Fabrication of fluorocarbon polymer-coated silver hollow-glass waveguides for the infrared by the liquid-phase coating method

Fluorocarbon polymer-coated silver hollow-glass waveguides have been fabricated based on the method of silver mirror reaction for silver, and the dipping method for the fluorocarbon polymer. The waveguides show low-loss properties for the infrared wavelengths except for the wavelength regions of large absorption of the polymer. Er:YAG laser light has been successfully transmitted through the flexible waveguides with small bending losses.     

Transmission properties of all-silica fibres for high-power Nd:YAG lasers

The transmission properties of two different types of all-silica fibres, step index and graded-index fibres, are investigated using a multimode high-power cw Nd:YAG rod laser. The reflections from the fibre surface back into the laser cavity affect the laser power and the beam parameters, waist diameter and divergence. A set-up for simultaneously measuring these values in front of and behind a fibre is presented. The maximum laser power transmitted by fibres is dependent upon the beam parameters, the fibre design and the surface conditions. An upper limit for the maximum divergence which can be coupled into a fibre with a certain numerical aperture without loss is given. The beam parameters behind the fibre, related to the input parameters, are presented.     

Passivation of laser induced defects in silicon by low energy hydrogen ion implantation

It is well established that the pulsed-laser annealing of as-implanted Si introduces electrically active defects. The aim of this paper is to show that these defects can be neutralized by low-energy hydrogen ion implantation. The techniques used for the sample characterization are current-voltage measurements and capacitance transient spectroscopy.     

The influence of the solubility limit on diffusion of as implants in silicon

Enhanced diffusion of implanted arsenic impurities in silicon during subsequent thermal annealing can be interpreted in terms of a system of reaction-diffusion equations. It is shown that for high doses the local solubility limit can considerably influence the reactions between the defects involved and thus markedly change the effective diffusion of As donors. A similar effect can be brought about by the presence of predoped donors/acceptors, which also can significantly accelerate/retard the effective diffusion of As implants. Furthermore, an explanation of some precipitation/clustering processes during a rapid/slow cooling-down is proposed. Finally, several contradictory experimental results published previously will be shown to be compatible with the present model.     

Bloch oscillations in one-dimensional photonic crystal coupled microcavity composed of single-negative materials

We have studied the propagation properties of electromagnetic waves in one-dimensional photonic crystal coupled microcavity structure composed of single-negative materials. Two Wannier-Stark ladders can be obtained by employing only one type of microcavity. The dynamics behavior of a Gaussian pulse transmitting through the structure is simulated theoretically. We demonstrated for the first time that even in this multilayered structure completely made of single-negative materials, the optical Bloch oscillations and Zener tunneling can also be attained.     

Yb：Y3A15O12晶体晶格振动光谱的研究

采用提拉法生长Y3A15O12（YAG）晶体和Yb^3＋掺杂原子数分数分别为5％，10％，15％，20％，25％，50％N100％的Yb：Y3A15O12（Yb：YAG）晶体。系统表征和分析了Yb^3＋掺杂浓度对拉曼光谱的影响。随着Yb^3＋掺杂浓度的增加，晶体的振动模式没有明显的变化，晶体结构没有改变；在370cm^-1和785cm^-1附近，振动吸收峰的半峰全宽逐渐增大。分析得出，Yb抖掺杂浓度对晶体的晶格、对称性、荧光寿命均有影响，从而可能影响到晶体的光谱和激光性能。     

Synthesis and optical properties of In-doped GaN nanocrystals

Indium-doped GaN nanocrystals with 5% and 10% In have been prepared by a low temperature solvothermal method using hexamethyldisilazane as the nitriding reagent. The nanocrystals show Raman bands at lower frequencies compared to GaN. Photoluminescence spectra of the In-doped GaN nanocrystals exhibit an increase in the FWHM with the decrease in the PL band energy, the band energy itself decreasing with increase in the In content.     

Theoretical and experimental study of a single frequency Tm,Ho:YLF laser

We present a theoretical and experimental analysis of a diode-pumped single frequency Tm,Ho:YLF laser. A new model for a diode-pumped Tm,Ho:YLF quasi-three-level laser is described. The influence of energy-transfer up-conversion (ETU) and ground-state re-absorption (GSA) has been taken into account. When the incident pump power is 2.8 W, a maximum single frequency output power of 118 mW is obtained from the Tm,Ho:YLF laser at room temperature. The line narrowing elements used are two solid etalons. The single frequency laser can be used as a seed laser for either a larger oscillator or an amplifier. The theoretical results are in good agreement with experimental data.     

Electrical behaviour of catalytic nanostructured CeO2/CuOx composites under air-methane gas impulses

Nanostructured composites based on copper oxide and cerium dioxide phases [CuO-CeO₂] were elaborated from sol-gel route, with weight fractions of CuO phase ranging between 0 and 0.4. They are interesting potential catalysts allowing conversion of CH₄ and CO into CO₂ and H₂O and might be used in miniaturized gas sensors. An electrical study of this nanostructured system was carried out to determine catalytic behaviours under air-methane impulses at 350 °C. The electrical analysis was based on a specific homemade electronic device. Time dependent interactions between gas pulses and solid catalyst (CuO/CeO₂) were analyzed from a frequency modification of the electronic device. Kinetic parameters were determined from a model describing adsorption and desorption of gases adapted to short interaction time between gas and solid. These time dependent electrical behaviours were then correlated with infrared spectroscopy analyses allowing time dependent analysis of methane conversion into CO₂ gas, for long interaction time between gas and solid.     

Effect of welding speed on butt joint quality of Ti–6Al–4V alloy welded using a high-power Nd:YAG laser

Annealed Ti–6Al–4V alloy sheets with 1 and 2 mm thickness are welded using a 4 kW Nd:YAG laser system. The effects of welding speed on surface morphology and shape, welding defects, microstructure, hardness and tensile properties are investigated. Weld joints without or with minor cracks, porosity and shape defects were obtained indicating that high-power Nd:YAG laser welding is a suitable method for Ti–6Al–4V alloy. The fusion zone consists mainly of acicular α′ martensite leading to an increase of approximately 20% in hardness compared with that in the base metal. The heat-affected zone consists of a mixture of α′ martensite and primary α phases. Significant gradients of microstructures and hardness are obtained over the narrow heat-affected zone. The laser welded joints have similar or slightly higher joint strength but there is a significant decrease in ductility. The loss of ductility is related to the presence of micropores and aluminum oxide inclusions.