飞秒脉冲光参量中的色散和高阶非线性效应研究

通过数值模拟超强超短激光脉冲泵浦下的MgO:LiNbO3晶体的光参量放大过程,讨论了群速度色散和高阶非线性效应对能量转换效率和脉冲波形的影响。结果表明,群速度色散会使泵浦光脉宽增加,功率密度降低;同时,大功率泵浦下高阶非线性效应的影响不可忽略,它会进一步减小能量转换效率,还会使信号光的频谱展宽。为了提高单位晶体长度的参量放大增益,可以通过引入初始啁啾来抵消群速度色散的影响。     

光参量产生器泵浦源的优化设计与实验研究

研究了作为光参量产生器的泵浦源的1064nm Nd∶YAG激光器输出特性和运转特性。通过调Q脉冲的速率方程的数值计算得到脉冲形状,分析了脉冲形状对光参量振荡的影响。在泵浦功率为9. 3W, Q 开关重复频率为20kHz时,输出TEM00模1064nm 激光平均功率为3. 20W,光光转换效率34. 4% ,峰值功率为60kW。高峰值功率、窄脉宽的泵浦源为产生高质量、宽调谐、高转换效率的光参量产生器创造了条件。     

窄线宽1064 nm掺镱光纤激光器泵浦MgO:PPLN中红外光学参量振荡器研究

提出了一种基于1064 nm掺镱光纤激光器泵浦MgO:PPLN的3.83 μm中红外光学参量振荡器。基于单谐振光学参量振荡器的阈值理论和线宽压窄前后的光束能量集中性理论,分析了不同泵浦光束聚焦深度下,谐振腔内光束分布情况以及线宽调制前后能量的不同集中程度对阈值和光-光转换效率所产生的影响。通过采用单个光纤布拉格光栅的方式压窄了泵浦光线宽,对比分析了在不同占空比下,泵浦光线宽压窄前后对中红外光学参量振荡器输出特性的影响。当泵浦功率为18 W,脉冲激光占空比为0.2%,脉宽为100 ns,泵浦光线宽为2.5 nm时,MgO:PPLN中红外光学参量振荡器获得功率为1.42 W的3.83 μm激光输出,光-光转换效率为7.9%。将线宽压窄到0.1 nm后,脉宽为2 ns,MgO:PPLN中红外光学参量振荡器获得最高功率为1.98 W的3.83 μm激光输出,光-光转换效率为11%,光束质量M2=1.89;同时相比于线宽压窄前激光输出效率提高了39.2%。     

DPL泵浦光分布对激光脉冲的影响

研究了端面泵浦二极管泵浦固体激光器中泵浦光分布对输出脉冲的影响.通过对端面抽运情形下光场运动方程进行研究,改变泵浦光的半径和功率,得出了输出脉冲峰值功率和脉冲宽度的变化规律.结果表明:泵浦半径增大,输出脉冲峰值功率减小,脉宽展宽.泵浦功率越小,输出光脉宽越大.     

MgO:PPLN中红外光参量振荡器的闲频光纵模特性研究EI北大核心CSCD

文中介绍了一种纳秒脉冲端面泵浦MgO:PPLN外腔光参量振荡器。基频光采用激光二极管泵浦的声光调Q Nd:YVO_(4)纳秒激光器,在声光Q开关的工作重复频率为120 kHz时,实现脉宽8.1 ns、最高输出功率7.03 W的1.064μm激光输出。通过将基频光聚焦至MgO:PPLN晶体内,外腔泵浦得到了脉冲宽度为4.7 ns,输出功率0.7 W的3μm闲频光。基频光-闲频光转换效率为9.95%,将基频光与闲频光的时域波形图傅里叶变换后对比,观察到光参量振荡过程对闲频光高阶纵模的抑制现象。该研究对实现窄线宽低噪声的中红外激光具有一定的参考价值。     

