双轴棱锥产生长距离近似无衍射光的新技术

提出了一种利用会聚透镜、轴棱锥等简单光学元件产生长距离近似无衍射光的新技术. 分别利用几何光学和衍射理论分析了该方法产生长距离近似无衍射光束的原理, 通过软件模拟了长距离近似无衍射光束的形成过程,得出了该光束在不同距离处的横向光强分布. 模拟结果显示该光束在较长距离处的横向光强分布满足Bessel分布. 从实验上获得了传播距离长达80 m、中心光斑发散角约为0.12 mrad的近似无衍射光束, 相比于国外学者最近的研究成果(Belyi et al. 2010 Opt. Exp. 18 1966)将传播距离延长了50多米,而光束发散角压缩了22倍.实验中, 对光束沿光轴传播时在不同距离处的光斑进行了拍摄,所得实验结果与理论分析基本符合.     

多子光束相干发射小目标探测研究

提出了一种多子光束相干发射方案以提高对远距离小目标的探测能力.将激光器发出的光束等功率地分为若干子光束,在空间按一定的排列平行发射.子光束来自同一激光源,具有很好的相干性,将在目标面上产生干涉.计算结果表明:子光束在目标面上产生干涉主峰,理想情况下,其峰值为单光束直接发射光强的N(N为子光束数目)倍,用此主峰照射目标实现探测;目标越小,此方案相对于直接发射的优势越突出.实际中应适当压缩光束发散角,以增大照射到目标上的总功率.发射镜的位置和角度抖动使目标面上光强闪烁且光斑畸变,为获得稳定、且峰值为单光束直接发射光强N倍的干涉主峰,发射镜的位移控制精度需达到0.1λ(λ为光波长),角度控制精度需达到0.2θ(θ为光束发散角).     

角隅全反镜谐振腔激光器的输出特性

 在高功率脉冲气体激光器中，用角隅反射镜作为全反镜，平行平面镜作为输出镜构成角隅全反镜谐振腔。对角隅腔激光器的输出特性和抗失调稳定性进行了研究，并与平凹腔和平平腔激光器进行了比较。实验结果表明：在角隅全反镜失调角为16 mrad时，角隅腔激光器的单脉冲输出能量下降9.2%，且近场输出光斑没有明显变化；而凹面全反镜失调角仅为0.4 mrad时，平凹腔激光器输出能量下降了9%，近场输出光斑严重变形。在输出镜正前方3.12 m处测量，当角隅镜偏转16.3 mrad时，激光器输出光斑与标准状态时的输出光斑重合；凹面全反镜失调角为0.4 mrad时，激光器输出光斑位移14 mm。经模式仪分析表明，角隅腔激光器近场光强分布均匀。     

用激光单缝衍射实验仪做扩展实验

在大学物理实验中,单缝衍射实验仪一般用来测量衍射光强分布和缝宽,本文对实验内容进行了扩展,增加了测量细丝直径、He-Ne激光束的光强分布、激光束光斑尺寸及发散角等内容.     

LD激光束准直整形模块的研制

SDL-5400型号GaAlAs LD激光器产生的是单模高斯光束,在相互垂直方向上光束发散角不相等,且存在像散。为得到共腰的圆形光斑,由复参数q和ABCD定律,设计出两相互垂直的柱面透镜和棱镜对准直整形模块,通过CCD标定方法,得到经准直整形后的LD激光束在弧矢方向上的远场发散角为0.53mrad,子午方向为0.64mrad。     

基于铒玻璃激光器的激光射击光学系统设计

为真实模拟实弹射击场景,降低军事射击训练成本,设计了一种基于铒玻璃激光器的激光射击光学系统。该系统采用两级激光扩束,将铒玻璃激光器出射光束发散角二次压缩,实现极小发散角光束出射,提升了激光射击过程的人眼安全性。铒玻璃激光器出射光束发散角为15 mrad,出射光斑直径0.3 mm,激光扩束倍率300倍,系统出射光束发散角达0.035mrad。距光学系统出光口1 km位置,激光光斑直径约为120 mm,可满足千米射击训练要求,突破了常规激光射击系统百米量级的作用距离限制。设计的光学系统总长度为364mm,结构简单,利于工程化,应用前景广阔。     

类氖锗X射线激光光学特性研究

本工作测量了类氖锗3s-3p X射线激光的23.2nm和23.6nm两条强激光跃迁线水平方向和垂直方向的空间分布,当靶长20mm时,X射线激光水平方向束发散角约为12mrad,主束指向偏离线状等离子体轴线约8mrad;垂直方向束发散角约为22mrad,本工作还采用钼/硅多层膜平面反射镜,对X射线激光进行正反射,获得了X射线激光双程放大的光学特性。 关键词：     

基于双程放大的毛细管放电69.8 nm激光增益特性

建立了类氖氩C线69.8 nm激光的双程放大实验后反射腔结构,利用45 cm长毛细管作为放电负载得到了其双程放大输出.在相同初始实验条件下,分别测量了单程放大输出与双程放大输出的激光脉冲光强、脉冲宽度以及激光束散角.通过对比单程与双程输出实验结果,利用双程放大激光光强的计算公式,分析得到了增益持续时间大于4 ns,以及增益在毛细管径向上的分布特点.以上结果为建立谐振腔进行毛细管放电类氖氩激光的多程放大实验奠定了基础.     

