真空紫外103-200 nm波段铝(Al)基高反射镜关键实验技术研究

The high reflective mirrors in 103-200 nm wavelength range are one important optical element in the fields of astronomical observation, free-electron laser, synchrotron radiation, and so on. The features of the reflective mirror affect the optical structures which can be used in this wavelength range. The most optical elements for the vacuum ultraviolet range used in the large setups in China are bought from aboard. The Al/MgF2 and Al/LiF mirrors have been studied in aboard. But in China, many problems need to be solved to obtain the mirrors with high reflectivity in vacuum ultraviolet range, especially in the wavelength of 103- 120 nm. In this project, we’ll focus on these fields shown in below. First one, finding out the relation of the pressure during evaporating with the evaporating rates of aluminum, and the substrate’s temperature to determine the suitable parameters for fabricating the mirrors. And optimizing the other parameters, such as the basic pressure before evaporating, the changed time between two coatings, the temperature of substrate for the second and third step, the thickness of fluoride for the first and second step to reduce the roughness of the coating to eliminate the valley occurred in the reflective curve as far as possible. Second, researching the distribution of the boats for aluminum to obtain the stable rate during the process of evaporation and a large range for the evaporating aluminum rate to change during the different evaporated processes. Third, a new method of fabricating the mirror is proposed, the coating of aluminum is evaporated on the substrate at the room temperature, then the substrate is heated to the temperature below 150°C, and the MgF2 or LiF with the thickness of 5 -10 nm will be fabricated on the surface of aluminum coating. And then the substrate will be heated to the temperature about 350°C, which is above the temperature 220°C used by Quijada. Last the MgF2 or LiF will be fabricated on this substrate. Fourth, the uniformity of the coating in Φ200mm is researched to obtain large scale mirrors. Fifth, the environments and cleaning the pollutions of the mirrors would be researched, such as the temperature, humidity, radiation of ultraviolet, vacuum oil, and so on. Many modern measuring instruments would be used to characterize the mirrors, such as the atomic force microscope (AFM) for surface roughness of mirror, spectrometer for reflectivity or transmittance, x ray photoelectron spectroscopy (XPS) and auger electron spectroscopy (AES) for the elements in films. The results of this research would provide the high reflective mirrors in the wavelength range of 103-200nm, and the technology for the ongoing related studies such as filters and polarizations in our country.

天文观测、同步辐射和自由电子激光等大型装置的工作波段都涵盖了真空紫外103-200 nm波段，反射镜的性能制约了可用光学系统的结构和实验效果。本项目拟采用蒸发镀膜方法开展103-200 nm波段内铝基高反射镜的关键实验技术方面的研究，主要内容：第一，分析蒸发速率、镀膜真空和基板温度三者相互制约的关系，权衡它们对反射率的影响，确定三者最佳的条件；优化工艺参数，降低表面粗糙度，减小凹峰；第二，探索蒸发舟的排布和舟与膜料的配合方式，找到稳定且蒸发速率变化区间大的组合；第三，改进已有薄膜沉积方法，进一步提高真空紫外铝基高反射镜的反射率；第四，Φ200 mm光学薄膜元件均匀性研究；第五，研究样品保存、污染源及清除方法和效果，提高反射镜使用寿命。通过本项目的研究，解决真空紫外铝基高反射镜制作的关键实验技术问题，填补国内在103-130 nm波段内的空白，为我国开展天文观测等相关领域的研究提供技术支撑。

天文观测、同步辐射和自由电子激光等大型装置的工作波段都涵盖了真空紫外103-200 nm波段，反射镜是光学系统中常用的元件之一，反射镜的性能制约了可用光学系统的结构和实验效果。本项目利用实验室现有的超高真空复合镀膜机开展了103-200 nm波段内铝基高反射镜的关键实验技术方面的研究，主要内容和重要结果：.（1）研究了Al薄膜制备工艺，发现采用钨丝舟比钨船舟制备铝薄膜的反射率好，蒸发速率快，镀膜真空好，不能使用钼材料的舟进行铝薄膜制备。.（2）研究了MgF2薄膜的结晶状态，发现温度高、薄膜厚，MgF2薄膜是多晶状态，薄膜厚度在50nm以下几乎是单晶状态，真空紫外波段MgF2薄膜作为保护层的厚度一般在20-50nm范围，所以其最多是部分单晶；.（3）研究了Al/MgF2反射镜，改进镀膜机的工作状态，提高镀膜真空的抽气方式，发现蒸发速率提高到一定程度，受抽速能力的限制，反射镜的反射率会出现下降情况；高低温两次制备保护层，200-300℃的制备的Al/MgF2反射镜性能好于室温、100℃和350℃的，350℃制备样品的反射率在112nm以下波段反射率高，30个月存放后长波段的反射率下降多，而200-300℃制备样品的稳定性好。.（4）研究了Al/LiF反射镜，发现在125nm处其反射率达到90%，由于LiF的吸湿性使得该反射镜在湿度为20%的环境下保存30个月时，反射率下降超过20%，湿度超过40%存放2个月反射率下降接近50%，该组合对反射镜的存放和使用环境要求高。.（5）研究了Al/LiF/MgF2反射镜，室温基板制备的反射镜的反射率低于高温基板制备的表层反射镜的反射率；在Φ30mm基板上制作的反射镜的反射率在107.5~115nm范围内为70~82%。时间稳定性和环境稳定性正在研究。.（6）获得了105-130nm波段MgF2薄膜光学常数，初步研究了121.6nm处的窄带滤光片，发现有待于解决蒸发速率和薄膜厚度控制精度之间的关系，从而提高窄带滤光片的性能。.通过这几年的研究，提高了铝基高反射镜的性能，掌握了铝基高反射镜制作的关键实验技术，填补国内在103-130 nm波段内的空白，为我国开展天文观测等相关领域的研究提供技术支撑。