Characterization and control of gamma and proton radiation effects on the performance of Nd:YAG and Nd:YLF lasers

The laser performance of Nd:YAG and Nd:YLF crystals longitudinally pumped at 800 mm was evaluated before and after exposure to ⁶⁰Co gamma rays and high energy (30-50 MeV) protons. Both forms of radiation created the same damage centers in the respective crystals, which reduced optimal output primarily by absorbing the laser emission. While the radiation induced loss at the lasing wavelength for high quality Nd:YAG reached a limiting value of ~0.015 cm^-1 at 100 krad exposure levels, the loss in Nd:YLF was significantly larger than in Nd:YAG for all comparable dosage levels, and did not appear to have a limiting value. Given the relatively short path lengths of the laser crystals that were tested, the loss could be overcome for both materials under pulse-pumped operation, demonstrating that certain Nd lasers can be effectively radiation hard by design. Additionally, for the first time, Cr³⁺ was codoped with Nd in YAG (with minimal Cr⁴⁺ formation) yielding a high performance material with a significantly reduced radiation susceptibility