Design and performance characteristics of a krypton chloride (λ = 222 nm) excimer laser

Development of a discharge-pumped krypton chloride (KrCl) laser operating at 222 nm wavelength is demonstrated. In this paper the design, successful realization and operating characteristics of KrCl excimer laser are reported. The laser is driven by a simple and efficient excitation technique using automatic UV pre-ionization with discharge-pumped self-sustained capacitor–capacitor (C–C) energy transfer circuit. The experimental investigations including output laser energy, temporal pulse parameters, emission spectra and beam profile of the KrCl laser were recorded. For high repetition rate operation, in-built, compact gas circulation system using tangential blower was incorporated. The laser was operated at 25 kV discharge voltage, gas mixture of 5 mbar HCl, 160 mbar kypton and neon as balance with a total gas pressure of ～2.5 bar. These experiments produced an efficient and reliable output energy of 25 mJ from an active volume of 60 cm³.     

The Scheme for X-ray Emission Enhancement in Groove Target

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重金属碲酸盐玻璃中Ho~(3+)的红外辐射特性

制备了高折射率Ho3+单掺和Ho3+/Yb3+共掺低声子能量重金属碲酸盐玻璃.根据Judd-Ofelt理论对吸收光谱进行拟合,求得Ho3+强度参数Ωt(t=2,4,6)分别为4.373×10-20,1.906×10-20和1.451×10-20cm2,并进一步计算了Ho3+在红外区各能级跃迁的振子强度、自发辐射跃迁概率、辐射寿命和荧光分支比等光谱参数.982 nm激发下,铋碲酸盐玻璃中Yb3+直接敏化Ho3+,在红外区产生有效红外发射.Ho3+吸收与发射截面在1.95和2.05μm处分别高达5.63×10-21和6.24×10-21cm2,大于Ho3+掺杂磷酸盐和氟化物玻璃,这有利于降低激光抽运阈值,实现高效Ho3+激光输出.较低的声子能量和较大的发射截面表明,Ho3+/Yb3+共掺杂铋碲酸盐玻璃有望成为良好的红外激光工作物质.     

Highly efficient degenerate four-wave mixing with multipass geometries in a polymer laser dye saturable amplifier

We demonstrate the use of highly efficient degenerate four-wave mixing for phase conjugation with multipass geometries in a polymer laser dye saturable amplifier. Phase-conjugate energy reflectivity of as much as 20,000% with a four-pass geometry in the longitudinally pumped polymer dye was obtained at 564 nm.     

类镍钽x射线激光实验研究

在神光II激光装置上进行了类镍钽近水窗x射线激光实验研究.利用基频、倍频联合驱动和双靶对接方案,在总能量400J的驱动激光能量下,获得了类镍钽4.48nm x射线激 光较强的输出,增益长度积达到5.5. 关键词： 类镍钽x射线激光 水窗 基频、倍频联合驱动     

A high-efficiency carbazine-122 dye laser

Highly efficient operation of a carbazine-122 dye laser has been achieved by pumping longitudinally with the second harmonic of a Nd:YAG laser. An overall energy conversion efficiency of 44% was obtained for the experimental conditions described.     

Laser ion acceleration in a mass limited targets

Laser interactions with mass-limited targets (MLT) are studied via 2D3V relativistic electromagnetic PIC simulations. Analytical estimates are derived to clarify the simulation results. MLT limit undesirable spread of absorbed laser energy out of the interaction zone. MLT, such as droplets, are shown here to enhance the achievable fast ion energy significantly. For given target dimensions, the existence is demonstrated of an optimum laser beam diameter when ion acceleration is efficient and geometrical energy losses are still acceptable. Ion energy also depends on target geometrical form and shaped targets are found to be preferable for high ion energy.     

Room-temperature Tm, Ho:LuLiF(4) laser with a novel quasi-end-pumping technique

A novel diode-pumped, efficient, quasi-end-pumping scheme that uses two lens ducts to achieve homogeneous pumping in a gain medium was proposed and evaluated. With this technique, room-temperature laser action at a pulse repetition frequency up to 20 Hz was demonstrated in 5%Tm, 0.5%Ho:LuLiF(4), which we grew by the Czochralski method. At 10 Hz a long-pulse laser output energy in excess of 24 mJ and a slope efficiency with respect to the incident pump energy of 10.7% were obtained.     

