Multipass amplifier with full utilization of the active element aperture

A four-pass amplifier with complete filling of the active rod aperture was designed. An output radiation energy of 12 J was achieved in a laser system comprising a master oscillator and a four-pass neodymium glass amplifier. Wavefront reversal was used to ensure that the divergence of the output radiation was close to the diffraction limit. The duration of the leading edge of radiation pulses was reduced to 4 nsec.