Growth, characterization and the fourth harmonic generation at 266 nm of K2Al2B2O7 crystals without UV absorptions and Na impurity

We utilize a combined technology to grow relatively pure K2Al2B2O7 crystals without sodium and UV absorptions aroused by Fe3+ ions. It is found that under reducing atmosphere, iron impurities can no longer substitute into the Al3+ sites in the crystal lattice. Thus, the as-grown crystals are free from the abnormal UV absorption from 200 nm to 300 nm. At the same time, KF flux prevents the inclusion of sodium into the crystal contrasted with the generally used NaF flux. Lattice parameters of the as-grown crystals were refined by powder X-ray diffraction and compared with those grown from NaF flux. Based on the measured refractive indices, new Sellmeier equations were derived from refractive index dispersion curves. Finally, FHG experiment of a QCW Nd:YAG laser at 266 nm demonstrated an output power of 440 mW, which is the highest record achieved in KABO crystal so far.

► KABO crystals without Na impurity and UV absorption were grown successfully.
► New Sellmeier equations were derived from the measured refractive indices data.
► 440 mW FHG output at 266 nm of a QCW Nd-laser was obtained.