多点抽运光纤激光器速率方程组的近似解析解

为了方便地对多点抽运光纤激光器的特性进行分析,采用保留上能级粒子再发射项主体部分的方法以提高精确度,解析求解了多点抽运掺镱光纤激光器的稳态二能级速率方程组,得到了光纤激光器的输出功率的近似解析解。并将输出功率的解析解与数值解进行了对比。结果表明,解析解与数值解差别小于5%。讨论了抽运光的利用效率与抽运点位置的关系,得到抽运源应该尽量靠近光纤端面的结论。同时,对比了单点抽运和多点抽运方案中抽运功率在光纤中的分布,可以看到,多点抽运时,抽运功率的分布较为均匀,能够缓解因包层对抽运光吸收引起的光纤局部过高的温升所造成的一系列问题,是实现大功率激光输出的良好选择。     

高冲程薄片激光器抽运结构的设计

为了实现薄片激光器高吸收转换效率的目的,采用多次抽运吸收的方式,结合光斑离轴非对称反射抛物面和光斑对称分布非球面的抽运结构,提出了一种可以提高非球面光束分布占空比的高冲程抽运的新方法。设计了多种不同抽运冲程的结构,使用ZEMAX模拟验证了24冲程抽运时的光路分布和光斑位置图,通过比尔吸收定律理论计算了不同抽运冲程下薄片晶体对抽运光的吸收效率。结果表明,所设计的24冲程、36冲程、40冲程和80冲程的抽运结构,其中36冲程的吸收效率的性价比最高。该研究对高功率、高冲程、小体积的抽运结构设计具有指导作用。     

Theory and operation of high-power CW and long-pulse dye lasers

A complete theoretical model for CW and long-pulse dye lasers is developed. The effects of excited singlet-state absorption of pump and laser fight and triplet absorption of pump and laser light are included. Expressions are derived for gain, actual dye transmission, and output power. Experimental work is presented to verify the theory and to obtain values of excited-state absorption cross sections for rhodamine 6G by matching experimental to theoretical curves.     

Edge- and end-pumped slab lasers with both efficient and uniform pumping

In conventional high-power slab lasers, the design is often a compromise between pump absorption efficiency and uniformity. In this paper, both are studied for diode-array-pumped slab lasers. We explore a method with which each can be separately optimized, so it becomes possible to have both high efficiency and uniformity in slab lasers with long optical pump paths. The method is applicable to composite and ceramic crystal slab lasers.     

Cascaded silicon Raman lasers as mid-infrared sources

It is shown by numerical simulations that cascaded silicon Raman lasers, in which the pump light undergoes multiple Stokes shifts in a silicon waveguide, can efficiently convert near-IR to mid-IR radiation. For pump wavelengths significantly below 2 mum, two-photon-absorption-induced free-carrier absorption degrades conversion efficiency, and the effective carrier lifetime determines the shortest possible pump wavelength     

Theoretical characterization of Raman oscillation with intracavitypumping of fiber lasers

Theoretical results relating to the generation of continuous-wave (CW) output from fiber lasers that are internally pumped with light generated from the stimulated Raman effect are presented. This investigation establishes the important fiber and resonator parameters, such as the fiber length and glass composition, dopant concentration, and pump power required to realize this new form of fiber laser arrangement. Three examples are studied: the Ho³⁺-doped silica fiber laser that is pumped at a wavelength of 1.15 μm, the Er ³⁺-doped silica fiber laser which is pumped at 1.48 μm and, the Tm³⁺-doped silica fiber laser which Is pumped at 1.625 μm. These three examples cover first Stokes pumping, second Stokes pumping, and first Stokes pumping with direct dopant absorption of the pump light, respectively. The simulations involve the use of simple numerical models comprising the spatially dependent field propagation equations (under the slowly varying field approximation) and the rate equations for the population densities. It is established that intracavity Raman pumping of fiber lasers with first Stokes radiation is efficient when the losses at the pump, Stokes and laser wavelengths are kept low (<10 dB/km). It is also established that second Stokes pumping is, even with direct absorption of the pump light, theoretically quite efficient and, as a result, the Er³⁺-doped silica fiber laser which is pumped with second Stokes radiation at 1.48 μm may provide the best demonstration of intracavity Raman pumping     

