Rotating lattice single crystal architecture on the surface of glass.

Defying the requirements of translational periodicity in 3D, rotation of the lattice orientation within an otherwise single crystal provides a new form of solid. Such rotating lattice single (RLS) crystals are found, but only as spherulitic grains too small for systematic characterization or practical application. Here we report a novel approach to fabricate RLS crystal lines and 2D layers of unlimited dimensions via a recently discovered solid-to-solid conversion process using a laser to heat a glass to its crystallization temperature but keeping it below the melting temperature. The proof-of-concept including key characteristics of RLS crystals is demonstrated using the example of Sb2S3 crystals within the Sb-S-I model glass system for which the rotation rate depends on the direction of laser scanning relative to the orientation of initially formed seed. Lattice rotation in this new mode of crystal growth occurs upon crystallization through a well-organized dislocation/disclination structure introduced at the glass/crystal interface. Implications of RLS growth on biomineralization and spherulitic crystal growth are noted.

Utilization of native oxygen in Eu(RE)-doped GaN for enabling device compatibility in optoelectronic applications.

The detrimental influence of oxygen on the performance and reliability of V/III nitride based devices is well known. However, the influence of oxygen on the nature of the incorporation of other co-dopants, such as rare earth ions, has been largely overlooked in GaN. Here, we report the first comprehensive study of the critical role that oxygen has on Eu in GaN, as well as atomic scale observation of diffusion and local concentration of both atoms in the crystal lattice. We find that oxygen plays an integral role in the location, stability, and local defect structure around the Eu ions that were doped into the GaN host. Although the availability of oxygen is essential for these properties, it renders the material incompatible with GaN-based devices. However, the utilization of the normally occurring oxygen in GaN is promoted through structural manipulation, reducing its concentration by 2 orders of magnitude, while maintaining both the material quality and the favorable optical properties of the Eu ions. These findings open the way for full integration of RE dopants for optoelectronic functionalities in the existing GaN platform.

Al nanogrid electrode for ultraviolet detectors.

Optical properties of Al nanogrids of different pitches and gaps were investigated both theoretically and experimentally. Three-dimensional finite-difference time-domain simulation predicted that surface plasmons at the air/Al interface would enhance ultraviolet transmission through the subwavelength gaps of the nanogrid, making it an effective electrode on GaN-based photodetectors to compensate for the lack of transparent electrode and high p-type doping. The predicted transmission enhancement was verified by confocal scanning optical microscopy performed at 365 nm. The quality of the nanogrids fabricated by electron-beam lithography was verified by near-field scanning optical microscopy and scanning electron microscopy. Based on the results, the pitch and gap of the nanogrids can be optimized for the best trade-off between electrical conductivity and optical transmission at different wavelengths. Based on different cutoff wavelengths, the nanogrids can also double as a filter to render photodetectors solar-blind.

Cascaded optical parametric oscillations generating tunable terahertz waves in periodically poled lithium niobate crystals.

We present a continuous-wave (cw) singly-resonant optical parametric oscillator (SROPO) based on MgO-doped periodically poled lithium niobate (PPLN) delivering single-frequency idler output from 2.33 to 5.32 microm. In this system, we observe additional spectral components that have been attributed to stimulated Raman lines in other studies. However, we are able to assign them unambiguously to cascaded optical parametric processes. The tunable forward and backward idler waves generated by these additional phase-matched oscillations have frequencies that are tunable around 3.5 and 1.5 THz, respectively.

Three-dimensional grain boundary spectroscopy in transparent high power ceramic laser materials.

Using confocal Raman and fluorescence spectroscopic imaging in 3-dimensions, we show direct evidence of inhomogeneous Nd(3+) distribution across grain boundaries (GBs) in Nd(3+):YAG laser ceramics. It is clearly shown that Nd(3+) segregation takes place at GBs leading to self-fluorescence quenching which affects a volume fraction as high as 20%. In addition, we show a clear trend of increasing spatial inhomogeneities in Nd(3+) concentration when the doping levels exceeds 3 at%, which is not detected by standard spectrometry techniques. These results could point the way to further improvements in what is already an impressive class of ceramic laser materials.