利用CCD准确测量激光远场发散角

 利用CCD面阵接收器,通过标定的方法,将其准确安置在长焦距透镜后焦面上,并找出CCD 象元数与原场发散角的对应关系,从而迅速确定远场发散角。同时用短焦距透镜对 光束限制光阑成像,测得近场光斑光强分布。以激光束振幅函数的傅里叶变换作为理想衍射 极限,将远场发散角与之比较,可以得到用几倍衍射极限的方法表示的实际光束质量。     

离轴90°抛物面镜焦斑特性分析

随着离轴抛物面反射聚焦镜在激光加工领域的广泛应用,如何提高其聚焦光斑质量成为一个嗫需解决的问题.理论上,抛物面反射聚焦方式可以消除球差的影响,得到高质量的聚焦光斑.但是抛物面反射镜是最难调整的反射镜系统之一,对光轴失准的敏感度极高.细微的失准引发的像散将大大降低焦斑的光强.为了深化对其的认识,通过几何光学和物理光学的方法,对离轴90°抛物面镜应用于激光聚焦光路时,光轴的角度失准对聚焦光斑造成的影响进行分析.结果表明,细微的角度失准将导致焦斑面积大大增加,从而大大降低了焦斑的光强.并通过二阶矩法证明了角度失准将导致抛物面镜焦平面附近产生一对互相垂直的焦线,同时证明了两焦线所处z平面与焦点F的绝对距离相等,并与入射偏角θ呈线性关系.焦线的存在使入射高斯光束转变为椭圆高斯光,降低了焦面处的峰值光强.抛物面镜对角度失准的敏感度非常高,几个mrad的失准角将导致焦面处的峰值光强下降一半.     

Intensity distribution of a capillary-discharge 46.9 nm soft X-ray laser

We realize a Ne-like Ar 46.9 nm soft X-ray laser pumped by a capillary discharge. The study of the laserpulse-intensity distribution is important for applications of soft X-ray lasers. The intensity distribution demonstrates the gain distribution, plasma radius, and axial plasma density that contribute to the study of the laser-pulse formation. To measure the intensity in different positions of the X-ray laser spot, we moved transversally an X-ray diode (XRD) assembled with a slit. We obtain the onedimensional intensity distribution. We find a laser divergence (FWHM) of 4.0 mrad. According to the gain-guided model, we calculate the intensity distribution. The measured divergence of 4.0 mrad roughly corresponds to a plasma radius a approximately equal to 230–250 μm and on-axis electron density n _e ≈ 8.0?10¹⁸ ?9.0?10¹⁸ cm ^?3. The results of calculations indicate that the divergence of the intensity distribution increases when the plasma radius decreases and the on-axis electron density increases.     

毛细管放电类氖氩69.8nm激光增益特性研究

建立了计算69.8nm激光增益系数的理论模型,根据实验参数,计算了在主脉冲电流为12 kA时,69.8nm激光增益系数最大值为0.32 cm~(-1).理论模拟了不同初始气压下增益系数在毛细管径向上的分布情况.对理论结果的分析表明,最佳的初始气压在12—14 Pa范围内,此时69.8nm激光增益系数的极值最大.实验上,利用毛细管放电装置和罗兰光谱仪,测量了不同气压下的69.8nm激光强度,实验确定的最佳气压为16 Pa,与理论结果相近.此外,实验测量的增益系数(0.4 cm~(-1))略高于理论计算的增益系数(0.32 cm~(-1)).     

Demonstration of soft x-ray laser of Ne-like Ar at 69.8 nm pumped by capillary discharge

The demonstration of a 69.8?nm laser on 3p 3P2 - 3s 1P1 (J=2-1) transition of Ne-like Ar pumped by capillary discharge is reported in this Letter. A main current of 12?kA with rise time of 43?ns was chosen to generate the plasma in a 35?cm long capillary filling with pressure of Ar as low as 11?Pa, resulting in a gain coefficient of 0.34?cm(-1) and gain-length product of 11 at 69.8?nm. Also observed is a weak laser on 3p 3D2 - 3s 3P1 (J=2-1) transition of Ne-like Ar at 72.6?nm in the same condition. In addition, multiwavelength lasing at 46.9, 69.8, and 72.6?nm was simultaneously realized in a capillary discharge plasma column, conditioning the pressure of Ar to 13?Pa.     

