Applications and performance of high power lasers and in the battlefield

This paper reviews the status and applications of a defensive weapon based on high power lasers, in the battlefield. Laser weapon is a novel concept which utilizes high power laser beam to traverse the distance into incoming objects at a speed of light, and then, destroy or disable it. Various types of lasers and configurations will be discussed in this review including gas lasers, solid state lasers, fiber lasers and the free-electron laser. We will discuss various configurations such as airborne laser (ABL), diode pumped crystals and disk lasers as well as heat-capacity lasers. Recent applications of ultrafast solid state lasers for non-lethal or low collateral damage applications will be presented.     

激光玻璃陶瓷的研究进展

激光玻璃陶瓷是继单晶和玻璃之后又一新型固体激光材料,具有声子能量低、化学稳定性高、机械性能优良、稀土离子可溶性大等优点,有望替代玻璃和单晶,在微芯片激光器、光纤放大器、高功率二极管抽运固态激光器以及其他高温、高热冲击、高腐蚀的特殊环境中有着重要应用,成为人们的研究热点.概述了激光玻璃陶瓷从诞生至今的发展历程,阐述了激光发射原理、激光玻璃陶瓷制备、分类及应用等,并展望了激光玻璃陶瓷的发展前景.     

钛宝石泵浦Cr,Nd:YAG微片的自调Q激光特性

用连续的钛宝石激光泵浦１mm厚的Cr^4 ,Nd^3 ;YAG晶体微片获得了１．０６４μm的自调Ｑ激光输出,输出的激光调Ｑ脉冲非常稳定,泵浦的阈值功率为３０mW,脉冲宽度为１００ns随着泵浦功率的变化,脉冲宽度保持不变,而重复率则在变化。斜率效率随着输出耦合镜透过度的变化而变化,当输出耦合率为５％时,斜率效率高20%.一研究有助于进一步发展激光二极管泵浦的全固化的自调Ｑ微片激光器。     

Inside Front Cover: An Ultraviolet Organic Thin‐Film Solid‐State Laser for Biomarker Applications (Adv. Mater. 1/2005)

Thin‐film organic solid‐state lasers operating in the ultraviolet wavelength region are fabricated using a novel spiro‐linked material as active organic layer in an optically pumped distributed feedback (DFB) structure in work reported by Riedl and co‐workers on p. 31. The laser wavelength is tunable between 377.7 nm and 395 nm, the shortest laser wavelength reported so far for thin‐film organic solid‐state lasers. The lasers' suitability for spectroscopic applications was tested by use as an excitation source for solutions containing the common fluorescent dyes Coumarin 6, Coumarin 152, and Rhodamine 6G.     

Polarisation behaviour of diode lasers with frequency selective feedback

The paper reviews recent results obtained with diode lasers used in external hybrid cavities with frequency selective feedback. Such cavities attract continuing interest for several reasons. They generate a tunable single laser mode with very low linewidths (usually a few tens of kilohertz). Very wide discrete tunable ranges over 100 nm for Fabry-Perot type and over 200 nm for quantum well lasers are achieved. They can be made to oscillate in a tunable mode having the desired polarization state,TE orTM and, in some cases, simultaneously atTE andTM. This is done by designing a cavity that increases strongly theTM/TE intensity ratio and by using coatings on one laser facet that greatly lower bothTE andTM reflectivities. High-speed polarization switching in the gigahertz range is possible by inserting passive or active polarization selecting elements in the cavity. For all these reasons hybrid external cavities are attractive for applications in optical metrology, spectroscopy and optical communications. Moreover, the external cavity configuration allows the study of physical mechanisms in the laser diode by inducing on purpose phenomena that would have been otherwise impossible to achieve with free-running lasers.     

新型激光晶体材料研究进展

对新型激光晶体近年比较活跃的两个研究方向,掺镱的激光晶体和拉曼激光晶体的研究状况进行了总结.掺镱晶体可以产生高功率的激光输出,是重要的研究方向;同时掺镱激光晶体还可以实现用激光二极管泵浦的超快激光输出.拉曼晶体可以方便地产生人们所需要的激光波长,具有潜在的应用.本文对于这两类晶体的优点、可能应用的方向及最新的发展方向进行了阐述.     

Passively Q-switched ceramic Nd3+:YAG/Cr4+:YAG lasers

Passively Q-switched ceramic Nd3+:YAG lasers with ceramic Cr4+:YAG saturable absorbers are demonstrated. When the lasers are pumped by a 1-W cw laser diode, optical-optical efficiency as great as 22% is obtained with Cr4+:YAG of initial transmission ranging from 94% to 79%. The results are similar to those in their crystalline counterparts. The operation of Brewster's angle and the polarization state of the laser output are also investigated.     

Lasing action in organic semiconductor thin films

Lasing action in optically pumped thin films of organic semiconductors has recently been demonstrated in a variety of materials employing a variety of cavity configurations. The excitation intensities required for lasing in optically pumped films are comparable to the electrical current densities achievable in light emitting devices based on these materials, opening the door to the possible realization of organic diode lasers. However, the design of diode laser structures is complicated by the relatively low charge carrier mobilities of organics. It has also been shown that the optical properties of organic films under electrical excitation are affected by the formation of polarons, imposing yet another obstacle for realization of these devices. The continuing research on organic diode lasers is motivated by the unique properties of these devices, such as narrow spectral emission linewidth and the temperature independence of laser output power and emission wavelength, which may be advantageous in a number of applications.     

