Lap Tak Cheng

Crystal growth and characterization of KTiOPO4 isomorphs from the self-fluxes

Abstract We report the crystal growth of KTiOPO 4 (KTP) and its isomorphs from the self-fluxes. Common features in the crystal growth properties of MTiOXO 4 within the M 2 O-TiO 2 -X 2 O 5 ternary, where M={K, Rb or Cs} and X={P or As (for M=Cs only)}, are noted. The solubility of these crystals in the M 5 X 3 O 10 and M 6 X 4 O 13 fluxes are presented. A previously unreported (00-1) growth face was observed in KTiOAsO 4 (KTA) and the morphological stability of this face in KTP is also discussed. Optimization of the crystal growth parameters allows us to grow inclusion-free crystals of up to 18×35×35 mm 3 from 250 ml charges. We discuss the domain characteristics of these crystals and present the optical, electro-optical and dielectric properties of these materials.

Properties of doped and undoped crystals of single domain KTiOAsO4

Large single crystals of KTiOAsO4 (KTA) measuring up to 35×31×58 mm3 (along abc) are grown from the pure potassium arsenate self-fluxes and from the tungstate flux using the seeded high-temperature solution growth technique. Small amounts of Fe2O3, Sc2O3, or In2O3 (∼0.2–0.4 wt %) are added to the melt to promote single-domain formation in the flux-grown crystals. We report here the linear optical and nonlinear optical properties of these crystals. We observed an unusually strong optical birefringence increase with Fe2O3 dopant concentration [δ(nz−nx)∼0.017/wt % Fe]. This increase leads to a blue shift in the second-harmonic generation cutoff wavelength of as much as 37 nm for a ∼0.47 wt % Fe-dopant level in KTA.

Quadratic hyperpolarizabilities of some organometallic compounds

Abstract The nonresonant quadratic molecular hyperpolarizabilities of several classes of Organometallic aromatic compounds were studied with DC electric-field-induced second-harmonic generation (EFISH) experiments using fundamental radiation at 1.91 μm. Our goal is to survey and assess various strategies by which electron densities from metal centers can be exploited for quadratic nonlinear optics. Relying on optimized experimental techniques, systematic studies on structure-property relations concerning metal centers, bonding patterns, conjugations, and effects of ligands were conducted. Results on some arene metal carbonyl π-complexes, metal carbonyl pyridine derivatives, square-planar metal aromatics, and metallocene derivatives are included.

Nonlinear optical and electro-optical properties of single crystal CsTiOAsO4

We report the development of a new nonlinear optical crystal CsTiOAsO4 (CTA). The relatively large cesium ion leads to a structural instability in the orthorhombic structure, which significantly affects its crystal growth properties. Modification of the crystal growth process, however, allows the growth of large inclusion‐free single crystals measuring up to 30×20×25 mm3. The refractive indices, nonlinear optical coefficients, electro‐optic coefficients, and dielectric properties of these crystals were measured using standard techniques. Compared to KTiOPO4, CTA has a smaller birefringence which makes it particularly suitable for frequency doubling Nd:YAG lasers operating near 1.32 μm. We also report the ferroelectric poling of multidomain CTA crystals and discuss possible extension of this poling process to other KTP isomorphs.

Development of the nonlinear optical crystal CsTiOAsO4 II. Crystal growth and characterization

Abstract We report here the crystal growth and characterization of the new nonlinear optical crystal CsTiOAsO 4 (CTA). We have studied the Cs 2 O-TiO 2 -As 2 O 5 ternary and identified the phase field within which orthorhombic CTA can be crystallized. Large inclusion-free single crystals measuring up to 30×20×25 mm 3 can be readily grown using the Cs 5 As 3 O 10 self-flux. As grown CTA crystals have the same crystal facets as KTP, although they tend to be multidomain. We present here two techniques for removing these domains: by trivalent oxide dopings and by ferroelectric poling. The refractive indices, nonlinear optical coefficients, electro-optic coefficients and dielectric properties of single domain CTA crystals are reported. Compared to the crystal KTiOPO 4 , the smaller birefringence of CTA makes it particularly suitable for frequency doubling fundamental wavelengths between 1.3 and 1.5 μm. Our results suggest that CTA should find practical applications in electrooptic and in frequency conversion applications, such as optical parametric oscillators and compact diode-pumped solid state lasers.

Degradation of carbon nanotube field emitters driven by anode adsorbed water

The field degradation of carbon nanotube field emitters in diode emission at constant current was demonstrated to be highly dependent upon the presence of water at partial pressures as low as 10−9Torr. The anode surface was also seen to significantly impact the degradation rate, with metallic Al films yielding the worst degradation rates. Coating the anode surface with a carbon or polymer film lowered the degradation rate. It is suggested that a majority of the degradation seen in nanotube field emission devices is due to ionization of water adsorbed at the anode surface.

Enhancing lifetime of carbon nanotube field emitters through hydrocarbon exposure

The effect of carbon containing gasses on the field emission degradation rate of carbon nanotube field emission devices has been measured. Long chain hydrocarbons were seen to form a carbonaceous deposit on the anode surface which effectively lowered the degradation rate. Simple hydrocarbons such as methane, ethylene, and acetylene reversed degradation by continually enhancing emission. This continuous enhancement was repeatable and continued over 500h. Carbon dioxide exposure at low partial pressures resulted in an increased field emission degradation rate similar to oxygen and water exposure as reported earlier.