自相关法测量飞秒激光双脉冲若干参量的研究EI北大核心CSCD

飞秒激光双脉冲在研究光泵浦的超快瞬态过程领域具有重要的应用价值,如何实现高准确度的飞秒激光双脉冲的实时测量显得尤为重要.本文提出了一种基于自相关法的飞秒激光双脉冲参量的测量方法,可实现对共光路传输、具有飞秒至皮秒级时间间隔的飞秒激光双脉冲的脉冲间隔、脉冲宽度和强度比的实时测量.实验中采用自相关仪测得了双折射晶体(钒酸钇)分束出的飞秒激光双脉冲的自相关曲线,并用非线性拟合算法求得了飞秒激光双脉冲的脉冲间隔、脉冲宽度和强度比参量.实验结果表明,本文方法与互相关测量方法相比,克服了参考脉冲参量的不确定性对检测准确度的影响,使测量平均准确度提高了48%以上.     

复杂激光脉冲波形的整形

介绍了用时空变换的方法对激光脉冲整形的原理；提出了由于硬边光通量调制器引入的动态的光脉冲强度空间分布的不一致性及其克服的方法，理论上用二维快速傅里叶变换（ＦＦＴ）进行了验证；最后计算了系统光强透过率和光束焦斑大小，调制狭缝宽度的关系，为了显示本系统的复杂脉冲整形能力，在实验上获得了惯性约束核聚变（ＩＣＦ）感兴趣的复杂激光脉冲波形。     

自相关法测量飞秒激光双脉冲若干参量的研究

飞秒激光双脉冲在研究光泵浦的超快瞬态过程领域具有重要的应用价值,如何实现高准确度的飞秒激光双脉冲的实时测量显得尤为重要.本文提出了一种基于自相关法的飞秒激光双脉冲参量的测量方法,可实现对共光路传输、具有飞秒至皮秒级时间间隔的飞秒激光双脉冲的脉冲间隔、脉冲宽度和强度比的实时测量.实验中采用自相关仪测得了双折射晶体(钒酸钇)分束出的飞秒激光双脉冲的自相关曲线,并用非线性拟合算法求得了飞秒激光双脉冲的脉冲间隔、脉冲宽度和强度比参量.实验结果表明,本文方法与互相关测量方法相比,克服了参考脉冲参量的不确定性对检测准确度的影响,使测量平均准确度提高了48%以上.     

信号光的调制对基于光纤光参量放大光脉冲源的改善

在理论上从四波混频的强度耦合方程出发,给出了基于光纤光参量放大(FOPA)光脉冲的光场表达式,并进一步分析了信号光被相位调制或强度调制后,光脉冲的频率啁啾和强度演化.结论指出：若信号光被强度调制,对所生成脉冲宽度无明显的影响,但可以提高消光比;若信号光被相位调制,所生成的脉冲具有更大的线性正啁啾,可以在相同的抽运功率条件下得到比无相位调制时更窄的脉冲.实验上给出了10 GHz工作速率下的结果,其结果与理论分析符合得很好.通过信号光的相位调制,在05 W平均抽运功率条件下得到了消光比22 dB,脉宽为5 关键词： 光纤参量放大 四波混频 光脉冲源 频率啁啾     

光参量啁啾脉冲放大中时间同步抖动对增益稳定性的影响

在考虑了光参量啁啾脉冲放大中的脉冲波形、相位失配和时间同步抖动情况下,给出了计算光参量啁啾脉冲放大增益特性更为完善的三波耦合理论模型。并在1 ns的时间同步抖动情况下,对比分析了光参量放大在小信号放大及饱和放大时的增益稳定性。光参量放大的时间同步抖动对增益影响非常大,使放大信号光脉冲的增益光谱发生了明显的偏移,波形不对称和整个增益降低;并且信号光光谱越宽,光参量放大间的时间同步抖动对其增益影响越严重;但随着参量放大增益饱和的出现和加深,信号光和抽运光之间的同步时间抖动对放大信号光的输出强度影响减弱,即在饱和放大处可以获得更稳定的放大信号光输出。     

