Tm3+ 掺杂ZrF4 -BaF2 -LaF3 -AlF3 -NaF-PbF2玻璃激光制冷中荧光再吸收效应的理论分析

固体材料的激光制冷是近年来发展起来的一个新的研究领域. 掺Tm³⁺的ZrF₄-BaF₂-LaF₃-AlF₃-NaF-PbF₂(ZBLANP)玻璃材料是激光冷却的典型材料之一. 与另一种制冷掺杂离子Yb³⁺相比,Tm³⁺具有更好的制冷潜力. 目前制约材料制冷的一个主要机理就是荧光再吸收. 首先根据Tm³⁺:ZBLANP的光谱参数,利用半经典的随机行走模型得到了不同情况下的平均荧光再吸收次数,随后分析了荧光光子界面出射的全反射效应,并对所得结果进行了修正. 计算结果表明,荧光再吸收会导致量子效率降低0.5%-1%,出射荧光波长红移达到2-10 nm,激光制冷的效率和功率降低. 为了有利于荧光出射和净制冷的实现, 宜采用小体积细长棒的制冷元. 关键词： 激光制冷 稀土离子 荧光再吸收     

Tm3+掺杂光纤激光制冷的理论分析

近年来，掺Tm³⁺：ZBLANP玻璃已成为固体材料激光冷却领域中最有希望的新材料之一，但有关掺Tm³⁺：ZBLANP光纤的激光冷却尚未见到理论研究与实验报道.本文采用一个简单的理论模型，就Tm³⁺：ZBLANP光纤的激光冷却进行了理论研究与分析，讨论了量子效率、抽运功率、背景吸收、出射荧光波长变化和环境黑体辐射等对激光制冷效果的影响，得到了一些有趣的重要结果，可为掺Tm³⁺：ZBLANP光纤的激光冷却实验提供可靠的理论 关键词： 固体激光冷却 反斯托克斯荧光 3+：ZBLANP光纤')" href="#">掺Tm³⁺：ZBLANP光纤     

Tm3+掺杂材料激光冷却的研究

固体材料的激光制冷又称反斯托克斯荧光制冷,是近年来刚兴起的全光学制冷技术。该技术的核心问题是制冷材料的选择。以Tm^3＋掺杂离子为例,从理论上分析了最小制冷能级间距与激光抽运速率的关系,研究了不同抽运速率下制冷功率与能级间距的关系以及热-光转换效率与能级间距的关系,获得了最佳热-光转换效率与抽运速率的关系。结果表明,最小的制冷能级间距约为4500cm^-1,能级间距在5000～6000cm^-1的宽度是比较合适的。最后探讨了Tm^3＋掺杂材料用于激光冷却的可行性,许讨论了制冷基体材料的合理选择问题。     

Simulation and experiment of the cooling effect of trapped ion by pulsed laser

We investigate the process of pulsed laser cooling using a self-constructed molecular dynamics simulation(MDSimulation) program. We simulate the Doppler cooling process and pulsed laser Doppler cooling process of a single ~(40)Ca~+ ion, and the comparison with the experimental results shows that this self-constructed MD-Simulation program works well in the weak laser intensity situation. Furthermore, we analyze the pulsed laser Doppler cooling process of a single ~(27)Al~+ ion. This program can be used to analyze the molecular dynamic process of various situations of Doppler cooling in an ion trap, which could give predictions and experimental guidance.     

Simulation of longitudinal dynamics of laser-cooled and RF-bunched C~(3+) ion beams at heavy ion storage ring CSRe

