Polarization effects in a KGd(WO4)2:Nd crystal

Data are presented that demonstrate that, when a laser beam polarized at 45° to the vertical (horizontal) is passed through plane-parallel plates cut from a Nd-doped (4%) potassium gadolinium tungstate crystal and placed between crossed polarizers, the intensity and polarization of the transmitted light are periodic functions of the angle of incidence of the light. When scanned in two mutually perpendicular directions, the plates exhibit highly anisotropic transmission. The polarization at the intensity minima and maxima at the analyzer output is not orthogonal, in contrast to uniaxial crystals.     

Highly Nd3+-doped Y3Al5O12 crystal fiber tip for laser thermotherapy

Based on phonon relaxation, a 12-at. % neodymium-doped YAG (Y3AlrO12) crystal fiber tip has been developed for photothermal conversion. The near-cylindrical tip, with an average diameter of 0.68 mm and a length of 1.8 mm, is fabricated on a 0.65-mm-thick 220-mm-long pure YAG single-crystal fiber by laser-heated growth. Pumped by an 810-nm wavelength diode laser with a pump power of less than 2 W, the temperatures of the tip reach 725 degrees C in air, 78 degrees C in egg white, and 79 degrees C in porcine liver, with acceptable reproducibilities and thermal response times. The photothermal conversion efficiency of the doped tip is approximately 89%, and the high stability of the tip is also proved. Experimental results show that the doped fiber tip is promising for laser thermotherapy applications.     

Spectral characterizations of Nd3+:KLa(WO4)2 crystal

The absorption and emission of Nd³⁺:KLa(WO₄)₂ crystal were investigated. The uniaxial crystal Nd³⁺:KLa(WO₄)₂ shows strong polarization dependence. The intensity of the absorption bands in E//c is about four times than that in E//a. The absorption cross section σ_a is 22.6 × 10^–20 cm² for E//c. The emission cross section at 1.069 μm is 2.09 × 10^–19 cm². The fluorescence lifetime is 157 μs at 300 K. The relationship of Nd³⁺ concentrations with fluorescence intensity and lifetime was discussed. The results show the ca 3 at % Nd³⁺ concentration in Nd³⁺:KLa(WO₄)₂ crystal is appropriate. Electronic Publication     

Spectral parameters of Nd3+ ion in Nd:KLa(WO4)2 crystal

The spectral parameters of Nd³⁺ ions in Nd:KLa(WO₄)₂ crystal have been investigated based on Judd-Ofelt theory. The spectral parameters were obtained: the parameters of oscillator strengths are Ω₂=3.0887×10^–20 cm², Ω₄=1.0375×10^–20 cm², Ω₆=1.0422×10^–20 cm², the radiative lifetime is 685 μs, the quantum efficiency is 30.7%, and the fluorescence branch ratios were calculated: β₁=0.432, β₂=0.475, β₃=0.089, β₄=0.004. Electronic Publication     

熔盐提拉法生长的Nd3+:KGd(WO4)2单晶的性能研究

采用熔盐提拉法生长出φ20mm×35mm的优质Nd3+KGd(WO4)2晶体,对晶体三个轴向的光谱进行了测试研究,结果表明a轴向的吸收和荧光谱峰最强,最适合于进行激光实验研究.采用脉冲氙灯泵浦φ3.5mm×26mm的激光器件,在1.067μm处得到125.5mJ的激光输出.在同等条件下对YAGNd激光晶体进行了激光实验研究,并对两种结果进行了比较,结果表明和YAGNd3+晶体相比,KGWNd3+晶体具有激光阈值低、效率高和输出光为偏振光等优点,因此在小型激光器的应用方面具有明显的优势.     

Laser-diode pumped passively Q-switched Nd3+:NaY(WO4)2 laser with Cr4+:YAG saturable absorber

A laser-diode pumped passively Q-switched new type crystal Nd³⁺:NaY(WO₄)₂ (known as Nd:NYW) laser with Cr⁴⁺:YAG saturable absorber has been realized. The dependence of pulse repetition rate, pulse energy, pulse width, and peak power on pump power for different small-signal transmission of Cr⁴⁺:YAG are measured. The coupled rate equations are used to simulate the Q-switched process of laser, and the numerical solutions agree with the experimental results.     

