Growth of Nd_xGd_1-xCa₄O(BO₃)₃ along phase-matching direction and passive mode-locking self-frequency-doubling characteristics

Nd_xGd_1-xCa₄O(BO₃)₃ (NdGdCOB) grown along the optimum phase-matching (PM) direction (θ = 66.8°, Φ = 132.6°) is reported for the first time in this paper. The utilization ratio of the as-grown crystals along the optimum PM direction is improved up to 95% when the optical devices were processed, while it is only 50% for the crystals grown along 〈0 1 0〉 direction. It often shows two large (1 5 0) facets and growth edge facets on the as-grown crystal surface. The small facets on the shoulders were determined as (2̄0 1) facets by X-rays. The (2̄0 1) edge facets will vanish and (0 1 0) edge facets will emerge when the crystal is tapered. The (0 1 0) edge facets which anchor at the three-phase-boundary (TPB) are the principal cause for the formation of (0 1 0) twins. Passive modulated Q-switched and mode-locking green laser operation at 530 nm were achieved in NdGdCOB crystal using a xenon flash lamp as the pump source, Cr⁴⁺:YAG crystal as the saturable absorber with a plane-concave cavity, which is also reported here for the first time.