Jiayue Xu

Thermal and Nonlinear Optical Properties of Ca4YO(BO3)3

Ca 4 YO(BO 3 ) 3 (YCOB) crystals have been grown using the vertical Bridgman method. The thermal properties of YCOB were measured for the first time to our knowledge. The specific heat is 729.7 J/kg K at 373K. The average thermal expansion coefficients along the a, b and c axes are 9.9×10 -6 /K, 8.2×10 -6 /K and 12.8×10 -6 /K. respectively, in the temperature range of 293-1173K. The thermal conductivities along the a, b and c axes are 1.83W/mK, 1.72W/mK and 2.17W/mK at 373K. The anisotropy in the measured thermal conductivities of YCOB is consistent with the experimental results of the thermal expansion. The SHG of a Nd: YAG laser was compared with that of a KDP crystal. The effective nonlinear coefficients (d eff ) of YCOB in type I phase matching directions of (θ, Φ)=(66.3°, 143.5°) and (65.9°, 36.5°) were estimated to be 1.45pm/V and 0.91pm/V, respectively. The bulk damage threshold was observed as 85GW/cm 2 for single pulse of a Nd:YAG laser with 10ns pulse duration.

Bridgman growth and characterization of nonlinear optical single crystals Ca4GdO(BO3)3

Nonlinear optical single crystals Ca 4 Gdo(BO 3 ) 3 (GdCOB) have been grown by the vertical Bridgman method. Bubble-free, twin-free and crack-free GdCOB single crystals 25 mm in diameter and 65 mm in length were obtained. The average thermal expansion coefficients along a-, b- and c-axes from 293 to 1273 K are 10.35 × 10 - 6 K - 1 , 7.78 ×10 - 6 K - 1 and 13.10 ×10 - 6 K - 1 , respectively. The bulk damage threshold is 130 GW cm - 2 for a single pulse of a mode-locked Nd:YAG laser with 35 ps pulse duration. The effective nonlinear coefficient (d e f f ) in the phase matching directions of (θ, Φ) = (66.8°, 132.6°) is 1.51 pm V - 1 .

Bridgman growth of bismuth tellurite crystals

The photorefractive crystal, Bi2TeO5, was grown by the modified Bridgman method for the first time. High purity Bi2O3 and TeO2 were used as starting materials and were mixed thoroughly with molar ratio of Bi2O3/TeO2 = 1 ∶ 1. Platinum crucible was fabricated with a seed well of 10 mm in diameter and several folds were pressed so that the spontaneous nuclei could be eliminated through competition. The crucible was sealed during the growth so that the evaporation of TeO2 was controlled effectively. By optimizing growth parameters, transparent and crack-free Bi2TeO5 crystal up to 25 mm in diameter and 40 mm in length was grown successfully.

Ferroelectric potassium lithium niobate crystals grown by the vertical Bridgman method

Ferroelectric potassium lithium niobate (KLN) single crystals are very promising candidates for direct second harmonic generation of semiconductor diode lasers. In this paper, crack-free KLN crystals up to 10 mm in diameter by 50 mm in length were grown by the modified vertical Bridgman method from potassium and lithium enriched solutions. Prior to growth, KLN powder was prepared by sintering the mixture of K2CO3, Li2CO3 and Nb2O5 at 850°C for 8 h. Two temperature zones were designed in the Bridgman furnace to prevent crystals cracking. The growth rate is less than 0.25 mm h−1 and the temperature gradient in the solid–liquid interface is about 20°C cm−1. The transparent KLN crystal has a very good transmittance in the 420–800 nm region with an absorption edge at 378 nm. Dielectric constant of e33 and e11 at room temperature are 127 and 376, respectively. Curie temperature of the crystal is about 380°C.

