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1

Ultraviolet electroluminescence from horizontal ZnO microrods/GaN heterojunction light-emitting diode array  

NASA Astrophysics Data System (ADS)

ZnO microrods were assembled on p-GaN substrate to form a heterostructural light-emitting diode (LED) array. Ultraviolet (UV) emission was obtained under a low forward bias of 3.5 V. The investigation on the electroluminescence, photoluminescence demonstrated three distinct electron-hole recombination processes. The relative intensity of these three emission bands changed with increase of the forward bias, and resulted in blue shift and spectral narrowing of electroluminescence. The present work provides a facile technique for micro-/nano-devices fabrication besides obtaining UV LED arrays.

Zhu, G. Y.; Xu, C. X.; Lin, Y.; Shi, Z. L.; Li, J. T.; Ding, T.; Tian, Z. S.; Chen, G. F.

2012-07-01

2

Determination of theanine in commercial tea by liquid chromatography with fluorescence and diode array ultraviolet detection.  

PubMed

Two liquid chromatographic methods that involve precolumn derivatization with o-phthaladehyde (OPA) and phenylisothiocyanate (PITC) with fluorescence and diode array UV detection for the determination of theanine have been developed. The chromatographic separations were achieved by reverse-phase high-performance liquid chromatography using octadecyl columns and gradient elution. The methods were applied to evaluate the theanine content of commercial tea leaves. The coefficient of variation of the peak area repeatability for within day (n = 8) and between day (n = 8 over 10 days) was lower than 3% for both of the methods. The estimated limit of detection (LOD) and limit of quantitation (LOQ) for the OPA method was 0.12 and 0.35 microg theanine, respectively. The PITC method was 500-fold more sensitive with LOD and LOQ values of 0.25 and 0.75 ng, respectively. The theanine content of the commercial tea samples varied from 2-5 mg/g leaf. The overall % recoveries for these methods ranged from 93-99.3. The sensitivity and simplicity of the method render them suitable for use in quality control laboratories. PMID:16968057

Thippeswamy, R; Gouda, K G Mallikarjun; Rao, Devavratha H; Martin, Asha; Gowda, Lalitha R

2006-09-20

3

Diode Laser Arrays  

NASA Astrophysics Data System (ADS)

Contributors; 1. Monolithic phase-locked semiconductor laser arrays D. Botez; 2. High power coherent, semiconductor laser master oscillator power amplifiers and amplifier arrays D. F. Welch and D. G. Mehuys; 3. Microoptical components applied to incoherent and coherent laser arrays J. R. Leger; 4. Modeling of diode laser arrays G. R. Hadley; 5. Dynamics of coherent semiconductor laser arrays H. G. Winfuland and R. K. Defreez; 6. High average power semiconductor laser arrays and laser array packaging with an emphasis for pumping solid state lasers R. Solarz; 7. High power diode laser arrays and their reliability D. R. Scifres and H. H. Kung; 8. Strained layer quantum well heterostructure laser arrays J. J. Coleman; 9. Vertical cavity surface emitting laser arrays C. J. Chang-Hasnain; 10. Individually addressed arrays of diode lasers D. Carlin.

Botez, Dan; Scifres, Don R.

2005-11-01

4

Simultaneous determination of six triazolic pesticide residues in apple and pear pulps by liquid chromatography with ultraviolet diode array detection.  

PubMed

A method is described for the simultaneous determination of diclobutrazol, flusilazole, flutriafol, hexaconazole, paclobutrazol, and tetraconazole in apple and pear pulps used in baby food at a limit of 0.01 mg/kg. Apple and pear pulp samples are subjected to selective solid-phase microdispersion (SPMD) with SPE-ED Matrix-38 and acetone-cyclohexane, and the extracts are cleaned up on a Florisil cartridge with hexane-cyclohexane-acetone. The extracts are then analyzed by liquid chromatography with ultraviolet detection, using an octadecylsilane column with a gradient-programmed acetonitrile-water mobile phase. Recoveries were determined by spiking apple and pear pulps with the 6 pesticides under investigation at 0.1, 0.05, 0.03, and 0.01 mg/kg. Six determinations were performed at each level for each pesticide. Recoveries were > or = 70% at the 0.01 mg/kg level. PMID:11601474

Bicchi, C; Cordero, C; Rubiolo, P; Occelli, A

2001-01-01

5

Determination of benzoylurea insecticide residues in tomatoes by high-performance liquid chromatography with ultraviolet-diode array and atmospheric pressure chemical ionization-mass spectrometry detection.  

PubMed

A simple and sensitive method using high-performance liquid chromatography/ mass spectrometry (LC/MS) was developed and validated for simultaneous determination of 5 benzoylurea insecticides-diflubenzuron, triflumuron, teflubenzuron, lufenuron, and flufenoxuron-in tomatoes. Residues were successfully separated on a C18 column by methanol-water isocratic elution. Detection was carried out by an ultraviolet diode array detector (UV-DAD) coupled with a quadrupole mass spectrometer, using atmospheric pressure chemical ionization (APCI) in negative-ion mode. The main ions were the deprotonated molecules [M-H]- for triflumuron, and the anions formed by elimination of hydrofluoric acid [M-H-HF]- for diflubenzuron and flufenoxuron, and [M-2H-HF] for lufenuron and teflubenzuron. The calibration plots were linear for both detectors over the range 0.05 to 10 microg/mL, and the method presented good quality parameters. The limits of detection for standard solutions were 0.008-0.01 mg/L (equivalent to 0.08-0.1 ng injected) for both detectors, and the limits of quantification (LOQs) were approximately 10 times lower than national maximum residue levels (MRLs). Depending on the compound and the detector, the LOQ values ranged from 0.2 to 0.4 ng injected. The optimum LC-UV-DAD/APCI-MS conditions were applied to the analysis of benzoylureas in tomatoes. The obtained recoveries from fortified tomato samples (50 g), extracted with ethyl acetate and purified by solid-phase extraction on silica sorbent, were 88-100 and 92.9-105% for the UV-DAD and MS detectors, respectively, with precision values (relative standard deviations) of 2.9-11 and 3.7-14%, respectively. The method was applied to 12 tomato samples from local markets, and diflubenzuron and lufenuron were detected in only one sample at concentrations lower than the MRLs. The results indicate that the developed LC/MS method is accurate, precise, and sensitive for quantitative and qualitative analysis at low levels of benzoylureas required by legislation. PMID:17955985

Markoglou, Anastasios N; Bempelou, Eleftheria D; Liapis, Konstantinos S; Ziogas, Basil N

2007-01-01

6

Nitride laser diode arrays  

NASA Astrophysics Data System (ADS)

One of the most desired features of the semiconductor blue/near UV laser diodes (LDs) is the possibility to obtain high output powers from the devices. This can be realized by means of multi emitter structures. We demonstrate the construction of violet blue multi-quantum-well (MQW) InGaN/GaN laser mini - bars, yet quite novel system in nitride-based devices. It consists of three laser stripes (3 ?m wide), closely spaced with 40 ?m pitch. The structures were fabricated on high pressure grown, low dislocation density substrates. Under cw operation the measured spectra demonstrate sharp, almost single line emission (FWHM around 1.43 Å at ? = 406 nm). Measurements of the optical far field pattern revealed that when operated below threshold the device was emitting light from all three stripes, whereas during lasing we observed the optical mode only in the area of the middle laser stripe. The behavior of optical mode suggests the formation of the so called supermode (coherent emission from all three devices) which was observed also in case of structures fabricated with wider ridges (of 7 ?m with 20 ?m pitch).

Holc, K.; Leszczynski, M.; Suski, T.; Czernecki, R.; Braun, H.; Schwartz, U.; Perlin, P.

2009-02-01

7

Performance improvements in diode laser arrays  

SciTech Connect

The average power performance capability of semiconductor laser diode arrays has improved dramatically over the past several years. Additionally, optical conditioning technologies have been developed that increase the effective radiance of stacked two-dimensional arrays by nearly two orders of magnitude. These performance improvements have been accompanied by cost reductions that now make feasible the replacement of flashlamp pump sources by laser diode arrays in a large variety of military and commercial solid state laser systems.

Beach, R.J.; Emanuel, M.A.; Freitas, B.L.; Benett, W.J.; Skidmore, J.A.; Carlson, N.W.; Solarz, R.W.

1994-06-01

8

The reliability of the laser diode arrays  

NASA Astrophysics Data System (ADS)

NASA is conducting a series of component-level tests, to better understand the reliability and the effects of a spacebased environment on the operation of diode-pumped, solid-state lasers by simulating the unique and harsh environment of launch, vacuum and radiation exposure of a typical mission. We report on our continuing work on high-power, laser-diode arrays (LDA) which are used as an energy source for several proposed and currently flying diode-pumped solid-state lasers missions (ICESAT, MESSENGER and LRO.) The laser-diode arrays are a critical component which can determine the reliability of the whole laser system. NASA needs reliability and performance data for these components to minimize the risks for space-based laser programs. We are concentrating on laser diode arrays emitting at 808 nm and operating quasi-cw with peak powers of ~100 watts per bar at 100 amps. The laser diode arrays are operated with a duty cycle from 0.6% to 2% and current pulses from 50 to 100 amps peak. We studied the effects of power cycling and temperature cycling on the performance of the diode arrays. We also conducted vacuum test as well as vibration and radiation tests. The laser diode arrays have accumulated more then 5.0 billion pulses during some of these tests and continue to operate within specifications.

Vasilyev, Aleksey; Troupaki, Elisavet; Allan, Graham R.; Kashem, Nasir B.; Stephen, Mark A.

2006-09-01

9

Millimeter wave monolithic schottky diode imaging arrays  

Microsoft Academic Search

Planar Schottky diodes are integrated with bow-tie antennas to form a one-dimensional array. The energy is focused onto the antennas through a silicon lens placed on the back of the gallium-arsenide substrate. A polystyrene cap on the silicon lens reduces the reflection loss. A self-aligning process with proton isolation has been developed to make the planar Schottky diodes with a

Chung-en Zah; Dayalan Kasilingam; John Steven Smith; David Rutledge; Tai-Chi Wang; Steven E. Schwarz

1985-01-01

10

International ultraviolet explorer solar array power degradation  

NASA Technical Reports Server (NTRS)

The characteristic electrical performance of each International Ultraviolet Explorer (IUE) solar array panel is evaluated as a function of several prevailing variables (namely, solar illumination, array temperature and solar cell radiation damage). Based on degradation in the current-voltage characteristics of the array due to solar cell damage accumulated over time by space charged particle radiations, the available IUE solar array power is determined for life goals up to 10 years. Best and worst case calculations are normalized to actual IUE flight data (available solar array power versus observatory position) to accurately predict the future IUE solar array output. It is shown that the IUE solar array can continue to produce more power than is required at most observatory positions for at least 5 more years.

Day, J. H., Jr.

1983-01-01

11

Monolithic Millimeter-Wave Diode Grid Frequency Multiplier Arrays.  

National Technical Information Service (NTIS)

Monolithic diode frequency multiplier arrays, including barrier-N-N(+) (BNN) doubler, multi-quantum-barrier-varactor (MQBV) tripler, Schottky-quantum-barrier-varactor (SQBV) tripler, and resonant-tunneling-diode (RTD) tripler arrays, have been successfull...

H. L. Liu X. Qin L. B. Sjogren W. Wu E. Chung

1992-01-01

12

SOI diode uncooled infrared focal plane arrays  

NASA Astrophysics Data System (ADS)

An uncooled infrared focal plane array (IR FPA) is a MEMS device that integrates an array of tiny thermal infrared detector pixels. An SOI diode uncooled IR FPA is a type that uses freestanding single-crystal diodes as temperature sensors and has various advantages over the other MEMS-based uncooled IR FPAs. Since the first demonstration of an SOI diode uncooled IR FPA in 1999, the pixel structure has been improved by developing sophisticated MEMS processes. The most advanced pixel has a three-level structure that has an independent metal reflector for interference infrared absorption between the temperature sensor (bottom level) and the infrared-absorbing thin metal film (top level). This structure makes it possible to design pixels with lower thermal conductance by allocating more area for thermal isolation without reducing infrared absorption. The new MEMS process for the three-level structure includes a XeF II dry bulk silicon etching process and a double organic sacrificial layer surface micromachining process. Employing advanced MEMS technology, we have developed a 640 x 480-element SOI diode uncooled IR FPA with 25-?m square pixels. The noise equivalent temperature difference of the FPA is 40 mK with f/1.0 optics. This result clearly demonstrates the great potential of the SOI diode uncooled IR FPA for high-end applications. In this paper, we explain the advances and state-of-the-art technology of the SOI diode uncooled IR FPA.

Kimata, Masafumi; Ueno, Masashi; Takeda, Munehisa; Seto, Toshiki

2006-03-01

13

Power semiconductor laser diode arrays characterization  

NASA Astrophysics Data System (ADS)

Nowadays, power semiconductor laser diode arrays are becoming a widespread source for a large variety of industrial applications. In particular, the availability of low-cost high-power laser diode arrays makes their use possible in the industrial context for material cutting, welding, diagnostics and processing. In the above applications, the exact control of the beam quality plays a very important role because it directly affects the reliability of the final result. In this paper, we present two different approaches useful for the characterization of the beam quality in laser diode arrays. The first one, starting from total intensity measurements on planes orthogonal to the beam propagation path, is able to deduce the working conditions of each laser setting up the array. The second one is aimed at the measurement of a global quality factor of the array itself; to this end, the empirical extension of the M2 concept to composite beams is presented along with some experimental results. As the first technique is especially intended for the non-destructive detection of design problems in the array itself and in the bias circuitry, the second one represents a powerful tool for the rapid on-line diagnostics of the laser beam during its use.

Zeni, Luigi; Campopiano, Stefania; Cutolo, Antonello; D'Angelo, Giuseppe

2003-09-01

14

The Fuge Tube Diode Array Spectrophotometer  

ERIC Educational Resources Information Center

We present the details for adapting a diode array UV-vis spectrophotometer to incorporate the use of polypropylene microcentrifuge tubes--fuge tubes--as cuvettes. Optical data are presented validating that the polyethylene fuge tubes are equivalent to the standard square cross section polystyrene or glass cuvettes generally used in…

Arneson, B. T.; Long, S. R.; Stewart, K. K.; Lagowski, J. J.

2008-01-01

15

Low-cost laser diode array  

Microsoft Academic Search

A substrate is used to fabricate a low-cost laser diode array. A substrate is machined from an electrically insulative material that is thermally conductive, or two substrates can be bonded together in which the top substrate is electrically as well as thermally conductive. The substrate thickness is slightly longer than the cavity length, and the width of the groove is

Barry L. Freitas; Jay A. Skidmore

1999-01-01

16

Enhanced light extraction in III-nitride ultraviolet photonic crystal light-emitting diodes  

Microsoft Academic Search

III-nitride photonic crystal (PC) ultraviolet (UV) light-emitting diodes (LEDs) were fabricated. Triangular arrays of the PCs with different diameters?periodicities were patterned using electron-beam lithography and inductively coupled plasma dry etching. The optical power output of LEDs was enhanced by a factor of 2.5 due to PC formation. It was observed that the optical enhancement factor depends strongly on the lattice

J. Shakya; K. H. Kim; J. Y. Lin; H. X. Jiang

2004-01-01

17

Enhanced light extraction in III-nitride ultraviolet photonic crystal light-emitting diodes  

Microsoft Academic Search

III-nitride photonic crystal (PC) ultraviolet (UV) light-emitting diodes (LEDs) were fabricated. Triangular arrays of the PCs with different diameters\\/periodicities were patterned using electron-beam lithography and inductively coupled plasma dry etching. The optical power output of LEDs was enhanced by a factor of 2.5 due to PC formation. It was observed that the optical enhancement factor depends strongly on the lattice

J. Shakya; K. H. Kim; J. Y. Lin; H. X. Jiang

2004-01-01

18

Performance measurements of hybrid PIN diode arrays  

SciTech Connect

We report on the successful effort to develop hybrid PIN diode arrays and to demonstrate their potential as components of vertex detectors. Hybrid pixel arrays have been fabricated by the Hughes Aircraft Co. by bump bonding readout chips developed by Hughes to an array of PIN diodes manufactured by Micron Semiconductor Inc. These hybrid pixel arrays were constructed in two configurations. One array format having 10 {times} 64 pixels, each 120 {mu}m square, and the other format having 256 {times} 256 pixels, each 30 {mu}m square. In both cases, the thickness of the PIN diode layer is 300 {mu}m. Measurements of detector performance show that excellent position resolution can be achieved by interpolation. By determining the centroid of the charge cloud which spreads charge into a number of neighboring pixels, a spatial resolution of a few microns has been attained. The noise has been measured to be about 300 electrons (rms) at room temperature, as expected from KTC and dark current considerations, yielding a signal-to-noise ratio of about 100 for minimum ionizing particles. 4 refs., 13 figs.

Jernigan, J.G.; Arens, J.F. (California Univ., Berkeley, CA (USA). Space Sciences Lab.); Kramer, G. (Hughes Aircraft Co., El Segundo, CA (USA)); Collins, T.; Herring, J. (Hughes Aircraft Co., Carlsbad, CA (USA)); Shapiro, S.L. (Stanford Linear Accelerator Center, Menlo Park, CA (USA)); Wilburn, C.D. (Micron Semiconductor, Inc., Longwood, FL (USA))

1990-05-01

19

Low-cost laser diode array  

DOEpatents

A substrate is used to fabricate a low-cost laser diode array. A substrate is machined from an electrically insulative material that is thermally conductive, or two substrates can be bonded together in which the top substrate is electrically as well as thermally conductive. The substrate thickness is slightly longer than the cavity length, and the width of the groove is wide enough to contain a bar and spring (which secures the laser bar firmly along one face of the groove). The spring also provides electrical continuity from the backside of the bar to the adjacent metalization layer on the laser bar substrate. Arrays containing one or more bars can be formed by creating many grooves at various spacings. Along the groove, many bars can be adjoined at the edges to provide parallel electrical conduction. This architecture allows precise and predictable registration of an array of laser bars to a self-aligned microlens array at low cost.

Freitas, Barry L. (Livermore, CA); Skidmore, Jay A. (Livermore, CA)

1999-01-01

20

Low-cost laser diode array  

DOEpatents

A substrate is used to fabricate a low-cost laser diode array. A substrate is machined from an electrically insulative material that is thermally conductive, or two substrates can be bonded together in which the top substrate is electrically as well as thermally conductive. The substrate thickness is slightly longer than the cavity length, and the width of the groove is wide enough to contain a bar and spring (which secures the laser bar firmly along one face of the groove). The spring also provides electrical continuity from the backside of the bar to the adjacent metalization layer on the laser bar substrate. Arrays containing one or more bars can be formed by creating many grooves at various spacings. Along the groove, many bars can be adjoined at the edges to provide parallel electrical conduction. This architecture allows precise and predictable registration of an array of laser bars to a self-aligned microlens array at low cost. 19 figs.

Freitas, B.L.; Skidmore, J.A.

1999-06-01

21

Reverse Current Blocking Diodes for Flexible Solar Array Protection.  

National Technical Information Service (NTIS)

A unique Solar Cell Blocking Diode for use on solar panels is described. The device has the physical characteristics of a solar cell and the electrical properties of conventional diodes currently used for solar array reverse current isolation and protecti...

E. Levy R. J. McGrath

1975-01-01

22

Ultraviolet GaN Single Quantum Well Laser Diodes  

Microsoft Academic Search

The ultraviolet laser diodes (LDs) whose active layers consisted of binary GaN were grown on epitaxially laterally overgrown GaN substrates by a metalorganic chemical vapor deposition method. For the first time, we observed the lasing emission from binary GaN active layer by current injection. The emission wavelength of GaN single quantum well LDs was 366.9 nm under pulsed current injection

Shin-ichi Nagahama; Tomoya Yanamoto; Masahiko Sano; Takashi Mukai

2001-01-01

23

Microlens frames for laser diode arrays  

DOEpatents

Monolithic microlens frames enable the fabrication of monolithic laser diode arrays and are manufactured inexpensively with high registration, and with inherent focal length compensation for any lens diameter variation. A monolithic substrate is used to fabricate a low-cost microlens array. The substrate is wet-etched or sawed with a series of v-grooves. The v-grooves can be created by wet-etching, by exploiting the large etch-rate selectivity of different crystal planes. The v-grooves provide a support frame for either cylindrical or custom-shaped microlenses. Because the microlens frames are formed by photolithographic semiconductor batch-processing techniques, they can be formed inexpensively over large areas with precise lateral and vertical registration. The v-groove has an important advantage for preserving the correct focus for lenses of varying diameter. 12 figs.

Skidmore, J.A.; Freitas, B.L.

1999-07-13

24

Microlens frames for laser diode arrays  

DOEpatents

Monolithic microlens frames enable the fabrication of monolithic laser diode arrays and are manufactured inexpensively with high registration, and with inherent focal length compensation for any lens diameter variation. A monolithic substrate is used to fabricate a low-cost microlens array. The substrate is wet-etched or sawed with a series of v-grooves. The v-grooves can be created by wet-etching, by exploiting the large etch-rate selectivity of different crystal planes. The v-grooves provide a support frame for either cylindrical or custom-shaped microlenses. Because the microlens frames are formed by photolithographic semiconductor batch-processing techniques, they can be formed inexpensively over large areas with precise lateral and vertical registration. The v-groove has an important advantage for preserving the correct focus for lenses of varying diameter.

Skidmore, Jay A. (Livermore, CA); Freitas, Barry L. (Livermore, CA)

1999-01-01

25

Optimum diode geometry in a two-dimensional photovoltaic array  

Microsoft Academic Search

The quantum efficiency and the crosstalk of a photodiode in a long wavelength IR 2D diode array are studied by numerically solving the 2D diffusion equation of photocarriers in an array environment. The quantum efficiency depends strongly on both the diode size and the junction depth, and can be expressed, to good accuracy, as a quadratic function of the two

Vikram Dhar; Vishnu Gopal

2000-01-01

26

Space Qualification of Laser Diode Arrays  

NASA Technical Reports Server (NTRS)

Laser instruments have great potential in enabling a new generation of remote-sensing scientific instruments. NASA s desire to employ laser instruments aboard satellites, imposes stringent reliability requirements under severe conditions. As a result of these requirements, NASA has a research program to understand, quantify and reduce the risk of failure to these instruments when deployed on satellites. Most of NASA s proposed laser missions have base-lined diode-pumped Nd:YAG lasers that generally use quasi-constant wave (QCW), 808 nm Laser Diode Arrays (LDAs). Our group has an on-going test program to measure the performance of these LDAs when operated in conditions replicating launch and orbit. In this paper, we report on the results of tests designed to measure the effect of vibration loads simulating launch into space and the radiation environment encountered on orbit. Our primary objective is to quantify the performance of the LDAs in conditions replicating those of a satellite instrument, determine their limitations and strengths which will enable better and more robust designs. To this end we have developed a systematic testing strategy to quantify the effect of environmental stresses on the optical and electrical properties of the LDA.

Troupaki, Elisavet; Kashem, Nasir B.; Allan, Graham R.; Vasilyev, Aleksey; Stephen, Mark

2005-01-01

27

Coherent polarization locking of a diode emitter array.  

PubMed

We present our work on the coherent combining of an array of diode emitters in a conventional diode bar configuration using the coherent polarization locking technique. An external laser cavity is designed so that the diode emissions from four diode emitters are spatially overlapped and passively phase locked via a series of birefringent walk-off crystals and a polarizing beam splitter. This concept was experimentally demonstrated up to 1030 mW of coherently combined power and was shown to increase the laser brightness of the diode bar by approximately 50 times. PMID:19571993

Ng, S P; Phua, P B

2009-07-01

28

Time-resolved electroluminescence studies of III-nitride ultraviolet photonic-crystal light-emitting diodes  

Microsoft Academic Search

Transient responses of III-nitride photonic-crystal (PC) ultraviolet (UV) light-emitting diodes (LEDs) were measured by picosecond time-resolved electroluminescence (EL) spectroscopy. Triangular arrays of PCs with different diameters\\/periodicities were fabricated on 333 nm UV LEDs for enhancing light extraction efficiency using electron-beam lithography and inductively coupled-plasma dry etching. With the incorporation of PCs on LEDs, the EL decay time constant tau decreases

J. Shakya; J. Y. Lin; H. X. Jiang

2004-01-01

29

1-D array of perforated diode neutron detectors  

NASA Astrophysics Data System (ADS)

Performance of a 4 cm long 64-pixel perforated diode neutron detector array is compared with an identical array of thin-film coated diodes. The perforated neutron detector design has been adapted to a 1-D pixel array capable of 120 ?m spatial resolution and counting efficiency greater than 12%. Deep vertical trenches filled with 6LiF provide outstanding improvement in efficiency over thin-film coated diode designs limited to only 4.5%. This work marks the final step towards the construction of a much larger array consisting of 1024 pixels spanning 10 cm. The larger detector array will be constructed with a sub-array of 64-pixel sensors, and will be used for small-angle neutron scattering experiments at the Spallation Neutron Source of Oak Ridge National Laboratory.

McNeil, Walter J.; Bellinger, Steven L.; Unruh, Troy C.; Henderson, Chris M.; Ugorowski, Phil; Morris-Lee, Bryce; Taylor, Russell D.; McGregor, Douglas S.

2009-06-01

30

Injection-seeding studies of diode laser array behavior  

SciTech Connect

By optical injection seeding of diode laser arrays with the output from a narrowband tunable master oscillator, we are able to actively probe these devices and study their inter-element coupling behavior and eigenmodes.

Hohimer, J.P.; Hadley, G.R.; Owyoung, A.

1987-01-01

31

Means for phase locking the outputs of a surface emitting laser diode array  

NASA Technical Reports Server (NTRS)

An array of diode lasers, either a two-dimensional array of surface emitting lasers, or a linear array of stripe lasers, is phase locked by a diode laser through a hologram which focuses the output of the diode laser into a set of distinct, spatially separated beams, each one focused onto the back facet of a separate diode laser of the array. The outputs of the diode lasers thus form an emitted coherent beam out of the front of the array.

Lesh, James R. (inventor)

1987-01-01

32

Monolithic millimeter-wave diode grid frequency multiplier arrays  

NASA Technical Reports Server (NTRS)

Monolithic diode frequency multiplier arrays, including barrier-N-N(+) (BNN) doubler, multi-quantum-barrier-varactor (MQBV) tripler, Schottky-quantum-barrier-varactor (SQBV) tripler, and resonant-tunneling-diode (RTD) tripler arrays, have been successfully fabricated with yields between 85 and 99 percent. Frequency doubling and/or tripling have been observed for all the arrays. Output powers of 2.4-2.6 W (eta = 10-18 percent) at 66 GHz with the BNN doubler and 3.8-10 W (eta = 1.7-4 percent) at 99 GHz with the SQBV tripler have been achieved.

Liu, Hong-Xia L.; Qin, X.-H.; Sjogren, L. B.; Wu, W.; Chung, E.; Domier, C. W.; Luhmann, N. C., Jr.

1992-01-01

33

Enhanced light extraction in III-nitride ultraviolet photonic crystal light-emitting diodes  

NASA Astrophysics Data System (ADS)

III-nitride photonic crystal (PC) ultraviolet (UV) light-emitting diodes (LEDs) were fabricated. Triangular arrays of the PCs with different diameters/periodicities were patterned using electron-beam lithography and inductively coupled plasma dry etching. The optical power output of LEDs was enhanced by a factor of 2.5 due to PC formation. It was observed that the optical enhancement factor depends strongly on the lattice constant and hole size of the PCs. The achievement of nitride PCs is expected to benefit many applications of III-nitride optoelectronics, particularly for the improvement of extraction efficiency in III-nitride deep-UV emitters (?<340 nm), which are crucial for many important applications, but presently have a very low quantum efficiency.

Shakya, J.; Kim, K. H.; Lin, J. Y.; Jiang, H. X.

2004-07-01

34

Mask-less ultraviolet photolithography based on CMOS-driven micro-pixel light emitting diodes.  

PubMed

We report on an approach to ultraviolet (UV) photolithography and direct writing where both the exposure pattern and dose are determined by a complementary metal oxide semiconductor (CMOS) controlled micro-pixellated light emitting diode array. The 370 nm UV light from a demonstrator 8 x 8 gallium nitride micro-pixel LED is projected onto photoresist covered substrates using two back-to-back microscope objectives, allowing controlled demagnification. In the present setup, the system is capable of delivering up to 8.8 W/cm2 per imaged pixel in circular spots of diameter approximately 8 microm. We show example structures written in positive as well as in negative photoresist. PMID:20052059

Elfström, D; Guilhabert, B; McKendry, J; Poland, S; Gong, Z; Massoubre, D; Richardson, E; Rae, B R; Valentine, G; Blanco-Gomez, G; Gu, E; Cooper, J M; Henderson, R K; Dawson, M D

2009-12-21

35

Applications of microlens-conditioned laser diode arrays  

SciTech Connect

The ability to condition the radiance of laser diodes using shaped-fiber cylindrical-microlens technology has dramatically increased the number of applications that can be practically engaged by diode laser arrays. Lawrence Livermore National Laboratory (LLNL) has actively pursued optical efficiency and engineering improvements in this technology in an effort to supply large radiance-conditioned laser diode array sources for its own internal programs. This effort has centered on the development of a modular integrated laser diode packaging technology with the goal of enabling the simple and flexible construction of high average power, high density, two-dimensional arrays with integrated cylindrical microlenses. Within LLNL, the principal applications of microlens-conditioned laser diode arrays are as high intensity pump sources for diode pumped solid state lasers (DPSSLs). A simple end-pumping architecture has been developed and demonstrated that allows the radiation from microlens-conditioned, two-dimensional diode array apertures to be efficiently delivered to the end of rod lasers. To date, pump powers as high as 2.5 kW have been delivered to 3 mm diameter laser rods. Such high power levels are critical for pumping solid state lasers in which the terminal laser level is a Stark level lying in the ground state manifold. Previously, such systems have often required operation of the solid state gain medium at low temperature to freeze out the terminal laser Stark level population. The authors recently developed high intensity pump sources overcome this difficulty by effectively pumping to much higher inversion levels, allowing efficient operation at or near room temperature. Because the end-pumping technology is scalable in absolute power, the number of rare-earth ions and transitions that can be effectively accessed for use in practical DPSSL systems has grown tremendously.

Beach, R.J.; Emanuel, M.A.; Freitas, B.L. [and others

1995-01-01

36

Interelement coupling in gain-guided diode laser arrays  

NASA Astrophysics Data System (ADS)

Below-threshold studies of an injection-locked gain-guided diode laser array show a far-field emission pattern with several lobes whose angular widths decrease with increasing frequency of the injected radiation. The concurrent increase in the far-field emission angle with the frequency of the injected radiation provides strong evidence that the interelement coupling in a gain-guided diode laser array depends upon the tilt of the wave front in the array cavity. These results provide insight into the coupling mechanism that dominates gain-guided array behavior and strongly suggest that these devices should be viewed as perturbed broad-area devices in which plane waves are undergoing multiple reflections between facets. This contrasts sharply with the coupled-mode picture, which is more appropriate for index-guided arrays.

Hohimer, J. P.; Hadley, G. R.; Owyoung, A.

1986-06-01

37

Online photolytic optical gating of caged fluorophores in capillary zone electrophoresis utilizing an ultraviolet light-emitting diode.  

PubMed

Photolytic optical gating (POG) facilitates rapid, on-line and highly sensitive analyses, though POG utilizes UV lasers for sample injection. We present a low-cost, more portable alternative, employing an ultraviolet light-emitting diode (UV-LED) array to inject caged fluorescent dyes via photolysis. Utilizing the UV-LED array, labeled amino acids were injected with nanomolar limits of detection (270 ± 30 nM and 250 ± 30 nM for arginine and citrulline, respectively). When normalized for the difference in light intensity, the UV-LED array provides comparable sensitivity to POG utilizing UV lasers. Additionally, the UV-LED array yielded sufficient beam quality and stability to facilitate coupling with a Hadamard transform, resulting in increased sensitivity. This work shows, for the first time, the use of an UV-LED for online POG with comparable sensitivity to conventional laser sources but at a lower cost. PMID:22911376

Gallagher, Elyssia S; Comi, Troy J; Braun, Kevin L; Aspinwall, Craig A

2012-09-01

38

Radiation effects in semiconductor laser diode arrays  

Microsoft Academic Search

The effects of radiation events are important for many of the present and future applications that involve optoelectronic components. Laser diodes show a strong resistance to degradation by gamma rays, prompt X-rays and (to a lesser extent), neutrons. This is due to the short carrier lifetime that is associated with stimulated emission and the high current injection conditions that are

Richard F. Carson

1988-01-01

39

High duty cycle hard soldered kilowatt laser diode arrays  

NASA Astrophysics Data System (ADS)

High-brightness laser diode arrays operating at a duty cycle of 10% - 20% are in ever-increasing demand for the optical pumping of solid state lasers and directed energy applications. Under high duty-cycle operation at 10% - 20%, passive (conductive) cooling is of limited use, while micro-coolers using de-ionized cooling water can considerably degrade device reliability. When designing and developing actively-cooled collimated laser diode arrays for high duty cycle operation, three main problems should be carefully addressed: an effective local and total heat removal, a minimization of packaging-induced and operational stresses, and high-precision fast axis collimation. In this paper, we present a novel laser diode array incorporating a built-in tap water cooling system, all-hard-solder bonded assembly, facet-passivated high-power 940 nm laser bars and tight fast axis collimation. By employing an appropriate layout of water cooling channels, careful choice of packaging materials, proper design of critical parts, and active optics alignment, we have demonstrated actively-cooled collimated laser diode arrays with extended lifetime and reliability, without compromising their efficiency, optical power density, brightness or compactness. Among the key performance benchmarks achieved are: 150 W/bar optical peak power at 10% duty cycle, >50% wallplug efficiency and <1° collimated fast axis divergence. A lifetime of >0.5 Ghots with <2% degradation has been experimentally proven. The laser diode arrays have also been successfully tested under harsh environmental conditions, including thermal cycling between -20°C and 40°C and mechanical shocks at 500g acceleration. The results of both performance and reliability testing bear out the effectiveness and robustness of the manufacturing technology for high duty-cycle laser arrays.

Klumel, Genady; Karni, Yoram; Oppenheim, Jacob; Berk, Yuri; Shamay, Moshe; Tessler, Renana; Cohen, Shalom

2010-02-01

40

Silicon PIN diode array hybrids for charged particle detection  

SciTech Connect

We report on the design of silicon PIN diode array hybrids for use as charged particle detectors. A brief summary of the need for vertex detectors is presented. Circuitry, block diagrams and device specifications are included. 8 refs., 7 figs., 1 tab.

Shapiro, S.L.; Dunwoodie, W.M.; Arens, J.F.; Jernigan, J.G.; Gaalema, S.

1988-09-01

41

Nanostructured High Performance Ultraviolet and Blue Light Emitting Diodes for Solid State Lighting  

SciTech Connect

We report on research results in this project which synergize advanced material science approaches with fundamental optical physics concepts pertaining to light-matter interaction, with the goal of solving seminal problems for the development of very high performance light emitting diodes (LEDs) in the blue and near ultraviolet for Solid State Lighting applications. Accomplishments in the duration of the contract period include (i) new means of synthesizing AlGaN and InN quantum dots by droplet heteroepitaxy, (ii) synthesis of AlGaInN nanowires as building blocks for GaN-based microcavity devices, (iii) progress towards direct epitaxial alignment of the dense arrays of nanowires, (iv) observation and measurements of stimulated emission in dense InGaN nanopost arrays, (v) design and fabrication of InGaN photonic crystal emitters, and (vi) observation and measurements of enhanced fluorescence from coupled quantum dot and plasmonic nanostructures. The body of results is presented in this report shows how a solid foundation has been laid, with several noticeable accomplishments, for innovative research, consistent with the stated milestones.

Arto V. Nurmikko; Jung Han

2007-03-31

42

Nanostructured High Performance Ultraviolet and Blue Light Emitting Diodes for Solid State Lighting  

SciTech Connect

We report on research results in this project which synergize advanced material science approaches with fundamental optical physics concepts pertaining to light-matter interaction, with the goal of solving seminal problems for the development of very high performance light emitting diodes (LEDs) in the blue and near ultraviolet for Solid State Lighting applications. Accomplishments in the second 12 month contract period include (i) new means of synthesizing AlGaN and InN quantum dots by droplet heteroepitaxy, (ii) synthesis of AlGaInN nanowires as building blocks for GaN-based microcavity devices, (iii) progress towards direct epitaxial alignment of the dense arrays of nanowires, (iv) observation and measurements of stimulated emission in dense InGaN nanopost arrays, (v) design and fabrication of InGaN photonic crystal emitters, and (vi) observation and measurements of enhanced fluorescence from coupled quantum dot and plasmonic nanostructures. The body of results is presented in this report shows how a solid foundation has been laid, with several noticeable accomplishments, for innovative research, consistent with the stated milestones.

Arto V. Nurmikko; Jung Han

2005-09-30

43

Photodiode arrays having minimized cross-talk between diodes  

DOEpatents

Photodiode arrays are formed with close diode-to-diode spacing and minimized cross-talk between diodes in the array by isolating the diodes from one another with trenches that are formed between the photodiodes in the array. The photodiodes are formed of spaced regions in a base layer, each spaced region having an impurity type opposite to that of the base layer to define a p-n junction between the spaced regions and the base layer. The base layer meets a substrate at a boundary, with the substrate being much more heavily doped than the base layer with the same impurity type. The trenches extend through the base layer and preferably into the substrate. Minority carriers generated by absorption of light photons in the base layer can only migrate to an adjacent photodiode through the substrate. The lifetime and the corresponding diffusion length of the minority carriers in the substrate is very short so that all minority carriers recombine in the substrate before reaching an adjacent photodiode.

Guckel, Henry (Madison, WI); McNamara, Shamus P. (Madison, WI)

2000-10-17

44

Far field description of laser diode arrays  

NASA Astrophysics Data System (ADS)

A new model is applied to describe the field distribution at the output of the LDAs. Formalism describing of the far-field radiation patterns of a laser arrays is presented, base on rigorous solutions of the Helmholtz equations. The beam-divergence angles normal and parallel to the junction plane are concluded. Theoretical results presented are in close agreement with the experiments. and the final result is expressed in a form convenient for diffraction analysis of LDAs beams.

Xu, Qiang; Han, Yiping; Zeng, Xiaodong

2009-11-01

45

Electrical Characterization of GaN Based Ultraviolet and Blue Light Emitting Diodes  

Microsoft Academic Search

Gallium nitride based ultraviolet (UV) and blue AlGaN\\/GaN\\/AlGaN double heterojunction structure light emitting diodes (LEDs) were electrically characterized using current-voltage (I-V) and capacitance-voltage (C-V) measurements as a function of frequency. An analysis of logarithmic plots of the forward I-V characteristics indicated that current in these diodes was proportional to x V , as opposed to nkT qV e \\/ ,

Alphonse-Marie Kamto Tegueu; Okechukwu Akp; Arindra Guha

46

Spectral conversion of InGaN ultraviolet microarray light-emitting diodes using fluorene-based red-, green-, blue-, and white-light-emitting polymer overlayer films  

Microsoft Academic Search

We report the fabrication of hybrid organic\\/inorganic semiconductor light-emitting devices that operate across the entire visible spectrum. The devices are based on a series of blue-, green-, and red-light-emitting polyfluorene materials that convert the emission from an array of micron-sized ultraviolet InGaN light-emitting diodes. We also demonstrate white-light-emitting versions of these hybrid devices by employing single films of carefully adjusted

G. Heliotis; P. N. Stavrinou; D. D. C. Bradley; E. Gu; C. Griffin; C. W. Jeon; M. D. Dawson

2005-01-01

47

Near-ultraviolet light-emitting diodes based on ?-conjugated linear silicon-backbone polymers  

Microsoft Academic Search

We report the basic device characteristics of light-emitting diodes (LEDs) based on linear silicon-backbone polymers, polysilanes, with a view to the possibility of employing them as an emissive material in a solid-state light source in the near-ultraviolet (NUV) or ultraviolet (UV) region. The LEDs we fabricated have a single-layer structure consisting of a thin film of polysilane polymer, together with

Hiroyuki Suzuki; Satoshi Hoshino; Chien-Hua Yuan; Michiya Fujiki; Seiji Toyoda; Nobuo Matsumoto

1998-01-01

48

Facet degradation of high-power diode laser arrays  

NASA Astrophysics Data System (ADS)

Micro-Raman facet temperatures of high-power diode lasers with different waveguide architectures are compared. For regular operation conditions, the thermal behavior of `unaged' arrays emitting in the 808-nm wavelength region with different architectures is similar, however, with an increased load thermal behaviors differ significantly and exhibit failure events at facet temperatures typically between 150 and 450 °C. From various experiments, among them facet temperature measurements for ultrahigh-power operation as well as by preparative failure analytics, we provide evidence that in arrays the front facets are significantly affected by device operation and influence the failure behavior of the whole high-power diode laser also in cases when the device failure is accompanied by dislocation creation inside the device.

Tomm, J. W.; Thamm, E.; Bärwolff, A.; Elsaesser, T.; Luft, J.; Baeumler, M.; Mueller, S.; Jantz, W.; Rechenberg, I.; Erbert, G.

49

High power diode laser array for an imaging laser radar sensor  

NASA Astrophysics Data System (ADS)

The use of surface-emitting distributed-feedback diode laser arrays in conjunction with microoptics lens arrays to assemble a 10 W power-class laser source exhibiting submilliradian beam divergence is demonstrated. Such a diode laser promises to serve as a low cost, compact, efficient illumination source for imaging laser radar applications. Attention is given to the configuration of the collimating array and the comparative performance of the diode laser array and Fabry-Perot lasers.

Macomber, S. H.; Mott, J. S.; Schwartz, B. D.; Setzko, R. S.

1992-06-01

50

Laser beam transformation technique for high-power laser diode linear arrays  

Microsoft Academic Search

This paper reports on a novel pair of microlens arrays (MLA's) for efficient coupling of the high aspect ratio optical beam emitted by high-power laser diode linear arrays (also referred to as laser diode bars) into the core of multimode optical fibers. These novel MLA's overcome the limitations observed when using high fill factors laser diode bars. The MLA designs

Paul Grenier; Yves Taillon; Min Wang; Patrice Topart; Daniel Asselin; André Parent

2006-01-01

51

Diode laser arrays for dynamic infrared scene projection  

Microsoft Academic Search

A novel concept for dynamic IR scene projection using IR diode lasers has been developed. This technology offers significant cost and performance advantages over other currently available projector technologies. Performance advantages include high dynamic range, multiple wavebands, and high frame rates. A projector system which utilizes a 16-element linear array has been developed and integrated into the millimeter wave\\/infrared (MMW\\/IR)

D. Brett Beasley; John B. Cooper

1993-01-01

52

Photon counting photodiode array detector for far ultraviolet (FUV) astronomy  

NASA Technical Reports Server (NTRS)

A compact, stable, single-stage intensified photodiode array detector designed for photon-counting, far ultraviolet astronomy applications employs a saturable, 'C'-type MCP (Galileo S. MCP 25-25) to produce high gain pulses with a narrowly peaked pulse height distribution. The P-20 output phosphor exhibits a very short decay time, due to the high current density of the electron pulses. This intensifier is being coupled to a self-scanning linear photodiode array which has a fiber optic input window which allows direct, rigid mechanical coupling with minimal light loss. The array was scanned at a 250 KHz pixel rate. The detector exhibits more than adequate signal-to-noise ratio for pulse counting and event location. Previously announced in STAR as N82-19118

Hartig, G. F.; Moos, H. W.; Pembroke, R.; Bowers, C.

1982-01-01

53

Qualification of Laser Diode Arrays for Mercury Laser Altimeter Mission  

NASA Technical Reports Server (NTRS)

NASA's requirements for high reliability, high performance satellite laser instruments have driven the investigation of many critical components; specifically, 808 nm laser diode array (LDA) pump devices. The MESSENGER mission is flying the Mercury Laser Altimeter (MLA) which is a diode-pumped Nd:YAG laser instrument designed to map the topography of Mercury. The environment imposed on the instrument by the orbital dynamics places special requirements on the laser diode arrays. In order to limit the radiative heating of the satellite from the surface of Mercury, the satellite is designed to have a highly elliptical orbit. The satellite will heat near perigee and cool near apogee. The laser power is cycled during these orbits so that the laser is on for only 30 minutes (perigee) in a 12 hour orbit. The laser heats 10 C while powered up and cools while powered down. In order to simulate these operational conditions, we designed a test to measure the LDA performance while being temperature and power cycled. Though the mission requirements are specific to NASA and performance requirements are derived from unique operating conditions, the results are general and widely applicable. We present results on the performance of twelve LDAs operating for several hundred million pulses. The arrays are 100 watt, quasi-CW, conductively-cooled, 808 nm devices. Prior to testing, we fully characterize each device to establish a baseline for individual array performance and status. Details of this characterization can be found in reference. Arrays are divided into four groups and subjected to the temperature and power cycling matrix are shown.

Stephen, Mark; Vasilyev, Aleksey; Schafer, John; Allan, Graham R.

2004-01-01

54

NANOSTRUCTURED HIGH PERFORMANCE ULTRAVIOLET AND BLUE LIGHT EMITTING DIODES FOR SOLID STATE LIGHTING  

Microsoft Academic Search

We report on research results in this project which synergize advanced material science approaches with fundamental optical physics concepts pertaining to light-matter interaction, with the goal of solving seminal problems for the development of very high performance light emitting diodes (LEDs) in the blue and near ultraviolet for Solid State Lighting applications. Accomplishments in the first 12 month contract period

Arto V. Nurmikko; Jung Han

2004-01-01

55

Nanostructured High Performance Ultraviolet and Blue Light Emitting Diodes for Solid State Lighting  

Microsoft Academic Search

We report on research results in this project which synergize advanced material science approaches with fundamental optical physics concepts pertaining to light-matter interaction, with the goal of solving seminal problems for the development of very high performance light emitting diodes (LEDs) in the blue and near ultraviolet for Solid State Lighting applications. Accomplishments in the duration of the contract period

Arto V. Nurmikko; Jung Han

2007-01-01

56

Nanostructured High Performance Ultraviolet and Blue Light Emitting Diodes for Solid State Lighting  

Microsoft Academic Search

We report on research results in this project which synergize advanced material science approaches with fundamental optical physics concepts pertaining to light-matter interaction, with the goal of solving seminal problems for the development of very high performance light emitting diodes (LEDs) in the blue and near ultraviolet for Solid State Lighting applications. Accomplishments in the second 12 month contract period

Arto V. Nurmikko; Jung Han

2005-01-01

57

Ultraviolet light emitting diode based on p-NiO/n-ZnO nanowire heterojunction  

NASA Astrophysics Data System (ADS)

We fabricated nanowire-based ultraviolet (UV) light emitting diodes (LEDs) consisting of ITO/p-NiO/n-ZnO nanowires/AZO/n-Si heterostructure by using a dimensional transition technique of 1D to 2D. The p-type NiO layer was directly deposited on the ZnO nanowire arrays, followed by the growth of ITO electrode, resulting in the full coverage of the top surface of the ZnO nanowires and their electrical interconnection. The current-voltage curve of the LED showed obvious rectifying characteristics with a threshold voltage of about 8 V and low leakage current. Under forward bias, this device exhibited UV electroluminescence located at around 380 nm coming from band edge transition of the ZnO and the broad visible emission peak around 450-650 nm was attributed to the n-ZnO defect level emission. The origin of the UV and visible emission were discussed in term of the energy band diagram of the p-NiO/n-ZnO nanowires heterjunctions.

Jung, Byung Oh; Kwon, Yong Hun; Seo, Dong Ju; Lee, Dong Seon; Cho, Hyung Koun

2013-05-01

58

Deep ultraviolet plasmon resonance in aluminum nanoparticle arrays.  

PubMed

Small aluminum nanoparticles have the potential to exhibit localized surface plasmon resonances in the deep ultraviolet region of the electromagnetic spectrum, however technical and scientific challenges make it difficult to attain this limit. We report the fabrication of arrays of Al/Al2O3 core/shell nanoparticles with a metallic-core diameter between 12 and 25 nm that display sharp plasmonic resonances at very high energies, up to 5.8 eV (down to ? = 215 nm). The arrays were fabricated by means of a straightforward self-organization approach. The experimental spectra were compared with theoretical calculations that allow the correlation of each feature to the corresponding plasmon modes. PMID:23725571

Maidecchi, Giulia; Gonella, Grazia; Proietti Zaccaria, Remo; Moroni, Riccardo; Anghinolfi, Luca; Giglia, Angelo; Nannarone, Stefano; Mattera, Lorenzo; Dai, Hai-Lung; Canepa, Maurizio; Bisio, Francesco

2013-07-23

59

Traveling-wave amplifier made from a laser diode array  

NASA Astrophysics Data System (ADS)

A traveling-wave amplifier has been fabricated from a ten-stripe, AlGaAs phase-locked injection laser array by antireflection coating both facets. A small-signal gain of 18.6 dB, when corrected for optical coupling efficiency, has been observed, resulting in over 100 mW of coherent optical power output. When the signal source is a single transverse and single longitudinal mode diode laser, the far-field radiation pattern is dominated by a single lobe with a divergence of 0.86 deg in the lateral plane.

