Ultraviolet-light generation in nitrogen-doped silica fiber

Nonlinear light transformations were observed in a nitrogen-doped silica fiber pumped with a Nd:YAG laser (lambda=1.06 microm) . Light generation in the spectral range 355-430nm was obtained with an efficiency of up to 2x10(-4) . The UV light was found to be the result of third-harmonic generation, stimulated Raman scattering of the third harmonic, and third-harmonic generation from the Stokes components of the pump light. Lasing based on the color centers of nitrogen-doped silica was observed in the range 380-430nm.     

Coherent control of high-order harmonics generated with intense femtosecond laser pulses

Experimental results and theoretical analysis on the coherent control of high-order harmonics with chirped femtosecond laser pulses are presented. The coherent control of high-order harmonic generation resulted in sharp harmonic spectra by compensating for induced harmonic chirp with the control of applied laser chirp and it was found to be crucial also in producing sharp and bright harmonics.Received: 18 November 2002, Published online: 8 July 2003PACS: 42.65.Ky Frequency conversion; harmonic generation, including higher-order harmonic generation - 32.80.-t Photon interactions with atoms - 42.65.Re Ultrafast processes; optical pulse generation and pulse compression     

Noncritically phase-matched second-harmonic generation in cesium lithium borate

Efficient generation of 236-nm light was demonstrated by use of noncritically phase-matched second-harmonic generation in cesium lithium borate. Noncritical phase matching provided approximately 20x the nonlinear drive for second-harmonic generation than beta-barium borate for 236-nm generation. The 236-nm wavelength is the fourth harmonic of a 946-nm Nd:YAG laser. Phase matching was accomplished at a crystal temperature of -15 degrees C.     

Continuous-wave frequency tripling and quadrupling by simultaneous three-wave mixings in periodically poled crystals: application to a two-step 1.19-10.71-microm frequency bridge

We observed cw third-harmonic generation in a periodically poled LiNbO(3) crystal by cascading optimally phase-matched second-harmonic and sum-frequency generation. Other processes, such as fourth-harmonic generation, are allowed by the flexibility of quasi-phase matching. We demonstrate a divide-by-nine (1.19- 10.71-microm) frequency chain that uses only two lasers.     

Dual-Frequency Generation in Quantum Cascade Lasers of the 8-μm Spectral Range

Results of an investigation of quantum cascade lasers of the 8-μm spectral range generating dual-frequency radiation at room temperature are presented. The dependences of radiation intensity for two lines of laser generation obtained as a result of investigation of the generation spectra revealed the presence of saturation and decay of the long-wavelength line of generation and linear growth of the intensity of the short-wavelength one. Based on analysis of the obtained data, a mechanism of the dual-frequency generation in the studied QCL samples is proposed Generation.     

Widely tunable terahertz-wave generation using an N-benzyl-2-methyl-4-nitroaniline crystal

Widely tunable terahertz (THz)-wave generation using difference frequency generation (DFG) in an organic N-benzyl-2-methyl-4-nitroaniline (BNA) crystal was demonstrated. To our knowledge, this is the first report of THz-wave generation by BNA DFG. Large, high-quality single crystals of BNA (phi 8 mm x 30 mm) were grown using the vertical Bridgman method. The nonlinear optical (NLO) coefficient d(33) of the BNA crystal is approximately 234 pm/V, which is the largest value reported for any yellow NLO material. The collinear phase-matching condition of the type-0 configuration is satisfied using a 0.7-1 microm band pump wavelength. We generated THz waves using an organic BNA crystal; the generation range is 0.1-15 THz.     

Verification of numerical simulation method for entropy generation of radiation heat transfer in semitransparent medium

The numerical simulation method of radiative entropy generation in participating media presented by Caldas and Semiao [Entropy generation through radiative transfer in participating media: analysis and numerical computation. JQSRT 2005;96:423-37] is extended to analyze the radiative entropy generation in the enclosures filled with semitransparent media. A discrete ordinates method is used to solve radiative transfer equation and radiative entropy generation. Two different examples are employed to verify the numerical simulation method of radiative entropy generation in the enclosure. Numerical results of dimensionless radiative entropy generation of enclosure are identical to that of entire thermodynamics analysis for the enclosure system. This numerical simulation method can be used in the entropy generation analysis of high-temperature systems such as boilers and furnaces, in which radiation is the dominant mode of heat transfer.     

Infrared laser generation by cascaded difference frequency generation combined with optical parametric oscillator

Optical Review - We introduce an infrared laser generation scheme by cascaded difference frequency generation (CDFG) combined with optical parametric oscillator (OPO). An inventive infrared laser...     

