I don't know anything about it either but I am gona try to talk to one of these mfr.s about the subject. This site has quite a bit of info:
Encyclopedia of Laser Physics and Technology - chromium-doped gain media, Cr:YAG, forsterite, alexandrite, Cr:LiSAF, Cr:LiCAF, Cr:LiSGAF, ZnSe, ZnS...