EBIS/T for X-Ray Spectroscopy
Since the electron energy can be sharply adjusted the Dresden EBIT/EBIS are excellent sources of electromagnetic radiation such as
- ultraviolet, UV/EUV
- visible light
Due to the ability to ionize almost all elements up to high ion charge states spectroscopic investigations can be done for a wide range of charge states and elements.
Applications of X-Ray Spectroscopy
X-ray emission of highly charged ion differs from those of the primary neutral atom (diagram lines). The main processes are direct excitation (DE), radiative recombination (RR) and dielectric recombination (DR). These processes are illustrated in the following scheme.
Direct Excitation (DE)
Radiative Recombination (RR)
Dielectronic Recombination (DR)
An electron from the electron beam excites an inner shell electron of a HCI. The created vacancy is then filled by an electron from an outer shell under emission of a photon with an energy equal to the difference of the orbital energies of the involved electrons.
An electron from the continuum (electron beam) is captured into an ionized atomic state under emission of a photon with an energy equal to the sum of the kinetic energy of the free electron and the binding energy of the state where the electron is captured.
An electron from the continuum (electron beam) is captured into an ionized atomic state by exciting a bound inner shell electron. This process appear as a resonance process if the energy from the capture process is equal to the required energy of the excitation process. During this process a highly excited ion arise which is stabilized under x-ray emission.
X-Ray Spectroscopy at EBIS/T (Examples)
Energy-dispersive X-ray Spectrometry
The intensity of x-rays emitted from EBIS/T is high enough to provide energy-dispersive as well as wavelength-dispersive x-ray spectroscopy. For example some x-ray spectra are shown on the right. The measurements were accomplished with a Si(Li) detector featuring a energy resolution of 133 eV at 5.9 keV photon energy. The left part of both Figures show x-rays from DE processes, while the right part presents RR x-ray transitions into different subshells.
Wavelength-dispersive X-ray Spectrometry
Wavelength-dispersive x-ray spectroscopy allows to measure highly resolved x-ray spectra and to resolve manifold individual x-ray transition, from different atomic states and from different ion charge states.
Electron Energy-Resolved X-ray Spectroscopy
For individual ion charge states at different electron beam energies x-rays from different basic processes (DE,RR,DR) can be observed. A Scatterplot is a two-dimensional visualization of the x-ray emission as a function of the electron beam energy. An example Scatterplot for highly charged krypton ions is shown on the right.
Time-resolved X-ray Spectroscopy
Dielectronic Recombination is a resonant process occurring at well-defined electron beam energies. Setting the electron beam energy to a resonance energy the line development of the individual ionisation states can be detected. This is possible if the x-ray were detected with additional time information, containing the ionisation time (time between ion trap closing and photon detection).
X-Ray Output from EBIS/EBIT
X-ray output from highly charged noble gas ions in dependence of the electron beam energy. The x-ray output of the strongest DE dipole transitions is given.
Radiation power P of the strongest DE dipole transition in noble gas ions.