修饰态布居的选择性激发对无反转激光的作用

以三能级V型系统为例研究修饰态布居的选择性激发对无反转激光增益的作用. 当非 相干驱动场的频谱宽度远小于驱动场产生的修饰态能级的间距时，非相干驱动场只将一个修 饰态的布居抽运至激发态. 借助原子的衰减通道，系统中形成单向布居转移通道，从而建立 修饰态布居的选择性激发. 利用修饰态布居的选择性激发，可以摆脱裸态共振无反转激光的 三个限制: (1) 不再要求辅助的低频驱动跃迁比高频激光跃迁具有更高的衰减速率；(2) 显 著降低非相干激发速率的阈值；(3) 无反转激光的线性增益不再反比于相干驱动场的强 关键词： 修饰态布居的选择性激发 无反转激光增益 原子衰减速率 非相干激发阈值速率     

利用基频与倍频脉冲控制扩展“ladder”式跃迁

利用含时量子波包动力学方法研究了两束基频与倍频脉冲控制下的扩展"ladder"式跃迁.通过基频与2倍频脉冲控制分子布居从|0,0态跃迁至|5,0与|5,2态;基频与3倍频脉冲控制分子布居从|0,0态跃迁至|5,3?与|6,2态.计算结果表明,利用两束基频与倍频脉冲,通过"ladder"式跃迁,可以得到近100%的布居跃迁概率.两束脉冲间的相对相位角影响分子的布居分布.当脉冲频率比为1:2时,布居以π为周期变化;当脉冲频率比为1:3时,布居以2π为周期变化.     

超短脉冲激光在硝基苯胺分子材料中的非共振传播

通过严格求解麦克斯韦-布洛赫方程,研究了超短脉冲激光与硝基苯胺分子材料的非共振相互作用.研究结果表明,当脉冲激光在该分子介质中以电荷转移态的激发能的二分之一非共振传播时,脉冲激光频谱中明显地出现了二次谐波成分,显示了该分子具有较强的双光子吸收性质.     

飞秒激光参数对非绝热耦合分子态布居的影响

利用含时波包法研究强飞秒泵浦-探测激光场中激光脉宽、波长和场强对非绝热耦合NaI分子各态布居的影响.波包在势能面上做周期性运动,周期约为1 000 fs.延时为200 fs时,波包第一次到达交叉区域分裂成两部分.波包在交叉区域的分裂情况影响各态布居.脉宽增长,NaI分子的激发概率增大,而解离概率减小.泵浦波长为共振波长318 nm时,激发概率最大.泵浦波长增长,NaI分子的解离概率减小.泵浦场强增大,激发概率增大,但解离概率不变.探测激光波长和场强不影响NaI分子各态布居分布.调节激光场参数可实现对波包运动的控制从而控制态布居的选择性分布.研究结果为实验上实现分子的光控制过程提供参考.     

二能级原子各态几率随脉冲面积变化的2π准周期衰减振荡

二能级原子各态几率随脉冲面积的变化过程将呈现2π准周期衰减振荡,这一结果可为研究任意强激光脉冲作用下的原子行为提供很好的普遍演变图象.     

利用多光子跃迁控制基态HF分子布居转移

采用波包动力学方法研究了HF分子基电子态的多光子跃迁. 激光场由两束频率比为1:2的重合红外脉冲构成. 态|0,0>作为初始态, 态|4,0>与态|4,2>分别作为目标态. 计算结果表明, 通过选取不同的共振频率, 可以控制布居跃迁至不同的目标态. 两束脉冲间的初相位差可以控制布居转移概率. 当初相位差为π/2的偶数倍时, 布居转移概率为最大值. 当初相位差为π/2的奇数倍时, 布居转移概率为最小值. 初相位差对于态|4,0>的布居影响大于态|4,2>. 关键词： 多光子跃迁 初相位 布居转移 波包     

利用蝴蝶型纳米结构下的极化门方案输出单个阿秒脉冲

理论研究了在蝴蝶型纳米结构下运用多周期极化门方案驱动He原子输出高次谐波以及阿秒脉冲的特点.结果表明,由于纳米结构表面的等离子共振增强现象,谐波截止能量得到延伸.同时,由于激光场呈现空间非均匀性,长量子路径对谐波的贡献被减弱.并且,在极化门控制下,谐波平台区的贡献只来源于单一的谐波辐射能量峰,进而形成一个147 eV的超长平台区.最后,通过叠加平台区的谐波,可获得一个持续时间在30 as的超短脉冲.     

