STUDY ON EXCESS CONDUCTION LOSS IN NORMAL METALS AT/BELOW SUB-MILLIMETER WAVELENGTHS

We have used the spatial dispersion theory to develop a rigorous model to investigate excess conduction loss in normal metals. We have used the model to account excess conduction loss and dissect the discrepancies between excess conduction loss measurements and classical theoretical predictions in normal metals at/below sub-millimeter wavelengths. Moreover, we have compared the results of this model with the results of the classical skin-effect model and classical relaxation-effect model. Our analysis shows that the conductivity is not only frequency but also wave vector dependent. The results of the calculations indicate a good quantitative agreement with the published experimental data for the room temperature excess conduction loss of normal metals at/below sub-millimeter wavelengths.     

Study on spatial dispersion theory of excess conduction loss in normal metals surface below terahertz frequencies

We have developed a rigorous model for analyzing excess conduction loss in normal metals surface by using the spatial dispersion theory. We have used the model to account excess conduction loss and dissect the discrepancies between excess conduction loss measurements and classical theoretical predictions in normal metals surface below terahertz frequencies. Our analysis shows that the conductivity is not only frequency but also wave vector dependent. We demonstrate good quantitative agreement with the published experimental data for the room temperature excess conduction loss of normal metals surface below terahertz frequencies.     

An improved formula for the surface resistance of normal metals at millimetre wavelengths

A number of researchers have reported discrepancies between surface resistance (SR) measurements and classical theoretical predictions in normal metals for millimetre wavelengths (MW). In this paper, a rigorous model is developed for analysing SR of normal metals. This model is based on quantum mechanical analysis of the spatial dispersion within the metal. We use the model to predict SR and eliminate the discrepancies between SR measurements and classical theoretical predictions in normal metals for MW. Moreover, we have compared the results of this model with that of the classical skin-effect model and classical relaxation-effect model. Our analysis shows that the conductivity is not only frequency- but also wave-vector-dependent for MW. We demonstrate that our model has good quantitative agreement with the published experimental data for the room temperature surface resistance of normal metals for MW.     

A New Theoretical Modeling of Surface Resistance in Normal Metals at Terahertz Frequencies

A number of researchers have reported discrepancies between surface resistance measurements and classical theoretical predictions for simple mm-wave and sub-mm-wave structures. We have developed a rigorous phenomenological model for analyzing surface resistance of normal metals. The model is based on quantum mechanical analysis for spatial dispersion within the metal. We have used the model to predict the surface resistance in normal metals at terahertz frequencies. Our analysis shows that the conductivity is not only frequency but also wave vector dependent. Moreover, we have compared the results of this model with the results of the classical skin-effect model and classical relaxation- effect model. We demonstrate that our model has good quantitative agreement with the published experimental data for the room temperature surface resistance of normal metals at terahertz frequencies range from the literature.     

飞秒激光热反射实验系统测量金属薄膜中的超快速热传递过程

飞秒激光热反射技术已经成为研究不同材料中超快速热传导过程的有效实验方法.实验中采用前表面加热、后表面探测的方法对不同厚度的Au薄膜进行了测量,通过比较表面电子温度可以得到超快速激光加热条件下Au薄膜材料中电子温度振荡的传递速度.结果表明瞬态条件下非平衡态电子是热量的主要载体,根据实验测量值拟合得到的能量传递速度接近于非...     

Modeling of a millimeter wave planar Schottky diode using both improved equivalent circuit model and 3D-EM model

In this paper, a planar Schottky varistor diode is studied and modeled by equivalent circuit method and three dimensional full wave electromagnetic (3D-EM) method, respectively. The diode's equivalent circuit is extracted from millimeter-wave small-signal S-parameter measurements. Since the package of the diode influences the electromagnetic field distribution at millimeter and sub-millimeter wavelengths, a 3D-EM model and an improved equivalent circuit model is applied to describe the field precisely. The simulated results of equivalent circuit, improved equivalent circuit and 3D-EM model are compared with the measured results. In addition, the effects caused by silver paste conductive adhesive are considered in 3D-EM model and improved equivalent circuit model. The results show that both the 3D-EM model and improved equivalent circuit model have good S-parameter consistency with measured results.     

Ultrasound absorption due to electrons and phonons in alkali liquid metals

The excess longitudinal ultrasonic absorption over and above the classical value in four alkali liquid metals near their melting points has been accounted for by the mechanisms of interaction of sound waves with the conduction electrons and the thermal phonons (Akhieser mechanism), both exhibiting a quadratic dependence on sound frequency. An expression, similar to the Bridgman relation for liquids, for the phonon conductivity in the liquid metals has been developed. This approach briefly reported here yields good results.     