Valley density profile for highly efficient x-ray lasers with good beam quality

A plasma with a valley density profile at the required electron density for high-gain operation of an x-ray laser could be obtained using a normally incident 300 ps laser pulse followed by a grazing-incident 300 ps laser pulse. Sudden heating of the valley plasma region by another grazing-incident 300 fs laser pulse would then yield a highly efficient x-ray laser beam with a deflecting angle of 2 mrad and a divergence angle of 4 mrad. Saturation operation of the x-ray laser beam at 32.6 nm could be achieved with a total pump energy of less than 100 mJ.     

Investigation of a highly saturated soft X-ray amplification in a capillary discharge plasma waveguide

The characterization of the laser beam intensity distribution of a highly saturated 46.9-nm soft X-ray laser excited by capillary discharges is reported. The laser produces a total output energy of 300 J/pulse by amplification in plasma channels having lengths up to 0.45 m. A regime of laser amplification, which is almost free from the effect of the refraction defocusing, is experimentally determined. This regime produces a soft X-ray laser beam with an intense sub-milliradiant component. In the longer active medium the laser intensity distribution reaches the divergence of 0.6 mrad, which approaches the limit of diffraction. A comparison of the experimental results with the simulations performed with a ray-tracing code shows that the small divergence of the beam could be attributed to the effect of a weak index waveguiding of the laser beam through the long plasma channels. PACS 42.55.Vc; 42.60.Jf     

Collisional excitation soft X-ray laser at 23.6 nm in a laser-produced cylindrical target

We have tested soft X-ray lasing in neon-like germanium with cylindrical targets where wave guiding and plasma confinement may affect lasing. An intense soft X-ray laser beam of 0.05 MW peak power and a narrow beam divergence (8 mrad) was produced at 23.6 nm with a 4 cm long straight cylindrical target of 0.72 mm inner diameter. Bending the cylindrical target to form a toroidal shape increased the lasing intensity by a factor of 3 accompanied with reduction of the beam divergence from 8 to 6 mrad.     

Role of the wall ablation in the operation of a 46.9 nmAr capillary discharge soft x‐ray laser

A capillary discharge pumped soft x‐ray laser operating at 46.9 nm on the 3p–3s transition of the Ne‐like Ar has been realized by pumping the active medium with a relatively slow current pulse (dI/dt ≈ 6 · 10¹¹ A/s). In order to study the role of the ablation in the production of the laser effect, the intensity of the amplified 46.9 nm line has been investigated using the same pumping current pulses in the plastic (polyacetal) and ceramic (Al₂O₃). We showed that the ablation of the capillary walls is unfavorable both for the compression and stability of the plasma and consequently for the soft x‐ray laser production. The amplification and lasing effects are observed only in the ceramic channel. The measurements of the line intensity at 46.9 nm showed the lasing with a gain‐length product of ≈ 9, a laser pulse energy of ≈ 5 μJ, a pulse duration of 1.3 ns and a beam divergence of ≈ 3.5 mrad. In addition, effect of the scaling of the time of lasing with the initial plasma diameter was demonstrated experimentally and compared with a one‐dimensional MHD model.     

Characterization of the 46.9-nm soft X-ray laser beam from a capillary discharge

Intense lasing had been obtained from argon plasma in the soft X-ray region from a capillary discharge plasma system. Different diagnostics have been used to characterize the lasing properties by recording the temporal, spatial, and spectral profiles of the emission. The divergence measurement indicates that the soft X-ray laser beam has good directionality with a divergence of 3.5 mrad. The spectrum of the laser beam measured using a transmission grating showed intense lasing line at 46.9 nm. Diffraction orders as high as 10th orders were observed. The temporal profile recorded with a vacuum diode showed a distinct laser peak with a pulse width ~1.2 ns (FWHM). In addition, the coherence of the X-ray laser beam was also confirmed from the high-contrast interference fringes (visibility ~85 %) recorded using double slits.     

Design of Highly Directive Ni-Like Ag X-Ray Laser at 13.9nm

We theoretically investigate a 13.9nm Ni-like Ag x-ray laser using a one-dimensional hydrodynamic code coupled with an atomic physics data package. The population inversion is transiently pumped by a grazing incident 0.5ps main pulse irradiating into an optimized plasma, which is generated by a normal incidence 300ps pulse and a subsequent grazing incidence 300ps pulse. The effect of the grazing-incidence angle on the source position of the output x-ray laser is investigated. Near zero deflecting angle is found for the peak output intensity of the Ni-like Ag x-ray lasers, with a small FWHM divergence of 5mrad. It is predicted that saturation can be achieved with a total pump energy of 165mJ.