Andrews, J. R.

1986-05-01

60

Animation of Diode Array Detection in High Performance Liquid Chromatography  

NSDL National Science Digital Library

This animation site deals specifically with diode array detection for liquid chromatography. The animations are short (one to two minutes) and can easily be shown in class as part of a lecture. They are extremely helpful in illustrating key components and concepts of chromatographic systems. Users are encouraged to explore the site and the other brief animations as well. Separate links to other simulations by the same company (TRSL) are also listed on ASDL. This site requires FLASH version 7 or higher in order to work properly.

2011-05-03

61

Diode-array-pumped repetitively pulsed neodymium phosphate glass laser  

SciTech Connect

Repetitively pulsed generation (200 {mu}s, 40 Hz) was obtained in a neodymium phosphate glass laser pumped by a 870-nm diode array. The maximum slope lasing efficiency with respect to the optical pump energy equal to 13% is restricted by the factor ({approx}0.23) of active-medium filling by the mode field. By adjusting the laser cavity, the single-transverse mode regime, in particular, the generation of the TEM{sub 00} mode is obtained in the entire range of pump energies. (active media. lasers)

Bogatov, A P; Drakin, A E; Miftakhutdinov, D R; Starodub, A N [P. N. Lebedev Physics Institute, Russian Academy of Sciences, Moscow (Russian Federation); Mikaelyan, G T [Inject Research and Manufacturing Enterprise, Saratov (Russian Federation)

2008-09-30

62

Protection circuitry for high-power diode laser arrays  

NASA Astrophysics Data System (ADS)

A comprehensive protection scheme is presented for use with high-power (~500 W dc input) diode laser arrays. The circuitry requires no separate power, using instead the voltage from the laser's power supply. Overcurrent and overvoltage silicon controlled rectifier crowbars are the primary protection circuits. In addition, tripping of either crowbar will turn off the main power to the laser's power supply. This feature makes use of a main power controller that incorporates two interlock loops, for protection against overtemperature, low coolant flow, undervoltage, and other undesirable conditions.

Saam, Brian T.; Conradi, Mark S.

1998-06-01

63

Low-cost diode arrays for the LIFE project  

NASA Astrophysics Data System (ADS)

One of the primary challenges of the Laser Inertial Fusion Engine (LIFE) project is the cost and availability of the laser diode arrays needed to pump the solid-state laser gain media in the system. Current projections indicate that the arrays need to be available for approximately one cent per Watt of output power, which is one to two orders of magnitude cheaper than currently available. This work focuses on potential manufacturing approaches to meet the projected specifications of the LIFE project. Special attention will be paid to requirements related to power density (25 kW/cm2), bar pitch (150 - 400 microns), output wavelength (87x), and fast-axis divergence (+/- 4 degrees). A summary of the supply limitations and cost ramifications of each requirement is presented. Also discussed are potential supply chain limitations that are anticipated as a result of the immense size of the LIFE project.

Feeler, Ryan; Junghans, Jeremy; Stephens, Ed

2011-02-01

64

Ultrashort Optical Pulse Generation from High Power Diode Arrays  

NASA Astrophysics Data System (ADS)

This thesis concerns the development of high power ultrashort pulsed laser sources using high power semiconductor lasers. The objective is to demonstrate the feasibility of extending new mode locking techniques recently developed for solid state lasers to high power diode lasers for subpicosecond pulse generation. This approach was demonstrated by actively mode-locking a 40-stripe multiple quantum well diode array in an external cavity that incorporated a single mode fiber for fast saturable absorber-like action, self phase modulation (SPM), and a six-prism sequence for group velocity dispersion (GVD) compensation. A two-stage injection-locked amplifier was constructed to study the gain characteristics of the 40-stripe diode array. The highest signal gain obtained was 26 dB and the highest cw power in a nearly diffraction limited far field lobe was 510 mW. These results also demonstrated a new technique for achieving large signal gain or high coherent output power from high power diode lasers. The application of ABCD formalism to design the high power array-fiber external cavity was presented. The effects of intracavity SPM and GVD on the short pulse performance were studied experimentally. Two distinct regimes of short pulse operation were observed. For positive or slightly negative total cavity GVD, the resulting pulses were relatively long and chirped. However, for strong negative GVD, soliton -like pulse shaping mechanism was observed. The pulses generated in this regime were short and nearly chirp free. The pulses as short as 0.65 ps with time-bandwidth product of 0.47 were generated. The peak power was estimated to be 6 watts. These are the shortest pulses generated directly from mode-locked high power semiconductor lasers. Because of being compact and efficient as well as its unique capability of producing both high peak power and subpicosecond pulses, this approach can potentially provide new ultrashort pulsed laser sources for experimental studies and engineering applications. (Copies available exclusively from MIT Libraries, Rm. 14-0551, Cambridge, MA 02139-4307. Ph. 617-253-5668; Fax 617-253-1690.).

Pang, Lily Yee

65

High-density pulsed laser diode arrays for SSL pumping  

NASA Astrophysics Data System (ADS)

Northrop Grumman Cutting Edge Optronics has developed a new laser diode array package with minimal bar-to-bar spacing. These High Density Stack (HDS) packages allow for a power density increase on the order of ~ 2.5x when compared to industry-standard arrays. This work contains an overview of the manufacturing process, as well as representative data for 5-, 10-, and 20-bar arrays. Near-field and power vs. current data is presented in each case. Power densities approaching 15 kW/cm2 are presented. In addition, power and wavelength are presented as a function of pulse width in order to determine the acceptable operational parameters for this type of array. In the low repetition rate Nd:YAG pumping regime, all devices are shown to operate with relatively low junction temperatures. A discussion of future work is also presented, with a focus on extending the HDS architecture to reliable operation at 300W per bar. This will enable power densities of approximately 25 kW/cm2.

Feeler, Ryan; Stephens, Edward

2010-04-01

66

A smile insensitive method for spectral linewidth narrowing on high power laser diode arrays  

NASA Astrophysics Data System (ADS)

To eliminate the smile effect in spectral linewidth narrowing on high power laser diode arrays, we have introduced a plane reflective mirror into a common Littrow configuration external cavity to enhance the correlation among emitters. By this way, we obtained uniform spectral distribution among emitters of a 64-elements laser diode array with 35 GHz linewidth and 41 W output laser power.

Yang, Zining; Wang, Hongyan; Li, Yuandong; Lu, Qisheng; Hua, Weihong; Xu, Xiaojun; Chen, Jinbao

2011-10-01

67

Characterization of High-power Quasi-cw Laser Diode Arrays  

NASA Technical Reports Server (NTRS)

NASA s requirements for high reliability, high performance satellite laser instruments have driven the investigation of many critical components; specifically, 808 nm laser diode array (LDA) pump devices. Performance and comprehensive characterization data of Quasi-CW, High-power, laser diode arrays is presented.

Stephen, Mark A.; Vasilyev, Aleksey; Troupaki, Elisavet; Allan, Graham R.; Kashem, Nasir B.

2005-01-01

68

Characterization of high-power quasi-cw laser diode arrays  

Microsoft Academic Search

NASA's requirements for high reliability, high performance satellite laser instruments have driven the investigation of many critical components; specifically, 808 nm laser diode array (LDA) pump devices. Performance and comprehensive characterization data of Quasi-CW, High-power, laser diode arrays is presented.

Mark A. Stephen; Aleksey Vasilyev; Elisavet Troupaki; Graham R. Allan; Nasir B. Kashem

69

365 nm Ultraviolet Laser Diodes Composed of Quaternary AlInGaN Alloy  

Microsoft Academic Search

Ultraviolet (UV) laser diodes (LDs), whose active layer were quaternary AlxInyGa1-x-yN single-quantum well structure, were grown on epitaxial lateral overgrown GaN substrates by a metalorganic chemical vapor deposition method. We investigated the lasing wavelength dependence of UV LDs on the threshold current density. As a result, we succeeded in fabricating 365 nm UV LDs which are useful for various industrial

Shingo Masui; Yuji Matsuyama; Tomoya Yanamoto; Tokuya Kozaki; Shin-Ichi Nagahama; Takashi Mukai

2003-01-01

70

Study of GaN-based Laser Diodes in Near Ultraviolet Region  

Microsoft Academic Search

Ultraviolet (UV) laser diodes (LDs) were grown on epitaxially laterally overgrown GaN substrates by a metalorganic chemical vapor deposition method. We fabricated three types of UV LDs whose active layers were (I) ternary InGaN, (II) quaternary AlInGaN and (III) binary GaN single quantum well (SQW) structures. We investigated the LD characteristics in detail in the near UV region. LDs whose

Shin-ichi Nagahama; Tomoya Yanamoto; Masahiko Sano; Takashi Mukai

2002-01-01

71

Phosphor-Conversion White Light Emitting Diode Using InGaN Near-Ultraviolet Chip  

Microsoft Academic Search

We fabricated a phosphor-conversion white light emitting diode (LED) using an InGaN chip that emits 400 nm near-ultraviolet (n-UV) light and phosphors that emit in the blue and yellow region. When the white LED was operated at a forward-bias current of 20 mA at room temperature (RT), the color temperature (Tcp), average color rendering (Ra), operating voltage (Vf) and luminous

Yukio Narukawa; Isamu Niki; Kunihiro Izuno; Motokazu Yamada; Yoshinori Murazaki; Takashi Mukai

2002-01-01

72

Characterization of 808 nm Quasi-constant Wave Laser Diode Arrays  

Microsoft Academic Search

High-power laser diode arrays are used for a variety of space-based laser programs as an energy source for diode-pumped solid-state lasers. Specifically, 1064 nm Nd:YAG lasers require laser diode arrays emitting at a wavelength of 808 nm that operate at quasi-cw peak powers of 100 Watts per bar. Reliability and performance data is needed for these components; particularly for operation

Mark Stephen; Aleksey Vasilyev

73

Improving Reliability of High Power Quasi-CW Laser Diode Arrays for Pumping Solid State Lasers  

NASA Technical Reports Server (NTRS)

Most Lidar applications rely on moderate to high power solid state lasers to generate the required transmitted pulses. However, the reliability of solid state lasers, which can operate autonomously over long periods, is constrained by their laser diode pump arrays. Thermal cycling of the active regions is considered the primary reason for rapid degradation of the quasi-CW high power laser diode arrays, and the excessive temperature rise is the leading suspect in premature failure. The thermal issues of laser diode arrays are even more drastic for 2-micron solid state lasers which require considerably longer pump pulses compared to the more commonly used pump arrays for 1-micron lasers. This paper describes several advanced packaging techniques being employed for more efficient heat removal from the active regions of the laser diode bars. Experimental results for several high power laser diode array devices will be reported and their performance when operated at long pulsewidths of about 1msec will be described.

Amzajerdian, Farzin; Meadows, Byron L.; Baker, Nathaniel R.; Barnes, Bruce W.; Baggott, Renee S.; Lockard, George E.; Singh, Upendra N.; Kavaya, Michael J.

2005-01-01

74

Thermal profile of high power laser diode arrays and implications in line-narrowing using external cavities  

Microsoft Academic Search

We present measurements and analysis of thermal profiles of high power laser diode arrays. We determine the limitations the profile imposes on the linewidth of the diode array in an external cavity configuration and discuss applications in optical pumping for hyperpolarized MRI. ©2002 Optical Society of America OCIS codes: (140.2010) Diode laser arrays; (140.3320) Laser cooling Hyperpolarized noble gases are

G. Blasche; B. B. Goldberg; M. S. Unlu

2003-01-01

75

Dominant ultraviolet electroluminescence from p-ZnO:As/n-SiC(6H) heterojunction light-emitting diodes  

NASA Astrophysics Data System (ADS)

Ultraviolet electroluminescence was demonstrated from a p-ZnO:As/n-SiC(6H) heterojunction light-emitting diode at room-temperature. The p-ZnO:As was fabricated by out-diffusion of arsenic atoms from a sandwiched GaAs interlayer on SiC substrate. The p-type doping was confirmed by both Hall and low-temperature photoluminescence measurements. Under forward bias, an intense ultraviolet emission centered at 384 nm was achieved from ZnO side of the diode. Furthermore, the light-output-current characteristic was determined to evaluate the high-efficiency electroluminescence performance of the diode.

Shi, Zhifeng; Xia, Xiaochuan; Yin, Wei; Zhang, Shikai; Wang, Hui; Wang, Jin; Zhao, Long; Dong, Xin; Zhang, Baolin; Du, Guotong

2012-03-01

76

Vacuum nano-hole array embedded organic light emitting diodes.  

PubMed

We demonstrated a nano-hole array (NHA) embedded structure that was fabricated for organic light emitting diodes (OLEDs) using a robust reverse transfer process. The NHA structure is proposed in this study as a strategy for maximizing the diffraction strength of two dimensional photonic crystals (PCs) by engineering vacuum nano-holes inside a dielectric slab. The electroluminescence (EL) intensity of the OLED was improved by more than twice. Such an optical enhancement was evaluated by using the angular dependence of photoluminescence (PL). The FDTD simulation was carried out to optimize the NHA structure for extraction of the emission induced from both vertical and horizontal dipoles. We explored the effect of the NHA structure on the extraction improvement converted from waveguide mode by measuring EL intensities of the devices with a hemisphere lens. In addition, the transfer process employed in this study yielded extremely low surface roughness, and thus outstanding electrical characteristics. PMID:24336917

Jeon, Sohee; Jeong, Jun-ho; Song, Young Seok; Jeong, Won-Ik; Kim, Jang-Joo; Youn, Jae Ryoun

2014-03-01

77

Spectrally narrowed external-cavity high-power stack of laser diode arrays  

PubMed Central

We describe an effective external cavity for narrowing the spectral linewidth of a multiarray stack of laser diode arrays. For a commercially available 279-W free-running five-array laser diode array operating at 60 A, we narrow the spectral linewidth to 0.40 nm at FWHM with 115 W of cw power output. This technique leads to the possibility of higher-efficiency, lower-cost production of hyperpolarized noble gases for magnetic resonance imaging.

Zhu, H.; Ruset, I. C.; Hersman, F. W.

2005-01-01

78

High power diode laser array for an imaging laser radar sensor  

Microsoft Academic Search

The use of surface-emitting distributed-feedback diode laser arrays in conjunction with microoptics lens arrays to assemble a 10 W power-class laser source exhibiting submilliradian beam divergence is demonstrated. Such a diode laser promises to serve as a low cost, compact, efficient illumination source for imaging laser radar applications. Attention is given to the configuration of the collimating array and the

S. H. Macomber; J. S. Mott; B. D. Schwartz; R. S. Setzko

1992-01-01

79

a Comparison of Different Coherent Deep Ultraviolet Generations Using Second Harmonic Generation with Blue Laser Diode Excitation  

NASA Astrophysics Data System (ADS)

Nano-focus beam applications of short wavelength approximately 220 nm now play important roles in engineering and industrial sections. At present, light sources at approximately 220 nm are commercially available but large size, difficult to maintain, and expensive. Compact wavelength tunable and cost effective light sources at approximately 220 nm are required. Laser diode with sum-frequency generation methods are employed to generated the shorter wavelength approximately 220 nm. This paper presents comparison of second harmonic generation schemes using a nonlinear optic crystal and two types of laser diode, which are a 440 nm single mode blue laser diode and a 450 nm multimode Fabry-Perot blue laser diode, has potential to generate wide tunable coherent deep ultraviolet-c at approximately 220 nm. Using the blue laser diode with the sum-frequency technique, a high second harmonic power is hardly observed due to low conversion efficiency. The best performance of second harmonic generation using blue laser diode, nonlinear optic crystal, and an high-Q external cavity laser diode was observed as 1.1 ?W second harmonic ultraviolet-c power at 224.45 nm ultraviolet-c wavelength and 5.75 nm ultraviolet wavelength tunability. In addition, the improvement of increasing second harmonic power approximately 220 nm and the limitation of wavelength tuning of short wavelength are also theoretically discussed in this paper.

Tangtrongbenchasil, C.; Nonaka, K.

2008-11-01

80

The design and fabrication of a GaN-based monolithic light-emitting diode array  

NASA Astrophysics Data System (ADS)

We report a new monolithic structure of GaN-based light-emitting diode (LED) which can be operated under high voltage or alternative current. Differing from the conventional single LED chip, the monolithic light-emitting diode (MLED) array contains microchips which are interconnected in series or parallel. The key chip fabrication processing methods of the monolithic LED array include deep dry etching, sidewall insulated protection, and electrode interconnection. A 12 V GaN-based blue high voltage light emitting diode was designed and fabricated in our experiment. The forward current—voltage characteristics of MLEDs were consistent with those of conventional single junction light emitting diodes.

Teng, Zhan; Yang, Zhang; Jing, Li; Jun, Ma; Zhiqiang, Liu; Xiaoyan, Yi; Guohong, Wang; Jinmin, Li

2013-09-01

81

InGaN-Based Nanorod Array Light Emitting Diodes  

NASA Astrophysics Data System (ADS)

We demonstrate the realization of the high-brightness and high-efficiency light emitting diodes (LEDs) using dislocation-free indium gallium nitride (InGaN)/gallium nitride (GaN) multi-quantum-well (MQW) nanorod (NR) arrays by metal organic-hydride vapor phase epitaxy (MO-HVPE). MQW NR arrays (NRAs) on sapphire substrate are buried in silicon dioxide (SiO2) to isolating individual NRs and to bring p-type NRs in contact with p-type electrodes. The MQW NRA LEDs have similar electrical characteristics to conventional broad area (BA) LEDs. However, due to the lack of dislocations and the large surface areas provided by the sidewalls of NRs, both internal and extraction efficiencies are significantly enhanced. At 20 mA dc current, the MQW NRA LEDs emit about 4.3 times more light than the conventional BA LEDs, even though overall active volume of the MQW NRA LEDs is much smaller than conventional LEDs.

Kim, Hwa-Mok; Cho, Yong Hoon; Kim, Deuk Young; Kang, Tae Won; Chung, Kwan Soo

2005-06-01

82

A rapid flip chip die bonding method for semiconductor laser diode arrays  

Microsoft Academic Search

We have developed a general method for rapidly bonding semiconductor laser arrays, optical traveling wave amplifier arrays, and other optoelectronic devices to silicon waferboards or submounts. Our method uses octagonal electrodeposited copper bosses to physically register with precision etched inverted pyramidal receptacles in the silicon. Flip-chip bonding of semiconductor laser diode arrays is significantly faster with this method than with

S. A. Merritt; F. Seiferth; V. Vusirikala; M. Dagenais; Y. J. Chen; D. R. Stone

1997-01-01

83

Polarization engineering in III-nitride based ultraviolet light-emitting diodes  

NASA Astrophysics Data System (ADS)

In this study, the polarization effect in III-nitride based ultraviolet (UV) light-emitting diodes (LEDs) has been investigated theoretically. Some specific designs in active region are proposed to reduce the polarization effect and, hence, improve the device performance. Simulation results show that by utilizing properly designed quaternary AlInGaN material in active region, the hole injection efficiency can be enhanced due to the reduction of polarization mismatch between hetero-layers. On the other hand, the electron leakage is suppressed owing to that the effective potential height for electrons is increased. Therefore, the performance of UV LEDs is significantly improved by the polarization engineering in active region.

Lin, Yu-Rui; Liou, Bo-Ting; Chang, Jih-Yuan; Kuo, Yen-Kuang

2013-03-01

84

Real-time monitoring of sulfur dioxide using ultraviolet light-emitting diode  

NASA Astrophysics Data System (ADS)

A compact and low-cost light-emitting diode (LED) with center wavelength of 295 nm and high light density was used measure the concentration of sulfur dioxide, which has a strong structured absorption band in the ultraviolet region 300 nm. Differential optical absorption spectroscopy (DOAS) was used to determine the concentration of sulfur dioxide using reference absorption spectrum due to 1000 ppm SO2. A sensitivity of about 1.5 ppm was achieved with a gas cell in 1-s integration time, enabling real-time monitoring of sulfur dioxide.

Zhong, Weijia; Lin, Hongze; Lou, Xiutao; Yan, Chunsheng; Mei, Liang

2014-02-01

85

Manufacturability of high power ultraviolet-C light emitting diodes on bulk aluminum nitride substrates  

NASA Astrophysics Data System (ADS)

As the technological challenges in obtaining high power ultraviolet-C light emitting diodes (LEDs) on bulk AlN substrates are being overcome, the next challenge faced is the manufacturability. One of these challenges consists of introducing a 10 × 10 mm substrate into a fabrication facility that is processing 2" and larger diameter substrates. This has been successfully carried out using a standard visible LED production facility that is involved in high volume manufacturing of blue LEDs. By introducing specifications on the substrates, the epitaxial wafers, and the fabrication process, the establishment of a pilot production process with pathways to high volume manufacturing has been established.

Grandusky, James R.; Zhong, Zhibai; Chen, Jasson; Leung, Charles; Schowalter, Leo J.

2012-12-01

86

Fabrication and simulation of ultraviolet AlGaInN light-emitting diodes  

Microsoft Academic Search

The ultraviolet AlGaInN light-emitting diode under study is grown on a c-face sapphire substrate by low-pressure horizontal-flow metalorganic chemical vapor deposition (MOCVD). With increasing input current from 10 to 100 mA, the main peak of the emission wavelength shifts from 368 to 372 nm. The room-temperature output power is 0.8 mW at 20 mA. Under continuous-wave operation, an output power

Sheng-Horng Yen; Bo-Jean Chen; Mei-Ling Chen; Yen-Kuang Kuo; Yi-An Chang; Hao-Chung Kuo

2006-01-01

87

Numerical study of polarization-doped AlGaN ultraviolet light-emitting diodes  

NASA Astrophysics Data System (ADS)

The AlGaN-based ultraviolet light-emitting diodes (UV LEDs) with specific design of polarization-induced p-type doping are investigated numerically. The proposed polarization-doped UV LEDs with different Al content graded AlGaN layers exhibit significant improvement for the light output power and carrier injection efficiency compared with the conventional AlGaN UV LED. The enhanced performance for polarization-doped UV LED is explained by the simulated energy band diagrams, distribution of carrier concentration and radiative recombination rate in the quantum wells.

Gao, Lili; Xie, Feng; Yang, Guofeng

2014-07-01

88

Directional and controllable edge-emitting ZnO ultraviolet random laser diodes  

NASA Astrophysics Data System (ADS)

Room-temperature ultraviolet random lasing action is demonstrated from a p-GaN/annealed i-ZnO:Al(3%)/n-ZnO:Al(5%) buried heterojunction diode with a 2 ?m rib waveguide. Excellent electrical-to-optical conversion efficiency is achieved by strong electrical and optical confinement of a buried heterojunction rib waveguide structure. Hence, emission intensity (threshold current) can be enhanced (reduced) by ~9 times (~40%). Directional emission as well as controllability on the number of the random lasing modes can also be achieved.

Liang, H. K.; Yu, S. F.; Yang, H. Y.

2010-03-01

89

Vacuum nano-hole array embedded organic light emitting diodes  

NASA Astrophysics Data System (ADS)

We demonstrated a nano-hole array (NHA) embedded structure that was fabricated for organic light emitting diodes (OLEDs) using a robust reverse transfer process. The NHA structure is proposed in this study as a strategy for maximizing the diffraction strength of two dimensional photonic crystals (PCs) by engineering vacuum nano-holes inside a dielectric slab. The electroluminescence (EL) intensity of the OLED was improved by more than twice. Such an optical enhancement was evaluated by using the angular dependence of photoluminescence (PL). The FDTD simulation was carried out to optimize the NHA structure for extraction of the emission induced from both vertical and horizontal dipoles. We explored the effect of the NHA structure on the extraction improvement converted from waveguide mode by measuring EL intensities of the devices with a hemisphere lens. In addition, the transfer process employed in this study yielded extremely low surface roughness, and thus outstanding electrical characteristics.We demonstrated a nano-hole array (NHA) embedded structure that was fabricated for organic light emitting diodes (OLEDs) using a robust reverse transfer process. The NHA structure is proposed in this study as a strategy for maximizing the diffraction strength of two dimensional photonic crystals (PCs) by engineering vacuum nano-holes inside a dielectric slab. The electroluminescence (EL) intensity of the OLED was improved by more than twice. Such an optical enhancement was evaluated by using the angular dependence of photoluminescence (PL). The FDTD simulation was carried out to optimize the NHA structure for extraction of the emission induced from both vertical and horizontal dipoles. We explored the effect of the NHA structure on the extraction improvement converted from waveguide mode by measuring EL intensities of the devices with a hemisphere lens. In addition, the transfer process employed in this study yielded extremely low surface roughness, and thus outstanding electrical characteristics. Electronic supplementary information (ESI) available: The contents include details about the FDTD modeling, PL specimen fabrication, OLED device fabrication, and PL/EL measurement set-up. Further information is provided relating to the NHA substrate as well. See DOI: 10.1039/c3nr05331h

Jeon, Sohee; Jeong, Jun-Ho; Song, Young Seok; Jeong, Won-Ik; Kim, Jang-Joo; Youn, Jae Ryoun

2014-02-01

90

Photon-counting array detectors for space and ground-based studies at ultraviolet and vacuum ultraviolet /VUV/ wavelengths  

NASA Technical Reports Server (NTRS)

The Multi-Anode Microchannel Arrays (MAMAs) are a family of photoelectric photon-counting array detectors, with formats as large as (256 x 1024)-pixels that can be operated in a windowless configuration at vacuum ultraviolet (VUV) and soft X-ray wavelengths or in a sealed configuration at ultraviolet and visible wavelengths. This paper describes the construction and modes of operation of (1 x 1024)-pixel and (24 x 1024)-pixel MAMA detector systems that are being built and qualified for use in sounding-rocket spectrometers for solar and stellar observations at wavelengths below 1300 A. The performance characteristics of the MAMA detectors at ultraviolet and VUV wavelengths are also described.

Timothy, J. G.; Bybee, R. L.

1981-01-01

91

High Power Laser Diode Array Qualification and Guidelines for Space Flight Environments.  

National Technical Information Service (NTIS)

High-power laser diode arrays (LDAs) are used for a variety of space-based remote sensor laser programs as an energy source for diode-pumped solid-state lasers. LDAs have been flown on NASA missions including MOLA, GLAS and MLA and have continued to be vi...

B. Meadows F. Amzajerdian F. LaRocca H. Leidecker J. Plante M. Stephen M. N. Ott N. Eegholm T. Jamison

2006-01-01

92

III-nitride blue and ultraviolet photonic crystal light emitting diodes  

Microsoft Academic Search

We present results on enhancement of 460 nm blue and 340 nm UV optical power output in III-nitride light emitting diodes (LEDs) using photonic crystals (PCs) under current injection. Triangular arrays of the PCs with diameter\\/periodicity of 300\\/700 nm were patterned using electron-beam lithography and inductively coupled plasma dry etching. The total power at 20 mA of 300×300 ?m2 unpackaged

T. N. Oder; K. H. Kim; J. Y. Lin; H. X. Jiang

2004-01-01

93

III-nitride blue and ultraviolet photonic crystal light emitting diodes  

Microsoft Academic Search

We present results on enhancement of 460 nm blue and 340 nm UV optical power output in III-nitride light emitting diodes (LEDs) using photonic crystals (PCs) under current injection. Triangular arrays of the PCs with diameter\\/periodicity of 300\\/700 nm were patterned using electron-beam lithography and inductively coupled plasma dry etching. The total power at 20 mA of 300×300 mum2 unpackaged

T. N. Oder; K. H. Kim; J. Y. Lin; H. X. Jiang

2004-01-01

94

Means for phase locking the outputs of a surface emitting laser diode array  

SciTech Connect

An array of injection phase-locked diode lasers is described utilizing as a master a separate laser source, and means for coupling light from the master laser source into each diode laser of the array of diode lasers. The array is fabricated in a body of semi-conductor material. Each diode laser has a back facet on one side of the body of semiconductor material and a front facet on an opposite side of the body of semiconductor material. The light coupling means comprises a hologram prepared for producing from the output of the master laser source a set of distinct, spatially separated beams, each one directed into the back facet of each diode laser . To assure emission of phase coherent light from the array of diode lasers, the hologram is positioned between the master laser source and the one side of the body of semiconductor material. The hologram is prepared by illuminating a holographic emulsion plate with an image of the array of diode lasers using coherent light of substantially the same wavelength as the master laser source, and a coherent reference beam of substantially the same wavelength as the master laser source.

Lesh, J.R.

1987-06-30

95

Self-assembled ordered arrays of nanoscale germanium Esaki tunnel diodes  

NASA Astrophysics Data System (ADS)

We have self-assembled regimented arrays of vertical ~100 nm diameter Ge Esaki tunnel diodes using nanosphere lithography. Measurements of the current-voltage characteristics of individual nanodiodes using conductive atomic force microscopy at room temperature reveal pronounced negative differential resistance under forward bias, with a peak to valley ratio of 2-4. These diode arrays could constitute a neuromorphic circuit architecture exhibiting collective computational activity.

Zhu, Kaigui; Wang, Wu; Shao, Qingyi; Zhao, Dongning; Lu, Yongfeng; Ianno, Natale

2011-04-01

96

Monolayer graphene film on ZnO nanorod array for high-performance Schottky junction ultraviolet photodetectors.  

PubMed

A new Schottky junction ultraviolet photodetector (UVPD) is fabricated by coating a free-standing ZnO nanorod (ZnONR) array with a layer of transparent monolayer graphene (MLG) film. The single-crystalline [0001]-oriented ZnONR array has a length of about 8-11 ?m, and a diameter of 100?600 nm. Finite element method (FEM) simulation results show that this novel nanostructure array/MLG heterojunction can trap UV photons effectively within the ZnONRs. By studying the I-V characteristics in the temperature range of 80-300 K, the barrier heights of the MLG film/ZnONR array Schottky barrier are estimated at different temperatures. Interestingly, the heterojunction diode with typical rectifying characteristics exhibits a high sensitivity to UV light illumination and a quick response of millisecond rise time/fall times with excellent reproducibility, whereas it is weakly sensitive to visible light irradiation. It is also observed that this UV photodetector (PD) is capable of monitoring a fast switching light with a frequency as high as 2250 Hz. The generality of the above results suggest that this MLG film/ZnONR array Schottky junction UVPD will have potential application in future optoelectronic devices. PMID:23495044

Nie, Biao; Hu, Ji-Gang; Luo, Lin-Bao; Xie, Chao; Zeng, Long-Hui; Lv, Peng; Li, Fang-Ze; Jie, Jian-Sheng; Feng, Mei; Wu, Chun-Yan; Yu, Yong-Qiang; Yu, Shu-Hong

2013-09-01

97

Optical Chaotic Communication Using Laser Diode Transmitter/Receiver Array  

NASA Astrophysics Data System (ADS)

We propose a new scheme of digital chaotic communication using the array of transmitter/receiver that consists of two self-pulsating laser diodes (LDs), i.e., a receiver LD and a transmitter LD. Part of the output of a transmitter LD is injected into the corresponding receiver LD that receives a chaotically encoded signal. A neutral density (ND) filter is placed after each transmitter LD to control the amount of light transmitted to and then injected into the corresponding receiver LD. According to the amount of the transmitter output which is injected into the receiver LD, two kinds of chaotic states with different Lyapunov exponents are induced in the receiver LD, and they are utilized to represent a binary digit. In addition, the distribution of the coupling factor between transmitter and receiver is used as a “key”. Only the proper receiver who has been previously given the “key” is able to choose an appropriate threshold of the Lyapunov exponent calculated from the detected chaotic signal that is necessary to decipher each binary bit and to decode finally the entire message. By numerically analyzing the bit error rate, particularly its dependence on the error of the optical confinement coefficient as well as on that of the injection current, we confirmed that the present scheme can provide superior security compared to the conventional chaotic masking scheme.

Ebisawa, Satoshi; Komatsu, Shinichi

2004-08-01

98

Laser diode edge sensors for adaptive optics segmented arrays: part 2, laser diode coupled integrated optics chip  

Microsoft Academic Search

Adaptive optics (AO) segmented array systems require los cost nm (piston) and (mu) rad (tilt) range displacement edge sensors to assist in establishing phase continuity between adjacent segments by measuring relative AO edge displacements. Preliminary laboratory experiments using Si based integrated optic (IO) chips coupled to laser diode sources were carried out to determine their suitability as low cost, miniature,

John L. Remo

1995-01-01

99

Laser beam transformation technique for high-power laser diode linear arrays  

NASA Astrophysics Data System (ADS)

This paper reports on a novel pair of microlens arrays (MLA's) for efficient coupling of the high aspect ratio optical beam emitted by high-power laser diode linear arrays (also referred to as laser diode bars) into the core of multimode optical fibers. These novel MLA's overcome the limitations observed when using high fill factors laser diode bars. The MLA designs are described. Results from modelling work show good coupling performances for laser diode bars with fill factors up to 75%. The technique for fabricating the complex surface profiles of the MLA's is discussed. Masters are first fabricated and MLA's are then replicated, so that volume production at low cost can be envisioned. The fabricated MLA's have been used for reshaping and fiber coupling the output of a 10-mm laser diode bar. An efficiency of 74% has been obtained when coupling into an optical fiber having a core diameter of 400 ?m and a numerical aperture of 0.22.

Grenier, Paul; Taillon, Yves; Wang, Min; Topart, Patrice; Asselin, Daniel; Parent, André

2006-03-01

100

Diode-laser-based sensor for ultraviolet absorption measurements of atomic mercury  

NASA Astrophysics Data System (ADS)

A new sensor has been developed for measuring atomic mercury using absorption spectroscopy with 254-nm radiation generated from two sum-frequency-mixed diode lasers. Beams from a 375-nm external-cavity diode laser and a 784-nm distributed feedback diode laser are mixed in a beta-barium-borate crystal to generate approximately 4 nW of ultraviolet radiation. The development of the sensor is described along with extensive characterization experiments in a mercury vapor cell in the laboratory. An accuracy of ±6% in the absolute concentration of atomic mercury has been demonstrated by comparison with equilibrium vapor pressure calculations. The detection limit is approximately 0.1 parts per billion of atomic mercury in a meter path length for 300-K gas and a 10-s integration time. The insensitivity of the sensor to broadband attenuation is demonstrated. Measurements of collision-broadening coefficients for air, N2, Ar, and CO2 are reported, and implementation of wavelength-modulation spectroscopy with the sensor is demonstrated. Finally, results are presented from measurements with the sensor in situ in the exhaust stream of an actual coal-fired combustor.

Anderson, T. N.; Magnuson, J. K.; Lucht, R. P.

2007-04-01

101

Advancement of High Power Quasi-CW Laser Diode Arrays For Space-based Laser Instruments  

NASA Technical Reports Server (NTRS)

Space-based laser and lidar instruments play an important role in NASA s plans for meeting its objectives in both Earth Science and Space Exploration areas. Almost all the lidar instrument concepts being considered by NASA scientist utilize moderate to high power diode-pumped solid state lasers as their transmitter source. Perhaps the most critical component of any solid state laser system is its pump laser diode array which essentially dictates instrument efficiency, reliability and lifetime. For this reason, premature failures and rapid degradation of high power laser diode arrays that have been experienced by laser system designers are of major concern to NASA. This work addresses these reliability and lifetime issues by attempting to eliminate the causes of failures and developing methods for screening laser diode arrays and qualifying them for operation in space.

Amzajerdian, Farzin; Meadows, Byron L.; Baker, nathaniel R.; Baggott, Renee S.; Singh, Upendra N.; Kavaya, Michael J.

2004-01-01

102

Preliminary Demonstration of Power Beaming With Non-Coherent Laser Diode Arrays.  

National Technical Information Service (NTIS)

A preliminary demonstration of free-space electric power transmission has been conducted using non-coherent laser diode arrays as the transmitter and standard silicon photovoltaic cell arrays as the receiver. The transmitter assembly used a high-power-den...

J. T. Kare F. Mitlitsky A. Welsberg

1999-01-01

103

Multiple-wavelength operation of a laser-diode array coupled to an external cavity  

NASA Astrophysics Data System (ADS)

We report a novel geometry for coupling a laser-diode array to an external cavity that produces a diffractively stabilized lasing wavelength separation between elements of the array. The geometry allows for control of the wavelengths and wavelength spacing and provides single-knob tuning of all the wavelengths while maintaining a nearly constant wavelength offset.

Papen, G. C.; Murphy, G. M.; Brady, D. J.; Howe, A. T.; Dallesasse, J. M.; Dejule, R. Y.; Holmgren, D. J.

1993-09-01

104

An Active Retrodirective Array with Bilateral Tunnel Diode Amplifiers.  

National Technical Information Service (NTIS)

The array factor of a 21-element retrodirective array, with bidirectional amplifiers integrated into the interconnecting transmission lines, is derived in this report. The directivity of the array for boresight and off-angle illumination is calculated for...

A. F. Snyder

1967-01-01

105

Time-resolved electroluminescence studies of III-nitride ultraviolet photonic-crystal light-emitting diodes  

NASA Astrophysics Data System (ADS)

Transient responses of III-nitride photonic-crystal (PC) ultraviolet (UV) light-emitting diodes (LEDs) were measured by picosecond time-resolved electroluminescence (EL) spectroscopy. Triangular arrays of PCs with different diameters/periodicities were fabricated on 333 nm UV LEDs for enhancing light extraction efficiency using electron-beam lithography and inductively coupled-plasma dry etching. With the incorporation of PCs on LEDs, the EL decay time constant ? decreases systematically with the increase of the etched sidewall area indicating the strong effect of the surface recombination. The surface recombination velocities on the p-type epitaxial surface and on the sidewall of etched holes on LEDs were determined to be 1.73×104 cm/s and 1.48×105 cm/s, respectively. The angular distribution of light emission from LEDs with PCs shows slight narrowing in far-field pattern. Because of the increased transient response along with enhanced light extraction, the incorporation of PCs in UV LEDs provide an effective method to control the modulation speed of UV LEDs, which could be very useful for many applications.

Shakya, J.; Lin, J. Y.; Jiang, H. X.

2004-09-01

106

III-nitride blue and ultraviolet photonic crystal light emitting diodes  

NASA Astrophysics Data System (ADS)

We present results on enhancement of 460 nm blue and 340 nm UV optical power output in III-nitride light emitting diodes (LEDs) using photonic crystals (PCs) under current injection. Triangular arrays of the PCs with diameter/periodicity of 300/700 nm were patterned using electron-beam lithography and inductively coupled plasma dry etching. The total power at 20 mA of 300×300 ?m2 unpackaged LED chips revealed an increase by 63% and 95% for the blue and UV LEDs, respectively, as a result of the PC formation. Possible ways for further improving enhancement of light extraction using PCs are discussed.

Oder, T. N.; Kim, K. H.; Lin, J. Y.; Jiang, H. X.

2004-01-01

107

Vacuum ultraviolet and ultrasoft x-ray diode detectors for tokamak plasmas  

SciTech Connect

Ultrasoft x-ray diode (USXRD) arrays have been used on DIII-D and ASDEX to study plasma edge radiation, in the photon energy range from 10 eV to 10 keV. The detectors are extremely useful and versatile due to their simplicity and compactness. Furthermore, absolute quantum efficiencies (QE) of many photocathodes such as vitreous C, Al, Cu, CuI, CsI, and Au have been measured in recent years. With filter technique, broadband resolution, E/..delta..Eapprox.1, is possible. Quantum-efficiency comparison of USXRD with semiconductor XRD is also presented to better understand the regions of applicability for each detector.

Lee, P.; Gernhardt, J.; Armentrout, C.J.; Snider, R.T.

1988-06-01

108

High-power pseudomorphic mid-ultraviolet light-emitting diodes with improved efficiency and lifetime  

NASA Astrophysics Data System (ADS)

Recent advances in mid-ultraviolet light-emitting diodes grown pseudomorphically on bulk AlN substrates have led to improved efficiencies and lifetimes. For a 266 nm device an output power of 66 mW at 300 mA has been achieved with an external quantum efficiency of 4.5%. More importantly, the lifetimes of these devices have been increased substantially. Testing of LEDs in both surface mount design (SMD) and TO-39 packages show L50 lifetimes well in excess of 1,000 hours under a variety of case temperatures and currents. Package-related catastrophic failures are eliminated through encapsulation and hermetic sealing, further reducing failure rates and extending the lifetime.

Moe, Craig G.; Grandusky, James R.; Chen, Jianfeng; Kitamura, Ken; Mendrick, Mark C.; Jamil, Muhammad; Toita, Masato; Gibb, Shawn R.; Schowalter, Leo J.

2014-03-01

109

Real-time monitoring and diagnosis of scintillation dosimeters using an ultraviolet light emitting diode.  

PubMed

Plastic scintillator fibre optic dosimeters (FODs) have advantages for both brachytherapy and external beam radiotherapy applications. Convenient real-time monitoring and diagnosis of such dosimeters are desirable because of changes in the optical circuit that may arise in use. In this paper, we propose and demonstrate a real-time method using ultraviolet light emitting diodes (LED) to stimulate the scintillator and to diagnose failures of FODs. Key aspects of the LED FOD dosimetry design are investigated, enabling the design of a stable and accurate real-time monitoring dosimetry system. We demonstrate experimentally that the real-time monitoring FOD system is convenient to be used to monitor FOD dosimeters and to diagnose their failures resulted from different mechanisms. PMID:18401065

Yin, Y; Lambert, J; McKenzie, D R; Suchowerska, N

2008-05-01

110

Improved calibration technique of the infrared imaging bolometer using ultraviolet light-emitting diodes.  

PubMed

The technique used until recently utilizing the Ne-He laser for imaging bolometer foils calibration [B. J. Peterson et al., J. Plasma Fusion Res. 2, S1018 (2007)] has showed several issues. The method was based on irradiation of 1 cm spaced set of points on a foil by the laser beam moved by set of mirrors. Issues were the nonuniformity of laser power due to the vacuum window transmission nonuniformity and high reflection coefficient for the laser. Also, due to the limited infrared (IR) window size, it was very time consuming. The new methodology uses a compact ultraviolet (uv) light-emitting diodes installed inside the vacuum chamber in a fixed position and the foil itself will be moved in the XY directions by two vacuum feedthroughs. These will help to avoid the above mentioned issues due to lack of a vacuum window, fixed emitters, higher uv power absorption, and a fixed IR camera position. PMID:21033981

Drapiko, E; Peterson, B; Alekseev, A; Seo, D C

2010-10-01

111

Improved calibration technique of the infrared imaging bolometer using ultraviolet light-emitting diodes  

SciTech Connect

The technique used until recently utilizing the Ne-He laser for imaging bolometer foils calibration [B. J. Peterson et al., J. Plasma Fusion Res. 2, S1018 (2007)] has showed several issues. The method was based on irradiation of 1 cm spaced set of points on a foil by the laser beam moved by set of mirrors. Issues were the nonuniformity of laser power due to the vacuum window transmission nonuniformity and high reflection coefficient for the laser. Also, due to the limited infrared (IR) window size, it was very time consuming. The new methodology uses a compact ultraviolet (uv) light-emitting diodes installed inside the vacuum chamber in a fixed position and the foil itself will be moved in the XY directions by two vacuum feedthroughs. These will help to avoid the above mentioned issues due to lack of a vacuum window, fixed emitters, higher uv power absorption, and a fixed IR camera position.

Drapiko, E.; Peterson, B. [National Institute for Fusion Science, 322-6 Oroshi-cho, Toki 509-5292 (Japan); Alekseev, A. [TRINITI OFTR, Troitsk, Moscow Region 142190 (Russian Federation); Seo, D. C. [National Fusion Research Institute, Daejeon 305-333 (Korea, Republic of)

2010-10-15

112

Design of deep ultraviolet light-emitting diodes with staggered AlGaN quantum wells  

NASA Astrophysics Data System (ADS)

The AlGaN-based deep ultraviolet light-emitting diodes (UV LEDs) with specific design of staggered AlGaN quantum wells are investigated numerically. The proposed UV LEDs with Al0.45Ga0.55N-Al0.5Ga0.5N-Al0.45Ga0.55N and Al0.5Ga0.5N-Al0.45Ga0.55N-Al0.5Ga0.5N staggered quantum well layers exhibit significant improvement for the light output power and carrier injection efficiency compared with the conventional AlGaN UV LED. The enhanced performance of the designed LEDs is explained by the simulated distribution of carrier concentration, radiative recombination rate and wave function overlap in the quantum wells.

Yang, G. F.; Xie, F.; Dong, K. X.; Chen, P.; Xue, J. J.; Zhi, T.; Tao, T.; Liu, B.; Xie, Z. L.; Xiu, X. Q.; Han, P.; Shi, Y.; Zhang, R.; Zheng, Y. D.

2014-08-01

113

Performance of high-power laser diode arrays for spaceborne lasers.  

PubMed

The adequacy of commercial quasi-continuous high-power laser diode arrays (HPLDAs) as pump sources for spaceborne lasers has been assessed by endurance tests up to 3 x 10(9) shots under various stress conditions, vacuum operation up to 0.36 x 10(9) shots, and proton radiation tests. Observations of the evolution of the electro-optic parameters and of the near-field patterns of the HPLDAs during endurance tests have revealed that some diode bars could reach the required lifetime of a multibillion shots, suggesting how to build long lifetime HPLDAs by proper selection of the diode bars. The robustness of the HPLDAs against the proton environment experienced in a typical low Earth orbit has been checked. Finally, high-power laser diode arrays have been operated under vacuum, showing a behavior similar to that of HPLDAs operating in atmospheric conditions. PMID:16855676

Durand, Yannig; Culoma, Alain; Meynart, Roland; Pinsard, Jean-Luc; Volluet, Gerard

2006-08-01

114

Long-Term Performance Tests on Laser Diode Arrays for the Current and Future Space Missions  

Microsoft Academic Search

NASA is conducting a series of component-level tests, to better understand the effects of a space-based environment on the operation of diode-pumped, solid state lasers simulating the unique and harsh environment of launch, vacuum and radiation exposure of a typical mission. We will report on our continuing work on high-power, laser- diode arrays which are used as an energy source

Aleksey Vasilyev; Elisavet Troupaki; Nasir B. Kashem; Mark A. Stephen

115

Fiber optic coupling of a microlens conditioned, stacked semiconductor laser diode array  

DOEpatents

The output radiation from the two-dimensional aperture of a semiconductor laser diode array is efficiently coupled into an optical fiber. The two-dimensional aperture is formed by stacking individual laser diode bars on top of another in a "rack and stack" configuration. Coupling into the fiber is then accomplished using individual microlenses to condition the output radiation of the laser diode bars. A lens that matches the divergence properties and wavefront characteristics of the laser light to the fiber optic is used to focus this conditioned radiation into the fiber.

Beach, Raymond J. (Livermore, CA); Benett, William J. (Livermore, CA); Mills, Steven T. (Antioch, CA)

1997-01-01

116

Improved performance of high average power semiconductor arrays for applications in diode pumped solid state lasers  

SciTech Connect

The average power performance capability of semiconductor diode laser arrays has improved dramatically over the past several years. These performance improvements, combined with cost reductions pursued by LLNL and others in the fabrication and packaging of diode lasers, have continued to reduce the price per average watt of laser diode radiation. Presently, we are at the point where the manufacturers of commercial high average power solid state laser systems used in material processing applications can now seriously consider the replacement of their flashlamp pumps with laser diode pump sources. Additionally, a low cost technique developed and demonstrated at LLNL for optically conditioning the output radiation of diode laser arrays has enabled a new and scalable average power diode-end-pumping architecture that can be simply implemented in diode pumped solid state laser systems (DPSSL`s). This development allows the high average power DPSSL designer to look beyond the Nd ion for the first time. Along with high average power DPSSL`s which are appropriate for material processing applications, low and intermediate average power DPSSL`s are now realizable at low enough costs to be attractive for use in many medical, electronic, and lithographic applications.

Beach, R.; Emanuel, M.; Benett, W.; Freitas, B.; Ciarlo, D.; Carlson, N.; Sutton, S.; Skidmore, J.; Solarz, R.

1994-01-01

117

Linear laser diode arrays for improvement in optical disk recording for space stations  

NASA Technical Reports Server (NTRS)

The design and fabrication of individually addressable laser diode arrays for high performance magneto-optic recording systems are presented. Ten diode arrays with 30 mW cW light output, linear light vs. current characteristics and single longitudinal mode spectrum were fabricated using channel substrate planar (CSP) structures. Preliminary results on the inverse CSP structure, whose fabrication is less critically dependent on device parameters than the CSP, are also presented. The impact of systems parameters and requirements, in particular, the effect of feedback on laser design is assessed, and techniques to reduce feedback or minimize its effect on systems performance, including mode-stabilized structures, are evaluated.

Alphonse, G. A.; Carlin, D. B.; Connolly, J. C.

1990-01-01

118

Improving Lifetime of Quasi-CW Laser Diode Arrays for Pumping 2-Micron Solid State Lasers  

NASA Technical Reports Server (NTRS)

Operating high power laser diode arrays in long pulse regime of about 1 msec, which is required for pumping 2-micron thulium and holmium-based lasers, greatly limits their useful lifetime. This paper describes performance of laser diode arrays operating in long pulse mode and presents experimental data on the active region temperature and pulse-to-pulse thermal cycling that are the primary cause of their premature failure and rapid degradation. This paper will then offer a viable approach for determining the optimum design and operational parameters leading to the maximum attainable lifetime.