Laser cooling of Li-like C~(3+)and O~(4+)relativistic heavy ion beams is planned at the experimental Cooler Storage Ring(CSRe). Recently, a preparatory experiment to test important prerequisites for laser cooling of relativistic~(12)C~(3+)ion beams using a pulsed laser system has been performed at the CSRe. Unfortunately, the interaction between the ions and the pulsed laser cannot be detected. In order to study the laser cooling process and find the optimized parameters for future laser cooling experiments, a multi-particle tracking method has been developed to simulate the detailed longitudinal dynamics of laser-cooled ion beams at the CSRe. Simulations of laser cooling of the~(12)C~(3+)ion beams by scanning the frequency of the RF-buncher or continuous wave(CW) laser wavelength have been performed. The simulation results indicate that ion beams with a large momentum spread could be laser-cooled by the combination of only one CW laser and the RF-buncher, and show the requirements of a successful laser cooling experiment. The optimized parameters for scanning the RF-buncher frequency or laser frequency have been obtained.Furthermore, the heating effects have been estimated for laser cooling at the CSRe. The Schottky noise spectra of longitudinally modulated and laser-cooled ion beams have been simulated to fully explain and anticipate the experimental results. The combination of Schottky spectra from the highly sensitive resonant Schottky pick-up and the simulation methods developed in this paper will be helpful to investigate the longitudinal dynamics of RF-bunched and ultra-cold ion beams in the upcoming laser cooling experiments at the CSRe.     

激光染料的反斯托克斯荧光制冷计算

从理论上研究了具有分子振动能级结构的激光染料分子的反斯托克斯荧光制冷总是根据吸收光谱和荧光发射谱,对Ｒｈｏｄａｍｉｎｅ１０１溶液的反斯托克斯我制冷有力进行了数值计算,得到了用该种材料实现激光制冷的条件与制冷效率相关的曲线。     

能量传递制冷机制中激光制冷的最佳泵浦频率和最大制冷效率

在能量传递型激光制冷中,对于非均匀线宽比较窄的情况,引起最大制冷效率的激发光频率不随温度的变化而变化最大制冷效率与温度呈三次暴的关系。对于非均匀线宽比较宽的情况。随着温度的降低,最佳激发光频率与非均匀线形的中心频率差越来越大,并在较低的温度下迅速拉大它们间的距离。由能量传递机制所引起的荧光制冷最大效率也随着温度的降低而越来越低,并在最后趋于零。它们随温度的降低而降低的规律与实验中得到的结论相符合。     

激光制冷中能级间距的选择

激光制冷问题的核心是材料的选择。荧光中心能级的间距是其中的一个关键指标。确定合理的能级间距有助于选择合适的激光制冷材料。能级间距决定了对激光制冷至关重要的两个因素:量子效率和无辐射跃迁速率。如果单纯地从制冷功率的角度来看,能级间距越大量子效率越高,也越有利于荧光制冷。但当能级间距宽到某一值后,制冷功率基本上保持不变。如果从热一光转换效率的观点来考察激光制冷的效率问题,能级间距宽度的合理取值就应该小得多。如果在选择激光制冷材料时,确定制冷功率具有第一位的重要性,那么,能级间距选择在5000cm^-1左右的宽度是比较合适的、这不仅可以确定较大的热－光转换效率,同时也基本上保证了很高的制冷功率。     

Theoretical and experimental investigations of a diode-pumped high-power continuous-wave 912 nm Nd:GdVO4 laser operation at room temperature

Based on the rate equation of Nd³⁺-doped quasi-three-level lasers, a theoretical model of diode-end-pumped continuous-wave 912 nm Nd:GdVO₄ laser is presented. Lasing threshold and slope efficiency considering reabsorption effect are calculated and analyzed. It is found that the output performance of 912 nm laser operating at room temperature is influenced remarkably by the reabsorption loss and spatial distribution of the pump beam and laser beam. In experiments, the output power and average slope efficiency of 912 nm laser were investigated under different conditions. After optimization at the parameters of laser medium, working temperature and spatial distribution of the pump beam, up to 16.2 W continuous-wave 912 nm laser output was obtained at incident pump power of 67.0 W, with an average slope efficiency of 41.7%, to the best of our knowledge, this is the highest output power of diode-pumped 912 nm Nd:GdVO₄ laser by far.     

