A method and apparatus are disclosed for controlling the output of a two chamber gas discharge laser comprising an oscillator gas discharge laser and an amplifier gas discharge laser that may comprise establishing a multidimensional variable state space comprising a coordinate system having at least two coordinates, each coordinate comprising a selected variable representing an operating parameter of the oscillator or the amplifier; tracking a multidimensional operating point in the multidimensional variable state space according to the variation of the selected variables in either or both of the oscillator or the amplifier to determine the position of the multidimensional operating point in the multidimensional state space; determining from the position of the multidimensional operating point in the multidimensional operating space a region from a plurality of defined regions in the multidimensional operating space in which the multidimensional operating point is located and identifying the region; based upon the identity of the identified region, and parameters of that region relative to the condition of an actuator in each of the oscillator and the amplifier, determining a necessary modification to the actuator for each of the oscillator and the amplifier to attempt to move the multidimensional operating point from the parameters indicated by the position of the multidimensional operating point being in the particular region to a preselected region in the coordinate system. The method and apparatus may also comprise establishing a multidimensional variable state space comprising a coordinate system having at least two coordinates, each coordinate comprising a selected variable representing an operating parameter of the oscillator or the amplifier; changing the gas mixture in one or both of the oscillator and amplifier by injection of at least one constituent gas in the gas mixture at least part of which injection for the respective oscillator and amplifier is based upon a calculated estimate of consumption of the at least one constituent gas in the gas mixture in the respective oscillator and amplifier from a prior change in the gas mixture; allowing the oscillator and amplifier to operate for a selected period of time with the changed gas mixture; determining the position of an operating point in the multidimensional variable state space and based upon the location of the operating point in the multidimensional state space determining a respective boost factor to modify the calculated estimate of consumption for the current change of the gas mixture in the respective oscillator and amplifier. A third dimension may be added relating to a spectral characteristic of the output of the oscillator or the amplifier, which may be bandwidth of the output of the amplifier, and including modifying that output with a beam correction device.