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In this work the design of Si / hybrid waveguides which contain a vertical infiltrated slot is studied. The case of slots infiltrated with a χ³ nonlinear material of relatively high refractive index (e.g. chalcogenide glasses) is specifically discussed. An optimized waveguide geometry with periodic refractive index modulation, a nonlinear figure of merit > 1 and minimum effective mode cross section is presented. Introducing a periodic refractive index variation along the waveguide allows the adjustment of the group velocity dispersion (GVD). Choosing the period accordingly, the phase matching condition for degenerate four wave mixing (GVD = 0) can be fulfilled at virtually any desired frequency and independently from the fixed optimized waveguide cross section.

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Lock-in infrared thermography is a well-established technique for measuring the thermal diffusivity of materials. A commonly-used method is to analyse the spread of a thermal wave along the surface of a thin sample or a filament, known as the slope method. In this work, an alternative technique is proposed, in which the phase delay of the thermal wave passing through sheets made of different metals is analysed using periodical laser heating. Different lock-in frequencies are used to obtain the frequency-dependent phase behaviour of thermal waves generated by the laser pulses. A subsequent curve fitting provides the coefficients required to determine the thermal diffusivity. To achieve a comparison with ambient conditions, the measurements are also performed in vacuum. A comparison with literature data substantiates that the proposed method is a robust approach for the determination of the thermal diffusivity in applications where the sample thickness exceeds the limits of the slope method