Mechanical properties anisotropy of PZNT93/7 single crystal

The mechanical properties of 93%Pb(Zn1/3Nb2/3)O3–7%PbTiO3 (PZNT93/7) single crystal were evaluated by microindentation and nanoindentation techniques. The (1 1 1) facet of the crystal exhibited excellent combination mechanical properties (Vickers microhardness Hv, fracture toughness Kc and elastic modulus Er) than those of (0 0 1) facet. The Hv on (1 1 1) and (0 0 1) facets were 3.71 GPa and 3.00 GPa, respectively. In-plane fracture toughness anisotropy was observed on both the (1 1 1) and (0 0 1) facets, the Kc value was low in the direction parallel to the domain wall but large in the direction perpendicular to it. The Er of (0 0 1) and (1 1 1) facets was independent of the load, Er(1 1 1) was measured to be about 130 GPa and Er(0 0 1) was about 110 GPa. The above results implied that (0 0 1) PZNT crystals would face a more severe challenge in device application due to their weaker combination mechanical properties but outstanding piezoelectric properties than those of (1 1 1) PZNT crystals.

EVALUATION OF PZNT FERROELECTRIC CRYSTALS GROWN BY DIFFERENT METHODS

ABSTRACT Relaxor ferroelectric (1−x)Pb(Zn1/3Nb2/3)O3-xPbTiO3(PZNT) crystals were grown from PZNT-PbO high temperature solution by flux Bridgman, bottom seeded solution growth (BSSG) and gas-cooling methods. PZNT wafers cutting from flux Bridgman and BSSG-grown crystals were homogenous while serious inclusions were observed in PZNT wafers grown by the gas-cooling method. The < 001 > -oriented PZNT crystals exhibited nearly the same dielectric/piezoelectric properties whatever the growth methods. However, the mechanical properties, such as Vickers Microhardness Hv and fracture toughness Kc of the crystal grown by gas-cooling method were much inferior. It was suggested that BSSG method is a potential approach for growing large-size and high-quality PZNT crystals.

Diode pumped CW mode-locked Yb:LuAG laser

Diode-pumped stable cw mode-locked laser in Yb:LuAG crystal was demonstrated. The pulse duration of 7.63ps was achieved without any negative dispersion elements. With pump of 8W, output power was 610mW with repetition rate of 86MHz.

Phase transitions and optical properties in 〈001〉 (1−x)PbZn1/3Nb2/3O3−xPbTiO3 single crystals

The effect of a constant electric field (0 < E < 5 kV/cm) on the optical properties of PbZn1/3Nb2/3O3−xPbTiO3 (PZN-xPT) crystals with x = 7 and 9% has been analyzed. It has been shown that, at temperatures close to the temperature of the transition from the rhombohedral [R(X)] phase to the tetragonal (T) phase, two induced phase transitions are observed in the electric field, which are associated with the appearance of new intermediate phases Ma and Mc [R(X)-Ma-Mc-T]. Correlation between these two transitions and the PbTiO3 content x has been found. The E-T phase diagrams have been obtained. The Mc phase in PZN-9PT crystals is found to remain the ground state after the removal of the electric field, whereas the Mc phase in PZN-7PT crystals is metastable and is transformed into the Ma phase after the removal of the electric field.

Optical properties of (1 - x)PbZn1/3Nb2/3O3-xPbTiO3 single crystals

The temperature dependence of the optical transmission and small-angle light scattering with and without applied constant electric field was studied in relaxor single crystals of 0.91PbZn1/3Nb2/3O3-0.09PbTiO3 (PZN-PT 91/9) and 0.93PbZn1/3Nb2/3O3-0.07PbTiO3 (PZN-PT 93/7) solid solutions in the region of two phase transitions: (i) from cubic paraelectric to tetragonal ferroelectric phase at T=Tc and (ii) from tetragonal ferroelectric to rhombohedral ferroelectric phase at T=Trt. In the absence of external electric field, only the phase transition at Tc proceeds in both PZN-PT 91/9 and PZN-PT 93/7 crystals according to a percolation mechanism and is accompanied by the appearance of a sharp maximum in the small-angle light scattering intensity curve. In PZN-PT 93/7 crystals, the application of a relatively weak electric field induces an additional percolation type phase transition at Trt.

Bridgman growth and optical properties of Gd:YCOB crystal

The high optical quality Gd:YCOB crystals with size of /spl phi/23 /spl times/ 50 mm have been grown by Bridgman technique. The optical properties of the crystals such as transmission spectrum, damage threshold, and THG performance were measured.