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Experimental investigations of the kinetic processes involved in a rubidium (Rb) Optically Pumped Alkali metal vapor Laser (OPAL)

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Please use this identifier to cite or link to this item: http://hdl.handle.net/1928/12837

Experimental investigations of the kinetic processes involved in a rubidium (Rb) Optically Pumped Alkali metal vapor Laser (OPAL)

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Title: Experimental investigations of the kinetic processes involved in a rubidium (Rb) Optically Pumped Alkali metal vapor Laser (OPAL)
Author: Zameroski, Nathan
Advisor(s): Rudolph, Wolfgang
Committee Member(s): Hager, Gordon
Hostutler, Tony
Lester, Luke
Fields, Doug
Department: University of New Mexico. Dept. of Electrical and Computer Engineering
Subject: Optically pumped alkali metal vapor lasers
rubidium
pressure broadening of rubidium
quenching of rubidium fluorescence
diode pumped alkali metal vapor lasers
LC Subject(s): Metal vapor lasers.
Rubidium.
Optical pumping.
Semiconductor lasers.
High power lasers.
Degree Level: Doctoral
Abstract: Diode or Optically Pumped Alkali metal vapor Lasers (DPALs or OPALs) are candidates for high power laser systems. These gas-phase three-level lasers are pumped on the alkali’s D2 transition, 2S1/2 →2P3/2, and support lasing on the D1 transition, 2P1/2 → 2S1/2. Collisional mixing using several hundred Torr of an additive gas such as methane or ethane transfers population from the 2P3/2 state to the 2P1/2 state. These gases are selected because of their large mixing rates (cross sections) and small quenching rates (cross sections) of the 2P states. Pressure broadening of the D1 and D2 transitions is a direct consequence of using several hundred Torr of buffer gas required for collisional mixing. The quenching kinetics (non radiative decay of excited states) of Rb 2P states by methane and ethane are reexamined with time resolved fluorescence techniques. A detailed analysis of the interplay between radiation trapping, the absorption and re-emission of resonant radiation in an atomic vapor, and quenching is carried out. Experimental results supported by theoretical simulations (calculations) bound the quenching cross sections (sigma)of methane and ethane at 40 oC to sigma≤ 0.02 Å2 and sigma ≤ 0.03 Å2, respectively. These values are about two orders of magnitude smaller than previously reported. The pressure broadening and collisional shift rates of the Rb D2 absorption line by methane, ethane, propane, butane, and helium are measured by using linear absorption spectroscopy at 40 oC. The rates of ethane, propane, and butane are measured for the first time. The broadening rates in (MHz/Torr) for C2H6, C3H8, and n-C4H10, are 28.1 ± 0.4, 30.5 ± 0.6, and 31.3 ± 0.6. The corresponding shift rates in (MHz/Torr) are -8.8 ± 0.2, -9.7 ± 0.2, and -10.0 ± 0.2. A pulsed Rb-methane OPAL is demonstrated. Slope efficiencies of 72 to 76% are obtained. A one dimensional (1D) rate equation model that includes the spectral overlap of the pump and the Rb D2 absorption line is used to model the system and interpret experimental data. The experimental data and the laser modeling results are in qualitative agreement for a range of experimental conditions (rubidium number density 0.84x1013 cm-3 to 2.1x1014 cm-3, methane concentration ~ 3.3x1018 cm-3 to 1.6x1019 cm-3 and pump intensities up to 120 kW/cm2). The temporal and bleaching (saturation) dynamics of the laser pulse and properties of the 795 nm laser beam are investigated. A hydrocarbon-free Rb-D2 (rubidium-deuterium) OPAL is demonstrated for the first time.
Graduation Date: May 2011
URI: http://hdl.handle.net/1928/12837


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