Broadband mid-infrared pulse via intra-pulse difference frequency generation based on supercontinuum from multiple thin plates

We report on the generation of optical pulses with a nearly one octave-spanning spectrum ranging from 1300 nm to2500 nm at 1 kHz repetition rate, which are based on intra-pulse difference frequency generation(DFG) in β-barium borate crystal(β-BBO) and passively carrier-envelope-phase(CEP) stabilized. The DFG is induced by few-cycle pulses initiated from spectral broadening in multiple thin plates driven by a Ti: sapphire chirped-pulse amplifier. Furthermore, a numerical simulation is developed to estimate the conversion efficiency and output spectrum of the DFG. Our results show that the pulses from the DFG have the potential for seeding intense mid-infrared(MIR) laser generation and amplification to study strong-field physics and attosecond science.

Theoretical research on terahertz wave generation from planar waveguide by optimized cascaded difference frequency generation

A novel scheme for high-efficiency terahertz(THz)wave generation based on optimized cascaded difference frequency generation(OCDFG)with planar waveguide is presented.The phase mismatches of each-order cascaded difference frequency generation(CDFG)are modulated by changing the thickness of the waveguide,resulting in a decrement of phase mismatches in cascaded Stokes processes and an increment of phase mismatches in cascaded anti-Stokes processes simultaneously.The modulated phase mismatches enhance the cascaded Stokes processes and suppress the cascaded anti-Stokes processes simultaneously,yielding energy conversion efficiencies over 25%from optical wave to THz wave at 100 K.

High-efficiency terahertz wave generation with multiple frequencies by optimized cascaded difference frequency generation

High-efficiency terahertz(THz) wave generation with multiple frequencies by optimized cascaded difference frequency generation(OCDFG) is investigated at 100 K using a nonlinear crystal consisting of a periodically poled lithium niobate(PPLN) part and an aperiodically poled lithium niobate(APPLN) part.Two infrared pump waves with a frequency difference ω_(T1) generate THz waves and a series of cascaded optical waves in the PPLN part by cascaded difference frequency generation(CDFG).The generated cascaded optical waves with frequency interval ω_(T1) then further interact in the APPLN part by OCDFG,yielding the following two advantages.First,OCDFG in the APPLN part is efficiently stimulated by inputting multi-order cascaded optical waves rather than the only two intense infrared pump waves,yielding unprecedented energy conversion efficiencies in excess of 37% at 1 THz at 100 K.Second,THz waves with M timesω_(T1) are generated by mixing the mth-order and the(m+M)th-order cascaded optical waves by designing poling period distributions of the APPLN part.

Creation of multi-frequency terahertz waves by optimized cascaded difference frequency generation

A new scheme which generates multi-frequency terahertz(THz)waves from planar waveguide by the optimized cascaded difference frequency generation(OCDFG)is proposed.A THz wave with frequencyω_(T1)is generated by the OCDFG with two infrared pump waves,and simultaneously a series of cascaded optical waves with a frequency intervalω_(T1)is generated.The THz wave with a frequency of M-timesω_(T1)is generated by mixing the m-th-order and the(m+M)-th-order cascaded optical wave.The phase mismatch distributions of cascaded difference frequency generation(CDFG)are modulated by changing the thickness of planar waveguide step by step,thereby satisfying the phase-matching condition from first-order to high-order cascaded Stokes process step by step.As a result,the intensity of THz wave can be enhanced and modulated by controlling the cascading order of OCDFG.

Energy Scaling of Terahertz Pulses Produced through Difference Frequency Generation

We study the energy scaling of terahertz (THz) emission through difference frequency generation of near-infrared pulses, and demonstrate that Gigawatt few-cycle THz transients at the central frequency of 30 THz are produced from GaSe crystal pumped by two pulses at 1.65 and 1.95 micrometers, with the high quantum yield of 28%. Our analysis indicates that the high yield of DFG originates from the largely reduced group velocity mismatch as the long-wavelength pumping pulses are employed.

