Ferroelectric thin films obtained by pulsed laser deposition

We review our significant results concerning pulsed laser deposition (PLD) of some ferroelectric compounds: (i) lead magnesium niobate Pb(Mg_1/3Nb_2/3)O₃ (PMN); (ii) lead magnesium niobate–lead titanate Pb(Mg_1/3Nb_2/3)O₃–PbTiO₃ (PMN–PT), with variable PT contents; (iii) La-doped lead zirconate titanate (Pb_1 − xLa_x)(Zr_0.65Ti_0.33)O₃ (PLZT); and (iv) Nb-doped lead zirconate titanate Pb_0.988(Zr_0.52Ti_0.48)_0.976Nb_0.024O₃ (PNZT). A parametric study has been performed in order to evidence the influence of the deposition parameters (laser wavelength, laser fluence, oxygen pressure, substrate type and temperature, RF power discharge addition, etc.) on the film properties and to identify the best growing conditions. Techniques including atomic force microscopy (AFM), X-ray diffraction (XRD), scanning electron microscopy (SEM), secondary ions mass spectroscopy (SIMS), transmission electron microscopy (TEM), electrical and ferroelectric hysteresis measurements have been used for layer characterization.     

Inter-BSs virtual private network for privacy and security enhanced 60 GHz radio-over-fiber system

A novel inter-basestations (inter-BSs) based virtual private network (VPN) for the privacy and security enhanced 60 GHz radio-over-fiber (RoF) system using optical code-division multiplexing (OCDM) is proposed and demonstrated experimentally. By establishing inter-BSs VPN overlaying the network structure of a 60 GHz RoF system, the express and private paths for the communication of end-users under different BSs can be offered. In order to effectively establish the inter-BSs VPN, the OCDM encoding/decoding technology is employed in the RoF system. In each BS, a 58 GHz millimeter-wave (MMW) is used as the inter-BSs VPN channel, while a 60 GHz MMW is used as the common central station (CS)–BSs communication channel. The optical carriers used for the downlink, uplink and VPN link transmissions are all simultaneously generated in a lightwave-centralized CS, by utilizing four-wave mixing (FWM) effect in a semiconductor optical amplifier (SOA). The obtained results properly verify the feasibility of our proposed configuration of the inter-BSs VPN in the 60 GHz RoF system.     

利用块状介质进行飞秒强激光脉冲的腔外压缩

高强度飞秒激光脉冲的腔外压缩是获得高次谐波阿秒脉冲驱动源的必要手段.实验研究了超强超短飞秒激光脉冲在经过块状介质后的光谱展宽和色散补偿压缩现象.单脉冲能量0.26 mJ,脉宽50 fs的激光脉冲经透镜在空气中聚焦后再入射到块状材料上,出射脉冲光谱被展宽到接近40 nm.由于在块状材料中的自聚焦效应,出射光束质量变好并保持较小的空间啁啾.利用熔融石英棱镜对补偿带有正色散的出射脉冲,最后得到＞0.1 mJ,19 fs的压缩脉冲.利用SPIDER装置测量了出射脉冲的脉宽和光谱相位.整个系统的能量效率大约为35%,压缩后的激光脉冲具有很好的空间分布和平滑的时域包络.实验结果实现了利用块状材料对飞秒激光脉冲的腔外压缩,这种方法将适用于对更高能量飞秒脉冲的压缩.     

Degenerated optical parametric chirped-pulse amplification with cesium lithium borate

A gain amplifier for degenerated optical parametric chirped-pulse amplification (OPCPA) with lithium triborate and cesium lithium borate (CLBO) crystals was demonstrated in a near-collinear configuration. The signal gain of the final energy amplifier with CLBO was approximately 6. After compression, the 123 fs pulse duration was obtained. Compared with potassium dihydrogen phosphate, it is confirmed that CLBO is more effective as a nonlinear crystal in a final power amplifier for terawatt or petawatt OPCPA systems. To our knowledge, this is the first demonstration of OPCPA with CLBO.     

Effect of the gas mixing technique on the production efficiency of ion beams extracted from an electron cyclotron resonance ion source

In this work the effect of gas mixing on the production efficiency of ion beams extracted from an ECR ion source has been studied with the JYFL 6.4 GHz electron cyclotron resonance ion source (ECRIS). It was found that the gas mixing affects strongly the confinement of ions in the plasma of the ECRIS. The information obtained can be used to minimize the consumption of expensive materials or isotopes and to reduce contamination of the plasma chamber. It was observed that the carbon contamination, which is built up when the MIVOC method is used could be decreased with the aid of the gas mixing technique. The best mixing gas for this purpose was found to be oxygen.     

Robust and ultralow-energy-threshold ignition of a lean mixture by an ultrashort-pulsed laser in the filamentation regime

Laser ignition(LI)allows for precise manipulation of ignition tinning and location and is promising for green combustion of automobile and rocket engines and aero-turbines under lean-fuel conditions with improved emission efficiency;however,achieving completely effective and reliable ignition is still a challenge.Here,we report the realization of igniting a lean methane/air mixture with a 100%success rate by an ultrashort femtosecond laser,which has long been regarded as an unsuitable fuel ignition source.We demonstrate that the minimum ignition energy can decrease to the sub-mJ level depending on the laser filamentation formation,and reveal that the resultant early OH radical yield significantly increases as the laser energy reaches the ignition threshold,showing a clear boundary for misfire and fire cases.Potential mechanisms for robust ultrashort LI are the filamentation-induced heating effect followed by exothermal chemical reactions,in combination with the line ignition effect along the filament.Our results pave the way toward robust and efficient ignition of lean-fuel engines by ultrashort-pulsed lasers.     

The optical properties of some steel surfaces with different surface preparations for high temperature use

A selective surface with large absorption for solar radiation and high reflectance for thermal infrared radiation was produced by use of surface oxidation of stainless steel. The surfaces were studied for use with concentrated light in a solar power plant at temperatures of 400°C and higher.In order to investigate the relation between surface treatment and optical properties, stainless steels (AISI 304 and 430) which were submitted to different chemical and mechanical surface treatments, were used. To increase the spectral selectivity, these surfaces were treated in air and in vacuum at different temperatures and times. The optical properties of these films were investigated. Visual and infrared spectral absorptances were measured at room temperature. The thermal hemispherical emittance and absorptance were obtained by a calorimetric method at 200°C. It was noticed that these chemically and mechanically treated stainless steel surfaces have good spectral properties without further oxidations. This is very important for high temperature uses. The best values are found for samples 7 and 8 under vacuum and air. These two samples with mechanically ground surfaces retained their selectivity and specularity after several hours oxidation. One can conclude that the surface ground treatment confers good selectivity on the steel surfaces for use in concentrating solar collectors with a working temperature of 500°C.Sample surfaces were subjected to long temperature ageing tests in order to gain some idea of the thermal stability of the surfaces. The results promise better-performing surface and the production of durable selective finishes at, possibly, lower cost than competing processes.     

Goldilocks focal zone in femtosecond laser ignition of lean fuels

Science China Technological Sciences - Laser ignition of lean fuels offers a promising route for green combustion with high combustion efficiency and low exhaust emissions. The fundamental...