利用蝴蝶型纳米结构下的极化门方案输出单个阿秒脉冲

理论研究了在蝴蝶型纳米结构下运用多周期极化门方案驱动He原子输出高次谐波以及阿秒脉冲的特点.结果表明,由于纳米结构表面的等离子共振增强现象,谐波截止能量得到延伸.同时,由于激光场呈现空间非均匀性,长量子路径对谐波的贡献被减弱.并且,在极化门控制下,谐波平台区的贡献只来源于单一的谐波辐射能量峰,进而形成一个147 eV的超长平台区.最后,通过叠加平台区的谐波,可获得一个持续时间在30 as的超短脉冲.     

利用蝴蝶型纳米结构下的极化门方案输出单个阿秒脉冲

理论研究了在蝴蝶型纳米结构下运用多周期极化门方案驱动He原子输出高次谐波以及阿秒脉冲的特点.结果表明,由于纳米结构表面的等离子共振增强现象,谐波截止能量得到延伸.同时,由于激光场呈现空间非均匀性,长量子路径对谐波的贡献被减弱.并且,在极化门控制下,谐波平台区的贡献只来源于单一的谐波辐射能量峰,进而形成一个147 eV的超长平台区.最后,通过叠加平台区的谐波,可获得一个持续时间在30 as的超短脉冲.     

HF和DF分子双光子布居转移过程中的同位素效应

通过求解含时薛定谔方程,研究了XF(X=H,D)分子体系双光子共振条件下布居转移过程中的同位素效应.对于这两个分子体系,基电子态上的振动能级v=0和v=2被考虑成初始态和目标态.详细讨论了激光场峰值强度和脉冲持续时间对布居转移过程的影响.脉冲持续时间需要长于860 fs才能保证DF分子体系可以获得较为显著的布居转移几率(大于80%),而对于HF分子体系,该参数只需长于460 fs.与HF分子体系相比,中间态v=1和较高的v=3振动态会对DF分子体系的双光子共振布居转移过程产生更重要的影响.     

Guided-Wave Two-Dimensional Acousto-Optic Scanner Using Proton-Exchanged Lithium Niobate Waveguide

Two-dimensional scanning of a 0.6328 mum guided-light beam has been realized using noncolinear acousto-optic (AO) coplanar Bragg diffraction together with colinear AO guided-mode to substrate radiation-mode conversion in a Z-cut Xpropagation LiNbO3 proton-exchanged (PE) waveguide. The two surface acoustic (SAW) waves utilized are at the center frequencies of 500 and 200 MHz, propagating in the Y and X axes, respectively. Two-dimensional scanning of approximately 720 resolvable light beam spots, namely, 18 40 (horizontal vertical) scanning, has been demonstrated using a light beam of 1.0 mm aperture. The total number of resolvable beam spots can be greatly increased from 720 by simply utilizing SAW transducers of larger bandwidth and a light beam of greater aperture. It should also be possible to significantly increase the diffraction efficiency from 3 % by optimizing the parameters of the PE waveguide and the SAWs.     

Femtosecond Transform-Limited Pulse Generation by Compensating for the Linear Chirp of SPM Spectra in Dispersion Shifted Fibers

A simple technique of pulse compression, based on the linear chirp compensation of self-phase modulation (SPM) spectra in dispersion shifted fibers, is demonstrated. The optimization procedure is carried out, for a short span of a single-mode fiber, using a parabolic law, which describes the behavior of the squared output pulse width versus the pump peak power in the case of Gaussian pulses. The experimental results give a minimum pulse duration of 233 fs, which is in good agreement with the model. Shorter and coherent pulses, down to 90 fs, have been obtained by inserting an interference filter at the optical output.     

Effect ofγ-radiation on the spectral luminescence characteristics of impure cadmium tungstate crystals

Results of a study of the effect of γ-radiation on the spectral luminescence properties of cadmium tungstate crystals doped with silver, bismuth, and molybdenum cations are presented. Spectral characteristics of the nondnnnoped crystals are briefly described. Absorption and photo and X-ray luminescence spectra of the crystals taken before and after exposure to γ-radiation (5.5·10⁴ Gy) are compared. It is found that the spectral characteristics of the crystals doped with silver, bismuth, and molybdenum cations do not change markedly after the exposure. The relation between the type of impurity-induced defects, individual characteristics of the impurity cations, and the character of the effect of γ-radiation on the spectral luminescence properties of impure crystals is analyzed (preliminarily). Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 64, No. 1, pp. 55–60, January–February, 1997.     