光参量啁啾脉冲放大中时间同步抖动对增益稳定性的影响

 在考虑了光参量啁啾脉冲放大中的脉冲波形、相位失配和时间同步抖动情况下,给出了计算光参量啁啾脉冲放大增益特性更为完善的三波耦合理论模型。并在1 ns的时间同步抖动情况下,对比分析了光参量放大在小信号放大及饱和放大时的增益稳定性。光参量放大的时间同步抖动对增益影响非常大,使放大信号光脉冲的增益光谱发生了明显的偏移,波形不对称和整个增益降低;并且信号光光谱越宽,光参量放大间的时间同步抖动对其增益影响越严重;但随着参量放大增益饱和的出现和加深,信号光和抽运光之间的同步时间抖动对放大信号光的输出强度影响减弱,即在饱和放大处可以获得更稳定的放大信号光输出。     

啁啾脉冲放大系统中光栅展宽器的性能与实验研究

论述了啁啾脉冲放大技术中运用单光栅展宽器结构将少光脉冲在时域进行啁啾展宽的原理及特性，导出了该展宽器所提供色散量的具体表达式及其展宽后激光脉冲宽度的计算，然后通过数值计算分析了其展宽因子及展宽比随各参量的之间的变化关系；本文在此基础上进一步获得了实验的测量结果。     

超短飞秒光脉冲产生技术

本文叙述了群速弥散补偿被动锁模环型染料激光器的特性;研究了产生极短飞秒光脉冲的条件和光脉冲强度分布的非对称性。该技术产生的最短光脉冲宽度为21 fs;光脉冲宽度可调范围从最短到500fs以上。实验和理论数据拟合证明光强分布为非对称双曲正割平方,非对称因子r在7到11之间。     

BBOⅠ类相位匹配光参量放大中群速失配的补偿

描述了在BBOⅠ类相位匹配的飞秒光参量放大（OPA）中，利用非共线结构和倾斜抽运光的脉 冲波面来完全补偿三波群速失配的方法.理论计算了三波群速匹配时，非共线角、相位匹配 角、抽运光的脉冲波面倾斜角随信号光波长的变化，并分析了对抽运光光斑尺寸的要求和对 空间走离长度的影响.结果表明，利用该方法不仅能够实现最大的参量带宽，而且能够完全 补偿飞秒OPA中三波的群速失配.此外，选取合适的抽运光光斑尺寸和非线性晶体的长度对提 高参量增益也至关重要. 关键词： 群速匹配 非共线相位匹配 脉冲波面倾斜 飞秒光参量放大     

超短脉冲激光光束在一维反射型体全息光栅中的衍射

基于Kogelnik的耦合波理论,研究了在色散效应的影响下,超短脉冲激光光束在反射型体全息光栅中衍射的性质.研究给出了衍射光及透射光在频谱域及时间域的振幅及强度分布、光栅的光谱宽度及衍射效率随光栅参量及入射条件的变化.数值研究的结果表明,在光栅记录介质色散效应的影响下,衍射光束的光谱宽度减小,脉冲展宽,衍射效率降低.通过适当的选取光栅参量及入射条件,可以控制衍射和透射光束的频谱和时间强度分布,得到满意的衍射和透射光束的带宽和波形,从而可以将其应用于脉冲整形等技术中.     

Effects of light quenching on the emission spectra and intensity decays of fluorophore mixtures

We examined a series of fluorophore mixtures to determine the wavelength selectivity of light quenching and the effects of light quenching on the emission spectra and intensity decays. Light quenching can be accomplished using a single excitation pulse train and quenching wavelength (one-beam) or with longer-wavelength quenching pulses time-delayed relative to the excitation pulses (two-beam). Both one-beam and two-beam light quenching were found to alter the intensity decays of the mixtures. The frequency-domain intensity decay data were analyzed to reveal the fractional intensity of each fluorophore in the mixture and the effects of light quenching on the fractional contribution of each fluorophore to the total intensity. Fluorophores were selected to provide a range of decay times and emission wavelengths. The extent of quenching in the mixtures was dependent on which fluorophore had the higher radiative decay rate and emission intensity at the quenching wavelength. A general theory is presented which describes the intensity decays in terms of the extent of quenching of each fluorophore and the time delay between excitation and quenching pulses. The effects of light quenching on the fractional intensities of each fluorophore in the mixture, recovered from the intensity decay analysis, were found to be in quantitative agreement with that predicted from steady-state measurements of light quenching and from the spectral properties of the fluorophores. The data on light quenching of mixtures demonstrate that light quenching may be used for selective quenching of fluorophores and thus of potential value for studies of multichromophoric systems.     