钕离子掺杂钇铝石榴石(Nd3+:Y3Al5O12)透明陶瓷研究进展

回顾了新一代激光工作物质Nd3+:Y3Al5O12透明陶瓷的发展历史,并与激光晶体进行了比较,介绍了其技术优势,同时简述了Nd3+:Y3Al5O12透明陶瓷的2种常用工艺.     

Free carrier absorption in self-activated PbWO4 and Ce-doped Y3(Al0.25Ga0.75)3O12 and Gd3Al2Ga3O12 garnet scintillators

Nonequilibrium carrier dynamics in the scintillators prospective for fast timing in high energy physics and medical imaging applications was studied. The time-resolved free carrier absorption investigation was carried out to study the dynamics of nonequilibrium carriers in wide-band-gap scintillation materials: self-activated led tungstate (PbWO₄, PWO) ant two garnet crystals, GAGG:Ce and YAGG:Ce. It was shown that free electrons appear in the conduction band of PWO and YAGG:Ce crystals within a sub-picosecond time scale, while the free holes in GAGG:Ce appear due to delocalization from Gd³⁺ ground states to the valence band within a few picoseconds after short-pulse excitation. The influence of Gd ions on the nonequilibrium carrier dynamics is discussed on the base of comparison the results of the free carrier absorption in GAGG:Ce containing gadolinium and in YAGG without Gd in the host lattice.     

Eutectic solidification in the system Al2O3/Y3Al5O12

The eutectic solidification in the system Al₂O₃/Y₂Al₅O₁₂ has been investigated. A Bridgman-type crystal-growing furnace was used in this investigation. A temperature gradient of 190° C/cm and growth rates which were varied between 2 and 12 cm/h were employed in the directional solidification studies. Three types of microstructure were observed depending upon the composition and the growth rate. At a growth rate of 4 cm/h and at compositions removed from the eutectic composition, a mixture of primary phase and fine eutectic dispersion was found. At growth rates between 2 and 12 cm/h at the eutectic composition, a colony type microstructure was most commonly observed. At growth rates above 4 cm/h at the eutectic composition, regions in the solidified ingot were found to have a highly oriented eutectic microstructure consisting of both rods and platelets. These eutectic microstructures indicate that coupled growth can occur in this system. The method of Sunquist and Mondolfo [15] was used to determine whether Y₃Al₅O₁₂ was the first phase to nucleate at the eutectic.     

Infrared-to-green up-conversion in Er3+, Yb3+-doped monoclinic KGd(WO4)2 single crystals

Optical spectroscopy of the green emission of erbium in KGd(WO₄)₂ (KGW) single crystals codoped with ytterbium ions is investigated. To do this, we firstly grew good-optical-quality KGW single crystals doped with Er³⁺ and Yb³⁺ at several dopant concentrations by the Top-seeded-solution-growth slow-cooling method (TSSG). Green photoluminescence of Er³⁺ in KGW host was studied at room temperature (RT) and low temperature (10 K) by means of Yb³⁺ sensitization after infrared excitation at 981 nm (10194 cm⁻¹). We calculated the emission and gain cross-sections and compared these with those of other known Er³⁺-doped laser materials like LiYF₄ :Er (YLF:Er) and Y₃Al₅O₁₂:Er (YAG:Er) at RT. Our study also focused on determining the optimal concentration of ions for generating the most intense green emission. We measured the lifetime of the green emission after infrared pump at several Yb³⁺ concentrations. From the low-temperature emission experiments, we determined the energy position of the sublevels of the ground state of erbium.     

Preparation of YVO4 powder from the Y2O3 + V2O5 + H2O system by a hydrolysed colloid reaction (HCR) technique

Prior to the formation of YVO₄ in the Y₂O₃ + V₂O₅ + H₂O system, two intermediate, partially hydrophobic, complex colloidal mixtures with metastable characteristics can be produced at room temperature and atmospheric pressure. The ball-milled system, having both hydrophobic and hydrophilic species, transforms into the stable yttrium orthovanadate phase due to intensive hydrolysis. At room temperature an orange mixture (possessing dispersed Y₂O₃ and 4Y₂O_3–P (OH) _p ^p+ ·2VO ₃ ^– , Y₂O_3–p (OH) _p ^p+ ·6VO ₃ ^– ·xH₂O-like heteroaggregations) formed by 20 h mixing at pH ca. 4.0 transforms slowly, another red-brown heavily flocculated colloidal mixture (with dispersed Y₂O₃ and Y₂O_3–p (OH) _p ^p+ ·V₁₀O ₂₈ ^6– ·yH₂O-like aggregation) formed by 70 h mixing at pH ca. 4.5 transforms rapidly into YVO₄ in water. During additional mixing of highly diluted red-brown mixtures this transformation can be completed at room temperature. At elevated temperatures (50–95 °C) the orange mixture precipitates into a red-brown decavanadate-type precipitatium which subsequently can also rapidly hydrolyse into an orthovanadate phase in the diluted aqueous systems. Both vanadium excess meta-and decavanadate-type aggregations exhibit amorphous character by X-ray diffraction.The semi-hydrophobic colloidal structure can modify the dissociation mechanism, which prevents the system from returning to the starting oxides, and gives a new HCR technique for YVO₄ preparation with a simple hydrolysis process at low temperatures and atmospheric pressure.     