光参量振荡器泵浦源的理论研究与优化设计

研究了作为光参量振荡器的泵浦源1064nm声光Q Nd:YAG激光器.从Nd:YAG激光特性出发,介绍了LD端面抽运Nd:YAG调Q固体激光器的特性,对谐振腔结构进行了等效、分析和数值计算,给出了稳腔条件和腔中振荡光斑随腔长的变化曲线.对调Q脉冲形成过程的速率方程进行了数值计算,得到脉冲形状,分析了泵浦光脉冲形状和脉宽对参量振荡信号光的影响.所得结果对产生高质量、宽调谐、高转换效率的光参量振荡器具有一定的指导意义.     

准连续LD侧面泵浦的Nd:YAG双制式脉冲激光器

报道了采用5个峰值功率为100 W的准连续激光器二极管侧面泵浦Nd:YAG棒,通过泵浦电流触发铌酸锂品体加压式Q开关,实现宽脉冲和窄脉冲交替输出的双制式脉冲激光.当泵浦能量为239 mJ、重复频率为40 Hz、泵浦脉宽500 μs时,获得长脉冲、窄脉冲交替输出的双制式脉冲激光,其中长脉冲、窄脉冲输出能量分别为33.5 mJ和18.3 mJ、脉冲宽度分别为480 μs和10 ns,光光转换效率分别为14%和7.7%.     

同步脉冲诱导的高功率中红外差频产生技术（特邀）

提出并实验探究了基于同步脉冲诱导的中红外差频产生技术,利用高速光电探测器将泵浦光脉冲转换为超短电信号,使其驱动宽带的幅度调制器,作用于可调谐连续激光器上,从而实现双色脉冲的稳定时域同步。利用了同步脉冲诱导的非线性差频过程,有效降低了光参量下转换的泵浦阈值,能够获得瓦量级的中红外超短脉冲输出,最大泵浦光转换效率达60%,且中心波长在3000~3175 nm范围内可调谐。得益于全保偏光纤架构,平均功率的不稳定度(STD/MEAN)在1 h内低至0.07%,展现了优异的长期稳定性。此外,该方案利用光-电-光高速调制实现高精度脉冲同步,免除了复杂的反馈电路,具有结构简单、即插即用、鲁棒性强的特点,为拓展中红外光源在野外的应用奠定了基础。     

波面倾斜脉冲泵浦的高效可见光飞秒光参量产生和放大器

利用脉冲波面倾斜技术补偿三波相互作用的群速度失配，建立了掺钛蓝宝石飞秒再生放大器输出倍频光泵浦共线类匹配ＢＢＯ晶体的光参量产生和放大器，其信号和空闲光输出调谐范围为０．４７～２．７μｍ，脉冲宽度为１００～１７０ｆｓ，重复率为１ｋＨｚ。脉冲最大输出能量为６．５μＪ，总能量转换效率大于１５％。     

有限脉宽脉冲泵浦下FRA中的走离和脉冲展宽

采用分步傅里叶算法数值求解非线性薛定谔方程组,模拟出有限脉宽脉冲泵浦下喇曼光纤放大器(FRA)中信号光的传输情况,研究了色散引起的走离效应和脉冲展宽对FRA的影响.结果表明:在有限脉宽脉冲泵浦的情况下,走离效应和脉冲展宽同时影响着FRA的最大作用距离和信号光幅度,当走离量较大时,走离效应对FRA的影响比脉冲展宽更明显,并且泵浦脉宽越小越易受到它的限制.     

Analysis of ultrashort-pulse second-harmonic generation in both phase- and group-velocity-matched structures

Second-harmonic generation (SHG) of ultrashort pulse in both phase- and group-velocity mismatch structures is studied theoretically in temporal and frequency domains taking account of the effects of group-velocity dispersion (GVD) and high-order phase mismatch. Under the plane-wave and pump undepletion approximation, a set of simple analytical expressions is derived in frequency domain for Gaussian pulse. Furthermore, a formula describing the SH pulse is obtained under pump depletion condition. The obtained expressions are valid in large range of interaction length and have features such as explicit form, high accuracy, and less computing time. Meanwhile, the influences of intensity, pulse duration, chirp coefficient and shape of pump pulses, as well as the linear loss of material, on the pulsewidth preservation length are investigated by numerical method. In the case of both phase- and group-velocity mismatch structures, the conversion efficiency larger than 45% could be obtained without pulse distortion for weak input ultrashort pulse.     