Amzajerdian, Farzin; Meadows, Byron L.; Baker, Nathaniel R.; Barnes, Bruce W.; Singh, Upendra N.; Kavaya, Michael J.

2007-01-01

119

Efficient side lobe suppression of laser diode arrays  

NASA Astrophysics Data System (ADS)

An optical technique is described which converts multilobed far-field patterns from in-phase laser arrays into a single-lobed pattern. The technique redistributes the output light from the laser array to produce a uniformly illuminated aperture. This filled aperture produces negligible side lobes, and efficiently channels the array power into the main lobe. Experiments performed on a ten-element Y-guide laser array show an increase in main lobe power from 51 to 90 percent of the total array power.

Leger, James R.; Swanson, Gary J.; Holz, Michael

1987-04-01

120

LASERS: Investigation of linear and two-dimensional arrays of semiconductor laser diodes in an external cavity  

Microsoft Academic Search

Linear and two-dimensional arrays of semiconductor laser diodes were investigated in an external cavity with mirrors of various curvatures. The principle characteristics of the output radiation were determined and feedback optimisation of the investigated system with a mirror (focal length F=1 cm) was carried out. This mirror made lasing possible for 6 diodes in a linear array and for 6

V. V. Apollonov; S. I. Derzhavin; V. I. Kislov; A. A. Kazakov; Yu P. Koval; V. V. Kuz'minov; D. A. Mashkovskii; A. M. Prokhorov

1997-01-01

121

Preliminary demonstration of power beaming with non-coherent laser diode arrays  

SciTech Connect

A preliminary demonstration of free-space electric power transmission has been conducted using non-coherent laser diode arrays as the transmitter and standard silicon photovoltaic cell arrays as the receiver. The transmitter assembly used a high-power-density array of infrared laser diode bars, water cooled via integrated microchannel heat sinks and focused by cylindrical microlenses. The diode array composite beam was refocused by a parabolic mirror over a 10 meter path, and received on a {approximately}15 x 25 cm panel of thinned single crystal high efficiency silicon solar cells. The maximum cell output obtained was several watts, and the cell output was used to drive a small motor. Due to operating constraints and unexpected effects, particularly the high nonuniformity of the output beam, both the distance and total received power in this demonstration were modest. However, the existing transmitter is capable of supplying several hundred watts of light output, with a projected received electric power in excess of 200 watts. The source radiance is approximately 5 x 10{sup 9} W/m{sup 2}-steradian. With the existing 20 cm aperture, useful power transmission over ranges to {approximately}100 meters should be achievable with a DC to DC efficiency of greater than 10%. Non-coherent sources of this type are readily scalable to powers of tens of kilowatts, and with larger apertures can be used directly for power transmission up to several kilometers. Future non-coherent diode laser sources may be suitable for power transmission over hundreds of kilometers. Also, the experience gained with non-coherent arrays will be directly applicable to power beaming systems using coherent diode arrays or other array-type laser sources.

Kare, J T; Militsky, F; Weisberg, A

1999-02-26

122

Preliminary demonstration of power beaming with non-coherent laser diode arrays  

SciTech Connect

A preliminary demonstration of free-space electric power transmission has been conducted using non-coherent laser diode arrays as the transmitter and standard silicon photovoltaic cell arrays as the receiver. The transmitter assembly used a high-power-density array of infrared laser diode bars, water cooled via integrated microchannel heat sinks and focused by cylindrical microlenses. The diode array composite beam was refocused by a parabolic mirror over a 10 meter path, and received on a {approximately}15{times}25&hthinsp;cm panel of thin film high efficiency silicon solar cells. The maximum cell output obtained was several watts, and the cell output was used to drive a small motor. Due to operating constraints and unexpected effects, particularly the high nonuniformity of the output beam, both the distance and total received power in this demonstration were modest. However, the existing transmitter is capable of supplying several hundred watts of light output, with a projected received electric power in excess of 200 watts. The source radiance is approximately 5{times}10{sup 9}&hthinsp;W/m{sup 2}-steradian. With the existing 20 cm aperture, useful power transmission over ranges to {approximately}100 meters should be achievable with a DC to DC efficiency of greater than 10{percent}. Non-coherent sources of this type are readily scalable to powers of tens of kilowatts, and with larger apertures can be used directly for power transmission up to several kilometers. Future non-coherent diode laser sources may be suitable for power transmission over hundreds of kilometers. Also, the experience gained with non-coherent arrays will be directly applicable to power beaming systems using coherent diode arrays or other array-type laser sources. {copyright} {ital 1999 American Institute of Physics.}

Kare, J.T. [Kare Technical Consulting, 222 Canyon Lakes Pl., San Ramon, California 94583 (United States); Mitlitsky, F.; Weisberg, A. [Lawrence Livermore National Laboratory, L-174, P.O. Box 808, Livermore, California 94551 (United States)

1999-01-01

123

Preliminary demonstration of power beaming with non-coherent laser diode arrays  

NASA Astrophysics Data System (ADS)

A preliminary demonstration of free-space electric power transmission has been conducted using non-coherent laser diode arrays as the transmitter and standard silicon photovoltaic cell arrays as the receiver. The transmitter assembly used a high-power-density array of infrared laser diode bars, water cooled via integrated microchannel heat sinks and focused by cylindrical microlenses. The diode array composite beam was refocused by a parabolic mirror over a 10 meter path, and received on a ~15×25 cm panel of thin film high efficiency silicon solar cells. The maximum cell output obtained was several watts, and the cell output was used to drive a small motor. Due to operating constraints and unexpected effects, particularly the high nonuniformity of the output beam, both the distance and total received power in this demonstration were modest. However, the existing transmitter is capable of supplying several hundred watts of light output, with a projected received electric power in excess of 200 watts. The source radiance is approximately 5×109 W/m2-steradian. With the existing 20 cm aperture, useful power transmission over ranges to ~100 meters should be achievable with a DC to DC efficiency of greater than 10%. Non-coherent sources of this type are readily scalable to powers of tens of kilowatts, and with larger apertures can be used directly for power transmission up to several kilometers. Future non-coherent diode laser sources may be suitable for power transmission over hundreds of kilometers. Also, the experience gained with non-coherent arrays will be directly applicable to power beaming systems using coherent diode arrays or other array-type laser sources.

Kare, Jordin T.; Mitlitsky, Fred; Weisberg, Andrew

1999-01-01

124

A Lunar Optical-Ultraviolet-Infrared Synthesis Array (LOUISA)  

NASA Technical Reports Server (NTRS)

This document contains papers presented at a workshop held to consider 'optical ultraviolet infrared' interferometric observations from the moon. Part 1 is an introduction. Part 2 is a description of current and planned ground-based interferometers. Part 3 is a description of potential space-based interferometers. Part 4 addresses the potential for interferometry on the moon. Part 5 is the report of the workshop's working groups. Concluding remarks, summary, and conclusions are presented in Part 6.

Burns, Jack O. (editor); Johnson, Stewart W. (editor); Duric, Nebojsa (editor)

1992-01-01

125

Coherent addition of high power laser diode array with a V-shape external Talbot cavity.  

PubMed

We designed a V-shape external Talbot cavity for a broad-area laser diode array and demonstrated coherent laser beam combining at high power with narrow spectral linewidth. The V-shape external Talbot cavity provides good mode-discrimination and does not require a spatial filter. A multi-lobe far-field profile generated by a low filling-factor phase-locked array is confirmed by our numerical simulation. PMID:19065232

Liu, B; Liu, Y; Braiman, Y

2008-12-01

126

Efficient Side Lobe Suppression of Laser Diode Arrays.  

National Technical Information Service (NTIS)

An optical technique is described which converts multilobed far-field patterns from in-phase laser arrays into a single-lobed pattern. The technique redistributes the output light from the laser array to produce a uniformly illuminated aperture. This fill...

J. R. Leger G. J. Swanson M. Holz

1987-01-01

127

By-pass diode design, application and reliability studies for solar cell arrays  

NASA Astrophysics Data System (ADS)

A planar-diffused structure is described for use as an unencapsulated by-pass or shunt diode in solar cell arrays. Design features result in reliable performance, low fabrication cost and ease of handling during assembly. Special consideration is given to heat dissipation related to the manner in which the diodes are mounted in the array. Operating life-test curves are presented which indicate excellent stability for continuous current levels as high as 8 amperes at a panel temperature of 60 C. Forward voltage drop for these diodes is less than 800 mV at 2.5 amperes and the reverse current is in the order of microamperes at 7 volts.

Giuliano, M.; Starley, D.; Warfield, D.; Schuyler, T.

128

Performance of a TiN-coated monolithic silicon pin-diode array under mechanical stress  

NASA Astrophysics Data System (ADS)

The Karlsruhe Tritium Neutrino Experiment (KATRIN) will detect tritium ?-decay electrons that pass through its electromagnetic spectrometer with a highly segmented monolithic silicon pin-diode focal-plane detector (FPD). This pin-diode array will be on a single piece of 500-?m-thick silicon, with contact between titanium nitride (TiN)-coated detector pixels and front-end electronics made by spring-loaded pogo pins. The pogo pins will exert a total force of up to 50 N on the detector, deforming it and resulting in mechanical stress up to 50 MPa in the silicon bulk. We have evaluated a prototype pin-diode array with a pogo-pin connection scheme similar to the KATRIN FPD. We find that pogo pins make good electrical contact to TiN and observe no effects on detector resolution or reverse-bias leakage current which can be attributed to mechanical stress.

VanDevender, B. A.; Bodine, L. I.; Myers, A. W.; Amsbaugh, J. F.; Howe, M. A.; Leber, M. L.; Robertson, R. G. H.; Tolich, K.; Van Wechel, T. D.; Wall, B. L.

2012-05-01

129

Discrete spectrum terahertz imaging using bow-tie diodes: optimized antenna designs and arrays  

NASA Astrophysics Data System (ADS)

Optimization routes to optimize the operation of InGaAs bow-tie diodes were demonstrated using simulations based on 3D finite-difference time-domain method. Calculations of the electromagnetic field amplitude distribution in a detector plane were performed. Three types of designs - bow-tie diode itself, log-periodic antenna and log-periodic antenna coupled with the bow-tie diode were analyzed; it was determined that frequency properties of such antennacoupled device can be tuned via variation of antenna shape and size. Multi-pixel InGaAs bow-tie diodes arrays of different designs - narrow band and broadband operation - were designed and fabricated. They were demonstrated to be well suited for continuous wave room temperature spectroscopic terahertz imaging at 0.58 THz and at 1.63 THz.

Minkevi?ius, Linas; Madeikis, Karolis; Kašalynas, Irmantas; Venckevi?ius, Rimvydas; Seliuta, Dalius; TamošiÅ«nas, Vincas; Valušis, Gintaras

2013-09-01

130

Geometrical Transformation of Linear Diode-Laser Arrays for Longitudinal Pumping of Solid-State Lasers.  

National Technical Information Service (NTIS)

A 200-stripe linear diode-laser array is geometrically transformed into a two-dimensional, symmetric virtual source with symmetric divergence to end-pump a Nd:YAG laser. The geometrical transformation is performed by two planes of diffractive optical elem...

J. R. Leger W. C. Goltsos

1992-01-01

131

High power external cavity laser diode arrays for the generation of hyperpolarized noble gases  

Microsoft Academic Search

Hyperpolarized noble gas magnetic resonance imaging promises to be a useful medical diagnostic tool due to its ability to image airways and brain function. A current limitation to widespread use is the time needed to generate gas quantities large enough for clinical patient imaging. Here I investigate line-narrowing of laser diode arrays in order to optimize the generation of hyperpolarized

Gregory Paul Blasche

2004-01-01

132

Analysis of the phase-locked laser diode array with an external cavity  

NASA Astrophysics Data System (ADS)

The nonlinear equations describing the steady state of the laser diode array (LDA) positioned inside an external cavity have been given. The relation between the photon density and the carrier density in the steady state has been reviewed. The characteristics of the steady state when the LDA operates in the in-phase mode and out-phase mode have been studied.

Zhang, Liping; Dou, Ruhai; Chen, Jianguo

2007-12-01

133

Characteristics of Ultraviolet Laser Diodes Composed of Quaternary AlxInyGa(1-x-y)N  

Microsoft Academic Search

Ultraviolet (UV) laser diodes (LDs) whose active layers were composed of quaternary AlxInyGa(1-x-y)N were grown on epitaxially laterally overgrown GaN substrates by a metalorganic chemical vapor deposition method. We investigated the Al and In mole fractions dependence of LD characteristics in the UV region. The emission wavelength of the LDs whose active layers consisted of Al0.03In0.02Ga0.95N single quantum well (SQW)

Shin-Ichi Nagahama; Tomoya Yanamoto; Masahiko Sano; Takashi Mukai

2001-01-01

134

Development and future of ultraviolet light-emitting diodes: UV-LED will replace the UV lamp  

NASA Astrophysics Data System (ADS)

Ultraviolet light-emitting diodes (UV-LEDs) have started replacing UV lamps. The power per LED of high-power LED products has reached 12 W (14 A), which is 100 times the values observed ten years ago. In addition, the cost of these high-power LEDs has been decreasing. In this study, we attempt to understand the technologies and potential of UV-LEDs.

Muramoto, Yoshihiko; Kimura, Masahiro; Nouda, Suguru

2014-06-01

135

Growth and characterization of blue and near-ultraviolet light-emitting diodes on bulk GaN  

Microsoft Academic Search

Blue and near-ultraviolet (UV) InGaN\\/GaN multiple-quantum-well light-emitting diodes (LEDs) were grown on GaN and sapphire substrates using metalorganic chemical vapor deposition. The homoepitaxial LEDs exhibited greatly improved microstructural and electrical properties compared to the devices grown on sapphire. As a result of defect reduction, the reverse-bias leakage current was reduced by more than six orders of magnitude. At forward bias,

X. A. Cao; Stephen F. LeBoeuf; Stephen D. Arthur; Danielle W. Merfeld; Mark P. D'Evelyn

2004-01-01

136

Blue and near-ultraviolet light-emitting diodes on free-standing GaN substrates  

Microsoft Academic Search

Blue and near-ultraviolet (UV) InGaN\\/GaN multiple-quantum-well light-emitting diodes (LEDs) with peak emission at 465 nm and 405 nm, respectively, were grown on GaN and sapphire substrates. The densities of surface and bulk defects in the homoepitaxially grown LEDs were substantially reduced, leading to a decrease in reverse currents by more than six orders of magnitude. At a typical operating current

X. A. Cao; S. F. LeBoeuf; M. P. D’Evelyn; S. D. Arthur; J. Kretchmer; C. H. Yan; Z. H. Yang

2004-01-01

137

Advantages of GaN Substrates in InAlGaN Quaternary Ultraviolet-Light-Emitting Diodes  

Microsoft Academic Search

We fabricated InAlGaN quaternary ultraviolet (UV)-light-emitting diodes (LEDs) on GaN substrates with a low dislocation density and on GaN templates consisting of n-GaN on sapphire substrates, and compared the characteristics of these LEDs. A UV LED on a GaN substrate showed a considerably higher output power than that on a GaN template and no saturation even at an injection current

Katsushi Akita; Takao Nakamura; Hideki Hirayama

2004-01-01

138

Influence of Electron Tunneling Barriers on the Performance of InGaN-GaN Ultraviolet Light-Emitting Diodes  

Microsoft Academic Search

InGaN-GaN multiple quantum well (MQW) ultraviolet (UV) light-emitting diodes (LEDs) with and without n-AlGaN electron tunneling barriers (ETBs), grown on sapphire substrates by metal organic chemical vapor deposition (MOCVD), are characterized by comparison with device simulation results. Compared with a conventional LED without the ETB, one of the proposed LEDs with the optimized ETB shows an 11% increase in normalized

K. C. Kim; Y. C. Choi; D. H. Kim; T. G. Kim; S. H. Yoon; C. S. Sone; Y. J. Park

2004-01-01

139

Physics of aligned arrays of single-walled NTs: From transistor to diode applications  

NASA Astrophysics Data System (ADS)

NTs have been originally proposed as a 1D high mobility semiconductor material for field-effect transistors (FET). This format is though appeared to be less practical due to low values of the currents through a single NT channel. On contrary, NT massive parallel arrays have already found implementation in flexible and RF electronics. Can we think of NT arrays being another semiconductor thin film materials? Where does the conventional knowledge apply for NT parallel array devices? This talk discusses specialized aspects of physics of electronic and optoelectronic device prototypes and presents recent results for NT FETs and LEDs (light-emitting diode) in parallel array geometries. Cross-talk between individual NTs in the array allows to beat the statistical "noise" in the device properties which appears due to randomized NT distribution in the array. Although, taking this into account, device-level characteristics should be used with a care to extract a single NT physical parameters.

Rotkin, Slava V.; Rogers, John A.

2011-03-01

140

Passive coherent combination of a diode laser array with 35 elements.  

PubMed

A monolithic diode laser array with 35 elements is operated as a coherent array through the use of a Self-Fourier cavity. By analyzing the far field interference pattern, the coherence was measured to be 0.57 with all 35 elements operating and was measured to be approximately constant for arrays with greater than 15 elements. These results are in rough agreement with previous analyses which predict a coherence equal to 0.65 for very large arrays of passively coupled laser elements and demonstrate how the use of regenerative feedback benefits the passive phasing of coherent laser arrays. These results demonstrate that it is possible to circumvent previous cold cavity theories that predict poor phasing properties for arrays with greater than ~10 elements. PMID:24718215

Corcoran, Christopher J; Durville, Frederic

2014-04-01

141

Buried graphene electrodes on GaN-based ultra-violet light-emitting diodes  

NASA Astrophysics Data System (ADS)

We report that the oxidation of graphene-based highly transparent conductive layers to AlGaN/GaN/AlGaN ultra-violet (UV) light-emitting diodes (LEDs) was suppressed by the use of SiNX passivation layers. Although graphene is considered to be an ideal candidate as the transparent conductive layer to UV-LEDs, oxidation of these layers at high operating temperatures has been an issue. The oxidation is initiated at the un-saturated carbon atoms at the edges of the graphene and reduces the UV light intensity and degrades the current-voltage (I-V) characteristics. The oxidation also can occur at defects, including vacancies. However, GaN-based UV-LEDs deposited with SiNX by plasma-enhanced chemical vapor deposition showed minimal degradation of light output intensity and I-V characteristics because the graphene-based UV transparent conductive layers were shielded from the oxygen molecules. This is a simple and effective approach for maintaining the advantages of graphene conducting layers as electrodes on UV-LEDs.

Kim, Byung-Jae; Lee, Chongmin; Mastro, Michael A.; Hite, Jennifer K.; Eddy, Charles R.; Ren, Fan; Pearton, Stephen J.; Kim, Jihyun

2012-07-01

142

High Output Power 365 nm Ultraviolet Light Emitting Diode of GaN-Free Structure  

NASA Astrophysics Data System (ADS)

We have fabricated high-power ultraviolet (UV) light emitting diodes (LEDs). Epi-layers of UV LEDs were grown on high-quality GaN templates with sapphire substrates, and then the GaN templates and the sapphire substrates were removed by using laser-induced liftoff and polishing techniques in order to reduce the absorption of UV light by the GaN layer. As a result, we obtained the GaN-free UV LEDs. When this UV LED was operated at a forward-bias pulsed current of 500 mA at room temperature (RT), the peak wavelength, the output power (Po), the operating voltage (Vf) and the external quantum efficiency (?ex) were 365 nm, 118 mW, 4.9 V and 6.9%, respectively. On the other hand, at a forward-bias direct current of 500 mA at RT, Po, Vf and ?ex were 100 mW, 4.6 V and 5.9%, respectively.

Morita, Daisuke; Sano, Masahiko; Yamamoto, Masashi; Murayama, Takashi; Nagahama, Shin-ichi; Mukai, Takashi

2002-12-01

143

Laser processing of gallium nitride-based light-emitting diodes with ultraviolet picosecond laser pulses  

NASA Astrophysics Data System (ADS)

The fabrication of optoelectronic devices such as light-emitting diodes (LEDs) typically involves photolithography steps, requiring specific lithography masks. This approach is expensive, inflexible and time consuming, in particular for prototyping. Therefore it would be attractive to replace these steps by direct writing techniques such as laser processing, which would speed up, for example the development and prototyping of new devices. Picosecond lasers provide a universal tool for material processing. Due to the short pulse length, material is removed by a process called "cold ablation," with minimal thermal damage to neighboring regions. As a result, better-defined structures with smoother and cleaner side walls can be fabricated compared to nanosecond-pulsed laser-based processing. We report on fully laser-processed planar gallium nitride-based LEDs fabricated using only ps laser processing for pattern definition and material removal. On the bare semiconductor wafer, isolation trenches and mesa structures are formed directly by ultraviolet ps laser pulse writing. For the direct deposition of patterned ohmic contact metallizations, the ps laser fabrication and subsequent use of high-resolution shadow masks is presented. Finally, the ps laser-processed LEDs are electrically and optically characterized and their characteristics compared with those of conventionally fabricated mesa LEDs.

Moser, Rüdiger; Kunzer, Michael; Goßler, Christian; Köhler, Klaus; Pletschen, Wilfried; Schwarz, Ulrich T.; Wagner, Joachim

2012-11-01

144

Investigation of ZnO-based ultraviolet light-emitting diodes  

NASA Astrophysics Data System (ADS)

Recently, ZnO-based semiconductors have been deposited on various substrates using various methods. Furthermore, they were used in ultraviolet light-emitting diodes (UVLEDs) due to inherent properties including wide direct bandgap and high binding energy. In this work, two different deposition systems were utilized to deposit the ZnO-based films. The resulted films were applied to fabricate the ZnO-based UVLEDs. Firstly, the high quality i-ZnO films were deposited as the active layer by using the vapor cooling condensation system to enhance the internal quantum efficiency. Secondly, the double-heterostructured MgZnO/ZnO/MgZnO layers were deposited as the active layer at low temperature using the vapor cooling condensation system to enhance light intensity. Furthermore, various component ratios of i- MgZnO and i-MgBeZnO films were deposited using a radio frequency (RF) magnetron co-sputter system. Consequently, the deposited films with various energy bandgaps were stacked alternately to form the active layer of multiple-quantum well (MQW) UVLEDs. The light emitting intensity of MQW UVLEDs was better than that of the traditional p-i-n UVLEDs. This phenomenon was attributed to the carrier confinement in well layers and improvement probability of radiative recombination.

Lee, Ching-Ting; Chang, Hao-Yu

2014-03-01

145

Polarization of III-nitride blue and ultraviolet light-emitting diodes  

NASA Astrophysics Data System (ADS)

Polarization-resolved electroluminescence studies of III-nitride blue and ultraviolet (UV) light-emitting diodes (LEDs) were performed. The LEDs were fabricated on nitride materials grown by metalorganic chemical vapor deposition on sapphire substrates (0001). Transverse electric (TE) polarization dominates in the InGaN/GaN quantum-well (QW) blue LEDs (?'=458 nm), whereas transverse magnetic (TM) polarization is dominant in the AlInGaN QW UV LEDs (?=333 nm). For the case of edge emission in blue LEDs, a ratio (r=I?/I?) of about 1.8:1 was observed between the EL intensities with polarization E?c (TE mode) and E?c (TM mode), which corresponds to a degree of polarization ~0.29. The UV LEDs exhibit a ratio r of about 1:2.3, corresponding to a degree of polarization ~0.4. This is due to the fact that the degree of polarization of the bandedge emission of the AlxInyGa1-x-yN active layer changes with Al concentration. The low emission efficiency of nitride UV LEDs is partly related to this polarization property. Possible consequences and ways to enhance UV emitter performances related to this unique polarization property are discussed.

Shakya, J.; Knabe, K.; Kim, K. H.; Li, J.; Lin, J. Y.; Jiang, H. X.

2005-02-01

146

Tunnel-injection GaN quantum dot ultraviolet light-emitting diodes  

NASA Astrophysics Data System (ADS)

We demonstrate a GaN quantum dot ultraviolet light-emitting diode that uses tunnel injection of carriers through AlN barriers into the active region. The quantum dot heterostructure is grown by molecular beam epitaxy on AlN templates. The large lattice mismatch between GaN and AlN favors the formation of GaN quantum dots in the Stranski-Krastanov growth mode. Carrier injection by tunneling can mitigate losses incurred in hot-carrier injection in light emitting heterostructures. To achieve tunnel injection, relatively low composition AlGaN is used for n- and p-type layers to simultaneously take advantage of effective band alignment and efficient doping. The small height of the quantum dots results in short-wavelength emission and are simultaneously an effective tool to fight the reduction of oscillator strength from quantum-confined Stark effect due to polarization fields. The strong quantum confinement results in room-temperature electroluminescence peaks at 261 and 340 nm, well above the 365 nm bandgap of bulk GaN. The demonstration opens the doorway to exploit many varied features of quantum dot physics to realize high-efficiency short-wavelength light sources.

Verma, Jai; Kandaswamy, Prem Kumar; Protasenko, Vladimir; Verma, Amit; Grace Xing, Huili; Jena, Debdeep

2013-01-01

147

Cavity ring-down spectroscopy with diode array  

NASA Astrophysics Data System (ADS)

A cavity ring-down spectroscopy with off-axis multipass cell and space separated detectors is suggested to record absorption spectrum without modulation of the diode laser intensity. The spectral resolution is ~0.0003 cm -1. The whole spectrum is obtained for a one continuous tuning of the laser frequency for ~20 ms. Apart from conventional CRDS a really needed rise time of the detectors are 1000 times slower. The recording of the whole spectrum for a one measurement give an additional possibilities of signal extraction at relatively high noise. The technique is applied to absorption measurement of NO2 in atmosphere.

Nikolaev, Igor V.; Ochkin, Vladimir N.; Spiridonov, Maxim V.; Tskhai, Sergei N.

2006-12-01

148

Design of microlens illuminated aperture array fabricated by aligned ultraviolet imprinting process for optical read only memory card system  

Microsoft Academic Search

A microlens illuminated aperture array (MLIAA) was designed for the multiprobe optical read only memory card system. As a method to integrate the microlens array (MLA) with the aperture array containing 1000×1000 apertures, an aligned ultraviolet imprinting process was used to satisfy the system objectives of reduced focal length and reduced spot size. An analysis using diffraction theory was performed

Hongmin Kim; Jeeseung Lee; Jiseok Lim; Seok-Min Kim; Shinill Kang; Young-Joo Kim; Christopher Busch

2006-01-01

149

Thermal properties of InGaN laser diodes and arrays  

NASA Astrophysics Data System (ADS)

Junction temperature of a laser diode (LD) determines the value of threshold current, maximum achievable power and device lifetime. In this work we studied this parameter by a method of comparing current-voltage characteristics measured under pulse bias (at various temperatures) with DC characteristic obtained at room temperature. As exemplary devices we chose various laser diode arrays and single emitter laser with different substrate thickness. The results show, that the primary factor determining thermal resistance of the device is the chip's surface, which means, that a dominating mechanism is related with a heat transfer between the chip and the heat sink.

Sta?czyk, Szymon; Kafar, Anna; Targowski, Grzegorz; Wi?niewski, Przemek; Makarowa, Irina; Suski, Tadeusz; Perlin, Piotr

2013-03-01

150

Qualification Testing of Laser Diode Pump Arrays for a Space-Based 2-micron Coherent Doppler Lidar  

NASA Technical Reports Server (NTRS)

The 2-micron thulium and holmium-based lasers being considered as the transmitter source for space-based coherent Doppler lidar require high power laser diode pump arrays operating in a long pulse regime of about 1 msec. Operating laser diode arrays over such long pulses drastically impact their useful lifetime due to the excessive localized heating and substantial pulse-to-pulse thermal cycling of their active regions. This paper describes the long pulse performance of laser diode arrays and their critical thermal characteristics. A viable approach is then offered that allows for determining the optimum operational parameters leading to the maximum attainable lifetime.

Amzajerdian, Farzin; Meadows, Byron L.; Baker, Nathaniel R.; Barnes, Bruce W.; Singh, Upendra N.; Kavaya, Michael J.

2007-01-01

151

Performance of a diode-array spectrometer in DOAS applications  

Microsoft Academic Search

A photodiode-array spectrometer for the detection of atmospheric trace gases has been developed to take diffuse solar zenith and, using a n artificial light source, horizontal long path measurements. Of the numerous factors involved in determining the minimum amount of a detectable gas, including its spectral characteristics, atmospheric phenomena and the algorithm used, the present study examines only the features

Giorgio Giovanelli; Fabrizio Ravegnani; R. Becca; Franco Evangelisti; Paolo Bonasoni; Ivan Kostadinov

1997-01-01

152

Transient thermal behavior of high power diode laser arrays  

Microsoft Academic Search

Reliability and lifetime of high power laser arrays are governed by their thermal properties. Thus the understanding of the thermal behavior such as thermal transients as well as the optimization of laser chips and mounting are key features for obtaining improved devices. We present numerical simulations of the active layer temperature employing the finite element method (FEM). Both continuous wave

Roland Puchert; Artur Bärwolff; M. Voss; U. Menzel; J. W. Tomm; J. Luft

2000-01-01

153

Application of three-step epitaxial process to dual trench epitaxial diode array.  

PubMed

The application of three-step Epitaxial (EPI) process to dual trench epitaxial diode array for high density phase change random access memory (PCRAM) was reported in this paper. With three-step EPI process condition, both vertical and lateral Arsenic auto-doping were suppressed effectively from Arsenic heavily-doped substrate. It was found that EPI layer (- 300 nm) with high-quality single crystalline and good thickness uniformity within 200 mm diameter wafer could be achieved. It was also found that both lateral and vertical Arsenic auto-doping concentration could be reduced by 2-3 orders by adding high temperature and low deposition rate EPI step before main EPI process, as compared to the conventional CVD EPI process. As a result, diode breakdown voltage was improved above 11 V and the On/Off current ratio of diode is greater than 9 orders of magnitude. PMID:23646599

Zhang, Chao; Wu, Guan-Ping; Song, Zhi-Tang; Liu, Bo; Wang, Lian-Hong; Liu, Yan; Yang, Zuoya; Feng, Songlin

2013-02-01

154

Single-lobe 'Y' coupled laser diode arrays  

NASA Astrophysics Data System (ADS)

'Y' coupled laser arrays have been fabricated with flared waveguides at the output facet to expand the near-field spot and increase the near-field fill factor to greater than 80 percent. The far-field radiation pattern is predominantly single-lobe, and power outputs of 150 mW CW have been obtained with threshold currents as low as 130 mA.

Welch, D. F.; Cross, P. S.; Scifres, D. R.; Streifer, W.

1987-03-01

155

The development and test of sealed multi-anode detectors based on microchannel array plates for use at ultraviolet wavelengths  

Microsoft Academic Search

An ultraviolet photon-counting detection system which uses a microchannel array plate and a cesium iodide photocathode is described. The construction, mode of operation, and preliminary evaluation results are discussed.

J. G. Timothy

1977-01-01

156

Application of ultraviolet light-emitting diode photocatalysis to remove volatile organic compounds from indoor air.  

PubMed

Photocatalytic oxidation (PCO) is a promising technology for indoor air purification due to low operating cost, potentially long service life, and low maintenance. Ultraviolet light-emitting diode (UVLED) is a new concept in the field of PCO, which has several advantages over conventional UV light sources. Limited research has been conducted using UVLED PCO for air treatment. This study demonstrated the potential application of UVLED for the removal of volatile organic compounds (VOCs; toluene and xylene) from indoor air under different operating conditions including flow rate (25-117 cubic feet per minute [cfm]), types of catalysts (Degussa P25, sol-gel TiO2, nitrogen-doped TiO2, clay TiO2, and Bi2O3), LED intensity, and humidity in a continuous reactor. About 7-32% VOC removal occurred depending on the experimental conditions. The results show that UVLED can activate different types of photocatalysts effectively. Implications: This study demonstrates the effectiveness of UVLED in photocatalytic oxidation applied for indoor air cleaning. Several TiO2 catalysts (Degussa P25, sol-gel TiO2, nitrogen-doped TiO2, clay TiO2, and Bi2O3) were used in the reactor to characterize the removal performance of indoor air pollutants, for example, VOCs. This is one of the very few studies that have, to date, examined toluene and xylene removal from indoor air using these catalysts with UVLED in a continuous reactor. The intent is to develop an energy-efficient continuous reaction system to remove VOCs from indoor air. The performance of the system was characterized with respect to air flow rate, humidity, types of catalysts, and light intensity. PMID:23019817

Sharmin, Rifath; Ray, Madhumita B

2012-09-01

157

A laser three-focus velocimeter using an array of laser diodes for simultaneous measurement of particle size and velocity  

Microsoft Academic Search

This paper describes a laser three-focus velocimeter for measurement of particle size and velocity to make the system compact and portable. An array of independently driven laser diodes is used to obtain the stable output of the laser beams without the thermal interference between the laser diodes and to exclude ambiguity of velocity direction. The method measuring velocity and size

Noboru Nakatani; Takanori Oshio; Toshiya Sakabe

1993-01-01

158

LASERS: Investigation of linear and two-dimensional arrays of semiconductor laser diodes in an external cavity  

NASA Astrophysics Data System (ADS)

Linear and two-dimensional arrays of semiconductor laser diodes were investigated in an external cavity with mirrors of various curvatures. The principle characteristics of the output radiation were determined and feedback optimisation of the investigated system with a mirror (focal length F=1 cm) was carried out. This mirror made lasing possible for 6 diodes in a linear array and for 6 × 5 diodes in a two dimensional array. A mirror with F=20 cm ensured lasing of 14 × 15 diodes. A study was made of the spatial coherence effects in the external cavity. These effects were accompanied by the appearance of an interference pattern in the far-field zone. An experimental confirmation was obtained of theoretical estimates of the dimensions of a linear array in which phase locking is possible.

Apollonov, V. V.; Derzhavin, S. I.; Kislov, V. I.; Kazakov, A. A.; Koval', Yu P.; Kuz'minov, V. V.; Mashkovskii, D. A.; Prokhorov, A. M.

1997-10-01

159

Multilevel Diode-Clamped Converter for Photovoltaic Generators With Independent Voltage Control of Each Solar Array  

Microsoft Academic Search

In photovoltaic (PV) power systems where a set of series-connected PV arrays (PVAs) is connected to a conventional two-level inverter, the occurrence of partial shades and\\/or the mismatching of PVAs leads to a reduction of the power generated from its potential maximum. To overcome these problems, the connection of the PVAs to a multilevel diode-clamped converter is considered in this

Sergio Busquets-Monge; Joan Rocabert; Pedro Rodriguez; Salvador Alepuz; Josep Bordonau

2008-01-01

160

Identification of natural dyes in archeological Coptic textiles by liquid chromatography with diode array detection  

Microsoft Academic Search

Reversed-phase HPLC with diode-array UV–Vis spectrophotometric detection has been used for identification of natural dyes in extracts from wool and silk fibres from archeological textiles. The examined objects originate from 4th to 12th Century Egypt and belong to the collection of Early Christian Art of the National Museum in Warsaw. Extraction from fibres was carried out with HCl solution containing

Jowita Orska-Gawry?; Izabella Surowiec; Jerzy Kehl; Hanna Rejniak; Katarzyna Urbaniak-Walczak; Marek Trojanowicz

2003-01-01

161

Pulse buildup dynamics of an actively mode-locked laser diode array in the external cavity  

Microsoft Academic Search

Dynamic pulse evolution characteristics of an actively mode-locked laser diode array in the external cavity have been investigated. Numerical calculations based on modified traveling-wave rate equations reproduce experimentally observed pulse and spectral width evolution and show that the buildup time is about 45 round-trips. We have also performed a theoretical analysis to understand which of the laser operating parameters would

Chi-Luen Wang; Jahn-Chung Kuo; C.-S. Chang; Ci-Ling Pan

1995-01-01

162

Determination of imidacloprid in vegetables by high-performance liquid chromatography with diode-array detection  

Microsoft Academic Search

An HPLC method is described for the determination of imidacloprid residues in vegetables at levels ranging from 0.01 to 0.60 mg\\/kg. The selection of the extraction and clean-up procedure is discussed. Spectral data obtained with diode-array detection allow the identification of imidacloprid residues. Thermospray mass spectrometric studies were carried out in combination with HPLC. The mean recoveries and standard deviations

Amadeo R. Fernandez-Alba; Antonio Valverde; Ana Agüera; Mariano Contreras; Serge Chiron

1996-01-01

163

Laser-diode-array-pumped pulsed Nd:YVO4 minidisk laser  

Microsoft Academic Search

A pulsed Nd:YVO4 mini disc laser pumped by a laser diode array is reported in this paper based on the end-pumping configuration with the linear plane-parallel cavity and the V- folded cavities respectively. The input-output properties and the output beam are characterized, analyzed and compared. The optical-to-optical conversion efficiency is about 51% for the plane-parallel cavity, 48% for the V-folded

Zhuang Zhuo; Tow C. Chong; Chin W. Kwek

1998-01-01

164

A theoretical model for Schottky diodes for excluding the sneak current in cross bar array resistive memory  

Microsoft Academic Search

Kirchhoff’s law was used to examine the electrical specifications of selection diodes, which are essential for suppressing the read interference problems in nano-scale resistive switching cross bar arrays with a high block density. The diode in the cross bar array with a 100 Mb block density should have a reverse\\/forward resistance ratio of > 108, and a forward current density

Gun Hwan Kim; Kyung Min Kim; Jun Yeong Seok; Hyun Ju Lee; Deok-Yong Cho; Jeong Hwan Han; Cheol Seong Hwang

2010-01-01

165

Demonstration of side coupling between high power laser diode array and double-clad fiber using sub-wavelength grating  

Microsoft Academic Search

A sub-wavelength gold-embedded silica binary grating for side coupling light emission from a 976-nm high-power laser diode array into the 400-?m-diameter inner cladding of a double-clad fiber was demonstrated with near 50% overall coupling efficiency. ©2010 Optical Society of America OCIS codes: (050.2770) Gratings; (140.2010) Diode laser arrays; (060.0060) Fiber optics and optical communications. For the realization of high-power fiber

Chieh-Wei Huang; Ding-Wei Huang; Chun-Lin Chang; Dong-Yo Jheng; Kuang-Yu Hsu; Chieh-Hsiung Kuan; Sheng-Lung Huang

2011-01-01

166

Coherent operation of injection-locked monolithic surface-emitting diode laser arrays  

NASA Astrophysics Data System (ADS)

A row of six surface-emitting GaAlAs laser diode arrays was locked in a coupled resonator configuration by means of interconnecting waveguides. An external master oscillator was injected into the first array in order to achieve single longitudinal mode operation and wavelength tunability. Spectral data show that all six devices were locked in a single longitudinal mode, with tunable operation of over 60 A. Far-field fringe visibilities greater than 60 percent were achieved at 100 mW output power.

Jansen, M.; Yang, J. J.; Heflinger, L.; Ou, S. S.; Sergant, M.

1989-06-01

167

Dynamic characteristics of far-field radiation of current modulated phase-locked diode laser arrays  

NASA Astrophysics Data System (ADS)

A versatile and powerful streak camera/frame grabber system for studying the evolution of the near and far field radiation patterns of diode lasers was assembled and tested. Software needed to analyze and display the data acquired with the steak camera/frame grabber system was written and the total package used to record and perform preliminary analyses on the behavior of two types of laser, a ten emitter gain guided array and a flared waveguide Y-coupled array. Examples of the information which can be gathered with this system are presented.

Elliott, R. A.; Hartnett, K.

1987-07-01

168

Geometrical transformation of linear diode-laser arrays for longitudinal pumping of solid-state lasers  

SciTech Connect

A 200-stripe linear diode-laser array is geometrically transformed into a two-dimensional, symmetric virtual source with symmetric divergence to end-pump a Nd:YAG laser. The geometrical transformation is performed by two planes of diffractive optical elements separated by a 2.6-cm gap. Discounting optical losses, a TEM00-mode slope efficiency of 56 percent is demonstrated. Methods of increasing the throughput efficiency of the diffractive elements (currently approximately 50 percent per element) re explored. A theoretical model for estimating the maximum useful pump array size in longitudinally pumped rod and fiber lasers shows that this pump geometry is close to optimum.

Leger, J.R.; Goltsos, W.C.

1992-05-26

169

Modal properties of an external diode-laser-array cavity with diffractive mode-selecting mirrors  

NASA Astrophysics Data System (ADS)

Coupled mode theory is used to describe the behavior of an external laser cavity consisting of a diode laser array and a diffractive mode-selecting mirror. The mirror is designed to establish a uniform-amplitude, uniform-phase fundamental mode. Coupled mode theory is then used to study the behavior of higher-order modes. We show that the maximum discrimination against higher-order modes occurs when the round-trip cavity length satisfies certain Talbot relations. In addition, this high modal discrimination can be maintained for arrays with large numbers of lasers without incurring significant loss in the fundamental mode.

Leger, James R.; Mowry, Greg; Li, Xu

1995-07-01

170

Dynamic characteristics of far-field radiation of current modulated phase-locked diode laser arrays  

NASA Technical Reports Server (NTRS)

A versatile and powerful streak camera/frame grabber system for studying the evolution of the near and far field radiation patterns of diode lasers was assembled and tested. Software needed to analyze and display the data acquired with the steak camera/frame grabber system was written and the total package used to record and perform preliminary analyses on the behavior of two types of laser, a ten emitter gain guided array and a flared waveguide Y-coupled array. Examples of the information which can be gathered with this system are presented.

Elliott, R. A.; Hartnett, K.

1987-01-01

171

Analytical theory of phase-locked arrays of antiguided diode lasers  

NASA Astrophysics Data System (ADS)

A general theory of periodic diode laser arrays is developed in the approximation of an effective complex refractive index described by a step periodic function. Rigorous expressions are derived for the elements of a translation matrix. Explicit expressions are obtained for the near-field and far-field patterns of finite array modes. The concept of 2D (Gamma) -factor and the explicit expression for it are presented. Accurate analytical expressions for key parameters characterizing the resonant and adjacent array modes are obtained for the resonant structure. By using an expansion, the radiation loss versus index-step curve is well approximated near resonance by a parabola, which gives curve half-width at half intensity only 10 to 15 percent less than numerically calculated values. The analogy between the resonant arrays of antiguides and DFB lasers is discussed, and differential equations for the slowly varying envelope are derived.

Napartovich, Anatoly P.; Botez, Dan

1997-06-01

172

In vitro bactericidal effects of near-ultraviolet light from light-emitting diodes on Helicobacter pylori.  

PubMed

We investigated whether near-ultraviolet light emitted from light-emitting diodes (LEDs) effects Helicobacter pylori viability and whether this new method can potentially apply to eradication therapy. Three H. pylori strains were used for near-ultraviolet (UV) LED irradiation experiments. Viability of isolates exposed to near-UV light was compared with controls by counting colony forming units. A time-dependent bactericidal effect of near-UV light was definitely observed. LED irradiation with near-UV light showed effective bactericidal activity against H. pylori strains. Eradication therapy with LED might provide a new avenue of treatment in patients refractory to eradication due to antibiotic resistance and/or adverse effects of antibiotics. PMID:24063529

Okamoto, Takeshi; Nishikawa, Jun; Yanai, Hideo; Nakamura, Hiroki; Takeuchi, Hiroaki; Kurai, Satoshi; Akada, Junko K; Sakaida, Isao

2013-12-01

173

Effect of AlGaN Si-Doped Barrier Layer on Optical Properties of Ultraviolet Light-Emitting Diodes  

NASA Astrophysics Data System (ADS)

InGaN/AlGaN ultraviolet light-emitting diodes (UV LEDs) with AlGaN barriers having various Si doping concentrations are grown by metal--organic chemical vapor deposition. The light output power of UV LEDs was obviously improved as a result of Si doping of the AlGaN barriers. Detail analysis of this improvement by simulation modeling showed that the increase in Si doping concentration in AlGaN barrier is beneficial for increasing electron injection efficiency and simultaneously the radiative recombination distribution.

Lu, Yu-Hsuan; Fu, Yi-Keng; Huang, Shyh-Jer; Su, Yan-Kuin; Xuan, Rong; Pilkuhn, Manfred H.

2013-01-01

174

Ultraviolet laser diodes grown on semipolar (2021) GaN substrates by plasma-assisted molecular beam epitaxy  

NASA Astrophysics Data System (ADS)

We demonstrate ultra-violet laser diodes emitting at 388 nm grown by plasma-assisted molecular beam epitaxy on semipolar (2021)GaN substrates under metal-rich conditions. The threshold current density and voltage of 13.2 kA/cm2 and 10.8 V were measured at room temperature for devices with the laser ridge waveguide oriented along the [1210] direction. We show smooth, atomically flat surface morphology after growth. The excellent structural quality of the laser heterostructure was corroborated by transmission electron microscopy.

Sawicka, M.; Muziol, G.; Turski, H.; Grzanka, S.; Grzanka, E.; Smalc-Koziorowska, J.; Weyher, J. L.; Chèze, C.; Albrecht, M.; Kucharski, R.; Perlin, P.; Skierbiszewski, C.

2013-06-01

175

A photon-counting photodiode array detector for far ultraviolet (FUV) astronomy  

NASA Technical Reports Server (NTRS)

A compact, stable, single-stage intensified photodiode array detector designed for photon-counting, far ultraviolet astronomy applications employs a saturable, 'C'-type MCP (Galileo S. MCP 25-25) to produce high gain pulses with a narrowly peaked pulse height distribution. The P-20 output phosphor exhibits a very short decay time, due to the high current density of the electron pulses. This intensifier is being coupled to a self-scanning linear photodiode array which has a fiber optic input window which allows direct, rigid mechanical coupling with minimal light loss. The array was scanned at a 250 KHz pixel rate. The detector exhibits more than adequate signal-to-noise ratio for pulse counting and event location.

Hartig, G. F.; Moos, H. W.; Pembroke, R.; Bowers, C.

1982-01-01

176

Detector arrays for photometric measurements at soft X-ray, ultraviolet and visible wavelengths  

NASA Technical Reports Server (NTRS)

The construction and modes of operation of the Multi-Anode Microchannel Array (MAMA) detectors are described, and the designs of spectrometers utilizing them are outlined. MAMA consists of a curved microchannel array plate, an opaque photocathode (peak quantum efficiency of 19% at 1216 A), and a multi-anode (either discrete- or coincidence-anode) readout array. Designed for use in instruments on spaceborne telescopes, MAMA can be operated in a windowless configuration in extreme-ultraviolet and soft X-ray wavelengths, or in a sealed configuration at UV and visible wavelengths. Advantages of MAMA include low applied potential (less than 3.0 kV), high gain (greater than 10 to the 6th electrons/pulse), low sensitivity to high-energy charged particles, and immunity to external magnetic fields of less than 500 Gauss

Timothy, J. G.; Mount, G. H.; Bybee, R. L.

1979-01-01

177

High Power Laser Diode Arrays for 2-Micron Solid State Coherent Lidars Applications  

NASA Technical Reports Server (NTRS)

Laser diode arrays are critical components of any diode-pumped solid state laser systems, constraining their performance and reliability. Laser diode arrays (LDAs) are used as the pump source for energizing the solid state lasing media to generate an intense coherent laser beam with a high spatial and spectral quality. The solid state laser design and the characteristics of its lasing materials define the operating wavelength, pulse duration, and power of the laser diodes. The pump requirements for high pulse energy 2-micron solid state lasers are substantially different from those of more widely used 1-micron lasers and in many aspects more challenging [1]. Furthermore, the reliability and lifetime demanded by many coherent lidar applications, such as global wind profiling from space and long-range clear air turbulence detection from aircraft, are beyond the capability of currently available LDAs. In addition to the need for more reliable LDAs with longer lifetime, further improvement in the operational parameters of high power quasi-cw LDAs, such as electrical efficiency, brightness, and duty cycle, are also necessary for developing cost-effective 2-micron coherent lidar systems for applications that impose stringent size, heat dissipation, and power constraints. Global wind sounding from space is one of such applications, which is the main driver for this work as part of NASA s Laser Risk Reduction Program. This paper discusses the current state of the 792 nm LDA technology and the technology areas being pursued toward improving their performance. The design and development of a unique characterization facility for addressing the specific issues associated with the LDAs for pumping 2-micron coherent lidar transmitters and identifying areas of technological improvement will be described. Finally, the results of measurements to date on various standard laser diode packages, as well as custom-designed packages with potentially longer lifetime, will be reported.

Amzajerdian, Farzin; Meadows, Byron; Kavaya, Michael J.; Singh, Upendra; Sudesh, Vikas; Baker, Nathaniel

2003-01-01

178

Laser diode end-pumped efficient coupling system based on microlens arrays  

NASA Astrophysics Data System (ADS)

Efficient pumped coupling is one of the important technologies of diode pumped solid state laser system applying end-pumped structure. This work present a novel pumped coupling optical system based on microlens arrays. In the coupling system, the light of laser diode stack is incident on an imaging microlens array, that cuts the beam into a number of beamlets. Subsequently these beamlets are overlapped in the pumped surface of laser media through an aspheric focusing lens. Then a high homogeneity pump field is realized. Furthermore, for different aspect ratios of the homogenized spot two microlens arrays with crossed cylindrical lenses are used to match different pump field size. Such coupling system was designed by ray tracing method using ZEMAXTM Non-Sequential Components analysis tools. The non-sequential raytracing simulation shows that a 5 × 5 mm2 Top-Hat intensity pump profile was got at a working distance of 40 mm and the homogeneity of the intensity distribution is better than 90%. In comparison with the traditional coupling optical system homogenization by means of microlens arrays is more flexible and requires a reduced number of optical components.