Temperature dependence in sputtering

We have obtained the result on the temperature dependence in sputtering of silver which is contrary to the current believes by taking steps to eliminate spurious effects due to changes of residual gas pressure and target temperature, and by determining the relevant energy range for thermal sputtering. The result i3 thought to be due basically to the thermal spike effect, and agreement is shown with a postulated thermal spike model, in which the instantaneous variation of spike temperature against thermal diffusivity is treated on the basis of Carslaw's solution of the normal heat conduction equation. The thermal diffusivity is shown to be proportionate to the thermal conductivity subject to a constant metal density in the temperature range 300–500K and a heat capacity that obeys the Dulong-Petit law which holds good for most metals at high temperatures (> θ_D). The thermal conductivity versus preheat target temperature curve matches the Makinson electronic thermal conductivity curve for metals.     

Optical properties of chalcogen-loaded zeolite (ZSM-5)

Sulfur, selenium, and tellurium were loaded into sub-millimeter size ZSM-5 single crystals, and the optical properties have been comparatively studied. S and Te show similar features, while Se is unique. S and Te have optical absorption edges at wavelengths of ～400 nm with transmission dips at ～450 nm, while Se has the edge at ～550 nm. The three materials provide photoluminescence at visible wavelengths, with the intensities of S and Te being stronger than that of Se by two orders. These optical properties imply that S and Te in the zeolite form small atomic units such as S₃ and Te₂, while Se condenses into single-chain structures.     

Ultrasound absorption in liquid metals

The excess longitudinal ultrasonic absorption over and above the classical value has been attributed to the solid-like mechanisms of the interaction of sound waves with the conduction electrons and the thermal phonons in liquid metals, both exhibiting a quadratic dependence on the sound frequency.     

基于二极管精确电路模型的183GHz分谐波混频器设计

针对亚毫米波混频二极管管对电路模型不够精确的问题,采用场路结合协同分析,将进出二极管的频率信号分类处理,建立了一种应用于亚毫米波分谐波混频器电路的反向并联二极管对精确电路模型。基于获取的管对精确电路模型,建立了全局性的分谐波混频器电路的集总元件等效电路模型,设计并实现了一款183GHz分谐波混频器。测试结果表明混频器在本振频率为92GHz、功率为2mW,射频频率176~192GHz范围内,双边带变频损耗小于6.8dB,等效噪声温度小于800K,在182GHz测得最小双边带变频损耗为4.9dB,与仿真数据吻合较好。     

Ultrafast dynamics in ZnO thin films irradiated by femtosecond lasers

The damage morphologies, threshold fluences in ZnO films were studied with femtosecond laser pulses. Time-resolved reflectivity and transmissivity have been measured by the pump-probe technique at different pump fluences and wavelengths. The results indicate that two-phase transition is the dominant damage mechanism, which is similar to that in narrow band gap semiconductors. The estimated energy loss rate of conduction electrons is 1.5 eV/ps.     

Investigation of the pump wavelength influence on pulsed laser pumped Alexandrite lasers

Recent theoretical modelling and experimental results have shown that excess lattice phonon energy created dur ing the non-radiative energy transfer from the ⁴T₂ pump manifold to the ²E storage level in Alexandrite when pumped with wavelengths shorter than ∼645 nm causes chaotic lasing output. Shorter pump wavelengths have also been associated with increased non-radiative energy decay and reduced laser efficiency. We report studies of fluorescence emission spectra of Alexandrite illuminated at a range of wavelengths from green to red, which demonstrate reduced fluorescence yield for shorter pump wavelengths at elevated crystal temperatures. Investigations of pulsed laser pumping of Alexandrite over the same spectral range demonstrated reduced pump threshold energy for longer pump wavelengths. High repetition rate pulsed pumping of Alexandrite at 532, 578 and 671 nm showed stable and efficient laser performance was only achieved for red pumping at 671 nm. These results support the theoretical model and demonstrate the potential for scalable, red laser pumped, all-solid-state Alexandrite lasers.PACS 42.60.Lh; 42.60.Mi     

New results on diffusion in fcc metals

The Kondo model for the diffusion of light particles in metals has provided a satisfactory explanation for the low temperature diffusion rates for muons in the fcc metals Cu and Al. Explicit experiments which show the strong dependence of muon behaviour on the presence of conduction electrons have now been performed belowT=1 K in Al. Challenging new diffusion studies on fcc metals such as Pt are also presented.     

