双激光脉冲打靶形成Gd等离子体的极紫外光谱辐射

高端芯片制造所需要的极紫外光刻技术位于我国当前面临35项"卡脖子"关键核心技术之首.高转换效率的极紫外光源是极紫外光刻系统的重要组成部分.本文通过采用双激光脉冲打靶技术实现较强的6.7 nm极紫外光输出.首先,理论计算Gd¹⁸⁺—Gd²⁷⁺离子最外层4d壳层的4p-4d和4d-4f能级之间跃迁、以及Gd¹⁴⁺—Gd¹⁷⁺离子最外层4f壳层的4d-4f能级之间跃迁对波长为6.7 nm附近极紫外光的贡献.其后开展实验研究,结果表明,随着双脉冲之间延时的逐渐增加,波长为6.7 nm附近的极紫外光辐射强度呈现先减弱、后增加、之后再减弱的变化趋势,在双脉冲延时为100 ns处产生的极紫外光辐射最强.并且,在延时为100 ns处产生的光谱效率最高,相比于单脉冲激光产生的光谱效率提升了33%.此外,发现双激光脉冲打靶技术可以有效地减弱等离子体的自吸收效应,获得的6.7 nm附近极紫外光谱宽度均小于单激光脉冲打靶的情形,且在脉冲延时为30 ns时刻所产生的光谱宽度最窄,约为单独主脉冲产生极紫外光谱宽度的1/3.同时...     

Parameter settings in a compact laser-nitriding system for titanium composed of a focused pulsed Nd:YAG laser and nitrogen gas blow

The aim of the present study was to form a nitride layer on a titanium (Ti) substrate through a compact laser-nitriding system comprising a focused pulsed Nd:YAG laser and nitrogen gas blow. To obtain a high-quality layer, the effects of pulse frequency and gas flow rate on the surface characteristics were investigated by using plasma emission analysis as well as X-ray analyses. Optical emission spectra from the laser-induced plasma mainly consisted of ionic Ti lines, and their intensities when the pulse frequency was 15 Hz were much higher than those for 8 Hz. Similarly, the reflections from the δ-TiN phase in the X-ray diffraction (XRD) pattern were enhanced when using 15 Hz. On the other hand, the flow rate of nitrogen gas blow had a significant effect on the thickness of the thin oxide layer that formed above the nitride layer. Using a lower flow rate resulted in the formation of a thicker oxide layer. The higher pulse frequency and the faster flow rate were beneficial for obtaining a higher-quality layer because of the enhancement of nitridation and the suppression of oxidation, respectively.     

通过超宽139La固体核磁共振波谱研究层状La(OH)2NO3

层状稀土氢氧化物是一类新型的稀土功能材料，本文采用固体核磁共振（SSNMR）方法研究了同时具备离子交换能力和非线性光学特性的层状La（OH）₂NO₃化合物，探讨了通过四极核CPMG（QCPMG）脉冲序列和变频谱图采集获取超宽¹³⁹La SSNMR谱图的方法，并描述了适用于此类实验的滤波方程和谱图重建方法.重建谱图同时包含四极核中心跃迁和卫星跃迁信息，本文使用QUEST软件对超宽¹³⁹La NMR谱图进行了模拟，获取的四极耦合常数C_Q和非对称因子η_Q均与CASTEP密度泛函理论计算值高度吻合.SSNMR实验结果证实层状La（OH）₂NO₃化合物属于非中心对称结构（P2₁），解决了对其结构长期以来存在的争论.     

三色圆偏振激光组合脉冲驱动氦原子产生椭圆偏振的阿秒脉冲

我们提出利用频率为ω,3ω和强度较弱的2ω组成的三色圆偏振激光组合脉冲驱动氦原子能够得到椭偏率较大的阿秒脉冲链的一种方法.通过强场近似方法,计算了氦原子在两色和三色圆偏振激光组合脉冲驱动下发射高次谐波谱及其合成阿秒脉冲链,比较了氦原子(初态为s态)在这两种情况下发射高次谐波谱的特点及其合成阿秒脉冲链椭偏率的大小,结果发现,在反旋的两色ω,3ω激光脉冲基础上加入了频率为2ω的第三色激光脉冲联合作用到氦原子上,所得到的阿秒脉冲链的椭偏率相对于双圆场情况下有所增加,通过调整ω,3ω激光的强度比,并且选择适当的第三色激光的强度,对初态为s态的原子,仍能够得到具有较大椭偏率的阿秒脉冲链.     

Generation of intense water window X-ray pulses by superposition of an initial state of the helium atom driven by a three-color field

We theoretically study the generation of high-order harmonics and attosecond pulses from the superposition of an initial state in helium atom driven by a three-color laser field. It is shown that when the initial state is chosen to be a single electronic state, due to the rapid depletion of the ground state, the efficiency of the spectral continuum will be decreased as the initial state increases. When the initial state is chosen to be the coherent superposition of the ground state and an arbitrary excited state, the efficiency of the spectral continuum can be enhanced compared to that from the single initial state. Further, with the optimization of the three-color laser beam, not only can the harmonic cutoff be extended to the water window X-ray region but also the spectral continuum is contributed by the single harmonic emission peak with the dominant short quantum path. Consequently, two combinations of the laser parameters can be found to generate the water window spectral continuum. By properly superposing some harmonics on the spectral continuum, a number of intense water window pulses with the duration of sub-35 as can be produced.     