Huang, Feng; Jia, Wenwu; Wang, Yuefeng; Hou, Junyan; Dong, Wei

2009-11-01

179

Chaotic Communication Using Asynchronous Laser Diode Transmitter/Receiver Array with Optical Feedback  

NASA Astrophysics Data System (ADS)

Chaotic secure communication in a chaotic laser diode transmitter/receiver array scheme (CLDTRAS) with optical feedback has been described. It uses an array of several transmitters/receivers consisting of a laser diode (LD) with optical feedback as a transmitter LD and one with optical injection as a receiver LD, and the difference in chaotic dynamics between these two types of transmitter/receiver array is utilized to encode a binary message. The effects of the parameter mismatches between the transmitter and receiver LDs on the bit error rate for CLDTRAS and on the synchronization have been studied and compared with each other. It has been shown that CLDTRAS is hardware-dependent and independent of chaos synchronization. Because communication is achieved with an asynchronous LD transmitter/receiver array, it becomes difficult to forge hardware and eavesdrop with forged hardware. Then, we investigate the bit error rate for CLDTRAS against channel noise to show that it is possible to communicate with smaller bit error than the conventional schemes.

Ebisawa, Satoshi; Komatsu, Shinichi

2007-08-01

180

Message encoding and decoding using an asynchronous chaotic laser diode transmitter receiver array  

NASA Astrophysics Data System (ADS)

We have numerically investigated a chaotic laser diode transmitter-receiver array scheme (CLDTRAS), which is a secure digital communication scheme using a difference between two types of transmitter-receiver array consisting of two self-pulsating laser diodes (LDs), i.e., a receiver LD and a transmitter LD. By analyzing the bit error rate, particularly its dependence on the parameter mismatches of the hardware and channel noise and on the correlation coefficient between a transmitter LD and receiver LD, we examined the problems of sensitivity to parameter mismatches and channel noise and a dependence on chaos synchronization between a transmitter LD and a receiver LD. The former makes communication difficult, and the latter makes it possible for an eavesdropper to estimate the receiver LD using chaos synchronization and to forge the hardware. Then we studied the effects of the bit error rate for various values of the threshold, which determines a binary message, and for various numbers of transmitters-receivers making up a LD transmitter-receiver array. It has been shown that a highly noise-tolerant and hardware-dependent communication scheme can be achieved with the LD transmitter-receiver array, whose transmitter and receiver LDs are asynchronous with respect to each other, by choosing the proper threshold and increasing the number of LD transmitters-receivers. Since it is possible to communicate without chaos synchronization, it becomes difficult to forge hardware and to eavesdrop with the forged hardware even if the key is stolen.

Ebisawa, Satoshi; Komatsu, Shinichi

2007-07-01

181

Message encoding and decoding using an asynchronous chaotic laser diode transmitter-receiver array.  

PubMed

We have numerically investigated a chaotic laser diode transmitter-receiver array scheme (CLDTRAS), which is a secure digital communication scheme using a difference between two types of transmitter-receiver array consisting of two self-pulsating laser diodes (LDs), i.e., a receiver LD and a transmitter LD. By analyzing the bit error rate, particularly its dependence on the parameter mismatches of the hardware and channel noise and on the correlation coefficient between a transmitter LD and receiver LD, we examined the problems of sensitivity to parameter mismatches and channel noise and a dependence on chaos synchronization between a transmitter LD and a receiver LD. The former makes communication difficult, and the latter makes it possible for an eavesdropper to estimate the receiver LD using chaos synchronization and to forge the hardware. Then we studied the effects of the bit error rate for various values of the threshold, which determines a binary message, and for various numbers of transmitters-receivers making up a LD transmitter-receiver array. It has been shown that a highly noise-tolerant and hardware-dependent communication scheme can be achieved with the LD transmitter-receiver array, whose transmitter and receiver LDs are asynchronous with respect to each other, by choosing the proper threshold and increasing the number of LD transmitters-receivers. Since it is possible to communicate without chaos synchronization, it becomes difficult to forge hardware and to eavesdrop with the forged hardware even if the key is stolen. PMID:17579693

Ebisawa, Satoshi; Komatsu, Shinichi

2007-07-10

182

Online Photolytic Optical Gating of Caged Fluorophores in Capillary Zone Electrophoresis Utilizing an Ultraviolet-Light Emitting Diode  

PubMed Central

Photolytic optical gating (POG) facilitates rapid, on-line and highly sensitive analyses, though POG utilizes UV lasers for sample injection. We present a lower-cost, more portable alternative, employing an ultraviolet (UV)-LED array to inject caged fluorescent dyes via photolysis. Utilizing the UV-LED array, labeled amino acids were injected with nanomolar limits of detection (270 ± 30 nM and 250 ± 30 nM for arginine and citrulline, respectively). When normalized for the difference in light intensity, the UV-LED array provides comparable sensitivity to POG utilizing UV lasers. Additionally, the UV-LED array yielded sufficient beam quality and stability to facilitate coupling with Hadamard transformation, resulting in increased sensitivity. This work shows, for the first time, the use of a UV-LED for online POG with comparable sensitivity to conventional laser sources but for lower cost.

Gallagher, Elyssia S.; Comi, Troy J.; Braun, Kevin L.; Aspinwall, Craig A.

2013-01-01

183

Development of ultraviolet electroabsorption modulators and light emitting diodes based on AlGaN alloys  

NASA Astrophysics Data System (ADS)

The research in this dissertation addressed the development of ultraviolet (UV) electroabsorption modulators and ultraviolet light emitting diodes (UV-LEDs), covering the spectral range from 360 to 265 nm. The materials system for both types of devices is the AlGaN alloys, either in bulk or quantum well (QW) form, grown by plasma-assisted molecular beam epitaxy (MBE). Potential applications of these devices either individually or in combination include UV non-line-of-sight free-space-optical communications, UV sensing and spectroscopic systems, Q-switched pulsed lasers, water/air purification and various medical applications. Optical modulators based on cubic III-V semiconductors have been the subject of extensive research over the past several years. Such devices are typically based on the quantum-confined Stark effect to modify the absorption spectrum of multiple-quantum-well active regions. On the other hand, in wurtzite III-Nitride semiconductors, strong electric fields are already present in the quantum wells due to intrinsic and piezoelectric polarizations; as a result, an even greater change in absorption is achievable, especially if the internal fields are compensated by the external bias so that the net field in the quantum wells is reduced. A number of UV electroabsorption modulators based on Schottky barriers on bulk GaN and GaN /AlGaN multiple quantum wells (MQWs) were designed, fabricated and characterized. Record modulation ratio of 30 % was obtained from bulk GaN Schottky barrier modulators at the excitonic resonant energy of 3.45 eV (360 nm) upon the application of 12 V reverse bias. Similarly, record modulation ratio of 43% was obtained from GaN / AlGaN MQWs Schottky barrier modulators at the excitonic resonant energy of 3.48 eV (356 nm) upon the application of 17 V reverse bias. The external quantum efficiency (EQE) of AlGaN based deep UV LEDS is relatively low (˜1% at 270 nm). This is generally attributed to the poor internal quantum efficiency (IQE) of this material system due to the high concentration of line and point defects. In the current work the deep UV-LED structures were grown on inexpensive and widely available sapphire substrates, which resulted in materials with dislocation density of 1010 cm-2. To prevent the non-radiative recombination of the injected electron-hole pairs, the active region of the devices were grown under conditions which lead to band structure potential fluctuations, which lead to exciton localization and thus efficient radiative recombination. Using such a growth method AlGaN MQWs emitting at 265 nm with an IQE as high as 58.8% were demonstrated. Using such QWs a number UV LEDs emitting in the spectral region from 340 to 265 nm were fabricated and evaluated at the die level. A number of milliwatt output power LEDs emitting at 280 nm were demonstrated.

Kao, Chen-Kai

184

Physical design and assembly process development of a multi-chip package containing a light emitting diode (LED) array die  

Microsoft Academic Search

This paper presents the physical design concept and process developments to construct a small module containing a chip with an array of miniature light emitting diodes (LED's) as well as the driver control circuitry for the LED array. The module is composed of a glass substrate consisting of a fanout pattern from the I\\/O bond pads of the fine pitch

Rao Bonda; T. Fang; K. Kaskoun; B. Lytle; G. Swan; J. W. Stafford; B. Marlin; G. Tam

1996-01-01

185

Physical design and assembly process development of a multichip package containing a light emitting diode (LED) array die  

Microsoft Academic Search

This paper presents the physical design concept and process developments to construct a small module containing a chip with an array of miniature light emitting diodes (LEDs) as well as the driver control circuitry for the LED array, The module is composed of a glass substrate consisting of a fanout pattern from the input\\/output (I\\/O) bond pads of the fine

R. Bonda; Treliant Fang; K. Kaskoun; W. H. Lytle; B. Marlin; G. Swan; J. W. Stafford; G. Tam

1997-01-01

186

Temperature dependence of optical wavelength shift as a validation technique for pulsed laser diode array thermal modeling  

Microsoft Academic Search

As with any electronic device, the performance and reliability of laser diode arrays (LDAs) is a strong function of the temperature at which the array operates. However, the electrical and optical environment in which the LDA operates makes direct temperature measurements difficult. Wavelength measurements can be used as a means to deduce temperature by exploiting the linear relationship between wavelength

Jason Carter; David Snyder; Jeny Reichenbaugh

2003-01-01

187

Theoretical and experimental studies of Schottky diodes that use aligned arrays of single-walled carbon nanotubes  

Microsoft Academic Search

We present theoretical and experimental studies of Schottky diodes that use aligned arrays of single-walled carbon nanotubes.\\u000a A simple physical model, taking into account the basic physics of current rectification, can adequately describe the single-tube\\u000a and array devices. We show that for as-grown array diodes, the rectification ratio, defined by the maximum-to-minimum-current-ratio,\\u000a is low due to the presence of metallic-single-walled

Xinning Ho; Lina Ye; Slava V. Rotkin; Xu Xie; Frank Du; Simon Dunham; Jana Zaumseil; John A. Rogers

2010-01-01

188

Inorganic-organic p-n heterojunction nanotree arrays for a high-sensitivity diode humidity sensor.  

PubMed

Large-area and ordered arrays (16 cm(2)) of an inorganic-organic p-n heterojunction nanotree (NT) were successfully fabricated. The nanotree arrays consist of ZnO nanorods (NRs) as backbones and CuTCNQ (TCNQ = 7,7,8,8-tetracyanoquinodimethane) NRs as branches. The sizes of CuTCNQ NRs can be tuned by the thickness of the Cu layer deposited on the surface of ZnO NR. The CuTCNQ/ZnO NT arrays displayed excellent diode nature and obvious size-dependent rectification ratios were observed. Moreover, the CuTCNQ/ZnO NT arrays were first applied for the fabrication of a diode-type humidity sensor, which displayed ultrahigh sensitivity and quick response/recovery properties at room temperature. The detection limitation of this new diode-type humidity sensor lowers to 5% relative humidity (RH). PMID:23721049

Wang, Ke; Qian, Xuemin; Zhang, Liang; Li, Yongjun; Liu, Huibiao

2013-06-26

189

A digital optical phase-locked loop for diode lasers based on field programmable gate array.  

PubMed

We have designed and implemented a highly digital optical phase-locked loop (OPLL) for diode lasers in atom interferometry. The three parts of controlling circuit in this OPLL, including phase and frequency detector (PFD), loop filter and proportional integral derivative (PID) controller, are implemented in a single field programmable gate array chip. A structure type compatible with the model MAX9382?MCH12140 is chosen for PFD and pipeline and parallelism technology have been adapted in PID controller. Especially, high speed clock and twisted ring counter have been integrated in the most crucial part, the loop filter. This OPLL has the narrow beat note line width below 1 Hz, residual mean-square phase error of 0.14 rad(2) and transition time of 100 ?s under 10 MHz frequency step. A main innovation of this design is the completely digitalization of the whole controlling circuit in OPLL for diode lasers. PMID:23020359

Xu, Zhouxiang; Zhang, Xian; Huang, Kaikai; Lu, Xuanhui

2012-09-01

190

UV to soft-x-ray surveys using a compact, biplanar diode array  

SciTech Connect

Biplanar vacuum diodes, long used for the diagnostics of laser-produced plasmas, have also been used as spectroscopic survey instruments for magnetically confined plasmas. The compact seven-channel diode array, developed at KMS Fusion, provides broadband (..delta..E/Eapprox. =1) channels of filtered cathodes to provide the spectral scan from 10 eV to about 5 keV (approximately 130 to 0.25 nm). Preliminary calibration results and calculations for a number of filters and cathodes are used to demonstrate that a satisfactory energy region may be obtained if an absorption edge of the cathode is below the mean energy of the desired channel and an absorption edge of the filter is above that energy. These devices are insensitive to neutron and gamma flux.

Armentrout, C.J.; Geddes, J.B.; Lee, P.; Canfield, L.R.

1988-08-01

191

Schottky barrier inhomogeneity for graphene/Si-nanowire arrays/n-type Si Schottky diodes  

NASA Astrophysics Data System (ADS)

The current-voltage characteristics of graphene/Si-nanowire (SiNW) arrays/n-type Si Schottky diodes with and without H2O2 treatment were measured in the temperature range of -150 ˜ 150 °C. The forward-bias current-voltage characteristics were analyzed on the basis of thermionic emission theory. It is found that the barrier height decreases and the ideality factor increases with the decreased temperatures. Such behavior is attributed to barrier inhomogeneities. It is shown that both Schottky barrier inhomogeneity and the T0 effect are affected by H2O2 treatment, implying that charge traps in the SiNWs have a noticeable effect on Schottky barrier inhomogeneity for graphene/SiNWs/n-type Si diodes.

Zeng, Jian-Jhou; Lin, Yow-Jon

2014-03-01

192

A digital optical phase-locked loop for diode lasers based on field programmable gate array  

NASA Astrophysics Data System (ADS)

We have designed and implemented a highly digital optical phase-locked loop (OPLL) for diode lasers in atom interferometry. The three parts of controlling circuit in this OPLL, including phase and frequency detector (PFD), loop filter and proportional integral derivative (PID) controller, are implemented in a single field programmable gate array chip. A structure type compatible with the model MAX9382/MCH12140 is chosen for PFD and pipeline and parallelism technology have been adapted in PID controller. Especially, high speed clock and twisted ring counter have been integrated in the most crucial part, the loop filter. This OPLL has the narrow beat note line width below 1 Hz, residual mean-square phase error of 0.14 rad2 and transition time of 100 ?s under 10 MHz frequency step. A main innovation of this design is the completely digitalization of the whole controlling circuit in OPLL for diode lasers.

Xu, Zhouxiang; Zhang, Xian; Huang, Kaikai; Lu, Xuanhui

2012-09-01

193

Quantitative Detection of Combustion Species using Ultra-Violet Diode Lasers  

NASA Technical Reports Server (NTRS)

Southwest Sciences is developing a new microgravity combustion diagnostic based on UV diode lasers. The instrument will allow absolute concentration measurements of combustion species on a variety of microgravity combustion platforms including the Space Station. Our approach uses newly available room temperature UV diode lasers, thereby keeping the instrument compact, rugged and energy efficient. The feasibility of the technique was demonstrated by measurement of CH radicals in laboratory flames. Further progress in fabrication technology of UV diode lasers at shorter wavelengths and higher power will result in detection of transient species in the deeper UV. High sensitivity detection of combustion radicals is provided with wavelength modulation absorption spectroscopy.

Pilgrim, J. S.; Peterson, K. A.

2001-01-01

194

Multiple detector focal plane array ultraviolet spectrometer for the AMPS laboratory  

NASA Technical Reports Server (NTRS)

The possibility of meeting the requirements of the amps spectroscopic instrumentation by using a multi-element focal plane detector array in a conventional spectrograph mount was examined. The requirements of the detector array were determined from the optical design of the spectrometer which in turn depends on the desired level of resolution and sensitivity required. The choice of available detectors and their associated electronics and controls was surveyed, bearing in mind that the data collection rate from this system is so great that on-board processing and reduction of data are absolutely essential. Finally, parallel developments in instrumentation for imaging in astronomy were examined, both in the ultraviolet (for the Large Space Telescope as well as other rocket and satellite programs) and in the visible, to determine what progress in that area can have direct bearing on atmospheric spectroscopy.

Feldman, P. D.

1975-01-01

195

Weekly verification of dosimetric data for virtual wedge using a 2D diode detector array.  

PubMed

A linac manufacturer has recommended that users measure virtual wedge (VW) angle and VW factor as a weekly quality assurance (QA) procedure. The purpose of this study was to investigate whether a 2D diode detector array (MapCHECK™) is a useful tool for the verification of dosimetric data for VW. Measurements were performed on 2 linear accelerators (4, 6, and 10 MV) at 10-cm depth for a field size of 10 × 10 cm(2) and with wedge angles of 15, 30, 45, and 60°. To verify the VW dose distributions generated by the treatment planning system (TPS), we confirmed that agreement between TPS data and measurements were ? 2% dose difference or 2-mm distance-to-agreement based on American Association of Physicists in Medicine Task Group Report 53 (AAPM TG-53). We present here the results of a 1-year evaluation of VW by means of a 2D diode detector array. The maximum 2-fold standard deviation of the measured wedge angle turned out to be within 1.0, and all measured VW factors to be 1.00 ± 0.03. Although >95% of the points measured for 6 and 10 MV were generally within the tolerance of the dose distribution as mentioned above, the percentage of agreement between the measured data for 4 MV and TPS data were somewhat below 90%. We also verified generally good reproducibility for the dose distribution. The 2-D diode detector array was thus found to be useful as a tool for weekly VW QA. PMID:20537885

Ogata, Toshiyuki; Koizumi, Masahiko; Sumida, Iori; Takahashi, Yutaka; Akino, Yuichi; Isohashi, Fumiaki; Konishi, Koji; Yoshioka, Yasuo; Inoue, Takehiro

2011-01-01

196

Water-cooled hard-soldered kilowatt laser diode arrays operating at high duty cycle  

NASA Astrophysics Data System (ADS)

High brightness laser diode arrays are increasingly found in defense applications either as efficient optical pumps or as direct energy sources. In many instances, duty cycles of 10- 20 % are required, together with precise optical collimation. System requirements are not always compatible with the use of microchannel based cooling, notwithstanding their remarkable efficiency. Simpler but effective solutions, which will not involve high fluid pressure drops as well as deionized water, are needed. The designer is faced with a number of challenges: effective heat removal, minimization of the built- in and operational stresses as well as precise and accurate fast axis collimation. In this article, we report on a novel laser diode array which includes an integral tap water cooling system. Robustness is achieved by all around hard solder bonding of passivated 940nm laser bars. Far field mapping of the beam, after accurate fast axis collimation will be presented. It will be shown that the design of water cooling channels , proper selection of package materials, careful design of fatigue sensitive parts and active collimation technique allow for long life time and reliability, while not compromising the laser diode array efficiency, optical power density ,brightness and compactness. Main performance characteristics are 150W/bar peak optical power, 10% duty cycle and more than 50% wall plug efficiency with less than 1° fast axis divergence. Lifetime of 0.5 Gshots with less than 10% power degradation has been proved. Additionally, the devices have successfully survived harsh environmental conditions such as thermal cycling of the coolant temperature and mechanical shocks.

Klumel, Genady; Karni, Yoram; Oppenhaim, Jacob; Berk, Yuri; Shamay, Moshe; Tessler, Renana; Cohen, Shalom; Risemberg, Shlomo

2010-04-01

197

Emitter failure and thermal facet load in high-power laser diode arrays  

NASA Astrophysics Data System (ADS)

We report on micro-Raman facet temperature measurements carried out in asymmetrically coated high-power laser diode arrays. Facet temperatures of up to 600 °C are reproducibly found for high-power operation. The data are modeled using an approach based on the finite element method. Thus we are able to infer the power management of the device from the facet temperature data. Up to 7% of the total heat power is concentrated at the front facet. Furthermore, we determine the thermal load at the front facet versus the operation current, which is a key parameter for modeling high-power devices.

Puchert, R.; Tomm, J. W.; Jaeger, A.; Bärwolff, A.; Luft, J.; Späth, W.

198

Field effect modulated nanofluidic diode membrane based on Al2O3/W heterogeneous nanopore arrays  

NASA Astrophysics Data System (ADS)

We developed Al2O3/W heterogeneous nanopore arrays for field effect modulated nanofluidic diodes. They are fabricated by transferring self-organized nanopores of anodic aluminium oxide into a W thin film. The nanopores are ~20 nm in diameter and 400 nm in length. After mild oxidation, approximately 10 nm WO3 grows on the surface of W, forming a conformal and dense dielectric layer. It allows the application of an electrical field through the surrounding W electrode to modulate the ionic transport across the entire membrane. Our experimental findings have potential applications in high throughput controlled delivery and electrostatic sorting of biomolecules.

Wu, Songmei; Wildhaber, Fabien; Bertsch, Arnaud; Brugger, Juergen; Renaud, Philippe

2013-05-01

199

Compact high-power diode-array-pumped Nd:CNGG laser employing CUSP geometry optical coupling  

Microsoft Academic Search

This paper presents the design of a Compact High Power Diode Array Pumped Nd:CNGG laser employing cusp geometry concentrator for optical coupling in the side pumped configuration. The design addresses two major issues that influence the performance of a Diode Pumped Solid State Laser i.e. choice of suitable laser material and optical coupling scheme. The design employs an Nd:CNGG rod

Amitav Mallik; Lalita Agrawal

1999-01-01

200

New silicon technologies enable high-performance arrays of single photon avalanche diodes  

NASA Astrophysics Data System (ADS)

In order to fulfill the requirements of many applications, we recently developed a new technology aimed at combining the advantages of traditional thin and thick silicon Single Photon Avalanche Diodes (SPAD). In particular we demonstrated single-pixel detectors with a remarkable improvement in the Photon Detection Efficiency at the longer wavelengths (e.g. 40% at 800nm) while maintaining a timing jitter better than 100ps. In this paper we will analyze the factors the currently prevent the fabrication of arrays of SPADs by adopting such a Red-Enhanced (RE) technology and we will propose further modifications to the device structure that will enable the fabrication of high performance RE-SPAD arrays for photon timing applications.

Gulinatti, Angelo; Rech, Ivan; Maccagnani, Piera; Cova, Sergio; Ghioni, Massimo

2013-05-01

201

Vertical pillar-superlattice array and graphene hybrid light emitting diodes.  

PubMed

We report a type of device that combines vertical arrays of one-dimensional (1D) pillar-superlattice (PSL) structures with 2D graphene sheets to yield a class of light emitting diode (LED) with interesting mechanical, optical, and electrical characteristics. In this application, graphene sheets coated with very thin metal layers exhibit good mechanical and electrical properties and an ability to mount, in a freely suspended configuration, on the PSL arrays as a top window electrode. Optical characterization demonstrates that graphene exhibits excellent optical transparency even after deposition of the thin metal films. Thermal annealing of the graphene/metal (Gr/M) contact to the GaAs decreases the contact resistance, to provide enhanced carrier injection. The resulting PSL-Gr/M LEDs exhibit bright light emission over large areas. The result suggests the utility of graphene-based materials as electrodes in devices with unusual, nonplanar 3D architectures. PMID:20608711

Lee, Jung Min; Choung, Jae Woong; Yi, Jaeseok; Lee, Dong Hyun; Samal, Monica; Yi, Dong Kee; Lee, Chul-Ho; Yi, Gyu-Chul; Paik, Ungyu; Rogers, John A; Park, Won Il

2010-08-11

202

A ten-element array of individually addressable channeled-substrate-planar AlGaAs diode lasers  

NASA Technical Reports Server (NTRS)

The fabrication of arrays of channeled-substrate-planar (CSP) AlGaAs diode lasers which emit up to 150 mW CW in a single spatial mode and are applicable to mulitchannel optical recording systems is described. The CSP diode lasers are incorporated in ten-array geometry, and each array is 1.95 nm in width and 100 microns in thickness and is cleaved to have a cavity length of 200 microns and coated to produce 90-percent reflectivity on the back facet and 10-percent reflectivity on the front facet. The array is attached to a thermoelectrically cooled submount. The optical output power versus input current characteristics for the array are evaluated, and the lateral far-field intensity profiles for each of the lasers (at 30 mW CW) and CW spectra of the lasers are analyzed.

Carlin, D. B.; Goldstein, B.; Bednarz, J. P.; Harvey, M. G.; Dinkel, N. A.

1987-01-01

203

Vertical conducting ultraviolet light-emitting diodes based on p-ZnO:As/n-GaN/n-SiC heterostructure  

NASA Astrophysics Data System (ADS)

Vertical conducting light-emitting diodes based on p-ZnO/n-GaN structure were fabricated on conductive n-SiC(6H) substrates. The p-ZnO:As films were prepared by arsenic out-diffusion from a sandwiched GaAs interlayer on a GaN/SiC template, and the AsZn-2VZn complex was considered to be the most probable defect contributing to the p-type conductivity of the ZnO:As films. Under forward bias, an intense ultraviolet emission at ~384 nm from the ZnO side was observed. The electroluminescence performance of the diode was remarkable in terms of its low emission onset and high-purity ultraviolet emission. Additionally, the unencapsulated diode showed good stability over a duration of 2 months.

Shi, Zhifeng; Zhang, Yuantao; Wu, Bin; Cai, Xupu; Zhang, Jinxiang; Xia, Xiaochuan; Wang, Hui; Dong, Xin; Liang, Hongwei; Zhang, Baolin; Du, Guotong

2013-04-01

204

Formation of self-aligned guard rings for monolithic Schottky-barrier diode arrays  

NASA Astrophysics Data System (ADS)

A method for fabricating self-aligned n-type guard rings in a body of p-type silicon for a silicide/Schottky-barrier diode array consists of depositing SiO2 with uniformly distributed phosphorus ions as a masking layer on the surface of the p-doped silicon body before etching the masking layer in the desired pattern of guard rings. N-type guard rings buried in the p-type silicon substrate are then formed by heating the structure to diffuse the phosphorus ions remaining on the surface functions as a mask for the remaining steps of the process which are to deposit metal over the entire surface of the structure and then form a silicide in those areas inside the SiO2 grid pattern by heating the structure. Metal not converted to a silicide is then removed by etching. The silicide and p-type silicon form a Schottky-barrier diode at their junction in areas inside the buried guard rings. Overlap of the silicide and the guard rings is minimized by this self-aligning technique to maximize the fill factor of the array.

Lin, True-Lon

1991-05-01

205

Calibration and linearity verification of capacitance type cryo level indicators using cryogenically multiplexed diode array  

NASA Astrophysics Data System (ADS)

In space application the precision level measurement of cryogenic liquids in the storage tanks is done using triple redundant capacitance level sensor, for control and safety point of view. The linearity of each sensor element depends upon the cylindricity and concentricity of the internal and external electrodes. The complexity of calibrating all sensors together has been addressed by two step calibration methodology which has been developed and used for the calibration of six capacitance sensors. All calibrations are done using Liquid Nitrogen (LN2) as a cryogenic fluid. In the first step of calibration, one of the elements of Liquid Hydrogen (LH2) level sensor is calibrated using 700mm eleven point discrete diode array. Four wire method has been used for the diode array. Thus a linearity curve for a single element of LH2 is obtained. In second step of calibration, using the equation thus obtained for the above sensor, it is considered as a reference for calibrating remaining elements of the same LH2 sensor and other level sensor (either Liquid Oxygen (LOX) or LH2). The elimination of stray capacitance for the capacitance level probes has been attempted. The automatic data logging of capacitance values through GPIB is done using LabVIEW 8.5.

Karunanithi, R.; Jacob, Subhash; Singh Gour, Abhay Singh; Das, M.; Nadig, D. S.; Prasad, M. V. N.

2012-06-01

206

Optical and Thermal Analyses of High-Power Laser Diode Arrays  

NASA Technical Reports Server (NTRS)

An important need, especially for space-borne applications, is the early identification and rejection of laser diode arrays which may fail prematurely. The search for reliable failure predictors is ongoing and has led to the development of two techniques, infrared imagery and monitoring the Temporally-resolved and Spectrally-Resolved (TSR) optical output from which temperature of the device can be measured. This is in addition to power monitoring on long term burn stations. A direct measurement of the temperature of the active region is an important parameter as the lifetime of Laser Diode Arrays (LDA) decreases exponentially with increasing temperature. We measure the temperature from time-resolving the spectral emission in an analogous method to Voss et al. In this paper we briefly discuss the measurement setup and present temperature data derived from thermal images and TSR data for two differently designed high-power 808 nanometer LDA packages of similar specification operated in an electrical and thermal environment that mimic the expected operational conditions.

Vasilyev, Aleksey; Allan, Graham R.; Schafer, John; Stephen, Mark A.; Young, Stefano

2004-01-01

207

Deep-ultraviolet light-emitting diodes for frequency domain measurements of fluorescence lifetime in basic biofluorophores  

NASA Astrophysics Data System (ADS)

We report on the development of deep-ultraviolet light-emitting diodes with AlGaN multiple-quantum-well active region for real-time fluorescence lifetime sensing in natural biofluorophores. The peak wavelengths of the devices are 340 and 280 nm, linewidth at half maximum approximately 10 nm, wall-plug efficiency up to 0.9%, output power in the milliwatt range, peak-to-background ratio up to four orders of magnitude, and cutoff frequencies for electrical modulation in the range of 100 MHz. Devices with high-frequency modulated output were demonstrated for frequency domain fluorescence lifetime measurements in basic biological autofluorophores (nicotinamide adenine dinucliotide, riboflavin, tyrosine, and tryptophan) with subnanosecond resolution.

Vita, P.; Kuril?ik, N.; Jurš?nas, S.; Žukauskas, A.; Lunev, A.; Bilenko, Y.; Zhang, J.; Hu, X.; Deng, J.; Katona, T.; Gaska, R.

2005-08-01

208

Characterization of biological materials by frequency-domain fluorescence lifetime measurements using ultraviolet light-emitting diodes  

NASA Astrophysics Data System (ADS)

Recently developed deep-ultraviolet light-emitting diodes (UV LEDs) emit at wavelengths short enough to excitate fluorescence in most biological autofluorophores. We demonstrate the possibility of harmonical modulation of the output of group-III-nitride based UV LEDs ranging from 255 to 375 nm at frequencies up to 200 MHz. This enables the application of UV LEDs for frequency-domain fluorescence lifetime sensing with subnanosecond resolution. We report on measurements of fluorescence decay time in common biofluorophores (tyrosine, tryptophan, NADPH, NADH, collagen, DPA, elastin and riboflavin) using commercially available UV LEDs. We demonstrate the capacity of a multichannel LED-based frequency-resolved measurement technique to discriminate between Bacillus globigii and a variety of ambient interferants such as diesel fuel, paper, cotton, dust, etc.

Žukauskas, A.; Vitta, P.; Kuril?ik, N.; Jurš?nas, S.; Bakien?, E.

2008-01-01

209

Electrochemical potentiostatic activation for improvement of internal quantum efficiency of 385-nm ultraviolet light-emitting diodes  

NASA Astrophysics Data System (ADS)

The electrochemical potentiostatic activation (EPA) method is proven to effectively improve the internal quantum efficiency (IQE) of 385-nm ultraviolet light-emitting diodes (UV-LEDs). UV-LEDs wafers were immersed into 1.0 M HCl solution, and an electric voltage of 3.0 V was applied to the p-type GaN layer in order to increase the hole concentration by breaking the MgH complex. Secondary ion mass spectroscopy analysis clearly indicates the successful removal of hydrogen atoms by the EPA process, which is a ˜35% reduction of the hydrogen concentration compared to the conventional N2 annealing. The light-output power was enhanced by ˜20% at an input current of 50 mA, which originated from an improvement of the IQE by ˜20%. The reverse leakage current was also lowered by about one order after the EPA process.

Choi, Hee Seok; Kim, Hak Jun; Lee, Jung Ju; Seo, Hyo Won; Tawfik, Wael Z.; Ha, Jun-Seok; Ryu, Sang-Wan; Jun, Seong Ran; Jeong, Tak; Lee, June Key

2013-10-01

210

AlGaN-based ultraviolet light-emitting diodes using fluorine-doped indium tin oxide electrodes  

NASA Astrophysics Data System (ADS)

In this paper, improved electrical and optical properties of aluminum gallium nitride (AlGaN)-based ultraviolet light-emitting diodes using fluorine-doped indium tin oxide (F-ITO) electrodes are reported. F-doping was found to increase the work function as well as the energy bandgap of the ITO and, thereby, reduce the Shottky barrier height in contact with p-(Al)GaN. As a result, the optical transmittance increased from 79.7% to 86.9% at 380 nm, while the specific contact resistance decreased from 1.04 × 10-3 ?.cm2 to 9.12 × 10-4 ?.cm2 after F-doping, which led to an increase in the output power from 2.41 mW to 5.99 mW.

Ju Chae, Dong; Yoon Kim, Dong; Geun Kim, Tae; Mo Sung, Yun; Doeck Kim, Moon

2012-02-01

211

Near-ultraviolet light-emitting diodes with transparent conducting layer of gold-doped multi-layer graphene  

NASA Astrophysics Data System (ADS)

We report on gold (Au)-doped multi-layer graphene (MLG), which can be used as a transparent conducting layer in near-ultraviolet light-emitting diodes (NUV-LEDs). The optical output power of NUV-LEDs with thermally annealed Au-doped MLG was increased by 34% compared with that of NUV-LEDs with a bare MLG. This result is attributed to the reduced sheet resistance and the enhanced current injection efficiency of NUV-LEDs by the thermally annealed Au-doped MLG film, which shows high transmittance in NUV and UV regions and good adhesion of Au-doped MLG on p-GaN layer of NUV-LEDs.

Cho, Chu-Young; Choe, Minhyeok; Lee, Sang-Jun; Hong, Sang-Hyun; Lee, Takhee; Lim, Wantae; Kim, Sung-Tae; Park, Seong-Ju

2013-03-01

212

Deep-Ultraviolet Light-Emitting Diodes Fabricated on AlN Substrates Prepared by Hydride Vapor Phase Epitaxy  

NASA Astrophysics Data System (ADS)

AlGaN-based deep-ultraviolet light-emitting diodes (DUV-LEDs) were fabricated on AlN substrates. The AlN substrates were prepared by growing thick hydride vapor phase epitaxy (HVPE)-AlN layers on bulk AlN substrates prepared by physical vapor transport (PVT). After growing an LED structure, the PVT-AlN substrates were removed by mechanical polishing. This process allowed the fabrication of DUV-LEDs on HVPE-AlN substrates with high crystalline quality and DUV optical transparency. The DUV-LEDs exhibited a single emission peaking at 268 nm through the HVPE-AlN substrates. The output power as high as 28 mW was obtained at an injection current of 250 mA.

Kinoshita, Toru; Hironaka, Keiichiro; Obata, Toshiyuki; Nagashima, Toru; Dalmau, Rafael; Schlesser, Raoul; Moody, Baxter; Xie, Jinqiao; Inoue, Shin-ichiro; Kumagai, Yoshinao; Koukitu, Akinori; Sitar, Zlatko

2012-12-01

213

High-output-power 255/280/310 nm deep ultraviolet light-emitting diodes and their lifetime characteristics  

NASA Astrophysics Data System (ADS)

255/280/310 nm deep ultraviolet light-emitting diodes (DUV LEDs) suitable for high-current operation are reported. Newly developed 1 mm sized chips are installed in a commercial package with a two-series configuration. At a forward current of 350 mA, we measured powers of 45.2, 93.3, and 65.8 mW for the 255, 280, and 310 nm LEDs, respectively. The corresponding external quantum efficiencies per serial circuit were 1.3, 3.0, and 2.4%, and successful chip scalability was demonstrated. The 50% lifetime of the 280 nm LED die was estimated to be 3000 h at a junction temperature of 30 °C.

Fujioka, A.; Asada, K.; Yamada, H.; Ohtsuka, T.; Ogawa, T.; Kosugi, T.; Kishikawa, D.; Mukai, T.

2014-06-01

214

Efficient ultraviolet-blue polymer light-emitting diodes based on a fluorene-based non-conjugated polymer  

NASA Astrophysics Data System (ADS)

Efficient UV-blue polymer light-emitting diodes based on a fluorene-based nonconjugated polymer, poly[2,7-(9,9-dihexylfluorene)-alt-4,4'-phenylether] (PFPE), are fabricated. The device with PFPE as emitting layer shows a very narrow ultraviolet-blue electroluminescence emission with a peak at 397 nm and a maximal external quantum efficiency of 1.07%. By blending PFPE into poly(N-vinylcarbazole) (PVK), the device performance can be further improved. A maximum external quantum efficiency of 1.81%, with a maximum irradiance power density of 1223 ?W/cm2, was reached by using a blend of PVK and PFPE in the weight ratio of 95:5 as emitting layer.

Huang, Fei; Niu, Yu-Hua; Liu, Michelle S.; Zhou, Xing-Hua; Tian, Yan-Qing; Jen, Alex K.-Y.

2006-08-01

215

Investigation of Light Extraction Efficiency in AlGaN Deep-Ultraviolet Light-Emitting Diodes  

NASA Astrophysics Data System (ADS)

Light extraction efficiency (LEE) in AlGaN deep-ultraviolet (DUV) light-emitting diodes (LEDs) is investigated using finite-difference time-domain simulations. For flip-chip and vertical LED structures, LEE is obtained to be <10% due to strong DUV light absorption in the p-GaN layer. In flip-chip LEDs, LEE of transverse-magnetic (TM) modes is found to be more than ten times smaller than that of transverse-electric (TE) modes, which explains the decreasing behavior of external quantum efficiency of DUV LEDs with decreasing wavelength. It is also found that vertical LED structures can have advantages over flip-chip structures for increasing LEE in the TM mode.

Ryu, Han-Youl; Choi, Il-Gyun; Choi, Hyo-Sik; Shim, Jong-In

2013-06-01

216

Over 200 mW on 365 nm ultraviolet light emitting diode of GaN-free structure  

NASA Astrophysics Data System (ADS)

We have remarkably improved the emission efficiency of 365 nm ultraviolet (UV) light emitting diode (LED). Rugged pattern is fabricated on the surface of LED chips in order to enhance the extraction efficiency. As a result, the extraction efficiency of this LED approximately increased by 50%. When this UV LED was operated at a forward-bias pulsed current of 500 mA at room temperature (RT), the peak wavelength, the output power (Po), the operating voltage (Vf) and the external quantum efficiency (ex) were 365 nm, 240 mW, 4.5 V and 14.1%, respectively. On the other hand, at a forward-bias direct current of 500 mA at RT, Po, Vf and ex were 210 mW, 4.3 V and 12.4%, respectively. The ex at 365 nm increased to double that of the reported value before. (

Morita, Daisuke; Sano, Masahiko; Yamamoto, Masashi; Nonaka, Mitsuhiro; Yasutomo, Katsuhiro; Akaishi, Kazuyuki; Nagahama, Shin-Ichi; Mukai, Takashi

2003-11-01

217

Injection-locking of gain-guided diode laser arrays: influence of the master beam shape.  

PubMed

According to a previously reported model [IEEE J. Quantum Electron. 27, 396 (1991)], the properties of injection-locked gain-guided diode laser arrays depend on the geometric characteristics of the master beam, such as the size of its waist and its incidence angle. Experimentally, two injection configurations are of particular interest: the focused injection, in which the master beam is focused on one stripe of the slave array, and the wide-beam injection, in which the master beam is shone on the whole or a part of the width of the array. We investigate experimentally and compare these two configurations. In particular, we show that, in agreement with our theory, changing the geometry of the master beam greatly alters the far-field patterns, the locking bandwidth, and the spectrum of the locked array. We also compare the injection angle sensitivity and the beam-steering properties of the two configurations. Observations confirm our predictions, and optimal configurations are proposed. PMID:20720848

Verdiell, J M; Rajbenbach, H; Huignard, J P

1992-04-20

218

New red phosphor for near-ultraviolet light-emitting diodes with high color-purity  

SciTech Connect

New red phosphors, Na{sub 5}Eu(MoO{sub 4}){sub 4} doped with boron oxide were prepared by the solid-state reaction. Their structure and photo-luminescent properties were investigated. With the introduction of boron oxide, the red emission intensity of the phosphors under 395 nm excitation is strengthened, with high color-purity (x = 0.673, y = 0.327). The single red light-emitting diode was obtained by combining InGaN chip with the red phosphor, bright red light can be observed by naked eyes from the red light-emitting diodes under a forward bias of 20 mA.

Wang, Zhengliang, E-mail: wzhl_ww@yahoo.com.cn [School of Chemistry and Biotechnology, Yunnan Nationalities University, Kunming, Yunnan 650031 (China)] [School of Chemistry and Biotechnology, Yunnan Nationalities University, Kunming, Yunnan 650031 (China); He, Pei; Wang, Rui [School of Chemistry and Chemical Engineering, Sun Yat-sen University, Guangzhou, Guangdong 510275 (China)] [School of Chemistry and Chemical Engineering, Sun Yat-sen University, Guangzhou, Guangdong 510275 (China); Zhao, Jishou [School of Chemistry and Biotechnology, Yunnan Nationalities University, Kunming, Yunnan 650031 (China)] [School of Chemistry and Biotechnology, Yunnan Nationalities University, Kunming, Yunnan 650031 (China); Gong, Menglian [School of Chemistry and Chemical Engineering, Sun Yat-sen University, Guangzhou, Guangdong 510275 (China)] [School of Chemistry and Chemical Engineering, Sun Yat-sen University, Guangzhou, Guangdong 510275 (China)

2010-02-15

219

Low-haze light extraction from organic light-emitting diode lighting with auxiliary electrode by selective microlens arrays.  

PubMed

Improved out-coupling efficiency and low haze of organic light-emitting diode (OLED) lighting with an auxiliary electrode are demonstrated by selective microlens arrays (SMLAs). The microlens arrays, aligned with the auxiliary electrode, were selectively fabricated, since the fully packed microlens arrays lead to OLED lighting with high haze. The external quantum efficiency and power efficiency of the devices with the SMLAs increased by 32% when compared with the devices without these arrays. Using the SMLAs, dark grid lines in the emission region became brighter, with a low haze, and the spectra of the emitted light had no shift. PMID:24321954

Hwang, Ju Hyun; Park, Tae Hyun; Lee, Hyun Jun; Choi, Kyung Bok; Park, Young Wook; Ju, Byeong-Kwon

2013-10-15

220

A superconducting focal plane array for ultraviolet, optical, and near-infrared astrophysics.  

PubMed

Microwave Kinetic Inductance Detectors, or MKIDs, have proven to be a powerful cryogenic detector technology due to their sensitivity and the ease with which they can be multiplexed into large arrays. A MKID is an energy sensor based on a photon-variable superconducting inductance in a lithographed microresonator, and is capable of functioning as a photon detector across the electromagnetic spectrum as well as a particle detector. Here we describe the first successful effort to create a photon-counting, energy-resolving ultraviolet, optical, and near infrared MKID focal plane array. These new Optical Lumped Element (OLE) MKID arrays have significant advantages over semiconductor detectors like charge coupled devices (CCDs). They can count individual photons with essentially no false counts and determine the energy and arrival time of every photon with good quantum efficiency. Their physical pixel size and maximum count rate is well matched with large telescopes. These capabilities enable powerful new astrophysical instruments usable from the ground and space. MKIDs could eventually supplant semiconductor detectors for most astronomical instrumentation, and will be useful for other disciplines such as quantum optics and biological imaging. PMID:22274494

Mazin, Benjamin A; Bumble, Bruce; Meeker, Seth R; O'Brien, Kieran; McHugh, Sean; Langman, Eric

2012-01-16

221

High-performance ultraviolet-blue light-emitting diodes based on an n-ZnO nanowall networks/p-GaN heterojunction  

NASA Astrophysics Data System (ADS)

Vertically aligned ZnO nanowall networks were grown on p-GaN/sapphire substrates by metal-organic chemical vapor deposition, and further heterojunction light-emitting diodes based on n-ZnO/p-GaN were fabricated. Highly efficient ultraviolet-blue emission was observed from the diode under forward bias, and it operated continuously for 8.5 h with decay of only 8.08% under a continuous current of 12 mA. The diode exhibited low emission onset and good stability. In addition, temperature-dependent electroluminescence and current-voltage behaviors of the diode were investigated to examine the thermal effects on light output power, spectral line shift, and temperature sensitivity of the resulting voltage.

Shi, Zhifeng; Zhang, Yuantao; Zhang, Jinxiang; Wang, Hui; Wu, Bin; Cai, Xupu; Cui, Xijun; Dong, Xin; Liang, Hongwei; Zhang, Baolin; Du, Guotong

2013-07-01

222

Electrically driven ultraviolet lasing behavior from phosphorus-doped p-ZnO nanonail array/n-Si heterojunction  

NASA Astrophysics Data System (ADS)

Electrically driven ultraviolet lasing behavior from p-ZnO:P nanonail array/n-Si heterojunction was demonstrated. Phosphorus-doped ZnO nanonail arrays were grown by chemical vapor deposition method. The constructed heterojunction with indium tin oxide films as the contacted electrodes demonstrated clear rectifying behavior, and the turn-on voltage was about 2.5 V. The p-n junction lowered the excitation threshold effectively and the electrically driven ultraviolet lasing behavior exhibited high monochromaticity: when the applied forward current reached 24 mA, distinct ultraviolet laser emission peaks were obtained at room temperature, and the full width at half maxims were 0.7, 0.9, and 0.5 nm, respectively. The three sharp peaks represented different lasing modes.

Zhang, Jun-Yan; Zhang, Qi-Feng; Deng, Tian-Song; Wu, Jin-Lei

2009-11-01

223

Integration of Micro-Light-Emitting-Diode Arrays and Silicon Driver for Heterogeneous Optoelectronic Integrated Circuit Device  

Microsoft Academic Search

In this paper, we proposed the possibility of implementing a single chip device for realizing optoelectronic integrated circuits (OEICs). Micro-light-emitting-diode (LED) arrays and a complementary metal--oxide--semiconductor (CMOS) pulse width modulation (PWM) silicon driver were proposed, designed, and fabricated on a single chip. The micro-LED arrays were separated by a dry etching method into 64 pixels of 8× 8, each with

Sang-Baie Shin; Ko-Ichiro Iijima; Jun-Ichi Chiba; Hiroshi Okada; Sho Iwayama; Akihiro Wakahara

2011-01-01

224

Quasi-instantaneous (less than 20 ps) phase locking in single-lobe Y-coupled laser diode arrays  

NASA Astrophysics Data System (ADS)

The time evolution of the far-field radiation pattern of an in-phase locked Y-coupled diode laser array has been observed with a streak camera. A strong central lobe 2.3 deg wide with faint secondary sidelobes separated by 15 deg forms in a time less than 20 ps. This indicates that the elements of the array are instantaneously locked in-phase.

Defreez, R. K.; Elliott, R. A.; Hartnett, K.; Welch, D. F.

1987-05-01

225

Quasi-instantaneous (less than 20 ps) phase locking in single-lobe Y-coupled laser diode arrays  

NASA Technical Reports Server (NTRS)

The time evolution of the far-field radiation pattern of an in-phase locked Y-coupled diode laser array has been observed with a streak camera. A strong central lobe 2.3 deg wide with faint secondary sidelobes separated by 15 deg forms in a time less than 20 ps. This indicates that the elements of the array are instantaneously locked in-phase.

Defreez, R. K.; Elliott, R. A.; Hartnett, K.; Welch, D. F.

1987-01-01

226

Coal liquefaction process streams characterization and evaluation: High performance liquid chromatography (HPLC) of coal liquefaction process streams using normal-phase separation with uv diode array detection  

SciTech Connect

This study demonstrated the considerable potential of using two-dimensional, high performance liquid chromatography (HPLC) with normal-phase separation and ultraviolet (UV) diode array detection for the examination of filtered process liquids and the 850{degrees}F{sup {minus}} distillate materials derived from direct coal liquefaction process streams. A commercially available HPLC column (Hypersil Green PAH-2) provided excellent separation of the complex mixture of polynuclear aromatic hydrocarbons (PAHs) found in coal-derived process streams process. Some characteristics of the samples delineated by separation could be attributed to processing parameters. Mass recovery of the process derived samples was low (5--50 wt %). Penn State believes, however, that, improved recovery can be achieved. High resolution mass spectrometry and gas chromatography/mass spectrometry (GC/MS) also were used in this study to characterize the samples and the HPLC fractions. The GC/MS technique was used to preliminarily examine the GC-elutable portion of the samples. The GC/MS data were compared with the data from the HPLC technique. The use of an ultraviolet detector in the HPLC work precludes detecting the aliphatic portion of the sample. The GC/MS allowed for identification and quantification of that portion of the samples. Further development of the 2-D HPLC analytical method as a process development tool appears justified based on the results of this project.

Clifford, D.J.; McKinney, D.E.; Hou, Lei; Hatcher, P.G. [Pennsylvania State Univ., University Park, PA (United States). Dept. of Materials Science and Engineering

1994-01-01

227

Silicon PIN diode array hybrids as building blocks for a vertex detector at an asymmetric B-factory.  

