A laser system comprises a seed module (33) operable to emit a pulse of a first laser beam followed by a pulse of a second laser beam and a plurality of amplification chambers each comprising a gain medium having a gain, wherein the plurality of amplification chambers are arranged to receive the pulse of the first laser beam (45) and amplify the first laser beam in a second order (PA3, PA2, PA1, PA0) and wherein the plurality of amplification chambers are further arranged to receive the pulse of the second laser beam (41) and amplify the second laser beam in a first order (PA0, PA1, PA2, PA3) which is the reverse of the second order. Saturation powers and small signal gain coefficients of the gain media are selected such that the pulse of the first laser beam experiences a total amplification which is less than the total amplification experienced by the pulse of the second laser beam.