碳纤维复合材料的激光清洗等离子体光谱在线检测研究

近年来碳纤维复合材料（CFRP）由于性能优异，受到工业领域广泛关注。采用激光清洗技术预处理碳纤维复合材料表面的污染物和环氧树脂等杂质，有利于改善碳纤维复合材料表面性能，提高碳纤维复合材料胶接界面的结合强度。在线检测激光清洗过程，实时判断碳纤维复合材料的表面清洗质量，是保证激光清洗效果的关键环节，也是激光清洗装置自动化、集成化的核心技术。激光诱导等离子体光谱技术可以快速分析材料表面元素变化，实现在线检测激光清洗表面状态，在激光清洗领域有很广的应用前景。采用Nd∶YAG高能量脉冲激光器产生的1 064 nm激光在空气环境中诱导产生等离子体，利用改进型光栅光谱仪(ME5000)获取等离子体光谱，在线检测激光清洗碳纤维复合材料。研究外界空气环境对等离子体光谱检测结果的影响，发现350~700 nm波段的元素谱线可用于碳纤维复合材料表面物质成分分析；采用电子扫描显微镜观测的激光清洗表面形貌和X射线电子能谱仪测得的元素变化共同表征等离子体光谱检测的有效性，通过采集不同激光能量以及不同作用次数的等离子体光谱图，获得碳纤维复合材料表层树脂物质通过激光单次清洗干净的阈值，研究激光清洗质量与激光诱导等离子体谱线成分及其强度变化的关系。结果表明：在获取的激光诱导等离子体光谱中，光谱图中谱线波长在393.3 nm的S(Ⅱ)和589.5 nm的S(Ⅱ)谱线可有效在线表征碳纤维复合材料表面清洗质量；激光单次去除干净表面环氧树脂的阈值为10.68 mJ；低激光能量时需要清洗多次可以去除干净表面树脂；高激光能量时清洗单次可使表面树脂去除干净，多次清洗易造成基体损伤。实验结果为激光清洗碳纤维复合材料的智能集成化应用提供工艺依据和技术支持。     

基于耦合Ginzburg-Landau方程的石墨烯锁模光纤激光器的暗暗孤子解及其稳定性

以耦合Ginzburg-Landau方程为模型,对石墨烯锁模光纤激光器中脉冲的动力学行为进行了详细地研究.首先,采用拟解法推导了该方程组的啁啾类暗暗孤子对解;其次,对啁啾类暗暗孤子对的传输特性及稳定性进行了数值研究.结果表明:合理选择系统参数,不仅可以得到啁啾类暗暗孤子对的精确解,而且该精确解还可以在一定的扰动下稳定传输.相关结果将为设计和改善石墨烯锁模光纤激光器的性能提供一定的理论依据.     

无序激光晶体及其超快激光研究进展

激光是受激辐射的光放大,所辐射的波长取决于增益介质中关键电子的能级结构,特别是其最外层电子的状态决定了可能实现的激光特性。激光发展60年来,激光晶体作为激光的重要激活材料,推动了激光技术的进步和普及,是一个研究历史长而又异常活跃的研究领域。当前,超短超强脉冲激光在加工、医疗、国防等关系国计民生的领域有重要需求,适合超短超强激光的激光晶体成为了本领域的研究热点,其关键是揭示最外层电子的影响因素及设计和生长具有宽波段发射性能的激光晶体。本论文从探讨影响激活离子光谱性能的关键因素出发,综述了以本课题组十余年研究的10余种无序激光晶体为主要部分的研究结果和进展,涉及晶体生长、晶体物理、激光器件设计及应用等工作,包含了高级、中级和低级对称性晶体及其获得的最短脉冲激光结果,希望能为本领域的后续研究提供一定的参考和借鉴。     

超高速光纤耦合声光调制器的设计及其应用

为实现小于10 ns光脉冲上升时间的超高速声光调制,该文提出一种光纤耦合声光调制器光脉冲时域响应的理论设计仿真方法。利用该方法对1064 nm和1550 nm工作波长光纤耦合声光调制器进行了仿真,结果预测器件的光脉冲上升时间分别为9.4 ns和9.1 ns;通过器件制作和测试验证,两个波长的器件实测光脉冲上升时间分别为9.74 ns和9.22 ns,实测与理论仿真结果偏差较小。文章最后对器件在超快光纤激光器种子源光脉冲选单、光纤水听阵列时分复用及潜在的宽带移频应用进行了介绍。     

Voltammetric and Impedimetric Detection of Interaction Between Dacarbazine and Nucleic Acids

Dacarbazine (DTIC) is a chemotherapy drug that is used for the treatment of Hodgkin's lymphoma, malignant melanoma, childhood solid tumors and soft tissue sarcoma. The surface confined interaction between DTIC and nucleic acids was investigated for the first time in this study by using both differential pulse voltammetry (DPV) and electrochemical impedance spectroscopy (EIS) in combination with disposable pencil graphite electrodes. The oxidation signals of DTIC and guanine were measured before and after interaction process using DPV technique. The interaction of DTIC with nucleic acids; poly[A], poly[G], or double stranded of poly[A]‐poly[T] and poly[G]‐poly[C] was also examined using DPV. Furthermore, EIS technique was utilized for detection of the interaction between DTIC and nucleic acids; ssDNA/dsDNA, poly[A], poly[G], or double stranded poly[A]‐poly[T] and poly[G]‐poly[C].