飞秒光参量放大技术原理及应用

飞秒光参量放大技术是一种获得宽带飞秒脉冲的有效手段.首先介绍了飞秒光参量放大技术的基本原理,并通过数值模拟显示了群速度失配及位相失配对信号转换过程的影响.数值计算结果表明:群速度失配及位相失配会导致转换效率下降,群速度失配还会导致脉冲发生畸变.其次,综述了该技术在超短脉冲特别是周期量级脉冲产生方面的研究进展,并介绍了Baltuska等设计的可以产生3.9 fs脉冲的非共线光参量放大装置.其中,详细讨论了超连续白光注入源、泵浦光角色散以及晶体选择三方面内容.最后介绍了该技术在高能飞秒脉冲产生方面取得的最新研究进展.     

基于氢气填充空芯光子晶体光纤的全光纤型气体拉曼光源特性

理论和实验研究了调Q光纤激光脉冲抽运基于氢气填充空芯光子晶体光纤气体腔的全光纤型气体拉曼光源的特性。抽运光脉冲波长为1064.7nm时,产生的Stokes频移光波长为1135.7nm。理论和实验结果均表明,产生的Stokes频移光脉冲宽度远小于抽运光脉冲,并且,Stokes频移光脉冲宽度随抽运光脉冲能量的提升而增加。此外,减小抽运光脉冲宽度,可以降低拉曼阈值抽运能量、提高Stokes频移光的转换效率。在重复频率为5kHz、脉冲宽度为125ns的调Q光纤激光脉冲抽运下,实验测得拉曼阈值抽运能量和拉曼阈值点处转换效率分别为2.13μJ和9.82%。     

信号光脉冲比抽运光窄12倍的内腔式KTP光参量振荡器

在闪光灯抽运的非稳腔Nd∶YAG被动调Q激光器腔内,放置非临界相位匹配KTP晶体,构成内腔式单谐振KTP光参量振荡器(OPO)。研究了输出信号光的波长调谐性能,获得1.57~1.60μm可调谐激光脉冲。实验结果表明,1.57μm信号光的输出能量随着光参量振荡器腔长的增加而减少,脉冲宽度随着腔长的增加而有所变化;抽运能量较大时,转换效率随着抽运能量的增加趋于饱和然后逐渐下降;对此给予了合理的理论解释。当光参量振荡器的腔长为5 cm,1.06μm抽运光脉冲宽度为30 ns时,输出的1.57μm信号光的脉冲宽度为2.5 ns,能量为21.3 mJ。1.57μm信号光的脉冲宽度仅为1.06μm抽运光脉冲的1/12,总的电光能量转换效率为0.128%。     

Generation of bright and dark soliton trains from continuous-wavelight using cross-phase modulation in a nonlinear-optical loop mirror

A simple technique for the simultaneous generation of bright and dark soliton trains from continuous-wave (CW) light is proposed and demonstrated theoretically. It is based on the optical switching characteristics of a nonlinear-optical loop mirror (NOLM) through which the CW signal is switched by a pump pulse train at another wavelength by the creation of cross-phase modulation-induced phase bias between the counter-propagating CW components. The transmitted and reflected signals exiting from the NOLM can then evolve, respectively, into bright and dark soliton trains in fibers with the appropriate group-velocity dispersion at the signal wavelength. Numerical simulations indicate that the generated solitons can be narrower than the pump pulses and that the scheme permits the conversion of nearly all of the CW energy into the soliton train energy without generating pulse pedestals     

