Time-of-flight Analysis of Hemispherical Deflection Analyzers Omer SISE 1 and Theo J.M. ZOUROS 2,3 1 Dept. of Science Education, Faculty of Education, Suleyman Demirel University, Isparta, Turkey 2 Dept. of Physics, Univ. of Crete, P.O Box 2208, GR Heraklion, Greece. 3 Tandem Accelerator Laboratory, INPP, NCSR Demokritos, GR Ag Paraskevi, Greece

Motivation The hemispherical deflector analyzer (HDA) has become increasingly popular in electron spectroscopy, due to several advantages including – a) superior energy resolution approaching the sub meV level, – b) the use of flexible transfer lens systems that can be operated in different modes, optimizing selectively transmission, spatial resolution or angular resolution and – c) high efficiency by using a fast, high-resolution two-dimensional position sensitive detector (PSD) BPU Aug 2015 Istanbul2

For conventional electron spectroscopy, the flight time of electrons in an analyzer of this type is unimportant. However – if an HDA is used to record phenomena varying rapidly in time as in synchrotron and free- electron laser (FEL) investigations, or – if it is coupled to another detector in an electron–electron coincidence setup, the travel times of the electrons through the analyzer become an important point of consideration BPU Aug 2015 Istanbul3 Neppl et al. 2014, Faraday Discussions Sise, 2011, PhD Thesis Time (ns) Sise et al. 2011, PRA

BPU Aug 2015 Istanbul4 The variation of the time spread Δ t and energy spread Δ E as a function of pass energy E 0. A suitable compromise between good energy resolution and good time resolution is clearly needed.

BPU Aug 2015 Istanbul5 The exit radius r π Theoretical background Zouros and Benis, 2002, JESRP Sise and Zouros, 2015, JSPEC Time of flight at the exit t π The 1/r potential of an ideal HDA

Elliptical orbits with the same kinetic energy for different α BPU Aug 2015 Istanbul6 Elliptical (Kepler) trajectories of charged particles in the ideal HDA

Ideal and Fringing Field HDA BPU Aug 2015 Istanbul7 In (d), the conventional fringing field HDA (black squares) is seen to have a much larger and asymmetric spread as a function of α, far from 1 st order focusing conditions. The two paracentric entries, however, have much narrower spreads demonstrating full 1 st order focusing, and therefore much improved energy resolution. The time-of-flight and the exit radius are plotted as a function of launching angle

BPU Aug 2015 Istanbul8 R 0 = mm R 0 = mm R 0 = 116 mm Calculated spot size and time- energy distributions c c

BPU Aug 2015 Istanbul9 R 0 = mm R 0 = mm R 0 = 116 mm Calculated spot size and time- energy distributions c c

BPU Aug 2015 Istanbul10 The two paracentric entries for the fringing field HDA are seen in (c) and (d) to have near ideal field HDA distributions.

BPU Aug 2015 Istanbul11 The two fringing field paracentric entries are seen to have near ideal field behavior Variation of the figures of merit g and G with pass energy E 0.

Summary and Conclusion We have explored for the first time, the time-of-flight properties of the biased paracentric HDA for the two special entry positions. Overall, both biased paracentric entries should prove themselves to be superior to the conventional HDA entry both in timing as well as in energy resolution applications BPU Aug 2015 Istanbul12

Acknowledgement BPU Aug 2015 Istanbul13 This research has been co-financed by the European Union and Greek national funds through OP: Education and Lifelong Learning, Research Program: THALES. References 1.T. J. M. Zouros and E. P. Benis, Journal of Electron Spectroscopy and Related Phenomena, vol. 125, no. 3, pp. 221–248, Omer Sise and Theo J. M. Zouros, Journal of Spectroscopy, vol. 2015, Article ID , 20 pages, SIMION v.8.1, url: 4.T. J. M. Zouros and E. P. Benis, Applied Physics Letters 86 (2005) The APAPES collaboration homepage: