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。     

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…     

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。     

基于空芯光纤中氢气受激拉曼散射的1.7μm光纤激光光源研究

报道了一种基于空芯光子晶体光纤中氢气受激拉曼散射的新型1.7μm光纤激光光源。建立了仅包含泵浦光和一阶斯托克斯光的简单稳态耦合波方程,并进行了仿真计算。采用自制的1550 nm纳秒脉冲光纤放大器,泵浦一段长约3 m、充高压氢气的商用空芯光子晶体光纤,利用氢气分子的转动受激拉曼散射实现了1705 nm斯托克斯波的有效转换。气压为1.2 MPa时,最大平均输出功率约0.5 W(单脉冲能量约为2.5μJ),最大光光转换效率约为32%(相对总的泵浦功率)。研究结果为实现高功率1.7μm波段近红外激光输出提供了一条有效的新途径。     

单程高增益1.9μm光纤气体拉曼激光器

报道了基于空心光子晶体光纤中氢气分子振动受激拉曼散射(SRS)的单程高增益1.9μm光纤气体激光器。用一个线偏振1064nm亚纳秒脉冲微芯激光器抽运一段长6.5m、充高压氢气的低损耗负曲率空心光纤,实现了到氢气分子一级振动斯托克斯波1907nm的有效转换。气压为2.3MPa时最大能量转换效率大于27%,相应的量子转换效率大于48%,激光平均功率约为10mW,峰值功率大于2000W。为实现高功率、窄线宽、大范围调谐的紧凑型中红外光纤激光器提供了一条潜在的有效途径。     

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。     

碘激光的H2振动受激拉曼阈值研究

首次实现了脉冲光解碘激光作为基频光的氢气振动受激拉曼变频,对碘激光的波长转换有着重要意义。在碘激光单脉冲能量100~130 mJ(脉宽100 ns)的条件下, 采用双次聚焦技术降低了高压氢气的振动受激拉曼变频的阈值,获得了波长为2900 nm中红外激光,光子转化效率最高达到8.7%。实验发现当拉曼介质氢气气压大于1 MPa后,一级斯托克斯光的拉曼转化效率不再随气压变化,并对这一现象进行了理论分析和归属。     

单纵模Nd:YAG激光抽运CH4中强后向受激拉曼散射

用单纵模Nd:YAG二倍频激光[波长532 nm,线宽△vp＜100 MHz,脉宽(半峰全宽)6.5 ns]抽运CH4气体,观察到很强的后向一级斯托克斯(BS1)受激拉曼散射,这与前人采用脉宽30 ns的单纵模抽运激光得到的绝大部分为后向受激布里渊散射(SBS)完全不同,其原因是脉宽6.5 ns与本实验条件下CH4的受激布里渊散射声子寿命接近,受激布里渊散射处于瞬态.理论计算表明,这时的受激布里渊散射瞬态增益系数已略小于后向一级斯托克斯的增益系数,而被其竞争抑制.当脉冲重复频率为2 Hz,抽运能量为95 mJ时,在1.1 MPa CH4中,后向一级斯托克斯的量子转换效率高达73%,其时间波形出现张弛振荡,脉宽被压窄到1.2 ns,从而使后向一级斯托克斯峰值功率达到了抽运激光功率的2.7倍,而且其光束质量要大大优于抽运激光的光束质量.用编制的准二维计算机模型程序相当好地再现了实验中后向一级斯托克斯的时间波形张弛振荡.     

