Magnetic field paralleliser for 2π electron-spectrometer and electron-image magnifier - Abstract - Introduction

Oct 19, 2026

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An electron-optical device forms electrons emitted over 2π steradians from a small-volume region into a beam with a half-angle of 2°. A magnetic field that diverges from 1 to 10−3 Tesla enables time-of-flight energy measurements with resolutions as low as 15 meV. Tests use multiphoton-ionisation electrons at 0–3 eV, with expectations of similar relative energy spread at higher energies. Adding an electric field enables selection of a solid angle from 0 to 4π steradians, and the apparatus can function as an electron-image magnifier with a few micrometers spatial resolution.

LanguageEnglish

CategoryResearch & Report

FormatPDF

Pages13

Reading Time33 min

AccessFree to download

1. Introduction

Background: measuring electron energies from weak sources

Parallelisation in an inhomogeneous magnetic field

Energy analysis methods and time-of-flight approach

Magnetic field paralleliser for 2π electron- spectrometer and electron-image magnifier To cite this article:P Kruit and FH Read 1983J.Phys.E:Sci.Instrum.16313 View the article online for updates and enhancements. You may also like -Electron beam spectroscopyO Klemperer -Oblique ion lens for use with imaging massspectrometer systemsJP Carrico,CB Johnson and KL Hallam -An analysing system for concurrent energyand angular distribution measurements ofcharged particles'emissionNK Krasnova,Yu K Golikov,Yu AKudinov et al. Magnetic field paralleliser for 2π electron-spectrometer and electron-imagemagnifier P Kruit +and FH Read÷ +FOM-Institute for Atomic and Molecular Physics,Kruislaan 407,1098 SJ Amsterdam,The NetherlandsDepartment of Physics,University of Manchester,Manchester M139PL,UK Received 9 July 1982,in final form 2 November 1982 Abstract.An electron-optical device has been constructed inwhich electrons originally emitted over 2π steradians from aregion of small volume are formed into a beam of half-angle 2°.The instrument makes use of a magnetic field that diverges from1 to 10-³Tesla.The energies of the electrons parallelised in thisway have been measured with a time-of-flight technique,givingenergy resolutions as low as 15 meV.Electrons of energy0-3eV,formed in multiphoton ionisation,were used for thesetests,but higher energies are expected to give a similar relativeenergy spread.Addition of an electric field at the source regionpermits the selection of a solid angle from 0up to 4π steradians.The device can also act as an electron-image magnifier,giving aspatial resolution of a few μm in the source plane.Detailedtheoretical and computational results on the properties of thenew apparatus are given,including consideration of the limitingrate of change of the magnetic field,the permissible electronenergies and the permissible dimensions of the electron source. # 1.Introduction The need sometimes arises to measure accurately the energies ofelectrons emitted from a very weak source.For example inexperiments on multiphoton ionisation of atoms or molecules anintense pulse of laser light is focused onto a very small region ina gas,and it may be desired to measure the energies of theresulting photoelectrons,but the number of such electrons perpulse may be severely limited either by the small probability forthe multiphoton process or by the need to limit the space-chargeeffects in the focus region.For example for a resolution of15 meV no more than about 100 electrons may be formed ina laser focus of 10μm diameter,and these electrons aredistributed over all directions and usually over a wide range ofenergies,at a pulse repetition rate that is typically of the order of10 Hz.In such experiments it becomes important in measuringthe electron energies to collect the electrons over as wide a rangeof initial directions as possible,preferably covering a solid angleof 2π or even 4π steradians.Clearly this is difficult to achievewith conventional designs of electron energy analysers becauseusually the energy resolution deteriorates rapidly as theacceptance angle is increased. This problem has been overcome using the properties of aninhomogeneous magnetic fied,as described earlier by Hsu andHirshfield (1976)and later by Beamson et al(1980,1981)in adesign of a new type of electron microscope,a photo-electron spectromicroscope.In the latter instrument electronsinitially emitted in all directions from a region of small volumesituated at the centre of a superconducting solenoid are formed into a nearly parallel beam.In the present instrument theparallelisation is achieved by placing the source between thepolepieces of an electromagnet.The Lorentz force ev×B causeseach emitted electron to spiral around a magnetic field line,andit follows this field line through an aperture in the polepieces intoa region of low and uniform field in which the field lines areagain parallel.In going from the high-field to low-field regionsth

FAQs

What does the magnetic field paralleliser do to the electron trajectories?

It guides electrons spiraling along magnetic field lines so they become nearly parallel in a region of low and uniform field, effectively parallelising and unspiralling the trajectories.

How are electron energies measured in this instrument?

The experiments use a time-of-flight technique with short electron pulses, giving energy resolutions down to about 15 meV.

Can the device select emission angles and also magnify images?

Yes. An electric field at the source allows selection of a solid angle from 0 to 4π steradians, and the diverging magnetic field produces transverse spatial magnification, enabling electron-image magnification with micrometer-scale resolution.

Oct 19, 2026

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