National Technical Information Service (NTIS)

Silicon PIN diode hybrid arrays are proposed as the ideal building blocks for a vertex detector at an asymmetric B-factory. The two-dimensional nature of the detector segmentation allows for the maximum in confusion elimination. Fine spatial resolution, o...

S. L. Shapiro

1990-01-01

228

Flexible and twistable non-volatile memory cell array with all-organic one diode-one resistor architecture  

NASA Astrophysics Data System (ADS)

Flexible organic memory devices are one of the integral components for future flexible organic electronics. However, high-density all-organic memory cell arrays on malleable substrates without cross-talk have not been demonstrated because of difficulties in their fabrication and relatively poor performances to date. Here we demonstrate the first flexible all-organic 64-bit memory cell array possessing one diode-one resistor architectures. Our all-organic one diode-one resistor cell exhibits excellent rewritable switching characteristics, even during and after harsh physical stresses. The write-read-erase-read output sequence of the cells perfectly correspond to the external pulse signal regardless of substrate deformation. The one diode-one resistor cell array is clearly addressed at the specified cells and encoded letters based on the standard ASCII character code. Our study on integrated organic memory cell arrays suggests that the all-organic one diode-one resistor cell architecture is suitable for high-density flexible organic memory applications in the future.

Ji, Yongsung; Zeigler, David F.; Lee, Dong Su; Choi, Hyejung; Jen, Alex K.-Y.; Ko, Heung Cho; Kim, Tae-Wook

2013-11-01

229

High-efficiency TEM00 Nd:YVO4 laser longitudinally pumped by a high-power laser diode array  

Microsoft Academic Search

A new simple, compact, and efficient optical device is presented which allows any commercially available laser diode arrays or stacks to longitudinally pump laser materials. A Nd:YVO4 laser was built and an optical-optical efficiency as high as 50% was demonstrated with a diffraction limited output beam.

Gilles Feugnet; Claude Bussac; Christian Larat; Muriel Schwarz; Jean-Paul Pocholle

1995-01-01

230

Identification of Natural and Early Synthetic Textile Dyes with HPLC and UV\\/Vis-Spectroscopy by Diode Array Detection  

Microsoft Academic Search

The separation and identification of complex mixtures of natural and synthetic textile dyes was investigated using HPLC with diode array detection. Separation was carried out on a reversed phase column with acetonitrile-phosphoric acid gradient elution. The results show that the anthraquinones from madder root and the insect dye cocheneal present in ancient red dyes can easily be distinguished from azo-dyes

Ch. H. Fischer; J. G. Rabe; M. Bischof

1990-01-01

231

Tunable picosecond pulse generation from an actively mode-locked laser diode array with intracavity chirp compensation  

Microsoft Academic Search

In this paper, we will present for the first time a tunable picosecond laser system based on a commercial laser diode array using the actively mode-locking technique. The novel feature is the incorporation of a folded dispersive delay line which served the functions of wavelength tuning and intracavity dispersion compensation, with good sidemode suppression and spatial mode control

Ci-Ling Pan; Chi-Luen Wang

1994-01-01

232

Fabrication of Efficient Light-Emitting Diodes With a Self-Assembled Photonic Crystal Array of Polystyrene Nanoparticles  

Microsoft Academic Search

A low-cost method of fabricating large photonic crystal arrays of hexagonal posts without the use of lithography is described, along with an application of enhancing light extraction efficiency in semiconductor light-emitting diodes (LEDs). Polystyrene spheres are deposited onto a wafer surface and then processed to achieve control over photonic crystal lattice properties in a method suitable for fast and repeatable

Aaron J. Danner; Benzhong Wang; Soo-Jin Chua; Jeong-Ki Hwang

2008-01-01

233

NUMERICAL ANALYSIS OF VIOLET-ULTRAVIOLET InGaN\\/InGaN LASER DIODES  

Microsoft Academic Search

The performance and optical properties of the InGaN multiple-quantum-well laser diodes are numerically studied with the LASTIP simulation program. In this work, the simulation results indicate that the double-quantum-well laser structure, operating in the spectral range from 385-410 nm, has the lowest threshold current. The simulation results also indicate that the double-quantum-well laser structure has the largest characteristic temperature as

Bo-Jean Chen; Sheng-Horng Yen; Mei-Ling Chen; Yen-Kuang Kuo

234

High-performance, high-reliability 880-nm diode laser bars and fiber-array packages  

NASA Astrophysics Data System (ADS)

The 880 nm diode laser is emerging as the source of choice for pumping Nd:YV04 laser crystals because it offers higher pumping efficiency than 808 nm diode lasers[1]. This paper reports on recent progress in the development of high power, high reliability, 880 nm laser bars. Specifically, high performance has been achieved based on Coherent's aluminum-free active (AAA) epitaxial structures while maintaining lifetimes greater than 10,000 hours. This includes 30% fill factor, 1 cm bars on conductively cooled packages (CCP) operating at 51 W with proven manufacturability. We observed power conversion efficiency (PCE) of up to 56%. These lasers have a far field fast axis divergence of 32° (FWHM), and slow axis divergence of <7° (FWHM). Typical value of the FWHM of output spectrum is 2.5 nm. These bars were used to build fiber array packages (FAPs) operating at 45 W. We have achieved FAP PCE of 50% and numerical aperture of <0.12. Reliability of both bars and FAP was shown to exceed 10000h MTBF.

Fouksman, M.; Lehconen, S.; Haapamaa, J.; Kennedy, K.; Li, J.

2006-03-01

235

Comprehensive design and analysis of diode laser arrays with an integrated phase shifter  

NASA Astrophysics Data System (ADS)

Diode laser arrays integrated with a phase shifter are investigated systematically based on the beam propagation method. Device parameters have been varied to obtain expected mode conversion. The passive waveguide loss and two main factors accounting for varied far-field profiles at different driving conditions are analysed. We demonstrate that on-axis main-lobe emission can be maintained by reducing the phase-shifter length within a certain scope. The far-field angle under the thermal lensing effect is theoretically proved to be nearly diffraction-limited by two-step etching. These optimizations are promising for on-axis nearly diffraction-limited laser emission with a higher output power.

Liu, Lei; Qu, Hongwei; Wang, Yufei; Ma, Chuanlong; Qi, Aiyi; Zhang, Siriguleng; Zheng, Wanhua

2014-01-01

236

A Single-Photon Avalanche Diode Array for Fluorescence Lifetime Imaging Microscopy  

PubMed Central

We describe the design, characterization, and demonstration of a fully integrated single-photon avalanche diode (SPAD) imager for use in time-resolved fluorescence imaging. The imager consists of a 64-by-64 array of active SPAD pixels and an on-chip time-to-digital converter (TDC) based on a delay-locked loop (DLL) and calibrated interpolators. The imager can perform both standard time-correlated single-photon counting (TCSPC) and an alternative gated-window detection useful for avoiding pulse pile-up when measuring bright signal levels. To illustrate the use of the imager, we present measurements of the decay lifetimes of fluorescent dyes of several types with a timing resolution of 350 ps.

Schwartz, David Eric; Charbon, Edoardo; Shepard, Kenneth L.

2013-01-01

237

Front-Light Source Using Inverted Organic Light-Emitting Diodes with Microcathode Arrays  

NASA Astrophysics Data System (ADS)

We have demonstrated an organic light-emitting diode (OLED) front-light source with a blinding microcathode array on a transparent electrode and a top-emission structure. Contrast ratio was improved by inserting MoO3 at the indium-tin-oxide (ITO)/Al interface. In a device of glass substrate/ITO/MoO3/meshed Al/lithium fluoride (LiF)/tris(8-hydroxyquinolinato) aluminum(III) (Alq3)/bis[N-(1-naphthyl)-N-phenyl] benzidine (?-NPD)/MoO3/semitransparent Au structure, the maximum luminance of top-side emission was 1,140 cd/m2, and the contrast ratio was 19:1. The transmittance was 44% at 555 nm.

Kohei Urata,; Shigeki Naka,; Hiroyuki Okada,

2010-04-01

238

Large-area anodized alumina nanopore arrays assisted by soft ultraviolet nanoimprint prepatterning.  

PubMed

Aluminium anodization under optimized conditions can naturally generate close-packed and aligned nanopore arrays, but the spatial extent of such regular pore arrangement is generally limited. Here we demonstrated the use of soft ultraviolet nanoimprint lithography to guide the formation of nanopores at specific locations, using an elastomer negative mold for the process. By anodizing at voltages which naturally led to the formation of pores with matching averaged interpore separation, pre-patterned triangular holes (diameter 100 nm, periodicity 350 nm) on aluminium thin films induced conformal growth of nanopores at pre-defined positions. In addition, pores in geometries other than close-packed patterns were prepared, with square pore arrangement being demonstrated in this work. The influence of the anodization voltage on the final pore formation was also studied. Our results illustrated the possibility to fabricate well-organized nanopore arrays with conditions far less stringent than those reported in literature, which has the potential to be adopted for applications where regular pore alignment are critical. PMID:22962742

Ng, S M; Wong, H F; Lau, H K; Leung, C W

2012-08-01

239

Continuous multicomponent stack gas analyzer using ultraviolet-photodiode-array spectroscopy  

NASA Astrophysics Data System (ADS)

Ammonia injection is frequently used to reduce emissions of nitrogen oxides from modern combustion plant. Accurate measurements of ammonia and nitric oxide are therefore required to ensure optimum operation of the NOx control system. Measurements of sulphur dioxide are also required to ensure compliance with legislation in most countries. An extractive analytical system has been developed for continuous measurements of ammonia, nitric oxide and sulphur dioxide concentrations in stack gases based on an ultraviolet spectrometer using a photodiode array detector operating in the 200nm region. The use of the photodiode array spectrometer enables the system to have a fast response time while maintaining excellent wavelength stability and reliability, since there are no moving parts in the main optical system. A high temperature sampling system is coupled to a hot sample cell to ensure that there is no degradation of the sample prior to measurement. Tests in the laboratory and at a combustion plant in Europe have shown practical detection limits of 1ppm for all of the target gases.

Stuart, Derek D.

1997-05-01

240

Pyramid Array InGaN/GaN Core--Shell Light Emitting Diodes with Homogeneous Multilayer Graphene Electrodes  

NASA Astrophysics Data System (ADS)

Pyramid array InGaN/GaN core--shell light-emitting diodes (LEDs) were fabricated by using a highly homogeneous multilayer graphene transparent conducting electrode. This novel electrode exhibited excellent optical, structural, and electrical properties. In this design, graphene connected each pyramid array as a top window electrode. The current-driven pyramid array InGaN/GaN core--shell LED was operated at a low current injection and exhibited bright electroluminescence. Our results suggest that graphene offers excellent current spreading and transparent conductive properties for nano- or microscale devices.

Kang, Junjie; Li, Zhi; Li, Hongjian; Liu, Zhiqiang; Li, Xiao; Yi, Xiaoyan; Ma, Ping; Zhu, Hongwei; Wang, Guohong

2013-07-01

241

Quality assurance of asymmetric jaw alignment using 2D diode array  

SciTech Connect

Purpose: A method using a 2D diode array is proposed to measure the junction gap (or overlap) and dose with high precision for routine quality assurance of the asymmetric jaw alignment.Methods: The central axis (CAX) of the radiation field was determined with a 15 × 15 cm{sup 2} photon field at four cardinal collimator angles so that the junction gap (or overlap) can be measured with respect to the CAX. Two abutting fields having a field size of 15 cm (length along the axis parallel to the junction) × 7.5 cm (width along the axis perpendicular to the junction) were used to irradiate the 2D diode array (MapCHECK2) with 100 MU delivered at the photon energy of 6 MV. The collimator was slightly rotated at 15° with respect to the beam central axis to increase the number of diodes effective on the measurement of junction gap. The junction gap and dose measured in high spatial resolution were compared to the conventional methods using an electronic portal imaging device (EPID) and radiochromic film, respectively. In addition, the reproducibility and sensitivity of the proposed method to the measurements of junction gap and dose were investigated.Results: The junction gap (or overlap) and dose measured by MapCHECK2 agreed well to those measured by the conventional methods of EPID and film (the differences ranged from ?0.01 to 0 cm and from ?1.34% to 0.6% for the gap and dose, respectively). No variation in the repeat measurements of the junction gap was found whereas the measurements of junction dose were found to vary in quite a small range over the days of measurement (0.21%–0.35%). While the sensitivity of the measured junction gap to the actual junction gap applied was the ideal value of 1 cm/cm as expected, the sensitivity of the junction dose to the actual junction gap increased as the junction gap (or overlap) decreased (maximum sensitivity: 201.7%/cm).Conclusions: The initial results suggest that the method is applicable for a comprehensive quality assurance of the asymmetric jaw alignment.

Kim, Sun Mo [Department of Medical Physics, Stronach Regional Cancer Centre, Southlake Regional Health Centre, Newmarket, Ontario L3Y 2P9, Canada and Radiation Medicine Program, Princess Margaret Hospital/University Health Network, Toronto, Ontario M5G 2M9 (Canada)] [Department of Medical Physics, Stronach Regional Cancer Centre, Southlake Regional Health Centre, Newmarket, Ontario L3Y 2P9, Canada and Radiation Medicine Program, Princess Margaret Hospital/University Health Network, Toronto, Ontario M5G 2M9 (Canada); Chmielewski, Renata; Abbas, Ahmar [Department of Medical Physics, Stronach Regional Cancer Centre, Southlake Regional Health Centre, Newmarket, Ontario L3Y 2P9 (Canada)] [Department of Medical Physics, Stronach Regional Cancer Centre, Southlake Regional Health Centre, Newmarket, Ontario L3Y 2P9 (Canada); Yeung, Ivan W. T.; Moseley, Douglas J. [Department of Medical Physics, Stronach Regional Cancer Centre, Southlake Regional Health Centre, Newmarket, Ontario L3Y 2P9 (Canada) [Department of Medical Physics, Stronach Regional Cancer Centre, Southlake Regional Health Centre, Newmarket, Ontario L3Y 2P9 (Canada); Radiation Medicine Program, Princess Margaret Hospital/University Health Network, Toronto, Ontario M5G 2M9 (Canada); Department of Radiation Oncology, University of Toronto, Ontario M5G 2M9 (Canada)

2013-12-15

242

MOCVD growth and characterization of ZnO nanowire arrays for advanced ultraviolet detectors  

NASA Astrophysics Data System (ADS)

Zinc oxide (ZnO) provides a unique wide bandgap biocompatible material system exhibiting both semiconducting and piezoelectric properties, and is a versatile functional material that has a diverse group of growth morphologies. Bulk ZnO has a bandgap of 3.37 eV that corresponds to emissions in the solar blind ultraviolet (UV) spectral band (240-280 nm). We have grown highly ordered vertical arrays of ZnO nanowires (NWs) and nanorods using a metal organic chemical vapor deposition (MOCVD) growth process on Si(111), SiO2, and sapphire substrates. The structural and optical properties of the grown vertically aligned ZnO nanostructure arrays were characterized by scanning electron microscopy (SEM), X-ray diffraction (XRD), and photoluminescence (PL) measurements. The unique diffraction pattern for ZnO(002) concurred with the SEM inspection indicating vertical orientation of the NWs and nanorods. UV detectors based on ZnO NWs offer high UV sensitivity and low visible sensitivity for applications such as missile plume detection and threat warning. An analytical model that can predict sensor performance with and without gain for a desired UV band of interest has also been developed that has the potential for substantial improvements in sensor performance and reduction in size for a variety of threat warning applications. In addition, testing and characterization of photomultiplier tubes (PMTs) exposed to eight individual UV LEDs having peak wavelengths ranging from 248 nm to 370 nm has been performed to provide a relative UV detection performance benchmark. Compared to PMTs, the NW arrays are expected to exhibit low noise, extended lifetimes, high quantum efficiency, and very low power requirements.

Rivera, Abdiel; Zeller, John; Manzur, Tariq; Sood, Ashok; Anwar, Mehdi

2012-10-01

243

A theoretical model for Schottky diodes for excluding the sneak current in cross bar array resistive memory.  

PubMed

Kirchhoff's law was used to examine the electrical specifications of selection diodes, which are essential for suppressing the read interference problems in nano-scale resistive switching cross bar arrays with a high block density. The diode in the cross bar array with a 100 Mb block density should have a reverse/forward resistance ratio of > 10(8), and a forward current density of > 10(5) A cm(-2) for stable reading and writing operation. Whilst normal circuit simulators are heavily overloaded when the number of cells (m) connected to one bit and word line is larger (m > 100), which is the desired range for high density cross bar arrays, the present model can provide a simple simulation. The validity of this new method was confirmed by a comparison with the previously reported method based on a voltage estimation. PMID:20739739

Kim, Gun Hwan; Kim, Kyung Min; Seok, Jun Yeong; Lee, Hyun Ju; Cho, Deok-Yong; Han, Jeong Hwan; Hwang, Cheol Seong

2010-09-24

244

A theoretical model for Schottky diodes for excluding the sneak current in cross bar array resistive memory  

NASA Astrophysics Data System (ADS)

Kirchhoff's law was used to examine the electrical specifications of selection diodes, which are essential for suppressing the read interference problems in nano-scale resistive switching cross bar arrays with a high block density. The diode in the cross bar array with a 100 Mb block density should have a reverse/forward resistance ratio of > 108, and a forward current density of > 105 A cm - 2 for stable reading and writing operation. Whilst normal circuit simulators are heavily overloaded when the number of cells (m) connected to one bit and word line is larger (m\\gg 100 ), which is the desired range for high density cross bar arrays, the present model can provide a simple simulation. The validity of this new method was confirmed by a comparison with the previously reported method based on a voltage estimation.

Kim, Gun Hwan; Kim, Kyung Min; Seok, Jun Yeong; Lee, Hyun Ju; Cho, Deok-Yong; Han, Jeong Hwan; Hwang, Cheol Seong

2010-09-01

245

InGaAs Schottky barrier diode array detector for a real-time compact terahertz line scanner.  

PubMed

We present a terahertz (THz) broadband antenna-integrated 1 × 20 InGaAs Schottky barrier diode (SBD) array detector with an average responsivity of 98.5 V/W at a frequency of 250 GHz, which is measured without attaching external amplifiers and Si lenses, and an average noise equivalent power (NEP) of 106.6 pW/?Hz. The 3-dB bandwidth of the SBD detector is also investigated at approximately 180 GHz. For implementing an array-type SBD detector by a simple fabrication process to achieve a high yield, a structure comprising an SiN(x) layer instead of an air bridge between the anode and the cathode is designed. THz line beam imaging using a Gunn diode emitter with a center frequency of 250 GHz and a 1 × 20 SBD array detector is successfully demonstrated. PMID:24216813

Han, Sang-Pil; Ko, Hyunsung; Park, Jeong-Woo; Kim, Namje; Yoon, Young-Jong; Shin, Jun-Hwan; Kim, Dae Yong; Lee, Dong Hun; Park, Kyung Hyun

2013-11-01

246

Slanted n-ZnO/p-GaN nanorod arrays light-emitting diodes grown by oblique-angle deposition  

NASA Astrophysics Data System (ADS)

High-efficient ZnO-based nanorod array light-emitting diodes (LEDs) were grown by an oblique-angle deposition scheme. Due to the shadowing effect, the inclined ZnO vapor-flow was selectively deposited on the tip surfaces of pre-fabricated p-GaN nanorod arrays, resulting in the formation of nanosized heterojunctions. The LED architecture composed of the slanted n-ZnO film on p-GaN nanorod arrays exhibits a well-behaving current rectification of junction diode with low turn-on voltage of 4.7 V, and stably emits bluish-white luminescence with dominant peak of 390 nm under the operation of forward injection currents. In general, as the device fabrication does not involve passivation of using a polymer or sophisticated material growth techniques, the revealed scheme might be readily applied on other kinds of nanoscale optoelectronic devices.

Lee, Ya-Ju; Yang, Zu-Po; Lo, Fang-Yuh; Siao, Jhih-Jhong; Xie, Zhong-Han; Chuang, Yi-Lun; Lin, Tai-Yuan; Sheu, Jinn-Kong

2014-05-01

247

Ultraviolet photoelectron spectroscopy on new heterocyclic materials for multilayer organic light emitting diodes  

Microsoft Academic Search

Electronic band structure of three heterocyclic model compounds: 5,12-dihydro-quinoxalino-2,3-b-phenazine; 7,18-dihydro-5,7,11,16,18,20,22-octa-aza-nonacene; and 1,3,5-Tris[(3-phenyl-6-tri-fluoro-methyl)-quinoxaline-2-yl]benzene was studied by ultraviolet photoelectron spectroscopy. We also determined their ionisation potential, between 5.3 and 6.0eV, suggesting that these materials can efficiently act as electron transporting layer in organic light emitting devices (OLEDs).

M. B. Casu; P. Imperia; S. Schrader; B. Falk; M. Jandke; P. Strohriegl

2001-01-01

248

Vertical AlGaN deep ultraviolet light emitting diode emitting at 322 nm fabricated by the laser lift-off technique  

Microsoft Academic Search

A vertical AlGaN deep ultraviolet (DUV) light emitting diode (LED) emitting at 322 nm was fabfricated by the laser lift-off technique. The emission area extended to the entire electrode uniformly, and the current crowding was suppressed effectively in the devices. As a result, the differential conductance of the vertical LED was improved by a factor of 5 and the operation

Koji Kawasaki; Choshiro Koike; Yoshinobu Aoyagi; Misaichi Takeuchi

2006-01-01

249

Large-area transparent conductive few-layer graphene electrode in GaN-based ultra-violet light-emitting diodes  

Microsoft Academic Search

We report on the development of a large-area few-layer graphene (FLG)--based transparent conductive electrode as a current spreading layer for GaN-based ultraviolet (UV) light-emitting diodes (LEDs). Large-area FLG was deposited on Cu using the chemical vapor deposition (CVD) method and subsequently transferred to the surface of the UV LED. UV light at a peak of 372 nm was emitted through

Byung-Jae Kim; Chongmin Lee; Younghun Jung; Kwang Hyeon Baik; Michael A. Mastro; Jennifer K. Hite; Charles R. Eddy; Jihyun Kim

2011-01-01

250

Development of gallium nitride-based ultraviolet and visible light-emitting diodes using hydride vapor-phase epitaxy and molecular beam epitaxy  

Microsoft Academic Search

Much of the work done on ultraviolet (UV) and visible III-Nitrides-based light emitting diodes (LEDs) involves growth by metal-organic chemical vapor deposition (MOCVD). In this dissertation, the growth, development, and fabrication of III-Nitrides-based UV and visible LEDs with very high photon conversion and extraction efficiencies using hydride vapor-phase epitaxy (HVPE) and radio frequency (rf) plasma-assisted molecular beam epitaxy (PAMBE) is

Jasper Sicat Cabalu

2006-01-01

251

Gradient Doping of Mg in p-Type GaN for High Efficiency InGaN–GaN Ultraviolet Light-Emitting Diode  

Microsoft Academic Search

The performance of a InGaN-GaN multiple quantum-well (MQW) ultraviolet (UV) light-emitting diode (LED) with an emission of 385 nm was enhanced by a gradient doping of Mg in the p-GaN layer. The optical output power was enhanced by 21% at an input current of 20 mA compared to that of a UV LED with a uniformly doped p-GaN layer. The

Min-Ki Kwon; Il-Kyu Park; Ja-Yeon Kim; Jeom-Oh Kim; Bongjin Kim; Seong-Ju Park

2007-01-01

252

A 48-pixel array of single photon avalanche diodes for multispot single molecule analysis  

NASA Astrophysics Data System (ADS)

In this paper we present an array of 48 Single Photon Avalanche Diodes (SPADs) specifically designed for multispot Single Molecule Analysis. The detectors have been arranged in a 12x4 square geometry with a pitch-to-diameter ratio of ten in order to minimize the collection of the light from non-conjugated excitation spots. In order to explore the tradeoffs between the detectors' performance and the optical coupling with the experimental setup, SPADs with an active diameter of 25 and of 50?m have been manufactured. The use of a custom technology, specifically designed for the fabrication of the detectors, allowed us to combine a high photon detection efficiency (peak close to 50% at a wavelength of 550nm) with a low dark count rate compatible with true single molecule detection. In order to allow easy integration into the optical setup for parallel single-molecule analysis, the SPAD array has been incorporated in a compact module containing all the electronics needed for a proper operation of the detectors.

Gulinatti, Angelo; Rech, Ivan; Maccagnani, Piera; Ghioni, Massimo

2013-01-01

253

Fast single-photon avalanche diode arrays for laser Raman spectroscopy.  

PubMed

We incorporate newly developed solid-state detector technology into time-resolved laser Raman spectroscopy, demonstrating the ability to distinguish spectra from Raman and fluorescence processes. As a proof of concept, we show fluorescence rejection on highly fluorescent mineral samples willemite and spodumene using a 128×128 single-photon avalanche diode (SPAD) array with a measured photon detection efficiency of 5%. The sensitivity achieved in this new instrument architecture is comparable to the sensitivity of a technically more complicated system using a traditional photocathode-based imager. By increasing the SPAD active area and improving coupling efficiency, we expect further improvements in sensitivity by over an order of magnitude. We discuss the relevance of these results to in situ planetary instruments, where size, weight, power, and radiation hardness are of prime concern. The potential large-scale manufacturability of silicon SPAD arrays makes them prime candidates for future portable and in situ Raman instruments spanning numerous applications where fluorescence interference is problematic. PMID:21931428

Blacksberg, Jordana; Maruyama, Yuki; Charbon, Edoardo; Rossman, George R

2011-09-15

254

A 48-pixel array of Single Photon Avalanche Diodes for multispot Single Molecule analysis  

PubMed Central

In this paper we present an array of 48 Single Photon Avalanche Diodes (SPADs) specifically designed for multispot Single Molecule Analysis. The detectors have been arranged in a 12×4 square geometry with a pitch-to-diameter ratio of ten in order to minimize the collection of the light from non-conjugated excitation spots. In order to explore the trade-offs between the detectors’ performance and the optical coupling with the experimental setup, SPADs with an active diameter of 25 and of 50µm have been manufactured. The use of a custom technology, specifically designed for the fabrication of the detectors, allowed us to combine a high photon detection efficiency (peak close to 50% at a wavelength of 550nm) with a low dark count rate compatible with true single molecule detection. In order to allow easy integration into the optical setup for parallel single-molecule analysis, the SPAD array has been incorporated in a compact module containing all the electronics needed for a proper operation of the detectors.

Rech, Ivan; Maccagnani, Piera; Ghioni, Massimo

2013-01-01

255

Proposed Use of Zero Bias Diode Arrays as Thermal Electric Noise Rectifiers and Non-Thermal Energy Harvesters  

NASA Astrophysics Data System (ADS)

The well known built-in voltage potential for some select semiconductor p-n junctions and various rectifying devices is proposed to be favorable for generating DC electricity at ``zero bias'' (with no DC bias voltage applied) in the presence of Johnson noise or 1/f noise which originates from the quantum vacuum (Koch et al., 1982). The 1982 Koch discovery that certain solid state devices exhibit measurable quantum noise has also recently been labeled a finding of dark energy in the lab (Beck and Mackey, 2004). Tunnel diodes are a class of rectifiers that are qualified and some have been credited with conducting only because of quantum fluctuations. Microwave diodes are also good choices since many are designed for zero bias operation. A completely passive, unamplified zero bias diode converter/detector for millimeter (GHz) waves was developed by HRL Labs in 2006 under a DARPA contract, utilizing a Sb-based ``backward tunnel diode'' (BTD). It is reported to be a ``true zero-bias diode.'' It was developed for a ``field radiometer'' to ``collect thermally radiated power'' (in other words, `night vision'). The diode array mounting allows a feed from horn antenna, which functions as a passive concentrating amplifier. An important clue is the ``noise equivalent power'' of 1.1 pW per root hertz and the ``noise equivalent temperature difference'' of 10° K, which indicate sensitivity to Johnson noise (Lynch, et al., 2006). There also have been other inventions such as ``single electron transistors'' that also have ``the highest signal to noise ratio'' near zero bias. Furthermore, ``ultrasensitive'' devices that convert radio frequencies have been invented that operate at outer space temperatures (3 degrees above zero point: 3° K). These devices are tiny nanotech devices which are suitable for assembly in parallel circuits (such as a 2-D array) to possibly produce zero point energy direct current electricity with significant power density (Brenning et al., 2006). Photovoltaic p-n junction cells are also considered for possible higher frequency ZPE transduction. Diode arrays of self-assembled molecular rectifiers or preferably, nano-sized cylindrical diodes are shown to reasonably provide for rectification of electron fluctuations from thermal and non-thermal ZPE sources to create an alternative energy DC electrical generator in the picowatt per diode range.

Valone, Thomas F.

2009-03-01

256

Coherent Beam Combining of High-Power Broad-Area Laser Diode Array in CW and Pulsed Modes  

SciTech Connect

We present experimental results on coherent beam combining from large arrays of high power broad-area semiconductor lasers. Our laser array consists of 47 high-power anti-reflection coated broad-area semiconductor lasers and each laser emitter is capable of emitting 1.8 W when uncoated with a maximum array output power of 80W. The total available power from the AR coated array is approximately 40W. By using an external V-shape cavity design, we experimentally demonstrated a coherently combined beam at the output power of {approx}13 W with the 0.07 nm FWHM spectrum linewidth that is limited by the sensitivity of the optical spectrum analyzer. We also discuss coherent beam combining of high power broad area laser diode array in current driver pulse mode operation.

Liu, Bo [ORNL; Liu, Yun [ORNL; Braiman, Yehuda [ORNL

2010-01-01

257

High speed GaN micro-light-emitting diode arrays for data communications  

NASA Astrophysics Data System (ADS)

Micro light-emitting diode (micro-LED) arrays based on an AlInGaN structure have attracted much interest recently as light sources for data communications. Visible light communication (VLC), over free space or plastic optical fibre (POF), has become a very important technique in the role of data transmission. The micro-LEDs which are reported here contain pixels ranging in diameter from 14 to 84?m and can be driven directly using a high speed probe or via complementary metal-oxide semiconductor (CMOS) technology. The CMOS arrays allow for easy, computer control of individual pixels within arrays containing up to 16×16 elements. The micro-LEDs best suited for data transmission have peak emissions of 450nm or 520nm, however various other wavelengths across the visible spectrum can also be used. Optical modulation bandwidths of over 400MHz have been achieved as well as error-free (defined as an error rate of <1x10-10) data transmission using on-off keying (OOK) non-return-to-zero (NRZ) modulation at data rates of over 500Mbit/s over free space. Also, as a step towards a more practical multi-emitter data transmitter, the frequency response of a micro-LED integrated with CMOS circuitry was measured and found to be up to 185MHz. Despite the reduction in bandwidth compared to the bare measurements using a high speed probe, a good compromise is achieved from the additional control available to select each pixel. It has been shown that modulating more than one pixel simultaneously can increase the data rate. As work continues in this area, the aim will be to further increase the data transmission rate by modulating more pixels on a single device to transmit multiple parallel data channels simultaneously.

Watson, Scott; McKendry, Jonathan J. D.; Zhang, Shuailong; Massoubre, David; Rae, Bruce R.; Green, Richard P.; Gu, Erdan; Henderson, Robert K.; Kelly, A. E.; Dawson, Martin D.

2012-10-01

258

High Power Efficiency AlGaN-Based Ultraviolet Light-Emitting Diodes  

NASA Astrophysics Data System (ADS)

High-efficiency AlGaN-based 355 nm UV light-emitting diodes (LEDs) grown on low-dislocation-density AlGaN/sapphire templates with an output power of 9.8 mW (22.7 mW) at a DC current of 40 mA (100 mA) are reported. The corresponding maximum external quantum efficiency and maximum power efficiency are 7.2 and 6.5%, respectively. Based on a rate equation model, a method is presented to derive the extraction as well as the injection and internal quantum efficiency as a function of the driving current. The thus obtained injection and internal quantum efficiencies amount to 51 and 47% at 40 mA, the extraction efficiency to 29%.

Passow, Thorsten; Gutt, Richard; Kunzer, Michael; Pletschen, Wilfried; Kirste, Lutz; Forghani, Kamran; Scholz, Ferdinand; Köhler, Klaus; Wagner, Joachim

2013-08-01

259

Semiconducting polymer diodes: Large size, low cost photodetectors with excellent visible-ultraviolet sensitivity  

SciTech Connect

Photodiodes fabricated from conjugated polymers exhibit excellent sensitivity to visible-UV radiation. The photosensitivity increases with reverse bias voltage. The photoresponse of diodes fabricated from poly(3-octyl thiophene) is relatively flat in the visible and near UV; for wavelengths shorter than 550 nm, the absolute sensitivity is greater than 0.3 A/W under reverse bias of 15 V, larger than that of commercial UV-enhanced Si photodiodes. Photodiodes made from poly[2-methoxy-5-(2[prime]-ethyl-hexyloxy)-1,4-phenylene vinylene], MEH-PPV, sensitized with C[sub 60], show similar sensitivity. The ease of fabrication into large size, arbitrary shapes, and even onto flexible substrates makes the polymer photodiode a novel photodetector with potential for use in a wide range of applications.

Yu, G.; Pakbaz, K.; Heeger, A.J. (Institute for Polymers and Organic Solids, University of California at Santa Barbara, Santa Barbara, California 93106-5090 (United States))

1994-06-20

260

Study of optical anisotropy in nonpolar and semipolar AlGaN quantum well deep ultraviolet light emission diode  

NASA Astrophysics Data System (ADS)

This paper analyzes the optical polarization characteristics and internal quantum efficiency (IQE) of an AlGaN based polar, nonpolar, and semipolar deep ultra-violet (UV) light emitting diode (LED). A one dimensional model is used to solve drift-diffusion, Poisson equations, and 6 × 6 k.p Schrodinger equations to investigate band structure and emission characteristics. The light emission polarization ratios of c-plane, nonpolar, and semipolar AlGaN based deep UV LEDs with different Al compositions and injection current were studied. The study shows that the optical polarization of the c-plane AlGaN based deep UV LED is dominated by the out-plane polarization as the Al composition increases. For nonpolar and semipolar structures, the light polarization direction is mainly dominated by the in-plane polarized light which is good for the surface emitting. Finally, influences of the IQE by changing the p-type activation energy, growth orientation, and nonradiatve lifetime are studied in this paper.

Wang, Chang-Pei; Wu, Yuh-Renn

2012-08-01

261

Deep-ultraviolet tailored- and low-refractive index antireflection coatings for light-extraction enhancement of light emitting diodes  

NASA Astrophysics Data System (ADS)

An omnidirectional antireflection (AR) coating for a deep-ultraviolet (UV) AR band is designed and fabricated on the sapphire substrate of a deep-UV flip-chip light-emitting diode (LED) device. The two-layer AR coating uses the tailored- and low-refractive index nanoporous alumina fabricated by glancing-angle deposition methodology. The AR coating effectively matches the refractive indices between the air and sapphire substrate. At close-to-normal angles of incidence, this AR coating almost completely eliminates the Fresnel reflection at the sapphire/air interface of the deep-UV LED device. The resulting improvement of the light-extraction efficiency by 8% is in good agreement with the simulation results. For a total thickness of 172 nm for the two-layer AR coating, extinction was negligible (<2%). The results show that nanoporous alumina thin films are excellent tailored- and low-refractive index thin film materials for high-performance deep-UV AR coating applications.

Yan, Xing; Shatalov, Max; Saxena, Tanuj; Shur, Michael S.

2013-04-01

262

365-nm ultraviolet-light-emitting diodes with an output power of over 400 mW  

NASA Astrophysics Data System (ADS)

We fabricated high power ultraviolet (UV) light emitting diodes (LEDs), whose emission wavelength is around 365 nm. We found that, in order to improve the external quantum efficiency (?ex) of UV LEDs, it is very important to reduce the optical self-absorption and the threading dislocation density (TDD) of epi-layers. Therefore, at first, UV LEDs epi-layers were grown on high-quality GaN templates (TDD = 2x 108/cm2) with sapphire substrates, and then the GaN templates and the sapphire substrates were removed by using laser-induced lift-off and polishing techniques. As a result, we obtained the low self-absorption and low TDD UV LEDs. When this UV LED was operated at a forward-bias pulsed current of 500 mA at room temperature (RT), the peak wavelength, the output power (Po), the forward voltage (Vf) and the ?ex were 365 nm, 410 mW, 5.3 V, 24%, respectively. Moreover, at a forward-bias direct current of 500 mA at RT, Po, Vf and ?ex were 360 mW, 5.0 V, 21%, respectively.

Morita, Daisuke; Sano, Masahiko; Yamamoto, Masashi; Matoba, Kousuke; Yasutomo, Katsuhiro; Akaishi, Kazuyuki; Kasai, Yoshio; Nagahama, Shin-Ichi; Mukai, Takashi

2004-07-01

263

Near-Ultraviolet Light-Emitting Devices Using Vertical ZnO Nanorod Arrays  

NASA Astrophysics Data System (ADS)

Reports on electroluminescence (EL) in solid-state, nanomaterial-based devices emitting in the lower wavelength range of the visible spectrum are limited, and the emission stability of these devices is rarely reported. We have fabricated light-emitting devices (LEDs) based on integration of n-ZnO nanorods and p-GaN films, which emit in the violet to near-ultraviolet (NUV) region. We also present data on the stability of EL in fabricated devices. Vertical arrays on ZnO nanorods, with estimated ZnO nanorod density ~108 cm-2, were grown on p-GaN films with typical length of ~4 ?m and width of ~120 nm. The NUV LEDs show low turn-on voltage (~3.0 V), small reverse saturation current (~10 ?A), and more than two orders of magnitude rectification ratio, all of which indicates a good-quality p- n junction at the p-GaN/ n-ZnO nanorod interface. The EL spectra of LEDs present an emission band centered at ~403 nm. Gaussian fitting of the EL peak revealed three emission peaks at 378 nm, 405 nm, and 431 nm with dominant emission in the NUV region. Significantly, the fabricated NUV LEDs present stable and repeatable EL characteristics, as revealed by bias-stress stability tests. The good electrical properties and stable EL performance make these nanostructure-based NUV LEDs potential candidates for mass production of next-generation lighting devices.

Jha, S.; Wang, C. D.; Luan, C. Y.; Liu, C. P.; Bin, H.; Kutsay, O.; Bello, I.; Zapien, J. A.; Zhang, W. J.; Lee, S. T.

2012-05-01

264

8xxnm kW conduction cooled QCW diode arrays with both electrically conductive and insulation submounts  

NASA Astrophysics Data System (ADS)

We present kW QCW vertical and horizontal arrays composed of 200W bars (peak power) at 8xxnm wavelength. We also present an unique Bar-on-Submount design using the electrically insulating submounts, which can provide a platform for simple and flexible horizontal array construction. The p-n junction temperature of the arrays under QCW operation is modeled with FEA software, as well as measured in this research. Updated reliability test results for these kW arrays will be also reported. As the examples, we present the performance of the vertical arrays with > 57% Wall-Plug-Efficiency and the horizontal arrays with < 23 degree fast axis divergence (FWHM), both with 808nm wavelength. The available wavelength for such arrays ranges from 780nm to beyond 1 um. Coherent also have the capability to produce the array with wide and relatively uniform spectrum for athermal pumping of solid-state lasers, by integrating diode lasers bars with different wavelength into single array.

Du, Jihua; Zhou, Hailong; Schleuning, David; Agrawal, Vivek; Morales, John; Hasenberg, Thomas; Reed, Murray

2008-03-01

265

Comprehensive Material Study of MOCVD grown Aluminum Indium Nitride and Development of Relaxed Template for Ultraviolet Diode Lasers  

NASA Astrophysics Data System (ADS)

AlGaN based conventional deep ultraviolet (UV) light emitting diodes (LEDs) grown on a sapphire or SiC substrate suffer from high threading dislocation density (TDD) (> 1 x 109 cm-2). The high quality bulk AlN substrate (TDD ˜ 1 x 104 cm-2) has shown promising results for high power deep UV LEDs but the substrates are not readily available yet. The performance of UV laser diodes (LDs) has been rapidly improved over the past few years. However, intrinsic valence band property of c-plane AlN could result in poor optical gain for c-plane LDs, especially in UV-C range. In this work, different approaches have been explored for further development of UV LEDs and LDs. The success of c-plane InGaN LEDs has been attributed to the indium induced local potential minima in a length scale shorter than the dislocation spacing. As a result, high internal quantum efficiency (IQE) can be achieved even with high TDD. UV LEDs could potentially benefit from this phenomenon by using AlInN as an active layer. However, due to the lack of understanding of this alloy, we start from the growth study of AlInN by metal organic chemical vapor deposition (MOCVD). High structural quality Al0.82In0.18N has been achieved on GaN, but large Stokes' shift of ˜0.6 eV and broad photoluminescence (PL) spectrum (˜0.3 eV) were also observed. The time resolved PL study revealed extremely long decay lifetime, suggesting the presence of deep traps. Electrical analysis of AlInN by capacitance -- voltage measurement showed n-type conductivity for UID Al0.82In0.18N, possibly due to oxygen. High quality semipolar (112¯2) Al0.76In 0.24N showed emission energy below the bandgap of GaN, allowing us to obtain the electroluminescence characteristics of AlInN. Appearance of a narrow peak under high injection current could shed a light on the emission property of AlInN. Semipolar substrates offer a number of advantages for UV emitting AlGaInN based laser diodes, including higher gain, an ability to operate with nearly transverse electric (TE) optical modes, and an ability to provide pseudo-substrates with tailorable lattice constants, something unavailable from bulk c-plane AlN substrates. AlInN and AlGaN lavers with various thicknesses and compositions have been grown on (202¯1) and (112¯2) bulk GaN substrates by MOCVD. With increasing thickness and Al composition, various defects -- c-plane misfit dislocations, cracks, and secondary defects -- were observed. The critical thickness of each process has been empirically estimated. We have also grown AlGaN on (202¯1) GaN, step grading to higher aluminum composition to minimize the generation of undesired defects. Multiple quantum wells (MQW) and LEDs were grown on a relaxed AlGaN on (202¯1) GaN. IQE measurements and the diode operation of near UV LEDs (lambda˜385 nm) on the relaxed buffer showed a promising result for device application of relaxed AlGaN template.

Chung, Roy B.

266

Polarization-induced pn diodes in wide-band-gap nanowires with ultraviolet electroluminescence.  

PubMed

Almost all electronic devices utilize a pn junction formed by random doping of donor and acceptor impurity atoms. We developed a fundamentally new type of pn junction not formed by impurity-doping, but rather by grading the composition of a semiconductor nanowire resulting in alternating p and n conducting regions due to polarization charge. By linearly grading AlGaN nanowires from 0% to 100% and back to 0% Al, we show the formation of a polarization-induced pn junction even in the absence of any impurity doping. Since electrons and holes are injected from AlN barriers into quantum disk active regions, graded nanowires allow deep ultraviolet LEDs across the AlGaN band-gap range with electroluminescence observed from 3.4 to 5 eV. Polarization-induced p-type conductivity in nanowires is shown to be possible even without supplemental acceptor doping, demonstrating the advantage of polarization engineering in nanowires compared with planar films and providing a strategy for improving conductivity in wide-band-gap semiconductors. As polarization charge is uniform within each unit cell, polarization-induced conductivity without impurity doping provides a solution to the problem of conductivity uniformity in nanowires and nanoelectronics and opens a new field of polarization engineering in nanostructures that may be applied to other polar semiconductors. PMID:22268600

Carnevale, Santino D; Kent, Thomas F; Phillips, Patrick J; Mills, Michael J; Rajan, Siddharth; Myers, Roberto C

2012-02-01

267

Development of proximity and electrostatically focused diodes for UV measurements from sounding rockets  

Microsoft Academic Search

This report describes the development of two types of imaging digicon detectors for ultraviolet measurements from rockets. The detectors consist of sealed tubes with a semitransparent photocathode of cesium iodide or cesium telluride. Photoelectrons accelerated to about 25 kV are detected by a silicon diode array. One tube has a ten by ten square array with proximity focussing and is

S. L. Russak; J. C. Flemming; R. E. Huffman; D. E. Paulsen; J. C. Larrabee

1979-01-01

268

High energy erbium laser end-pumped by a laser diode bar array coupled to a Nonimaging Optic Concentrator  

NASA Astrophysics Data System (ADS)

A high energy Er 3+, Yb 3+:glass laser end pumped by a laser diode array emitting at 980 nm coupled to a Nonimaging Optic Concentrator (NOC) is demonstrated. Energy up to 100 mJ and a 16% slope efficiency are achieved in a plano-plano laser cavity. The energy transfer coefficient from Yb 3+ to Er 3+ is estimated by a new method.

Tanguy, E.; Feugnet, G.; Pocholle, J. P.; Blondeau, R.; Poisson, M. A.; Duchemin, J. P.

1998-01-01

269

High-power, low-divergence, linear array of quasi-diffraction-limited beams supplied by tapered diodes  

Microsoft Academic Search

We describe for the first time to our knowledge the performance for a linear array of tapered laser diodes with both fast- and slow-axis collimation using a microlens for fast-axis collimation and a laser-written phase plate for slow-axis collimation and correction of the residual fast-axis errors from lens aberrations, thermal lensing, astigmatism, pointing errors, and other wavefront distortions. The phase

Gilbert L. Bourdet; Imen Hassiaoui; Roy McBride; J. F. Monjardin; Howard Baker; Nicolas Michel; Michel Krakowski

2007-01-01

270

Sampling and identification of natural dyes in historical maps and drawings by liquid chromatography with diode-array detection  

Microsoft Academic Search

A simple and rapid liquid chromatographic with diode-array UV–vis spectrophotometric detection (HPLC–DAD) method for identification of natural dyes has been developed. Chromatographic retention of carminic acid, indigotin, crocetin, gambogic acid, alizarin and purpurin has been studied. The mobile phase consisted of 40mM SDS–10mM phosphate buffer solution (pH 2.3)–0.1% TFA (eluent A) and acetonitrile (eluent B) using a programmed gradient (5%

Rosario Blanc; Teresa Espejo; Ana López-Montes; David Torres; Guillermo Crovetto; Alberto Navalón; José Luis Vílchez

2006-01-01

271

Buildup of steady-state picosecond pulses in an actively mode-locked laser-diode array  

Microsoft Academic Search

An experimental study has been made of the temporal and spectral characteristics of an actively mode-locked laser-diode array in an external cavity as it evolves to the steady state. It is found that the buildup time to steady-state picosecond pulses takes less than 45 round trips. The number of clusters of the longitudinal-mode spectrum reduces during the evolution and finally

Jahn-Chung Kuo; C.-S. Chang; Ci-Ling Pan

1991-01-01

272

Tunable Picosecond Pulse Generation from an Actively Mode-Locked Laser Diode Array with Intracavity Chirp Compensation  

Microsoft Academic Search

Wavelength-tunable picosecond pulses have been generated from an actively mode-locked laser diode array in an external cavity. The cavity incorporated a folded dispersive delay line which provided functions of pulse compression, wavelength tuning and spatial mode control. By varying the group velocity dispersion inside the cavity, the laser pulse width was intra-cavity compressed from 44 to 25 ps. The laser

Chi-Luen Wang; Ci-Ling Pan

1994-01-01

273

Stable 4 W CW solid-state green source pumped by fibre-coupled diode-laser arrays  

Microsoft Academic Search

A high-power Nd:YAG laser end-pumped by a fibre-coupled diode-laser array system is described. When operated at 1 ?m, the device produced 10 W of output power in the TEM00 transverse mode with a slope efficiency of 43%. The system was operated using both 600 ?m and 400 ?m core, 0·37 N.A. multimode fibres for delivery of the pump radiation, and

C. Yelland; W. Sibbett

1996-01-01

274

Localized Surface Plasmon-Enhanced Nitride-Based Light-Emitting Diode With Ag Nanotriangle Array by Nanosphere Lithography  

Microsoft Academic Search

We describe a method to enhance the light output power of nitride-based light-emitting diodes (LEDs) through the coupling of multiple quantum wells (MQWs) with localized surface plasmon (LSP). The LSP was generated on an Ag nanotriangle array (NTA) on a 40-nm-thick p-type GaN layer beneath the p-pad of the LED, which was partially etched by inductively coupled plasma system. The

C. C. Kao; Y. K. Su; C. L. Lin; J. J. Chen

2010-01-01

275

Determination of imipenem and rifampicin in mouse plasma by high performance liquid chromatography–diode array detection  

Microsoft Academic Search

A high performance liquid chromatographic (HPLC) method for the determination of imipenem and rifampicin was developed and validated. The method involves plasma deproteinisation with methanol, gradient elution on a RP-18 column and diode array detection. Separation was carried out in 8min using a mobile phase composed of methanol and 0.2M borate buffer (pH 7.2). Imipenem and rifampicin were detected at

R. Fernández-Torres; M. A. Bello-López; M. Callejón-Mochón; J. C. Jiménez-Sánchez

2008-01-01

276

Determination of p?Methoxyamphetamine by Capillary Electrophoresis with Diode Array Detection from Urine and Plasma Samples  

Microsoft Academic Search

In recent years, a number of newer designer drugs have entered the illicit drug market. The amphetamine derivatives represent the largest group of designer drugs. This paper describes a method for quantifying p-methoxyamphetamine in human plasma and urine by capillary electrophoresis with a diode array detector. Using an aqueous pH 2.5 phosphate buffer, CE analysis gave peaks with good symmetry

Maria Nieddu; Gianpiero Boatto; Loredana Sini; Giuseppina Dessì

2007-01-01

277

High-performance liquid chromatographic screening method for mycotoxins using new retention indexes and diode array detection  

Microsoft Academic Search

A reversed-phase high-performance liquid chromatographic (RP-HPLC) screening method for the determination of mycotoxins has been developed. The toxins were characterized by retention indexes and on-line UV spectra produced with a diode array detector (DAD). Retention indexes of mycotoxins exhibiting a wide range of polarities and chemical structures were determined during linear gradient elution with an acetonitrile\\/ water solvent system. The

Pirjo Kuronen

1989-01-01

278

Direct determination of pyrethrins in pyrethrum extracts by reversed-phase high-performance liquid chromatography with diode-array detection  

Microsoft Academic Search

A simple, rapid method for the direct determination of six pyrethrin esters in pyrethrum extracts by reversed-phase high-performance liquid chromatography with diode-array detection has been described. The separation of the six esters was based on a binary mobile phase optimization, temperature control and the use of a C8 octyl column with 5-?m particles. Diode array detection and quantitation were selectively

I-Hsiung Wang; Venkatraman Subramanian; Richard Moorman; James Burleson; Jinren Ko

1997-01-01

279

Monolithic two-dimensional surface-emitting arrays of GaAs/AlGaAs diode lasers  

NASA Technical Reports Server (NTRS)

Monolithic two-dimensional arrays of GaAs/AlGaAs diode lasers with light emission normal to the surface have been obtained by fabricating edge-emitting quantum-well lasers coupled with external mirrors that deflect the radiation from the laser facets by 90 degrees. Linear arrays of GaAs/AlGaAs devices in which one of the laser facets was cleaved while the other facet and an adjacent 45 degree deflector were formed by ion-beam-assisted etching (IBAE) have been reported. For the arrays reported in this section, IBAE was used to form all of the laser facets and the deflecting mirrors. A mass transport process of the type employed to fabricate two-dimensional arrays of GaInAsP/InP lasers coupled with deflecting mirrors is not known for AlGaAs.

