Hg蒸汽中通过双光子共振四波差频产生调谐真空紫外辐射

利用Hg原子6¹S₀—6¹D₂和6¹S₀—6³D₂双光子共振的四波差频(2ω₁—ω₃),获得了真空紫外相干辐射(ω₄)。当入射光之一(ω₃)波长调谐时,产生的真空紫外光也是调谐的,调谐范围为184.9-187.5nm.本文对非线性频率变换过程的机 关键词：     

引入量子干涉的双光子共振非简并四波混频

研究了级联四能级系统中双光子共振非简并四波混频(NFWM)由于加入耦合光场而产生的量子干涉效应，发现在强耦合场作用下NFWM频谱呈现AT劈裂，它反映的是两个缀饰态的能级.量子干涉还使NFWM信号被抑制或增强.此方法牵涉到三光子共振，因此可以成为研究原子或分子高激发态的有效光谱学工具. 关键词： 四波混频 量子干涉     

汞蒸汽中利用四波和频产生125nm附近可调谐真空紫外激光

以氩为匹配气体的汞蒸汽四波和频实验中,一束泵浦光(ω₁)与汞原子6¹S₀—7¹S₀严格双光子共振,当另一束泵浦光(ω₃)在汞原子7¹S₀—9¹P₁跃迁的蓝端调频时,产生可调谐的真空紫外(VUV)激光(ω₄=2ω₁+ω₃),其 关键词：     

应用双光子共振非简并四波混频测量Ba原子里德伯态

使用具有中间态的双光子共振非简并四波混频(NFWM)测量了Ba原子J＝0和J＝2的偶宇称里德伯线系，与现代实验方法不同，本方法是纯光学的方法，其光路简单，检测的是相干光，而不是电子或离子信号.当用窄带宽的激光时，本技术对里德伯能级的窄光谱结构可以获得消多普勒的分辨率. 关键词： 四波混频 里德伯态     

双光子共振非简并四波混频测量Ba原子里德伯态的碰撞展宽和频移

采用双光子共振非简并四波混频测量了Ar缓冲气压引起的Ba原子里德伯6snd ¹D₂谱线系的碰撞展宽和频移, 计算了n=16---33的碰撞展宽截面和频移截面. 本方法是一种纯光学的测量技术, 当采用窄带激光器时可以获得里德伯态的消多普勒光谱. 与传统实验方法测量到的里德伯态纵向弛豫的碰撞展宽不同, 本方法可以研究碰撞引起的两能态间横向弛豫的展宽.     

基于氧化镁晶体中级联四波混频过程的紫外飞秒光脉冲产生

紫外波段飞秒激光脉冲是研究超快化学和超快物理相关过程的重要工具,实现波长可调谐的宽带紫外飞秒光脉冲将有助于推动超快动力学及相关领域的研究.本文报道了以两束400 nm的飞秒光脉冲作为级联四波混频的抽运源,在氧化镁晶体中产生9阶频率上转换和5阶频率下转换边带信号的实验结果.边带波长范围从350 nm到450 nm连续可调谐,这些边带信号的发散角和波长与级联四波混频理论预测结果吻合.紫外边带相对于入射光的整体转化效率约为1.2%.同时,高阶边带的光谱形状呈现高斯型,其谱宽理论上支持傅里叶转换极限脉宽为20—50 fs.本文展示了一种高效产生波长可连续调谐的紫外飞秒光脉冲的便捷方法,为基于紫外超短脉冲的相关研究提供了有效工具.     

汞蒸汽中双光子共振四波和频产生125nm的相干辐射

利用汞原子6~1S_0—7~1S_0双光子共振四波和频产生了125nm的相干辐射.对双光子共振增强效应、双光子共振克尔(Kerr)效应进行了研究.讨论了平面波和聚焦情况下最佳相位匹配的条件.实验中还观测到了四波参量振荡和四波差频的信号输出.     

激发态吸收的简并四波混频

从理论和实验两方面讨论了外泵浦场存在时四能级模型的饱和吸收体激发态简并四波混频过程,结果显示外泵浦场强对激发四波混频信号强度有较大的影响,在外场由小到大的变化过程中,信号强度经历一个由小到大再到小的过程. 关键词：     

Reflectivity Characteristics of Resonant Four Wave Mixing Generated in Erbium-Doped Optical Fibers

Resonant four-wave mixing (RFWM) based on the photo-induced refractive index change in erbium-doped optical fibers is demonstrated experimentally. The erbium-doped fibers act as a saturable absorber at 1.536 μm pump wavelength. Dependence of efficiency of RFWM on the pump power, the dopant concentration, the fiber length, and the signal modulation frequency are analyzed using three types of erbium-doped fibers differing in dopant concentration. It is found that a signal modulation frequency higher than 10 kHz is required for the correct measurement. The RFWM efficiency is improved with an increase in the input pump power in a range up to 1.5 mW and the highest reflectivity of 5.1% is attained. The highest RFWM efficiency is achieved at αgsL ∼ 5 dB, which is in good agreement with the theory.     

