R. Gaumé, B. Viana, D. Vivien, and G. P. Aka, "Crystal host requirements for Yb-based high power lasers and laser properties of Yb:YCOB composites,"
in Advanced Solid-State Lasers, M. Fermann and L. Marshall, eds.,
Vol. 68 of Trends in Optics and Photonics Series
(Optical Society of America, 2002), paper WB2.