The effects of physical parameters on the gain and efficiency of Cherenkov type FEL

In this paper, the effects of physical parameters on the gain and efficiency of Cherenkov type FEL are studied through simulative compute. The results show that the permittivity ε and periodic length λ_(?) of wiggler magnetic filed are two important parameters which influence the properties of laser. The magnitude ε has effect on the properties of gain, and the choice of wigger λ_(?) can increase gain and efficiency of the laser. The calculation results show that the gain and efficiency of Cherenkov type FEL are considerably higher than those of Compton-Raman type FEL under some conditions with proper parameters.     

Connection between parameters of the Murrell–Sorbie and Fayyazuddin potentials

A connection between the Murrell–Sorbie and the Fayyazuddin potential energy functions were established by obtaining conversion matrices that convert the former's parameters into the latter and vice versa. This was attained by rearranging the Fayyazuddin potential into another, but equivalent, form comparable to the Murrell–Sorbie function with the aid of series expansion. A list of 71 sets of Fayyazuddin diatomic parameters were generated by applying one of the conversion matrices on the Huxley–Murrell data [J. Chem. Soc. Faraday Trans. II 79, 323 (1983)]. Verification of the developed conversion matrices was performed by plotting the Murrell–Sorbie and the Fayyazuddin functions using the Huxley–Murrell data and the converted data, respectively. Potential energy plots of typical (OSi) and extreme (FO, BeS and HH) diatomic parameters exhibit very good agreement between the two potential functions considered, thereby confirming the conversion matrices’ validity. Slight discrepancies of the plotted diatomic energy curves further suggest the comparative suitability of the Fayyazuddin potential for curve-fitting harder, rather than softer, bonds.     

Continuous and pulsed ultrasound-assisted extraction of carob’s antioxidants: Processing parameters optimization and identification of polyphenolic composition

Polyphenols in carobs have recently attracted great attention due to their wide range of biological and health promoting effects. A comprehensive study was conducted to find an optimum method for the extraction, purification and characterization of these valuable bioactive substances. Under this framework, the ultrasound-assisted extraction (UAE) of polyphenols from carob pulp was optimized by the maximization of the yield in total phenolics using response surface methodology. In particular, the effects of solid-solvent ratio, solvent concentration, extraction time, sonication amplitude, and sonication mode were investigated and optimized using a complete experimental design. In comparison to conventional extraction techniques, UAE offered a higher yield of antioxidants and a shorter processing time. Solid-phase extraction was evaluated as a clean-up strategy prior to the electrophoretic analysis of extracts. The results from the analysis of real samples revealed the predominance of gallic acid and highlighted the great influence of the ripening stage on carobs composition.     

Interface effect of graphene–TiO2 photoanode with CuO nanorod counter electrode on solar conversion efficiency and enhanced external quantum efficiency

Optical and Quantum Electronics - In this paper, a simulation analysis of 40 Gb/s wavelength division multiplexing system of 32 channels is implemented through RZ modulation format by...     

The absorption efficiency of submicron amorphous carbon particles between 2.5 and 40 μm

Submicronic amorphous carbon particles have been studied in the near-and middle-infrared at room temperature and their properties measured. Two different production methods have been used: (a) arc striking in an argon controlled atmosphere; (b) burning of hydrocarbons in air. TEM analysis allows determination of grain morphology and size distributions. Particle shapes appear to be influenced by different production methods, established by comparing our results with those of samples produced by means of focused laser pulses. Grain dimensions are strongly ambient pressure dependent since collisional growth is active in particle formation. All the absorption extinction curves indicate a general λ⁻¹ fall-off, with small humps at 8, 11 and 12 μm. A band at about 13 μm is observed only for grains obtained by burning hydrocarbons. Possible temperature effects on the absorption wavelength dependence have been noted by comparing our observations with those of commercial lamp-black performed at liquid helium temperature.     