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。     

单纵模Nd∶YAG激光抽运CH_4中强后向受激拉曼散射

用单纵模Nd∶YAG二倍频激光[波长532 nm,线宽Δνp<100 MHz,脉宽(半峰全宽)6.5 ns]抽运CH4气体,观察到很强的后向一级斯托克斯(BS1)受激拉曼散射,这与前人采用脉宽30 ns的单纵模抽运激光得到的绝大部分为后向受激布里渊散射(SBS)完全不同,其原因是脉宽6.5 ns与本实验条件下CH4的受激布里渊散射声子寿命接近,受激布里渊散射处于瞬态。理论计算表明,这时的受激布里渊散射瞬态增益系数已略小于后向一级斯托克斯的增益系数,而被其竞争抑制。当脉冲重复频率为2 Hz,抽运能量为95 mJ时,在1.1 MPa CH4中,后向一级斯托克斯的量子转换效率高达73%,其时间波形出现张弛振荡,脉宽被压窄到1.2 ns,从而使后向一级斯托克斯峰值功率达到了抽运激光功率的2.7倍,而且其光束质量要大大优于抽运激光的光束质量。用编制的准二维计算机模型程序相当好地再现了实验中后向一级斯托克斯的时间波形张弛振荡。     

High Efficient C6H12 Raman Laser Enhanced by DCM Fluorescence

We report the first-order Stokes output （wavelength of 627.6 nm） from C6H12 enhanced by DCM dye fluorescence with high energy conversion efficiency of 47.9%, quantum conversion efficiency of 56.5%. To our knowledge, it is the highest conversion efficiency of stimulated Raman scattering obtained from liquid Raman laser. A 532nm frequency doubled Nd：YAG laser with 8 Hz repetition rate is employed as the pump source, and the enhancement medium is DCM dye solution in ethanol. The conversion efficiencies at various pump energies and various pump repetition rates are measured and analysed. The enhancement mechanism of SRS together with its potential application is discussed.     

355 nm脉冲激光在甲烷中的高效多波长拉曼转换

 研究了脉冲Nd:YAG激光（355 nm）泵浦的甲烷中多级Stokes光的产生和惰性气体对其转换效率的影响，其中一级和二级Stokes光的最大能量转换效率分别可达71%和38%（对应量子效率为79%和48%），大大高于已往文献报道的20%。在0.5 MPa下，可同时获得322 nm（3.6%），355 nm（24.5%），396 nm（24.3%），448 nm（22.3%）和515 nm（9.3%）的多波长输出。甲烷压力对多级Stokes转换有显著影响：高气压利于产生高效的一级Stokes光，而低气压则适合于高级Stokes光的产生。根据级联受激拉曼散射(SRS)和四波混频(FWM)理论对实验结果进行了分析，结果表明甲烷中高级Stokes光的产生是SRS和FWM协同作用的结果。加入的氦气增强了甲烷中Stokes光的转换效率，而氩气的作用恰恰相反，利用热透镜效应可以很好地解释这些现象。     

High efficiency picosecond pulse C6H12 Raman laser amplified by DCM fluorescence

In this paper, the Stimulated Raman Scattering (SRS) Stokes wave pumped by a picosecond pulse laser in cyclohexane (C₆H₁₂) enhanced by the fluorescence of 4-(Dicyanomethylene)-2-methyl-6-(p-dimethylaminostyryl)-4H-pyran (DCM) is studied in the experiment. 249 ps pulse laser from Nd:YAG laser second harmonic generation at 532 nm is used as the pumping source. The results indicate that the energy conversion efficiency is raised by the increase of the pumping energy, and the high conversion efficiency depends on the proper selection of the DCM concentration. The high energy conversion efficiency of the first Stokes enhanced by fluorescence of 37.3% is obtained. The fluorescence enhancing mechanism of the picosecond SRS Stokes wave is discussed.     

LiIO3晶体的受激拉曼散射

 采用腔外单次通过方式,测量了LiIO₃晶体在532 nm皮秒脉冲下的受激拉曼散射。实验中观察到3级斯托克斯线（556.07,582.30, 611.76 nm）和1级反斯托克斯线（509.57 nm）,由此可计算出其频率间隔为820 cm^-1。测量了LiIO₃晶体各级拉曼散射谱线的阈值和增益系数,受激拉曼散射的整体转换效率达到56%。基于LiIO₃晶体实现了皮秒外腔式拉曼激光器的运转,双波长输出总转换效率为27%,最大输出能量1.4 mJ。     

Optical suppression of second-order stimulated Brillouin scattering in a simple focused beam cell

It has been investigated experimentally that the output energy and pulse-durational profile of first-order Stokes depend on the effective gain length due to the presence of the second-order SBS. The experimental results indicate that when the energy of an incident pump laser is strong enough and the effective gain length is relatively long, the self-accumulation of energy of first-order Stokes is enough to adequately reach a high peak power point to activate the second-order. The second-order SBS restrains the output energy of first-order to a great extent and plays an optical suppression role.     

