INVESTIGATION OF A CASCADE LASER SYSTEM -- THE EXCITATIONS AND INTERACTIONS OF NITROGEN IN THE ULTRAVIOLET AND THE NEAR INFRARED

In this investigation optical interactions between electronic-vibrational states of the diatomic N(,2) molecule are studied. As a system of interactions, nitrogen leads to a broader understanding of cascade systems in general. Laser oscillation in N(,2) occurs quite readily in electrical discharges on an ultraviolet and a near infrared system of emission bands, among others. While the mechanisms that produce population inversions for the uv oscillations have previously been established for the most part, the dominant mechanisms for the ir bands were not at all certain. This work sought specific information about N(,2) as a lasing material and clarified that the ir-laser transitions are excited partly through a cascade involving uv-laser transitions. A concise theory of cascade interactions and excitations was developed to predict both spontaneous and stimulated emission strengths. A more sophisticated theory which took the electron-energy distribution of the laser's excitation into account was used to predict spectra. An important outcome of this theoretical and experimental investigation is how well the spectral measurements bear out the theory. The typical 3-level rate-equation theory was extended for a pulsed laser application to a 4-level system including cascade. This research concluded that the Franck-Condon Principle can be a powerful quantitative tool (not simply qualitative) to use in analyzing interactions.