We propose a highly efficient quasi-cw Nd:YAG rod laser with a novel side-p
umping design that uses microlens-free diode stacks. We demonstrate 320-W o
utput power with 28% electrical-to-optical efficiency, which is, to our kno
wledge, the highest efficiency reported for diode-pumped solid-state lasers
. (C) 2001 Optical Society of America.