A line narrowed high average power high pulse repetition laser micro-photolithography light source bandwidth control system comprising: a bandwidth metrology module configured to measure the bandwidth of a laser output light pulse beam produced by the light source and to provide a bandwidth measurement; a bandwidth error signal generator configured to receive the bandwidth measurement and a bandwidth setpoint and to provide a bandwidth error signal; a multi-stage actuator system comprising: a coarse bandwidth correction actuator adapted to induce a first modification of the light source that influences the bandwidth of the laser output light pulse beam and targeting large amplitude disturbances occurring at low frequency; and a fine bandwidth correction actuator adapted to induce a second modification of the light source that influences the bandwidth of the laser output light pulse beam and targeting small amplitude disturbances occurring at high frequency; characterized by further comprising: an active spectral controller configured to calculate a fine bandwidth correction actuator signal and a coarse bandwidth correction actuator signal on the basis of the bandwidth error signal provided by the bandwidth error signal generator, to provide said fine bandwidth correction actuator signal to said fine bandwidth correction actuator and to provide said coarse bandwidth correction actuator signal to said coarse bandwidth correction actuator. a bandwidth metrology module configured to measure the bandwidth of a laser output light pulse beam produced by the light source and to provide a bandwidth measurement; a bandwidth error signal generator configured to receive the bandwidth measurement and a bandwidth setpoint and to provide a bandwidth error signal; a multi-stage actuator system comprising: a coarse bandwidth correction actuator adapted to induce a first modification of the light source that influences the bandwidth of the laser output light pulse beam and targeting large amplitude disturbances occurring at low frequency; and a fine bandwidth correction actuator adapted to induce a second modification of the light source that influences the bandwidth of the laser output light pulse beam and targeting small amplitude disturbances occurring at high frequency; characterized by further comprising: an active spectral controller configured to calculate a fine bandwidth correction actuator signal and a coarse bandwidth correction actuator signal on the basis of the bandwidth error signal provided by the bandwidth error signal generator, to provide said fine bandwidth correction actuator signal to said fine bandwidth correction actuator and to provide said coarse bandwidth correction actuator signal to said coarse bandwidth correction actuator. a coarse bandwidth correction actuator adapted to induce a first modification of the light source that influences the bandwidth of the laser output light pulse beam and targeting large amplitude disturbances occurring at low frequency; and a fine bandwidth correction actuator adapted to induce a second modification of the light source that influences the bandwidth of the laser output light pulse beam and targeting small amplitude disturbances occurring at high frequency; characterized by further comprising: an active spectral controller configured to calculate a fine bandwidth correction actuator signal and a coarse bandwidth correction actuator signal on the basis of the bandwidth error signal provided by the bandwidth error signal generator, to provide said fine bandwidth correction actuator signal to said fine bandwidth correction actuator and to provide said coarse bandwidth correction actuator signal to said coarse bandwidth correction actuator. an active spectral controller configured to calculate a fine bandwidth correction actuator signal and a coarse bandwidth correction actuator signal on the basis of the bandwidth error signal provided by the bandwidth error signal generator, to provide said fine bandwidth correction actuator signal to said fine bandwidth correction actuator and to provide said coarse bandwidth correction actuator signal to said coarse bandwidth correction actuator.