1988-01-01

280

Silicon PIN diode hybrid arrays for charged particle detection: Building blocks for vertex detectors at the SSC  

SciTech Connect

Two-dimensional arrays of solid state detectors have long been used in visible and infrared systems. Hybrid arrays with separately optimized detector and readout substrates have been extensively developed for infrared sensors. The characteristics and use of these infrared readout chips with silicon PIN diode arrays produced by MICRON SEMICONDUCTOR for detecting high-energy particles are reported. Some of these arrays have been produced in formats as large as 512 /times/ 512 pixels; others have been radiation hardened to total dose levels beyond 1 Mrad. Data generation rates of 380 megasamples/second have been achieved. Analog and digital signal transmission and processing techniques have also been developed to accept and reduce these high data rates. 9 refs., 15 figs., 2 tabs.

Kramer, G.; Gaalema, S.; Shapiro, S.L.; Dunwoodie, W.M.; Arens, J.F.; Jernigan, J.G.

1989-05-01

281

Improve beam quality of high-power laser diode array stacks by external-cavity technique  

NASA Astrophysics Data System (ADS)

Because of its own structure's limitation, the beam divergence angle of the semiconductor laser is very large. In the fastaxis direction, the beam plays good quality and can be collimated less than 1° by using cylindrical micro-lens. However, in the slow-axis direction, the beam quality is too poor to be collimated to a small pattern. This could limit its application in the fields which need high beam quality. For high-power laser diode array (LDA), external-cavity technique can make all the emitters working in the same wavelength, and can improve their beam quality. In this paper, direct feedback method was employed to achieve cross-injection between 25 emitters of a LD bar by using a stripe mirror. At a certain cavity length, after the reflection of the external-cavity mirror's reflective stripe, the beam with large slow-axis divergence angle will feedback to the spacer region between the emitters and lose its energy, or would exactly feedback to the neighbor emitter. Simultaneously, the beam with small divergence angle would output from the transparent stripe of the external-cavity mirror. The slow-axis divergence of the stacks with two bars was suppressed from 6°to 2°by using this technique.

Pi, Haoyang; Xin, Guofeng; Qu, Ronghui; Fang, Zujie

2010-11-01

282

Online diode-array UV spectroscopy of sulfur and nitrogen compounds  

NASA Astrophysics Data System (ADS)

On-line real-time monitoring of the gas-phase concentrations of sulfur containing molecules such as sulfur dioxide (SO2), hydrogen sulfide (H2S), carbon disulfide (CS2) and nitrogen containing molecules such as nitric oxide (NO), nitrogen dioxide (NO2), nitrous oxide (N2O) and ammonia (NH3) is of major importance in pollution monitoring and reduction and in the optimization of many gas-phase industrial processes. A UV optimized non-solarizing fiber-optic based diode-array analyzer system utilizing a 10,000 hour MTBF Xenon pulsed source has been developed and proven on-line. An on-board chemometric prediction engine allows for the simultaneous multi-component analysis of measured spectra of sample gases in real-time. Fiber-optic coupling of the analyzer to the gas flow cell housed within the sampling system allows intrinsically safe measurement to be carried out on samples gases at temperatures up to 310 C and pressures to 60 barg. Detection sensitivity down to ppm levels have been realized including such measurement applications as NH3, NO and H2S monitoring.

Driver, Richard D.; Stein, Israel M.

1999-12-01

283

Visible light initiated polymerisation of styrenic monolithic stationary phases using 470 nm light emitting diode arrays  

PubMed Central

Poly(styrene-co-divinylbenzene) monolithic stationary phases have been synthesised for the first time by photoinitiated polymerisation. An initiator composed of (+)-S-camphorquinone/ethyl-4-dimethylaminobenzoate/N-methoxy-4-phenylpyridinium tetrafluoroborate was activated using a 470 nm light emitting diode array as the light source. Spatially controlled polymerisation of styrenic monoliths has been achieved within specific sections of a 100 µm i.d. polytetrafluoroethylene (PTFE)-coated fused silica capillary using simple photo-masking. The sharpness of the edges was confirmed by optical microscopy, while scanning electron microscopy was used to verify a typical porous, globular morphology. Flow resistance data was used to assess the permeability of the monoliths and they were found to have good flow through properties with a flow resistance of 0.725 MPa cm?1 at 1 µl min?1 (water, 20°C). Conductivity profiling along the length of the capillary was used to assess their lateral homogeneity. Monoliths which were axially rotated during polymerisation were found to be homogeneous along the whole length of the capillary. The monolithic stationary phases were applied to the reversed phase gradient separation of a mixture of proteins. Column fabrication showed excellent reproducibility with the retention factor (k) having a RSD value of 2.6% for the batch and less than 1.73% on individual columns.

Walsh, Zarah; Levkin, Pavel A.; Paull, Brett; Svec, Frantisek; Macka, Mirek

2010-01-01

284

Determination of amlodipine enantiomers in pharmaceuticals using capillary electrophoresis separation and diode array detection.  

PubMed

The present work describes a capillary zone electrophoresis (CZE) separation technique coupled with on-capillary diode array detector (DAD) for highly reliable enantioselective determination of amlodipine (AML) in commercial tablets. For the separation of AML enantiomers, (2-hydroxypropyl)-beta-cyclodextrin (HP-beta-CD) was an appropriate chiral selector providing complete enantioresolution. Optimized separation conditions consisted of 50 mmol/l glycine-acetate buffer, pH 3.2, 50 mg/ml HP-beta-CD. Hydroxyethylcellulose (HEC, 0.2% w/v) served as an electroosmotic flow (EOF) suppressor in this buffer. DAD detection was used for the characterization of the composition of separated zones according to differences in corresponding UV-VIS spectra (scanned in interval 200-800 nm). It was demonstrated, comparing reference and real spectra of the analytes, that the proposed separation method was selective enough to produce pure (non-mixed, i.e. spectrally homogeneous) analyte zones without any interfering compound. Successful validation and application of the proposed CZE-DAD method suggest its routine use in enantioselective control of AML in pharmaceuticals. PMID:19320277

Mikus, P; Maráková, K; Valásková, I; Havránek, E

2009-02-01

285

Determination of retinyl palmitate in ointment by HPLC with diode array detection.  

PubMed

A simple and rapid HPLC with diode array detection method was developed for the determination of retinyl palmitate present together with other active substances in an ointment. Chromatographic separation was performed on 100 RP-18 Lichrospher column of particle size 5 microm. The mobile phase was methanol:water (98:2, v/v) and flow rate was 2.0 mL/min in isocratic mode. Samples were analyzed for 30 min. Spectophotometric detection was conducted at 325 nm. Under these conditions, the method featured high sensitivity, good precision and comparability of results as proven by the method validation and statistical analysis of the results. The limits of detection and determination were 0.4317 mg/100 mL and 1.3081 mg/100 mL, respectively, recovery values were measured at three levels 80%, 100% and 120% and yielded 101.05%, 101.34% and 100.43%, respectively. The linearity range was checked from 2 mg/100 mL to 10 mg/100 mL. The precision and inter-day precision of the method was expressed by relative standard deviation value and did not exceed 1.68%. PMID:20873414

Kwiecie?, Anna; Hubicka, Urszula; Krzek, Jan

2010-01-01

286

Instrumentation: Photodiode Array Detectors in UV-VIS Spectroscopy. Part II.  

ERIC Educational Resources Information Center

A previous part (Analytical Chemistry; v57 n9 p1057A) discussed the theoretical aspects of diode ultraviolet-visual (UV-VIS) spectroscopy. This part describes the applications of diode arrays in analytical chemistry, also considering spectroelectrochemistry, high performance liquid chromatography (HPLC), HPLC data processing, stopped flow, and…

Jones, Dianna G.

1985-01-01

287

Application of GaN-based ultraviolet-C light emitting diodes--UV LEDs--for water disinfection.  

PubMed

GaN-based ultraviolet-C (UV-C) light emitting diodes (LEDs) are of great interest for water disinfection. They offer significant advantages compared to conventional mercury lamps due to their compact form factor, low power requirements, high efficiency, non-toxicity, and overall robustness. However, despite the significant progress in the performance of semiconductor based UV LEDs that has been achieved in recent years, these devices still suffer from low emission power and relatively short lifetimes. Even the best UV LEDs exhibit external quantum efficiencies of only 1-2%. The objective of this study was to investigate the suitability of GaN-based UV LEDs for water disinfection. The investigation included the evaluation of the performance characteristics of UV LEDs at different operating conditions as well as the design of a UV LED module in view of the requirements for water treatment applications. Bioanalytical testing was conducted using Bacillus subtilis spores as test organism and UV LED modules with emission wavelengths of 269 nm and 282 nm. The results demonstrate the functionality of the developed UV LED disinfection modules. GaN-based UV LEDs effectively inactivated B. subtilis spores during static and flow-through tests applying varying water qualities. The 269 nm LEDs reached a higher level of inactivation than the 282 nm LEDs for the same applied fluence. The lower inactivation achieved by the 282 nm LEDs was compensated by their higher photon flux. First flow-through tests indicate a linear correlation between inactivation and fluence, demonstrating a well designed flow-through reactor. With improved light output and reduced costs, GaN-based UV LEDs can provide a promising alternative for decentralised and mobile water disinfection systems. PMID:21115187

Würtele, M A; Kolbe, T; Lipsz, M; Külberg, A; Weyers, M; Kneissl, M; Jekel, M

2011-01-01

288

Patterning the Cone Mosaic Array in Zebrafish Retina Requires Specification of Ultraviolet-Sensitive Cones  

PubMed Central

Cone photoreceptors in teleost fish are organized in precise, crystalline arrays in the epithelial plane of the retina. In zebrafish, four distinct morphological/spectral cone types occupy specific, invariant positions within a regular lattice. The cone lattice is aligned orthogonal and parallel to circumference of the retinal hemisphere: it emerges as cones generated in a germinal zone at the retinal periphery are incorporated as single-cell columns into the cone lattice. Genetic disruption of the transcription factor Tbx2b eliminates most of the cone subtype maximally sensitive to ultraviolet (UV) wavelengths and also perturbs the long-range organization of the cone lattice. In the tbx2b mutant, the other three cone types (red, green, and blue cones) are specified in the correct proportion, differentiate normally, and acquire normal, planar polarized adhesive interactions mediated by Crumbs 2a and Crumbs 2b. Quantitative image analysis of cell adjacency revealed that the cones in the tbx2b mutant primarily have two nearest neighbors and align in single-cell-wide column fragments that are separated by rod photoreceptors. Some UV cones differentiate at the dorsal retinal margin in the tbx2b mutant, although they are severely dysmorphic and are eventually eliminated. Incorporating loss of UV cones during formation of cone columns at the margin into our previously published mathematical model of zebrafish cone mosaic formation (which uses bidirectional interactions between planar cell polarity proteins and anisotropic mechanical stresses in the plane of the retinal epithelium to generate regular columns of cones parallel to the margin) reproduces many features of the pattern disruptions seen in the tbx2b mutant.

Raymond, Pamela A.; Colvin, Steven M.; Jabeen, Zahera; Nagashima, Mikiko; Barthel, Linda K.; Hadidjojo, Jeremy; Popova, Lilia; Pejaver, Vivek R.; Lubensky, David K.

2014-01-01

289

White light emission from blue and near ultraviolet light-emitting diodes precoated with a Sr3SiO5:Ce3+,Li+ phosphor.  

PubMed

White-light-emitting diodes (WLEDs) were fabricated by combining a yellow Sr3SiO5:Ce3+, Li+ phosphor with a blue light-emitting diode (LED) (460 nm chip) or a near ultraviolet (n-UV) LED (405 nm chip), respectively. Color temperature (Tc) of Sr3SiO5:Ce3+, Li+-based WLEDs could be tuned from 6500 to 100,000 K (blue LED pumping) and from 4900 to 50,000 K (n-UV LED pumping) without mixing with other phosphors. The blue LED-pumped WLED showed excellent white light (luminous efficiency=31.7 lm/W, Tc=6857 K) at 20 mA. This WLED showed a stable color coordinates property against an increase of the forward current. An n-UV LED-pumped WLED also showed bright white light (25.0 lm/W, 5784 K) at 20 mA. PMID:18059961

Jang, Ho Seong; Jeon, Duk Young

2007-12-01

290

Large-area transparent conductive few-layer graphene electrode in GaN-based ultra-violet light-emitting diodes  

NASA Astrophysics Data System (ADS)

We report on the development of a large-area few-layer graphene (FLG)--based transparent conductive electrode as a current spreading layer for GaN-based ultraviolet (UV) light-emitting diodes (LEDs). Large-area FLG was deposited on Cu using the chemical vapor deposition (CVD) method and subsequently transferred to the surface of the UV LED. UV light at a peak of 372 nm was emitted through the FLG-based transparent conductive electrode. The current spreading effects of FLG were clearly evident in both the optical images of electroluminescence (EL) and current-voltage (I-V) characteristics. Degradation of the FLG-based transparent conductive electrode could be induced by high power operation. Our results indicate that a large-area FLG-based electrode on GaN offers excellent current spreading and ultra-violet transparency properties when compared to the standard optoelectronic indium tin oxide (ITO) contact layer.

Kim, Byung-Jae; Lee, Chongmin; Jung, Younghun; Hyeon Baik, Kwang; Mastro, Michael A.; Hite, Jennifer K.; Eddy, Charles R.; Kim, Jihyun

2011-10-01

291

Improved cation valence state in molybdenum oxides by ultraviolet-ozone treatments and its applications in organic light-emitting diodes  

NASA Astrophysics Data System (ADS)

The authors demonstrate a thick MoO3 layer (60 nm) as a good short reduction layer in organic light emitting diodes (OLEDs), which is especially useful for large-area and flexible OLEDs to prevent short circuit issues. The crystallization of organic material and the increase of driving voltage induced by a thick MoO3 layer in OLEDs were resolved by a simple ultraviolet-ozone (UV-ozone) treatment. Ultraviolet photoelectron spectroscopy, X-ray photoelectron spectroscopy, contact angle, and atomic force microscope analyses revealed that a longer UV-ozone treatment resulted in an optimized fraction of oxygen vacancies in MoO3, which is responsible for the improved device performance.

Shi, Xiao-Bo; Xu, Mei-Feng; Zhou, Dong-Ying; Wang, Zhao-Kui; Liao, Liang-Sheng

2013-06-01

292

Characterization of a novel two dimensional diode array the ''magic plate'' as a radiation detector for radiation therapy treatment  

SciTech Connect

Purpose: Intensity modulated radiation therapy (IMRT) utilizes the technology of multileaf collimators to deliver highly modulated and complex radiation treatment. Dosimetric verification of the IMRT treatment requires the verification of the delivered dose distribution. Two dimensional ion chamber or diode arrays are gaining popularity as a dosimeter of choice due to their real time feedback compared to film dosimetry. This paper describes the characterization of a novel 2D diode array, which has been named the ''magic plate'' (MP). It was designed to function as a 2D transmission detector as well as a planar detector for dose distribution measurements in a solid water phantom for the dosimetric verification of IMRT treatment delivery. Methods: The prototype MP is an 11 x 11 detector array based on thin (50 {mu}m) epitaxial diode technology mounted on a 0.6 mm thick Kapton substrate using a proprietary ''drop-in'' technology developed by the Centre for Medical Radiation Physics, University of Wollongong. A full characterization of the detector was performed, including radiation damage study, dose per pulse effect, percent depth dose comparison with CC13 ion chamber and build up characteristics with a parallel plane ion chamber measurements, dose linearity, energy response and angular response. Results: Postirradiated magic plate diodes showed a reproducibility of 2.1%. The MP dose per pulse response decreased at higher dose rates while at lower dose rates the MP appears to be dose rate independent. The depth dose measurement of the MP agrees with ion chamber depth dose measurements to within 0.7% while dose linearity was excellent. MP showed angular response dependency due to the anisotropy of the silicon diode with the maximum variation in angular response of 10.8% at gantry angle 180 deg. Angular dependence was within 3.5% for the gantry angles {+-} 75 deg. The field size dependence of the MP at isocenter agrees with ion chamber measurement to within 1.1%. In the beam perturbation study, the surface dose increased by 12.1% for a 30 x 30 cm{sup 2} field size at the source to detector distance (SDD) of 80 cm whilst the transmission for the MP was 99%. Conclusions: The radiation response of the magic plate was successfully characterized. The array of epitaxial silicon based detectors with ''drop-in'' packaging showed properties suitable to be used as a simplified multipurpose and nonperturbing 2D radiation detector for radiation therapy dosimetric verification.

Wong, J. H. D.; Fuduli, I.; Carolan, M.; Petasecca, M.; Lerch, M. L. F.; Perevertaylo, V. L.; Metcalfe, P.; Rosenfeld, A. B. [Centre for Medical Radiation Physics, University of Wollongong, NSW 2522, Australia and Faculty of Medicine, University of Malaya, Kuala Lumpur 50603 (Malaysia); Centre for Medical Radiation Physics, University of Wollongong, NSW 2522 (Australia); Illawarra Cancer Care Centre, Wollongong Hospital, NSW 2500, Australia and Centre for Medical Radiation Physics, University of Wollongong, NSW 2522 (Australia); Centre for Medical Radiation Physics, University of Wollongong, NSW 2522 (Australia); SPA BIT, Kiev, Ukraine, 04136 (Ukraine); Centre for Medical Radiation Physics, University of Wollongong, NSW 2522 (Australia)

2012-05-15

293

Compact high-power diode-array-pumped Nd:CNGG laser employing CUSP geometry optical coupling  

NASA Astrophysics Data System (ADS)

This paper presents the design of a Compact High Power Diode Array Pumped Nd:CNGG laser employing cusp geometry concentrator for optical coupling in the side pumped configuration. The design addresses two major issues that influence the performance of a Diode Pumped Solid State Laser i.e. choice of suitable laser material and optical coupling scheme. The design employs an Nd:CNGG rod of (phi) 3mm X 10mm dimension, fluid cooled through coaxial flow tube of 5mm diameter. Light from a Quasi-CW laser diode array stack of 2 cm X 1 cm dimension is coupled through a cusp geometry concentrator of 18mm aperture. The system is capable of generating a high average power of approximately 30W at an input of 800W peak power. Optimum performance of the system has been compared with that of Nd:YAG laser operating under similar conditions. Nd:CNGG is found to be more efficient at higher input energies.

Mallik, Amitav; Agrawal, Lalita

1999-11-01

294

Thin Ni film on graphene current spreading layer for GaN-based blue and ultra-violet light-emitting diodes  

NASA Astrophysics Data System (ADS)

We introduced a thin nickel (Ni) film onto graphene as a current spreading layer for GaN-based blue and ultraviolet (UV) light emitting diodes (LEDs). The thin Ni film was confirmed to improve the electrical properties of the graphene by reducing the sheet and contact resistances. The advantages of Ni on graphene were more remarkable in UV LEDs, in which the operation voltage was reduced from 13.2 V for graphene alone to 7.1 V. As a result, UV LEDs with Ni on graphene showed a uniform and reliable light emission, at ~83% of electroluminescence of indium tin oxide.

Shim, Jae-Phil; Hoon Seo, Tae; Min, Jung-Hong; Mo Kang, Chang; Suh, Eun-Kyung; Lee, Dong-Seon

2013-04-01

295

Enhancement of light output power in ultraviolet light emitting diodes using graphene film on self-assembled Au nanocluster by agglomeration process  

NASA Astrophysics Data System (ADS)

We applied graphene network on Au nanoclusters as a transparent and current spreading electrode in GaN-based ultraviolet (UV) light emitting diode (LED). The electroluminescence (EL) of UV-LEDs with graphene film on Au nanoclusters was enhanced by 10% at injection current of 20 mA, while keeping reasonably good injected current-voltage (I-V) characteristics. This result is attributed to the reduction of absorption at UV wavelength region, effective current spreading and injection by reduced sheet and contact resistance, and texturing effect through Au nanocluster.

Seo, Tae Hoon; Shin, GangU; Kyoung Kim, Bo; Choi, Chel-Jong; Lee, Changhyup; Jong Kim, Myung; Suh, Eun-Kyung

2013-12-01

296

Improvement of near-ultraviolet InGaN-GaN light-emitting diodes through higher pressure grown underlying GaN layers  

Microsoft Academic Search

The 410-nm near-ultraviolet (near-UV) InGaN-GaN multiple quantum-wells light-emitting diodes (LEDs) with low-pressure-grown (200 mbar) and high-pressure-grown (400 mbar) Si-doped GaN underlying layers were grown on c-face sapphire substrates by metal-organic vapor phase epitaxy. Increasing the growth pressure during the initial growth of the underlying n-type GaN epilayers of the near-UV InGaN-GaN LEDs was found to reduce the amount of threading

Ru-Chin Tu; Chun-Ju Tun; Shyi-Ming Pan; Hai-Ping Liu; Ching-En Tsai; J. K. Sheu; Chang-Cheng Chuo; Te-Chung Wang; Gou-Chung Chi; In-Gann Chen

2003-01-01

297

Validation of dynamic MLC-controller log files using a two-dimensional diode array.  

PubMed

Intensity-modulated radiation therapy (IMRT) delivered with multi-leaf collimator (MLC) in the step-and-shoot mode uses multiple static MLC segments to achieve intensity modulation. For typical IMRT treatment plans, significant numbers of segments are delivered with monitor units (MUs) of much less than 10. Verification of the ability of the linear accelerator (linac) to deliver small MU segments accurately is an important step in the IMRT commissioning and quality assurance (QA) process. Recent studies have reported large discrepancies between the intended and delivered segment MUs. These discrepancies could potentially cause large errors in the delivered patient dose. We have undertaken a systematic study to evaluate the accuracy of the dynamic MLC log files, which are created automatically by our commercial MLC workstation after each delivery, in recording the fractional MU delivered in the step-and-shoot mode. Two linac models were evaluated with simple-geometry leaf sequences and delivered with different total MUs and different nominal dose rates. A commercial two-dimensional diode array was used for the measurement. Large discrepancies between the intended and delivered segment MUs were found. The discrepancies were larger for small MU segments at higher dose rate, with some small MU segments completely undelivered. The recorded fractional MUs in the log files were found to agree with what was delivered within the limits of our experimental uncertainty. Our results indicate that it is important to verify the delivery accuracy of small MU segments that could potentially occur in a patient treatment and that the log files are useful in checking the integrity of the linac delivery once validated. Thus validated log files can be used as a QA tool for general IMRT delivery and patient-specific plan verification. PMID:12772987

Li, Jonathan G; Dempsey, James F; Ding, Li; Liu, Chihray; Palta, Jatinder R

2003-05-01

298

An X-Band Array Antenna Module with GAAS Impatt Diode Amplifier. Volume 1: Text.  

National Technical Information Service (NTIS)

The construction of a MIC twin transceiver module is described. It contains three stage GaAs IMPATT diode amplifiers with 1 W cw output and 20 dB gain at 9 GHz, analog ferrite phase shifters, PIN-diode switches, and balanced mixers. Test methods for trans...

H. Steyskal

1979-01-01

299

Measurement and modeling of microlenses fabricated on single-photon avalanche diode arrays for fill factor recovery.  

PubMed

Single-photon avalanche diode (SPAD) imagers typically have a relatively low fill factor, i.e. a low proportion of the pixel's surface is light sensitive, due to in-pixel circuitry. We present a microlens array fabricated on a 128×128 single-photon avalanche diode (SPAD) imager to enhance its sensitivity. The benefits and limitations of these light concentrators are studied for low light imaging applications. We present a new simulation software that can be used to simulate microlenses' performance under different conditions and a new non-destructive contact-less method to estimate the height of the microlenses. Results of experiments and simulations are in good agreement, indicating that a gain >10 can be achieved for this particular sensor. PMID:24663744

Pavia, Juan Mata; Wolf, Martin; Charbon, Edoardo

2014-02-24

300

Novel spatial-mode selection using distributed feedback gratings in single-mode resonant antiguided diode laser arrays  

NASA Astrophysics Data System (ADS)

A distributed feedback (DFB) grating located below the active region in resonant antiguided diode laser arrays (ROW-LDFB arrays) provides not only frequency discrimination, but also serves as a novel in-phase spatial-mode selector that remains effective to high drive levels. Previously, spatial-mode discrimination has been accomplished by placing loss in the high effective- index interelement regions, suppressing modes with significant interelement field. However, the presence of interelement loss could lead to self-pulsations due to saturable absorption at high drive levels. The DFB grating is typically located above the active region in single-frequency semiconductor laser arrays due to ease of fabrication. In this configuration, however, the optical feedback as a result of the grating is virtually equal for all array modes. As a result, grating-based array-mode selection is not possible. When positioned below the active region in antiguided arrays, however, the amount of optical field overlap with the lower grating layer becomes array-mode-dependent, The array mode with the highest coupling to the grating experiences the greatest amount of optical feedback. That is, the grating simultaneously operates as a longitudinal-mode (frequency) discriminator and as a spatial-mode (array-mode) selector. As will be discussed, this method of spatial-mode selection has attractive advantages over more common techniques such as the incorporation of interelement loss or intracavity spatial filters. The theory of ROW-LDFB operation is described in detail and design considerations for in-phase array-mode operation are addressed. The effects of various AR/HR coatings on device behavior are presented. In addition, the statistical implications of random cleave locations relative to the DFB grating phase are included in the analysis. 20-element facet-coated ROW-LDFB arrays operate up to 0.45 W in a single in-phase array mode and at a single frequency. Experimental results confirm theoretical predictions for resonant in-phase array mode operation to high output powers.

Nesnidal, Michael Paul

1998-11-01

301

Single-element optical injection locking of diode-laser arrays  

DOEpatents

By optically injecting a single end-element of a semiconductor laser array, both the spatial and spectral emission characteristics of the entire laser array is controlled. With the output of the array locked, the far-field emission angle of the array is continuously scanned over several degrees by varying the injection frequency.

Hadley, G. Ronald (Albuquerque, NM); Hohimer, John P. (Albuquerque, NM); Owyoung, Adelbert (Albuquerque, NM)

1988-01-01

302

Single-element optical injection locking of diode-laser arrays  

DOEpatents

By optically injecting a single end-element of a semiconductor laser array, both the spatial and spectral emission characteristics of the entire laser array is controlled. With the output of the array locked, the farfield emission angle of the array is continuously scanned over several degrees by varying the injection frequency.

Hadley, G.R.; Hohimer, J.P.; Owyoung, A.

1986-10-07

303

Low noise Sb-heterostructure diode detectors for W-band imaging arrays without RF amplification  

NASA Astrophysics Data System (ADS)

The figure of merit for RF detectors, noise-equivalent power (NEP), is determined by the noise divided by the sensitivity. Thus, the challenge is to design a diode structure that has low junction resistance while maintaining a large nonlinearity. This work presents sensitivity and noise measurements for Sb-heterostructure backward diodes with varying barrier thicknesses and cross-sectional areas. Nominal diode areas are 2x2mm2 and 3x4mm2 with 15Å and 20Å barriers. The best NEP measured to date is 1.19 pW/rtHz at 36.5 GHz.

Moyer, Harris P.; Hsu, Tsung-Yuan; Bowen, R. L.; Boegeman, Y. K.; Deelman, P. W.; Thomas, S., III; Hunter, Andrew T.; Schulman, Joel N.; Luukanen, Arttu; Grossman, Erich N.

2005-05-01

304

High intensity light emitting diode array as an alternative exposure source for the fabrication of electrophoretic microfluidic devices.  

PubMed

A commercially available array of light emitting diodes (LEDs), namely a UV Shark series LED high flux array, was evaluated as a light source for photolithographic patterning of SU-8 photoresist for the fabrication of templates suitable to make poly(dimethylsiloxane) (PDMS) microchips for electrophoresis. At a distance of 15 cm from the substrate, a relatively even intensity of 0.76+/-0.05 mW/cm(2) was obtained over an area sufficient for patterning a 10 cm (4 in.) silicon wafer. The exposure source was evaluated using a spiral mask design covering a 10 cm wafer. PDMS replicates of this template made in a 25 microm thick layer of SU-8 3025 showed little variation in width over the surface of the substrate, with a variation of 3.2% RSD (n=36) and a maximum range in widths of 7.8% of the mean channel width. The use of the optional metal reflector available with the LED array provided partial collimation of the light allowing near vertical structures to be produced across the entire wafer, something which was not possible without the reflector. SU-8 masters prepared using the LED array were compared to masters made using an alternative cheap lithographic source, namely a gel crosslinker. The SU-8 features were much narrower with the LED array than the crosslinker due to the multiple light sources in the crosslinker. A PDMS microchip made using a SU-8 template created using the Shark UV LED array was used for the electrophoretic separation of three anionic fluorescent dyes, with efficiencies up to 32,000 plates. Given that the LED array can be purchased and assembled for less than US$ 500, the Shark UV LED array is a promising alternative to more expensive lithographic light sources and will have significant appeal to many researchers wishing to undertake research in microfluidics around the world. PMID:18930463

Breadmore, Michael C; Guijt, Rosanne M

2008-12-01

305

Diffraction-limited emission from a diode laser array in an apertured graded-index lens external cavity  

NASA Astrophysics Data System (ADS)

A gain-guided coupled-stripe GaAs/GaAlAs diode laser array in an external cavity configuration consisting of a graded refractive index lens and a 25-micron stripe apertured mirror was studied. Output power of almost 500 mW was obtained from the cavity under pulsed operation. A centered, single-lobed far-field radiation pattern which did not steer with the drive current was observed up to 4.1I(th). At 2I(th) approximately 94 percent of the 102-mW output power is contained in the 0.8 deg full width half-maximum central lobe.

Chang-Hasnain, C.; Welch, D. F.; Scifres, D. R.; Whinnery, J. R.; Dienes, A.

1986-09-01

306

Diode-array pumping of Er[sup 3+]/Yb[sup 3+] co-doped fiber lasers and amplifiers  

SciTech Connect

The sensitization of erbium-doped fibers with ytterbium is well established as a technique for increasing the choice of pump wavelengths for the erbium system. Single-mode double-clad Er[sup 3+]/Yb[sup 3+] co-doped fibers are shown to be suitable for diode array pumping at around 960 nm. A fiber laser with 96 mW output power at 1.53 [mu]M and a power amplifier exhibiting a small signal gain of 24 dB and a saturated output power of +17 dBm are reported.

Minelly, J.D.; Barnes, W.L.; Laming, R.I.; Morkel, P.R.; Townsend, J.E.; Payne, D.N. (Southampton Univ. (United Kingdom)); Grubb, S.G. (Amoco Technology Co., Naperville, IL (United States))

1993-03-01

307

Design limitations of highly parallel free-space optical interconnects based on arrays of vertical cavity surface-emitting laser diodes, microlenses, and photodetectors  

Microsoft Academic Search

We utilize a novel diffraction formalism to study the crosstalk effect in a highly parallel free-space optical interconnect based on two-dimensional arrays of surface-emitting laser diodes, microlenses, and photodetectors. The diffraction induced crosstalk between adjacent laser diodes in each detector to the system limitations is investigated. Optimum design rules and formulas are given for the first time, to include the

Suning Tang; Ray T. Chen; Lara Garrett; Dave Gerold; Maggie M. Li; Srikanth Natarajan; Jielun Lin

1994-01-01

308

Nonlinear dynamics and synchronization of an array of single mode laser diodes in external cavity subject to current modulation  

NASA Astrophysics Data System (ADS)

We study the dynamics of an array of single mode laser diodes subject to filtered feedback provided by an external reflection grating. Our numerical simulations show that by modulating the injection current the array can be phase synchronized leading to high power coherent emission. The output peak power density can be varied by tuning the modulation frequency and can be resonantly enhanced once the frequency matches the inverse of external cavity round trip time and mode-locking behavior is realized. Both non-resonant and resonant injection current modulation results in an excellent degree of phase synchronization and coherence at certain modulation amplitudes and frequencies that is manifested by coherent enhancement of far-field optical intensity.

Liu, B.; Braiman, Y.; Nair, N.; Lu, Y.; Guo, Y.; Colet, P.; Wardlaw, M.

2014-08-01

309

Vertically p-n-junctioned GaN nano-wire array diode fabricated on Si(111) using MOCVD  

NASA Astrophysics Data System (ADS)

We demonstrate the fabrication of n-GaN:Si/p-GaN:Mg nanowire arrays on (111) silicon substrate by metal organic chemical vapor deposition (MOCVD) method .The nanowires were grown by a newly developed two-step growth process. The diameter of as-grown nanowires ranges from 300-400 nm with a density of 6-7 × 107 cm-2. The p- and n-type doping of the nanowires is achieved with Mg and Si dopant species. Structural characterization by X-ray diffraction (XRD) and high-resolution transmission electron microscopy (HRTEM) indicates that the nanowires are relatively defect-free. The room-temperature photoluminescence emission with a strong peak at 370 nm indicates that the n-GaN:Si/p-GaN:Mg nanowire arrays have potential application in light-emitting nanodevices. The cathodoluminscence (CL) spectrum clearly shows a distinct optical transition of GaN nanodiodes. The nano-n-GaN:Si/p-GaN:Mg diodes were further completed using a sputter coating approach to deposit Au/Ni metal contacts. The polysilazane filler has been etched by a wet chemical etching process. The n-GaN:Si/p-GaN:Mg nanowire diode was fabricated for different Mg source flow rates. The current-voltage (I-V) measurements reveal excellent rectifying properties with an obvious turn-on voltage at 1.6 V for a Mg flow rate of 5 sccm (standard cubic centimeters per minute).

Park, Ji-Hyeon; Kim, Min-Hee; Kissinger, Suthan; Lee, Cheul-Ro

2013-03-01

310

Technique for Radiometer and Antenna Array Calibration with a Radiated Noise Diode  

NASA Technical Reports Server (NTRS)

This paper presents a new technique to calibrate a microwave radiometer and antenna array system. This calibration technique uses a radiated noise source in addition to two calibration sources internal to the radiometer. The method accurately calibrates antenna arrays with embedded active devices (such as amplifiers) which are used extensively in active phased array antennas.

Srinivasan, Karthik; Limaye, Ashutosh; Laymon, Charles; Meyer, Paul

2009-01-01

311

Highly efficient, spectrally pure 340 nm ultraviolet emission from AlxGa1-xN nanowire based light emitting diodes  

NASA Astrophysics Data System (ADS)

High crystal quality, vertically aligned AlxGa1-xN nanowire based double heterojunction light emitting diodes (LEDs) are grown on Si substrate by molecular beam epitaxy. Such AlxGa1-xN nanowires exhibit unique core-shell structures, which can significantly suppress surface nonradiative recombination. We successfully demonstrate highly efficient AlxGa1-xN nanowire array based LEDs operating at ˜340 nm. Such nanowire devices exhibit superior electrical and optical performance, including an internal quantum efficiency of ˜59% at room temperature, a relatively small series resistance, highly stable emission characteristics, and the absence of efficiency droop under pulsed biasing conditions.

Wang, Q.; Connie, A. T.; Nguyen, H. P. T.; Kibria, M. G.; Zhao, S.; Sharif, S.; Shih, I.; Mi, Z.

2013-08-01

312

Monolithic arrays of grating-surface-emitting diode lasers and quantum well modulators for optical communications  

NASA Technical Reports Server (NTRS)

The electro-optic switching properties of injection-coupled coherent 2-D grating-surface-emitting laser arrays with multiple gain sections and quantum well active layers are discussed and demonstrated. Within such an array of injection-coupled grating-surface-emitting lasers, a single gain section can be operated as intra-cavity saturable loss element that can modulate the output of the entire array. Experimental results demonstrate efficient sub-nanosecond switching of high power grading-surface-emitting laser arrays by using only one gain section as an intra-cavity loss modulator.

Carlson, N. W.; Evans, G. A.; Liew, S. K.; Kaiser, C. J.

1990-01-01

313

A PIN diode controlled dual-tuned MRI RF coil and phased array for multi nuclear imaging.  

PubMed

MR imaging of nuclei other than hydrogen has been used to investigate metabolism in humans and animals. However, MRI observable nuclei other than hydrogen are not as abundant and as a result the image SNR is lower. Dual-tuned radio frequency (RF) coils are developed for these studies in which high-resolution structural images are acquired using hydrogen and metabolic information is acquired by exciting the other nucleus. Using a dual-tuned coil, the experimenter avoids the inconvenience of moving the patient out and replacing the RF coil for imaging different nuclei. This also eliminates image registration problems. However, the common scheme of using trap circuits for dual-tuned operation results in increased coil losses as well as problems in obtaining optimal tuning and matching at both frequencies. Here, a new approach is presented using PIN diodes to switch the coil between two resonance frequencies. This design eliminates the need for the trap circuit and associated losses from the self-resistance of the trap circuit inductors. At the operating frequencies we used, the equivalent series resistance of an inductor is higher than that of the PIN diodes. In order to test the efficacy of this new approach, we first built two surface coils of identical geometry, one with the conventional trap circuits and one with the PIN diode switches. We also studied the performances of both coils when the coils are divided into shorter conductors segments by adding more tuning elements. It is known that dividing the coil into shorter conductor segments helps reduce radiation and electric field losses. We explored this effect for both coils at both operating frequencies. Finally, a dual-tuned receive-only phased array was designed and built with the PIN diode circuit to switch between two resonance frequencies. A conventional dual-tuned birdcage coil was designed and built to transmit RF power. A unique feature of this coil is that the RF power is fed through two separate sets of four ports for more uniform 1H and 23Na excitation. We demonstrated that the performance is significantly improved at both frequencies with the PIN diode switched dual-frequency operation compared to an identical coil with a trap circuit. PMID:20393229

Ha, Seunghoon; Hamamura, Mark J; Nalcioglu, Orhan; Muftuler, L Tugan

2010-05-01

314

Enhanced Light Output Power of Near-Ultraviolet Light-Emitting Diodes with Au-Doped Graphene for Transparent and Current-Spreading Electrode  

NASA Astrophysics Data System (ADS)

We report the implementation of Au-doped graphene film as a transparent and current-spreading electrode (TCSE) in GaN-based near-ultraviolet (UV) light-emitting diode (LED) to achieve good UV emission efficiency. The TCSE effects of Au-doped graphene film were clearly seen in both the electroluminescence (EL) and current--voltage (I--V) characteristics. The EL output power of 380-nm wavelength UV-LEDs with Au-doped graphene film was enhanced by about 20% at an injection current of 20 mA compared with that of conventional UV-LEDs. The increase of the light output power is attributed to the high UV transmittance of graphene, effective current spreading, and injection.

Seo, Tae Hoon; Chae, Seung Jin; Kim, Bo Kyoung; Shin, GangU; Lee, Young Hee; Suh, Eun-Kyung

2012-11-01

315

Note: design and characterization of an optical light source based on mixture of white and near-ultraviolet light emitting diode spectra.  

PubMed

An optical light source based on a solid-state lighting technology is designed. Main components of the light source are a phosphor-converted white and a near-ultraviolet (near-UV) light emitting diodes (LEDs), the spectral power distributions (SPDs) of which are mixed using a fiber optic combiner. The near-UV LED is used for improving insufficient SPDs of the white LED at shorter wavelengths of the visible radiation. Stable direct current power supplies are also designed and used to operate each of the LED separately. Three steps of the driving current can be selected by means of serial resistors altered with a commutator at nominal current values of ?40%, ?50%, and ?69%. The light source can be used for many characteristic measurements within the scope of photometry and colorimetry. PMID:21529055

Sametoglu, Ferhat; Celikel, Oguz

2011-04-01

316

Improved light emission through an AlGaN coalescence layer of 365-nm ultraviolet lighting-emitting diodes on patterned sapphire substrates  

NASA Astrophysics Data System (ADS)

Ultraviolet (UV), 365-nm light-emitting diodes (LEDs) were grown on an AlGaN template on patterned sapphire substrates (PSS) and then compared with those grown on a conventional GaN template. Complete coalescence was achieved by using AlGaN up to 4.9% Al composition, although the AlGaN template displayed more dislocations than the GaN template. The 365-nm UV LEDs on the AlGaN template showed no emission absorption in the template, as seen in the GaN template, because AlGaN is sufficiently far from the absorption edge of GaN. As a result, a total emission enhancement about 4 times stronger than that obtained w hat using the GaN template was obtained at 80 mA.

Kwak, Young-Sun; Lee, Jun-Youb; Choi, Hye-Rin; Kim, Do-Hyung; Lee, Dong-Seon; Jeon, Seong-Ran; Kong, Bo-Hyun; Cho, Hyung-Koun

2013-03-01

317

Migration enhanced lateral epitaxial overgrowth of AlN and AlGaN for high reliability deep ultraviolet light emitting diodes  

NASA Astrophysics Data System (ADS)

We report on the growth of low-defect thick films of AlN and AlGaN on trenched AlGaN/sapphire templates using migration enhanced lateral epitaxial overgrowth. Incoherent coalescence-related defects were alleviated by controlling the tilt angle of growth fronts and by allowing Al adatoms sufficient residence time to incorporate at the most energetically favorable lattice sites. Deep ultraviolet light emitting diode structures (310 nm) deposited over fully coalesced thick AlN films exhibited cw output power of 1.6 mW at 50 mA current with extrapolated lifetime in excess of 5000 hours. The results demonstrate substantial improvement in the device lifetime, primarily due to the reduced density of growth defects.

Jain, R.; Sun, W.; Yang, J.; Shatalov, M.; Hu, X.; Sattu, A.; Lunev, A.; Deng, J.; Shturm, I.; Bilenko, Y.; Gaska, R.; Shur, M. S.

2008-08-01

318

AlGaN-based deep ultraviolet light-emitting diodes grown on nano-patterned sapphire substrates with significant improvement in internal quantum efficiency  

NASA Astrophysics Data System (ADS)

We report high-performance AlGaN-based deep ultraviolet light-emitting diodes grown on nano-patterned sapphire substrates (NPSS) using metal-organic chemical vapor deposition. By nanoscale epitaxial lateral overgrowth on NPSS, 4-?m AlN buffer layer has shown strain relaxation and a coalescence thickness of only 2.5 ?m. The full widths at half-maximum of X-ray diffraction (002) and (102) ?-scan rocking curves of AlN on NPSS are only 69.4 and 319.1 arcsec. The threading dislocation density in AlGaN-based multi-quantum wells, which are grown on this AlN/NPSS template with a light-emitting wavelength at 283 nm at room temperature, is reduced by 33% compared with that on flat sapphire substrate indicated by atomic force microscopy measurements, and the internal quantum efficiency increases from 30% to 43% revealed by temperature-dependent photoluminescent measurement.

Dong, Peng; Yan, Jianchang; Zhang, Yun; Wang, Junxi; Zeng, Jianping; Geng, Chong; Cong, Peipei; Sun, Lili; Wei, Tongbo; Zhao, Lixia; Yan, Qingfeng; He, Chenguang; Qin, Zhixin; Li, Jinmin

2014-06-01

319

Transparent conductive oxide films mixed with gallium oxide nanoparticle/single-walled carbon nanotube layer for deep ultraviolet light-emitting diodes  

PubMed Central

We propose a transparent conductive oxide electrode scheme of gallium oxide nanoparticle mixed with a single-walled carbon nanotube (Ga2O3 NP/SWNT) layer for deep ultraviolet light-emitting diodes using spin and dipping methods. We investigated the electrical, optical and morphological properties of the Ga2O3 NP/SWNT layers by increasing the thickness of SWNTs via multiple dipping processes. Compared with the undoped Ga2O3 films (current level 9.9?×?10-9 A @ 1 V, transmittance 68% @ 280 nm), the current level flowing in the Ga2O3 NP/SWNT increased by approximately 4?×?105 times and the transmittance improved by 9% after 15 times dip-coating (current level 4?×?10-4 A at 1 V; transmittance 77.0% at 280 nm). These improvements result from both native high transparency of Ga2O3 NPs and high conductivity and effective current spreading of SWNTs.

2013-01-01

320

282-nm AlGaN-based deep ultraviolet light-emitting diodes with improved performance on nano-patterned sapphire substrates  

NASA Astrophysics Data System (ADS)

We first report AlGaN-based deep ultraviolet light-emitting diodes (UV-LEDs) grown on nano-patterned sapphire substrates (NPSS) prepared through a nanosphere lithography technique. The AlN coalescence thickness on NPSS is only 3 ?m due to AlN's nano-scaled lateral growth, which also leads to low dislocation densities in AlN and epi-layers above. On NPSS, the light-output power of a 282-nm UV-LED reaches 3.03 mW at 20 mA with external quantum efficiency of 3.45%, exhibiting 98% better performance than that on flat sapphire. Temperature-dependent photoluminescence reveals this significant enhancement to be a combination of higher internal quantum efficiency and higher light extraction efficiency.

Dong, Peng; Yan, Jianchang; Wang, Junxi; Zhang, Yun; Geng, Chong; Wei, Tongbo; Cong, Peipei; Zhang, Yiyun; Zeng, Jianping; Tian, Yingdong; Sun, Lili; Yan, Qingfeng; Li, Jinmin; Fan, Shunfei; Qin, Zhixin

2013-06-01

321

Compound Ag nanocluster-graphene electrodes as transparent and current spreading electrodes for improved light output power in near-ultraviolet light emitting diodes  

NASA Astrophysics Data System (ADS)

We introduced a two-dimensional graphene network on a Ag nanocluster as a transparent and current spreading electrode (TCSE) for a near-ultraviolet light emitting diode (NUV-LED), and compared the performance with those with graphene electrodes or conventional indium tin oxide (ITO) electrodes. The current–voltage characteristics and electroluminescence (EL) data showed that compound Ag nanocluster-graphene (CA-G) electrodes operated well as TCSEs in NUV-LED devices. The forward voltage at an input current of 20 mA was 4.06 V for the NUV-LED of current spreading electrodes with CA-G electrodes, which is only slightly higher than the value 3.96 V with ITO electrodes as TCSEs. The EL intensity of NUV-LEDs with CA-G electrodes also showed a slight increase, compared to that of NUV-LEDs with planar ITO transparent conducting electrodes.

Seo, Tae Hoon; Kim, Seongjun; Jong Kim, Myung; Kim, Hyunsoo; Suh, Eun-Kyung

2014-05-01

322

Efficient and high-power AlGaN-based ultraviolet light-emitting diode grown on bulk GaN  

SciTech Connect

By introducing thick bulk GaN as a substrate, we improved the performance of an AlGaN-based ultraviolet (UV) light-emitting diode (LED). The output power exceeds 3 mW at the injection current of 100 mA under a bare-chip geometry. Internal quantum efficiency is estimated as more than 80%, and the peak wavelength is 352 nm. The maximum power exceeds 10 mW at a large current injection of 400 mA, with an operation voltage of less than 6 V. These results indicate that an efficient UV LED is intrinsically possible by the combination of appropriate device design and the nitride substrate. By introducing packaging technology to enhance extraction efficiency, we will have a compact and efficient UV light source in the wide wavelength range of 200--360 nm, similar to conventional longer-wavelength LEDs. {copyright} 2001 American Institute of Physics.

