超短光脉冲作用下的二能级原子

考虑到光场的振幅随时间分布的影响时,我们重新研究了光场与二能级原子相互作用的跃迁几率问题。在强光信号作用下,经过一定的数学代换后,上能级几率的求解可归结为类希尔方程求解;在弱光信号作用下,利用转动波近似(RWA),给出了二能级原子跃迁几率的解析表达式,并讨论了几种典型脉冲光场的分布。     

Time and distance constraints on accelerating cosmological models

The absence of guidance from fundamental physics about the mechanism behind cosmic acceleration has given rise to a number of alternative cosmological scenarios. These are based either on modifications of general relativistic gravitation theory on large scales or on the existence of new fields in Nature. In this Letter we investigate the observational viability of some accelerating cosmological models in light of 32 age measurements of passively evolving galaxies as a function of redshift and recent estimates of the product of the cosmic microwave background acoustic scale and the baryonic acoustic oscillation peak scale. By using information-criteria model selection, we select the best-fit models and rank the alternative scenarios. We show that some of these models may provide a better fit to the data than does the current standard cosmological constant dominated (ΛCDM) model.     

Particle sizing by time-resolved Mie calculations—A numerical study

If a small transparent particle is illuminated with a short laser pulse, the signals of the individual scattering light orders appear temporally successively. Since to each scattered light order belongs a specific optical path through the particle, the particle size can be determined from the time difference between the detected scattered light signals. For the case of a detector position within the backscatter region, which especially is important in measuring practice, the time difference between the specular reflection signal and the signal after a single internal reflection (refraction of second order) must to be evaluated. In the numerical simulation we generate the concerned scattered light signals by using time-resolved Mie calculations and in this paper we present the geometrical models, which permit a correct interpretation of the temporal behavior of these pulse-induced scattered light signals.     

343 nm飞秒激光制备微孔阵列以增强聚氨酯合成革透湿性

为了提高聚氨酯(PU)合成革透湿性,分别使用343 nm飞秒激光和作为对比的1030 nm飞秒激光及1064 nm纳秒激光制备微孔阵列。采用扫描电镜(SEM)和3D激光扫描显微镜对比研究了微孔形貌。结果表明,343 nm飞秒激光可以制备出效果最佳的微孔。此外,分析了3种激光与PU涂层的作用机理,揭示了343 nm飞秒激光合成革微钻孔过程仅表现为光化学烧蚀,光化学和光热烧蚀同时发生于1030 nm飞秒激光钻孔过程,而1064 nm纳秒激光只显示了光热烧蚀。激光合成革表面钻孔后,测量其透湿性和抗张力。结果显示: 微孔密度越大,皮革透湿性(WVP)越大而抗张力越低,脉冲重叠的增加会导致WVP的增加和抗张力的下降;同时,随着脉冲重叠从91.7%降到50%,微孔直径从45 μm降低到30 μm,而微孔锥度从0.7°增加到12.1°;当脉冲重叠率为91.7%,微孔密度为2550/cm²时,最大的WVP增长率为306%。     

基于自衍射效应的自参考光谱干涉方法的研究

研究一种基于非线性透明光学介质中的自衍射和自参考光谱干涉的新方法来进行飞秒激光脉冲测量. 实验中, 基于此新方法设计一种简单装置, 对800 nm 中心波长, 约40 fs 近无啁啾飞秒激光脉冲进行测量, 并与自参考光谱相干电场重建法测量结果进行比较, 得到了一致的结果. 此新方法与相应的装置结构简单, 可以对深紫外到中红外光谱范围的飞秒脉冲进行测量. 关键词： 飞秒激光脉冲 自参考光谱干涉 自衍射 脉冲测量     

Nonlinear polarization rotation-induced pulse shaping in a stretched-pulse ytterbium-doped fiber laser

We report on controllable pulse shaping in a Yb-doped stretched-pulse fiber laser followed by a high-power chirped pulse amplifier. We demonstrate that the pulses after an extra-cavity grating pair change their intensity profile from Lorentz to Gaussian and then to sech2 shapes by adjusting the intra-cavity polarization through a quarter-wave plate inside the fiber laser cavity. The laser pulses with different pulse shapes exhibit pulse-to-pulse amplitude fluctuation of -- 1.02%, while the sech2-shaped pulse train is provided with a more stable free-running repetition rate as a result of the stronger self-phase modulation in the fiber laser cavity than Lorentz- and Gaussian-shaped pulse trains.     

微型同轴脉管制冷机最低制冷温度影响因素的实验研究

本文对微型同轴脉管制冷机最低制冷温度的影响因素进行了实验研究。试验结果表明:在其他运行参数不变的情况下,随着氢浓度的逐渐减少,最低制冷温度也逐渐降低,当氢的摩尔浓度小于20％时,其最低制冷温度和纯氦相差不大。不同的氢氦配比下,该脉管制冷机的最佳运转频率为16.7 Hz。随着系统平均压力的提高,最低制冷温度也随之下降,但变化幅度越来越小。     

光子计数技术及其在弱光计量中的应用

从光子计数原理出发,介绍光子计数系统的构成,分析光电倍增管的脉冲幅度分布,并叙述光子计数技术在弱光计量中的实际应用。     

Amplified low-repetition-rate fs pulsewidth measuring and DLA caused pulse broadening

Amplified low-repetition-rate fs pulse is generated with dye laser amplifier(DLA). The pulsewidth is measured with a computer-aided autocorrelator and the fs pulsewidth broadening caused by the dispersion of the DLA is analyzed. Furthermore, the autocorrelator introduced in this paper could be used as a low scanning autocorrelator to measure high-repetition-rate pulsewidth.     

The optimum bandwidth of chirp signals in ultrasonic applications

A new formula for the pulse-compression ratio achievable with linear FM pulses (chirp signals) in ultrasonic applications is derived. The calculations take into account the frequently omitted effects of the transfer function of an ultrasonic transducer. For a squared-cosine type transducer spectrum, the optimum chirp signal bandwidth is 1.14 times the 6 dB bandwidth of the transducer. The pulse-compression ratio is 2.24 dB lower than in the case of an ideal broadband transducer. Measurements show a close agreement with the presented theory.