Ryan M. Roth

Arabic Morphological Tagging, Diacritization, and Lemmatization Using Lexeme Models and Feature Ranking

We investigate the tasks of general morphological tagging, diacritization, and lemmatization for Arabic. We show that for all tasks we consider, both modeling the lexeme explicitly, and retuning the weights of individual classifiers for the specific task, improve the performance.

Resonant-plasmon field enhancement from asymmetrically illuminated conical metallic-probe tips.

Optical-field enhancement and confinement for an asymmetrically illuminated nanoscopic Au tip suspended over a planar Au substrate is investigated both numerically and experimentally. The spatial field distribution of the tip-sample system was calculated using the full 3D finite-difference time-domain method. The calculation enables investigation of the effects of the substrate-tip placement, angle of incidence, and spectral response. The tip plasmon response leads to a significant (up to ~70 times) local field enhancement between the tip and substrate. The enhancement is found to be extremely sensitive to the tip-sample separation distance. Tip-enhanced Raman scattering experiments were performed and the numerical results provide a consistent description of the observed field localization and enhancement.

CATiB: The Columbia Arabic Treebank

The Columbia Arabic Treebank (CATiB) is a database of syntactic analyses of Arabic sentences. CATiB contrasts with previous approaches to Arabic treebanking in its emphasis on speed with some constraints on linguistic richness. Two basic ideas inspire the CATiB approach: no annotation of redundant information and using representations and terminology inspired by traditional Arabic syntax. We describe CATiBs representation and annotation procedure, and report on inter-annotator agreement and speed.

Compositional and structural changes in LiNbO3 following deep He+ ion implantation for film exfoliation

The physical mechanism of He-ion-based exfoliation in Z-cut LiNbO3 is investigated. Rutherford backscattering/channeling, nuclear-reaction analysis, and transmission electron microscopy are used to examine the compositional and structural changes caused by deep ion implantation followed by thermal annealing. Lattice disruption, He-bubble formation, and Li depletion are observed in the implantation region, as well as the onset of exfoliation. The implications of these observations for the crystal ion slicing method are discussed.

Electro-optically tunable second-harmonic-generation gratings in ion-exfoliated thin films of periodically poled lithium niobate

The authors demonstrate that thin, single-crystal films fabricated by ion exfoliation of a bulk periodically poled LiNbO3 (PPLN) crystal reduced the tuning voltages for electro-optically tunable harmonic generation in PPLN devices. The tuning voltage of ±150V resulted in 0.5nm total tuning of the second harmonic signal in the authors’ 10-μm-thick device, compared to an order of magnitude higher tuning voltage value needed in a comparable bulk device.

Polarization-tunable plasmon-enhanced extraordinary transmission through metallic films using asymmetric cruciform apertures

Plasmon-enhanced transmission of light incident on a periodic array of nanoscale, asymmetric cruciform patterns is demonstrated. The corresponding transmission spectra are shown to be polarization dependent and possess unique properties, such as the existence of isosbestic points for which the transmission is polarization insensitive. Transmission peaks corresponding to localized surface plasmon resonances and extended surface plasmons are also identified.

Terahertz wave generation and propagation in thin-film lithium niobate produced by crystal ion slicing

Terahertz phonon-polariton generation and real-space imaging with femtosecond optical pulses are demonstrated in a 10‐μm-thick film of single-crystalline lithium niobate that was generated through crystal ion slicing. The film dispersion properties were characterized throughout the polariton wavelength range of 5–100μm, revealing substantial slab waveguide behavior at the longer wavelengths.

Low-voltage planar-waveguide electrooptic prism scanner in Crystal-Ion-Sliced thin-film LiNbO3.

We report on the use of thin, i.e. 10 microm-thick, single-crystal LiNbO3, in low-voltage electrooptic prism scanners. These devices are fabricated by electric-field poling of a series of electrooptic prisms in a bulk crystal followed by high-energy ion implantation and subsequent etching of the poled samples. Such a single-crystal thin-film scanner, while having the same scanning functionality as with a bulk device, has an order-of-magnitude reduction in its required voltage; for example, a series of two prisms, of 2mm in total length, yields a deflection angle of 0.7 at 100V compared to more than 1.7kV for the same device in standard 200 microm-thick LiNbO3 wafers.

X-ray microbeam probing of elastic strains in patterned He+ implanted single-crystal LiNbO3

X-ray microprobing is used to investigate buried elastic strain resulting from deep He+ implantantion in LiNbO3. The implantation regions are defined lithographically and strain fields mapped with spatial- and energy-resolved x-ray microdiffraction to characterize the resulting structures. The structurally modified regions are found to retain their lateral lithographic definition, with the buried implantation being in strong compression.

Integrable wide-free-spectral-range Fabry–Perot optical filters using free-standing LiNbO 3 thin films

We demonstrate the use of free-standing thin films of a complex oxide for chip-scale optical filtering. The films are used as low-order etalons with very large free spectral ranges that exceed 6.78 THz (> 50 nm at 1550 nm) and use a small chip area (< 500 microm2) when they are integrated. The films are produced by crystal ion slicing; this process exfoliates a micrometers-thin layer of single-crystal optical material from a bulk parent by means of high-energy-ion implantation. The etalons, which are 10 microm thick with Ag deposited on both surfaces, are integrated into a silica-on-silicon waveguide block.