Enhanced Laser Cooling of Rare-Earth-Ion-Doped Glass Containing Nanometer-Sized Metallic Particles

The enhanced laser cooling performance ofrare-earth-ions-doped glasses containing small particles is predicted. Thisis achieved by the enhancement of local field around rare earth ions, owingto the surface plasmon resonance of small metallic particles. The role ofenergy transfer between ions and the particle is theoretical discussed.Depending on the particle size and the ion emission quantum efficiency, theenhancement of the absorption and the fluorescence is predicted. Moreover,taking Yb³⁺-doped ZBLAN as example, the cooling power and heat-lightconverting efficiency are calculated. It is finally concluded that theabsorption and the fluorescence are greatly enhanced in these compositematerials, the cooling power is increased compared to the bulk material.     

Laser cooling of recombining electron-ion plasma

A method of producing and confining ultracold electron-ion plasma with a strongly nonideal ion subsystem is considered. The method is based on the laser cooling of plasma ions by the radiation resonant with the ion quantum transition. A model is developed for the laser cooling of recombining plasma. Computer simulation based on this model showed that the ion nonideality parameter can be as large as ～100. The data obtained demonstrate that the production of ultracold nonideal plasma is quite possible.     

Tomographic reconstruction of 2D-OH<Superscript>∗</Superscript>-chemiluminescence distributions in turbulent diffusion flames

A theoretical model on actively Q-switched Nd³⁺-doped quasi-three-level laser including the energy transfer upconversion and the ground state reabsorption is developed. The analytical expressions of the fractional thermal loading and the average output power are obtained, and the influence of ETU effects on laser performance for different repetition rate is analyzed. The average output power and the thermal focal length of the Q-switched 946 nm laser are acquired in experiment. The good agreement between the experimental data and theoretical results demonstrates the reliability of the theoretical model.     

Fluorescence reabsorption and its effects on the local effective excitation lifetime

A spectral theory of fluorescence reabsorption is presented that allows us to describe the effects of radiation trapping, which especially occurs in barrel-polished laser rods, as an effective change of the excitation lifetime. This effect causes a local fluorescence lifetime difference in the laser medium and thus a local change in the quantum efficiency. The theory is compared to experimental results obtained with an Er³⁺:YAG rod with good agreement.     

Characteristics investigation of Yb3+:YAG crystals for optical refrigeration

Yb³⁺:YAG crystal is one excellent material for developing high-power radiation-balanced lasers (RBLs). An experimental study of the laser cooling performances of YAG crystals with various doping Yb³⁺ concentrations, especially for application of RBLs, is reported here. With improved Yb³⁺ doping concentration in YAG crystal, though the resonance absorption coefficient increases, the corresponding external quantum efficiency has been found to decrease with the average fluorescence wavelength being red shifted, which is detrimental to anti-Stokes fluorescence (ASF) cooling. The decrease of the external quantum efficiency can cause the first zero crossing wavelength to red shift, which is not conducive to RBLs. Based on the comprehensive study of the cooling characteristics of the series of Yb³⁺-doped YAG crystals, the optimal Yb³⁺ doping concentration for ASF cooling has been suggested.     

敏化离子Ce3+对Er3+∶YAG的1.6μm波长激光性能的影响

测定了Ce³⁺,Er³⁺∶YAG中Ce³⁺离子的吸收截面.用从能级跃迁速率方程和激光传输方程推出的表达式计算了1.6μm波长激光的阈值能量(功率)和斜率效率.表明在Ce³⁺,Er³⁺∶YAG中,Ce³⁺对Er³⁺离子的激光性能影响与激活离子Er³⁺的浓度、晶棒大小有关.短晶棒或浓度低的晶体加入Ce³⁺可降低Er 关键词：     

