Submitted to 1 1 DOI: 10.1002/adfm.((please add manuscript number)) Composite Ceramic Er:YAG Laser Gain Media** By Elizabeth R. Kupp*, Gary L. Messing, Julie M. Anderson, Venkatraman Gopalan, John Q. Dumm, Charles Kraisinger, Nikolay Ter-Gabrielyan, Larry D. Merkle, Mark Dubinskii, Vida K. Castillo-Simonaitis and Gregory J. Quarles [*] Dr. E. R. Kupp, Prof. G. L. Messing, J. M. Anderson, Prof. V. Gopalan Department of Materials Science and Engineering and Materials Research Institute The Pennsylvania State University 121 Steidle Building, University Park, PA 16802 (USA) E-mail: kupp@matse.psu.edu J. Q. Dumm, Dr. C. Kraisinger AMDC II-VI Incorporated 375 Saxonburg Blvd., Saxonburg, PA 16056 (USA) Dr. N. Ter-Gabrielyan, Dr. L. D. Merkle, Dr. M. Dubinskii Attn: AMSRD-ARL-SE-EO US Army Research Laboratory 2800 Powder Mill Rd., Adelphi, MD 20783 (USA) Dr. V. K. Castillo-Simonaitis, Dr. G. J. Quarles VLOC II-VI Incorporated 7826 Photonics Dr., New Port Richey, FL 34655 (USA) [**] This work was supported by the High Energy Laser program of the Joint Technology Office under BAA 05-DE-01 Keywords: Optically active materials, yttrium aluminum garnet, tape casting, laser gain media, composites A significant problem with laser gain media, whether single crystal or polycrystalline, is thermal management. While pure yttrium aluminum garnet (YAG) has a high thermal conductivity relative to other laser gain media, the active elements which are doped into YAG to allow it to lase (e.g. Nd 3+ , Yb 3+ and Er 3+ ) can significantly degrade its thermal properties. To address this problem, composite parts are fabricated, generally by diffusion bonding, with