重复频率下飞秒激光驱动产生的X射线焦斑测量

为了获取强激光驱动产生的X射线光源焦斑尺寸和空间分辨率,设计了刃边及双网格方法,其中刃边厚度为0.2 m,双网格分别为400目铜网格和394 lp/cm的镍网,利用X射线CCD作为探测元件。Ti宝石激光在能量1 J、脉宽40 fs、频率10 Hz、激光功率密度约为4.41018 W/cm2的条件下,重复频率加载圆盘Cu靶。在中国工程物理研究院25 TW激光装置上首次获得了X射线的焦斑及网格图像,并推算了该装置的X射线焦斑尺寸为43 m,而网格空间分辨力为34 m。结果表明该刃边及双网格方法适合强激光驱动产生的X射线焦斑尺寸测定。     

飞秒激光驱动纳米多孔靶产生X射线转化效率实验研究

利用多孔结构原理,研制了厚度为100 m、孔隙率为70%的纳米多孔铜靶,密度比为固体铜的30%。实验在中国工程物理研究院星光Ⅲ激光装置飞秒激光束上进行,激光功率密度大于1.61018 W/cm2,脉宽为30 fs。利用16 bit单光子CCD获取了X射线能谱,测得铜K线光子产额为2.9108 photonsr-1s-1,转换效率为0.008 38%。与压制加工的平面Cu靶相比,多孔结构靶的X射线产额约为平面靶的1.8倍,表明纳米多孔结构能够有效增强飞秒激光能量吸收,提高超热电子和X射线转化效率。     

飞秒激光-物质相互作用产生Kα X射线

用无色散X射线谱仪分别在靶前后测量了飞秒激光辐照铜箔产生的Kα X射线,获得了能量转换效率。入射激光脉冲宽度33 fs,能量在50 mJ～5 J,强度1017～1019 W/cm2。靶后发射的Kα X射线强度随入射激光能量的增加而增加,其单色性较靶前好。采用100 μm厚靶,其能量转换率为2.2×10-5。     

光学成像法和穿孔法测量飞秒激光焦斑特征

超短超强激光焦斑参数的精确测量是深入开展精密物理实验的前提。在SILEX-Ⅰ激光装置上,采用光学成像法和穿孔法测量了μJ级能量下的激光焦斑特性,采用光学成像方法得到了激光主瓣大小及能量集中度信息,通过穿孔法得到了激光能量透过率与不同大小孔径的关系曲线,并对两种方法得到的测量结果进行了比对研究。研究结果表明,光学焦斑测量法和穿孔法都可以比较准确地反映激光焦斑的能量分布情况,得到的能量分布偏差小于10%。     

飞秒激光-物质相互作用产生Kα X射线

 用无色散X射线谱仪分别在靶前后测量了飞秒激光辐照铜箔产生的Kα X射线,获得了能量转换效率。入射激光脉冲宽度33 fs,能量在50 mJ～5 J,强度10₁₇～10₁₉ W/cm₂。靶后发射的Kα X射线强度随入射激光能量的增加而增加,其单色性较靶前好。采用100 μm厚靶,其能量转换率为2.2×10_-5。     

叠片法测量脉冲X射线源焦斑

介绍了叠片法测量脉冲X射线源焦斑的原理。对确定结构和尺寸的金属、薄膜叠片及测试系统布局,数值计算了叠片法的空间分辨及对均匀分布线光源的输出响应,得到响应曲线半高宽与焦斑尺寸的对应关系。计算结果表明,叠片法不适用于测量小于2 mm的焦斑。在感应电压叠加器上开展了阳极杆箍缩二极管实验,采用叠片法测量二极管X射线源轴向焦斑,与针孔照相结果基本相符,说明叠片法可用于脉冲X射线源焦斑尺寸测量。     

高重复频率激光对光学材料损伤特性的研究

研究了几种红外窗口材料的高重复频率Ｎｄ：ＹＡＧ激光和Ｃｕ蒸气激光体损伤规律，发现样品损伤有明显积累效应。经过分析，发现高重复频率激光损伤是一处微观损伤积累过程，并引入吸收元的概念建立了一个简单的损伤积累模型。     

飞秒激光脉冲的谐波频率分辨光学开关法测量研究

建立了一台谐波频率分辨光学开关法(FROG)飞秒脉冲测量装置，利用该装置进行了掺钛蓝宝石飞秒激光脉冲的测量研究.在二次谐波自相关测得的时域和频域信号基础上，结合对信号光强度分布的计算机迭代处理，得到了有关飞秒激光电场、光谱及其相位的信息，所得脉宽与干涉测量的结果基本一致. 关键词： 频率分辨光学开关法(FROG) 迭代计算 飞秒激光 自相关     

飞秒激光脉冲的频率分辨偏振光学开关法测量研究

建立了一台频率分辨偏振光学开关（PG FROG）法飞秒脉冲测量装置，利用该装置对“极光Ⅱ号”飞秒激光放大系统进行了测量.在利用偏振光学开关法测得的时域和频域信号基础上，结合对信号光强度分布的计算机迭代处理，得到了有关飞秒激光电场、光谱及其相位的信息；并且对系统工作在不同状态时的激光脉冲进行了测量和比较分析，给出了有关该系统较详细的电场、光谱、相位以及啁啾状况.结果显示，当系统工作在零啁啾附近时，该系统输出的激光脉冲的电场、光谱和相位分布较规则，相位起伏较小；当系统偏离零啁啾状态时，虽然电场和光谱变化不很明显，但相位分布变化剧烈. 关键词： 频率分辨偏振光学开关(PG FROG)法 飞秒激光 自相关     

