Dynamically stable lasers from commercial Nd:YAG modules with high beam quality and single-frequency: The correct choice of the fundamental waist size at the rod

Diode-side pump Nd:YAG rod modules are widely available, reliable and commercially very attractive for building continuous-wave solid-state lasers in the 10-1000 W range. Newer technologies such as fiber or thin disk lasers are generally much more expensive but have the benefit of better beam quality and higher output powers if necessary. By using well-known techniques for designing dynamically stable resonators (DSRs), lasers with high extraction efficiency and high beam quality (fundamental mode, TEM₀₀) can be obtained also with diode side-pumped modules. However, a successful project for a dynamic stable laser depends critically on the correct choice of the fundamental mode diameter within the rod. DSR design rules are based on the beam waist, w₃, at the rod principal planes by considering the rod as a thin thermal lens, which differs significantly from real resonators. Here we give guidelines and criteria on how to establish the correct diameter in each case. Using off-the-shelf 75 W Nd:YAG modules it was possible to obtain linearly polarized TEM₀₀-mode output of 30 W with M²=1.08 from a single module, M²=1.2 and 76.5 W of output power using two modules and 100.5 W of polarized, continuous output with M²=1.8. A single-frequency ring laser was also built, using two modules, generating 51.6 W of fundamental wave single-frequency output.