Nishida, Toshio; Saito, Hisao; Kobayashi, Naoki

2001-08-06

323

Performance enhancements in optoelectrical properties of InGaN\\/GaN light-emitting diodes with micro-hole arrayed indium-tin-oxide layer  

Microsoft Academic Search

We demonstrated that the InGaN\\/GaN multiple quantum wells (MQWs) light-emitting diodes (LEDs) with micro-hole arrays exhibit better performance in optoelectrical properties than do the conventional LEDs. With injection current of 20 mA, by employing the micro-hole array on top surface of the LED structure, the room-temperature output power conversion efficiency and external quantum efficiency were increased 28.7% and 14.3%, respectively,

Chia-Hui Fang; Jen-Cheng Wang; Tzer-En Nee

2010-01-01

324

Sb-doped p-ZnO/Ga-doped n-ZnO homojunction ultraviolet light emitting diodes  

NASA Astrophysics Data System (ADS)

ZnO p-n homojunction light emitting diodes were fabricated based on p-type Sb-doped ZnO/n-type Ga-doped ZnO thin films. Low resistivity Au/NiO and Au/Ti contacts were formed on top of p-type and n-type ZnO layers, respectively. Au/NiO contacts on p-type ZnO exhibited a low specific resistivity of 7.4×10-4 ? cm2. The light emitting diodes yielded strong near-band-edge emissions in temperature-dependent and injection current-dependent electroluminescence measurements.

Chu, S.; Lim, J. H.; Mandalapu, L. J.; Yang, Z.; Li, L.; Liu, J. L.

2008-04-01

325

A model for the nearly single lobed far-field in a diode array traveling-wave amplifier  

NASA Astrophysics Data System (ADS)

A model is presented to explain some of the optical properties of traveling-wave amplifiers made from gain-guided diode laser arrays. The model describes the amplifier as a complex volume diffraction grating with the grating period being the array period. The volume grating has an aperture limited by the width of the array. Experimental measurements of the far-field pattern and the diffraction efficiency into the side-lobes as a function of the incident angle of the injected signal are compared to calculations based on the model. Good fits are obtained to both sets of experimental data with only gain and refractive index modulation as parameters. New data are presented for the diffraction efficiency of the volume grating as a function of the current to the amplifier. These data are fit to this same model using the same parameters and assuming that the gain and index modulation at each current are proportional to the measured gain at the same current less the value of the gain at zero current. The implications of this model to amplifiers and lasers will be discussed.

Andrews, John R.; Paoli, T. L.; Burnham, R. D.

1988-01-01

326

Coupled-mode analysis of gain and wavelength oscillation characteristics of diode laser phased arrays  

NASA Astrophysics Data System (ADS)

The lasing wavelengths and gain characteristics of the modes of phase-locked arrays of channel-substrate-planar (CSP) lasers are presented. The gain values for the array modes are determined from complex coupling coefficients calculated using the fields of neighboring elements of the array. The computations show that, for index guided lasers which have nearly planar phase fronts, the highest order array mode will be preferred. The 'in-phase' or fundamental mode, which produces only one major lobe in the far-field radiation pattern, has the lowest modal gain of all array modes. The modal gain differential between the highest order and fundamental modes is less than 10/cm for weak coupling between the elements.

Butler, J. K.; Ettenberg, M.; Ackley, D. E.

1985-05-01

327

XRD (X-Ray Diode) Array, the Grazing Incidence Spectrometer, and the X-Ray Imaging Camera on PBFA (Particle Beam Fusion Accelerator) II.  

National Technical Information Service (NTIS)

Target diagnostics on PBFA II will include a time-resolved x-ray diode array, an energy-resolved, time-integrated x-ray camera and a grazing incidence spectrometer. A clean vacuum, independent of that on PBFA II, will be supplied to the detectors to maint...

M. S. Derzon M. A. Sweeney P. Grandon H. C. Ives R. P. Kensek

1988-01-01

328

High-Power CW Diode-Laser-Array-Pumped Solid-State Lasers and Efficient Non-Linear-Optical Frequency Conversion.  

National Technical Information Service (NTIS)

The goals of this program were: development of high-power, cw diode-laser-array-pumped, Nd:YAG lasers, and efficient nonlinear frequency conversion of their output. Two minislab laser heads constructed as a single high power dual-head oscillator (96W, mul...

W. Tulloch T. Rutherford R. K. Route R. L. Byer

1997-01-01

329

Process monitoring of anaerobic azo dye degradation by high-performance liquid chromatography–diode array detection continuously coupled to membrane filtration sampling modules  

Microsoft Academic Search

Process integrated microfiltration and ultrafiltration based membrane sampling modules were compared by means of HPLC with diode array detection based monitoring of an anaerobic azo dye biodegradation process. The sampling matrix consisted of anaerobic sludge from a municipal wastewater treatment plant. The hydrolysed azo dye Reactive Black 5 (RB5-H) and three products (ionic and nonionic) released from reductive cleavage under

Alexander Plum; Gerd Braun; Astrid Rehorek

2003-01-01

330

DETERMINATION OF CARBENDAZIM IN WATER BY HIGH-PERFORMANCE IMMUNOAFFINITY CHROMATOGRAPHY ON-LINE WITH HIGH-PERFORMANCE LIQUID CHROMATOGRAPHY WITH DIODE-ARRAY OR MASS SPECTROMETRIC DETECTION  

EPA Science Inventory

An automated method for the determination of carbendazim in water that combines high-performance immunoaffinity chromatography (HPIAC), high-performance liquid chromatography (HPLC) in the reversed-phase mode, and detection by either UV-Vis diode array detector (DAD) spectroscopy...

331

Determination of steroid sex hormones in urine matrix by stir bar sorptive extraction based on monolithic material and liquid chromatography with diode array detection  

Microsoft Academic Search

A simple, rapid and sensitive method for simultaneous determination of six steroid sex hormones in urine matrix was developed by the combination of stir bar sorptive extraction (SBSE) with high performance liquid chromatography (HPLC) and diode array detection (DAD). A poly (methacrylic acid stearyl ester–ethylene dimethacrylate) was synthesized and selected as SBSE extraction medium. To achieve the optimum extraction performance,

Xiaojia Huang; Dongxing Yuan; Benli Huang

2008-01-01

332

Variable-Color Light-Emitting Diodes Using GaN Microdonut arrays.  

PubMed

Microdonut-shaped GaN/Inx Ga1-x N light-emitting diode (LED) microarrays are fabricated for variable-color emitters. The figure shows clearly donut-shaped light emission from all the individual microdonut LEDs. Furthermore, microdonut LEDs exhibit spatially-resolved blue and green EL colors, which can be tuned by either controlling the external bias voltage or changing the size of the microdonut LED. PMID:24677202

Tchoe, Youngbin; Jo, Janghyun; Kim, Miyoung; Heo, Jaehyuk; Yoo, Geonwook; Sone, Cheolsoo; Yi, Gyu-Chul

2014-05-01

333

GaAs pillar array-based light emitting diodes fabricated by metal-assisted chemical etching  

NASA Astrophysics Data System (ADS)

We demonstrate GaAs pillar array-based light emitting diodes (LEDs) with axial p-i-n junctions fabricated using a room-temperature metal-assisted chemical etching (MacEtch) method. Variations in vertical etch rates for all three doping types of GaAs are investigated as a function of etching temperature, oxidant/acid concentration ratio, and dilution of the etching solution. Control over nanopillar morphologies is demonstrated, simply through modification of the etching conditions. Optical emission enhancement from the MacEtched p-i-n GaAs nanopillar LED is observed, relative to the non-etched planar counterpart, through room-temperature photoluminescence and electroluminescence characterization.

Mohseni, Parsian K.; Hyun Kim, Seung; Zhao, Xiang; Balasundaram, Karthik; Dong Kim, Jeong; Pan, Lei; Rogers, John A.; Coleman, James J.; Li, Xiuling

2013-08-01

334

Recover soft x-ray spectrum using virtual flat response channels with filtered x-ray diode array.  

PubMed

A method for the recovery of soft x-ray spectra in indirect-drive inertial confinement fusion experiments is presented. Virtual detection channels with bandpass responses are obtained using linear combinations of the channel response functions of a filtered x-ray diode array and a weighted correction is introduced to improve the recovery. These virtual channels can be used to calculate radiation fluxes in some specific photon energy bands and hence to recover the spectrum of the whole photon energy range from 80 eV to 4.5 keV. Examples are listed which demonstrate the capability of this method to unfold various spectra such as Planck spectra with different radiation temperatures and to obtain x-ray flux of certain narrow energy interval. PMID:23206046

Tianming, Song; Jiamin, Yang; Rongqing, Yi

2012-11-01

335

Screening of grapes and wine for azoxystrobin, kresoxim-methyl and trifloxystrobin fungicides by HPLC with diode array detection.  

PubMed

The Quinone outside Inhibitors (QoI) are one of the most important and recent fungicide groups used in viticulture and also allowed by Integrated Pest Management. Azoxystrobin, kresoxim-methyl and trifloxystrobin are the main active ingredients for treating downy and powdery mildews that can be present in grapes and wines. In this paper, a method is reported for the analysis of these three QoI-fungicides in grapes and wine. After liquid-liquid extraction and a clean-up on commercial silica cartridges, analysis was by isocratic HPLC with diode array detection (DAD) with a run time of 13 min. Confirmation was by solid-phase micro-extraction (SPME), followed by GC/MS determination. The main validation parameters for the three compounds in grapes and wine were a limit of detection up to 0.073 mg kg(-1), a precision not exceeding 10.0% and an average recovery of 93% +/- 38. PMID:16019828

De Melo Abreu, Susana; Correia, Manuela; Herbert, Paulo; Santos, Lúcia; Alves, Arminda

2005-06-01

336

Floral classification of honey using liquid chromatography-diode array detection-tandem mass spectrometry and chemometric analysis.  

PubMed

A high performance liquid chromatography-diode array detection-tandem mass spectrometry (HPLC-DAD-MS/MS) method for the floral origin traceability of chaste honey and rape honey samples was firstly presented in this study. Kaempferol, morin and ferulic acid were used as floral markers to distinguish chaste honey from rape honey. Chromatographic fingerprinting at 270 nm and 360 nm could be used to characterise chaste honey and rape honey according to the analytical profiles. Principal component analysis (PCA), partial least squares (PLS), partial least squares-discrimination analysis (PLS-DA) and soft independent modeling of class analogy (SIMCA) were applied to classify the honey samples according to their floral origins. The results showed that chaste honey and rape honey could be successfully classified by their floral sources with the analytical methods developed through this study and could be considered encouraging and promising for the honey traceability from unifloral or multifloral nectariferous sources. PMID:24128567

Zhou, Jinhui; Yao, Lihu; Li, Yi; Chen, Lanzhen; Wu, Liming; Zhao, Jing

2014-02-15

337

Recover soft x-ray spectrum using virtual flat response channels with filtered x-ray diode array  

NASA Astrophysics Data System (ADS)

A method for the recovery of soft x-ray spectra in indirect-drive inertial confinement fusion experiments is presented. Virtual detection channels with bandpass responses are obtained using linear combinations of the channel response functions of a filtered x-ray diode array and a weighted correction is introduced to improve the recovery. These virtual channels can be used to calculate radiation fluxes in some specific photon energy bands and hence to recover the spectrum of the whole photon energy range from 80 eV to 4.5 keV. Examples are listed which demonstrate the capability of this method to unfold various spectra such as Planck spectra with different radiation temperatures and to obtain x-ray flux of certain narrow energy interval.

Tianming, Song; Jiamin, Yang; Rongqing, Yi

2012-11-01

338

Monitoring and identification of residues of anabolic preparations in slaughtered cattle by HPLC with diode array detection.  

PubMed

The new combination of isocratic high performance liquid chromatography (HPLC) with on line UV spectrum detection via a diode array configuration has been applied to the detection and identification of anabolics present in application sites of cattle. Combination of the characteristic retention time in the HPLC chromatogram and a comparison of the full spectrum between 190-400 nm of the anabolic components with that of a standard resulted in a very reliable identification. By means of this method 117 samples of application sites were investigated for the presence of anabolic residues. Of the xenobiotic anabolics , 19-nortestosterone (NT) was found most frequently (in 96 cases), whereas diethylstilbestrol (DES) was found in only 11 cases. In all samples the identification of NT and DES was confirmed by high resolution gas chromatography-mass spectrometry (GCMS). PMID:6740892

Jansen, E H; van Blitterswijk, H; Stephany, R W

1984-04-01

339

High-brightness diode laser arrays integrated with a phase shifter designed for single-lobe far-field pattern.  

PubMed

High-brightness, edge-emitting diode laser arrays integrated with a phase shifter have been designed and fabricated at a wavelength of about 910 nm. Stable out-of-phase mode is generated through coupling evanescently and converted to be nearly in-phase by the phase modulation from the phase shifter. With a very simple manufacture process, stable single-lobe far-field pattern is achieved in the slow axis when the continuous wave output power exceeds 460 mW/facet, and the divergence angle is only 2.7 times the diffraction-limited value. Such device shows a promising future for high-brightness application with low cost and easy fabrication. PMID:23903137

Liu, Lei; Zhang, Jianxin; Ma, Shaodong; Qi, Aiyi; Qu, Hongwei; Zhang, Yejin; Zheng, Wanhua

2013-08-01

340

On-line post-column photochemical derivatization in liquid chromatographic--diode-array detection analysis of binary drug mixtures.  

PubMed

HPLC methods were developed for the analysis of pharmaceutical creams containing binary drug mixtures (betamethasone valerate-chlorocresol; hydrocortisone-miconazole nitrate; desonide pivalate-chlorhexidine; dexamethasone-clotrimazole; triamcinolone acetonide-econazole nitrate). The chromatographic separations were performed on C-18 and cyano columns under reversed-phase conditions. A post-column on-line photochemical reactor (irradiation at 254 nm) was arranged between the analytical column and the diode-array detector to enhance the performance of the method. Two UV spectra (photoreactor on and off) were obtained for each analyte and these additional sources of information proved to be useful for the unambiguous identification of the various analytes. The method was applied to the quality control of commercial creams using a solid-phase extraction procedure for the sample clean-up. PMID:8818033

Di Pietra, A M; Andrisano, V; Gotti, R; Cavrini, V

1996-06-01

341

Investigation of the strain induced optical transition energy shift of the GaN nanorod light emitting diode arrays.  

PubMed

Strain in the semiconductor light emitting layers has profound effect on the energy band structure and the optical properties of the light emitting diodes (LEDs). Here, we report the fabrication and characterization of GaN nanorod LED arrays. We found that the choice of nanorod passivation materials results in the variation of strain in the InGaN/GaN quantum wells, and thus the corresponding change of light emission properties. The results were further investigated by performing Raman measurement to understand the strain of nanorods with different passivation materials and by calculating the optical transition energy of the devices under the influence of strain-induced deformation potential and the piezoelectric polarization field. PMID:21747560

Chen, Liang-Yi; Huang, Hung-Hsun; Chang, Chun-Hsiang; Huang, Ying-Yuan; Wu, Yuh-Renn; Huang, JianJang

2011-07-01

342

Analysis of injection-locked gain-guided diode laser arrays  

NASA Astrophysics Data System (ADS)

A new model for injection-locked gain guided laser arrays is proposed. Diffraction-limited and single-lobe operation of injection-locked arrays is attributed to coherent summation of several transverse modes that are phase locked by injection. The model predicts far-field and near-field patterns, locking bandwidth, beam-steering properties, and locked output power. The effects of varying the master power, beam shape, position, and incidence angle on the slave array facet are also studied. Theoretical and experimental results are compared.

Verdiell, Jean-Marc; Frey, Robert; Huignard, Jean-Pierre

1991-03-01

343

Vertically p-n-junctioned GaN nano-wire array diode fabricated on Si(111) using MOCVD.  

PubMed

We demonstrate the fabrication of n-GaN:Si/p-GaN:Mg nanowire arrays on (111) silicon substrate by metal organic chemical vapor deposition (MOCVD) method .The nanowires were grown by a newly developed two-step growth process. The diameter of as-grown nanowires ranges from 300-400 nm with a density of 6-7 × 10(7) cm(-2). The p- and n-type doping of the nanowires is achieved with Mg and Si dopant species. Structural characterization by X-ray diffraction (XRD) and high-resolution transmission electron microscopy (HRTEM) indicates that the nanowires are relatively defect-free. The room-temperature photoluminescence emission with a strong peak at 370 nm indicates that the n-GaN:Si/p-GaN:Mg nanowire arrays have potential application in light-emitting nanodevices. The cathodoluminscence (CL) spectrum clearly shows a distinct optical transition of GaN nanodiodes. The nano-n-GaN:Si/p-GaN:Mg diodes were further completed using a sputter coating approach to deposit Au/Ni metal contacts. The polysilazane filler has been etched by a wet chemical etching process. The n-GaN:Si/p-GaN:Mg nanowire diode was fabricated for different Mg source flow rates. The current-voltage (I-V) measurements reveal excellent rectifying properties with an obvious turn-on voltage at 1.6 V for a Mg flow rate of 5 sccm (standard cubic centimeters per minute). PMID:23455517

Park, Ji-Hyeon; Kim, Min-Hee; Kissinger, Suthan; Lee, Cheul-Ro

2013-04-01

344

Quasi-isotropic VHF antenna array design study for the International Ultraviolet Explorer satellite  

NASA Technical Reports Server (NTRS)

Results of a study to design a quasi-isotropic VHF antenna array for the IUE satellite are presented. A free space configuration was obtained that has no nulls deeper than -6.4 dbi in each of two orthogonal polarizations. A computer program named SOAP that analyzes the electromagnetic interaction between antennas and complicated conducting bodies, such as satellites was developed.

Raines, J. K.

1975-01-01

345

Technique for Radiometer and Antenna Array Calibration with Two Antenna Noise Diodes  

NASA Technical Reports Server (NTRS)

This paper presents a new technique to calibrate a microwave radiometer and phased array antenna system. This calibration technique uses a radiated noise source in addition to an injected noise sources for calibration. The plane of reference for this calibration technique is the face of the antenna and therefore can effectively calibration the gain fluctuations in the active phased array antennas. This paper gives the mathematical formulation for the technique and discusses the improvements brought by the method over the existing calibration techniques.

Srinivasan, Karthik; Limaye, Ashutosh; Laymon, Charles; Meyer, Paul

2011-01-01

346

Measurement of mounting-induced strain in high-power laser diode arrays  

Microsoft Academic Search

Thermally induced strain caused by device packaging is studied in high-power semiconductor laser arrays by a novel non-invasive technique. Measurements with intentionally strained laser array devices for 808 nm emission reveal spectral shifts of quantum-confined optical transitions in the optical active region. These shifts by up to 10 meV serve as a measure for strain and are compared with model

Jens W. Tomm; Ralf Mueller; A. Baerwolff; Dirk Lorenzen

1999-01-01

347

A ZnO cross-bar array resistive random access memory stacked with heterostructure diodes for eliminating the sneak current effect  

NASA Astrophysics Data System (ADS)

We report cross-bar array resistive random access memory (RRAM) devices based on a ZnO thin film fabricated at room temperature. To prevent the sneak current path in a conventional cross-bar array device, two types of heterostructure diodes, a NiO/ZnO p-n junction and a WO3/ZnO tunnel barrier both stacked on cross-bar array RRAM were employed. With rectifying characteristics and high forward current density, the sneak current path was effectively eliminated. We believe that the proposed structures are promising for cross-bar type RRAM applications.

Won Seo, Jung; Baik, Seung Jae; Kang, Sang Jung; Hong, Yun Ho; Yang, Ji Hwan; Lim, Koeng Su

2011-06-01

348

Ultra high brightness laser diode arrays for pumping of compact solid state lasers and direct applications  

NASA Astrophysics Data System (ADS)

High Power Laser Diodes (HPLD) are increasingly used in different fields of applications such as Industry, Medicine and Defense. Our significant improvements of performances (especially in power and efficiency) and a reproducible manufacturing process have led to reliable, highly robust components. For defense and security applications these devices are used predominantly for pumping of solid state lasers (ranging, designation, countermeasures, and sensors). Due to the drastically falling price per watt they are more and more replacing flash lamps as pump sources. By collimating the laser beam even with a bar to bar pitch of only 400?m. cutting edge brightness of our stacks.is achieved Due the extremely high brightness and high power density these stacks are an enabling technology for the development of compact highly efficient portable solid state lasers for applications as telemeters and designators on small platforms such as small UAVs and handheld devices. In combination with beam homogenizing optics their compact size and high efficiency makes these devices perfectly suited as illuminators for portable active imaging systems. For gated active imaging systems a very short pulse at high PRF operation is required. For this application we have developed a diode driver board with an efficiency several times higher than that of a standard driver. As a consequence this laser source has very low power consumption and low waste heat dissipation. In combination with its compact size and the integrated beam homogenizing optics it is therefore ideally suited for use in portable gated active imaging systems. The kWatt peak power enables a range of several hundred meters. The devices described in this paper mostly operate at wavelength between 800 nm and 980nm. Results from diodes operating between 1300 nm and 1550 nm are presented as well.

Kohl, Andreas; Fillardet, Thierry; Laugustin, Arnaud; Rabot, Olivier

2012-10-01

349

Ultraviolet emission from Sb-doped p-type ZnO based heterojunction light-emitting diodes  

SciTech Connect

Heterojunction light emitting diodes (LEDs) were fabricated by making Au/Ni top Ohmic contacts on Sb-doped p-type ZnO film with low specific contact resistivity and Al/Ti back Ohmic contacts on n-type Si substrate. Near-band edge and deep-level emissions were observed from the LED devices at both low temperatures and room temperature, which is due to band-to-band and band-to-deep level radiative recombinations in ZnO, respectively. The electroluminescence emissions precisely match those of photoluminescence spectra from Sb-doped p-type ZnO, indicating that the ZnO layer acts as the active region for the radiative recombinations of electrons and holes in the diode operation.

Mandalapu, L. J.; Yang, Z.; Chu, S.; Liu, J. L. [Quantum Structures Laboratory, Department of Electrical Engineering, University of California at Riverside, Riverside, California 92521 (United States)

2008-03-24

350

Multi-Spectral Solar Telescope Array. IV - The soft X-ray and extreme ultraviolet filters  

NASA Technical Reports Server (NTRS)

NASA's Multi-Spectral Solar Telescope Array uses various combinations of thin foil filters composed of Al, C, Te, Be, Mo, Rh, and phthalocyanine to achieve the requisite radiation-rejection characteristics. Such rejection is demanded by the presence of strong EUV radiation at longer wavelengths where the specular reflectivity of multilayer mirrors can cause 'contamination' of the image in the narrow band defined by the Bragg condition.

Lindblom, Joakim F.; O'Neal, Ray H.; Walker, Arthur B. C., Jr.; Powell, Forbes R.; Barbee, Troy W., Jr.; Hoover, Richard B.

1991-01-01

351

In-phase locking in diffraction-coupled phased-array diode lasers  

NASA Astrophysics Data System (ADS)

The lateral locking mechanism in diffraction-coupled arrays is examined experimentally and theoretically. The arrays were Schottky barrier restricted, ridge waveguide standard double heterostructure devices grown by metalorganic chemical vapor deposition techniques with five, seven, and eleven stripes. The effects of reflection on the supermodes are analyzed; reflection coefficients are calculated using the Gaussian beam approximation for light in the unguided section. Double-lobe and single-lobe far-field patterns are studied. The effective modal reflectivities for the in-phase and out-of-phase supermodes are evaluated; it is observed that the effective modal reflectivity for the in-phase supermode is always higher than that of the out-of-phase supermodes. Good correlation of the data is obtained and it is noted that reflection in the common section of a diffraction-coupled array can produce in-phase coupling between the adjacent waveguides thereby stabilizing the single-lobe far-field radiation pattern.

Wang, S.; Wilcox, J. Z.; Jansen, M.; Yang, J. J.

1986-06-01

352

Optical and Electronic Properties of InGaN\\/GaN Multi-Quantum-Wells Near-Ultraviolet Lighting-Emitting-Diodes Grown by Low-Pressure Metalorganic Vapour Phase Epitaxy  

Microsoft Academic Search

The near-ultraviolet lighting-emitting-diodes (UV-LEDs) with the InGaN\\/GaN multi-quantum-well (MQW) structure were grown by low-pressure metalorganic vapour phase epitaxy. The double crystal x-ray diffraction revealed a distinct second-order satellite peak. The near-ultraviolet InGaN\\/GaN MQW LEDs have been successfully fabricated to emit at 401.2 nm with narrow FWHM of 14.3 nm and the forward voltage of 3.6 V at 20 mA injection

Zhong-Hui Li; Zhi-Jian Yang; Zhi-Xin Qin; Yu-Zhen Tong; Tong-Jun Yu; Shu Lu; Hua Yang; Guo-Yi Zhang

2003-01-01

353

EVALUATION OF NIACIN LC METHODS BY DIODE ARRAY\\/SPECTRAL ANALYSIS  

Microsoft Academic Search

Three extraction\\/LC methods for the determination of niacin in food materials have been qualitatively evaluated by spectral analysis procedures using a photodiode array detection system. This system allows visual inspection of multiple wavelength scans to identify presence of multiple components under LC peaks. It also allows calculation of a Similarity Index (SI) by means of library match software that compares

Denis E. Lacroix; Wayne R. Wolf; Thomas M. Hindsley

2002-01-01

354

Asymmetric sampled grating laser diode for a multi-wavelength laser array  

Microsoft Academic Search

We proposed an asymmetric sampled grating laser for an MLA. As expected in the theoretical calculation, it was confirmed experimentally that lasing action took place at the-1st order reflection wavelength by the control of sampled gratings combined with the index shifter. A 4-channel laser array was realized which was composed of asymmetric sampled grating lasers of different sampling periods.

Sang-Wan Ryu; Sung-Bock Kim; Jae-Sik Sim; Jeha Kim

2002-01-01

355

High-resolution pulse-counting array detectors for imaging and spectroscopy at ultraviolet wavelengths  

NASA Technical Reports Server (NTRS)

The performance characteristics of multianode microchannel array (MAMA) detector systems which have formats as large as 256 x 1024 pixels and which have application to imaging and spectroscopy at UV wavelengths are evaluated. Sealed and open-structure MAMA detector tubes with opaque CsI photocathodes can determine the arrival time of the detected photon to an accuracy of 100 ns or better. Very large format MAMA detectors with CsI and Cs2Te photocathodes and active areas of 52 x 52 mm (2048 x 2048 pixels) will be used as the UV solar blind detectors for the NASA STIS.

Timothy, J. Gethyn; Bybee, Richard L.

1986-01-01

356

P-type Cu--Ti--O nanotube arrays and their use in self-biased heterojunction photoelectrochemical diodes for hydrogen generation.  

PubMed

Copper and titanium remain relatively plentiful in the earth's crust; hence, their use for large-scale solar energy conversion technologies is of significant interest. We describe fabrication of vertically oriented p-type Cu-Ti-O nanotube array films by anodization of copper rich (60% to 74%) Ti metal films cosputtered onto fluorine doped tin oxide (FTO) coated glass. Cu-Ti-O nanotube array films 1 mum thick exhibit external quantum efficiencies up to 11%, with a spectral photoresponse indicating that the complete visible spectrum, 380 to 885 nm, contributes significantly to the photocurrent generation. Water-splitting photoelectrochemical pn-junction diodes are fabricated using p-type Cu-Ti-O nanotube array films in combination with n-type TiO 2 nanotube array films. With the glass substrates oriented back-to-back, light is incident upon the UV absorbing n-TiO 2 side, with the visible light passing to the p-Cu-Ti-O side. In a manner analogous to photosynthesis, photocatalytic reactions are powered only by the incident light to generate fuel with oxygen evolved from the n-TiO 2 side of the diode and hydrogen from the p-Cu-Ti-O side. To date, we find under global AM 1.5 illumination that such photocorrosion-stable diodes generate a photocurrent of approximately 0.25 mA/cm (2), at a photoconversion efficiency of 0.30%. PMID:18540655

Mor, Gopal K; Varghese, Oomman K; Wilke, Rudeger H T; Sharma, Sanjeev; Shankar, Karthik; Latempa, Thomas J; Choi, Kyoung-Shin; Grimes, Craig A

2008-07-01

357

Photoelectric characteristics of diodes in prototype photosensitive pixels for a monolithic array infrared photodetector  

SciTech Connect

Test photodiodes in the form of mesa structures with different areas from 30 Multiplication-Sign 30 to 100 Multiplication-Sign 100 {mu}m in size are fabricated based on a Cd{sub x}Hg{sub 1-x}Te/Si structure at x = 0.235, grown by molecular-beam epitaxy (MBE). The current-voltage characteristics of the diodes are measured in the dark and under background light conditions. The experimental results are compared with theoretical calculations. It is found that the dependence of the photodiode photocurrent and dark current on the mesa structure size appears in the mesa size ranges from 30 Multiplication-Sign 30 to 80 Multiplication-Sign 80 {mu}m. The dark current decreases and the photocurrent increases with decreasing mesa size. The mechanisms affecting the behavior of current-voltage characteristics are discussed.

Sorochkin, A. V., E-mail: alexandersm@mail.ru; Varavin, V. S.; Predein, A. V.; Sabinina, I. V.; Yakushev, M. V. [Russian Academy of Sciences, Rzhanov Institute of Semiconductor Physics, Siberian Branch (Russian Federation)

2012-04-15

358

Ultraviolet light-emitting diodes grown by plasma-assisted molecular beam epitaxy on semipolar GaN (2021) substrates  

NASA Astrophysics Data System (ADS)

Multi-quantum well (MQW) structures and light emitting diodes (LEDs) were grown on semipolar (2021) and polar (0001) GaN substrates by plasma-assisted molecular beam epitaxy. The In incorporation efficiency was found to be significantly lower for the semipolar plane as compared to the polar one. The semipolar MQWs exhibit a smooth surface morphology, abrupt interfaces, and a high photoluminescence intensity. The electroluminescence of semipolar (2021) and polar (0001) LEDs fabricated in the same growth run peaks at 387 and 462 nm, respectively. Semipolar LEDs with additional (Al,Ga)N cladding layers exhibit a higher optical output power but simultaneously a higher turn-on voltage.

Sawicka, M.; Chèze, C.; Turski, H.; Muziol, G.; Grzanka, S.; Hauswald, C.; Brandt, O.; Siekacz, M.; Kucharski, R.; Remmele, T.; Albrecht, M.; Krysko, M.; Grzanka, E.; Sochacki, T.; Skierbiszewski, C.

2013-03-01

359

Ultraviolet light-emitting diodes grown by plasma-assisted molecular beam epitaxy on semipolar GaN (2021) substrates  

SciTech Connect

Multi-quantum well (MQW) structures and light emitting diodes (LEDs) were grown on semipolar (2021) and polar (0001) GaN substrates by plasma-assisted molecular beam epitaxy. The In incorporation efficiency was found to be significantly lower for the semipolar plane as compared to the polar one. The semipolar MQWs exhibit a smooth surface morphology, abrupt interfaces, and a high photoluminescence intensity. The electroluminescence of semipolar (2021) and polar (0001) LEDs fabricated in the same growth run peaks at 387 and 462 nm, respectively. Semipolar LEDs with additional (Al,Ga)N cladding layers exhibit a higher optical output power but simultaneously a higher turn-on voltage.

Sawicka, M.; Grzanka, S.; Skierbiszewski, C. [Institute of High Pressure Physics, Polish Academy of Sciences, Sokolowska 29/37, 01-142 Warsaw (Poland) [Institute of High Pressure Physics, Polish Academy of Sciences, Sokolowska 29/37, 01-142 Warsaw (Poland); TopGaN Sp. z o.o., Sokolowska 29/37, 01-142 Warsaw (Poland); Cheze, C. [TopGaN Sp. z o.o., Sokolowska 29/37, 01-142 Warsaw (Poland) [TopGaN Sp. z o.o., Sokolowska 29/37, 01-142 Warsaw (Poland); Paul-Drude-Institut fuer Festkoerperelektronik, Hausvogteiplatz 5-7, 10117 Berlin (Germany); Turski, H.; Muziol, G.; Krysko, M.; Grzanka, E.; Sochacki, T. [Institute of High Pressure Physics, Polish Academy of Sciences, Sokolowska 29/37, 01-142 Warsaw (Poland)] [Institute of High Pressure Physics, Polish Academy of Sciences, Sokolowska 29/37, 01-142 Warsaw (Poland); Hauswald, C.; Brandt, O. [Paul-Drude-Institut fuer Festkoerperelektronik, Hausvogteiplatz 5-7, 10117 Berlin (Germany)] [Paul-Drude-Institut fuer Festkoerperelektronik, Hausvogteiplatz 5-7, 10117 Berlin (Germany); Siekacz, M. [Institute of High Pressure Physics, Polish Academy of Sciences, Sokolowska 29/37, 01-142 Warsaw (Poland) [Institute of High Pressure Physics, Polish Academy of Sciences, Sokolowska 29/37, 01-142 Warsaw (Poland); Paul-Drude-Institut fuer Festkoerperelektronik, Hausvogteiplatz 5-7, 10117 Berlin (Germany); Kucharski, R. [Ammono S.A., Czerwonego Krzyza 2/31, 00-377 Warsaw (Poland)] [Ammono S.A., Czerwonego Krzyza 2/31, 00-377 Warsaw (Poland); Remmele, T.; Albrecht, M. [Leibniz Institute for Crystal Growth, Max-Born Strasse 2, Berlin 12489 (Germany)] [Leibniz Institute for Crystal Growth, Max-Born Strasse 2, Berlin 12489 (Germany)

2013-03-18

360

High power ultraviolet light emitting diodes based on GaN/AlGaN quantum wells produced by molecular beam epitaxy  

SciTech Connect

In this paper, we report on the growth by molecular beam epitaxy and fabrication of high power nitride-based ultraviolet light emitting diodes emitting in the spectral range between 340 and 350 nm. The devices were grown on (0001) sapphire substrates via plasma-assisted molecular beam epitaxy. The growth of the light emitting diode (LED) structures was preceded by detailed materials studies of the bottom n-AlGaN contact layer, as well as the GaN/AlGaN multiple quantum well (MQW) active region. Specifically, kinetic conditions were identified for the growth of the thick n-AlGaN films to be both smooth and to have fewer defects at the surface. Transmission-electron microscopy studies on identical GaN/AlGaN MQWs showed good quality and well-defined interfaces between wells and barriers. Large area mesa devices (800x800 {mu}m{sup 2}) were fabricated and were designed for backside light extraction. The LEDs were flip-chip bonded onto a Si submount for better heat sinking. For devices emitting at 340 nm, the measured differential on-series resistance is 3 {omega} with electroluminescence spectrum full width at half maximum of 18 nm. The output power under dc bias saturates at 0.5 mW, while under pulsed operation it saturates at approximately 700 mA to a value of 3 mW, suggesting that thermal heating limits the efficiency of these devices. The output power of the investigated devices was found to be equivalent with those produced by the metal-organic chemical vapor deposition and hydride vapor-phase epitaxy methods. The devices emitting at 350 nm were investigated under dc operation and the output power saturates at 4.5 mW under 200 mA drive current.

Cabalu, J. S.; Bhattacharyya, A.; Thomidis, C.; Friel, I.; Moustakas, T. D.; Collins, C. J.; Komninou, Ph. [Department of Electrical and Computer Engineering, Boston University, Boston, Massachusetts 02215 and Center of Photonics Research, Boston University, Boston, Massachusetts 02215 (United States); U.S. Army Research Laboratory, Adelphi, Maryland 20783 (United States); Physics Department, Aristotle University, 54124 Thessaloniki (Greece)

2006-11-15

361

Self-powered ultraviolet photodetectors based on selectively grown ZnO nanowire arrays with thermal tuning performance.  

PubMed

A self-powered Schottky-type ultraviolet photodetector with Al-Pt interdigitated electrodes has been fabricated based on selectively grown ZnO nanowire arrays. At zero bias, the fabricated photodetector exhibited high sensitivity and excellent selectivity to UV light illumination with a fast response time of 81 ms. By tuning the Schottky barrier height through the thermally induced variation of the interface chemisorbed oxygen, an ultrahigh sensitivity of 3.1 × 10(4) was achieved at 340 K without an external power source, which was 82% higher than that obtained at room temperature. According to the thermionic emission-diffusion theory and the solar cell theory, the changes in the photocurrent of the photodetector at zero bias with various system temperatures were calculated, which agreed well with the experimental data. This work demonstrates a promising approach to modulating the performance of a self-powered photodetector by heating and provides theoretical support for studying the thermal effect on the future photoelectric device. PMID:24728006

Bai, Zhiming; Chen, Xiang; Yan, Xiaoqin; Zheng, Xin; Kang, Zhuo; Zhang, Yue

2014-05-28

362

Determination of analytes in medical herbs extracts by SPE coupled with two-dimensional planar chromatography in combination with diode array scanning densitometry and HPLC-diode array detector.  

PubMed

The purpose of this study is to demonstrate an application of 2-D high-performance planar chromatography-diode array detector (DAD) and HPLC-DAD after solid-phase extraction (SPE) for identification and quantitative analysis of pesticides (isoproturon, aziprotryne, hexazinone, flufenoxuron, methabenzthiazuron, procymidone, and ?-cypermethrin) in Melissa officinalis L. (Labiatae) samples. The procedure described for the determination of compounds is inexpensive and can be applied to routine analysis of analytes in medical herbs' samples after preliminary cleanup and concentration by SPE. Average recoveries on C18 SPE cartridges of pesticides eluted with 5 mL tetrahydrofuran by the proposed HPLC-DAD method, before and after 2-D-high-performance planar chromatography separation of analytes from M. officinalis L. samples spiked with pesticide at a concentration level of 10 ?g/g in plant material are presented. Method validation parameters for the quantification of pesticides by the proposed HPLC-DAD after SPE method are also presented. PMID:21171173

Tuzimski, Tomasz

2011-01-01

363

Quantitative analysis of Cistanches Herba using high-performance liquid chromatography coupled with diode array detection and high-resolution mass spectrometry combined with chemometric methods.  

PubMed

We aim to determine the chemical constituents of three species of Cistanches Herba using HPLC coupled with diode array detection and high-resolution MS. Ten phenylethanoid glycosides were identified and further quantified as marker substances by HPLC coupled with diode array detection method. The separation was conducted using an Agilent TC-C18 column with 0.1% formic acid and methanol as the mobile phases under gradient elution. The analytical method was fully validated in terms of linearity, sensitivity, precision, repeatability as well as recovery, and subsequently applied to evaluate the quality of 36 batches of Cistanche plants. The chemometric procedures (i.e., hierarchical clustering analysis and principal component analysis) were used to compare different species of Cistanches Herba, leading to successful classification of the Cistanche samples in accordance with their origins. In conclusion, this study provides a chemical basis for quality control of Cistanches Herba. PMID:23576377

Lu, Danyi; Zhang, Jiayu; Yang, Zhenya; Liu, Hongming; Li, Sha; Wu, Baojian; Ma, Zhiguo

2013-06-01

364

Coherent beam combining of high power broad-area laser diode array with a closed-V-shape external Talbot cavity.  

PubMed

We have coherently combined a high-power broad-area laser diode array by using a feedback loop closed off-axis external Talbot cavity. The off-axis feedback from two gratings provides transverse-mode control of broad-area lasers. The Talbot configuration of the external cavity implements diffractive coupling among laser diodes. Feedback from two gratings increases external cavity quality factor and spectrum selection capability. As a result, spatial coherence was improved and spectral linewidth was narrowed down. The high visibility of the far-field profile indicates that high spatial coherence was achieved. We also observed symmetric far-field profiles indicating that laser array was phase locked to in-phase and out-of-phase super-modes, respectively. Transition between these super-modes was observed by tuning one grating's tilted angle. PMID:20389757

Liu, B; Liu, Y; Braiman, Y

2010-03-29

365

Coherent Beam Combining of High Power Broad-Area Laser Diode Array with a Closed-V-shape External Talbot Cavity  

SciTech Connect

We have coherently combined a high-power broad-area laser diode array by using a feedback loop closed off-axis external Talbot cavity. The off-axis feedback from two gratings provides transverse-mode control of broad-area lasers. The Talbot configuration of the external cavity implements diffractive coupling among laser diodes. Feedback from two gratings increases external cavity quality factor and spectrum selection capability. As a result, spatial coherence was improved and spectral linewidth was narrowed down. The high visibility of the far-field profile indicates that high spatial coherence was achieved. We also observed symmetric far-field profiles indicating that laser array was phase locked to in-phase and out-of-phase super-modes, respectively. Transition between these super-modes was observed by tuning one grating's tilted angle.

Liu, Bo [ORNL; Liu, Yun [ORNL; Braiman, Yehuda [ORNL

2010-01-01

366

Photonic power delivery through optical fiber using very high power laser diode arrays  

NASA Astrophysics Data System (ADS)

Described is a system that will provide isolated electric power for a circuit that drives the core reset of a pulsed power modulator. This can be accomplished by coupling light from a number of diode laser bars to bundles of 200 micrometers multimode optical fibers. This is then coupled to photo- voltaic power converters that will deliver 16 V 29 mA of electricity from 1 watt of optical power. Spot size at the bundle face is a Gaussian ellipse with a major axis of 0.9 mm radius and a minor axis of 0.118 mm with a maximum full angle divergence of 16 X 2.4 degrees. Data is presented from four 20 W laser bars coupled to four bundles of 12 fibers generating a total of 24 W of electrical power. Various schemes are used to maximize coupling into the optical fiber while limiting the number of optical components, and comparing components such as fresnel and aspheric lenses and lens ducts for effectiveness and cost. This will provide a completely isolated low power source for high voltage, high current environments where traditional isolation techniques yield inadequate isolation or prove too cumbersome.

Heino, Matthew; Saethre, Robert

1999-05-01

367

Atomically sharp 318 nm Gd:AlGaN ultraviolet light emitting diodes on Si with low threshold voltage  

NASA Astrophysics Data System (ADS)

Self-assembled AlxGa1-xN polarization-induced nanowire light emitting diodes (PINLEDs) with Gd-doped AlN active regions are prepared by plasma-assisted molecular beam epitaxy on Si substrates. Atomically sharp electroluminescence (EL) from Gd intra-f-shell electronic transitions at 313 nm and 318 nm is observed under forward biases above 5 V. The intensity of the Gd 4f EL scales linearly with current density and increases at lower temperature. The low field excitation of Gd 4f EL in PINLEDs is contrasted with high field excitation in metal/Gd:AlN/polarization-induced n-AlGaN devices; PINLED devices offer over a three fold enhancement in 4f EL intensity at a given device bias.

Kent, Thomas F.; Carnevale, Santino D.; Myers, Roberto C.

2013-05-01

368

Quantitative analysis of flavonols, flavones, and flavanones in fruits, vegetables and beverages by high-performance liquid chromatography with photo-diode array and mass spectrometric detection  

Microsoft Academic Search

A high-performance liquid chromatographic (HPLC) separation method with photo-diode array (PDA) and mass spectrometric (MS) detection was developed to determine and quantify flavonols, flavones, and flavanones in fruits, vegetables and beverages. The compounds were analysed as aglycones, obtained after acid hydrolysis of freeze-dried food material. Identification was based on retention time, UV and mass spectra by comparison with commercial standards,

Ulla Justesen; Pia Knuthsen; Torben Leth

1998-01-01

369

Simultaneous determination of tryptophan, kynurenine, kynurenic and xanthurenic acids in honey by liquid chromatography with diode array, fluorescence and tandem mass spectrometry detection  

Microsoft Academic Search

A liquid chromatography method using diode array-fluorescence detection and atmospheric pressure chemical ionization mass spectrometry (LC-DAD-FLD and LC–APCI-MS\\/MS) was developed to quantify the levels of tryptophan (TRP), kynurenine (KYN), kynurenic (KYNA) and xanthurenic (XA) acids in honey. This procedure involved isolating the compounds of interest via solid-phase extraction (SPE) with mixed-mode polymeric cartridges. Chromatographic separation of the analytes was performed

María E. Soto; Ana M. Ares; José Bernal; María J. Nozal

2011-01-01

370

Diode array pumped, non-linear mirror Q-switched and mode-locked Nd : YVO 4 laser — a good tool for powder SHG measurement  

Microsoft Academic Search

A non-linear mirror consisting of a lithium triborate crystal and a dichroic output coupler are used to mode-lock (passively)\\u000a an Nd : YVO4 laser, pumped by a diode laser array. The laser can operate both in cw mode-locked and simultaneously Q-switched and mode-locked\\u000a (QML) regime. The peak power of the laser while operating in QML regime is much higher but

P. K. Datta; Chandrajit Basu; S. Mukhopadhyay; S. K. Das; G. K. Samanta; Antonio Agensi

2004-01-01

371

750 mW, 1.06 um, CW TEM00 output from a Nd:YVO4 laser end pumped by a single 20 stripe diode array  

Microsoft Academic Search

We report the highest electrical to optical conversion efficiency (12.5%), and the highest cw output power (750 mW), from any solid state laser crystal end pumped by a single multiple stripe diode laser array. The optical slope efficiency, which refers to the 1.06 mum output power divided by the optical pump power incident on the end face of our laser

R. A. Fields; M. Birnbaum; C. L. Fincher; J. Berger; D. F. Welch; D. R. Scifres; W. Streifer

1988-01-01

372

Analysis of multicomponent formulations containing pseudoephedrine HCl and chlorpheniramine maleate using first-derivative spectroscopy on a diode-array spectrophotometer.  

PubMed

Pseudoephedrine HCl and chlorpheniramine maleate are compounds which have overlapping UV spectra in solutions of phosphate buffer (pH 7.2), water, and 0.1 M HCl. The quantitation of both compounds was achieved by using first-derivative spectroscopy on a diode-array spectrophotometer. The application of this method for the analysis of content uniformity testing and measuring dissolution profiles was demonstrated. PMID:3585742

Hoover, J M; Soltero, R A; Bansal, P C

1987-03-01

373

Long-Term Monitoring of Pesticides and Polar Transformation Products in Ground Water Using Automated Online Trace-Enrichment and Liquid Chromatography with Diode Array Detection  

Microsoft Academic Search

An automated system using on-line trace-enrichment, separation by liquid chromatography with a gradient elution and diode array detection is described for monitoring pesticides in ground water. Two systems were used for covering the wide range of polarities of the targeted pesticides: the first one consisted of a PLRP-S precolumn and a C18 analytical column for moderately polar to non polar

S. Dupas; S. Guenu; V. Pichon; A. Montiel; B. Welte; M. C. Hennion

1996-01-01

374

Improved light output of GaN-based vertical light emitting diodes using SiO2 nanotube arrays and transparent metal oxide current conduction layer  

Microsoft Academic Search

The use of a refractive index matching (RIM) structure with indium zinc oxide (IZO) transparent conduction layer and SiO2 nanotube (SiO2-NT) arrays to improve light extraction of vertical structure KOH-etched GaN-based light emitting diodes (VLEDs) is demonstrated. Compared to regular VLED with KOH-roughened surface, it shows considerable gains in light emitted critical angle and light output power by 21.3° and

Shui-Jinn Wang; Pei-Ren Wang; Der-Ming Kuo; Hsiun-Rong Kuo; Jian-Shian Kuo

2011-01-01

375

High-power CW Nd:GdVO 4 solid-state laser end-pumped by a diode-laser-array  

Microsoft Academic Search

A high-power CW Nd:GdVO4 laser end-pumped by a diode-laser-array has been demonstrated. TEM00 mode output power of 5.05 W was obtained at the incident pump power of 12 W, leading to an optical conversion efficiency of 42.1%, while the slope efficiency was determined to be 47.6%. These results were shown to be slightly better than those achieved with Nd:YVO4 crystal

Junhai Liu; Zongshu Shao; Xianlin Meng; Huaijin Zhang; Li Zhu; Minhua Jiang

1999-01-01

376

Multiresidue method for fourteen fungicides in white grapes by liquid–liquid and solid-phase extraction followed by liquid chromatography–diode array detection  

Microsoft Academic Search

A quantitative, selective and sensitive HPLC method for the analysis of 14 fungicides in white grapes for vinification is described. The proposed method is based on liquid–liquid extraction (LLE) and solid-phase extraction (SPE) followed by liquid chromatography and diode array detection (HPLC–DAD). Dichloromethane–acetone (75:25, v\\/v) was the most appropriate solvent mix for extracting fungicides in white grapes. Silica cartridges resulted

R. Rial Otero; B. Cancho Grande; J. Simal Gándara

2003-01-01

377

Determination of phenolic compounds at low ?g 1 ?1 levels by various solid-phase extractions followed by liquid chromatography and diode-array detection  

Microsoft Academic Search

An off-line solid-phase extraction was carried out to determine thirteen phenolic compounds, which included eleven EPA priority phenols, using reversed-phase liquid chromatography and diode-array detection. Two different sorbents, carbon and a highly cross-linked styrene-divinylbenzene copolymer, were compared for the preconcentration process. To increase the retention of the most polar compounds, mainly phenol, tetrabutylammonium bromide was used as an ion-pair reagent

E. Pocurull; M. Calull; R. M. Marcé; F. Borrull

1996-01-01

378

Three-dimensional mapping of quantum wells in a GaN/InGaN core-shell nanowire light-emitting diode array.  

