Title

Investigation of induced third-order resonant phenomena in single amorphous zinc selenide and cascaded zinc selenide/semiconductor-doped glass

Date of Completion

January 1999

Keywords

Engineering, Electronics and Electrical|Physics, Optics

Degree

Ph.D.

Abstract

In this work two induced, third order nonlinear effects were demonstrated. Both phenomena were induced on weak probe beams by a pumping beam in the resonant regime of the nonlinear materials. Both demonstrations were phase independent and were accomplished with low power considering the short interaction lengths. ^ The first phenomena demonstrated was a reduction in a monochromatic probe signal due to a pump signal. The pump and probe were perpendicularly propagated and intersect within a three millimeter square of amorphous zinc selenide. The reduction effect written onto the probe follows a nonlinear profile which saturates with a five percent reduction of the probe signal, while the pump maintains a linear absorption profile. The saturation of the induced effect occurs at low intensity of less than 12 W cm−2. For a helium neon probe, at 632.8 nanometers, the pump induced change in the index of refraction, Δn, and the induced change in the absorption coefficient, Δα, were analyzed in the saturation region using Fresnel equations and found to have the values of Δn = 0.0049 and Δα = 0.0038 mm −1. While resonant saturation effects have been seen in semiconductor doped glass before those effects required a copropagating pump that was eight orders of magnitude more intense. ^ The second portion of this work was centered on amorphous zinc selenide cascaded with semiconductor doped glass. The glass is doped with quantum dots of cadmium sulfur selenide that is available from Schott Glass. The pump used was in the resonant regime and copropagated with a white light source as a probe and both were introduced and removed from the cascaded materials by multimode fibers. The cascaded materials acted as a single period grating which preferentially allowed certain wavelengths to pass. When the material was pumped the preferential pass was reversed. The difference between the probe in the pumped and unpumped state was an expanding sinusoidal with a relative change of ±20%. The preferential pass and the pump induced shift in the preferential regions is comparable to resonance Fabry Perot etalons with an induced change in the optical path length but is considerably more robust. ^

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