组合光纤中受激拉曼散射和四波混频研究

在抽运光和耦合条件不变的情况下,研究了熔接组合的非零色散位移单模光纤(NZDSF)和标准单模光纤(SMF)中的受激拉曼散射(SRS)和四波混频(FWM)产生和传输特征。采用532 nm脉冲激光抽运NZDSF,从20 m处开始产生以LP₀₁模传输的SRS第一级Stokes光;紧接着在30 m处产生了FWM,SRS受到FWM抑制,传输模式逐渐转化为LP₁₁模;经过80 m处熔接点后,由于熔接处双锥光纤结构使光场模式互相干涉,光波模式恢复为LP₀₁模,FWM受到抑制。该现象和机理有利于抑制密集波分复用(DWDM)系统中光学非线性失真和促进光孤子通信系统的发展。     

非线性光学 非线性光散射、振荡与谐波产生

O4372006054148355nm Nd∶YAG激光在H2中的高效一级斯托克斯转换=High-efficiency first-order Stokes conversion in H2pumped by a Nd∶YAGlaser at355nm[刊,中]/冷静(中科院大连化物所分子反应动力学国家重点实验室.辽宁,大连(116023)),花晓清…//光学学报.—2006,26(7).—1078-1082对脉冲Nd∶YAG激光(355nm)在H2和H2∶He-Ar混合气体中的受激喇曼散射(SRS)进行了研究。在0.5MPa的氢气中,同时测量到从二级反斯托克斯到三级斯托克斯的多波长输出,其总转化效率达88%;而高压下只剩下一级和二级斯托克斯输出,其中二级斯托克斯最大…     

355nm Nd∶YAG激光在H_2中的高效一级斯托克斯转换

对脉冲Nd∶YAG激光(355 nm)在H2和H2∶He-Ar混合气体中的受激拉曼散射(SRS)进行了研究。在0.5 MPa的氢气中,同时测量到从二级反斯托克斯到三级斯托克斯的多波长输出,其总转化效率达88%;而高压下只剩下一级和二级斯托克斯输出,其中二级斯托克斯最大能量转化效率达44%(对应量子效率为63%)。由于高级斯托克斯的竞争,纯氢气中一级斯托克斯的最大能量转换效率不超过43%。通过向3 MPa氢气中掺入2 MPaAr气后,很好地抑制了二级斯托克斯的产生,从而获得了能量转换效率高达71%(对应量子效率为83%)的一级斯托克斯输出。对四波混频和级联受激拉曼散射在氢气多级斯托克斯产生中的作用以及惰性气体对它们的影响进行了讨论。     

355 nm Nd:YAG激光在H2中的高效一级斯托克斯转换

对脉冲Nd:YAG激光(355 nm)在H2和H2:He-Ar混合气体中的受激拉曼散射(SRS)进行了研究.在0.5 MPa的氢气中,同时测量到从二级反斯托克斯到三级斯托克斯的多波长输出,其总转化效率达88%;而高压下只剩下一级和二级斯托克斯输出,其中二级斯托克斯最大能量转化效率达44%(对应量子效率为63%).由于高级斯托克斯的竞争,纯氢气中一级斯托克斯的最大能量转换效率不超过43%.通过向3 MPa氢气中掺入2 MPaAr气后,很好地抑制了二级斯托克斯的产生,从而获得了能量转换效率高达71%(对应量子效率为83%)的一级斯托克斯输出.对四波混频和级联受激拉曼散射在氢气多级斯托克斯产生中的作用以及惰性气体对它们的影响进行了讨论.     

