The Vertical-Cavity Surface-Emitting Laser (VCSEL) is a new type of microcavity semiconductor laser with new and unusual characteristics. It is designed to have very high reflectivity mirrors with cavity length on the order of the wavelength of light, making possible dynamical studies in the smallest of laser cavities. Only one single longitudinal mode is supported within the gain spectrum of the active semiconductor material, thus requiring the cavity length to be an integer multiple of the emission wavelength. This short cavity length and a wide output aperture, on the order of five microns, provide for a high Fresnel number. The combination of the high Fresnel number and of the richness of nonlinear effects in GaAs makes the VCSEL an ideal candidate for the study of spatio-temporal dynamics in nonlinear optics. In this dissertation we report on the longitudinal and transverse characteristics of VCSELs under injection-locking. Unique features appear experimentally in the longitudinal nonlinear dynamics of this system including beam coupling, four-wave mixing, new frequency generation, subharmonic bifurcation, and enhanced relaxation oscillations, opening a route to chaos. Coherent Energy Transfer (CET) takes place between a strong monochromatic injection frequency and all the frequencies contained in the VCSEL's laser emission just above threshold, leading to asymmetric gain. The high Fresnel number of the VCSEL makes it an interesting candidate for the study of transverse pattern behavior under injection-locking. We have forced high-order transverse modes and observed transverse instabilities including optical vortices. We have found three ways of generating vortices in VCSELs; these are the helicoidal phase mask, the Gaussian-beam-induced vortices, and the injection-locked TEM*₀₁ mode.
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