Experiments and Numerical Simulations in Nonlinear Beam Propagation and Kinematic Modelocking

Experiments and numerical simulations are performed in nonlinear beam propagation in ruby. Transverse self and cross-phase modulation effects are studied with two polarizations of an argon-ion laser beam and a weak HeNe laser probe. A HeNe laser probe beam exhibits a deflection of nearly 12 mrad when a 1.5 W, 514.5 nm laser beam is injected into the ruby rod at an angle to the probe. The copropagating geometry is also studied where the azimuthally symmetric transverse beam encoding leads to complex ring structures in both the HeNe and argon-ion laser beams. The extraordinary component of a cw argon-ion laser beam propagating through a ruby crystal exhibits a power dependent deflection. A divergence angle of nearly 6 mrad between the ordinary and extraordinary beam is measured when 500 mW of 514.5 nm radiation is injected into the ruby rod. A simple theory for the anisotropic nonlinear index of refraction and a numerical simulation of the coupled nonlinear wave equations in (2 + 1) dimensions give good agreement with the experimental results. Experiments are performed on a coupled cavity, moving mirror, ring dye laser. Existing models for the modelocking mechanism are analyzed in light of the results of various experiments performed in this study. We find that thresholds exist for the onset and instability of kinematic modelocking (KML) as a function of pump power. The pulse length dependence on mirror velocity and cavity detuning was determined, and asymmetries in the mirror velocity were found. With the inclusion of prisms in the external cavity, the modelocking is found to be more stable with pulses shorter than 3 psec being produced by the KML mechanism. A numerical investigation is performed on a unidirectional laser coupled to a linear phase-variant cavity. The Maxwell -Bloch equations are solved for a two-level gain medium with a causal filter and spontaneous noise injection. Atomic and cavity parameters, as well as the external mirror velocities, are varied to investigate the KML phenomena. Incipient pulse formations are seen in the cm/sec velocity regime, however, the dynamics do not give rise to full modelocking.