A new low phonon energy host, KPb2Cl5, which is much more stable than the lanthanide trichlorides is of current interest for direct mid-infrared rare earth lasers that operate at room temperature. Crystals currently grown by the Bridgman method in sealed silica ampoules are subject to contamination and stress that degrades the optical quality. SensArray will optimize the Czochralski method that was demonstrated in Phase I for growth from a stoichiometric melt. This method facilitates seeded growth of oriented crystals that have a minimum level of residual stress. Growth of and KPb2Cl5 and KPb2Cl5:Er3+ single crystals will be carried out in a chlorinating atmosphere in a demountable fused silica system. Feed will be prepurified by zone-refining. Final purification will be carried out in-situ prior to crystal growth. The process will not require the use of glove boxes or other special handling techniques. Process parameters common to all Czochralski growth implementations will be optimized. Post growth treatment methods will be applied to limit the formation light scattering structures. Crystals will be characterized using x-ray diffraction, chemical analysis, preferential etching and polarized light microscopy.
Benefits: Two benefits will emerge from this work. The first is development of a cost-effective crystal growth process that will be applicable to the entire range of rare earth doped KPb2Cl5. The required equipment is modular, readily constructed from commercial components and suited for replication and introduction into the commercial setting. Extension of the technology to other chlorides will require a minimum of new resources and process development. The second benefit lies with the laser host. KPb2Cl5, is a new low phonon energy host, which is much more stable than the lanthanide trichlorides is of current interest for efficient direct mid-infrared lasers based on trivalent rare earths that operate at room temperature. The material may be fabricated and packaged in a laser device without elaborate precaution. The potential exists for operation and manufacture of a portable hand held device. Applications are in pollution control, spectroscopy, ground vehicle protection, remote sensing, countermeasures and imaging.
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