Robert Uhrin

Top seeded solution growth of Cr3+: LiCaAlF6 in HF atmosphere

Abstract Single crystals of the tunable laser material, Cr 3+ : LiCaAlF 6. were grown via a top seeded solution method from LiF enriched melts. A weight sensing feedback system was used for diameter control. Boules were grown along [10 1 0] at 20 rpm and 0.75 mm/h in a flowing atmosphere of N 2 -HF. Cr 3+ was dispersed along the boule with a measured distribution coefficient ( k ) of 1.0. External quality was excellent with faceted growth in a flat solid-liquid interface. Internal quality was good but scattering defects, observed by He-Ne laser, were distributed primarily near the boule core. Traces of OH - were found in the boules by infrared spectroscopy. The scattering is related to defects, e.g. dislocations of particles, believed to arise from thr thermal conditions.

The hydrothermal growth of zircon

Abstract Single crystals of zircon were grown hydrothermally at 700 °C and 25000 psi using a mineralizer of 2 m KF-1 m LiF and a thermal gradient of 20 °C. Under these conditions growth rates of up to 0.25 mm/day surface have been obtained on (100) seeds. Several mm of good crystal growth on 1 cm 2 seeds have been achieved. The growth quality may be limited by small inclusions of wadeite and OH impurity. Wadeite can be controlled by the amount of KF and OH incorporation is inhibited by Li. Large crystals require more extensive seed development.

Crystal Growth And Evaluation Of Rare Earth Orthogallates For Laser Hosts

Single crystals of the perovskite-related rare earth orthogallates have been grown and examined for laser hosts. LaGaO3 in pure form generally contains color centers or other intrinsic defects which lead to a high absorption from the ultra-violet to about 600 nm. NdGaO3 can be grown in large clear boules with proper care. Most orthogallates contain some twins which limit optical quality. Twins can be eliminated in growth by a judicious choice of mixed crystals involving La-Nd, La-Gd, or La-Y crystal compositions which have their lattice constants adjusted to an ideal cubic unit cell. We have grown crystals of one atomic percent Nd:LaGaO3 for specific evaluation. The fluorescent lifetime was measured as 225 μs. We also report absorption spectra and fluorescent emission data for this crystal.

Perovskite Related Substrates for Superconductor Films — Rare Earth Orthogallates

High quality single crystal thin films of the new oxidic high, TC superconductors are desirable for microwave, infrared, and Josephson junction devices. Initial attempts to grow films have utilized substrates of many available single orystals. All of the latter have been mixed oxides or other materials which do not possess the perovskite or a derivative type structure. SrTiO3 has been the single exception and favorable high current capacity films have been deposited by several groups.1–3 Unfortuntely, SrTiO3, is grown by the flame fusion method and has some unfavorable characteristics of price, quality, size, and certain physical properties, e.g. high dielectric constant, high loss, lattice constant mismaoch, or cleavage.

Crystal Growth and Spectroscopic Properties of U3+:LiYF4

Trivalent uranium-doped LiYF4, crystals have been grown and evaluated as potential diodepumped lasers. Strong fluorescence in the range of 2.1 - 2.6 μm has been measured with a 170 μs lif e time.

Multilayer E-Beam Deposition and Annealing of Yba 2 Cu 3 O 7-δ Thin Films on Lagao 3 Substrates

Thin films of YBa 2 Cu 3 O 7‐δ have been deposited on samples of LaGaO 3 substrates by multilayer E‐beam evaporation. Alternating layers of Cu, Y2O 3 , and BaF 2 were deposited on polished (001) substrates. An annealing study was performed to thoroughly blend the layers and minimize substrate interdiffusion. Films were prepared by annealing in wet oxygen at temperatures between 800 °C and 1000 °C. Four point resistance versus temperature curves were obtained to determine the superconducting transition temperature and transition width. Auger depth profiling was performed as a function of annealing cycle to determine the amount of blending of the layers and quantify any substrate diffusion..

Growth Status of Nd,Cr:GSGG

The development of Nd,Cr:GSGG has progressed rapidly over the past few years. Two inch diameter and larger boules have been grown core free with flat interfaces. The early problems of attaining low loss at 1.06 μm, the cost and availability of scandium, and growth problems have been alleviated. The crystal composition and trace impurities in starting materials must be controlled rigidly. Active laser testing of 1/4 x 3 inch rods has demonstrated slope efficiencies of greater than 7%. Wavefront distortions at 1.06μm with a Zygo interferometer are A/4 PV along [111] for 3 inch lengths or comparable to Nd:YAG. Loss factors at 1.06Pm are typically <0.006 cm-1 or several times that of the best Nd:YAG. This may be caused by impurities, crystal quality, or intrinsic loss of the gallium garnets. The size of present boules has yielded 1/4 x 4 inch cylindrical rods and 6 x 20 x 100 mm3 slabs. These may possess growth striae which introduce a noticeable birefringence when viewed normal to the growth axis. Striae can be minimized by more stringent temperature control but their effects are governed by the stress optic coefficients. The latter must be measured accurately. The growth of 2 inch boules is discussed along with problems associated with the growth of larger crystals.