Enhancement of light extraction efficiency in OLED with two-dimensional photonic crystal slabs

Light extraction efficiency of organic light emitting diode (OLED) based on various photonic crystal slab (PCS) structures was studied. By using the finite-difference time-domain (FDTD) method, we investigated the effect of several parameters, including filling factor and lattice constant, on the enhancement of light extraction efficiency of three basic PCSs, and got the most effective one. Two novel designs of "interlaced" and "double-interlaced" PCS structures based on the most effective basic PCS structure were introduced, and the "interlaced" one was proved to be even more efficient than its prototype. Large enhancement of light extraction efficiency resulted from the coupling to leaky modes in the expended light cone of a band structure, the diffraction in the space between columns, as well as the strong scattering at indium-tin-oxide/glass interfaces.     

Relationships between experienced listener ratings of multichannel audio quality and naïve listener preferences

The preferences of a large number of na?ve listeners were elicited in response to a selection of multichannel audio items that had been degraded in quality by using band-limiting and down-mixing algorithms. Relationships were sought between these preference ratings and the quality judgements of experienced listeners in an attempt to determine whether one could be predicted from the other. Results suggest that a simple regression model can be used to do this with adequate results, but that a better prediction can be successfully based on experienced listener ratings of timbral and spatial fidelity. There is a difference between na?ve and experienced listeners in the weightings of the fidelities and their relationship to overall quality.     

Photolytical XeF(C–A) laser amplifier of femtosecond optical pulses: gain measurements and pump efficiency

Gain characteristics of a photolytically driven XeF(C–A) laser amplifier are studied experimentally in the unsaturated amplification regime. The gaseous active medium is optically pumped by vacuum-ultraviolet (VUV) radiation from two large-area multichannel surface discharges initiated along opposite walls of the amplifier chamber. A total gain factor of 10² is obtained for the ultrashort optical pulses under multipass amplification in the active volume of 40?×?18?×?4 cm³ dimensions with a spatially homogeneous gain distribution. Spectral measurements reveal a good conservation of the seed pulse spectrum. Small-signal gain reaching 2×10^-3 cm^-1 is observed for the blue-green seed pulses of 150 fs duration, as well as for the continuous seed radiation at 488 nm. The obtained gain values, being compared with the gain calculated for the measured pumping radiation power, indicate that the quantum yield of the XeF(B) formation as a result of the XeF₂ photodissociation is high and approaches unity within the spectral band of the XeF₂ VUV photodissociation continuum.     

New relations between ℓN-scattering cross sections and neutral current parameters

New relations which connect cross sections with neutral current parameters have been obtained in deep inelastic and (quasi-)elastic _v ^(?) N-,e ^±(μ^±)N-scattering; the relations are independent of the structure functions and formfactors of the nucleon. A known example is the Paschos-Wolfenstein relation in _v ^(?) N-scattering. The relations have been obtained with allowance for the contribution of the extraZ′-boson which makes it possible to use them both for extractions of the Standard Model parameters (ρ, sin²θ _w ) and for the search for some manifestations of new physics.     

Spatial chirp in Ti:sapphire multipass amplifier

The spatial chirp generated in the Ti:sapphire multipass amplifier is numerically investigated based on the onedimensional(1D) and two-dimensional(2D) Frantz–Nodvik equations. The simulation indicates that the spatial chirp is induced by the spatially inhomogeneous gain, and it can be almost eliminated by utilization of proper beam profiles and spot sizes of the signal and pump pulses, for example, the pump pulse has a top-hatted beam profile and the signal pulse has a super-Gaussian beam profile with a relatively larger spot size. In this way, a clear understanding of spatial chirp mechanisms in the Ti:sapphire multipass amplifier is proposed, therefore we can effectively almost eliminate the spatial chirp and improve the beam quality of a high-power Ti:sapphire chirped pulse amplifier system.     

高效率多程折叠Nd∶YVO_4激光放大器

采用具有近共焦、非稳腔特点的多程折叠光路结构,使激光光束多次通过增益介质,实现了高提取效率的激光放大器。实验中在注入22W种子激光的条件下,以43.9%的提取效率得到了63W的激光输出,斜效率超过52%,激光放大器的输出光束质量从种子激光的M2X=2.08,M2Y=1.92变为M2X=2.84,M2Y=1.79。     

