Beam depolarization and gain saturation in neodymium rods 85 mm in diameter

An experimental investigation was made of the depolarization and gain saturation in rod amplifiers utilizing phosphate (OPS1110) and silicate (GLS6) neodymium glass active elements 85 mm in diameter and 300 mm long. The pulse duration was 35 ns. The total energy losses due to the depolarization were determined for a beam diameter of 80 mm (in the phosphate glass the losses reached 3–6%, whereas in the silicate glass they were 4–7%). The distributions of the losses across the rod cross section were found for different radial distributions of the small-signal gain. The gain saturation was determined for energy densities 1–6 J/cm² at the amplifier input. The saturation value of the energy density amounted to 4.5 ± 0.4 J/cm² for the phosphate glass and 8.0 ± 0.7 J/cm² for the silicate glass.