Power limits of a YAG:Er laser

The power limits of a repetitively Xe-flashlamp pumped YAG: Er laser with 40% at % dopant concentration, have been determined. The limits result from thermal effects. These limits as well as the threshold can be reduced by selective pumping of the ⁴I upper laser level.     

A long-pulse xenon ion laser as a pumping source for dye lasers

A simple xenon ion laser that is either sealed or has a gas flow mode is described. The laser delivered long pulses ( 15 μs) of almost 1 kW peak power. It has been used to pump a dye laser employing the same configuration as cw dye lasers. The system is inexpensive and can be mode-locked, enabling it to yield ultrashort pulses comparable in duration to those delivered by cw argon laser-pumped dye lasers but with much higher peak powers.     

双端抽运的掺Yb^3＋双包层光纤激光器中合作发光效应

合作发光效应、热效应以及非线性效应限制了单根掺Yb^3＋光纤激光器输出功率的进一步提高。根据能级间的吸收与辐射，分析了掺Yb^3＋双包层光纤中的合作发光效应，分析表明，随着Yb^3＋的掺杂浓度的增大，光纤中合作发光增强，抽运光越强，合作发光也越强。实验研究了输出功率61．6W，斜率效率为55％的双端抽运的掺Yb^3＋双包层光纤激光器的合作发光效应，研究表明，随着抽运光功率的增大，合作发光强度增强，掺杂浓度越大，光纤中合作发光效应也越强。这一结果有利于进一步提高掺Yb^3＋光纤激光器的效率。     

双光子抽运随机激光器中辐射光能量的演化

基于非相干反馈随机激光器的扩散方程理论，将扩散方程中的增益项改写为饱和形式，并利用有限差分方法，研究了双光子抽运随机激光器中辐射光能量随时间演化特性.对扩散方程的数值求解给出了系统辐射光能量由自发辐射开始，经历小信号增益状态得到放大，再到由于增益饱和形成稳态输出的整个演化过程.表明介质的无序导致了在较低能量情况下也能获得饱和增益这样的非线性效应.结果为研究获得双光子抽运随机激光器的稳态输出提供了理论依据. 关键词： 随机激光器 双光子抽运 饱和效应 无序介质中的光学效应     

Numerical investigation of spin-torque using the Heisenberg model

We present numerical calculations of the spin transfer torque resulting in current-induced domain wall motion. Rather than the conventional micromagnetic finite difference or finite element method, we use an atomistic/classical Heisenberg spin model approach, which is well suited to study geometrically confined domain walls. We compute the behaviour of domain walls in a one dimensional chain when currents are injected using adiabatic and non-adiabatic spin torque terms. Our results are compared to analytical calculations and are found to agree very well for small current densities. At larger current densities deviations are observed, which can be attributed to the approximations used in the analytical calculations.     

Spontaneous emission from a ladder three-level atom in anisotropic photonic crystals

We investigate the spontaneous radiation from a ladder three-level atom embedded in a three-dimensional anisotropic photonic crystal with an external driving field. The properties of the spontaneous emission are dependent strongly on the relative position of the middle level from the band edge. Due to the Autler-Townes splitting by the action of the driving field, the external driving field can also affect the properties of the spontaneous emission. The population exchanged between the upper and the middle levels decreases as the detuning of the external driving field frequency from the corresponding transition frequency increases. The properties of the emission field can be changed or so much as controlled by choosing suitable intensity of the external driving field. The emission spectrum is more complex, and dependent on the location of the observer in this case.     

双端泵浦保偏光纤激光器

 以两台808 nm半导体激光器LD1和LD2为泵浦源,对光纤激光器双端泵浦进行了研究,获得了6.5 W的激光输出。实验分别测出了LD1和LD2半导体激光器单端泵浦和双端泵浦时的输出功率,对双端泵浦输出功率与单端泵浦功率之和进行了比较,利用双端泵浦提高了泵浦效率和输出激光功率。同时测量了输出激光的偏振度,通过计算得到双端泵浦输出激光的偏振度为0.5。     

半导体泵浦铷蒸气激光器国内首次出光北大核心CSCD

采用体光栅对商用线阵半导体激光器进行线宽压缩,得到线宽0.1nm、中心波长780.2nm、最高连续输出功率80W的泵浦激光输出。为了降低热效应,通过外加斩波器将泵浦光转化为脉冲模式,脉宽440μs,占空比为1∶5。采用长度为5mm的铷金属饱和蒸气作为增益介质,并在常温下充入33kPa乙烷和47kPa氦气,进行了出光实验。在泵浦峰值功率35.4W,铷吸收池温度120℃时,得到峰值功率600mW的795nm铷激光输出,斜率效率为1.7%。     

泵浦光强对激光相位共轭波非线性效应的影响

分析了泵浦光强对激光相位共轭谐振腔中探测光场的作用。基于稳定性定理,通过确定系统的Lyapunov指数,数值计算了在不同泵浦光强下的激光相位共轭波的非线性效应。结果显示,泵浦光强是系统的控制参量。调节泵浦光强的数值,系统的动力学性质发生了改变,可以呈现一周期、二周期、四周期以及倍周期分岔、周期并缩和混沌现象。     

Some theoretical and practical aspects in the separation of humic substances by combined liquid chromatography methods

Permanent need to understand nature, structure and properties of humic substances influences also separation methods that are in a wide scope used for fractionation, characterization and analysis of humic substances (HS). At the first glance techniques based on size-exclusion phenomena are the most useful and utilized for relating elution data to the molecular mass distribution of HS, however, with some limitations and exceptions, respectively, in the structural investigation of HS. The second most abundant separation mechanism is reversed-phase based on weak hydrophobic interactions beneficially combined with the step gradients inducing distinct features in rather featureless analytical signal of HS. Relatively great effort is invested to the developments of immobilized-metal affinity chromatography mimicking chelate-forming properties of HS as ligands in the environment. Surprisingly, relatively less attention is given to the ion-ion interactions based ion-exchange chromatography of HS. Chromatographic separation methods play also an important role in the examination of interactions of HS with pesticides. They allow us to determine binding constants and the other data necessary to predict the mobility of chemical pollutants in the environment. HS is frequently adversely acting in analytical procedures as interfering substance, so more detailed information is desired on manifestation of its numerous properties in analytical procedures. The article topic is covered by the review emphasizing advances in the field done in the period of last 10 years from 2000 till 2010.