Saturable Absorber Cr(4)+:(Sr, Ca)Gd(4)(SiO(4))(3)O Crystals as Q Switches for a Diode-Pumped Nd(3)+:KGd(WO(4))(2) Laser

Passive Q switching of a diode-pumped Nd(3+):KGd(WO(4))(2) laser is demonstrated by use of Cr(4+):SrGd(4)(SiO(4))(3)O and Cr(4+):CaGd(4)(SiO(4))(3)O crystals as saturable absorbers. An average output power of 40 mW was obtained with a pulse repetition rate of ~0.4 MHz.     

Spectroscopic properties of Er3+ ions in La2(WO4)3 crystal

Er³⁺-doped La₂(WO₄)₃ single crystals were grown by the Czochralski technique. The absorption spectra, fluorescence spectra and fluorescence decay curves of the crystals were measured at room temperature. The spectroscopic parameters, including intensity parameters Ω_t (t = 2, 4, 6), spontaneous emission probability, fluorescence branching ratio, radiative lifetime, and stimulated emission cross-section were estimated. The fluorescence decay curves of fluorescence manifolds ⁴I_13/2, ⁴I_11/2, and ⁴S_3/2 were measured for crystal and powder samples, respectively. The effect of radiation trapping on the spectroscopic parameters was discussed. Green up-conversion fluorescence bands centered at wavelengths of 530 nm and 550 nm were observed when the crystal was excited at 977 nm. The possible up-conversion mechanisms were proposed.     

High-resolution transmission electron microscopy analysis of the microstructures of Cr4+:Y3Al5O12 double-clad crystal fibers prepared by LHPG method

In order to unravel the relation of the nanostructure of Cr⁴⁺:Y₃Al₅O₁₂ (Cr⁴⁺:YAG) crystal fibers controlled by the laser-heated pedestal growth (LHPG) technique with different growth conditions, the nanostructural analysis of Cr:YAG crystal fiber was investigated by high-resolution transmission electron microscopy (HRTEM), which offers nano-scale information in the core region and inner/outer cladding interface and the mechanism of inter-diffusion process during growth. HRTEM analysis indicates that the core has high crystallinity and a sharp core/inner-cladding interface. γ-Al₂O₃ nanocrystals were formed during YAG/SiO₂ inter-diffusion. To further enhance the Cr⁴⁺ concentration in YAG crystal fiber, the Cr⁴⁺ ions were replenished using an electron gun to deposit Cr₂O₃ and divalent-ion oxide (CaO or MgO) on the source rod circumference before LHPG. It was observed that Ca²⁺ diffuses into the source rod more efficiently than Mg²⁺, while generating fewer defects and stacking faults.     

激光区熔定向凝固Al2O3/Y3Al5O12 (YAG)共晶的组织与断裂韧性

采用激光区熔高温度梯度快速定向凝固技术从熔体中直接制备Al2O3/Y3Al5O12(YAG)共晶自生复合陶瓷,以研究其在超高温度梯度(1.0×106 K/m)下的快速凝固组织特征及与激光工艺参数的关系,并对其力学性质进行分析.研究结果表明:凝固组织强烈地受激光扫描速度与功率密度的影响,当二者匹配时,Al2O3相和Y3Al5O12(YAG)相呈现均匀一致,连续分布的层状耦合共晶结构,共晶间距细小(1～2 μm),且随扫描速度的增大逐渐减小;所制备的Al2O3/Y3Al5O12(YAG)共晶陶瓷硬度高达19.5 GPa,断裂韧性达到3.6 MPa·m1/2.