TY - JOUR TI - Rare-earth-doped single-crystal YAG fibers grown by the laser heated pedestal growth technique DO - https://doi.org/doi:10.7282/T32B91G8 PY - 2017 AB - The laser-heated pedestal growth (LHPG) technique is an unconventional method for growth of single-crystal (SC) fibers with the advantages of high pulling rates and crucible-free processing when compared to more conventional techniques such as the Czochralski technique. In this dissertation, the processing of rare-earth (RE3+) doped yttrium aluminum garnet, Y3Al5O12, (YAG) fibers using the LHPG technique was significantly improved upon as the result of the development of a new, more accurate method to align the CO2 laser along with the minimization of waveguide irregularities. Initially, the dominant loss mechanism in the fabricated SC fibers was bulk scattering, resulting from thermal stresses in the core due to inadequate alignment. Once these stresses were remedied by the implementation of new alignment techniques, absorption became the dominant loss mechanism with minimal scattering. For short fiber lengths, the absence of diameter control did not prove to be critical. However, when fibers exceeded 30 cm in length, the waveguide would couple low-order modes to high-order modes that can become radiation modes at longer lengths. By implementing a diameter control feedback loop, these effects were minimized. The fibers were characterized by studying the optical properties of an undoped and doped air-clad SC YAG fiber (typically 330 μm in diameter). The total attenuation and scattering loss was measured using visible and NIR lasers. The lowest losses were achieved with the growth of a 1 m long SC fiber - lower than any currently published. The total attenuation of the YAG fibers is now below 0.3 dB/m, at 1064 nm. This loss is primarily attributed to the bulk absorption of the raw material, with as little as 0.02 dB/m of this loss coming from scattering in RE doped YAG fibers. At non-absorbing wavelengths, the 0.5% Ho:YAG fibers have an equivalently low loss. This low loss is critical for applications of YAG fibers, specifically regarding lasing of 0.5% Ho:YAG. Lasing has been demonstrated with increasing slope efficiency as the quality of the crystal fiber was improved. At 72.3%, the fiber’s slope efficiency with respect to incident pump power is approaching the slope efficiency for bulk Ho:YAG lasers. KW - Materials Science and Engineering LA - eng ER -