A narrow band laser system having two laser subsystems. The first laser subsystem is configured to provide a very narrow band pulsed output beam which is used to injection seed the second laser subsystem where the narrow band pulsed seed beam is amplified to produce a narrow band pulsed output beam. A pulse power supply is provided which is specially configured to precisely time the discharges in the two laser subsystem so that the discharges are properly synchronized. Preferred embodiments include a pulse power system with a pulse transformer unit having two sets of transformer cores. A single upstream pulse compression circuit provides high voltage pulses in parallel to the primary windings of all of the cores in both sets. Separate secondary conductors (one passing through one set of cores and the other passing through the other set of cores) provide very high voltage pulses respectively to separate downstream circuits supplying discharge pulses to the electrodes in each of two separate laser chambers. Preferred embodiments include KrF, ArF and F2 systems. In these preferred embodiments, line narrowing may be accomplished within the resonant cavity of the seed laser or the output of the seed laser could be line narrowed using a pre-gain filter.