Kinetics of Higher Lying Potassium States after Excitation of the D2 Transition in the Presence of Helium
Date of Award
Doctor of Philosophy (PhD)
Department of Engineering Physics
Glen P. Perram, PhD
A kinetic model for the performance of a potassium Diode Pumped Alkali Laser (DPAL), including the role of higher lying states is developed to assess the impact on device efficiency and performance. A rate package for a nine level kinetic model including recommended rate parameters is solved under steady-state conditions. Energy pooling and far wing absorption populates higher lying states, with single photon and Penning ionization leading to modest potassium (K) dimer ion concentrations. The fraction of the population removed from the basic three levels associated with the standard model is less than 10% for all reasonable laser conditions, including pump intensities up to 100 kW/cm2 and K densities as high as 1016 cm-3.To benchmark this new model, fluorescence emitted by a high power, transverse ow potassium DPAL was collected to characterize the highly excited state population at total alkali densities of N = 0:15 – 1:87 x 1014 cm-3, buffer gas pressures of P = 250 – 1200 Torr, and pump intensities of Ip = 20 – 60 kW/cm2, with and without methane. The population in these states was found to be less than 5% for all cases. The effects of these higher energy levels are demonstrated on a potassium-helium system with pump intensities larger than Ip > 5 kW/cm2 with moderate number densities N = 0:1 – 10 x 1013 cm-3. The additional heat loading due to the quenching of the higher states is minimal, < 1% of the spin-orbit mixing heat load. This extra heat has a small effect on both Strehl and efficiency in the static system, but these can be recovered with ow velocities commensurate with transit times across the pump volume < 0:1 s.
DTIC Accession Number
Wallerstein, Austin J., "Kinetics of Higher Lying Potassium States after Excitation of the D2 Transition in the Presence of Helium" (2018). Theses and Dissertations. 1943.