The effect of hydrogen on the 585.3-nm helium-neon nuclear-pumped laser
Shaban, Yasser Ragab
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https://hdl.handle.net/2142/22993
Description
Title
The effect of hydrogen on the 585.3-nm helium-neon nuclear-pumped laser
Author(s)
Shaban, Yasser Ragab
Issue Date
1993
Doctoral Committee Chair(s)
Miley, George H.
Department of Study
Nuclear Engineering
Discipline
Nuclear Engineering
Degree Granting Institution
University of Illinois at Urbana-Champaign
Degree Name
Ph.D.
Degree Level
Dissertation
Keyword(s)
Engineering, Nuclear
Language
eng
Abstract
The use of hydrogen as an admixture gas in the ($\sp3$He)$\sp4$He-Ne laser at the 2P$\sb1$-1S$\sb2,$ 585.3-nm Ne transition has been found to be more effective in depopulating the lower excited laser state, 1S$\sb2,$ than the use of heavy inert (noble) gases. Experimental results using the U of Illinois TRIGA reactor to pump this laser mixture at 585.3 nm feature the lowest threshold power density ever reported for visible nuclear-pumped, e-pumped and heavy ion beam-pumped lasers. The threshold neutron flux for the above transition was $1.5 \times 10\sp{13}$ n/(cm$\sp2$-sec), corresponding to threshold pumping power density 43 $\pm$ 2 mW/cm$\sp3.$ This is the second-lowest threshold power density observed for NPLs over all wavelengths, second only to the Soviet results on Ar-Xe infrared lasers (2.05 and 2.65 $\mu$m) that have a threshold power of $\sim20$ mW/cm$\sp3.$
Preceding the actual laser experiments, a series of gain experiments were carried out with various $\sp3$He:Ne:H$\sb2$ gas mixtures to guide us to the appropriate mixture ratio needed for lasing. The laser cell, 100 cm long and 1.5 cm in diameter, was fitted with a chopper fan placed in front of the rear mirror. Lasing was observed for $\sp3$He:Ne:H$\sb2$ mixture ratios 5.3:2.7:2, 5.6:2.9:1.5, and 6:3:1 with total pressures 2023, 2140, and 1928 torr respectively. Lasing was also observed for $\sp4$He:Ne:H$\sb2$ mixture ratio 2.7:5.6:1.7 with total pressure 990 torr, where lasing was pumped by a $\sp{10}$B-coated tube.
A unique internal energy transfer (IET) model was developed to explain qualitatively and quantitatively the energy transfer mechanisms from the neon excited atom to the quencher atom. The IET model favors the use of open-shell atoms for faster energy transfer (quenching). The IET model suggests that the quenching of the lower excited laser level with hydrogen and argon atoms occurs at thermal energy (0.1 eV), whereas the quenching of the upper excited laser level with hydrogen and argon atoms occurs at 1.4 eV and 0.3 eV, respectively. A general kinetic model was developed, and it estimates the threshold power density to be 40 mw/cm$\sp3$ and the laser efficiency to be 1.7%. In contrast, the measured laser efficiency was found to be only 0.013% which is in good agreement with the laser efficiencies of the He-Ne-Ar, 585.3 nm reported in the USSR and at Sandia National Lab, which are 0.1% and 0.01%, respectively.
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