Top-seeded Solution Method Research Articles

Periodic poling of magnesium-oxide-doped stoichiometric lithium niobate grown by the top-seeded solution method

Magnesium-oxide-doped stoichiometric lithium niobate has been produced using the technique of top-seeded solution growth from a lithium-rich melt. Optical tests, performed with a combination of argon-ion laser lines, have confirmed a previously published result (at 532 nm) that this material has superior resistance to photorefractive damage. This material has been shown, for the first time, to be amenable to periodic poling. Optical parametric oscillator tests have shown that this material maintains the advantages of periodically poled, congruent, un-doped lithium niobate while showing no evidence of photorefractive damage under typical operating conditions. Operating wavelengths as a function of quasi-phase-matching period and temperature have been measured for the optical parametric oscillator, providing useful new information about refractive-index dispersion in this material. This work establishes periodically poled, magnesium-oxide-doped stoichiometric lithium niobate as a viable material for nonlinear optics.

Observations of the absorption, infra-red emission, and excitation spectra of Cr in

Photoluminescence and optical absorption in Cr-doped were observed for the first time and studied within the 300-800 nm spectral region and over a 7-300 K temperature range. `Nominally pure' crystals, with Cr impurities detected by means of EPR, and intentionally Cr-doped crystals grown by the top-seeded solution method were studied. Cr doping results in additional absorption over the whole visible region, increasing towards the band-edge area (at ), and wide absorption bands centred at about 470 nm, 575 nm, and 610 nm. At 74 K, exposure to optical excitation with results in luminescence in the near-infra-red region consisting of four sharp lines, (781.65 nm, ), (776.4 nm, ), (768.8 nm, ), (766.8 nm, ), and several additional weak emission lines. The luminescence excitation spectrum for each A line consists of two complex bands centred at 630 nm and at 400 nm for T = 74 K. With decreasing temperature, all of the sharp lines, such as the zero-phonon lines of in , shift to lower energies, which is opposite to the behaviour of such lines for ionic crystals. The thermal shift for the line is the largest, . Taking into consideration EPR data, temperature transformations, and the lifetime of the sharp emission lines ( at 70 K), we argue that the and lines are lines, i.e. originating from zero-phonon transitions of single ions replacing ions. The nature of the emission lines is not quite clear, but can be considered to originate from ions exchange coupled with other, unknown defects (including exchange-coupled pairs) or with -type transitions of centres perturbed by nearest-site hole polarons, or .

Crystal growth, spectroscopy, and laser performance of Nd^3+:KYF_4

Nd3+-doped KYF4 boules (5 cm long by 2 cm diameter) have been grown by the top-seeded solution method. The broad absorption spectra near 800 nm and the long (>500 μs) fluorescence lifetime of the 4F3/2 laser state in this host are attractive diode-pump features with advantages over Nd3+:Y3Al5O12 and Nd3+:YLF4. We have investigated cw and Q-switched operation of Nd3+:KYF4 end pumped by a Ti: sapphire laser. Absorbed power slope efficiencies of 30% have been measured, but thermal effects limit input powers to 300 mW into the crystal.

Surface analysis of Ln2−xCexCuO4 (Ln = Pr and Nd) single crystals grown by the top seeded solution method

Large single crystals of Ln2−xCexCuO4 (Ln = Pr and Nd), of the average size of approximately 5 mm × 5 mm × 1 mm, were grown by the top seeded solution growth (TSSG) technique. The optical constants of the crystals were determined by variable angle spectroscopic ellipsometry (VASE) and the results seem to indicate that a 1.5 eV absorption peak appears in the undoped material and is weakened and shifted downward in energy upon annealing. The compositions and crystal structure were examined using rutherford backscattering spectroscopy (RBS) with ion beam channeling. Also, the effect of annealing on the crystalline structure was probed by ion beam channeling. The orientation and lattice parameters of the crystals were determined by X-ray diffraction and the superconductivity of the specimens was monitored using a SQUID magnetometer. The results indicate that the crystals grown by the TSSG method are very uniform in composition and well-oriented. However, analysis of the RBS data indicated up to 1% Pt inclusion in the crystals from contact with the Pt crucibles. The inclusion of Pt acted to quench the superconducting transition temperatures and Pt was found to substitute for Cu.

Growth of Large KTP Crystal and Wavelength Conversion.

We report the fabrication and the characterization of large KTP crystals. The crystals were grown for approximately forty days by a top-seeded solution method using a K6P4O3 flux. The size was 32×42×87mm3 in a×b×c axes. A very high level of structural perfection was observed by synchrotron x-ray topography. But large changes of the refractive index were observed between growth sectors and successive changes of the index from the intial part of the growth near the seed to the final part were observed inside individual growth sectors. This may explain the different values of the phase matching angle reported in many laboratories.

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

Single crystals of the tunable laser material, Cr3+: LiCaAlF6. 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 [1010] at 20 rpm and 0.75 mm/h in a flowing atmosphere of N2-HF. Cr3+ 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.

Seeded solution growth of β″- Al2O3 single crystals

Single crystals of β″- Al 2 O 3 were grown by the top seeded solution method from a Li 2 O- V 2 O 5 flux. Similar methods were also applicable to liquid phase epitaxial growth of β″- Al 2 O 3 films on selected substrates. Seed crystals and substrates included β″- Al 2 O 3, β- Al 2 O 3, MgAl 2 O 4 and LaMgAl 11 O 19. Phase diagram studies provided an optimum range of compositions and temperatures for growth in platinum containers. A composition of 23 wt% Na 2 O,54 wt% Al 2 O 3, and 23 wt% LiVO 3 enabled growth to occur at temperatures of 1450–1550°C. Single crystal platelets of cm size were grown with fair quality but still contained small flux inclusions which led to delamination. Epitaxial films of up to 100 μm thickness were successfully grown on [111] oriented MgAl 2O 4.