Growth of borate-based crystals for UV laser generation by the micro-pulling down technique

International audienceTo generate an ultraviolet laser light from a crystal, the only efficient way is currently by frequency conversion of a visible of near-infrared source. For that purpose, several crystals can be used if they possess high non-linear properties, wide window of transparency and high optical damage threshold. A lot of crystals of the borate family have more or less these characteristics. Borates are considered as essential materials for the achievement of lasers able to replace excimer lasers and more generally for solid state lasers in the blue-UV range. Among crystals of the borate family, one can cite -BaB 2 O 4 (BBO), LiB 3 O 5 (LBO), CsB 3 O 5 (CBO), CsLiB 6 O 10 (CLBO), Ca 5 (BO 3) 3 F (CBF), and YCa 4 O(BO 3) 3 (YCOB) widely used for efficient second harmonic generation (SHG) of Nd:YAG lasers. Despite recent significant progress in growth and characterization, these crystals also have some drawbacks such as difficult crystal growth or hygroscopicity. The Czochralski technique is generally the technique used for growing borate crystals. This method does not allow both quickly growing the samples and enhancing their crystal quality and optical properties. By else, it is time consuming. On the contrary, the production of crystal fibers by specific growing method can present a solution to the drawbacks of the Czochralski technique. The most common methods used to grow crystalline fibers are laser heated pedestal growth (LHPG) and micro-pulling down ( µ-PD) techniques [1-3]. They have shown to be versatile methods for the growth of high quality crystals of a large variety of materials. By else, in addition to their unique set of properties allowing various uses in optoelectronic devices, the final shape of crystal fibers is suitable for physical and optical testing, reducing time and cost of preparation. In addition, this specific shape of crystal fibers is directly usable for laser applications with an interlacing length/thickness ratio allowing to combine the advantages of fiber lasers and crystalline lasers, in particular the large heat exchange surface. The goal of this presentation is to resume the state of the art of our team in this research field