The claimed invention is a tunable injection seeded very narrow band F2 lithography laser. The laser combines modular design features of prior art long life releasable lithography lasers with special F2 line narrowing and tuning techniques. This techniques are applied to a seed beam which is operated in a first gain medium. This seed beam is then used to stimulate narrow band lasing in a second gain medium. The resulting very narrow band laser beam is useful for integrated circuit lithography. One preferred embodiment of the invention comprises a laser chamber (211), a gas module (202), a control module (205), a line narrowing module (206), and a pulse power supply module (208).