Transparent high optical quality and large Ti-sapphire (Ti 3þ -doped Al 2 O 3 ) single crystals have been grown by the Kyropoulos technique (KT) for optical amplification. The present work shows that by the utilization of KT growth technology and the optimization of the growth conditions it is possible to grow Ti-doped Al 2 O 3 , 100 mm in diameter and 5 kg in weight. We have demonstrated that large Ti(0.25 atom %)-doped Al 2 O 3 crystals show high chemical homogeneities and good optical properties and amplify the energy without any special annealing. Ti-doped sapphire crystals are for high power laser applications and particularly for the shortest pulses ever produced from a laser oscillator.
Ribbon and rod sapphire pulling has been performed in three different crystal growth equipments in order to study the effect of the installation, of the atmosphere, of the die shape, of the feed material and of the pulling rate on the distribution, number and diameter of the characteristic voids (micro-bubbles) in the crystals. The location of the bubbles in the crystals depends on the die geometry; however, in most cases they are essentially located close to the crystal periphery and then can be efficiently removed by lapping. After statistical analysis of the results, it is demonstrated that the number of gas moles incorporated in the crystals, inside the voids, is totally independent of any growth parameter. It is also shown that the bubble diameter depends only on the pulling rate. Consequently, for a given pulling rate, the number of bubbles auto-adjusts in order to satisfy the constant molar gas incorporation.
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