Angle-resolving time-of-flight electron spectrometer for near-threshold precision measurements of differential cross sections of electron-impact excitation of atoms and molecules.
This article presents a new type of low-energy crossed-beam electron spectrometer for measuring angular differential cross sections of electron-impact excitation of atomic and molecular targets. Designed for investigations at energies close to excitation thresholds, the spectrometer combines a pulsed electron beam with the time-of-flight technique to distinguish between scattering channels. A large-area, position-sensitive detector is used to offset the low average scattering rate resulting from the pulsing duty cycle, without sacrificing angular resolution. A total energy resolution better than 150 meV (full width at half maximum) at scattered energies of 0.5-3 eV is achieved by monochromating the electron beam prior to pulsing it. The results of a precision measurement of the differential cross section for electron-impact excitation of helium, at an energy of 22 eV, are used to assess the sensitivity and resolution of the spectrometer.
Lange
M
M
Centre for Antimatter-Matter Studies, Research School of Physical Sciences and Engineering, The Australian National University, Canberra 0200 ACT, Australia. michael.lange@mpihd.mpg.de
Matsumoto
J
J
Setiawan
A
A
Panajotović
R
R
Harrison
J
J
Lower
J C A
JC
Newman
D S
DS
Mondal
S
S
Buckman
S J
SJ