Compact all-fiber gas Raman light source based on hydrogen-filled hollow-core photonic crystal fiber pumped with single-mode Q-switched fiber laser

We report a compact all-fiber gas Raman light source based on hydrogen-filled HC-PCF gas cell with a SM Q-switched fiber laser as the Raman pump source. Theoretical model of the hydrogen SRS based on HC-PCF pumped with Q-switched fiber laser is also analyzed. Simulated results show that the Stokes pulse is much narrower than the pump pulse, and both the Stokes pulse duration and conversion efficiency are increased with the pump pulse energy of the same duration pump pulses. The experimental results are in agreement with the theoretical results in change trend. For the 120 ns pump pulses with the repetition rate of 5 kHz, the threshold pump energy and conversion efficiency at the threshold are 1.146 μJ and 2.69%.     

Efficient third-harmonic generation of a picosecond laser pulsewith time delay

A new configuration based on the polarization-mismatching scheme with time delay for efficient frequency tripling conversion is proposed in this paper. The calculated results showed that the requirement for the efficient frequency tripling conversion of a 1-ps laser pulse is not only the optimization of peak intensity of the second-harmonic pulse, but also the optimization of the pulse duration ratio and temporal difference between the o-polarization second-harmonic pulse and the e-polarization first-harmonic pulse due to group-velocity mismatch among the interacting pulses. With the proposed scheme the group velocity mismatch can be compensated. Overall energy conversion efficiency increases from 55% to 75% under the optimized conditions at the intensity of 6 GW/cm². The temporal shape of the third-harmonic pulse with 1 ps pulse duration has no subpulses. The optimization of the efficient frequency tripling conversion for intensities of over 75 GW/cm² is also described. The results showed that the maximum tripling energy conversion efficiency is close to 80% with the optimized doubler and tripler     

The effect of pulse walkoff on stimulated Raman scattering in fibers

We have experimentally investigated stimulated Raman scattering in single-mode fibers in the regime of large Raman Stokes pulse walkoff from the pump pulse by the effect of group-velocity dispersion. Measurements are made with 36 ps duration pulses at 532 nm produced from a frequency-doubled and harmonically mode-locked Nd:YAG laser. We find that for 20 percent conversion, the Raman output is produced about two walkoff lengths into the fiber as a pulse of approximately the same duration as the input pulse. We also find that the Raman pulse is produced with a strong frequency chirp.     

飞秒光参量放大过程中高阶非线性效应的影响

用计算机仿真模拟了高强度飞秒激光抽运下的光参量放大 (OPA)过程 ,着重讨论了高阶非线性效应对参量转化效率和波形的影响。为了抑制高阶非线性效应对放大信号光波形的调制 ,改善波形质量 ,防止信号光的能量倒流回抽运光 ,并为进一步从抽运光中抽取出尽可能多的能量 ,提高参量转化效率 ,引入了适当的相位失配以抵消高阶非线性效应。利用级联非线性相移从理论上解释了这一物理原因     

改进的高功率飞秒脉冲系统理论研究

理论分析了由掺镱光纤放大器、高非线性光纤(HNLF)和光栅对组成的高功率飞秒脉冲产生系统。由于掺镱光纤放大器固有的有限带宽效应会导致脉冲抛物波形和线性啁啾的畸变,影响脉冲的压缩。在放大器和光栅对之间引入高非线性光纤,可以在展宽脉冲频谱的同时也保持波形和线性啁啾。针对高非线性光纤计算了不同的非线性系数和色散参量对压缩脉冲宽度和压缩效率的影响。研究表明,较高的非线性系数可以进一步降低最小压缩脉冲宽度,但是压缩效率随光纤长度增加而下降的趋势也变得越显著;较低的色散参量有利于得到更短的压缩脉冲,并且相对较高色散参量不会显著地降低压缩效率;在一定范围内,通过延长高非线性光纤可以缩短压缩脉冲,同时需要兼顾压缩效率。