This PDF file contains the front matter associated with SPIE Proceedings Volume 10727, including the Title Page, Copyright information, Table of Contents, Author and Conference Committee lists.

Despite a rapidly-growing demand for efficient man-made DUV light sources, widespread adoption of AlGaN-based DUV LEDs is currently obstructed by extremely poor extraction of DUV photons due to the intrinsic material properties of AlGaN including low hole concentration and poor light extraction efficiency (LEE). Conventional LEE-enhancing techniques used for GaInN-based visible LEDs turned out to be ineffective for DUV LEDs due to a strong absorption of DUV light by p-GaN contact layer, and predominant TM polarized anisotropic emission from Al-rich AlGaN multi-quantum well (MQW) active region grown on c-plane sapphire substrate. Therefore, a new LEE-enhancing approach addressing the unique intrinsic property of AlGaN DUV LEDs is strongly desired. In this study, we present DUV LEDs having arrays of TC shaped active mesas coated with MgF2/Al reflectors on the inclined sidewalls to extract strong TM-polarized in-plane emission trough the sapphire substrate. Ray tracing simulations reveal that the TC DUV LEDs show an isotropic emission pattern and much enhanced light-output power in comparison with stripe-type DUV LEDs with the same MgF2/Al reflectors. Consistent with the ray tracing simulation results, the TC DUV LEDs show an isotropic emission pattern with 37.1% higher light-output power as well as lower operating voltage than the stripe-type DUV LEDs. Based on our results, we suggest strategies to design an optimized DUV LEDs for further enhancing the optical and electrical performances simultaneously. In addition, we propose a next generation DUV LED with an array of Al nanoparticles capable of enhancing IQE and LEE simultaneously by surface plasmon resonance coupling.

Among alternative nanomaterials for energy related photonic applications, one-dimensional semiconductor nanowires are of a great interest due to their physical properties coming from electronic or quantum confinement. In particular, ZnO nanowires (or nanorods) has been widely investigated since ZnO has many unique properties such as wide direct band gap, large exciton binding energy and relatively high refractive index. Large optical gain also makes ZnO a well suited material for energy transfer in hybrid systems and especially optical energy transfer. There are however two issues remaining to be addressed, one is related to the control in size and dispersion in nanowires array and the other is related to the modeling of nanowires arrays. In this study, we report on a theoretical study on ZnO nanowires, in order to reach a better understanding of the mechanisms that govern the light propagation in nanowires arrays. A phenomenological model has been developed and discussed. The model is able to describe the experimentally measured light transmission nanowires arrays. A slab of nanospheres and rough layers with thickness waviness were combined to simplify the nanowires structure description. This phenomenological description was proved to be feasible by fitting the experimental data. As a conclusion, light transmitted by randomly distributed nanowires can be explained by the combination of Mie theory and a rough Fresnel reflection at the interfaces.

AlGaN-based ultraviolet (UV) light sources have recently attracted much research interest due to their potential candidate to replace excimer and mercury lamps. However, their output power is limited by the inefficient p-type doping at high Al composition AlGaN. In this talk, we will report on the electron-beam-pumped UV light sources, where multiple ultrathinGaN wells are used to enhance the internal quantum efficiency and to reach deep UV range such as 230 nm. And UV light source with wavelength varing from 285-232 nm with corresponded output power of 23-160 mW have been achieved under pulse mode.

Ultraviolet hyperspectral interferometric (UHI) microscopy is a novel molecular imaging technique that retrieves wideband, high-resolution spectral information of the wavelength-dependent real part of the refractive index (i.e., dispersion), and the total attenuation coefficient of biological samples in the deep-ultraviolet (UV) spectral region. This method enables highly sensitive, label-free molecular imaging with sensitivity to various dispersion-causing and absorptive biomolecules that play an important role in diseases, including cancer. UHI also provides insight into structure of biological samples by yielding quantitative phase maps with subcellular spatial resolution and nanometer-scaled sensitivity. In this work, we give a detailed description of the UHI system, signal processing methods, and demonstrate its ability to quantify the dispersive and absorptive properties of biological samples in the deep-UV spectral region (240-450 nm). We will show dispersion, absorption, and quantitative phase data from red blood cells, as well as nucleated cells (e.g., granulocytes). We will also assess the deep-UV dispersion and absorptive properties of important biomolecules (e.g., DNA, RNA, NADH, FAD, collagen, cytochrome C, and hemoglobin). Finally, we will discuss potential biomedical applications, including identification of various blood abnormalities and imaging of histology slides for cancer detection and staging.

