13.9nm光栅分束器及相关问题研究

【作者】 谭鑫；

【导师】 付绍军；

【作者基本信息】 中国科学技术大学 ， 同步辐射及应用， 2008， 博士

【摘要】 X射线干涉仪技术是测量等离子体的电子密度的主要手段,Mach-Zehnder干涉仪系统是干涉仪诊断等离子体的典型系统,所能给出的等离子体信息充分,准确;等离子体诊断过程高效,便捷。该干涉系统的核心部件为X射线分合束光栅,开展X射线分合束光栅的研究是构建等离子体诊断用X射线Mach-Zehnder干涉系统的基础和前提,对等离子体诊断的研究有非常深刻的影响和意义。本文把研究的内容定位于等离子体诊断技术,其中重点关注的是基于衍射光栅的X射线Mach-Zehnder干涉系统及其核心部件X射线激光分合束光栅。近来,随着等离子体应用的日益广泛,等离子体诊断技术突飞猛进,基于衍射光栅的X射线Mach-Zehnder干涉系统就是在这样的背景下出现的准确,高效,便捷的诊断技术。目前,国内X射线多层膜分束镜的研究已经取得重要进展,基于多层膜分束镜的干涉仪系统在等离子诊断中以获得重要信息。等离子诊断用X射线光棚分束器课题受到了国家自然科学基金委员会与中国工程物理研究院联合基金资助,国家863探索基金资助,作者在导师组的指导下从事了课题的研究工作。作者的主要工作有以下几个方面:一.干涉系统预调整方法研究及预调整光栅的研制该干涉系统中用于等离子体诊断的X射线激光是非可见光,对干涉系统的预调整需使用可见光进行,这一特点就要求用于等离子体诊断的干涉系统的分束器必须还同时存在一块用于干涉光路调整的调整光栅(其线密度较低)。这块调整光栅决定着干涉系统的预调整精度,进而影响最终获得的等离子体诊断信息,因而其重要性不言而喻。目前,美国人的做法是利用机械刻划的方法制作低线密度光栅后与高线密度的工作光栅进行拼接,而这种方法存在诸多缺点。为克服这些缺点对干涉系统调整精度的影响,对调整光栅的研究将十分有意义。作者提出了使用双频光栅作为调整光栅的方法。双频光栅中的低线密度光栅完全能够满足低线密度的要求,且双频光栅与工作光栅是同时利用全息曝光工艺制作在同一基底上的,其从根本上解决了光栅拼接过程中的问题。作者结合该干涉系统对工作光栅与调整光栅的要求,对双频调整光栅的线密度进行了设计,并且在理论上推导了双频光栅在制作过程中的误差;对双频调整光栅用于该干涉系统预调整可能产生的误差进行了定量的分析,确定了双频调整光栅的可行性。作者结合双频调整光栅制作过程的误差分析在制作过程中对其进行有效的控制,实现了在同一基底上同时制作双频调整光栅与工作光栅光刻胶掩模。最后,对其线密度,线密度关系,双频光栅线条平行度这三个对干涉系统调整精度有显著影响的参数进行了实际测量。其中,双频光栅线条平行度测量系统是作者自行搭建的一套高精度平行度测量系统,具有很高的扩展性。测量结果表明所制作的双频调整光栅的各项参数与设计相吻合,用于该干涉系统预调整将获得较高的预调整精度。二.X射线激光Laminar分合束光栅的研制基于衍射光栅的X射线干涉系统的核心部件就是分合束光栅,他是最近兴起的等离子体诊断技术的核心部件。鉴于干涉系统的特殊要求,其0级与1级衍射光构成了干涉系统的两臂,且0级与1级衍射效率也要尽量接近,故其0级与1级的衍射效率是分合束光栅的重要参数。由于其特殊要求,必须先对其进行槽型的选择和设计而后进行制作研究工作。作者通过计算对比了在波长13.9nm的X射线激光入射情况下的闪耀槽型光栅、正弦槽型光栅和Laminar槽型光栅的0级与1级衍射效率,且结合制作工艺确定了制作Laminar槽型光栅作为X射线分合束光栅。Laminar光栅不但能够获得较高的0级与1级衍射效率且制作过程相对简单,参数控制相对容易。而后,对Laminar工作光栅的线密度等槽型参数进行了理论设计得到了最优化的槽型参数。作者在获得最优槽型参数后,使用全息曝光-离子束刻蚀工艺对Laminar工作光栅进行了制作研究。结合制作工艺讨论了Laminar工作光栅制作过程中可能出现的问题并给出了解决方法。经过实验研究成功制作了Laminar工作光栅。最后对Laminar工作光栅衍射效率进行了测量,测量结果表明所制作的Laminar工作光栅的0级与1级衍射效率达到了预期结果,完全满足干涉系统成像需要,为等离子体诊断的干涉系统研究奠定了基础。更多还原