神光Ⅱ升级装置激光加速质子照相初步实验研究

在神光Ⅱ升级装置上开展了首轮激光加速质子对间接驱动快点火靶内爆过程的照相实验研究。通过激光与靶参数的优化,获得了能量高于18 MeV的质子束。通过静态客体的照相,获得了优于20 m的高空间分辨网格图像,为开展时间分辨的啁啾质子照相奠定了基础。开展了质子动态照相实验,获得了内爆压缩晚期的质子照相图像。实验发现内爆区域质子照相图像存在大量排空现象。内爆压缩区域不足以阻挡如此大范围质子束,证明了其中存在电磁场使得质子向外排开。动态照相的质子能量较低,分析是ns激光打靶过程产生的X射线及等离子体对质子加速存在影响。后续实验中需要进一步优化靶的屏蔽设计。     

Short-laser-pulse-driven emission of energetic ions into a solid target from a surface layer spalled by a laser prepulse

An efficient emission of picosecond bunches of energetic protons and carbon ions from a thin layer spalled from a organic solid by a laser prepulse is demonstrated numerically. We combine the molecular dynamics technique and multi-component collisional particle-in-cell method with plasma ionization to simulate the laser spallation and ejection of a thin (∼20–30 nm) solid layer from an organic target and its further interaction with an intense femtosecond laser pulse. In spite of its small thickness, a layer produced by laser spallation efficiently absorbs ultrashort laser pulses with the generation of hot electrons that convert their energy to ion energy. The efficiency of the conversion of the laser energy to ions can be as high as 20%, and 10% to MeV ions. A transient electrostatic field created between the layer and surface of the target is up to 10 GV/cm. Received: 13 March 2001 / Accepted: 20 March 2001 / Published online: 20 June 2001     

Efficient electrooptically Q-switched Er:Cr:YSGG laser oscillator-amplifier system with a Glan-Taylor prism polarizer

A relatively simple efficient electrooptically Q-switched Er:Cr:YSGG laser oscillator-amplifier system in a line has been demonstrated. A Glan-Taylor prism and a cubic LiNbO₃ crystal are used as the polarizer and modulator, respectively. Using the line scheme, one can adjust the system elements easily and achieve a good Q-switched-to-free-running pulse energy ratio of 75% and an energy amplification coefficient of 1.8. As short as 80 ns of the leading edge of a stable single pulse and 132 ns in FWHM with an energy of 24.5 mJ are generated. We also investigate the effects of the pump energy and the delay time on the postlasing, the stable single-pulse operation, the prelasing, the laser buildup time, and the Q-switched pulse width. The laser system demonstrated can be used for the effective ablation of soft and hard tissues.     

YAB晶体中Yb3+到Er3+的能量传递

1.55 μm波段是光通讯的一个重要波段,而且对人眼安全,有高的大气透过率,因此可以广泛应用于通讯和遥感测距等领域。由于Er³⁺离子对商品化的InGaAs激光二极管的抽运波长不能有效吸收,因此一般通过在基质中共掺杂Yb³⁺和Er³⁺离子来获得1.55 μm波段激光输出。采用助熔剂法生长了不同Yb³⁺和Er³⁺掺杂浓度的YAl₃(BO₃)₄(YAB)晶体。运用速率方程模型研究了晶体中Yb³⁺到Er³⁺能量传递过程,得到了根据Yb³⁺离子的荧光寿命计算能量传递系数的简单计算公式。计算了不同掺杂离子浓度的YAB晶体中的能量传递系数等相关参数。结果表明,在YAB晶体中,Yb³⁺到Er³⁺能量传递非常有效,YAB晶体可以作为一种能获得1.55 μm激光输出的良好介质材料。     

Demonstration of high-trapping efficiency and narrow energy spread in a laser-driven accelerator

Laser-driven electron accelerators (laser linacs) offer the potential for enabling much more economical and compact devices. However, the development of practical and efficient laser linacs requires accelerating a large ensemble of electrons together ("trapping") while keeping their energy spread small. This has never been realized before for any laser acceleration system. We present here the first demonstration of high-trapping efficiency and narrow energy spread via laser acceleration. Trapping efficiencies of up to 80% and energy spreads down to 0.36% (1 sigma) were demonstrated.     