Sorting of bending magnets for the SSRF booster

The Shanghai Synchrotron Radiation Facility(SSRF)booster ring,a full energy injector for the storage ring,is deigned to accelerate the electron beam energy from 150MeV to 3.5GeV that demands high extraction efficiency at the extraction energy with low beam loss rate when electrons are ramping.Closed orbit distortion(COD)caused by bending magnet field uniformity errors which affects the machine performance harmfully could be effectively reduced by bending magnet location sorting.Considering the affections of random errors in measurement,both ideal sorting and realistic sorting are studied based on measured bending magnet field uniformity errors and one reasonable combination of bending magnets which can reduce the horizontal COD by a factor of 5is given as the final installation sequence of the booster bending magnets in this paper.     

Measurement of nonlinear coefficient of optical fiber based on small chirped soliton transmission

We measure the waveform and phase curves of short optical pulses before and after transmission over different lengths of fibers by use of the pulse analyzer with the frequency-resolved optical gating (FROG),and numerically simulate pulse evolution under the experimental conditions.The nonlinear coefficient of the fiber is given by comparing the experimental results with the numerical ones.Difference between the experiment and numerical simulation is analyzed.     

Resonance scattering of canonical elastic shells in absorbing fluid medium

Resonance scattering of elastic spherical shell and cylindrical shell while the surrounding fluid medium has absorption is studied. The normal mode solution derived using exact elastic theory and the separation of variables is still applicable. However, the scattering form function has to be modified for the absorbing medium, otherwise the unreasonable result would be obtained. The backscattering form function in the absorbing medium is redefined, and the form function of elastic spherical and cylindrical shell with vacuum or solid matter filled is calculated in various absorption conditions. The results show that the absorption of surrounding fluid leads to notable attenuation of the coincidence resonances in the mid-frequency, but it has a little influence on the low-frequency resonance scattering induced by the filler inside the shell.     

Single-beam self-referenced phase-sensitive surface plasmon resonance sensor with high detection resolution

A versatile and low-cost single-beam self-referenced phase-sensitive surface plasmon resonance(SPR)sensing system with ultra-high resolution performance is presented.The system exhibits a root-mean-square phase fluctuation of ±0.0028.over a period of 45 min.i.e.a resolution of±5.2×10-9 refractive index units.The enhanced performance has been achieved through the incorporation of three design elements:a true single-beam configuration enabling complete self-referencing so that only the phase change associated with SPR gets detected,a differential measurement scheme to eliminate spurious signals not related to the sensor response,and the elimination of retardation drifts by incorporating temperature stabilization in the liquid crystal phase modulato .Our design should bring the detection sensitivity of non-labeling SPR biosensing closer to that achievable by conventional fluorescence-based techniques.     

Influences of SiO2 protective layers and annealing on the laser-induced damage threshold of Ta2O5 films

Ta2O5 films are prepared on BK7 substrates with conventional electron beam evaporation deposition.The effects of SiO2 protective layers and annealing on the laser-induced damage threshold (LIDT) of the films are investigated.The results show that SiO2 protective layers exert little influence on the electric field intensity(EFI)distribution,microstructure and microdefect density but increase the absorption slightly.Annealing iS effective on decreasing the microdefect density and the absorption of the films.Both SiO2 protective layers and annealing are beneficial to the damage resistance of the films and the latter is more effective to improve the LIDT.Moreover,the maximal LIDT of Ta2O5 films is achieved by the combination of SiO2 protective layers and annealing.     

A stereo matching algorithm using multi-peak candidate matches and geometric constraints

Gray cross correlation matching technique is adopted to extract candidate matches with gray cross correla- tion coefficients less than some certain range of maximal correlation coefficient called multi-peak candidate matches. Multi-peak candidates are extracted corresponding to three closest feature points at first. The corresponding multi-peak candidate matches are used to construct the model polygon. Correspondence is determined based on the local geometric relations between the three feature points and the multi-peak candidates. The disparity test and the global consistency checkout are applied to eliminate the remaining ambiguous matches that are not removed by the local geometric relational test. Experimental results show that the proposed algorithm is feasible and accurate.