【Abstract】 The plasma is widely used in economy, industry and society. Soft X-ray Mach-Zehnder interferometer is an invaluable tool to probe the electron density gradient and electron density of larger variety plasma. Hereby, it is very important to the plasma diagnosis, X-ray Laser and so on. Experiments were conducted using either a wavefront-division interferometer based on Lloyd’s mirror, or an amplitude division interferometer. While simplicity is an advantage of the Lloyd’s mirror interferometer, the amplitude division interferometer has the advantage of producing interferograms of significantly higher quality, which display high fringe visibility over the entire field of view.In this thesis, the author focuses on the Diagnosis of the Plasmas. And The soft x-ray diffraction grating Mach-Zehnder interferometer is the emphases. This work is supported by National Science Foundation of China, 863 Project. The piece resistance of the author work are:1, Laminar grating as the splitter grating in the Soft X-ray laser Mach-Zehnder interferometerThe diffraction grating interferometer (DGI) is based on a skewed Mach-Zehnder configuration. The diffraction gratings are designed to split the incoming soft x-ray laser beam evenly into two orders. Elongated grazing incidence mirrors are used to direct the beams towards the second grating, where they are recombined to produce the interference pattern. The diffracted zero and first order beams from a diffraction grating form the two arms of the interferometer. The grating is positioned at a small glancing incidence angle (<10°) with respect to the soft X-ray laser beam to generate zero and first diffracted order beams of approximately equal intensities. The zero and first diffracted order beams’ diffraction efficiency product is similarly important, because it can make the DGI get a high throughput. So the diffraction grating used as a splitter grating is very important to the diagnosis result of the plasma. At the wavelength 13.9nm which our DGI uses, there must be a new pattern grating used as the splitter grating.Comparing with the one based on thin film beam splitters, the DGI based on the laminar grating splitters has the advantages of a high throughput and a high robustness. Comparing with interferometers based on the blaze grating splitters, its throughput is approximately equal (>6percent per arm) and the laminar grating is easy to be fabricated.The laminar grating as beam splitter of interferometer was designed for 13.9nm. Then the grating was fabricated by using the holographic ion beam etching method and measured by synchrotron radiation at the National Synchrotron Radiation Laboratory (NSRL) of China. The calculated and measured results of the grating efficiency and their efficiency product were compared.2, The pre-aligned of the system and the fabrication of the pre-aligned-gratingThe diffraction grating interferometer (DGI) is based on a skewed Mach-Zehnder configuration shown in Fig. 1. The diffraction gratings are designed to split the incoming soft x-ray laser beam evenly into two orders. Elongated grazing incidence mirrors are used to direct the beams towards the second grating, where they are recombined to produce the interference pattern. The diffracted zero and first order beams from a diffraction grating form the two arms of the interferometer. The grating is positioned at a small glancing incidence angle (<10°) with respect to the soft X-ray laser beam to generate zero and first diffracted order beams of approximately equal intensities. The diffraction grating interferometer must be pre-aligned by a visible light like a He-Ne laser, because soft X-ray laser(SXRL) is a sightless light. To ensure that the SXRL and the He-Ne laser beams follow the same path, the diffraction gratings were ruled with two vertically separated regions(pre-aligned grating region & SXRL grating region) with different line densities. The ratio of the line densities(50 multiples upwards) in these two regions corresponds to the ratio of the wavelengths between the SXRL and the He-Ne laser. At present, Grating Tilling Technology and Exposure Tilling Technology had been used in the fabrication process of the diffraction grating. Using this kind of diffraction grating, the DGI will obtain high pre-aligned precision, but the fabrication process of the diffraction gratings is complicated and difficult, in addition there are some other problems.Herein a soft x-ray laser interferometer using a double-frequency grating(DFG) as the pre-alinged grating. The wavelength of the SXRL in our DGI is 13.9nm, and the wavelength of the He-Ne laser is 632.8nm. Using DFGs, the fabrication process of the diffraction gratings will be predigested and the problems begot by Grating Tilling Technology and Exposure Tilling Technology will be avoid.更多还原