强激光长程传输中受激拉曼散射对光束特性的影响

依照受激拉曼散射(SRS)半经典理论从物质激发感应出的三阶非线性极化率X~(3)出发,在强激光长程传输受激拉曼散射中建立了泵浦(传输)激光相位与斯托克斯(Stokes)光强相耦合的理论模型。它清楚地说明了SRS效应影响泵浦激光光束特性,其中包括时间特性及空间特性(光束质量)的物理机制及影响因素。理论分析与实验结果符合得较好。实验还测得了不同转换效率η_s情况下传输后的泵浦光及Stokes光的时间过程特性。结果表明,在小转换效率的条件下,泵浦光时间特性基本不受SRS效应的影响;而当转换效率η_s>5％时,泵浦光脉宽随η_s增大而被逐渐压缩。     

KrF激光泵浦H2受激拉曼放大

利用KrF激光泵浦高压H_2,在同轴前向的受激拉曼散射(SRS)作用下,产生受激拉曼放大,1阶Stokes光对泵浦光的转换效率为17.2％,并对影响放大过程和转换效率的若干因素作了分析。     

宽带泵浦激光的聚焦位置对SRS发生过程的影响

 结合SRS实验,重点研究了聚焦位置对Raman介质中的物理过程、Stokes光的输出特性的影响,比较了SRS阈值和转换效率的实验结果与理论预期。     

温度变化对单模石英光纤受激拉曼散射附加峰的影响

用10 m长单模石英光纤进行受激拉曼散射温度特性研究, 实验中发现在泵浦光和一级Stokes左右出现了附加峰(称为双峰), 其峰强度随温度的升高(80～295 K)呈现先增加后减弱现象。当温度达到295 K时, 一级Stokes双峰消失。由受激四光子混频理论计算可知,这种双峰现象是受激四光子混频的结果。同时对SRS一级Stokes所产生的受激四光子混频的Stokes频移随温度升高由706.9 cm-1增大到712.9 cm-1和其半宽度由1.75 nm增至2.18 nm的现象也进行了解释。     

Ba(NO3)2晶体受激拉曼散射的角度分布和脉冲压缩

报道了利用重复频率为30 Hz,波长为532 nm 的Nd∶YAG倍频激光单次通过抽运硝酸钡（Ba(NO3)2）晶体（晶体由水溶液降温法生长,长度为48 mm,横截面为10 mm×10 mm）,获得高效率的一阶（563 nm）,二阶（599 nm）和三阶（639 nm）斯托克斯光的实验结果.硝酸钡晶体沿着［110］晶轴方向切割.观测到一、二、三阶斯托克斯光呈锥形环分布,一、二、三阶斯托克斯光的散射外边缘与抽运光轴线间的夹角大小分别为1.7°,3.5°,5.0°.同时也观测到Ba(NO3)2的SRS角度分布与抽运光强度无关.定性分析认定,Ba(NO3)2的SRS角度分布主要是由相位匹配过程决定的.测得抽运光、一、二、三阶斯托克斯光的脉宽分别为11.6 ns,9.8 ns,8.4 ns和4.5 ns.当抽运光功率密度约为150 W/cm2时,获得一、二、三阶斯托克斯光的最大光光转换效率,分别为33.5%,8.8%和3.4%. 此外,由于晶体中的热沉积效应,观察到了Ba(NO3)2晶体的SRS转换效率饱和现象.     

基于Nd∶YAG/Cr∶YAG复合晶体的全固态紫外激光器

被动调Q产生1064 nm脉冲激光在腔外聚焦后入射到KTP中,产生532 nm的倍频光,再通过LBO和频产生355 nm激光。当抽运功率为3.4 W时,基频光调Q输出平均功率为350 mW,峰值功率达3.5 kW。腔外二倍频532 nm绿光输出平均功率为110 mW,用Ⅰ类相位匹配LBO晶体和频获得36 mW的355 nm的紫外激光输出,三倍频效率(1064~355 nm)达到10.2%。由于Cr∶YAG晶体达到饱和吸收后,会呈现出各向异性的特征,对基频光的偏振状态有很大影响。实验中必须合理放置复合晶体,使基频光的偏振状态为近似线偏振以提高转换效率。     

