The complex refractive index components, n and k, have been studied for thin films of several common dielectric materials with a low to medium refractive index as functions of wavelength and stoichiometry for mid-infrared (MIR) wavelengths within the range 1.54-14.29 μm (700-6500 cm(-1)). The materials silicon oxide, silicon nitride, aluminum oxide, aluminum nitride, and titanium oxide are prepared using room temperature reactive sputter deposition and are characterized using MIR variable angle spectroscopic ellipsometry. The investigation shows how sensitive the refractive index functions are to the O2 and N2 flow rates, and for which growth conditions the materials deposit homogeneously. It also allows conclusions to be drawn on the degree of amorphousness and roughness. To facilitate comparison of the materials deposited in this work with others, the index of refraction was also determined and provided for the near-IR and visible ranges of the spectrum. The results presented here should serve as a useful information base for designing optical coatings for the MIR part of the electromagnetic spectrum. The results are parameterized to allow them to be easily used for coating design.

12 13We report the material properties of 26 granular analogue materials used in 14 ana-14 logue modelling laboratories. We determined physical characteristics such as bulk 15 density, grain size distribution, and grain shape, and performed ring shear tests to 16 determine friction angles and cohesion, and uniaxial compression tests to evaluate 17 the compaction behaviour. Mean grain size of the materials varied between c. 100 18 and 400 µm. Analysis of grain shape factors show that the four different classes of 19 granular materials (14 quartz sands, 5 dyed quartz sands, 4 heavy mineral sands 20 and 3 size fractions of glass beads) can be broadly divided into two groups consist-21 ing of 12 angular and 14 rounded materials. Grain shape has an influence on friction 22 angles, with most angular materials having higher internal friction angles (between 23 c. 35° and 40°) than rounded materials, whereas well-rounded glass beads have the 24 lowest internal friction angles (between c. 25° and 30°). We interpret this as an ef-25 2 fect of intergranular sliding versus rolling. Most angular materials have also higher 26 basal friction angles (tested for a specific foil) than more rounded materials, sug-27 gesting that angular grains scratch and wear the foil., Most materials have an inter-28 nal cohesion in the order of 20-100 Pa except for well-rounded glass beads, which 29show a trend towards a quasi-cohesionless (C <20 Pa) Coulomb-type material. The 30 uniaxial confined compression tests reveal that rounded grains generally show less 31 compaction than angular grains. We interpret this to be related to the initial packing 32 density after sifting, which is higher for rounded grains than for angular grains. Ring-33 shear test data show that angular grains undergo a longer strain-hardening phase 34 than more rounded materials. This might explain why analogue models consisting of 35 angular grains accommodate deformation in a more distributed manner prior to 36 strain localisation than models consisting of rounded grains.

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A monolithic coupling scheme for mid-infrared quantum cascade laser arrays is investigated with respect to brightness enhancement. The tree-shaped resonator enables parallel coupling of six laser elements into a single element by means of several Y-junctions. Phase-locking is observed on the basis of far field analysis, and leads to in-phase emission on both sides of the device. The experimental results match calculated far field profiles and demonstrate a high level of modal control when driven far above threshold. Whereas optical power measurements confirm negligible coupling losses, the slope efficiency is below the theoretically expected value, which is attributed to modal competition. Additional evaluation of near fields and spectral characteristics provides background on the modal dynamics of the sophisticated cavity and reveals limitations to coherent beam combining. The findings pave the way to improved coupling efficiency and brightness scaling of a single facet emitting compact quantum cascade laser array.