Yb: High Power/high Energy Pulsed Laser Characteristics Of ReCOB Crystals

Among the various Yb-ion laser crystals, Yb doped rare-earth calcium oxyborates possess a unique position owing to the particularly large Stark splitting of its ground state, particularly long fluorescence lifetime, and particularly small stimulated emission cross-section. These crystals are of low threshold for laser oscillation, and of extraordinarily high energy capability, thus they are expected to find wide applications in high-power or high-energy solid-state lasers.In this work we conducted, by use of simple plano-concave resonators under longitudinal pumping conditions with a high-power diode laser, a comprehensive,systematic, and deep, experimental investigation into the continuous-wave（cw）,passive Q-switching, and acousto-optic Q-switching laser performance of the Yb:ReCOB crystals, yielding a number of results of important innovative significance.Highly efficient high-power cw laser operation was realized both at the long-wavelength emission peak around 1085 nm and in the main emission band over a wavelength range of 1020-1050 nm. The highest output power was 14.1 W produced at 1084 nm; whilst the output power generated in the main emission band could reach 23.0 W at 1045 nm, the optical-to-optical and slope efficiencies being respectively 57% and 70%, with respect to the incident pump power.High-power or high-energy passively Q-switched laser action was achieved with Yb:ReCOB crystals, with Cr⁴⁺:YAG or GaAs crystal serving as the saturable absorber.In the passively Q-switched operation with Cr⁴⁺:YAG, the maximum average output power produced was 15.6 W, with a pulse energy and duration being 0.17 mJ and 22ns; while the highest pulse energy amounted to 1.28 mJ, with corresponding average power, pulse duration, and peak power being respectively 4.1 W, 5.0 ns, and 256 kW.In the case of GaAs as the saturable absorber, a maximum average output power of5.7 W was generated at 167 kHz of pulse repetition rate, with the shortest pulse duration of 153 ns; at a low repetition rate of 1.0 kHz, the average output power could reach 1.02 W, with pulse energy, duration, and peak power being 1.02 mJ, 13.6 ns,and 75 kW, respectively.Stable actively Q-switched laser operation was realized over a range of 0.2-30 kHz, with an acousto-optic Q-switch having 50 W of rf power and 50 mm of interaction length. The highest average output power reached 10.2 W at 30 kHz of repetition rate, with pulse duration of 108 ns; while operating at the lowest 0.2 kHz,the laser action yielded the maximum pulse energy of 4.75 mJ, with pulse duration and peak power being 11 ns and 432 kW.The results achieved in our work represent the highest level ever achieved in the experimental research of compact, cw or passively Q-switched, Yb and Nd lasers operating at repetition rates higher than 1 kHz in the 1-mm near-infrared region.