Diode-side-pumped joule-level square-rod Nd:glass amplifier with 1 Hz repetition rate and ultrahigh gain

An effective diode-side-pumped joule-level square-rod Nd:glass multipass amplifier with 1 Hz repetition rate is developed. A Pockels cell is used to extend the amplification-pass to twelve-pass. The linear depolarization compensation method and adaptive optics based wavefront aberration correction method are used to minimize the thermal effects. Combined with the relay-imaging technology and beam-shaping method, good beam quality is obtained. Under the small-signal gain of 3.23 and the input energy of 50 µJ, the output energy of 1 J and the net gain of 2×104 are realized. The effective energy-extraction efficiency in the whole aperture of Nd:glass rod is 12%. The total wavefront aberration is 1.1 µm (peak valley). The Strehl Ratio is 0.62, and 90% of far-field energy is concentrated in 3 times the diffraction limit. The near-field modulation index of twelve-pass amplification at 1 J is 1.4.