Time-of-flight Analysis of Hemispherical Deflection

Analyzers Omer SISE1 and Theo J.M.

ZOUROS2,3

1Dept. of Science Education, Faculty of Education, Suleyman Demirel University, 32260 Isparta, Turkey2Dept. of Physics, Univ. of Crete, P.O Box 2208, GR 71003 Heraklion, Greece. E-mail: tzouros@physics.uoc.gr

3Tandem Accelerator Laboratory, INPP, NCSR Demokritos, GR 15310 Ag Paraskevi, Greece

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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).

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• 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.

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Neppl et al. 2014, Faraday Discussions

Sise, 2011, PhD ThesisTime (ns)Sise et al. 2011, PRA

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The variation of the time spread Δt and energy spread ΔE as a function of pass

energy E0.

A suitable compromise between good energy resolution and good time resolution is clearly

needed.

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The exit radius rπ

Theoretical background

Zouros and Benis, 2002, JESRPSise and Zouros, 2015, JSPEC

Time of flight at the exit tπ

The 1/r potential of an ideal HDA

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Elliptical orbits with the same kinetic energy for different α

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Elliptical (Kepler) trajectories of charged particles in the ideal HDA

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Ideal and Fringing

Field HDA

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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 1st order focusing conditions.

The two paracentric entries, however, have much narrower spreads demonstrating full 1st order focusing, and therefore

much improved energy resolution.

The time-of-flight and the exit radius are plotted as a

function of launching angle

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R0 = 82.55 mm R0 = 101.6 mm R0 = 116 mm

Calculated spot size and time-energy distributions

c

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R0 = 82.55 mm R0 = 101.6 mm R0 = 116 mm

Calculated spot size and time-energy distributions

c

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

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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 E0.

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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.

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Acknowledgement

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This research has been co-financed by the European Union and Greek national funds through OP: Education and Lifelong Learning, Research Program: THALES.References1. T. J. M. Zouros and E. P. Benis,  Journal of Electron Spectroscopy and

Related Phenomena, vol. 125, no. 3, pp. 221–248, 2002. 2. Omer Sise and Theo J. M. Zouros, Journal of Spectroscopy, vol. 2015,

Article ID 153513, 20 pages, 2015. 3. SIMION v.8.1, url: http://simion.com4. T. J. M. Zouros and E. P. Benis, Applied Physics Letters 86 (2005)

094105.5. The APAPES collaboration homepage: http://apapes.physics.uoc.gr/