Abstract: A low-or no-silica, low- or no-alkali phosphate glass useful as a laser amplifier in a multiple pass, high energy laser system having a high thermal conductivity, K.sub.90.degree. C. >0.85 W/mK, a low coefficient of thermal expansion, .alpha..sub.20.degree.-300.degree. C. <80.times.10.sup.-7 /.degree.C., low emission cross section, .sigma.<2.5.times.10.sup.-20 cm.sup.2, and a high fluorescence lifetime, .tau.>325 .mu.secs at 3 wt. % Nd doping, consisting essentially of (on an oxide composition basis):______________________________________ Mole % ______________________________________ P.sub.2 O.sub.5 52-72 Al.sub.2 O.sub.3 0-<20 B.sub.2 O.sub.3 >0-25 ZnO 0-31 Li.sub.2 O 0-5 K.sub.2 O 0-5 Na.sub.2 O 0-5 Cs.sub.2 O 0-5 Rb.sub.2 O 0-5 MgO >0-<30 CaO 0-20 BaO 0-20 SrO 0-<20 Sb.sub.2 O.sub.3 0-<1 As.sub.2 O.sub.3 0-<1 Nb.sub.2 O.sub.5 0-<1 Ln.sub.2 O.sub.3 up to 6.5 PbO 0-<5 SiO.sub.2 0-3 ______________________________________whereinLn.sub.2 O.sub.