Cultural and Generational Differences in The Joy Luck Club

Amy Tan is one of the prominent Chinese American writers that have emerged since the 1980s. Her first novel The Joy Luck Club, which was published in 1989, brought her instant success. The story explores conflicts between two generations and two different cultures. Set in China and in the United States, the novel is woven by stories of four Chinese mothers and their four daughters. Though short in form, it is really worth detailed interpretation and appreciation. This paper will mainly discuss the cultural and generational differences reflected in the story with the conflict of one pair of the mother and daughter--Suyuan Woo and Jing-mei Woo as the main examples. The author of this paper believes that with the realization of the globalization, different cultures are fusing now

In vitro and in vivo cell tracking of chondrocytes of different origin by fluorescent PKH 26 and CMFDA

Tissue engineering techniques for cartilage re-pair to heal defects in joint surfaces is a clinical practice. Harvested autologous chondrocytes are expanded in culture and delivered in a suitable carrier medium back into the patient>s joint de-fect. The defect is then subsequently filled by new cartilage. Whether the cells in the repair tissue originate from the engineered tissue of the host or are derived from the surrounding original cartilage remains a relevant question for the ap-plied therapy. To answer this several methods exist to track cells, such as transfection of cells with LacZ carrying viruses, radio labeling with 111 IN or 51 Cr or fluorescent labeling with FDA. However, these techniques have drawbacks such as they may influence cellular properties, are radioactive and or quickly lose their tracking ability. New fluorescent probes are easier to handle and do not to interfere with cells. PKH 26劌 is a relatively new cell-labeling agent, but few data exist on the application of this dye in chondrocytes in vitro and in vivo. 5-chloromethylfluorescein diacetate - CMFDA (¨cell tracker green〔) is an established fluores-cent probe for imaging the dynamic processes of cell proliferation in vitro and in vivo. Likewise, several studies exist on different cell types. However, little data are available for chondro-cytes. The first aim of the study was to evaluate qualitative differences in fluorescence pattern after labeling of articular, auricular and costal chondrocytes. Secondly, we evaluated the influ-ence of labeling with CMFDA on cellular adhe-sion properties. The third aim was to compare the duration of cell labeling of chondrocytes of different origin with established CMFDA as stan-dard and PKH 26潴 for 3 cell generations in vitro and 12 weeks in vivo. We show that chondro-cytes from different origin can be labeled effec-tively with both PKH 26潴 and CMFDA. The PKH 26潴 labeled articular chondrocytes maintained fluorescence longer than CMFDA in vitro and in vivo. A higher percentage of articular chondro-cytes remained stained at 63 days than auricular or costal chondrocytes.

Mid-IR dual-wavelength difference frequency generation in uniform grating PPLN using index dispersion control

A novel widely tunable dual-wavelength mid-IR difference frequency generation （DFG） scheme with uniform grating periodically poled lithium niobate （PPLN） is presented in this paper. By using the temperature-dependent dispersion property of PPLN, the quasi-phase matching （QPM） peak for the pump may evolve into two separate ones and the wavelength spacing between them increases with the decrease of the crystal temperature. Such two pump QPM peaks may allow simultaneous dual-wavelength mid-IR laser radiations while properly setting the two fundamental pump wavelengths. With this scheme, mid-IR dual-wavelength laser radiations at around 3.228 and 3.548, 3.114 and 3.661, and 3.019 and 3.76 μm, are experimentally achieved for the crystal temperatures of 90, 65, and 30 ℃, respectively, based on the fiber laser fundamental lights.

Computational Analysis of the Effect of Nano Particle Material Motion on Mixed Convection Flow in the Presence of Heat Generation and Absorption

The present study is concerned with the physical behavior of the combined effect of nano particle material motion and heat generation/absorption due to the effect of different parameters involved in prescribed flow model.The formulation of the flow model is based on basic universal equations of conservation of momentum,energy and mass.The prescribed flow model is converted to non-dimensional form by using suitable scaling.The obtained transformed equations are solved numerically by using finite difference scheme.For the analysis of above said behavior the computed numerical data for fluid velocity,temperature profile,and mass concentration for several constraints that is mixed convection parameterλt,modified mixed convection parameterλc,Prandtl number Pr,heat generation/absorption parameterδ,Schmidt number Sc,thermophoresis parameter Nt,and thermophoretic coefficient k are sketched in graphical form.Numerical results for skin friction,heat transfer rate and the mass transfer rate are tabulated for various emerging physical parameters.It is reported that in enhancement in heat,generation boosts up the fluid temperature at some positions of the surface of the sphere.As heat absorption parameter is decreased temperature field increases at position X=π/4 on the other hand,no alteration at other considered circumferential positions is noticed.