非平衡涨落问题的微观唯象分析理论(Ⅱ)——物理系统中的非平衡涨落与由信息理论所求得的热传导精确结果的比较

本文将文献[10]所建立的非平衡涨落统计的微观唯象分析理论与对一般的涨落-耗散表示式的修正方法,直接应用于一、二与三维光子热传导与金属中的电子热传导的研究中,并将所得结果与由信息理论方法所建立的线性谐振子链的非平衡涨落的精确模型所求得的精确结果进行了比较,两者相当符合。从而证实了文献[10]所建立的非平衡涨落统计的微观唯象分析理论是正确的。     

Comparative theoretical analysis of continuous wave laser cutting of metals at 1 and 10 μm wavelength

We present a derivation and, based on it, an extension of a model originally proposed by V.G. Niziev to describe continuous wave laser cutting of metals. Starting from a local energy balance and by incorporating heat removal through heat conduction to the bulk material, we find a differential equation for the cutting profile. This equation is solved numerically and yields, besides the cutting profiles, the maximum cutting speed, the absorptivity profiles, and other relevant quantities. Our main goal is to demonstrate the model’s capability to explain some of the experimentally observed differences between laser cutting at around 1 and 10 μm wavelengths. To compare our numerical results to experimental observations, we perform simulations for exactly the same material and laser beam parameters as those used in a recent comparative experimental study. Generally, we find good agreement between theoretical and experimental results and show that the main differences between laser cutting with 1- and 10-μm beams arise from the different absorptivity profiles and absorbed intensities. Especially the latter suggests that the energy transfer, and thus the laser cutting process, is more efficient in the case of laser cutting with 1-μm beams.     

Electronic structure of H and He in metal vacancies

The electronic structure of H and He impurities in metals is calculated using the Gunnarsson-Hjelmberg method of solving the Kohn-Sham equation. The jellium model is used for the metal. The differences between interstitial and substitutional impurity sites are emphasized. For normal metallic densities it is found that both impurities favour sites of lower than average conduction electron density because here the impurity electrons can relax to a situation of lower kinetic energy.     

Noise-figure limit of fiber-optical parametric amplifiers and wavelength converters: experimental investigation

Recent theoretical work predicts that the quantum-limited noise figure of a x(3)-based fiber-optical parametric amplifier operating as a phase-insensitive in-line amplifier or as a wavelength converter exceeds the standard 3-dB limit at high gain. The degradation of the noise figure is caused by the excess noise added by the unavoidable Raman gain and loss occurring at the signal and the converted wavelengths. We present detailed experimental evidence in support of this theory through measurements of the gain and noise-figure spectra for phase-insensitive parametric amplification and wavelength conversion in a continuous-wave amplifier made from 4.4 km of dispersion-shifted fiber. The theory is also extended to include the effect of distributed linear loss on the noise figure of such a long-length parametric amplifier and wavelength converter.     

Calculation of the contribution of conduction electrons to the atomic factors of simple metals

An expression for the Fourier transform of the screening electron density of simple metals has been derived using smooth nonlocal model potentials of simple metals. The expression describes the contribution of conduction electrons to the atomic factors of X-ray scattering in simple metals. Aluminum was used as an example for numerical checking. Comparison with the results of similar calculations for the form factor of the Krasko-Gurskii model potential shows the importance of taking the nonlocality of the model potential into account.     

5个不同波长的激光及其线偏振激光辐照人正常膀胱组织光学特性

采用双积分球系统和光辐射测量技术的基本原理以及运用生物组织的光学模型,研究了476.5, 488, 496.5, 514.5和532 nm激光及其线偏振激光辐照人正常膀胱组织的光学特性。结果表明：组织对激光及线偏振激光的总衰减系数和散射系数均随着波长的增大而减小,而且线偏振激光与非线偏振激光入射是有明显的差异。吸收系数是随着波长的增大而缓慢地减小,但有一些起伏,而与是否线偏振光入射无明显差异。平均散射余弦也是随着波长的增大而减小,而且线偏振激光与非线偏振激光入射是有明显的差异。光学穿透深度则是随着波长的增大而增大,而有一些起伏。折射率在这5个波长范围内的值在(1.37～1.44)之间。Kubelka-Munk二流模型下组织对同一波长的激光及其线偏振激光的吸收系数、散射系数、总衰减系数和有效衰减系数没有显著性差异(P＞0.05)。组织对不同波长的激光或其线偏振激光的吸收系数、散射系数、总衰减系数和有效衰减系数则有些是有明显的差异。