A laser pulse includes a flat top shape. Another aspects provides a method and system for creating laser pulse amplification with a flat top and/or square shape, by only using phase modulation. In yet another aspect, a method and system create a flat top and/or square-shaped laser pulse in a reversible manner such that the stretched spectrum can be recompressed to their original duration with essentially no loss of pulse energy. A further aspect includes a method of making a fixed optic capable to creating flat top or square pulse amplification.