Temperature characteristics and stabilization of orthogonal polarization two-frequency Nd3+:YAG microchip lasers

The temperature dependence of the beat frequency and polarization azimuth of fiber-guiding laser diode pumped Nd(3+):YAG microchip lasers emitting orthogonal linear polarization at two frequencies is investigated, and we found a resemblance to the features that result from the application of mechanical force. The experimental observations are well described by the cavity model, which indicates that temperature change induces weak phase anisotropy in addition to the original phase anisotropy with general mutually inclined axes of anisotropy. With a servo control to keep the beat frequency constant, the beat and central laser frequencies are simultaneously stabilized to within +/-0.1 MHz and +/-0.35 GHz, respectively.     

Generation of doughnutlike vortex beam with tunable orbital angular momentum from lasers with controlled Hermite-Gaussian modes

This study demonstrates successive higher-order Hermite-Gaussian (HG(0,m)) mode operations in a microchip solid-state laser with a controlled off-axis laser diode (LD) pumping and generation of the corresponding doughnutlike laser beam of tunable ring diameter and orbital angular momentum, by experimentally focusing a Hermite-Gaussian mode (HGM) lasing beam into an astigmatic mode converter (AMC) with a mode-matching lens. Based on the successful generation of stable doughnutlike vortex beams by combining the LD off-axis pumping of microchip lasers and an AMC, this study proposes a design for a compact, solid doughnutlike vortex laser beam generator that combines three elements (i.e., laser cavity, mode-matching lens, and AMC) into one practical device. The desired doughnutlike vortex beam with different orbital angular momentum is easily generated by simply controlling the lateral off-axis pump position and pump beam shape on the laser crystal by numerical simulation.     

Investigation of continuous-wave and Q-switched microchip laser characteristics of Yb:YAG ceramics and crystals

Continuous-wave and passively Q-switched microchip laser performance of Yb:YAG ceramics and single-crystals was investigated. Highly efficient continuous-wave Yb:YAG laser performance was observed at 1030 nm and 1049 nm for both Yb:YAG ceramics and crystals with different transmissions of output couplers. The laser performance of Yb:YAG ceramic is comparable to that of Yb:YAG single crystal. Meanwhile, the laser performance of laser-diode pumped Yb:YAG/Cr⁴⁺:YAG all-ceramics- and all-crystals-combination passively Q-switched microchip lasers were investigated. Sub-nanosecond laser pulses with peak power over 150 kW were obtained with different Yb:YAG/Cr⁴⁺:YAG combinations. Linearly polarized laser was observed in Yb:YAG/Cr⁴⁺:YAG all-crystals combination and circular polarized laser was obtained in Yb:YAG/Cr⁴⁺:YAG all-ceramics combination. The best laser performance was obtained with Yb:YAG/Cr⁴⁺:YAG all-crystals combination.     

GHz重复频率固体飞秒激光技术进展及应用前景

针对惯性仪表的复合校准问题,设计了基于离心-温度复合装置的自学习切换控制方法,实现了高精度、高均匀性的温度场控制。根据离心机不同工况下的温度箱控制系统结构不同,切换控制方案可满足系统在高低温下的精度要求,自学习PID控制算法解决了控制过程中存在的温度波动问题。离心机旋转状态下和非旋转状态下的实验结果表明：该控制系统性能良好,在-55～80 ℃内的温度控制误差在±0.1 ℃之内。     

干扰吸收峰影响下TDLAS温度测量方法研究

固体飞秒激光器以其体积小、成本低、使用寿命长、稳定性高、技术较为成熟等特点,受到市场的广泛青睐。重复频率是飞秒激光器的一个重要参数,在实际应用中,高重复频率能带来高效率、高精度等诸多重要优势。本文介绍了SESAM锁模、KLM锁模、高次谐波锁模等常用的GHz固体飞秒激光器锁模技术及发展情况,阐述了GHz飞秒光源在激光加工、距离测量、光谱测量等应用场景中突出的性能优势,并对GHz重复频率固体飞秒激光技术的发展方向进行了预测,为推动GHz重复频率固体激光器技术的完善与提升提供借鉴。     

Analysis of dual-wavelength oscillation in a broad-area diode laser operated with an external cavity

Apodizing holographic gratings used in an external cavity have shown to be effective to control the modal content of multimode broad-area diode lasers, providing single longitudinal-mode and single lateral-mode emission. They can also be designed to provide Littrow reflection at two wavelengths. We observed stable oscillation at two wavelengths in a diode laser with an external cavity ended with such a grating. This is not a common behavior for homogeneously broadened gain media. We present simulations of the behavior of this laser based on a rate equation analysis. The effects of spatial hole burning and spontaneous emission are examined.     