Experimental verification of the effects of optical wavelength on the amplitude of laser generated ultrasound in polymer-matrix composites

Laser ultrasound is now integrated into the manufacturing process of some of the most modern aircraft for the inspection of composite parts. Unfortunately, for some material and process combinations, laser-ultrasound suffers from a lack of sensitivity. In laser-ultrasound generation, optical penetration depth plays a very important role. It was shown that changing the generation wavelength from the 10.6 microm of the CO2 laser to the 3-4 microm range can significantly improve generation efficiency. In this paper, ultrasonic displacements are compared to measurements of optical penetration depth in different polymer-matrix composites. Ultrasonic waves were generated using an optical parametric oscillator operating in the 3.0-3.5 microm band and optical penetration depth spectra were evaluated using quantitative photoacoustic spectroscopy. The relative amplitudes of the generated ultrasonic waves track closely the optical penetration depth spectra. These results experimentally demonstrate the importance of optical penetration in the laser-ultrasound generation process.     

磷化镓高功率太赫兹共线差频源的研究

在众多实现太赫兹辐射的方法中, 非线性光学共线差频能够实现高功率、宽波段、连续可调谐的太赫兹波辐射. 理论分析表明, 各向同性磷化镓晶体, 在1064 nm附近波长激光共线差频下具有毫米量级的相干长度, 能够满足高功率宽波段的太赫兹辐射条件.实验证明, 磷化镓晶体共线差频实现高功率宽波段的太赫兹光辐射, 其太赫兹光波长调谐范围为95.9–773.4 μm (0.39–3.13 THz), 最高峰值功率7 W位于频率2.0 THz处.该实验结果与理论计算基本保持一致. 关键词： 太赫兹源 磷化镓 共线差频     

Milliwatt-level mid-infrared (10.5-16.5 μm) difference frequency generation with a femtosecond dual-signal-wavelength optical parametric oscillator

We demonstrate the generation of mid-infrared radiation using a femtosecond dual-signal-wavelength optical parametric oscillator and difference frequency generation in an extracavity gallium selenide or silver gallium diselenide crystal. This system generates up to 4.3?mW of average mid-infrared power. Its spectra can be tuned to between 10.5?μm and 16.5?μm wavelength (952 cm^-1-606 cm^-1) with more than 50 cm^-1 spectral bandwidth. We demonstrate that the power and spectra of this system are temporally very stable.     

High field phenomena in thin plasma nitrided SiO2 films

The effects of high field tunnel electron injection on the electrical properties of Al - thin plasma nitrided SiO₂ films - Si (p-type) structures are studied. Under high field injection, it has been observed that electron trapping, positive charge generation near the Si-SiO₂ interface (slow states) and fast state generation at the Si-SiO₂ interface have taken place. After high temperature N₂ annealing, the nitridation induced electron trap density is considerably decreased. Furthermore, under high field injection the generation rate of both the slow states and the interface states and consequently, the degradation rate of the nitrided oxide films have been also decreased after annealing.     

利用各向同性半导体晶体差频产生可调谐THz辐射的理论研究

理论研究了利用剩余射线带色散补偿相位匹配原理，在Ⅲ-Ⅴ族和Ⅱ-Ⅳ族光学各向同性的半导体非线性晶体中差频产生可调谐THz波的可行性问题.根据这些半导体材料的色散特性，并以近简并点双共振KTP-OPO的可调谐相干双波长输出作为差频抽运源，对它们的相位匹配能力、差频增益特性、品质因数以及差频过程中的相干长度进行了理论分析和计算，确定了ZnTe晶体是在共线相位匹配情况下较为理想的THz波差频晶体，而InP晶体则更适合用于非共线相位匹配情况. 关键词： 非线性光学 THz辐射 差频 各向同性半导体晶体     

铅烷发生反应的非新生态氢机理

文章采用流动注射氢化物发生-石英管电热原子化-原子吸收光谱法检测实验系统,检测铅烷发生反应中反应物的量和产生的铅烷的量之间的关系,以阐明K₂Cr₂O₇体系铅烷发生的机理。实验结果表明,反应体系中酸首先与NaOH发生中和反应,随后过量的酸参与KBH₄和K₂Cr₂O₇的氧化还原反应(消耗的酸与KBH₄摩尔比为一常数9.95±0.42)。铅烷发生反应与氧化还原反应同步发生,且产率随酸量的增加而增加的实验结果表明：铅烷发生反应是由氧化剂和硼氢化钾之间的氧化还原反应所诱导的。至此,证实ⅣA族Ge,Sn,Pb的氢化物发生反应都是非新生态氢机理。     

Generation of continuous variable Einstein-Podolsky-Rosen entanglement via the Kerr nonlinearity in an optical fiber

We report on the generation of a continuous variable Einstein-Podolsky-Rosen (EPR) entanglement using an optical fiber interferometer. The Kerr nonlinearity in the fiber is exploited for the generation of two independent squeezed beams. These interfere at a beam splitter and EPR entanglement is obtained between the output beams. The correlation of the amplitude (phase) quadratures is measured to be 4.0+/-0.2 (4.0+/-0.4) dB below the quantum noise limit. The sum criterion for these squeezing variances 0.80+/-0.03<2 verifies the nonseparability of the state. The product of the inferred uncertainties for one beam (0.64+/-0.08) is well below the EPR limit of unity.     

