Off-axis eight-pass neodymium glass laser amplifier with high efficiency and excellent energy stability

A new relay-imaged off-axial eight-pass laser amplifier with several joules energy and 1 Hz repetition rate was demonstrated. The extraction efficiency and pulse-to-pulse energy stability were greatly improved. Under the single-pass small-signal gain of 3.6, a net gain of 900 and an effective extraction efficiency of 42.4% in the beam aperture were realized. Pulse-to-pulse energy stability of 0.83% (peak-valley) and 0.17% (root-mean-square) was achieved by the significant saturation of eight-pass amplification, which, to the best of our knowledge, is the best energy stability in several-joules-class amplifiers. The far-field quality was 2.52 times the diffraction limit, and the near-field modulation of the 90% beam aperture was 1.28. No parasitic oscillations or pencil beams were observed. Moreover, another key feature of the proposed amplifier was the ability to remarkably improve the pulse contrast with a unique design.