Pumping gas lasers by the235U(n,ff)FFreaction has the advantage of depositing large energies per reaction (∼200 MeV), and by using235UF6, a volumetric energy source is achieved. Factors in235UF6pumping of a He gas relating to neutron attenuation and fission product transport within a laser tube are treated in detail. Neutron attenuation is found not to be significant for tube sizes and pressure ranges anticipated for laser applications. Maximum power can be deposited in a laser tube when the tube radius is at least as large as the range of the fission fragments. The maximum power is deposited in the helium gas when the tube radius equals the fission‐fragment range and the UF6partial pressure to total pressure ratio is 0.15 corresponding to a UF6‐He mixing ratio of approximately 1 : 6.