physics at Rutgers University and a master's in optical engineering at the University of Rochester. Before becoming an editor, John worked as an engineer at RCA, Exxon, Eastman Kodak, and GCA Corporation.