Abstract: A high power laser with chirped pulse amplification to produce extremely high power ultrashort pulses is disclosed. A pulse stretcher and methods of stretching a laser pulse are also disclosed. The pulse stretcher comprises: a first diffraction grating (G1) arranged to receive and disperse a seed laser pulse; transfer optics (CM) arranged to collect the dispersed pulse and direct it to a transmission diffraction grating (G2) which is either the first diffraction grating or a second diffraction grating; the transmission diffraction grating arranged to collimate the collected pulse to a reflector (BM), the reflector arranged such that the pulse is reflected back through the pulse stretcher via the transmission diffraction grating. The pulse stretcher provides better phase noise performance of the output pulse, and therefore a reduction in the noise floor to improve contrast pedestal.