Saturation effects on phosphorescence anisotropy measurements at high laser pulse energies

Triplet spectroscopic methods such as time-resolved phosphorescence anisotropy permit successful measurement of slow rotational diffusion of membrane proteins. However, these methods are potentially subject to saturation phenomena. We present theoretical and experimental studies of how high excitation energy densities can complicate measurements of phosphorescence intensity and anisotropy. Increases in excitation laser pulse energy initially increase phosphorescence intensity. Further increases then lead to phosphorescence saturation. As a consequence, the initial phosphorescence anisotropy decreases and approaches zero at very high excitation energies. The relative standard deviation of anisotropies measured in any system reaches a minimum at some particular excitation energy density. These results allow us to define optimum experimental conditions for time-resolved phosphorescence anisotropy measurements. For example, for excitation of erythrosin chromophores at typical wavelengths by the center of a Gaussian laser beam, optimum pulse energies in microjoules are approximately 5.0R ², whereR is the beam 1/e² radius in mm.     

电致发光衰减测量系统的搭建及应用

发光衰减是发光的重要过程,测量发光寿命对研究发光机理十分重要,但传统研究在概念和方法上存在两个差错：(1)概念上认为衰减等同于激发态数目的减少,而忽视了衰减是发光强度的下降,两者是不同的概念;(2)方法上基于激发态规律推导,假设的边界条件不符合实际,没有实验的支持。同时,传统方法对设备的要求很高,且只限于光致发光。为了纠正差错,降低成本,搭建了一套全新的电致发光衰减测量系统,可用于所有可以周期激发的发光类型。从能量转换原理出发,采用周期激发,用脉冲间隔时间作为时间尺度来度量发光衰减持续的时间,通过脉冲间隔时间与发光寿命的对比,相应地发光强度有不同的变化,根据该现象简便地测量出发光寿命。基于该原理搭建的发光衰减测量系统,实验结果表明了发光强度随着激发频率,先保持不变然后逐渐下降,通过测量下折点即能够推算出发光衰减寿命,而且还发现发光衰减寿命与初始发光强度呈正相关的关系。认为发光寿命是发光强度的变化,是区别于传统研究以激发态数目为研究对象的一大创新,同时通过实验证明了发光寿命与初始亮度相关,也拓展了对发光寿命的新认识。     

Spectral migration and decay characteristics of triplet excitations in glassy benzophenone

Spectral and kinetic properties of triplet excitons in thin films of glassy benzophenone were studied at temperatures between 4.2 and 220 K. The influence of the film thickness on the lifetime and nature of their phosphorescence decay was observed and discussed. It was shown that studies of spectral diffusion in thin glassy films of benzophenone must take into account the dependence of the emission lifetime on the recording wavelength and the influence of the excitation intensity on the phosphorescence decay process, among other factors. The hypothesis is put forward that the characteristics of the temperature transformations of the spectra (displacements, changes in band half-widths) are related to phase transitions and relaxation processes in the glassy benzophenone. Fiz. Tverd. Tela (St. Petersburg) 40, 1052–1055 (June 1998)     

Measuring modulated luminescence using non-modulated stimulation: ramping the sample period

Conventional methods of recording linearly modulated (LM) optically stimulated luminescence (OSL) require control over either the exciting light intensity, or the ability to pulse the source. For many light sources (e.g. constant-power CW lasers, arc lamps and synchrotrons) this can be problematic. Directly analogous results to LM-OSL can, however, be achieved with non-modulated excitation sources, by ramping the sample period (RSP) of luminescence detection. RSP-OSL has the distinct advantage over LM-OSL in that, since the excitation remains at full power, data accumulation times (that can be considerable) can be reduced by typically 50%. RSP methods are universally applicable and can be employed, for example, where the excitation source is constant heat, rather than light: here, iso-thermal decay of phosphorescence becomes recorded as a sequence of peaks, corresponding to de-trapping of charge from different defect levels, and is particularly useful for analysing shallow-trap effects. RSP methods are also useful in providing significant compaction of data sets, where signal analysis is required of overlapping systems having a wide range of decay kinetics.     