Methylation in DNA is a controlling factor in gene expression, embryonic development, and has been found to be important in infections and cancer. From a basic biology point of view, great heterogeneity has been found in methylation levels within tissues, so questions arises as to how and why. We show that methylated-DNA (m-DNA) can be distinguished from non-methylated (n-DNA) with nano-bowtie- and resonance- enhanced Raman spectra. By tuning the bowtie antenna to the resonance wavelength, both gains can be realized. Two additional Raman peaks in the 1200 – 1700 cm-1 band appear with methylation: one at 1239 cm^-1 and the other at 1639 cm_-1; a weak peak near 1000 cm-1 also appears with methylation. We also find that the two spectral features, although the latter with slight modification, can be used to distinguish the methylation state even when the DNA is denatured, as we show when we induce crystallization of the salts in the solution with increased excitation power, or allow it to happen naturally via solvent evaporation, and the DNA is trapped within the salt crystals. A comparison between liquid/solution to dried/denatured state m-DNA shows a general broadening of the larger lines and a transfer of spectral weight from the ~1470 cm^-1 vibration to two higher energy lines. The applicability of the resonance-Raman in these spectra is shown by demonstrating that the Raman spectral characteristics hardly change as the Raman resonance in excitation wavelength is approached. Finally, we comment on real signal gain in this double-resonance system.

There is growing research interest in UV plasmonics, in part because the UV regime has seen comparatively little activity compared to the visible, NIR/IR, and THz regimes, but also because of application areas such as UV sources and detectors, label-free fluorescence detection of biomolecules, and photocatalysis. There is a rich spectrum of materials that exhibit plasmonic response in the UV. Although no single material can be considered the “best” for all applications, Al is the most often utilized. Our research has focused on Al, Mg, Ga, and their alloys. We have developed deposition methods and top-down and bottom-up patterning methods, and utilized materials analysis methods to gain understanding of the UV plasmonic response of these materials. We have also enabled materials such as Mg and Ga to be used in applications such as enhanced fluorescence. Studies of native fluorescence modification from Al and Mg plasmonic structures show some key differences between the two materials, which I will explain. I will also discuss some plasmonic structures that exhibit very large UV enhancements, some of which can be readily fabricated by nanosphere lithography methods.

Far-ultraviolet (FUV) spectroscopy gives rich information about changes in the electronic states of molecules from interactions in condensed phase. We are investigated electronic states of molecules in the condensed ionic environment such as gel electrolytes, ionic liquids, and deep eutectic solvents. To measure the FUV spectra for liquid and solid nondestructively and feasibly, attenuate total reflectance (ATR) spectroscopy were developed to measure spectra of liquid, gel and solid samples in the 140-300 nm region. In this paper, we discuss about changes by interaction due to ionic environment in the electronic state of poly (ethylene glycol) (PEG) in gel electrolytes with Li salts, and deep eutectic solvents composed of acetamide and Li salts.

The detection of high energy radiation relies frequently on its conversion to visible or near-ultraviolet light by means of scintillator crystals. As the generated visible light then needs to be detected outside the crystal, it is of paramount importance to model the complete system involving the scintillator, the conversion process and the final detection outside the crystal. In this work we present a general modeling scheme of such detection process. Taking into account the bulk scintillator crystal shape and the precise geometry of the scintillator output interface (at micron or nanometric scale), we evaluate the performance of the system in terms of the number of photons and their spatial distribution on the detector. This numerical tool can be used, for example, to assess the performance of image reconstruction techniques used for Positron Emission Tomography (PET) scanners. The influence of nanostructures placed on top of the output interface on the overall response is analyzed and compared to that of a plane exit surface. Our results indicate that the electromagnetic response of the scintillator output interface plays a crucial role in the final detection.

The status and future prospect of ultraviolet (UV) detector are summarized briefly according to main applications. In particular, the wide bandgap semiconductor-based UV sensor product and technology are focused here. SiC and GaNbased product are widely used for various applications and new technologies are developed from material to system integration. The main targets for the UV sensor development are high sensitivity, high speed, small size and multi functions. Especially, the avalanche photodiode detector (APD) will be a key device for UV flame detection, UV imaging, and UV communications.

