Laser machining fundamentals:micro,nano,atomic and close-to-atomic scales

With the rapid development in advanced industries,such as microelectronics and optics sectors,the functional feature size of devises/components has been decreasing from micro to nanometric,and even ACS for higher performance,smaller volume and lower energy consumption.By this time,a great many quantum structures are proposed,with not only an extreme scale of several or even single atom,but also a nearly ideal lattice structure with no material defect.It is almost no doubt that such structures play critical role in the next generation products,which shows an urgent demand for the ACSM.Laser machining is one of the most important approaches widely used in engineering and scientific research.It is high-efficient and applicable for most kinds of materials.Moreover,the processing scale covers a huge range from millimeters to nanometers,and has already touched the atomic level.Laser–material interaction mechanism,as the foundation of laser machining,determines the machining accuracy and surface quality.It becomes much more sophisticated and dominant with a decrease in processing scale,which is systematically reviewed in this article.In general,the mechanisms of laser-induced material removal are classified into ablation,CE and atomic desorption,with a decrease in the scale from above microns to angstroms.The effects of processing parameters on both fundamental material response and machined surface quality are discussed,as well as theoretical methods to simulate and understand the underlying mechanisms.Examples at nanometric to atomic scale are provided,which demonstrate the capability of laser machining in achieving the ultimate precision and becoming a promising approach to ACSM.

“稳外资”如何影响“稳投资”——来自《外商投资产业指导目录》的新证据

持续扩大外资市场准入是新时代适应经济全球化趋势的必然要求,也是推动更高水平对外开放的关键举措。作为中国政府促进经济高质量发展的重要抓手,厘清“稳外资”与“稳投资”工作间的内在联系对于构建国内国际双循环相互促进的新发展格局具有重要政策含义。基于此,本文在收集整理中国历年《外商投资产业指导目录》信息的基础上实证考察外资市场准入对内资企业投资的影响。结果表明:外资市场准入放开有助于内资企业投资增长。较之限制类、允许类政策,鼓励外资进入的政策效果更为积极。机制分析表明外资市场准入可通过竞争效应、溢出效应、激励效应和资源配置效应促进企业投资增长。异质性分析发现外资市场准入的影响在西部地区、普通城市、非资本密集型以及民营企业中更为明显。此外,高新区政策与外资市场准入可以起到政策协同作用。