532 nm Nd:YAG激光的高效多波长受激喇曼转化

 Nd:YAG二倍频激光(532 nm)泵浦H2中的受激喇曼散射产生多级斯托克斯。其中一级、二级和三级斯托克斯的最高量子转换效率分别可达66%,60%和19%。在0.44 MPa下,可同时获得1 579 nm(19%),954 nm(30%),683 nm(33%),532 nm(14%),436 nm(3.7%)和368 nm(1.4%)的多波长输出。H2压力对多级斯托克斯转换有显著影响：高气压有利于产生高效的一级斯托克斯,而低气压则适合于高级斯托克斯和反斯托克斯的产生。     

Generation of UV laser light by stimulated Raman scattering in D2, D2/Ar and D2/He using a pulsed Nd:YAG laser at 355nm

A pulsed Nd:YAG laser at 355nm is used to pump Raman cell filled with D_2, D_2/Ar and D_2/He. With adequately adjusted parameters, the maximum photon conversion efficiency of the first-order Stokes light (S_1, 396.796nm) reaches 33.33% in D_2/Ar and the stability of S_1 in pure D_2 is fairly high, the energy drift being less than 10% when the pump energy drifts in the range of 5%. The conversion efficiency and stability, which are functions of the composition and pressure of the Raman medium and the energy of pump laser, are investigated. The result has been used to optimize the laser transmitter system for a differential absorption lidar system to measure NO_2 concentration profiles.     

Effect of buffer gas on the generation of eye-safe 1.54 μm radiation using the stimulated Raman scattering technique in CH4

Experimental results on the generation of 1.54 μm eye-safe radiation in pure CH₄, CH₄:He and CH₄:Ar mixtures pumped by the fundamental of an Nd:YAG laser, using the stimulated Raman scattering (SRS) technique, are described. A decrease in the energy conversion efficiency and degradation in the beam quality of S₁ was observed in pure CH₄ at high pump energies. This problem was overcome in CH₄:He and CH₄:Ar mixtures. Compared with the first Stokes (1.54 μm) energy conversion efficiency in pure CH₄, at a pump energy of 126 mJ, an enhancement of 50% in energy conversion efficiency was observed in the CH₄:Ar mixture (60% argon concentration) and as much as 100% in the CH₄:He mixture (60% helium concentration). The use of these buffer gas mixtures improved the spatial beam quality of the Stokes radiation considerably and also resulted in raising the pump threshold for optical breakdown of the Raman gain medium.     

Generation of UV and VIS laser light by stimulated Raman scattering in H2, D2, and H2/He using a pulsed Nd:YAG laser at 355 nm

2 ), deuterium (D₂), and mixtures of hydrogen and helium (H₂/He), versus Raman gas pressure and input pump energy of the pulsed Nd:YAG laser at 355 nm, are reported. Photon conversion efficiencies of 50% and 27% are achieved at the first Stokes lines (S₁) in H₂ and D₂, respectively. As a result, ultraviolet and visible laser light (274–503 nm) was generated with energies ranging from a few mJ up to several tens of mJ. Received: 5 January 1998/Revised version: 3 June 1998     

Effect of buffer gas on the generation of eye-safe 1.54 μm radiation using the stimulated Raman scattering technique in CH4

Experimental results on the generation of 1.54 μm eye-safe radiation in pure CH₄, CH₄:He and CH₄:Ar mixtures pumped by the fundamental of an Nd:YAG laser, using the stimulated Raman scattering (SRS) technique, are described. A decrease in the energy conversion efficiency and degradation in the beam quality of S₁ was observed in pure CH₄ at high pump energies. This problem was overcome in CH₄:He and CH₄:Ar mixtures. Compared with the first Stokes (1.54 μm) energy conversion efficiency in pure CH₄, at a pump energy of 126 mJ, an enhancement of 50% in energy conversion efficiency was observed in the CH₄:Ar mixture (60% argon concentration) and as much as 100% in the CH₄:He mixture (60% helium concentration). The use of these buffer gas mixtures improved the spatial beam quality of the Stokes radiation considerably and also resulted in raising the pump threshold for optical breakdown of the Raman gain medium.     

