Accurate determination of nonlinear optical parameters of semiconductors at infrared wavelengths

Nonlinear optics covers the vast field of irradiance dependent interactions between light and materials, including generation of light in a second order medium through processes such as optical parametric oscillation or self attenuation of light in a third order medium. It is important to determine the relevant material parameters which control the efficiency of the interactions. In extracting material parameters from experimental results, many assumptions of questionable validity are often made to simplify calculations. In this work, a numerical model was developed, with as few assumptions on laser beam parameters as possible, to describe the interactions of arbitrary, complex four dimensional electro-magnetic fields with a nonlinear medium.;Second harmonic generation (SHG) is a second order nonlinear optical phenomenon in which an incident light beam at one frequency generates light at twice the frequency. In this work, SHG in a newly grown material, CdSiP 2 was investigated and the first efficient harmonic generation in this crystal was accomplished at a mid-wave infrared wavelength. Excellent agreement between experimental results and theory was obtained, with no free parameters, using a numerical model which accurately modeled spatial and temporal beam profiles.;An area of third order nonlinear optics is self action, where nonlinear absorption and refraction in a medium are dependent on the irradiance of the incident light. Nonlinear absorption in semiconductors is a coupled process where intrinsic two photon absorption generates free carriers which in turn modify the linear absorption via free carrier absorption. In addition, the generated free carriers alter the phase of the beam through nonlinear refraction. Thermal effects also play a role since the nonlinear absorption leads to heat rise within the material which in turn generates a thermal lens. All of these coupled processes occur simultaneously in the nonlinear medium. Investigation of these effects in the semiconductor InP was conducted and for the first time, a self consistent set of intrinsic two photon absorption coefficients and free carrier nonlinear absorption cross-sections were found at two different infrared wavelengths. Values of the free carrier absorption coefficients of InP determined by nonlinear absorption measurements have not been previously reported.