A single-scan dual-energy low-dose cone-beamCT (CBCT) imaging technique that exploits a filter-strip array is summarized in this paper. The filter-strip array installed between the x-ray source and the scanned object is reciprocated during a scan. The x-ray beams through the slits would generate relatively low-energy x-ray projection data, while the filtered beams would make high-energy projection data. An iterative image reconstruction algorithm that uses an adaptive-steepest-descent method to minimize image total-variation under the constraint of data fidelity was applied to reconstructing the image from the low-energy projection data. Since the high-energy projection data suffer from a substantially high noise level due to the beam filtration, the algorithm exploits the joint sparsity between the low- and high-energy CT images for image reconstruction of the high-energy CT image. The feasibility of the proposed technique has been earlier demonstrated by the use of various phantoms in the experimental CBCT setup. Based on the proposed dual-energy imaging, a material differentiation was also performed and its potential utility has been shown. In this work, we summarize the technique emphasizing task-specific optimization nature of the imaging in medical applications. A choice of beam-filtering material and its thickness, filter-strip array design, scanning configurations, and image reconstruction algorithm have been systematically investigated therefore.

Flat UV lamps comprising large arrays of microcavity plasmas, and capable of efficiently generating in the wavelength from VUV to UV-B radiation, have been developed by the team of University of Illinois and Eden Park Illumination. UV light is desirable for a number of chemical processes and disinfection methods available commercially but conventional UV light sources suffer from several drawbacks, including undesirable form factors and operational concerns regarding the use of mercury. Microplasmas are non-equilibrium, low-temperature plasma sources which have high power loading (several hundred kW/cm3), thereby enabling them to efficiently form UV-generating excimer molecules. This work has focused on leveraging microplasma array technology to realize low-temperature UV lamps that are flat and designed to have a scalable, slim form factor (total thickness less than ~5 mm). Each microcavity (less than a sub-millimeters in its cross-sectional dimensions) was fabricated through a series of microfabrication techniques, and the spatial variation of the electric field strength in each microcavity was tailored through the cavity cross-section and electrode geometry to efficiently generate deep UV radiation. UV light tiles capable of producing fluences up to 200 mW/cm2 at 172 nm which generates more than 25 watts of average power from a lamp of only 16 square inches in active surface area. Details concerning lamp performance of UV lamps having emitting wavelengths specifically in 146, 172, 222, and 308 nm will be discussed. The potential applications of the microplasma UV lighting tiles such as photochemistry, semiconductor processes, environmental and biomedical applications will be discussed.

Photodynamic inactivation is a method widely used to eliminate pathogen micro-organisms. This involves the application of different wavelengths and sources. The ai m of this work is to evaluate the inactivation effect of red light on Escherichia coli applying continuous and partial exposures, and compare with the effect produced by a less used radiation: UVA. We measured survival curves by spectrophotometry and obtained cell cultures. Our results show that red light applied together with methylene blue in continuous and interrupted exposures has not inactivation effect on E. coli. However, UVA radiation applied without photosintetizer exhibits a delay in the first phase of replication process with similar consequences on exponential and stationary phases. It is interesting to explore in the future the use of different compounds which could enhance the effect of UVA radiation.

AlGaN-based back-illuminated solar blind ultraviolet asymmetric metal-semiconductor-metal (MSM) photodetectors with high quantum efficiency have been fabricated on a sapphire substrate. To improve the performance of the Photodiodes (PDs), AlGaN absorber layer was grown on high quality AlN template on the sapphire substrate by hightemperature metal organic vapor phase epitaxy. To improve AlN template quality, high-temperature above 1300°C and low V/III ratios was applied. By inserting middle-temperature intermediate AlN layers, high-quality 2.5μm crack free 2- inch AlN template has been achieved. The XRD rocking curve full width at half maximum (FWHM) of AlN (002) is 169 arcsec, wihile the FWHM of (102) peak is 332arcsec. A 150nm AlGaN absorber layer of Al compositon 48% was further grown on the AlN template. The PL spectrum peaks at 274nm with a full width at harf maximum of 9.2nm, corresponding to the band edge emission of Al_0.48Ga_0.52N. The photoconductive mode was demonstrated with a Al_0.48Ga_0.52N PDs having different contacts. Unlike the conventional MSM photodetectors having a symmetric electrode, Ti/Al/Ni/Au and Ni/Au contact layers were deposited. The photoresponse cruve of PDs shows a sharp cut-off at 280 nm and peaks at 272nm. Owing to the high quality AlN template with the back-illuminated of the device, a solar-blind Al_0.48Ga_0.52N Schottky photodetectors with 28% external quantum efficiency at zero bias was achieved.