Nonlinear and Anisotropic Effects in Magnetically Tuned Laser Amplifiers

• Main Author: Dienes, Andrew
• Format: Others
• Published: 1967
• Online Access: https://thesis.library.caltech.edu/10120/1/Dienes_A_1967.pdf; Dienes, Andrew (1967) Nonlinear and Anisotropic Effects in Magnetically Tuned Laser Amplifiers. Dissertation (Ph.D.), California Institute of Technology. doi:10.7907/AF03-T980. https://resolver.caltech.edu/CaltechTHESIS:03302017-091624259 <https://resolver.caltech.edu/CaltechTHESIS:03302017-091624259>

<p>Using semiclassical radiation theory and a density matrix formalism we analyze the nonlinear characteristics of a gas laser amplifier operating with two optical frequency signals of arbitrary polarization and having an axial magnetic field. Both perturbational solutions, valid for relatively weak intensities and solutions valid for arbitrarily strong fields are obtained for two nonlinear effects: the saturation interaction of the electromagnetic waves, and the generation of combination tones. An arbitrary amount of Doppler broadening is considered throughout.</p> <p>The detailed treatment of J = 1 to J = 0 model yields the frequency, magnetic field and polarization dependence of the nonlinear effects. The results are presented analytically and graphically and are discussed using physical arguments. It is found that only saturation but no combination tone generation occurs for two opposite circularly polarized input signals while both are, in general, present for two arbitrary linearly or elliptically polarized fields. For two opposite circular waves the interaction is found to comprise three parts, each with a different behavior: self saturation, common level mutual saturation and a coherent double quantum interaction. The total interaction (coupling) between the two fields is always weak. The limiting case of a single linearly polarized field is considered separately, the zero magnetic field "dip" and the nonlinear behavior of the Faraday rotation is discussed.</p> <p>For two linearly (or elliptically) polarized waves the three nonlinear processes listed above take place between opposite circular components. In addition a modulation of the population inversion densities occurs due to the presence of two different frequencies with the same circular polarization. This results in the generation of new frequencies and also contributes to the coupling between the input fields. The coupling depends on the magnetic field, and on the frequency separation and the polarization states of the signals. The limiting case of zero magnetic field is examined. It is found that the medium is made effectively anisotropic by the nonlinear interactions. The polarization vectors of two linearly polarized fields rotate apart unless the angle between them is zero or 90 degrees.</p> <p>The results are extended to the general J_a to J_b transition. In zero magnetic field the nonlinear effects are found to depend on ΔJ, while for nonzero magnetic field resonances in the interaction occur whenever the frequency difference between two opposite circularly polarized transitions that have common level equals the frequency separation of the input fields. Combination tone generation takes place for all but two opposite circularly polarized signals.</p>