Theoretical Model Analysis of Absorption of a Three Level Diode Pumped Alkali Laser

This paper models the absorption phenomena of light in a three level diode pumped alkali laser system. Specifically this model calculates for a user defined set of system parameters the attenuation of the input pump beam and characteristics of the bleached wave. Using Wolfram's Mathematica 6.0 software all necessary physics for an accurate description of absorption was modeled from first principles: energy levels, cross sections, spin-orbit kinetic processes, saturation frequencies, pump attenuation, and differential transmittance, which is a representation of the bleached wave. A specific DPAL scenario was simulated, 455K system temperature, alkali concentration of 6.1 1013, and a system pressure of 200 torr of He and 600 torr of Ethane. For a range of initial input intensities the linear approximation to the beam attenuation predicted consistently a differential transmittance value of 70%. It was concluded that the linear approximation is a good indicator of the distance a bleached wave penetrates an absorbing cell. This model was also benched marked against the quasi two level model. In the limit of high system pressure the simulated model converged to the same population inversion as that of the quasi two level regime. Finally, within the quasi two level regime a closed analytic equation was developed to describe under what conditions the system would lase.