Laser-Pumped Ruby: a Study of Bistability, Instability and Nonlinear Beam Propagation.

In the first part of this thesis we discuss an experimental and theoretical study of ruby as a passive medium, in particular absorptive nonlinear beam propagation. An intense laser beam propagating through a two level absorbing medium can be nonuniformly absorbed causing nonuniform phase and intensity changes on the beam. The outer region of the beam can be absorbed while the central region propagates virtually unhindered because of medium saturation. The effect is like having the beam pass through an intensity dependent aperture which encodes the beam by Fresnel diffraction. The second part of the thesis focuses on several new bistability effects which we observed in the cw ruby laser. Experimental studies of the ruby laser have revealed that it can exhibit bistability in both its polarization state and in its output direction. The c.w. ruby laser under the right conditions can spontaneously switch polarization state as well as output direction just by changing the pump power. Finally, motivated by the still unsolved problem of irregular undamped spiking of the pulsed ruby laser, we present an experimental study of the c.w. laser and characterize the dynamical states of regular and irregular self-pulsing that the laser can exhibit. This system operates under continuous excitation and allows for the observation of dynamical instabilities which are intrinsic to the laser mechanism.