Long-wavelength vertical-cavity surface-emitting lasers for high-speed applications and gas sensing

Long-wavelength InGaAlAs-InP vertical-cavity surface-emitting lasers (LW-VCSELs) covering the wavelength range from 1.3 to 2.3 mum are presented. Furthermore, these lasers can be fabricated in a novel high-speed design-reducing parasitics to enable bandwidths in excess of 11 GHz at 1.55 mum. To the best of the authors' knowledge, this is the fastest 1.55 mum VCSEL ever presented. As a proof-of-concept one- and two-dimensional arrays have been fabricated with high yield. All devices use a buried tunnel junction for current confinement and a dielectric backside reflector with integrated electroplated gold-heatsink. This concept enables CW operation at room temperature with typical single-mode output powers above 1 mW. Both, wavelength range and modulation performance, together with VCSEL features such as operation voltage around IV and power consumption as low as 10-20 mW enable applications in tunable diode laser spectroscopy (TDLS) and optical data transmission. Error-free data transmission at 10 Gbit/s over 22 km which can be readily applied in uncooled coarse wavelength division multiplex passive optical networks is presented. A laser hygrometer using a 1.84 mum VCSEL demonstrates the functionality of TDLS systems with VCSELs.     

Power-scalable system of phase-locked single-mode diode lasers

The direct use of diode lasers for high-power applications in material processing is limited to applications with relatively low beam quality and power density requirements. To achieve high beam quality one must use single-mode diode lasers, however with the drawback of relatively low optical output powers from these components. To realize a high-power system while conserving the high beam quality of the individual emitters requires coherent coupling of the emitters. Such a power-scalable system consisting of 19 slave lasers that are injection locked by one master laser has been built and investigated, with low-power diode lasers used for system demonstration. The optical power of the 19 injection-locked lasers is coupled into polarization-maintaining single-mode fibers and geometrically superimposed by a lens array and a focusing lens. The phase of each emitter is controlled by a simple electronic phase-control loop. The coherence of each slave laser is stabilized by computer control of the laser current and guarantees a stable degree of coherence of the whole system of 0.7. An enhancement factor of 13.2 in peak power density compared with that which was achievable with the incoherent superposition of the diode lasers was observed.     

532 nm Nd:YVO4/KTP激光器的I2分子吸收谱线的观测及频率稳定的研究

激光二极管抽运的固体激光器可用于光学计量,长度测量,相干光通信,激光雷达等方面,高精度应用要求激光器的频率稳定。碘分子在５３２ｎｍ附近在上百条强的吸收谱线,采用单频Ｎｄ;ＹＶＯ４／ＫＴＰ激光对碘的一些吸收谱线作了观测,并进行了激光频率稳定的研究,这些吸收谱线是１９９７年９月国际米定义咨询委员会推荐作为频标的９组５３２ｎｍ碘吸收谱线之外的新的参考谱线。     

Two-wavelength, passive self-injection-controlled operation of diode-pumped cw Yb-doped crystal lasers

We demonstrate and investigate a peculiar mode of cw Yb3+-doped crystal laser operation when two emissions, at two independently tunable wavelengths, are simultaneously produced. Both emissions are generated from a single pumped volume and take place in either a single beam or spatially separated beams. The laser employs original two-channel cavities that use a passive self-injection-locking (PSIL) control to reduce intracavity loss. The advantages of the application of the PSIL technique and some limitations are shown. The conditions for two-wavelength multimode operation of the cw quasi-three-level diode-pumped Yb3+ lasers and the peculiarity of such an operation are carried out both theoretically and experimentally. The results reported are based on the example of a Yb3+:GGG laser but similar results are also obtained with a Yb3+:YAG laser. The laser operates in the 1023-1033-nm (1030-1040-nm) range with a total output power of 0.4 W. A two-wavelength, single longitudinal mode generation is also obtained.     

Observation of CO and CO(2) absorption near 1.57 microm with an external-cavity diode laser

Near-IR and visible room-temperature diode lasers in broadly tunable external-cavity configurations are becoming commercially available for gas-sensing applications. Near 1.57 mum, a coincidence of overtone and combination-band transitions from CO, CO(2), OH, and H(2)O is particularly interesting for combustion and combustor emissions monitoring. We report initial observations of the room-temperature absorption of CO and CO(2) made with a commercial external-cavity diode laser.     

Efficient Continuous-Wave and Q-Switched Operation of a 946-nm Nd:YAG Laser Pumped by an Injection-Locked Broad-Area Diode Laser

The efficient, low-threshold operation of a 946-nm Nd:YAG laser pumped by an injection-locked broad-area diode laser is reported. The implications of pump-beam quality for efficient, low-threshold operation, particularly with intrinsically inefficient transitions, are discussed in the context of previously published models. Results are presented showing that the M(2) = 1.3 pump beam of the injection-locked diode laser enabled a cw slope efficiency of 48% and a threshold of 52 mW to be attained. When Q-switched, 335 mW of pump power gave 27-ns, 5.2-muJ pulses. These were frequency doubled to obtain 19-ns, 1-muJ pulses at 473 nm. These results represent significant improvements over similar systems pumped by free-running broad-area diode lasers or arrays.