Evidence of high harmonics from echo-enabled harmonic generation for seeding x-ray free electron lasers

Echo-enabled harmonic generation free electron lasers hold great promise for the generation of fully coherent radiation in x-ray wavelengths. Here we report the first evidence of high harmonics from the echo-enabled harmonic generation technique in the realistic scenario where the laser energy modulation is comparable to the beam slice energy spread. In this experiment, coherent radiation at the seventh harmonic of the second seed laser is generated when the energy modulation amplitude is about 2-3 times the slice energy spread. The experiment confirms the underlying physics of echo-enabled harmonic generation and may have a strong impact on emerging seeded x-ray free electron lasers that are capable of generating laserlike x rays which will advance many areas of science.     

Ten gigabits per second 16-level quadrature amplitude modulated millimeter-wave carrier generation using dual-drive Mach-Zehnder modulators incorporated photonic-vector modulator

A novel photonic-vector modulator architecture for the generation of 16 quadrature amplitude modulation (16 QAM) millimeter-wave carriers using dual-drive Mach-Zehnder modulators is proposed. Experimental generation of 5 Gbits/s 4 amplitude shift-keying (4 ASK) and 10 Gbits/s 16 QAM modulated 42 GHz carriers is reported. The multilevel modulated millimeter-wave signals are demodulated using an electrical receiver and its error-vector magnitude (EVM) estimated from the measurements, obtaining EVMs of -21.04 and -18.33 dB for 4 ASK and 16 QAM modulation formats, respectively.     

竹炭分离富集铋及氢化物发生原子荧光和等离子体质谱法测定

以竹炭为固相萃取材料,建立了顺序注射在线微填充柱固相萃取分离富集痕量铋的方法,吸附在微填充柱上的铋(络合物)可用稀硝酸溶液(2.5 mol·L-1)洗脱回收.洗脱液与硼氢化钠溶液混合进行氢化物发生(HG)反应,氢化物经气液分离后与原子荧光(AFS)联用,或直接将洗脱液引入电感耦合等离子体质谱(ICP-MS),实现了对生...     

Scales of mass generation for quarks, leptons, and majorana neutrinos

We study 2-->n inelastic fermion-(anti)fermion scattering into multiple longitudinal weak gauge bosons and derive universal upper bounds on the scales of fermion mass generation by imposing unitarity of the S matrix. We place new upper limits on the scales of fermion mass generation, independent of the electroweak symmetry breaking scale. Strikingly, we find that the strongest 2-->n limits fall in a narrow range, 3-170 TeV (with n=2-24), depending on the observed fermion masses.     

CdSeS合金结构量子点的多激子俄歇复合过程

多激子效应通常是指吸收单个光子产生多个激子的过程,该效应不仅可以为研究基于量子点的太阳能电池开拓新思路,还可以为提高太阳能电池的光电转换效率提供新方法.但是,超快多激子产生和复合机制尚不明确.这里以CdSeS合金结构量子点为研究对象,研究了其多激子生成和复合动力学.稳态吸收光谱显示, 510, 468和430 nm附近的稳态吸收峰,分别对应1S_(3/2)(h)-1S(e)(或1S), 2S_(3/2)(h)-1S(e)(或2S)和1P_P(3/2)(h)-1P(e)(或1P)激子的吸收带.通过飞秒时间分辨瞬态吸收光谱和纳秒时间分辨荧光光谱两种时间分辨光谱技术对CdSeS合金结构量子点的超快动力学进行了探究,结果显示, 1S激子的双激子复合时间大概是80 ps,这一时间比传统量子点的双激子复合时间(小于50 ps)延长了近一倍,结合最近发展的超快界面电荷分离技术,在激子湮灭之前将其利用起来,这一时间的延长将有很大的应用前景;其中,在2S和1P激子中除上述双激子复合外,还存在一个通过声子耦合路径的空穴弛豫过程,时间大概是5—6 ps.最后,利用纳秒时间分辨荧光光谱得到该样品体系单激子复合的时间约为200 ns.