Abstract: Atoms in a neodymium:glass rod 20 are excited to a substantially spatially uniform metastable state by flashlamps 21. A flowing fluid 26 cools the flashlamps, but not the rod; so that low temperature gradients are maintained in the rod during isothermal laser operation. Automatic control means 22 turn off the electrical power supply 24 when the temperature in the rod reaches a predetermined limit. A flowing fluid 23 then cools the rod, at a rate low enough to avoid thermal stress therein, while it is not lasing. Segments of reflectors 25 focus the pump photons in the rod so as to substantially balance the cylindrical lensing action of the rod against the radial attenuation through it, and thus to provide substantially uniform density of stored energy in the rod.