Molecular tagging thermometry for transient temperature mapping within a water droplet

We present the progress made in developing a molecular tagging thermometry (MTT) technique for achieving spatially and temporally resolved temperature measurements within a small water droplet over a solid surface. For MTT measurement, a pulsed laser is used to tag phosphorescent 1-BrNp.Mbeta-CD.ROH molecules premixed with water. Long-lived laser-induced phosphorescence is imaged at two successive times after the same laser excitation pulse. The temperature measurement is achieved by taking advantage of the temperature dependence of the phosphorescence lifetime, which is estimated from the intensity ratio of the acquired phosphorescence image pair. The measured transient temperature distributions can be used to quantify the unsteady heat transfer process inside convectively cooled water droplets over smooth or rough surfaces.     

Investigation on the improvement of red phosphorescence in CaTiO3:Pr3+ nanoparticles

Red phosphorescence in nanosized CaTiO₃:Pr³⁺ phosphors has been investigated by measuring the spectra of emission and excitation, as well as the charging and decay processes. The emission intensity and the persistent time have been improved. More energy traps have been observed in nanoparticles compared to the bulk powders. The integral emission intensity from the nanoparticles is remarkably greater than that from the bulk. A phosphorescence recombination mechanism through tunneling in nanoparticles is discussed.     

Intra-dot relaxation and dephasing rates from time-resolved photoluminescence from InAs quantum dot ensembles

An ensemble of InAs quantum dots with ground state transition energies centered at 1.216 eV and density 10¹¹dots/cm² has been studied by time-resolved photoluminescence (PL). The wavelength of the 100-fs excitation pulse was tuned through the ground (excited) state transitions, resulting in resonant (optical phonon sideband) PL. The decay of the PL was time resolved with a streak camera in the interval 1.5–3 ns to avoid scattered laser light. The intensity of the PL was recorded with its polarization both parallel with and perpendicular to the excitation polarization (along one of the crystal’s cleave axes); the ratio is 2.22 at low temperatures and low excitation. A phenomenological rate equation analysis is made, separating the excitations into two classes, one polarized along the excitation polarization and the other unpolarized (either that way immediately after the excitation pulse or scattered from the first class). Excellent fits to the data lead to the conclusion that both classes decay radiatively with a lifetime of 1 ns, and a transfer from the polarized to the unpolarized species takes place with a distribution time of 12 ns at low temperatures and low excitation, dropping rapidly toward zero for temperatures above 30 K and for intense excitation levels. The polarization of a coherently excited ground state exciton should dephase with a rate equal to the sum of the radiative rate plus the inverse of this distribution time.     

Time-resolved photoluminescence on the stimulated emission in polycrystalline ZnO nanoparticles

The detailed room temperature stimulated emission including its optical characteristics from ZnO nanoparticles, which were prepared by a homogenous precipitation method, has been investigated by the time-resolved spectroscopy. The light emission originates from a free exciton recombination at a lower excitation level; the amplified spontaneous emission appears at a moderate excitation level, in which the threshold excitation intensity is 0.65 GW cm⁻². The resonant stimulated emission was observed in ZnO nanoparticles at a higher excitation intensity. Also, the emission lifetime is drastically reduced. Compared to the fluorescence decay curves, the time-resolved spectrum of the stimulated emission suggests the Gaussian-like decay time with only a few of picoseconds. The dynamic processes of lasing behavior and the characteristics of lasing emission in ZnO nanoparticles could provide the information on the crystal quality, the exciton and the lasing action in the particles.     

磷光寿命法研究无保护流体室温磷光的重原子效应和发光动力学参数

以两种卤代萘为模型化合物，基于磷光寿命的定义τ＝τ^-，τ0＝1／kp和其与各速率常数的关系，导出了一种类似于Stern-Volmer方程的线性方程：τ0／τ＝（kp_kic)/kp=1 kic/kp=1 Ksv.c。通过测定不同重原子微扰剂浓度时的磷光寿命，探讨了从两种途径计算流体室温磷光发射相关动力学参数的可行性和方法，通过这些参数对比讨论了KI和TINO3两种重原子微扰剂对这两种卤代萘无保护流体室温磷光发射的重原子效应的差异。