采用透镜列阵与光谱色散改善三倍频小焦斑辐照均匀性

通过数值模拟研究了高功率激光驱动器的光束均匀辐照情况, 分析了三倍频激光辐照下小焦斑的光强分布及空间功率谱. 采用透镜列阵可降低光束近场畸变的影响并控制靶面焦斑的包络形状; 采用二维光谱色散匀滑技术可明显地消除焦斑内部大反衬度的强度调制, 且该方法在焦斑非常小的情况下也仍然有效. 大量的数值模拟结果表明, 光谱色散匀滑技术应用于尺寸不同的焦斑时, 其效果是有差异的. 对大焦斑而言, 光谱色散匀滑主要抹平其内部细密的条纹, 即消除中高空间频率范围的强度调制; 对小焦斑而言, 光谱色散匀滑主要消除中低空间频率范围的强度调制, 故将影响焦斑的整体包络形状. 本文所得的数值结果对间接驱动实验中激光束匀滑方案的选择和优化具有参考价值.     

平面激光诱导荧光实验中激励激光的光束整形

分析了激励激光光强分布对平面激光诱导荧光（PLIF）实验中荧光强度的影响。基于柱面微透镜列阵设计了一套激光片状光束匀滑整形系统,并根据PLIF实验的具体要求,通过光线追迹方法优化了系统参数。建立了片状光束整形实验系统,对染料激光进行了匀滑整形,获得了不均匀性〈4%的均匀片状光束,满足了PLIF实验所需。在此基础上建立了PLIF实验系统,获得了酒精灯火焰和CH4/air预混火焰中OH的二维荧光分布。     

金等离子体M带谱强度的定量测量

在"神光II"多束高功率激光装置上利用列阵透镜匀滑钕玻璃波长0.53μm的强激光幅照平面金(Au)靶时产生X射线,本文给出了X射线绝对转换效率ξx。研究了多束倍频激光叠加驱动靶形成X射线背景光源辐射金M壳层1.8—3.1Kev带谱的特性,获得了不同激光功率密度及不同角度驱动靶面等几种条件下X射线能谱的定量测量结果和能谱分布。     

随机位相菲涅耳透镜阵列激光束匀化

为降低干涉带来的影响,将一种随机位相分布引入菲涅耳透镜阵列,对阵列中每一个菲涅耳透镜施加0或π的二值化位相变化,打乱阵列位相的周期性排布,减少微透镜后多光束在匀化面干涉带来的影响.通过数值计算对激光束的匀化过程进行了模拟,设计的菲涅耳透镜口径为0.5 mm,焦距为6mm,阵列数目为20×20,光斑整体均匀度达到90%,光束能量利用率达到96%.利用设计和制备的16台阶随机位相型菲涅耳透镜阵列对1 064nm波长的激光光束进行匀化,均匀度为83%,光束能量利用率为89%.研究结果表明,通过引入随机位相可有效减少干涉带来的影响,提高微透镜阵列对单模高斯光束的匀束效果.     

利用部分相干光和同心角偏差透镜列阵实现二维靶面均匀辐照

提出利用部分相干光通过透镜列阵系统实现靶而的均匀辐照, 透镜列阵能获得边缘陡峭且顶部较平坦的准近场焦斑, 透镜列阵的适当同心度偏差又使各子束的斑纹相互稍微错开, 使干涉斑纹变密, 而入射的激光是空间相干性减少了的部分相干光, 可进一步抑制了透镜列阵系统焦斑的小尺度不均匀性. 使用广义衍射积分理论, 对高斯-谢尔光束通过透镜列阵光学系统的焦斑光强分布进行了详细的二维模拟研究, 比较了完全相干光与部分相干光经过透镜列阵的匀滑效果. 数值模拟表明, 应用同心度偏差和适当离焦时, 可实现焦斑均匀性和能量利用率同时达到最佳的效果.     