Low-threshold lasing in stimulated Raman lasers with nanosecond pumping

We have studied the conditions resulting in maximum lowering of the excitation threshold for pulsed stimulated Raman (SRS) lasers. It has been shown theoretically that in order to achieve the lowest possible values of laser radiation pulse energy needed to excite lasing in SRS lasers, we need high reflection of the cavity mirrors and low losses at the wavelength of the 1st Stokes component, high reflection of the output mirror at the wavelength of the pump radiation, and also matching of the confocal parameters for the exciting laser radiation and the cavity with each other and with the length of the Raman-active medium. The experimentally achieved excitation threshold for an SRS laser based on a barium nitrate crystal was 6 μJ, which quantitatively corresponds well to the calculation results. Lasing of up to five Stokes components simultaneously occurred. The efficiency for conversion of the laser radiation to one component was as high as 39%. __________ Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 75, No. 2, pp. 284–290, March–April, 2008.     

Coaxial Multi-Wavelength Generation in YVO_4 Crystal with Stimulated Raman Scattering Excited by a Picosecond-Pulsed 1064 Laser

The multiwavelength characteristics of stimulated Raman scattering(SRS) in YVO_4 crystal excited by a picosecond laser at 1064 nm are investigated theoretically and experimentally. Laser output with seven wavelengths is achieved coaxially and synchronously at 894, 972, 1175, 1312, 1486, 1713 and 2022 nm in a YVO_4 crystal. The maximum total Raman output energy is as high as 2.77 m J under the pump energy of 7.75 m J. A maximum total Raman conversion efficiency of 47.8% is obtained when the pump energy is 6.54 m J. This is the highest order of Stokes components and the highest output energy generated by YVO_4 reported up to date. This work expands the Raman spectrum of YVO_4 crystal to the near-IR regime, with seven wavelengths covered at the same time,paving the way for new wavelength generation in the near-IR regime and its multiwavelength application.     

High-power tunable terahertz generation from a surface-emitted THz-wave parametric oscillator based on two MgO:LiNbO3 crystals

A high-powered tunable terahertz wave (THz-wave) has been parametrically generated via a surface-emitted THz-wave parametric oscillator (TPO) pumped by a multi-longitudinal-mode Q-switched Nd:YAG laser. The effective parametric gain length was enlarged by employing two MgO:LiNbO₃ crystals. The tunable THz-wave radiation from 0.8 to 2.8 THz was realized via varying phase-matching angle between the pump wave and the Stokes wave. The maximum THz-wave radiation was 173.9 nJ/pulse at 1.7 THz as the pump energy was 82 mJ, corresponding to an energy conversion efficiency of about 2.12 × 10⁻⁶ and a photon conversion efficiency of about 0.035%. The first-order, the second-order and the third-order Stokes waves were observed during the experiments.     

Investigation of SRS conversion of XeCl laser emission in lead vapor,methane, and hydrogen

We have thus optimized the conditions for SRS conversion of XeCl-laser emission in lead vapor, methane, and hydrogen. The greatest influence on the conversion efficiency is exerted for an SRS cell with lead by the divergence of the pump radiation, the focusing geometry, and the type of buffer gas. The maximum efficiency with respect to absorbed UV energy was ∼57% when xenon gas was used as the buffer, corresponding to 85% of the photon efficiency. The converted radiation could be continuously tuned in the 457.6–459.3 nm band. Addition of a light gas such as helium or hydrogen to methane raised the efficiency of conversion into Stokes components in methane to ∼24 %.