Analytical model for rare-earth-doped fiber amplifiers and lasers

An analytical model for two-, three-, and four-level system rare-earth-doped fiber amplifiers and lasers is presented. The theory is applicable to dopants such as erbium, neodymium, thulium; praseodymium, and ytterbium. Fiber-amplifier gain is expressed in terms of attenuation coefficients, intrinsic saturation powers, and cross-saturation powers at the pump and signal wavelengths. These parameters can be directly determined from one- and two-beam fiber-transmission measurements. System-independent formulas are given for the slopes and thresholds of ring and linear fiber lasers. Good agreement between theory and experiment has been shown for erbium-doped fiber amplifiers and lasers and thulium-doped fiber lasers. Because of the finite-pump-level lifetime, three- and four-level models predict a flattening of the fiber laser slope at higher pumping powers when the fiber is shorter than the optimum length. Approximate system-independent solutions are also given for fiber amplifiers with excited-state absorption at either the pump or signal wavelengths. A novel technique, requiring only one tunable light source, is proposed for finding the best pump wavelength when pump ESA is present. The two-level analytical model recently developed for erbium-doped fibers is a special case of this theory     

掺镱双包层光纤激光器热应力场的理论研究

针对高功率掺镱双包层光纤激光器(DCFL)的热应力模型,对影响热应力场分布、包层表面最大热应力的参数如:纤芯半径、泵浦方式、泵浦吸收系数进行了研究.结果表明,热破坏作用主要集中于纤芯和包层表面;减小纤芯半径或增加光纤长度能够降低包层表面的最大热应力值;双端对称泵浦较之其它泵浦方式性能更优;采用非均匀泵浦吸收系数方案在降低包层表面最大热应力的同时,维持了高功率输出.     

Thermal effects in kilowatt fiber lasers

Thermal effects and their influences on kilowatt ytterbium-doped double-clad (YDDC) fiber lasers are studied through numerical modeling. Solutions to suppress the thermal effects in the YDDC fiber lasers under bidirectional end pump and distributed pump are presented and compared for the first time. It is shown that lower operating temperature and more uniform heat dissipation in fibers can be obtained by optimizing the arrangement of pump powers, pump absorption coefficients, and fiber lengths.     

High-power and tunable operation of erbium-ytterbium Co-doped cladding-pumped fiber lasers

We describe erbium-ytterbium co-doped fiber lasers in different free-running and tunable configurations. The lasers were cladding-pumped by high-power multimode diode sources. We compare pumping at 915 and 980 nm. With a free-running laser, we obtained slope efficiencies of up to 50% with 915-nm pumping and 38% with 980-nm pumping, with respect to absorbed pump power. We reached a double-ended output power of 16.8 W from the free-running laser. Thanks to a high rare-earth concentration and a small inner cladding area (possible with the high-brightness pump sources we used), the operating pump absorption of the fiber reached 8 dB/m. With such high absorption, short fibers with high nonlinear thresholds are possible even with cladding pumping. The tunable fiber laser had a tuning range from 1533 to 1600 nm and emitted 6.7 W of output power at 1550nm in a high-brightness, single-polarization, narrow linewidth beam.     

1064 nm波段泵浦掺铥光纤激光器的理论研究

文章对1064 nm波段泵浦掺铥光纤激光器进行理论分析,以获得到对实际研究有用的结论.先从理论分析计算了1064 nm泵浦掺铥光纤激光器的粒子速率方程和传输方程,并在传输方程中考虑了泵浦光和激光本征吸收影响.利用matlab软件理论模拟不同长度光纤的正反向泵浦光和激光在光纤中的分布.模拟讨论了输出功率与最佳光纤长度的关系,以及激光本征吸收系数和掺铥离子浓度对输出功率的影响.最佳光纤长度时的激光输出功率最高.考虑激光本征吸收是合理的,较小的本征吸收有较高的最大的输出功率.存在一个最佳的掺杂离子浓度使得输出功率最大.     

