Greater than 12 W of average output power has been generated from a diode-pumped Yb:YAG cladding-pumped planar waveguide laser. The laser radiation developed is linearly polarized and diffraction limited in the guiding dimension. A slope efficiency of 0.5 W͞W with a peak optical -optical conversion efficiency of 0.31 W͞W is achieved. In a related structure, greater than 8 W of Q-switched average output power has been generated from a Nd:YAG cladding-pumped planar waveguide laser by incorporation of a Cr 41 :YAG passive Q switch monolithically into the waveguide structure. Pulse widths of 3 ns and pulse-repetition frequencies as high as 80 kHz have been demonstrated. A slope efficiency of 0.28 W͞W with a peak optical -optical conversion efficiency of 0.21 W͞W is achieved.

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The surface structure development of loaded ferritic polycrystalline steel and a monocrystalline nickel sample was studied. In situ investigations were carried out using a tensile testing module designed for atomic force microscopes (AFM). Prior to investigation the unloaded steel and nickel samples were polished mechanically and electrolytically, respectively. The grain size of the polycrystalline steel was measured to be about 3 µm. At each level of deformation up to fracture (from ε = 0 up to ε ≈ 10% for steel and ε ≈ 45% for nickel) a fixed area of about 80 × 80 µm 2 was examined by AFM in contact mode. On loading the polycrystalline sample the surface roughness increases and visible mesoscopic structures of about 25 µm in diameter appear. The fractal dimension df of the surface topography was analyzed and it was found that df starts to increase at the yield strength and finally ends in a plateau. Investigation of the nickel monocrystal showed the formation of well-characterized slip bands and non-regular substructures beyond a short elastic region. The development of the fractal dimension is similar to that of the polycrystalline steel sample. The results obtained are discussed in the framework of mesomechanics.The non-destructive damage characterization of materials and the evaluation of lifetime are important tasks for materials science. Thus a lot of work has been done to investigate the dependence of microstructural change on the material damage.During recent years the description of plastic deformation and fracture has resulted in the framework of mesomechanics [1]. Being an intermediate stage between the mechanics of continuous media and dislocation theory this approach suggests a concept of hierarchical structural levels of solid plastic deformation.At the first stage gliding begins locally at places with high stress concentrators. Gliding is then accompanied by the rotation of the surrounding material (cf. [2]), which results in new stress concentrations at other places. At the next stage cooperative translational-rotational vortex structures (the movement of a local region of crystal must include the combination of shear and rotation because of self-organization of the structure; this is confirmed by numerical calculations) are formed [3,4]. This process can be replicated at different structure levels, and hence fractal structures can be created. Fractal refers to the behaviour that apparently disordered structures on various scales are self-similar [5]. Thus successive deformation of a solid is not only described by the formation of real structures at the atomic level (e.g. dislocations, stacking faults), but also by various mesoscale mechanisms of the system.The characteristic parameter to describe this process is the fractal dimension d f . The deviation of d f from the value 2 is a measure of the fissured appearance or geometric complexity of a structure.In principle, it should be possible to use the fractal dimension to predict the failure of materials. In contrast to the surface roughness, the...

We report on adhesive-free bonded (AFB ® ) polycrystalline CVD diamond surfaces to sapphire, YAG and optically coated YAG surfaces to form robust and stress free composite components. Considering the high thermal conductivity of CVD diamond with respect to YAG or sapphire, AFB ® diamond/sapphire and diamond /YAG composites can be ideal components for thermal management of high power solid-state laser systems.We ascribe the attractive bonding forces at the interface between diamond and sapphire and other single crystals such as YAG and spinel largely to Van der Waals forces. Contrary to chemical bonds, Van der Waals forces consist of non-localized dipole-dipole interactions that manifest their long range effects by allowing relative movement between two bonded surfaces of different coefficients of thermal expansion, thus avoiding local stress during thermal cycling.CVD diamond surfaces result in a much wider compatibility range for forming stress-free or low-stress composites compared to alumina compound single crystal counterparts. Feasibility of forming AFB ® stress-free interfaces between diamond and optically coated oxide surfaces marks an important step in widening the range of AFB ® for solid state laser and electronic applications.Hamaker constants have been determined for all three dissimilar composites with CVD diamond as one component.

In this paper the investigation of r.f.‐sputter‐deposited Ta, Ta‐N and Ta‐N‐O thin films is presented. Using atomic force microscopy in combination with sheet resistance measurements, Auger electron spectroscopy and x‐ray diffraction, the thin film properties and microstructure are examined. Two crystalline modifications of Ta (tetragonal β‐Ta and bcc α‐Ta) are reported. By incorporation of nitrogen and/or oxygen into the Ta films, nanocrystalline and quasi‐amorphous structures can be achieved. Finally, the usefulness of the films as diffusion barriers in Cu‐based metallization systems is described.© 1997 John Wiley & Sons, Ltd.