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, , , , and thin films were fabricated by pulsed laser deposition at high and low temperatures resulting in crystalline single-phase normal, inverse, as well as disordered spinel oxide thin films with smooth surface morphology. The dielectric function, determined by spectroscopic ellipsometry in a wide spectral range from 0.5 to 8.5 eV, is compared with the magneto-optical response of the dielectric tensor, investigated by magneto-optical Kerr effect spectroscopy in the spectral range from 1.7 to 5.5 eV with an applied magnetic field of 1.7 T. Crystal field, inter-valence, and inter-sublattice charge transfer transitions, and transitions from to metal cation 3d or 4s bands are identified in both the principal diagonal elements and the magneto-optically active off-diagonal elements of the dielectric tensor. Depending on the degree of cation disorder, resulting in local symmetry distortion, the magneto-optical response is found to be strongest for high crystal quality inverse spinels and for disordered normal spinel structure, contrary to the first principle studies of and . The results presented provide a basis for deeper understanding of light-matter interaction in this material system that is of vital importance for device-related phenomena and engineering. [ABSTRACT FROM AUTHOR]

Zinc oxide microwire lasers show whispering gallery mode lasing, exhibiting high Q-factors. The energetic positions of the lasing modes agree with those calculated from a simple plane wave model. The characteristic temperature of the microlasers was determined from temperature dependent measurements. Additionally, the authors demonstrate the successful growth of MgZnO/ZnO core-shell heterostructures by pulsed laser deposition. [ABSTRACT FROM AUTHOR]

Lasing on whispering gallery modes was excited by optical pumping in single zinc oxide microwires fabricated by a simple carbothermal evaporation process. The experimentally observed laser modes agree precisely with the predicted energetic positions obtained from a plane wave model. Systematic diameter dependent measurements have been carried out for diameters of the microwires between 3 and 12 μm. The investigated microlasers are found to have a lasing threshold of about 170 kW/cm2 at 10 K. [ABSTRACT FROM AUTHOR]

The authors demonstrate an optically pumped ZnO distributed feedback laser operating at 383 nm. For a large temperature range between 10 and 270 K, the device lased in a single longitudinal mode. Mode selection was accomplished via a third order diffraction grating, which was dry etched into a 120 nm thick Si3N4 layer deposited on the ZnO active region. They observed a spectral linewidth of 0.4 nm, a pump threshold intensity of 0.12 MW/cm2, and a peak output power of 14 mW. From wavelength versus temperature measurements, they deduced a temperature tuning coefficient of the ZnO refractive index of 9×10-5 K-1. [ABSTRACT FROM AUTHOR]

This article presents a topical literature survey on types of coherent states in bare and functionalized ZnO nano‐ and microwire microcavities, together with own new approaches of the authors. By optical excitation, coherent emission from electron–hole plasma and from exciton‐polariton Bose–Einstein condensates, both up to room temperature, have been observed by various research groups. The impact of the interplay between the excitation properties and geometry of the structures as well as of the charge carrier dynamics on the emission behavior of the structures has been discussed. For different cavity types spectrally tunable mono‐/dual‐mode laser operation as well as propagation of coherent polariton states have been demonstrated. Further functionalization of the bare structures in hybrid systems allows optimization and engineering of the cavity as well as the polariton mode structure and the design of sophisticated light–matter states. Nano‐ and microwire microcavities and waveguides have a great potential for applications in optical data transport and manipulation for future on‐chip communication and computation. For room temperature applications, the material ZnO is auspicious. Schmidt‐Grund et al. review state‐of‐the‐art miniaturized ZnO lasers based on high‐quality self‐organized grown bare and further functionalized nano‐ and microstructures and present a novel approach for further enhancing the lasing performance. [ABSTRACT FROM AUTHOR]

Abstract: ZnO films with different 3d transition metal doping (Ti, Co, Mn) were prepared by pulsed laser deposition. The occurrence of positive magnetoresistance (MR) was studied in dependence on temperature. Large positive MR was observed in Co- and Mn-doped ZnO films at 5 K. Zn0.98Mn0.02O films show a positive MR up to ∼ 31% at 5 K. The positive MR for Co- and Mn-doped ZnO films decreases drastically from 5 K to 50 K. Positive MR was also observed in Zn0.9998Ti0.0002O films at 290 K, while negative MR was observed at 5 K. Clear stripe-like magnetic domain pattern was observed by magnetic force microscopy for the Zn0.9998Ti0.0002O films, indicating the possible ferromagnetism at room temperature due to Ti3+-ions in a polarized spin state. [Copyright &y& Elsevier]

Voigt points represent propagation directions in anisotropic crystals along which optical modes degenerate, leading to a single circularly polarized eigenmode. They are a particular class of exceptional points. Here, we report the fabrication and characterization of a dielectric, anisotropic optical microcavity based on nonpolar ZnO that implements a non-Hermitian system and mimics the behavior of Voigt points in natural crystals. We prove the exceptional-point nature by monitoring the complex-square-root topology of the mode eigenenergies (real and imaginary parts) around the Voigt points. Polarization state analysis shows that these artificially engineered Voigt points behave as vortex cores for the linear polarization and sustain chiral modes. Our findings apply to any planar microcavity with broken cylindrical symmetry and, thus, pave the way for exploiting exceptional points in widespread optoelectronic devices such as vertical cavity surface emitting lasers and resonant cavity light emitting diodes. [ABSTRACT FROM AUTHOR]