多色非相干光入射ICF黑腔受激布里渊散射分析

为研究多色非相干激光入射ICF黑腔的受激布里渊散射（SBS）和受激拉曼散射（SRS）发展情况,建立了一维受激散射稳态谱分析模型,并发展了相应的数值模拟程序。分析了不同频率激光激发的受激散射光通过共用等离子体波耦合的物理图像以及影响背散光谱的物理因素。针对波长差0.3 nm的等强度双色光入射封底金腔的SBS进行了模拟分析,结果表明:采用双色光有效抑制了SBS;SBS光谱劈裂成间距为0.3 nm的两个峰;波长较长的入射光对应的SBS光获得了较大的增益;如果固定激光总强度和总带宽,则存在抑制SBS的最优光束数目。     

“神光-Ⅱ”装置倍频激光直接驱动冲击波平面性的实验研究

 设计了3套针对“神光-Ⅱ”倍频激光直接驱动的透镜阵列均匀辐照系统，并对冲击波的平面性进行了实验研究。结果表明，冲击波的平面性与透镜阵列参数、平面靶厚度、靶面位置等有关，采用列阵元数为121的透镜阵列进行激光束匀滑驱动的冲击波平面性最好，间接说明它在靶面的激光辐照是最均匀的；另外，随着靶厚的增加，冲击波平面性变差，平面区变小；而且冲击波平面性随靶面离焦位置的变化成一定的周期性变化，第2套透镜阵列焦点处的冲击波平面性最好。     

527 nm激光辐照盘靶受激布里渊散射光角分布

 在“星光Ⅱ”激光装置上，开展了527 nm激光与金盘靶和铝盘靶相互作用实验，研究了激光辐照盘靶的受激布里渊散射光散射机制，获得了散射光能量角分布。实验结果表明：激光辐照金盘靶时，在入射激光能量大致相同的情况下，受激布里渊散射光能量在匀滑的条件下比没有匀滑时低一个数量级以上（背反能量除外），束匀滑对散射光的抑制作用十分明显。在匀滑条件下，越靠近背反方向，散射光能量越大。散射光能量分布沿方位角的变化不大。激光辐照铝盘靶时，散射光能量分布的离散性较大。     

神光Ⅱ激光装置的全口径背向散射测量系统

报道了基于神光Ⅱ激光装置的全口径背向散射测量系统。系统通过激光聚焦透镜收集激光等离子体相互作用产生的散射光;两个热能量卡计分别测量波长348~354 nm范围的受激布里渊散射和波长400~700 nm范围的受激拉曼散射产生的散射光。该系统可以测量散射光的能量、功率和光谱图像,提供优于0.5 nm光谱分辨和10 ps时间分辨的光谱物理信息。同时采用PIN二极管阵列对聚焦透镜外侧附近的近背向散射光信息进行测量。     

基于双柱透镜慢轴准直激光二极管堆栈光束匀化系统

为实现高功率激光二极管堆栈光束的匀化与整形,提出基于双柱透镜慢轴准直的匀化系统。利用双柱透镜实现对高填充因子激光二极管慢轴方向光束发散角度的压缩,降低成像型多孔径光束积分器中微透镜的数值孔径,减小匀化系统体积。通过三个限定条件确定了双柱透镜参数取值范围,并通过像差分析对双柱透镜进行了优化,实现慢轴方向光束剩余发散角度1.74。结合成像型多孔径光束积分器,设计了激光二极管堆栈的匀化系统,并进行了实验测试。实验结果表明,在中心光斑尺寸约为6 mm6 mm范围内,光斑不均匀性为8.11%。     

Magnetic properties of epitaxial-grown exchange-coupled FePt/FeRh bilayer films

The propagation of a laser beam through a micro-lens array (MLA) was simulated using Finite Time Difference Domain (FDTD) method. The intensity distribution at different output planes away from the micro-lens array surface was investigated. As compared to the focal plane, the intensity distribution observed at those out-of-focus planes varies, which is attributed to the interference and diffraction of output laser beams. The simulated results were counter checked by placing a physical MLA under an illumination of a 488 nm continuous wave Argon Ion laser and images were captured for different output planes. Both simulation and experimental results show a great similarity in terms of the distribution patterns. By changing the lens sag height with respect to the lens diameter, the full width at half maximum (FWHM) of the focused laser spot and its corresponding maximum energy flux were analyzed. A FWHM of 160 nm can be achieved by proper selection of lens sag height. It is also found that the energy flux is proportional to numerical aperture (NA).     