高峰值266nm紫外激光器

报道了一种激光二极管(LD)端面泵浦的Nd:YAG声光Q开关高峰值功率266nm紫外激光器。该激光器采用紧凑的平平腔结构,LBO和BBO分别作为其二倍频和四倍频晶体。分别利用高偏振比LD阵列(40∶1)、低偏振比LD阵列(5∶1)及低偏振LD阵列腔内放置布氏片结构进行了实验。当注入功率为25W、调制频率为10kHz时,以上结构分别得到功率0.85,0.61和0.72W的266nm紫外光输出。其中,采用高偏振比LD阵列的输出功率最高,单脉冲能量为85μJ,脉宽为5ns,峰值功率高达17kW,泵浦光到紫外光的光-光转换率达3.4%。     

Efficient nanosecond optical parametric oscillators based on periodically poled KTP emitting in the 1.8-2.5-mum spectral region

The use of periodically poled KTiOPO(4) as a gain medium in efficient nanosecond optical parametric oscillators pumped by a flash-lamp-pumped Q-switched Nd:YAG laser is demonstrated. Parametric radiation in the 1.8-2.5-mu m spectral region was achieved when the crystal temperature was tuned from 10 to 100 degrees C. A maximum total output energy of 1.8 mJ was obtained at a pump level of 3.5 mJ. Stable operation was achieved, with conversion efficiencies reaching 50%. No gray tracking or laser damage was observed, even for pump intensities of 450MW/cm(2).     

Comparative study of spectral narrowing of a pulsed Ti:Sapphire laser using pulsed and CW injection seeding

We report a comparative study of a pulsed as well as continuous-wave (cw) injection seeding of a Ti:Sapphire laser pumped by aQ-switched frequency-doubled Nd³⁺:YAG laser for achieving narrow spectral bandwidth. The results have indicated that the Ti:Sapphire laser using either a pulsed or a cw injection seeding could achieve efficient energy extraction in a narrow spectral bandwidth. In the case of pulsed injection seeding, the injection energy required for the complete injection seeding critically depended upon the timing of the Ti:Sapphire laser with respect to the delayed onset of the slave laser. On the other hand, in the case of cw injection seeding, the spectral bandwidth of the Ti:Sapphire laser was efficiently narrowed down to approximately 0.01 cm^–1 with an injection power of less than 1 mW. In both types of injection seeding, characteristics observed experimentally were compared with those obtained by a numerical simulation code based on the one-dimensional rate-equation model.     

原子团簇对飞秒激光的吸收

使用800nm飞秒脉冲激光研究了Xe,Ar,He等原子团簇对激光的吸收.实验结果表明,脉冲阀门的工作压力、所使用的气体种类等因素对团簇的尺寸及团簇对激光的吸收影响很大.在阀门工作压力为20×10⁵Pa、激光功率密度为1×10¹⁵W/cm²的条件下,Xe团簇对激光的吸收高达45%.激光预脉冲的存在会降低原子团簇对激光能量的吸收.离子能量测量结果表明,团簇对激光的高效吸收导致较高离子温度等离子体的生 关键词： 原子团簇 飞秒激光 能量吸收效率 高能离子     

600-mJ,double-pulse 2-microm laser

An efficient double-pulse Ho:Tm:YLF 2-microm laser with total Q-switched output energy of 600 mJ has been demonstrated. A double-pulse pair is obtained per pump pulse. By operation of the laser in a double-pulse format, the residual energy stored among the Tm ions is transferred to the Ho atoms that were de-excited by the extraction of the first Q-switched pulse. Thus, the overall laser efficiency is increased by 61%.     

THz generation via optical rectification with ultrashort laser pulse focused to a line

We report on efficient THz pulse generation via optical rectification with femtosecond laser pulses focused to a line by a cylindrical lens. This configuration provides phase-matched conditions in the superluminal regime. 35 pJ THz pulses have been generated with this technique in a stoichiometric LiNbO₃ crystal pumped by 2 μJ femtosecond laser pulses at room temperature. An unusual superquadratic rise of the THz pulse energy with the laser pulse energy has been observed at high laser energies. This extraordinary energy dependence of the THz generation efficiency is explained by self-focusing of the laser beam in the crystal. Z-scan measurements and comparison of the THz pulse spectra created with laser pulses having different energies confirm this interpretation.