Laser developments and study of Rydberg and autoionizing Rydberg states in Tm, La and At using resonant ionization laser spectroscopy
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Date
2020-05
Authors
Mostamand, Maryam
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Abstract
The resonant ionization laser ion source is an element-selective, efficient and versatile ion source
which generates radioactive ion beams at on-line mass separator facilities. Elements with complex
atomic structures and incomplete spectroscopic data require ionization scheme development. A
grating-tuned titanium:sapphire (Ti:Sa) laser was used in applications for spectroscopy studies.
A regiment of automated and continuous frequency-doubled and frequency tripled scans was
developed to investigate different energy regions and electronic configurations of the elements. An
intra-cavity frequency doubled chromium:forsterite laserwas built, to cover the spectral gap between
the orange and red wavelengths as these are not attainable using Ti:Sa lasers. Laser resonance
ionization spectroscopy has been performed on lanthanum (La) and thulium (Tm) at TRIUMF’s
off-line laser ion source test stand to identify the highest efficiency ionization scheme for delivery
of radioactive ion beams. Upon identification of possible two-step Ti:Sa laser based ionization
schemes, systematic laser resonance ionization spectroscopy was performed by conducting laser
scans across Rydberg states, ionization potentials, and auto-ionizing states. The spectroscopy of
high-lying Rydberg states and auto-ionizing Rydberg states allowed to confirm and remeasure the
ionization potential of Tm and La atom with improved accuracy. In-source resonance ionization
spectroscopy of the purely radioactive astatine (At) atom was performed at the ISAC/TRIUMF
radioactive ion beam facility to search for an efficient ionization scheme throughout auto-ionizing
states. Apart from developing and implementing resonance ionization spectroscopy (RIS) schemes
for elements, the issue of isobaric contamination in radioactive ion beam (RIB) delivery was
addressed. On the newly implemented ion guide laser ion source (IG-LIS) for isobarically pure
i
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RIB, operating modes and parameters were being developed and optimized. Design improvements
are being implemented into the prototype for more robust and efficient on-line operation, and based
on simulation (SIMION 8.0.4) studies further refinements are being implemented on the quadrupole
ion guide based IG-LIS and a higher efficiency octupole based IG-LIS is being proposed.
Description
Keywords
Laser developments, Laser ion source, Laser resonance ionization spectroscopy, Lanthanum (La), Thulium (Tm), Astatine (At), Ion guide laser ion source (IG-LIS), Ti:Sa lasers, Cr:forsterite laser, Grating tuned laser, Ionization potential (IP) measurement, Rydberg states, Autoionizing states, SIMION simulation