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Recent progress of experimental fluid mechanics for EUV sources
DENG Weiwei, ZHAI Tianqi, GAO Lihao, XU Chenghao, ZHAO Xinyan, LIU Yanchu
 doi: 10.6052/1000-0992-23-044
Abstract(222) HTML(41) PDF(70)
The extreme ultraviolet (EUV) source is the enabling component of the EUV lithography. The commercialized EUV source is based on laser produced plasma from tin droplet target. EUV source is essentially a fluid-state light source, which involves rich and complex fundamental fluid mechanics problems with four characteristic time scales ranging from picoseconds to milliseconds. This review surveys the research progress of experimental fluid dynamics for EUV sources. First, the fundamental and technical aspects of the generation and control of jet, droplet and liquid film targets are introduced. Second, the dynamic response of the three types of targets to pulsed lasers were summarized, with an emphasis on droplet targets. Finally, in order to improve the stability, brightness and life the EUV sources, three key research topics in experimental fluid mechanics worthy of attention are proposed: (i) the precise generation and manipulation of fine tin droplet targes with long spacing at high frequencies; (ii) the quantitative physical picture of the expansion and radiation of the laser produced plasma, and (iii) the deformation and fragmentation mechanism of droplet targets and suppression, collection and cleaning technologies for debris.
Review and prospect on the efficient synthetic jet
LU Yiran, WANG Jinjun
 doi: 10.6052/1000-0992-23-038
Abstract(163) HTML(78) PDF(36)
As a significant active flow control method, the synthetic jet has been considered to be promising and of great potential in applications. Due to its superior control performance, synthetic jets have wide application in improving aerodynamic characteristics of aircrafts, suppressing vibration and noise, cooling electronic devices and etc. In recent years, a large number of synthetic jet models with higher accuracy have been proposed and the underlying mechanism of the efficient entrainment has been explored more vividly. The optimization of the synthetic jet actuator and further improving its controlling efficiency has attracted more and more attention. The optimization of the actuator and its application are summarized from three aspects respectively, i.e., the actuator structure, the geometric parameters and the actuating signal. Moreover, the possible issues for future investigation have been suggested.
Fundamental principles and research progress of non-Hermitian mechanical systems
GENG Linlin, YUAN Jinbo, CHENG Wen, HU Gengkai, ZHOU Xiaoming
 doi: 10.6052/1000-0992-23-034
Abstract(345) HTML(83) PDF(166)
Non-Hermitian theory, originated from quantum mechanics, is a theoretical framework for investigating the dynamics of open systems. New phenomena can be revealed with this theory, including exceptional point, chiral mode switching, and topological skin effect, which provide novel concepts for unusual wave and vibration control. This review will provide a comprehensive introduction to basic concepts of non-Hermitian theory in terms of classical mechanical systems, clarify the relationship between classical and non-Hermitian systems, and summarize the cutting-edge research progress in this field. Exceptional points and parity-time symmetry in non-Hermitian systems are firstly introduced. Then, the perturbation theory near exceptional points and its application to enhanced sensitivity are presented. Subsequently, the eigenvalue topological structure near exceptional points and eigenmode evolution in the process of dynamical encircling of exceptional points are discussed. Finally, the topological phase property of non-Hermitian mechanical systems is introduced.

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