同带抽运高效率光纤放大器

以光纤光栅为谐振腔搭建了波长为1020 nm的光纤激光器,并通过两级级联放大获得了590 mW的最大输出功率. 利用获得的波长为1020 nm的激光进行了波长为1064 nm种子光同带抽运放大,实验研究了不同增益光纤长度时放大器的输出功率和转换效率. 当增益光纤长度为8.5 m时,放大器最大输出功率为385 mW,斜率效率为81%. 进行了波长为976 nm的半导体激光器直接抽运波长为1064 nm种子光的实验. 在增益光纤长度最优时,其斜率效率为56.4%. 实验结果表明,同带抽运方式比传统抽运方式具有更高的转换效率. 研究结果可为波长为1020 nm的激光高功率放大和波长为1064 nm的光纤激光高功率同带抽运放大提供一定的参考. 关键词： 同带抽运 光纤放大器 斜率效率     

用于多程放大系统光束反转器的等离子体电极电光开关

等离子体电极电光开关将用在多程放大系统光束反转器中,作为输出控制和抑制主放大前系统内的自激振荡,由于光束反转器空间限制,等离子体电极电光开关采用一体化结构设计。介绍了紧缩型等离子体电极电光开关特性,以及在多程放大系统中的应用。实验结果表明,等离子体电极电光开关具有优良的开关性能,全口径静态透过率为94%,开关效率为989%,能够有效抑制放大器产生的自激振荡。     

高效率多程折叠Nd:YVO4激光放大器

采用具有近共焦、非稳腔特点的多程折叠光路结构,使激光光束多次通过增益介质,实现了高提取效率的激光放大器.实验中在注入22W种子激光的条件下,以43.9%的提取效率得到了63 W的激光输出,斜效率超过52%,激光放大器的输出光束质量从种子激光的M2X=2.08,M2Y=1.92变为M2X=2.84,M2Y=1.79.     

超短脉冲染料放大器中的参数研究

对超短脉冲染料放大器(DLA)中放大的自发辐射(ASE)随泵浦强度变化的关系进行了实验研究,为了求得具有高储能、低自发辐射背景噪声的染料激光放大器的泵浦强度,我们用速率方程对实验结果进行了解析分析,获得了染料激光放大器的泵浦强度与染料参数(浓度、增益长度等)的近似关系式,以及相应条件下染料激光放大器储能和小信号增益的表达式,并与实验进行了比较.二者符合较好,从而为染料激光放大器的设计提供了参考.     

High efficiency diode-pumped slab oscillator and amplifier for space-based application

The design and performance of conduction-cooled, laser diode-pumped oscillator and amplifier slab laser featuring high efficiency, high pulse energy and high beam quality for space-based application are reported. The oscillator was a diode-pumped Q-Switched Nd:YAG slab laser using unstable resonator, and the amplifiers were two zig-zag Nd:YAG slabs based on a side-pumped slab geometry. A near diffraction-limited output of 450 mJ in a 10 ns pulse at a repetition rate of 20 Hz was obtained, corresponding to an optical-to-optical conversion efficiency of over 20%.     

LD侧泵浦Nd：YAG板条双程功率放大器初步研究

对二极管激光侧泵浦Nd：YAG板条双程功率放大器进行了初步的研究,给出了激光器的数值模拟结果,建立了二极管侧面泵浦Nd:YAG板条激光主振荡-多程放大(MOPA)系统;在100Hz重复频率时,实验获得单脉冲能量为51.9mJ的输出,光束质量M2小于2,脉冲能量起伏小于2%, 实验结果与数值计算结果相符合。     

主振荡功率放大装置中的放大自发辐射效应和能量提取效率

建立了放大自发辐射(ASE)和相干激光能流耦合的模型,使用迭代算法,计算了长方体形状放大级中的ASE能流和相干激光能流的分布以及放大级出口0.5 m处的ASE分布,并讨论了入射光强、饱和光强对输出功率及能量提取效率的影响。对于增益区呈长方体、增益系数沿流场方向呈抛物线分布的放大级的计算结果表明：输入光的存在不仅会降低放大级中ASE光强的大小,而且将改变ASE的分布,使放大级中ASE能流的极大值向入口处移动;在饱和光强一定的情况下,输出功率和能量提取效率将随着入射功率的增大而增大;在入射光强一定的情况下,输出功率将随着饱和光强的增大而增大,而能量提取效率将随着饱和光强的增大而减小。