Temperature Dependence of Resonant Four Wave Mixing in Erbium-Doped Optical Fibers

Temperature dependence of resonant four-wave mixing (RFWM) in an erbium-doped optical fiber without amplification is investigated experimentally. A large change in the refractive index resulting from the transition absorption is induced in the erbium-doped fiber. The maximum reflectivity of RFWM at 0.3 m fiber length increases from 4.1% to 5.5% with change in temperature from 40°C to - 196°C. The temperature-dependent reflectivity characteristics correspond to the change in the absorption cross section at 1.53 μm wavelength.     

四波混频过程中差频与和频的竞争研究

在以惰性气体Xe为非线形介质,利用双光子共振四波混频差频(2PR4WDM,ω-=2ωUV-ωT)技术,产生可调谐相干真空紫外激光(VUV)的实验中,观察到产生的VUV在一些特定波长附近出现共振衰减.这些波长对应着伴随过程四波混频和频的双共振增强.对四波混频过程进行了比较粗略的定量的处理,考虑到泵浦光在传播途中的衰减,得到的结论能很好地解释观察到的差频输出的衰减现象,差频输出的衰减是由于双共振四波混频和频(ω+=2ωUV+ωT)与差频竞争的结果.     

单模光纤中四波混频的自诱导相位匹配

报道了无双折射单模光纤中四波混频的一种新型相位匹配方式,这种相位匹配仅由抽运光产生的自相位调制和互相位调制的共同作用即可提供,文中报道了实验结果,并从理论上成功地解释了该四波混频相位匹配的机理,与实验符合得很好。     

利用自发四波混频测量光子晶体光纤色散

使用脉宽为1.6ps的脉冲光抽运0.6m长的光子晶体光纤,测量由光纤中自发四波混频过程所产生光子对的频谱,并利用所获得的相位匹配数据确定了待测光纤的色散。当抽运光的中心波长以1nm的步长,在1037～1047nm的范围内变化时,通过可调谐滤波器和单光子探测器测量光子晶体光纤产生的信号和闲频光子对的频谱,从而获得11组四波混频相位匹配数据。然后使用阶跃有效折射率模型对所获得的相位匹配数据进行拟合,得出待测光子晶体光纤的纤芯半径和包层空气比的有效值分别为0.949μm和29.52%,并在此基础上计算了光纤的色散及全频谱范围内的四波混频相位匹配曲线。实验结果显示,曲线预测值与实测值之间误差小于0.1%。     

Phase Matching Property of Cross Polarization Four Wave Mixing in BaTiO3 Crystal

Four wave mixing (FWM) is of considerable interest in generation of a phase conjugate beam with photorefractive crystals. The common methods of FWM are parallel polarization FWM and cross polarization FWM. In this paper, we analyze the phase matching property of the latter. First, we consider the phase matching condition, and derive equations representing the angler relationship of interacting beams. Then, we consider the phase mismatching which is caused by shift of the probe beam angle from the phase matching condition, and calculate the effect of the shift of this angle on the amount of phase mismatching. We also determine and closely examine the coupling constant.     

在单晶硅中用相干光耦合方法压缩短脉冲和超短脉冲

提出一种新型的相干光耦合压缩短脉冲和超短脉冲的方法。以硅为非线性材料，经计算表明：在材料的破坏阈值之内，出射信号光脉冲的脉宽可被压缩到入射光脉宽的７０％。计算了泵浦能量密度，泵浦光与信号光夹角等与脉宽压缩量的关系。     

Origins of Unstable Operations and Properties of Self-Pumped Four Wave Mixing in BaTiO3 Crystal

Self-pumped four wave mixing (SPFWM) in single BaTiO₃ crystal is experimentally studied because of its fast response and rather simple optical system. The origins of unstable operations are shown and classified: unstable operation of self-pumped phase conjugate mirror (SPPCM), floating dust in the laser beam path, competition between beam path loops, and competition between groups of index gratings. The reflectivities and the buildup times are measured as they relate to incident conditions, i.e. the geometry of beam paths and interaction regions, and four cases are given. Large reflectivity was obtained when buildup time was short, probably because of large coupling strength. The measured buildup times lie between 0.5 s and 0.6 s at the total incident beam power of about 5.5 mW, so that fast response of SPFWM was confirmed.     

瑞利增强非简并四波混频的时域不对称性研究

基于场关联原理,采用非相干光时延四波混频法研究了瑞利增强非简并四波混频的时域特性.利用二阶场关联函数理论揭示出混频信号在时域的细微变化,发现信号展示出时域不对称性并且在τ<0时会出现振荡结构,而这种时域不对称性反映了该三阶非线性极化过程的特点.     

Generation of Laser Light via Ultrasonic Four-wave Mixing

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