Development of a UV-laser Based Ultra-High Resolution Angle-Resolved Photoemission Capability for Electronic Structure Studies

9704045德索将在材料研究司和多学科活动办公室的支持下，在科罗拉多大学开发最先进的高分辨率光电发射能力。该仪器的一个新颖和特别强大的方面将是开发和使用高功率飞秒紫外激光系统作为电子材料光电发射实验的激发源。紫外光激光系统将提供：(1)比其他方法(包括最好的同步加速器的摇摆器或波荡器源)获得的光子通量高出数量级。(2)非常高的能量分辨率(1-10 meV)，取决于脉冲的时间长度。(3)更容易控制光子的偏振(线性、圆形等)，这对获得电子态的对称性非常有帮助。(4)由于电子的平均自由程在低动能下变得很长，所以体感度大大提高。对于体电子结构的研究，这将克服当今光电子发射的主要困难之一，并为许多材料系统的研究开辟了技术途径，这些材料系统到目前为止还没有产生足够高质量的表面来进行可靠的光电发射实验。(5)基于泵浦-探测的光电子能谱，它将使我们能够(A)研究费米能级附近的空能级。这可能会取代反向光电发射作为这一目的的选择，因为反向光电发射具有分辨率低(电子伏安的十分之几)、低计数率，并对样品表面造成损害。(B)通过改变泵浦光束和探测光束之间的延迟来研究系统的动力学。该系统将使用最先进的电子能谱和激光仪器。据我们所知，这种强大的组合目前在世界上任何地方都不存在。所要求的仪器还将填补大博尔德地区现有技术的一个漏洞，并将提供给当地科学界。***

9704045 Dessau A state-of-the-art high resolution photoemission capability will be developed at the University of Colorado with support from The Division of Materials Research and The Office of Multidisciplinary Activities. A novel and particularly powerful aspect of the instrumentation will be the development and usage of a high power femtosecond UV laser system as an excitation source for photoemission experiments of electronic materials. The UV-laser system will provide: (1) a photon flux orders of magnitude higher than is achievable by other means, including the best wiggler or undulator sources at a synchrotron. (2) Very high energy resolution (1-10 meV), depending upon the temporal length of the pulses. (3) Greater ease in controlling the photon polarization (linear, circular, etc.), which is very helpful for obtaining the symmetry of the electronic states. (4) Much greater bulk sensitivity because the electron mean free paths get very long at low kinetic energies. For studies of the bulk electronic structure, this will overcome one of the major difficulties of photoemission today, and open up the technique to the study of many materials systems which have not to date yielded high enough quality surfaces for reliable photoemission experiments. (5) Pump-Probe based photoemission which will enable us to (a) Study the unoccupied levels near the Fermi energy. This may replace inverse photoemission as the too of choice for this purpose, as inverse photoemission suffers from poor resolution (a few tenths of an eV), low count rates, and is damaging to a sample surface. (b) Study the dynamics of the system by varying the delay between the pump and the probe beams. The system will make use of the most advanced electron spectroscopic and laser instrumentation. To our knowledge, this powerful combination does not currently exist anywhere in the world. The requested instrumentation will also fill a hole in the techniques available in the greater Boulder area, and will be available to the local scientific community. ***