Plasmas created by extreme ultraviolet lasers

20世纪60年代早期激光的发明导致了高功率（100万瓦）红外和可见脉冲激光聚焦在固体目标上以产生热（50万开尔文）等离子体的实验。在近50年的研究中，激光相互作用的物理学、羽流膨胀的物理学以及许多重要的应用都得到了较详细的阐明。当聚焦在固体目标上时，可见光/红外激光在大部分脉冲持续时间内不会穿透固体，而是被密度比固体密度小100- 1000倍的膨胀等离子体羽吸收。然而，将激光波长降至极紫外线（EUV），使激光能够穿透固体，并直接在固体密度下产生等离子体。PI进行的初步建模研究表明，EUV激光辐射与大多数固体目标的相互作用将导致不透明度迅速下降（因此目标“漂白”）。最初，EUV光子能量的衰减长度被漂白，然后是另一个衰减长度，因此“漂白波”在亚纳秒的时间尺度上通过固体目标传播。与相同脉冲能量和焦点光斑直径的红外或可见光辐射相比，更大量的目标物质被有效地烧蚀。由于缺乏足够的高能（10微焦耳）实验室EUV激光器进行实验，很少有建模工作来阐明对极紫外光激光产生的等离子体的理解。然而，可靠的毛细管放电激光器工作在波长46.9 nm（光子能量26.4 eV），产生高达1毫焦耳/脉冲和一百万瓦的峰值功率已经在科罗拉多州立大学（CSU）开发出来。我们建议建立模拟模型来解释极紫外激光产生的等离子体的发射光谱和质谱仪结果。我们将使用约克大学的高功率红外激光器测试光谱仪诊断，并与CSU合作进行光谱和质谱仪测量，以与模拟模型进行比较。一种新型激光产生的等离子体将被研究，它对热致密物质、激光切割和烧蚀以及固体材料光刻的研究具有潜在的影响，与微机电系统（MEMS）制造相关的年收益高达700亿美元的行业。

The invention of the laser in the early 1960s led to experiments where high power (> million Watts) infra-red and visible pulsed lasers were focused onto solid targets in order to produce hot (> 0.5 million degrees Kelvin) plasmas. In almost 50 years of study, the physics of the laser interaction, the physics of the expanding plume and many important applications have been elucidated in some detail. When focussed onto solid targets, visible/infra-red lasers do not penetrate to the solid for most of the pulse duration, but are absorbed in the expanding plasma plume at densities 100- 1000 times smaller than the solid density. Dropping the laser wavelength into the extreme ultra-violet (EUV), however, enables the laser to penetrate into the solid and to create plasma directly at the solid density. Initial modelling studies that have been undertaken by the PI show that the interaction of EUV laser radiation with most solid targets will cause a rapid drop in opacity (so that the target 'bleaches'). Initially an attenuation length for the EUV photon energy is bleached and then another attenuation length, so that a 'bleaching wave' propagates through the solid target on a sub-nanosecond timescale. A much more massive amount of target material is effectively ablated than can occur with infra-red or visible radiation of the same pulse energy and focal spot diameter. Little modelling work has been undertaken to elucidate understanding of EUV laser-produced plasmas because of the lack of sufficiently energetic (> 10 microJoules) laboratory EUV lasers for experiments. However, reliable capillary discharge lasers operating at wavelength 46.9 nm (photon energy 26.4 eV) producing up to 1 milliJoule/pulse and peak powers of a million Watts have been developed at the Colorado State University (CSU). We propose to develop simulation models to interpret emission spectra and mass spectrometer results from EUV laser produced plasmas. We will test spectrometer diagnostics using the University of York high power infra-red laser and in collaboration with CSU make spectral and mass spectrometer measurements for comparison to the simulation models. A new class of laser-produced plasma will be studied with potential impact in the study of warm dense matter, laser cutting and ablation and solid material lithography with relevance to the $70B p.a. revenue industry associated with the manufacture of microelectromechanical systems (MEMS).