不同泵浦波长光纤激光器模式不稳定效应对比

一般认为,光纤激光器模式不稳定效应主要来自于泵浦源量子亏损和增益光纤泵浦吸收所产生的热效应。理论分析了光纤中的热源,发现诱发模式不稳定的热效应主要来源于泵浦吸收、其次是量子亏损;利用课题组开发的仿真软件SeeFiberLaser对该结论进行仿真。仿真结果表明:泵浦吸收系数越低,光纤中的最高温度和温度梯度越低,越有利于抑制热致折射率光栅的形成,提高模式不稳定阈值。搭建了纤芯/包层直径为30/400 μm的前向泵浦掺镱光纤激光振荡器,对比研究了中心波长为976 nm 、915 nm和940 nm的泵浦源泵浦时激光器的模式不稳定阈值特性。结果表明,分别采用中心波长为976 nm 、915 nm和940 nm 的半导体激光器作为泵浦源时,激光器模式不稳定阈值分别为279 W、502 W和697 W,光光转化效率分别为67.7%、61%和63%。由此可以发现,泵浦吸收系数对模式不稳定阈值的影响大于量子亏损对模式不稳定阈值的影响,通过改变泵浦波长降低泵浦吸收系数可以有效提升模式不稳定阈值。优化泵浦波长,兼顾量子效率和泵浦吸收系数,是光纤激光器实现高光束质量高模式不稳定阈值的重要技术路线之一。     

Pump-induced bleaching of the saturable absorber in short-pulse Nd:YAG/Cr/sup 4+/:YAG passively Q-switched microchip lasers

Bleaching of the saturable absorber by pump light increases the length of the pulse generated in a passively Q-switched Nd:YAG/Cr/sup 4+/:YAG microchip laser and decreases the pulse energy. This effect is greatest when transmitted pump light is nearly focused in the Cr/sup 4+/:YAG and when pumping is sufficiently intense to bleach the absorption of the Nd:YAG. Both effects are important in short-pulse microchip lasers. The maximum repetition rate of a passively Q-switched Nd:YAG/Cr/sup 4+/:YAG microchip laser is correlated with the pulsewidth. In general, it decreases as the pulsewidth gets shorter.     

缓冲气体压力对铷原子吸收特性的影响

铷原子吸收线宽很窄,通过充入定量缓冲气体,可以加宽铷原子的泵浦吸收线宽,从而可以提高铷原子对泵浦光的吸收效率。通过计算模拟,找到入射泵浦光谱宽、入射泵浦强度和缓冲气体压力之间的对应关系,找到最佳的实验工作条件,最终实现铷原子对离泵浦中心频率一定范围内的泵浦吸收效率很高,同时保证在泵浦谱宽范围内的总泵浦吸收效率也很高。模拟结果显示：随着缓冲气体压力的增大,铷原子吸收线宽不断增加,但是泵浦光的总吸收效率下降的并不明显。     

Scaling of dye lasers with improved laser dyes

Dye lasers are widely used in spectroscopic research because they provide tunable, coherent radiation. They employ highly fluorescent organic compounds, possessing some specific spectroscopic properties, dissolved in organic solvents. These liquid media are cooled by circulation. The liquid media, the dye solutions, have no scaling limitation. However, large dye lasers that generate high-energy and high average-power outputs do not exist because of the lack of a scalable pump source. Presently, pulsed and CW lasers and short-pulse small flashlamp are mainly used for pumping laser dyes. Only these pump sources are able to overcome the excessive triplet-state losses (TSLs) present in presently available laser dyes. These TSLs result, in part, from fairly large triplet absorption coefficients, ε_T(λ_F), of transient triplet-state dye molecules generated during excitation. Using new laser dyes that possess smaller triplet absorption coefficients should not only improve laser-action efficiencies, but should also allow pumping with large, long-pulse flashlamps and possibly with laser diode arrays and incoherent light sources. These pump sources are scalable and therefore would further increase overall outputs. This paper details TSL, vibronic spin–orbit interactions in heterocyclics, and other spectroscopic parameters affecting laser-action properties. Pump sources for dye lasers, especially flashlamps, are also reviewed. Criteria that can be used to identify candidate laser dyes for efficient long-pulse operation are provided. These are the so-called quasi-aromatics (QAs), five- and six-membered heterocyclics, and are identified as possessing small ε_T(λ_F) values. The pyrromethene–BF₂ complexes are representatives of such QAs. There should be many candidates that exhibit efficient laser action in different spectral regions, under long-pulse, large flashlamp pumping.     