An evaluation of target irradiation uniformity based on spatial-spectrum analysis

The irradiation uniformity of target spots in high-power laser driver is evaluated based on spatial-spectrum analysis. Spatial spectrum can display the detailed spatial intensity structure of the spots and show the spatial frequency modes smoothed by the beam smoothing techniques. This evaluating model is applied to two kinds of typical target spots obtained with a lens array and a random phase plate, respectively, and its validity is found to be independent of the spot profile and the degree of intensity modulation. The uniformity evaluations based on this model are in good agreement with the fractional power above intensity.     

Beam delivery system with a non-digitized diffractive beam splitter for laser-drilling of silicon

We report a beam-delivery system consisting of a non-digitized diffractive beam splitter and a Fourier transform lens. The system is applied to the deep-drilling of silicon using a nanosecond pulse laser in the manufacture of inkjet printer heads. In this process, a circularly polarized pulse beam is divided into an array of uniform beams, which are then delivered precisely to the process points. To meet these requirements, the splitter was designed to be polarization-independent with an efficiency>95%. The optical elements were assembled so as to allow the fine tuning of the effective overall focal length by adjusting the wavefront curvature of the beam. Using the system, a beam alignment accuracy of<5 μm was achieved for a 12-mm-wide beam array and the throughput was substantially improved (10,000 points on a silicon wafer drilled in ~1 min). This beam-delivery scheme works for a variety of laser applications that require parallel processing.     

Laser processing of micro-optical components in quartz

Laser induced backside wet etching combined with the diffractive gray tone phase mask has been used for the fabrication of a micro-lens array with a single lens diameter of 1 mm and a micro-prism in quartz. The micro-lens array was tested as beam homogenizer for high power XeCl excimer laser yielding a clear improvement in the quality of the laser beam.The optimum fluence range for fabrication of micro-lenses by laser induced backside wet etching using 1.4 M pyrene in THF solution and 308 nm irradiation wavelength is 1-1.6 J/cm². The etching mechanisms of LIBWE are based on a combination of pressure and temperature jumps at quartz-liquid interface.     

SLD seeded all fiber cascaded nanosecond pulsed amplifier

A Super-luminescent Diode (SLD) seeded all fiber cascaded pulsed laser system is reported. The signal line width is 8 nm confined by spectrum filers between stages, much wider than Laser Diode (LD) seeded laser. The wide spectrum of the seed source gives a good opportunity to get higher stimulated brillouin scattering threshold than LD seeded laser. The system emits up to 50 W pulses at a wavelength of 1064 nm and a repetition rate of 20 kHz with peak power 250 kW and beam quality M2 < 1.8. No SBS or SRS are observed and its output power is limited only by available pump power.     

利用消衍射透镜列阵及光谱色散平滑实现焦斑均匀辐照

提出将空间域的透镜列阵法和时间域的光谱色散平滑法结合起来实现靶面的均匀辐照. 消衍射型透镜列阵能获得边缘陡峭且顶部较平坦的准近场焦斑，光谱色散平滑则能有效地抹平焦斑内部由多光束干涉引起的细密条纹. 数值结果显示，通过该方案能获得均匀性较好的焦斑. 进一步分析了光谱色散平滑单元中位相调制和光栅的参数对辐照均匀性的影响，发现参数的选取要在焦斑均匀性和能量利用率之间取得合理平衡，以在整体上获得最佳的均匀辐照效果. 关键词： 光谱色散平滑 透镜列阵 衍射 多光束干涉     

Hyperboloid cylinder-plane lens for shaping laser diode array beam

A high coupling efficiency, simple structure refractive lens was designed; a hyperboloid cylinder-plane lens was proposed to reduce the divergence angle of the laser diode array beam in the fast axis direction. Based on the ray-tracing method, the shape of the input refractive surface of the designed lens is determined by numerical analysis, and designed as aspherical profile in one direction. When the beam from source point reaches the input surface of the lens, it is refracted and becomes a parallel output beam in the fast axis direction. The expressions for describing the irradiance behind the lens are also derived.     

受激布里渊散射相位共轭镜产生高质量短脉冲XeCl激光

利用受激布里渊散射相位共轭镜改善ＸｅＣｌ激光光束质量和压缩脉冲宽度，给出了脉宽与泵浦能量、焦点位置的关系。光脉冲宽度从５０ｎｓ压缩到１７ｎｓ，光束发散角也减小到原来的１／３，散射光功率密度也较泵浦光得到了提高。