激光二极管纵向抽运（Tm，Ho）：YLF激光器的研究

对激光二极管端面抽运(Tm，Ho)：YLF固体激光器的激光特性进行了研究。根据激光二极管抽运准三能级系统的特性，详尽地分析了能量在Tm^3 离子和Ho^3 离子之间的传递过程，给出了(Tm，Ho)：YLF激光器准三能级的速率方程，对上转换及激光下能级粒子再吸收对激光二极管抽运(Tm，Ho)：YLF激光器运转的影响进行了理论分析，得出了(Tm，Ho)：YLF激光器的阈值抽运功率和斜率效率的解析表达式。同时对(Tm，Ho)：YLF微片激光器的激光特性进行了实验研究，当保持晶体温度为19℃时，阈值抽运功率为425mW，斜率效率为22．5％，最大光—光转换效率为17．4％，并且在将晶体保持在四个不同的温度下，给出了激光输出功率随抽运功率变化的实验结果。将理论与实验结果进行比较，发现吻合得比较好。     

Lifetime measurements with the pinhole method in presence of radiation trapping: II—application to Yb<Superscript>3+</Superscript> doped ceramics and crystals

In this paper, we present an experimental verification of a theoretical model for the evaluation of the results of the so-called pinhole method for the measurement of the upper level lifetime in doped optical materials where the resonant reabsorption of the emitted fluorescence determines significant radiation trapping effects. As an experimental verification of the model, we measured the lifetime of the upper laser level of Yb³⁺ in various crystals and ceramic samples usually employed for the realization of solid state laser sources.     

Yb3+离子掺杂钨酸钾钆晶体的光谱参数

从Yb³⁺:KGd(WO₄)₂(KGW)的吸收谱和荧光谱出发,利用倒易理论计算其各个光谱参量,如吸收截面,受激发射截面,辐射寿命等.由于Yb³⁺:KGW晶体较适合用作二极管泵浦的激光器的材料,而激光二极管所发出的光是偏振光,晶体又是双折射晶体,因此研究了泵浦光的不同通光方向和偏振方向对Yb³⁺:KGW晶体荧光光谱的影响.实验表明在不同情况下其对晶体荧光强度影响较大,因此在设计用激光二极管泵浦的激光器时,应考虑合适的泵浦光偏振方向和入射在晶体上的轴向,其中泵浦光的通光方向比泵浦光偏振方向对晶体的荧光强度的影响更大.对按晶轴切割的这两种晶体,相同实验条件下,荧光强度I_c>I_b>I_a.对于按折射率主轴切割的来说,荧光强度I_Np>I_Ng>I_Nm.在通光方向为c轴,偏振方向平行b轴时得到了最大的荧光强度.     

LD侧面抽运Nd：YAG陶瓷激光器运转条件下归一化热参数优化理论及实验研究

考虑激光提取对介质内非辐射跃迁的抑制作用，建立和完善LD侧面抽运Nd：YAG陶瓷激光器运转条件下增益介质的发热模型，通过实验测量激光器斜率效率和增益介质吸收的抽运功率来推导出归一化热参数.通过归一化热参数，讨论了影响Nd：YAG陶瓷介质内热沉积的主要因素，研究结果表明：增益介质内热沉积对激光提取效率、交叠效率以及掺杂浓度的变化比较敏感.为有效减少热沉积，对所研究的掺杂原子百分比浓度为1.0%的Nd：YAG陶瓷多模激光器的输出耦合镜进行优化选择，激光提取效率提高到0.905，归一化热参数降低到0.474.研究结果可为进一步研究陶瓷激光器中热效应以及冷却方案设计等提供一定参考. 关键词： 热沉积 归一化热参数 Nd：YAG陶瓷     

Spectral characteristics of a Yb-doped Y<Subscript>2</Subscript>O<Subscript>3</Subscript> ceramic laser

We report the experimental observation of random wavelength emission and intensity-dependent central-wavelength shift in a diode-pumped Yb³⁺-doped Y₂O₃ ceramic laser. We show experimentally that, like conventional lasers, the emission of the laser has fixed well-defined transverse modes; however, its instantaneous emission wavelengths change randomly with time. The central wavelength of the laser emission also shifts with the intracavity light intensity. A model was developed to describe the spectral behavior of Yb³⁺-doped lasers. We show that the observed random wavelength emission and central lasing wavelength shift of the laser could be well explained based on the strong reabsorption of light in the gain medium. PACS 42.55.Rz; 42.60.Mi; 42.55.Xi