THz wave generation by repeated and continuous frequency conversions from pump wave to high-order Stokes waves

We propose a novel scheme for THz wave generation by repeated and continuous frequency conversions from pump wave to high-order Stokes waves(HSWs).The repeated frequency conversions are accomplished by oscillations of Stoke waves in resonant cavity(RC)where low-order Stokes waves(LSWs)are converted to high-order Stokes waves again and again.The continuous frequency conversions are accomplished by optimized cascaded difference frequency generation(OCDFG)where the poling periods of the optical crystal are aperiodic leading to the frequency conversions from low-order Stokes waves to high-order Stokes waves uninterruptedly and unidirectionally.Combined with the repeated and continuous frequency conversions,the optical-to-THz energy conversion efficiency(OTECE)exceeds 26%at 300 K and 43%at 100 K with pump intensities of 300 MW/cm^(2).

Transient analysis of Casson fluid thermo-convection from a vertical cylinder embedded in a porous medium: Entropy generation and thermal energy transfer visualization

Thermal transport in porous media has stimulated substantial interest in engineering sciences due to increasing applications in filtration systems,porous bearings,porous layer insulation,biomechanics,geomechanics etc.Motivated by such applications,in this article,a numerical study of entropy generation impacts on the heat and momentum transfer in time-dependent laminar incompressible boundary layer flow of a Casson viscoplastic fluid over a uniformly heated vertical cylinder embedded in a porous medium is presented.Darcy’s law is used to simulate bulk drag effects at low Reynolds number for an isotropic,homogenous porous medium.Heat line visualization is also included.The mathematical model is derived and normalized using appropriate transformation variables.The resulting non-linear time-dependent coupled governing equations with associated boundary conditions are solved via an implicit finite difference method which is efficient and unconditionally stable.The outcomes show that entropy generation and Bejan number are both elevated with increasing values of Darcy number,Casson fluid parameter,group parameter and Grashof number.To analyze the heat transfer process in a two-dimensional domain,plotting heat lines provides an excellent approach in addition to streamlines and isotherms.It is remarked that as the Darcy number increases,the deviations of heat lines from the hot wall are reduced.

Analysis of the Per Capita Generation of Municipal Solid Waste by Socioeconomic Strata in Veracruz, Mexico, Using a Statistical Experimental Design

The management of municipal solid waste （MSW） is currently one of the major environmental concerns in Mexico. Therefore, municipalities must develop local programs for prevention and integrated management of MSW based on the data of MSW generation; however, these are scarce and diffuse. It is known that the MSW generation is affected by many factors, including life level. Given the importance of having reliable data, the objective of this study was to determine the per capita MSW generation of a small urban locality in the state of Veracruz and test whether there were significant statistic differences of per capita M SW generation among the life levels. The households were randomly sampled according to the Mexican standard of reference and were classified as popular, middle and residential. The per capita MSW generation determined was 0.355 kg·inhab^-1.day^-1. This value was lower than the value estimated by the national reference, suggesting that it might be overestimated and consequently lead to errors in estimating installations costs for the MSW treatment. The result of the experimental design revealed that there were significant statistic differences in the per capita MSW generation among the three socioeconomic strata. This study will allow the municipality to establish better strategies within the municipal program and differential rate for the provision of public clean service and it also provides a solid basis for future research under similar conditions.

Generation of Higher Terahertz Harmonics in Nonlinear Paraelectrics under Focusing in a Wide Temperature Range

It is theoretically investigated the generation of higher harmonics of two-dimensional and three-dimensional terahertz electromagnetic beams in nonlinear crystals. The attention is paid to crystalline paraelectrics like SrTiO3 under the temperatures 60 - 200 K, these crystals possess the cubic nonlinearity. The bias electric field is applied to provide the dominating quadratic nonlinearity. The initial focusing of the beams not only increases the efficiency of generation of higher harmonics, but alto makes possible to select maxima of different higher harmonics at some distances from the input. At lower temperatures the nonlinearity behaves at smaller input amplitudes, whereas at higher temperatures the harmonic generation can be observed at higher frequencies up to 1.5 THz. In three-dimensional beams the peak amplitudes of higher harmonics can be bigger than in two-dimensional beams, but the ratios of these peak values to the maximum values of the focused first harmonic are smaller than in two-dimensional beams.

Compact mid-infrared dual-comb spectrometer over 3-4μm via intra-pulse difference frequency generation in LiNbO_(3) waveguides

The mid-infrared optical frequency comb is a powerful tool for gas sensing.In this study,we demonstrate a simple midinfrared dual-comb spectrometer covering 3±4μm in Li Nb O_(3)waveguides.Based on a low-power fiber laser system,the mid-infrared comb is achieved via intra-pulse difference frequency generation in the Li Nb O_(3)waveguide.We construct pre-chirp management before supercontinuum generation to control spatiotemporal alignment for pump and signal pulses.The supercontinuum is directly coupled into a chirped periodically poled Li Nb O_(3)waveguide for the 3±4μm idler generation.A mid-infrared dual-comb spectrometer based on this approach provides a 100 MHz resolution over25 THz coverage.To evaluate the applicability for spectroscopy,we measure the methane spectrum using the dualcomb spectrometer.The measured results are consistent with the HITRAN database,in which the root mean square of the residual is 3.2%.This proposed method is expected to develop integrated and robust mid-infrared dual-comb spectrometers on chip for sensing.