High-repetition-rate high-beam-quality 43 W ultraviolet laser with extra-cavity third harmonic generation

High-power, high-repetition-rate extra-cavity third harmonic generation of 355 nm with high beam quality has been developed. The acoustic-optical Q-switched Nd:YVO₄ MOPA laser including 2- and 4-stage amplifiers was used as the IR source. With the extra-cavity frequency conversion of LBO crystals, 30.2 W TEM₀₀-mode 355 nm UV laser was obtained with a 2-stage amplifier MOPA laser, and the optical-to-optical (1064 nm to 355 nm) conversion efficiency was up to 30%. Enhanced 43 W TEM₀₀ UV laser at 60 kHz was achieved with a 4-stage amplifier MOPA IR laser, and pulse duration was 10.7 ns corresponding to the peak power as high as 67 kW, with single pulse energy of 0.72 mJ. The optical–optical efficiencies from IR and diodes to UV were 28% and 10% respectively.     

三倍频Nd∶YAG激光抽运氧气中的受激拉曼和布里渊散射

报道了三倍频脉冲Nd∶YAG激光(355 nm)在两种不同带宽模式下抽运氧气中受激拉曼散射(SRS)和受激布里渊散射(SBS)的实验研究。在宽带(约1 cm-1)抽运模式下,只测到了前向受激拉曼散射,而没有观察到后向散射,其一级和二级斯托克斯最大能量转换效率可达22%和8%。在窄带(约0.003 cm-1)模式下,前向、后向受激拉曼散射和受激布里渊散射都测量到了,但大部分抽运能量都转换到受激布里渊散射,其转换效率可达67%。测量了两种带宽模式下各散射组分在它们最佳转换时的波形;窄带情况下后向受激拉曼散射和受激布里渊散射的脉宽分别可压窄至1.5 ns和2.3 ns,不到抽运脉宽的三分之一,使得受激布里渊散射峰值功率可大大高于抽运功率。对氧气中前向、后向受激拉曼散射和受激布里渊散射之间的竞争进行了讨论。     

三倍频Nd:YAG激光抽运氧气中的受激拉曼和布里渊散射

报道了三倍频脉冲Nd：YAG激光（355nm）在两种不同带宽模式下抽运氧气中受激拉曼散射（SRS）和受激布里渊散射（SBS）的实验研究。在宽带（约1cm^-1）抽运模式下,只测到了前向受激拉曼散射,而没有观察到后向散射,其一级和二级斯托克斯最大能量转换效率可达22％和8％。在窄带（约0．003cm^-1）模式下,前向、后向受激拉曼散射和受激布里渊散射都测量到了,但大部分抽运能量都转换到受激布里渊散射,其转换效率可达67％。测量了两种带宽模式下各散射组分在它们最佳转换时的波形;窄带情况下后向受激拉曼散射和受激布里渊散射的脉宽分别可压窄至1．5ns和2．3ns,不到抽运脉宽的三分之一,使得受激布里渊散射峰值功率可大大高于抽运功率。对氧气中前向、后向受激拉曼散射和受激布里渊散射之间的竞争进行了讨论。     

Efficient rotational Raman conversion of XeCl laser radiation in H2

2 is investigated with a XeCl laser. It is shown that energy conversion to rotational Stokes radiation can be efficiently obtained by properly choosing the focusing geometry of pump radiation and the pressure of the Raman medium even at moderate pulse energies. Energy conversion to the first rotational Stokes at 313.8 nm with efficiencies as high as 38% is obtained with a circularly polarised XeCl pump beam of 10-mJ energy focused in 30 bar of H₂. The spectral and optical characteristics of the pump and the rotational Stokes radiation are analysed. Received: 29 May 1996/Revised version: 7 March 1997