Efficient Gallium–Arsenide Disk Laser

Means that may optimize the efficiency of semiconductor disk lasers (optically pumped vertical external-cavity surface-emitting lasers) are discussed: the direct pumping of the quantum wells (QWs), the optimization of the interaction of the QWs with pump and laser field and the reduction of resonator losses by employing a dielectric/semiconductor Bragg reflector on the front face of the disk. GaAs-AlGaAs-quantum-well disk lasers designed accordingly achieved slope efficiencies of 67% and optical efficiencies of 55% (based on the absorbed pump power) with output powers well above 1 W and a pump absorption efficiency of 80%. With an additional simple pump re-imaging an output power of 1.6 W was realized with an optical efficiency of 50% related to the incident pump power.     

基于PPLN晶体的单频绿光激光器的研究

随着激光技术的不断发展,单频激光器以其良好的单色性、高效率、窄带宽等优点广泛运用于激光测距、激光医疗、激光光谱学等领域。实现激光器单频输出的方法有很多种,采用的是短程吸收法;将PPLN晶体与Nd:YVO₄晶体之间间距缩短至1 mm,并做成绿光模组的形式,实现单纵模输出。当温度为28.5℃,LD泵浦抽运功率为0.8 W时,获得60 mW的单频绿光输出,光光转换率达7.1%,其线宽为120 MHz,实现了单频绿光激光器的又一突破。     

参量匹配对双色双共振多光子电离几率的影响

以寻求提高共振增强多光子电离(REMPI)几率的物 理参量为研究目的,采用光和物质相互作用的密度矩阵方程 理论,数值模拟了双色双共振多光子电离过程中泵浦和探测光的参量匹配对电离几率的影响 。结果发现,一定条件下,提高电离 几率的最佳匹配条件是:1) 两束激光强度、脉冲宽度均相等且取值较大; 2) 两束激光无 相 对延迟,输出频率和相应激发跃 迁共振。对1+1+1经探测光双光子共振吸收电离过程,电离几率对探测光更敏感。实际应用 中,若不能保证最佳匹配条件 的实现,应尽量提高探测光的强度、脉冲宽度及近共振吸收;若实验条件不能实现激光频率 和相应跃迁的共振激发,可采 用失谐量互补的两束激光同时作用于系统,通过双光子共振吸收过程提高电离几率。     

熔锥型光纤侧面泵浦耦合器的研究

该文采用泵浦光纤预拉方法得到一款泵浦耦合效率82%,信号光通过率98%,信号输入与泵浦输入隔离度33 dB,泵浦光反向隔离度24 dB的高效熔锥型侧面泵浦耦合器。将该耦合器应用于自制的20 W脉冲激光器,实现了峰值功率为7 kW的稳定激光输出。研究结果表明,所研制的熔锥型光纤侧面泵浦耦合器在高功率光纤激光器和光纤放大器中具有很好的应用前景。     

Efficient and scalable side pumping scheme for short high-power optical fiber lasers and amplifiers

A new and simple method of pumping short high-power optical fiber lasers and amplifiers is described. In our approach, several passive coreless optical fibers are brought into direct contact alongside a single rare-earth doped active fiber which constitutes the active medium of the laser (amplifier). Pump light is delivered through the passive coreless fibers and penetrates into the active fiber via evanescent field coupling. To enhance the pump absorption in the gain medium, high-order spatial modes are excited in the pump delivery fibers, and an active fiber with high concentration of the dopant ions is used. As a demonstration of the viability of our approach, test results are reported on a 12-cm-long Er/sup +3/-Yb/sup +3/ codoped phosphate glass fiber laser. The laser output reaches 5 W using 23-W pumping into six coreless fibers. Above threshold, the laser has /spl sim/24% optical-to-optical conversion efficiency (with /spl sim/64% being the theoretical maximum). The linearity of the input-output characteristic for the laser suggests that the output power can be scaled up by applying higher pump power.