Noise-like pulse generation from a thulium-doped fiber laser using nonlinear polarization rotation with different net anomalous dispersion

A mode-locked thulium-doped fiber laser(TDFL) based on nonlinear polarization rotation(NPR) with different net anomalous dispersion is demonstrated. When the cavity dispersion is-1.425 ps^2, the noise-like(NL) pulse with coherence spike width of 406 fs and pulse energy of 12.342 nJ is generated at a center wavelength of 2003.2 nm with 3 dB spectral bandwidth of 23.20 nm. In the experimental period of 400 min, the 3 dB spectral bandwidth variation, the output power fluctuation, and the central wavelength shift are less than 0.06 nm, 0.04 d B, and0.4 nm, respectively, indicating that the NPR-based TDFL operating in the NL regime holds good long-term stability.

我国人才分布现状及主要影响因素

根据我国现行人才标准,以2010年全国第六次人口普查和2011年全国统计年鉴为依据,以省级行政区域为单位,统计2010年本科及以上学历人口的密度分布,发现当代全国人才分布极不均衡,东部地区高于西部地区,京、沪、津、苏、浙、陕、卾、黑、吉、辽等人才密度高.国家政策、经济社会发展水平、高等院校布局及自然环境等因素共同作用,促使高学历人口向大中城市、发达地区集聚.

杜威哲学的现代意义

评价杜威实用主义的现代意义,需要在马克思在哲学上的革命变更和西方哲学由近代到现代的转型的大背景下考察杜威哲学的根本意义及其与西方哲学发展趋势及马克思主义哲学的关系。本文认为杜威哲学的根本意义是对现实生活和实践的强调;杜威的哲学改造适应了西方哲学现代变革的潮流;杜威哲学与马克思的哲学有着原则区别,但在超越近代哲学的局限性、体现现代哲学的发展趋势上二者殊途同归。。

危机时刻的文学批评——以钱锺书、奥尔巴赫、巴赫金为对照的阐释

钱锺书抗战时期撰写的《谈艺录》,与奥尔巴赫的《摹仿论:西方文学中现实的再现》和巴赫金的《拉伯雷和他的世界》都是在民族的危机时刻写就的,三者可以被视为世界比较文学事件作对照性阅读。这三本书无论就体例、风格、方法学以及世界观而言都极为不同。但它们既成于战时,作者面对文明崩解以及个体生命的困顿,都有不能已于言者的反思,而他们所展现的宏大历史视野、浑厚的学术知识、锐利的批评洞见,俨然为“发愤著书”平添现代意涵。有关这三位学者及其论述的阐释所在多有,但最值得注意的,与其说是个别著作的深入解析,不如说是面对“危机时刻”,钱锺书、奥尔巴赫、巴赫金为何及如何从文学入手,寻求因应之道,他们在批评文字里所投注的情感以及赖以发挥的意象。由此可以考察除了历史因缘外,三部经典为我们带来的方法学启示和与此时此地的文化政治的关联。

当代研究生价值观现状及其在人口学变量上的差异分析

为了解当代硕士研究生的价值观取向,采用中国人价值观问卷(Chinese Value Questionnaire,CVQ)调查河南省6个城市8所高校的1112名硕士研究生。结果发现,当代研究生价值观八个维度上的得分在3.37~4.78之间,认同度由强到弱依次为才能务实、品格自律、人伦情感、公共利益、守法从众、家庭本位、金钱权力、名望成就;当代研究生价值观在性别、家庭所在地、硕士类型、所读院校、读研之前的学历、家庭结构等人口学变量上差异显著,在是否为独生子女、年级上差异不显著。

试论当代仿古玉与传统仿古玉的区别

仿古玉是中国古代玉器发展到一定阶段的特殊产物,历史上以宋代、清代为代表。当代仿古玉在现代科技水平和时代风格的影响下,既继承传统,相比传统又存在着较大区别。文章以材料使用、工艺特点以及艺术风格为主要研究对象,对传统与当代仿古玉的区别进行了论述与总结,并对当代仿古玉的发展方向提出思考和建议。