Studies of medium infrared materials for nonlinear optical devices

Abstract

The thesis describes the characterisation of ternary II-IV-V2 and I-III-VI2 semiconductors with a view to their application in medium infrared nonlinear optical devices. An extensive state-of-the-art of the properties of ternaries is presented. Detailed studies on linear optical and some other properties have been made of silver thiogallate (AgGaS₂). Phasematched second harmonics were generated in AgGaS₂ near a noncritical matching region. Transmission ranges of thirteen ternary compounds have been studied experimentally and basic physical phenomena identified. Two theoretical models have been developed; a semi-empirical force-constant model for predicting the infrared cut-offs, and a modified Sellmeier formula for the representation of refractive index dispersion.

Methods for interpolating refractive indices have been studied in detail and the Sellmeier parameters for ternaries and some other medium infrared nonlinear materials are presented. Phase-matching conditions for second harmonic generation, parametric oscillation, up-conversion and down-conversion have been analysed for the following compounds; AgGaS Z' AgGaSe Z' ZnGeP₂ ZnSiAs₂ CdGeAs₂ Ag₃AsS₃, Ag₃SbS₃, a-HgS, Te and CdSe. Particular emphasis is placed on techniques involved in the generation of tunable infrared radiation.

Finally described is an entirely new method of generating infrared radiation tunable over a wide wavelength. range by the down-conversion of the outputs of a parametric oscillator with limited tuning.

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