Intracavity second-harmonic generation of diode-pumped continuous-wave, single-frequency 1.3νmNd:YLiF₄ lasers

We report on the comparative performance of intracavity frequency-doubled continuous-wave (cw) single-frequency Nd:YLiF₄ ring oscillators lasing on the ∼1.3νm⁴F_3/2-⁴I _13/2 transition using either periodically poled KTiOPO₄ (ppKTP) or birefringent-phase-matched BiB₃O₆ (BiBO) and LiB₃O₅ (LBO) nonlinear crystals. Using a single-end diode pumping scheme, a watt-level of tunable single-frequency radiation in the 650-660nm red spectral range was obtained, limited by the saturated gain and thermal effects of the laser crystal. The best performance in terms of red beam quality, tuning range and power (∼1W) was achieved with the temperature-tuned highly nonlinear (second-order nonlinear effective coefficient d_eff∼8.9pmV^-1) ppKTP crystal at 657nm. Up to ∼0.7W of single-frequency power with a degraded transverse beam quality could be achieved at 661nm using a type-I cut critically phase-matched BiBO crystal (d_eff∼2.5pmV^-1), while the insertion of a type-I cut LBO crystal (d_eff∼0.8pmV^-1) yielded less than 0.3W red power at identical operating conditions. Owing to a robust passive frequency stability and to their intrinsic short-term narrow linewidth (Δν<3MHz), these solid-state laser sources are well suited to high-resolution spectroscopy in the lower wavelength part of the red spectrum.