高重复频率脉冲激光能量测量（英文）

设计了一种用于高重复频率脉冲激光能量测量的峰值保持电路。电路由电荷积分器、2阶低通滤波器、时间延迟触发器和峰值保持器组成,通过将光电流脉冲转换成电压脉冲,电压脉冲的峰值与对应电流脉冲所包含的能量成正比。实验测量结果表明：该电路可以测量脉宽〈10 ns,重复频率≥2 kHz的重频窄脉冲激光的脉冲能量,且工作稳定,其线性动态范围≥140倍。该电路可应用于光电阵列探测系统中,能实现较高的空间分辨力。     

Ultra-short efficient laser-driven hard X-ray source operated at a kHz repetition rate

Ultra-short bursts of hard X-ray radiation are generated by interaction of high-contrast femtosecond laser pulses with a jet of liquid Ga. The X-ray emission shows a strong dependence on the angle of incidence and polarization of the laser beam, consistent with the processes of resonant absorption and vacuum heating. As much as 60% of the total X-ray emission consists of [_Ga]K radiation (9.22–9.25 keV) with a photon flux of 6×10⁹ photons/(ssrad). Using this novel X-ray source, static diffraction patterns from a GaAs(111) crystal were recorded with an acquisition time of 2 s. PACS 52.38.Ph; 52.59.Px; 52.50.Jm     

Programmable focal spot shaping of amplified femtosecond laser pulses

We describe the programmable spatial beam shaping of 100-kHz, 4-microJ amplified femtosecond pulses in a focal plane by wave-front modulation. Phase distributions are determined by a numerical iterative procedure. A nonpixelated optically addressed liquid-crystal light valve is used as a programmable wave-front tailoring device. Top-hat, doughnut, square, and triangle shapes of 20-microm size are obtained in a focal plane. Their suitability for femtosecond laser machining is demonstrated.     

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Ring coded imaging technology with high detection efficiency was put forward to diagnose space distribution for low intensity X-ray spot with several tens to hundred of keV. In this paper, the relations of detection efficiency and signal – noise ratio varied with the ring geometric parameters were researched. The coaxial imaging technology was resolved by employing the design of local micro joins on the ring aperture, and simulating the influence of micro joint area size on imaging quality. The ring aperture imaging system was developed and the Unique-II X-ray spot imaging experiment was implemented. The results show that the space distribution of the X-ray spot is approximate a ‘saddle’ shape, and the intensity in the middle part is lower than both sides along the long axis of the elliptical surface; this conclusion is consistent with pin-hole image; the detection efficiency of ring is evidently more than that of pin. Finally, the effects of and the R-L method and Wiener method used to restore the image are analyzed.     

硬X射线焦斑环孔编码成像的理论与实验研究

针对几十~百keV能量的低强度X射线焦斑源测量,建立了高探测效率环孔编码成像技术。研究给出了环孔成像效率和信噪比与环孔结构参数的关系,采用微联结的环孔结构设计并模拟了联结区尺寸对成像质量的影响,解决了环孔结构同轴成像技术难题。所建立环孔成像系统应用于Unique-II X射线焦斑源成像实验。结果表明,X射线焦斑的空间分布近似为‘马鞍’形状,而且中间部分的强度低于两侧的强度,与针孔成像结果相似,但环孔的探测效率明显高于针孔的效率。最后,分析了维纳滤波与R-L两种复原图像方法的效果。     

飞秒激光在铝膜中驱动冲击波的特性

为探索研究飞秒激光在材料中驱动冲击波的相关特性,采用激光脉冲频域干涉测试技术对脉冲宽度35 fs、脉冲能量0.7 mJ、功率密度1014 W/cm2量级的飞秒激光脉冲在200 nm厚铝膜中驱动冲击波的过程进行了实验测量。通过测量冲击波在铝膜中的渡越时间,获得激光脉冲在铝材料中驱动的冲击波平均速度约为6 km/s;通过对不同时刻铝膜自由面频域干涉场测量结果的分析,获得铝材料自由表面速度达1 km/s,根据平面冲击波的关系,推算其冲击压强达到9 GPa。     

飞秒激光在铝膜中驱动冲击波的特性

为探索研究飞秒激光在材料中驱动冲击波的相关特性,采用激光脉冲频域干涉测试技术对脉冲宽度35fs、脉冲能量0.7mJ、功率密度1014W/cm2量级的飞秒激光脉冲在200nm厚铝膜中驱动冲击波的过程进行了实验测量。通过测量冲击波在铝膜中的渡越时间,获得激光脉冲在铝材料中驱动的冲击波平均速度约为6km/s;通过对不同时刻铝膜自由面频域干涉场测量结果的分析,获得铝材料自由表面速度达1km/s,根据平面冲击波的关系,推算其冲击压强达到9GPa。     

Generation of low-timing-jitter femtosecond pulse trains with 2 GHz repetition rate via external repetition rate multiplication

Generation of low-timing-jitter 150 fs pulse trains at 1560 nm with 2 GHz repetition rate is demonstrated by locking a 200 MHz fundamental polarization additive-pulse mode-locked erbium fiber laser to high-finesse external Fabry-Perot cavities. The timing jitter and relative intensity noise of the repetition-rate multiplied pulse train are investigated.     

Bonding of glass with femtosecond laser pulses at high repetition rates

We report on the welding of fused silica with ultrashort laser pulses at high repetition rates. Femtosecond laser pulses were focused at the interface of two optically contacted fused silica samples. Due to the nonlinear absorption in the focal volume and heat accumulation of successive pulses, the laser acts as a localized heat source at the focus position. Here, we analyze the influence of the laser and processing parameters on the amount of molten material. Moreover, we determine the achievable breaking stress by a three point bending test. With optimized parameters up to 75% of the breaking stress of the bulk material have been obtained.