Attempts to grow β-BaB 2 O 4 (β-BBO) crystal fibers by the micro-pulling down technique. Characterization by Raman micro-spectroscopy

Barium metaborate (β-BaB 2 O 4 or β-BBO) is known to be an excellent nonlinear optical material with a wide transmission range 190–3500 nm and a high damage threshold (10 GW.cm −2). BaB 2 O 4 has two modifications : the low temperature b phase and the high temperature a phase with a centrosymmetric crystal structure which has no utility in second order harmonic generation. In early works, the β-BaB 2 O 4 crystals were grown below the a-b transition temperature (T~920°C) by using flux methods leading to crystals exhibiting more or less inclusions detrimental to their properties. More recently, the successful growth of high quality β-BaB2O4 without any flux from a supercooled BaB 2 O 4 composition melt was reported [1-3]. The aim of this talk is to present the results presently obtained on the growth of β-BBO crystal fibers directly from the melt without any flux. To investigate their behaviour during pulling, the crystals obtained were thoroughly characterized by Raman micro-spectroscopy.