PubMed

Correlated atom probe tomography, cross-sectional scanning transmission electron microscopy, and cathodoluminescence spectroscopy are used to analyze InGaN/GaN multiquantum wells (QWs) in nanowire array light-emitting diodes (LEDs). Tomographic analysis of the In distribution, interface morphology, and dopant clustering reveals material quality comparable to that of planar LED QWs. The position-dependent CL emission wavelength of the nonpolar side-facet QWs and semipolar top QWs is correlated with In composition. PMID:23919559

Riley, James R; Padalkar, Sonal; Li, Qiming; Lu, Ping; Koleske, Daniel D; Wierer, Jonathan J; Wang, George T; Lauhon, Lincoln J

2013-09-11

379

Determination of steroid sex hormones in water and urine matrices by stir bar sorptive extraction and liquid chromatography with diode array detection  

Microsoft Academic Search

In this study, stir bar sorptive extraction and liquid desorption followed by high performance liquid chromatography with diode array detection (SBSE–LD–HPLC\\/DAD) were combined for the simultaneous determination of nine steroid sex hormones (estrone, 17?-estradiol, 17?-estradiol, 17?-ethynylestradiol, diethylstilbestrol, mestranol, progesterone, 19-norethisterone and norgestrel) in water and urine matrices.During the method development, it has been demonstrated that equilibrium time, ionic strength and

C. Almeida; J. M. F. Nogueira

2006-01-01

380

Low-noise low-jitter 32-pixels CMOS single-photon avalanche diodes array for single-photon counting from 300 nm to 900 nm  

NASA Astrophysics Data System (ADS)

We developed a single-photon counting multichannel detection system, based on a monolithic linear array of 32 CMOS SPADs (Complementary Metal-Oxide-Semiconductor Single-Photon Avalanche Diodes). All channels achieve a timing resolution of 100 ps (full-width at half maximum) and a photon detection efficiency of 50% at 400 nm. Dark count rate is very low even at room temperature, being about 125 counts/s for 50 ?m active area diameter SPADs. Detection performance and microelectronic compactness of this CMOS SPAD array make it the best candidate for ultra-compact time-resolved spectrometers with single-photon sensitivity from 300 nm to 900 nm.

Scarcella, Carmelo; Tosi, Alberto; Villa, Federica; Tisa, Simone; Zappa, Franco

2013-12-01

381

Improving the optical performance of InGaN light-emitting diodes by altering light reflection and refraction with triangular air prism arrays.  

PubMed

The effect of triangular air prism (TAP) arrays with different distance-to-width (d/w) ratios on the enhancement of light extraction efficiency (LEE) of InGaN light-emitting diodes (LEDs) is investigated. The TAP arrays embedded at the sapphire/GaN interface act as light reflectors and refractors, and thereby improve the light output power due to the redirection of light into escape cones on both the front and back sides of the LED. Enhancement in radiometric power as high as 117% and far-field angle as low as 129° are realized with a compact arrangement of TAP arrays compared with that of a conventional LED made without TAP arrays under an injection current of 20 mA. PMID:22212800

Kang, Ji Hye; Kim, Hyung Gu; Chandramohan, S; Kim, Hyun Kyu; Kim, Hee Yun; Ryu, Jae Hyoung; Park, Young Jae; Beak, Yun Seon; Lee, Jeong-Sik; Park, Joong Seo; Lysak, Volodymyr V; Hong, Chang-Hee

2012-01-01

382

Largely enhanced efficiency in ZnO nanowire/p-polymer hybridized inorganic/organic ultraviolet light-emitting diode by piezo-phototronic effect.  

PubMed

ZnO nanowire inorganic/organic hybrid ultraviolet (UV) light-emitting diodes (LEDs) have attracted considerable attention as they not only combine the high flexibility of polymers with the structural and chemical stability of inorganic nanostructures but also have a higher light extraction efficiency than thin film structures. However, up to date, the external quantum efficiency of UV LED based on ZnO nanostructures has been limited by a lack of efficient methods to achieve a balance between electron contributed current and hole contributed current that reduces the nonradiative recombination at interface. Here we demonstrate that the piezo-phototronic effect can largely enhance the efficiency of a hybridized inorganic/organic LED made of a ZnO nanowire/p-polymer structure, by trimming the electron current to match the hole current and increasing the localized hole density near the interface through a carrier channel created by piezoelectric polarization charges on the ZnO side. The external efficiency of the hybrid LED was enhanced by at least a factor of 2 after applying a proper strain, reaching 5.92%. This study offers a new concept for increasing organic LED efficiency and has a great potential for a wide variety of high-performance flexible optoelectronic devices. PMID:23339573

Yang, Qing; Liu, Ying; Pan, Caofeng; Chen, Jun; Wen, Xiaonan; Wang, Zhong Lin

2013-02-13

383

Disinfection of B. SUBTILIS Cells in Suspension Using Ultraviolet Light Emitting Diodes (leds) in the Presence of TiO2  

NASA Astrophysics Data System (ADS)

The concentration of vegetative Bacillus subtilis (B. subtilis) in phosphate buffered saline decreased when subjected to ultraviolet (UV) light from light emitting diodes (LEDs) in the presence of 0.01% Degussa P25 titanium dioxide (TiO2) as compared to a sample that contained bacteria only, a sample of bacteria that contained 0.01% TiO2, and bacteria that was subjected to the same UV light but no TiO2. The starting concentration of each sample was on the order of 104 colony forming units per milliliter (CFU/mL) and the time required for complete kill was less than 100min when the peak wavelength was 370 nm for the four LED light source at a total LED power of 0.8 milliWatts (mW), decreasing to less than 75 min for a total LED power of 3 mW. Changing the peak wavelength by 7 nm to 377 nm decreased the kill of vegetative B. subtilis to less than 1 log at 100 min for 5 mW total LED power. This work was performed under Federal Contract W9113M-09-C-0136 in support of the Radiance Technologies, Inc., prime contract from US Army SMDC, Huntsville, AL.

Province, Dennis W.; O'Neil, Shannon; Higgins, Keri; Smith, Paul J.; Dooley, Kristin; Curtis, Joey; Grippo, Adam M.; Rino, John W.; Allen, Susan D.

2011-06-01

384

Light Improvement of Near Ultraviolet Light-Emitting Diodes by Utilizing Lattice-Matched InAlGaN as Barrier Layers in Active Region  

NASA Astrophysics Data System (ADS)

The effects of lattice-matched InAlGaN used as barriers in the active region were investigated in near ultraviolet light-emitting diodes (LEDs). By changing the thickness of InAlGaN barriers, it is observed that there exists an optimal thickness. Besides the better carrier confinement in the case of using thick barriers, the simulation results showed that hole distribution in the case of using wide barriers should also play a role in the improvement of optical performance. Hence, an excessive increment in the width of barriers will degrade the optical performance contrarily, owing to the accumulated stress and the difficulty in hole transport in the active region from thick barriers. In addition, the calculated energy bandgap of InAlGaN is higher than that of GaN, which is beneficial for increasing the capability of carrier confinement and simultaneously enhancing the radiative recombination. Under 100 mA, the light output power of the LED with 7.3-nm-thick In0.018Al0.09Ga0.892N barriers can be increased by 36% as compared with the LED with GaN barrier.

Lu, Yu-Hsuan; Fu, Yi-Keng; Huang, Shyh-Jer; Su, Yan-Kuin; Xuan, Rong; Pilkuhn, Manfred H.; Chen, Ying-Chih

2013-08-01

385

Out-of-plane high-density piezoresistive silicon microwire/p-n diode array for force- and temperature-sensitive artificial whisker sensors  

NASA Astrophysics Data System (ADS)

We propose an out-of-plane high-aspect-ratio 'whisker-like' microwire array sensor for use in multisite contact force and temperature detection with high spatial resolution. Although the wire element has two terminal electrodes, the device consists of force-sensitive wire arrays where one end of the wire is attached to the substrate and the other end is free to be touched. We fabricated a force-sensitive wire array based on p-type (p-) silicon with 3 µm diameter and 30 µm length (1 ? cm) assembled over an n-type (n-) silicon substrate (3-6 ? cm), which resulted in a p-silicon wire/p-n diode system array. Due to the piezoresistance effect of the p-silicon wire, the electrical conductance changes upon contact of an individual wire with an object. The shift in the rectifying current-voltage (I-V) curves of the embedded p-n diode depends on the temperature through the silicon wire. Thus, the same alignment can be used as a force sensor and a temperature sensor. Both force- and temperature-sensitive microwire sensor arrays with a small detection area (~20 µm2) and high spatial resolution (~100 µm in pitch) have potential in numerous applications, including artificial electronic fingertips in a robot hand/prosthetics, multisite sensing of contact force, shear force, surface roughness and slip, and local temperature sensing capabilities.

Ikedo, Akihito; Ishida, Makoto; Kawano, Takeshi

2011-03-01

386

Measurement of mounting-induced strain in high-power laser diode arrays  

NASA Astrophysics Data System (ADS)

Thermally induced strain caused by device packaging is studied in high-power semiconductor laser arrays by a novel non-invasive technique. Measurements with intentionally strained laser array devices for 808 nm emission reveal spectral shifts of quantum-confined optical transitions in the optical active region. These shifts by up to 10 meV serve as a measure for strain and are compared with model calculations. We demonstrate that different packaging techniques cause different packaging-induced strains. We also show that the packaging-induced strain portion, which gets transmitted through the solder material, differs for different packaging technologies. An intentionally strain- reduced packaging technique is shown to transmit about one quarter of the potential packaging-induced strain towards the optical active layer, whereas another packaging technique, which provides highly reliable 'single-chip' devices is found to transmit about half of the potential amount. Spatially resolved measurements demonstrate strain gradients within the devices. Also temporal strain evolution is monitored. We show that 'the burn-in' is accompanied by strain accumulation whereas for long-term operation strain relaxation occurs.

Tomm, Jens W.; Mueller, Ralf; Baerwolff, A.; Lorenzen, Dirk

1999-11-01

387

Quantification of polyacetylenes in apiaceous plants by high-performance liquid chromatography coupled with diode array detection.  

PubMed

Polyacetylenes are known for their biofunctional properties in a wide range of organisms. In the present study, the most frequently occurring polyacetylenes, i.e. falcarinol, falcarindiol, and falcarindiol-3-acetate, were determined in six genera of the Apiaceae family. For this purpose, a straightforward and reliable method for the screening and quantification of the polyacetylenes using high-performance liquid chromatography coupled with diode array and mass spectrometric detection without tedious sample clean-up has been developed. Peak assignment was based on retention times, UV spectra, and mass spectral data. Quantification was carried out using calibration curves of authentic standards isolated from turnip-rooted parsley and Ligusticum mutellina, respectively. The references were unambiguously identified by Fourier transform-IR (FT-IR) spectroscopy, GC-MS, HPLC-MSn in the positive ionization mode, and 1H NMR and 13C NMR spectroscopy. To the best of our knowledge, the occurrence of falcarindiol-3-acetate in Anthriscus sylvestris and Pastinaca sativa has been reported for the first time. The data revealed great differences in the polyacetylene contents and varying proportions of individual compounds in the storage roots of Apiaceous plants. The results of the present study may be used as a suitable tool for authenticity control and applied to identify novel sources devoid or particularly rich in polyacetylenes, thus facilitating breeding programs for the selective enrichment and depletion of these plant secondary metabolites, respectively. PMID:21950154

Kramer, Maike; Mühleis, Andrea; Conrad, Jürgen; Leitenberger, Martin; Beifuss, Uwe; Carle, Reinhold; Kammerer, Dietmar R

2011-01-01

388

Simultaneous determination of 11 bioactive compounds in Jaeumganghwa-tang by high performance liquid chromatography-diode array detection  

PubMed Central

Background: Jaeumganghwa-tang (JEGH) is a traditional Korean herbal medicine for the treatment of chronic bronchitis, nephritis and diabetes mellitus. Objective: A high performance liquid chromatography-diode array detector (HPLC-DAD) method was developed for simultaneous determination of 11 major compounds such as 5- hydroxymethylfurfural, mangiferin, paeoniflorin, nodakenin, naringin, hesperidin, decursinol, berberine, glycyrrhizin, atractylenolide III and decursin, in JEGH. Materials and Methods: The separation was conducted on Shishedo C18 column with gradient elution of 0.1% trifluoroacetic acid–acetonitrile. Detection of wavelength was set at 205, 250, 280 and 330 nm. Results: The developed analysis showed a good linearity (R2 >0.9997). The range of limit of detection and limit of quantification were observed from 0.04 to 0.43 and from 0.11 to 1.30, respectively. The intra- and inter-day test relative standard deviations (RSD) were less than 3% and the accuracy was 95.98-108.44%. The recoveries were between 92.75% and 109.19% and RSD range of recoveries was measured from 0.52% to 2.78%. Conclusion: This HPLC-DAD method can be successfully applied for simultaneous determination of 11 major compounds in JEGH samples.

Yun, Bo-Ra; Weon, Jin Bae; Lee, Jiwoo; Eom, Min Rye; Ma, Choong Je

2014-01-01

389

Determination of free and total phenolic acids in plant-derived foods by HPLC with diode-array detection.  

PubMed

A high-performance liquid chromatographic (HPLC) method with diode-array detection (DAD) was used to identify and quantify free and total phenolic acids (m-hydroxybenzoic acid, p-hydroxybenzoic acid, protocatechuic acid, gallic acid, vanillic acid, syringic acid, o-coumaric acid, m-coumaric acid, p-coumaric acid, caffeic acid, ferulic acid, sinapic acid, chlorogenic acid, and ellagic acid) in plant foods. Free phenolic acids were extracted with a mixture of methanol and 10% acetic acid. Bound phenolic acids were liberated using first alkaline and then acid hydrolysis followed by extraction with diethyl ether/ethyl acetate (1:1). All fractions were quantified separately by HPLC. After HPLC quantification, results of alkali and acid hydrolysates were calculated to represent total phenolic acids. Ellagic acid was quantified separately after long (20 h) acid hydrolysis. The methods developed were effective for the determination of phenolic acids in plant foods. DAD response was linear for all phenolic acids within the ranges evaluated, with correlation coefficients exceeding 0.999. Coefficients of variation for 4-8 sample replicates were consistently below 10%. Recovery tests of phenolic acids were performed for every hydrolysis condition using several samples. Recoveries were generally good (mean >90%) with the exceptions of gallic acid and, in some cases, caffeic acid samples. PMID:12059140

Mattila, Pirjo; Kumpulainen, Jorma

2002-06-19

390

Liquid chromatographic-diode-array detection multiresidue determination of rice herbicides in drinking and paddy-field water.  

PubMed

A sensitive, rapid, and simple multiresidue method for the simultaneous determination of six postemergence herbicides currently used in rice cultivation--metsulfuron methyl, bensulfuron methyl, pyrazosulfuron ethyl, bentazone, bispyribac sodium, and cyhalofop butyl--in drinking and paddy-field water is presented. Water samples were extracted with solid-phase extraction cartridges. Final determination was made by LC with diode-array detection. The extraction efficiencies of C18 and HLB cartridges were compared. The average recovery obtained for these compounds for the lowest spiked level (0.1 microg/L) varied from 70 to 122% for C18 and 75-119% for HLB, with RSDs of 11 and 8.3%, respectively. The method had good linearity, and the lower detection limit for the pesticides studied varied from 0.03 to 0.04 microg/L. The proposed method was also tested in paddy-field water, with recovery studies giving good results with low RSDs at 1.0 microg/L. PMID:19714989

Roehrs, Rafael; Zanella, Renato; Pizzuti, Ionara; Adaime, Martha B; Pareja, Lucía; Niell, Silvina; Cesio, María V; Heinzen, Horacio

2009-01-01

391

Determination of polyacetylenes in carrot roots (Daucus carota L.) by high-performance liquid chromatography coupled with diode array detection.  

PubMed

A new high-performance liquid chromatographic method with diode array detection was developed for the separation and simultaneous determination of the carrot polyacetylenes falcarindiol (FaDOH), falcarindiol 3-acetate (FaDOAc) and falcarinol (FaOH) in carrot root extracts. The optimal chromatographic conditions were achieved on a C18 column with a linear gradient elution of water and acetonitrile as mobile phases, at the flow rate of 1.0 mL/min. All calibration curves of the three carrot polyacetylenes showed good linear regression (R2 > 0.998) within the test ranges. The developed method showed good precision for quantification of all polyacetylenes with overall intraday and interday variation of less than 3.3% and with average recovery rates of 99.2, 96.8 and 99.7% for FaDOH, FaDOAc and FaOH, respectively. The LOD (S/N = 3) and LOQ (S/N = 10) were less than 0.19 and 0.42 microg/mL, respectively, for all analytes. The established method was successfully used to determine the spatial distribution of FaDOH, FaDOAc and FaOH in six carrot genotypes (Bolero, Independent, Line 1, Mello Yello, Purple Haze and Tornado) by analysing peeled carrots and the corresponding peels for these polyacetylenes. PMID:17444217

Christensen, Lars P; Kreutzmann, Stine

2007-03-01

392

High-performance liquid chromatography with diode-array detection cotinine method adapted for the assessment of tobacco smoke exposure.  

PubMed

Smoking is considered to be one of the main risk factors for cancer and other diseases and is the second leading cause of death worldwide. As the anti-tobacco legislation implemented in Europe has reduced secondhand smoke exposure levels, analytical methods must be adapted to these new levels. Recent research has demonstrated that cotinine is the best overall discriminator when biomarkers are used to determine whether a person has ongoing exposure to tobacco smoke. This work proposes a sensitive, simple and low-cost method based on solid-phase extraction and liquid chromatography with diode array detection for the assessment of tobacco smoke exposure by cotinine determination in urine. The analytical procedure is simple and fast (20 min) when compared to other similar methods existing in the literature, and it is cheaper than the mass spectrometry techniques usually used to quantify levels in nonsmokers. We obtained a quantification limit of 12.30 ?g/L and a recovery of over 90%. The linearity ranges used were 12-250 and 250-4000 ?g/L. The method was successfully used to determine cotinine in urine samples collected from different volunteers and is clearly an alternative routine method that allows active and passive smokers to be distinguished. PMID:24668723

Bartolomé, Mónica; Gallego-Picó, Alejandrina; Huetos, Olga; Castaño, Argelia

2014-06-01

393

Multivariate curve-resolution analysis of pesticides in water samples from liquid chromatographic-diode array data.  

PubMed

Liquid chromatographic-diode array detection data recorded for aqueous mixtures of 11 pesticides show the combined presence of strongly coeluting peaks, distortions in the time dimension between experimental runs, and the presence of potential interferents not modeled by the calibration phase in certain test samples. Due to the complexity of these phenomena, data were processed by a second-order multivariate algorithm based on multivariate curve resolution and alternating least-squares, which allows one to successfully model both the spectral and retention time behavior for all sample constituents. This led to the accurate quantitation of all analytes in a set of validation samples: aldicarb sulfoxide, oxamyl, aldicarb sulfone, methomyl, 3-hydroxy-carbofuran, aldicarb, propoxur, carbofuran, carbaryl, 1-naphthol and methiocarb. Limits of detection in the range 0.1-2 ?g mL(-1) were obtained. Additionally, the second-order advantage for several analytes was achieved in samples containing several uncalibrated interferences. The limits of detection for all analytes were decreased by solid phase pre-concentration to values compatible to those officially recommended, i.e., in the order of 5 ng mL(-1). PMID:21215852

Maggio, Rubén M; Damiani, Patricia C; Olivieri, Alejandro C

2011-01-30

394

Scintillation induced response in passively-quenched Si-based single photon counting avalanche diode arrays.  

PubMed

An optical electrical model which studies the response of Si-based single photon counting arrays, specifically silicon photomultipliers (SiPMs), to scintillation light has been developed and validated with analytically derived and experimental data. The scintillator-photodetector response in terms of relative pulse height, 10%-90% rise/decay times to light stimuli of different rise times (ranging from 0.1 to 5 ns) and decay times (ranging from 1 to 50 ns), as well as for different decay times of the photodetector are compared in theory and simulation. A measured detector response is used as a reference to further validate the model and the results show a mean deviation of simulated over measured values of 1%. PMID:21263706

Spanoudaki, Virginia Ch; Levin, Craig S

2011-01-17

395

InGaN/GaN microcolumn light-emitting diode arrays with sidewall metal contact.  

PubMed

In this study, we produce InGaN/GaN microcolumn LED (MC-LED) arrays having nonpolar metal sidewall contacts using a top-down method, where the metal contacts only with the sidewall of the columnar LEDs with an open top for transparency. The trapezoidal profile of the as-etched columns was altered to a rectangular profile through KOH treatment, exposing the nonpolar sidewalls. While the MC-LED with no treatment emitted no light because of the etch-damaged region, the MC-LEDs with KOH treatment exhibited much improved the electrical properties with the much higher shunt resistance due to the removal of the etch-damaged region. The optical output power was strongest for the MC-LED with a 5-min treatment indicating an almost complete removal of the damaged region. PMID:24104122

Kong, Duk-Jo; Bae, Si-Young; Kang, Chang-Mo; Lee, Dong-Seon

2013-09-23

396

Toward a new ultraviolet diode laser: luminescence and p-n junctions in ZnO films  

NASA Astrophysics Data System (ADS)

In order to develop electroluminescent and laser devices based on the ultraviolet exciton emission of ZnO, it will be important to fabricate good p-n junctions. As-grown ZnO is normally of n-type because of oxygen vacancies and zinc interstitials acting as donors. Making p-type ZnO has been more difficult, believed due to self-compensation by intrinsic defects such as the donors Vo and Zni, or possibly by hydrogen as an unintentional extrinsic donor. In this work, we demonstrate that reactively sputtered, vacuum- annealed ZnO films can be changed from n-type to moderate p- type by adjusting the oxygen/argon ratio in the sputtering plasma. We report the properties of p-n homojunctions fabricated in this way and characterize transport in the films by Hall measurements. Ohmic contacts were formed by deposition of Au/Al. Our finding of p-type conductivity in apparently intrinsic ZnO formed by reactive sputtering is not inconsistent with calculated defect formation enthalpies if account is taken of the higher chemical potential of the atomic (ionic) oxygen reservoir represented by the sputter plasma, compared to the molecular oxygen reservoir assumed in the calculation of formation enthalpies. Photoluminescence of the sputtered and annealed films is characterized mainly by the 3.27 eV exciton peak at room temperature.

Xiong, Gang; Wilkinson, John; Tuzemen, S.; Ucer, K. B.; Williams, Richard T.

2002-04-01

397

High-performance liquid chromatography-diode array and electrospray-mass spectrometry analysis of non-allowed substances in cosmetic products for preventing hair loss and other hormone-dependent skin diseases.  

PubMed

A simple high-performance liquid chromatography (HPLC) method with ultraviolet diode array (UV-DAD) and electrospray ionisation mass spectrometry (ESI-MS) detection has been developed for the determination of minoxidil, progesterone, estrone, spironolactone, canrenone, hydrocortisone and triamcinolone acetonide in cosmetic products. The presence of these substances in commercial cosmetic samples is prohibited. The compounds were separated by reversed phase chromatography with water (0.1% trifluoroacetic acid) and acetonitrile gradient elution and detected by UV-DAD at 230, 254 and 280 nm and by ESI-MS positive ionisation mode. Benzoic acid was used as internal standard. Linearity was studied with UV-DAD detection from 1.50 to 1,000 microg/ml or mug/g range, depending on the different compounds and type of cosmetic preparation and with ESI-MS in the 50-1,000 ng/ml or ng/g range. Good determination coefficients (r(2)>or=0.99) were found in both UV and ESI-MS. At three concentrations spanning the linear dynamic ranges of both UV-DAD and ESI-MS assay, mean recoveries were always higher than 90% for the different analytes. This method was successfully applied to the analysis of substances under investigations illegally added in cosmetic cream and lotions, sold on internet web sites to prevent hair loss and other hormone-dependent skin diseases, like acne and hirsutism. PMID:18656319

De Orsi, Daniela; Pellegrini, Manuela; Pichini, Simona; Mattioli, Donatella; Marchei, Emilia; Gagliardi, Luigi

2008-11-01

398

Rapid separation and identification of furocoumarins in Angelica dahurica by high-performance liquid chromatography with diode-array detection, time-of-flight mass spectrometry and quadrupole ion trap mass spectrometry.  

PubMed

High-performance liquid chromatography with diode-array detection (HPLC/DAD), time-of-flight mass spectrometry (HPLC/TOFMS) and quadrupole ion trap mass spectrometry (HPLC/QITMS) were used for separation, identification and structural analysis of furocoumarins in Angelica dahurica. Two furocoumarins (imperatorin and isoimperatorin) in Angelica dahurica extract were identified unambiguously by comparing their relative retention times, characteristic ultraviolet information and accurate mass measurement. A formula database of known furocoumarins in Angelica dahurica was established, against which the other 21 furocoumarins were identified effectively based on the accurate extract masses and formulae acquired by HPLC/TOFMS. In order to distinguish the isomers, multi-stage mass spectrometry (MSn, ion trap mass spectrometry) was used. General fragmentation behavior of the furocoumarins in the ion trap mass spectrometer was studied by the two furocoumarin standards, and their fragmentation rules in MS(n) spectra were summarized. These deduced fragmentation rules of furocoumarins were successfully implemented in distinguishing the three groups of isomers in Angelica dahurica by HPLC/QITMS. By using the three different analytical techniques, 23 furocoumarins in Angelica dahurica were tentatively identified within 30 min. Finally, HPLC/TOFMS fingerprints of Angelica dahurica were established by which it can be concluded that a rapid and effective method based on the three analytical techniques for identification of chemical components was established. This can provide help for further quality control of Angelica dahurica and pharmacology mechanism study of furocoumarins in Angelica dahurica. PMID:19530154

Zhang, Hai; Gong, Chungui; Lv, Lei; Xu, Yuanjie; Zhao, Liang; Zhu, Zhenyu; Chai, Yifeng; Zhang, Guoqing

2009-07-01

399

Quaternary ultraviolet AlInGaN MQW laser diode performance using quaternary AlInGaN electron blocking layer.  

PubMed

The effect of polarization-matched Al(0.25)In(0.08)Ga(0.67)N electron-blocking layer (EBL) on the optical performance of ultraviolet Al(0.08)In(0.08)Ga(0.84)N/Al(0.1)In(0.01)Ga(0.84)N multi-quantum well (MQW) laser diodes (LDs) was investigated. The polarization-matched Al(0.25)In(0.08)Ga(0.67)N electron blocking layer (EBL) was employed in an attempt to reduce the polarization effect inside the active region of the diodes. The device performance which is affected by piezoelectric was studied via drift-diffusion model for carrier transport, optical gain and losses using the simulation program of Integrated System Engineering Technical Computer Aided design (ISE TCAD). The optical performance of the LD using quaternary Al(0.25)In(0.08)Ga(0.67)N EBL was compared with the LD using ternary Al(0.3)Ga(0.7)N EBL where both materials have the same energy band gap of Eg = 3.53 eV. The self-consistent ISE-TCAD simulation program results showed that the polarization-matched quaternary Al(0.25)In(0.08)Ga(0.67)N EBL is beneficial as it confines the electrons inside the quantum well region better than ternary Al(0.3)Ga(0.7)N EBL. The results indicated that the use of Al(0.25)In(0.08)Ga(0.67)N EBL has lower threshold current and higher optical intensity than those for Al(0.3)Ga(0.7)N EBL. The effect of Al(0.25)In(0.08)Ga(0.67)N EBL thickness on the performance of LDs has also been studied. Results at room temperature indicated that lower threshold current, high slope efficiency, high output power, and high differential quantum efficiency DQE occurred when the thickness of Al(0.25)In(0.08)Ga(0.67)N EBL was 0.25 µm. PMID:21643179

Ghazai, A J; Thahab, S M; Abu Hassan, H; Hassan, Z

2011-05-01

400

High power and high efficiency kW 88x-nm multi-junction pulsed diode laser bars and arrays  

NASA Astrophysics Data System (ADS)

There is great interest in the development of high-power, high-efficiency and low cost QCW 88x-nm diode laser bars and arrays for pumping solid state lasers. We report on the development of kW 88x-nm diode laser bars that are based on a bipolar cascade design, in which multiple lasers are epitaxially grown in electrical series on a single substrate. Multiple laser junctions, each of which is based on nLight's high performance 88x-nm epitaxial design, are separated by low resistance tunnel junctions with resistance as low as 8.0x10-6 ?-cm2. Optimization of bar geometry and wafer fabrication processes was explored for electrical and optical performance improvement in double-junction diode lasers. A QCW power of 630 W was demonstrated in a 3-mm wide mini-bar with 3-mm cavity length. Peak efficiency of 61% was measured with 200 ?s and 14 Hz pulses, at a heatsink temperature of 10 °C. Further power scaling was demonstrated in a 1-cm wide bar with 3-mm cavity length, where a record high peak power of 1.77 kW was measured at 1 kA drive current. Ongoing work for further power scaling includes development of triple-junction diode laser bars and double-junction bar-stack that emits < 10kW optical power.

Chen, Zhigang; Bai, John; Dong, Weimin; Guan, Xingguo; Zhang, Shiguo; Elim, Sandrio; Bao, Ling; Grimshaw, Mike; Devito, Mark; Kanskar, Manoj

2014-03-01

401

Determination of alkenes in cracking products by normal-phase high-performance liquid chromatography-diode array detection.  

PubMed

Alkene content determinations in fluid catalytic cracking (FCC) liquid products were performed by means of normal-phase high-performance liquid chromatography (NP-HPLC) with diode array detection (UV/DAD). Separation of alkenes from aromatic hydrocarbons was performed on amino-modified silica gel column with n-heptane as mobile phase. The column has a little affinity to alkenes and saturated hydrocarbons and a pronounced affinity to aromatic compounds. The problem of alkenes and saturates co-elution on this column type was overcome with the detection system, UV/DAD, sensitive and selective to alkenes, while saturates are inactive in UV field. Total alkene content was determined as a sum of mono- and dialkene groups quantified by external standard method. Validation and verification of the developed method proved their applicability. The following criteria were used to validate the HPLC-DAD method: selectivity, linearity, precision, limits of detection and quantification. Alkene contents were quantified with the external standard method of wide calibration range, so both low and high alkene contents can be determined by the single calibration. Correlation coefficients were higher than 0.99. Precision was evaluated as repeatability and intermediary precision with relative standard deviations less than 5%. Some structural investigation of alkene groups was performed to confirm the assumption. Proposed method was compared with certified NMR method. Six commercial motor gasoline samples were analyzed by these two methods. Obtained results indicate good agreement between alkene content determined by both methods. The developed method was applied to the determination of alkene content in liquid FCC products in the boiling range from 70 degrees C to 190 degrees C. PMID:19296961

Tomi?, Tatjana; Babi?, Sandra; Nasipak, Nada Uzorinac; Ruszkowski, Maja Fabuli?; Skrobonja, Livijana; Kastelan-Macan, Marija

2009-05-01

402

Simultaneous determination of eight flavonoids in propolis using chemometrics-assisted high performance liquid chromatography-diode array detection.  

PubMed

A fast analytical strategy of second-order calibration method based on the alternating trilinear decomposition algorithm (ATLD)-assisted high performance liquid chromatography coupled with a diode array detector (HPLC-DAD) was established for the simultaneous determination of eight flavonoids (rutin, quercetin, luteolin, kaempferol, isorhamnetin, apigenin, galangin and chrysin) in propolis capsules samples. The chromatographic separation was implemented on a Wondasil™ C18 column (250mm×4.6mm, 5?m) within 13min with a binary mobile phase composed of water with 1% formic acid and methanol at a flow rate of 1.0mLmin(-1) after flavonoids were only extracted with methanol by ultrasound extraction for 15min. The baseline problem was overcome by considering background drift as additional compositions or factors as well as the target analytes, and ATLD was employed to handle the overlapping peaks from analytes of interest or from analytes and co-eluting matrix compounds. The linearity was good with the correlation coefficients no less than 0.9947; the limit of detections (LODs) within the range of 3.39-33.05ngmL(-1) were low enough; the accuracy was confirmed by the recoveries ranged from 91.9% to 110.2% and the root-mean-square-error of predictions (RMSEPs) less than 1.1?g/mL. The results indicated that the chromatographic method with the aid of ATLD is efficient, sensitive and cost-effective and can realize the resolution and accurate quantification of flavonoids even in the presence of interferences, thus providing an alternative method for accurate quantification of analytes especially when the complete separation is not easily accomplished. The method was successfully applied to propolis capsules samples and the satisfactory results were obtained. PMID:24907544

Sun, Yan-Mei; Wu, Hai-Long; Wang, Jian-Yao; Liu, Zhi; Zhai, Min; Yu, Ru-Qin

2014-07-01

403

Simultaneous determination of six bioactive compounds in Evodiae Fructus by high-performance liquid chromatography with diode array detection.  

PubMed

A simple and reliable high-performance liquid chromatography method with diode array detection (HPLC-DAD) was developed and validated for the simultaneous determination of six bioactive components, rutaevine, limonin, evodiamine, rutaecarpine, N-formyldihydrorutaecarpine and dihydroevocarpine, in the traditional Chinese medicine Evodiae Fructus (Wuzhuyu in Chinese). HPLC separation was conducted on an Agilent Eclipse C18 column (4.6 × 150 mm, 5 µm) at 35°C with a mixture of mobile phase A [tetrahydrofuran-0.02% phosphoric acid (16 : 35)] and mobile phase B (acetonitrile) (gradient elution as follows: 0 min, 22% B; 23 min, 22% B; 24 min, 75% B) at a flow rate of 1 mL/min, and the DAD detection wavelength was set at 220 nm. A linear relationship within the range of investigated concentrations was observed for the six compounds, with correlation coefficients greater than 0.999. The average recovery yields of the six compounds ranged from 98.39 to 104.96%. The HPLC-DAD method was validated by its repeatability [relative standard deviation (RSD) < 2.0%] and intra-day and inter-day precision (RSD < 2.0%). The method was successfully applied to the simultaneous determination of the six previously mentioned components in Evodiae Fructus. It is the first report of a simultaneous qualitative and quantitative analysis for three classes of bioactive components in Wuzhuyu, including the indolequinazoline alkaloids, quinolone alkaloid and limonoids. Based on these results, it is suggested, for possible future revision of the Chinese Pharmacopoeia, that the total contents of evodiamine and rutaecarpine are not less than 0.15% and the total contents of rutaevine and limonin are not less than 0.50%. PMID:23377650

Tang, Xiaolong; Huang, Zhifang; Chen, Yan; Liu, Yunhua; Liu, Yuhong; Zhao, Junning; Yi, Jinhai

2014-02-01

404

Spectral light measurements in microbenthic phototrophic communities with a fiber-optic microprobe coupled to a sensitive diode array detector  

SciTech Connect

A diode array detector system for microscale light measurements with fiber-optic microprobes was developed; it measures intensities of 400-900-nm light over >6 orders of magnitude with a spectral resolution of 2-5 nm. Fiber-optic microprobes to measure field radiance or scalar irradiance were coupled to the detector system and used for spectral light measurements in hypersaline microbial mats and in laminated phototrophic communities of coastal sediments. The vertical distribution of major photopigments of microalgae, cyanobacteria, and anoxygenic phototrophic bacteria could be identified from extinction maxima in measured radiance spectra at 430-550 nm (Chl a and carotenoids), 620-625 nm (phycocyanin), 675 nm (Chl a), 745-750 nm (BChl c), 800-810 nm, and 860-880 nm (BChl a). Scalar irradiance spectra exhibited a different spectral composition and a higher light intensity at the sediment surface as compared to incident light. IR light thus reached 200% of incident at the sediment surface. Maximal light penetration was found for IR light, whereas visible light was strongly attenuated in the upper 0-2 mm of the sediment. Measurements of photon scalar irradiance (400-700 nm) were combined with microelectrode measurements of oxygenic photosynthesis in the coastal sediment. With an incident light intensity of 200 [mu]Einst m[sup [minus]2]s[sup [minus]1], photon scalar irradiance reached a maximum of 283 [mu]Einst m[sup [minus]2]s[sup [minus]1] at the sediment surface. The lower boundary of the euphotic zone was 2.2 mm below the surface at a light intensity of 12 [mu]Einst m[sup [minus]2]s[sup [minus]1]. 20 refs., 6 figs.

Kuehl, M. (Univ. of Aarhus (Denmark)); Joergensen, B.B. (Max-Planck-Inst. for Marine Microbiology, Bremen (Germany))

1992-12-01

405

Determination of acibenzolar-S-methyl and its acidic metabolite in soils by HPLC-diode array detection.  

PubMed

A simple and accurate method for the analysis of acibenzolar-S-methyl (benzo[1,2,3]thiadiazole-7-carbothioic acid-S-methyl ester; CGA 245 704; ASM) and its major conversion product, benzo[1,2,3]thiadiazole-7-carboxylic acid (CGA 210 007; BTC), in soils is presented. ASM extraction from soil samples was performed using acetonitrile and BTC was extracted with a mixture of potassium phosphate buffer (0.5 M, pH 3) and acetonitrile (70:30 %, v/v). Both extracts were directly analyzed in a high-performance liquid chromatography-diode array detection (HPLC-DAD) system. Pesticide separation was achieved on a C18 (4.6 mm × 150 mm, 5 ?m) analytical column with a isocratic elution of acetonitrile:water 40:60 % (v/v) with 0.6 mL L?¹ acetic acid at a flow rate of 1 mL min?¹. Linear regression coefficients (r (2)) of the external calibration curves were always above 0.9997. The limits of detection (LOD) and quantification (LOQ) of the method were 0.005 and 0.02 mg kg?¹ for ASM, and 0.01 and 0.05 mg kg?¹ for BTC, respectively. Recoveries were investigated at six fortification levels and were in the range of 90-120 % for ASM and 74-96 % for BTC with relative standard deviations (RSDs) below 11 % in all cases. The method was also validated by analyzing freshly spiked soil samples with 2.7% organic matter content at 0.5 mg kg?¹ level, with slightly lower recovery values only for ASM. Moreover, recoveries for intermediate aged residues of the analytes were similar to fresh residues. This method was also applied to determine ASM half-life (t(½) = 8.7 h) and the rate of the acidic metabolite formation. PMID:21726155

Myresiotis, Charalampos K; Papadakis, Emmanouil N; Vryzas, Zisis G; Papadopoulou-Mourkidou, Euphemia

2011-01-01

406

AlN/AlGaN short-period superlattice sacrificial layers in laser lift-off for vertical-type AlGaN-based deep ultraviolet light emitting diodes  

NASA Astrophysics Data System (ADS)

Large-area (~1 cm2) laser lift-off (LLO) wafer separation of Al0.45Ga0.55N layers from AlN/sapphire templates has been demonstrated by using 200-period AlN/Al0.22Ga0.78N short-period superlattice (SPSL) sacrificial layers instead of conventional GaN photoabsorbing layers. The SPSL functions as the photoabsorbing and mechanically weakened layer in the LLO process. This SPSL-assisted LLO technique promises future progress of vertical-type deep ultraviolet light emitting diodes and freestanding AlN-AlGaN bulk substrates.

Takeuchi, Misaichi; Maegawa, Tomohiro; Shimizu, Hiroshi; Ooishi, Shin; Ohtsuka, Takumi; Aoyagi, Yoshinobu

2009-02-01

407

AlN\\/AlGaN short-period superlattice sacrificial layers in laser lift-off for vertical-type AlGaN-based deep ultraviolet light emitting diodes  

Microsoft Academic Search

Large-area (~1 cm2) laser lift-off (LLO) wafer separation of Al0.45Ga0.55N layers from AlN\\/sapphire templates has been demonstrated by using 200-period AlN\\/Al0.22Ga0.78N short-period superlattice (SPSL) sacrificial layers instead of conventional GaN photoabsorbing layers. The SPSL functions as the photoabsorbing and mechanically weakened layer in the LLO process. This SPSL-assisted LLO technique promises future progress of vertical-type deep ultraviolet light emitting diodes

Misaichi Takeuchi; Tomohiro Maegawa; Hiroshi Shimizu; Shin Ooishi; Takumi Ohtsuka; Yoshinobu Aoyagi

2009-01-01

408

Optimizing the accuracy of a helical diode array dosimeter: A comprehensive calibration methodology coupled with a novel virtual inclinometer  

SciTech Connect

Purpose: The goal of any dosimeter is to be as accurate as possible when measuring absolute dose to compare with calculated dose. This limits the uncertainties associated with the dosimeter itself and allows the task of dose QA to focus on detecting errors in the treatment planning (TPS) and/or delivery systems. This work introduces enhancements to the measurement accuracy of a 3D dosimeter comprised of a helical plane of diodes in a volumetric phantom. Methods: We describe the methods and derivations of new corrections that account for repetition rate dependence, intrinsic relative sensitivity per diode, field size dependence based on the dynamic field size determination, and positional correction. Required and described is an accurate ''virtual inclinometer'' algorithm. The system allows for calibrating the array directly against an ion chamber signal collected with high angular resolution. These enhancements are quantitatively validated using several strategies including ion chamber measurements taken using a ''blank'' plastic shell mimicking the actual phantom, and comparison to high resolution dose calculations for a variety of fields: static, simple arcs, and VMAT. A number of sophisticated treatment planning algorithms were benchmarked against ion chamber measurements for their ability to handle a large air cavity in the phantom. Results: Each calibration correction is quantified and presented vs its independent variable(s). The virtual inclinometer is validated by direct comparison to the gantry angle vs time data from machine log files. The effects of the calibration are quantified and improvements are seen in the dose agreement with the ion chamber reference measurements and with the TPS calculations. These improved agreements are a result of removing prior limitations and assumptions in the calibration methodology. Average gamma analysis passing rates for VMAT plans based on the AAPM TG-119 report are 98.4 and 93.3% for the 3%/3 mm and 2%/2 mm dose-error/distance to agreement threshold criteria, respectively, with the global dose-error normalization. With the local dose-error normalization, the average passing rates are reduced to 94.6 and 85.7% for the 3%/3 mm and 2%/2 mm criteria, respectively. Some algorithms in the convolution/superposition family are not sufficiently accurate in predicting the exit dose in the presence of a 15 cm diameter air cavity. Conclusions: Introduction of the improved calibration methodology, enabled by a robust virtual inclinometer algorithm, improves the accuracy of the dosimeter's absolute dose measurements. With our treatment planning and delivery chain, gamma analysis passing rates for the VMAT plans based on the AAPM TG-119 report are expected to be above 91% and average at about 95% level for {gamma}(3%/3 mm) with the local dose-error normalization. This stringent comparison methodology is more indicative of the true VMAT system commissioning accuracy compared to the often quoted dose-error normalization to a single high value.

Kozelka, Jakub; Robinson, Joshua; Nelms, Benjamin; Zhang, Geoffrey; Savitskij, Dennis; Feygelman, Vladimir [Sun Nuclear Corp., Melbourne, Florida 32940 (United States); Department of Physics, University of South Florida, Tampa, Florida 33612 (United States); Canis Lupus LLC, Sauk County, Wisconsin 53561 (United States); Division of Radiation Oncology, Moffitt Cancer Center, Tampa, Florida 33612 (United States); Sun Nuclear Corp., Melbourne, Florida 32940 (United States); Division of Radiation Oncology, Moffitt Cancer Center, Tampa, Florida 33612 (United States)

2011-09-15

409

The XRD (x-ray diode) array, the grazing incidence spectrometer, and the x-ray imaging camera on PBFA II  

SciTech Connect

Target diagnostics on PBFA II will include a time-resolved x-ray diode array, an energy-resolved, time-integrated x-ray camera and a grazing incidence spectrometer. A clean vacuum, independent of that on PBFA II, will be supplied to the detectors to maintain more reproducible calibrations. We also describe the diagnostics and outline the calculations which determined the shielding required. Based on the calculations the background due to bremsstrahlung in the least sensitive diagnostic is 12 eV/pixel. The appropriate shielding is being built to field these diagnostics. 8 refs., 6 figs., 1 tab.

Derzon, M.S.; Sweeney, M.A.; Grandon, P.; Ives, H.C.; Kensek, R.P.; Mix, L.P.; Stygar, W.A.

1988-01-01

410

Comparative study of fourteen alkaloids from Uncaria rhynchophylla hooks and leaves using HPLC-diode array detection-atmospheric pressure chemical ionization/MS method.  

PubMed

The purpose of the study is to compare alkaloid profile of Uncaria rhynchophylla hooks and leaves. Ten oxindole alkaloids and four glycosidic indole alkaloids were identified using HPLC-diode array detection (DAD) or LC-atmospheric pressure chemical ionization (APCI)-MS method, and a HPLC-UV method for simultaneous quantification of major alkaloids was validated. The hooks are characterized by high levels of four oxindole alkaloids rhynchophylline (R), isorhynchophylline (IR), corynoxeine (C) and isocorynoxeine (IC), while the leaves contained high level of two glycosidic indole alkaloids vincoside lactam (VL) and strictosidine (S). The presented methods have proven its usefulness in chemical characterization of U. rhynchophylla hooks and leaves. PMID:22223371

Qu, Jialin; Gong, Tianxing; Ma, Bin; Zhang, Lin; Kano, Yoshihiro; Yuan, Dan

2012-01-01

411

Light Extraction Enhancement in AlGaInP-Based Vertical Light Emitting Diodes by Using Circular Micro-Contact Array  

NASA Astrophysics Data System (ADS)

We have demonstrated that light output power of vertical AlGaInP-based light emitting diodes (LEDs) can be enhanced through use of a circular n+-GaAs/Ni/Ge/Au micro-contact array and an ITO current-spreading layer. We designed three different circular micro-contact arrays with different total areas and diameters for use as n-type electrodes in vertical AlGaInP LEDs. For comparison, LEDs with a normal linear-patterned n-type electrode were also fabricated. The results show that the circular micro-contact array for use an n-electrode in the vertical AlGaInP-based LEDs, greatly improved the uniformity of light output intensity, followed by increase in light output power. In addition, we also found that the total area of a circular micro-contact array and the thickness of the ITO current-spreading layer were important parameters for enhancing the light output power of the AlGaInP-based LEDs, due to a reduced light absorption in the circular micro-contact array and in the ITO layer.

Seo, Jae Won; Kim, Yong Deok; Kwak, Joon Seop

2013-10-01

412

Simultaneous determination of seven azole antifungal drugs in serum by ultra-high pressure liquid chromatography and diode array detection.  

PubMed

Azole antifungals are a group of fungistatic agents that can be administered orally or parenterally. The determination of the concentrations of these antifungals (miconazole, fluconazole, ketoconazole, posaconazole, voriconazole, itraconazole, and its major active metabolite, hydroxy-itraconazole) in serum can be useful to adapt the doses to pharmacological ranges because of large variability in the absorption and metabolism of the drugs, multiple drug interactions, but also potential resistance or toxicity. A method was developed and validated for the simultaneous determination of these drugs in serum utilizing ultra-high pressure liquid chromatography and diode array detection (UHPLC-DAD). After a simple and rapid liquid-liquid extraction, the pre-treated sample was analysed on an UHPLC-DAD system (Waters Corporation(®)). The chromatographic separation was carried out on an Acquity BEH C18 column (Waters Corporation) with a gradient mode of mobile phase composed of acetonitrile and aqueous ammonium bicarbonate 10·0 M pH10. The flow rate was 0·4 ml/min and the injection volume was 5 ?l. The identification wavelength varied according to the drug from 210 to 260 nm. The method was validated by the total error method approach by using an analytical validation software (e•noval V3·0 Arlenda(®)). The seven azole antifungals were identified by retention time and specific UV spectra, over a 13-minute run time. All calibration curves showed good linearity (r(2)>0·99) in ranges considered clinically adequate. The assay was linear from 0·05 to 10 mg/l for voriconazole, posaconazole, itraconazole, hydroxy-itraconazole, and ketoconazole, from 0·3 to 10 mg/l for fluconazole, and from 0·1 to 10 mg/l for miconazole. The bias and imprecision values for intra- and inter-assays were lower than 10% and than 15%, respectively. In conclusion, a simple, sensitive, and selective UHPLC-DAD method was developed and validated to determine seven azole antifungal drugs in human serum. This method is applicable to patient samples, and can be applied successfully to clinical applications and therapeutic drug monitoring. PMID:24635400

Mistretta, V; Dubois, N; Denooz, R; Charlier, C

2014-01-01

413

High performance InGaN/GaN nanorod light emitting diode arrays fabricated by nanosphere lithography and chemical mechanical polishing processes.  

PubMed

We fabricated InGaN/GaN nanorod light emitting diode (LED) arrays using nanosphere lithography for nanorod formation, PECVD (plasma enhanced chemical vapor deposition) grown SiO(2) layer for sidewall passivation, and chemical mechanical polishing for uniform nanorod contact. The nano-device demonstrates a reverse current 4.77nA at -5V, an ideality factor 7.35, and an optical output intensity 6807mW/cm(2) at the injection current density 32A/cm(2) (20mA). Moreover, the investigation of the droop effect for such a nanorod LED array reveals that junction heating is responsible for the sharp decrease at the low current. PMID:20588606

Chen, Liang-Yi; Huang, Ying-Yuan; Chang, Chun-Hsiang; Sun, Yu-Hsuan; Cheng, Yun-Wei; Ke, Min-Yung; Chen, Cheng-Pin; Huang, Jianjang

2010-04-12

414

A crossbar-type high sensitivity ultraviolet photodetector array based on a one hole-one nanorod configuration via nanoimprint lithography.  

PubMed

Single crystalline vertical ZnO nanorods were grown in a one hole-one rod configuration using a hydrothermal method with a patterned polymer template generated by nanoimprint lithography, allowing precise control over the position and density of the ZnO nanorods. An 8×8 ZnO nanorod-based ultraviolet photodetector array is demonstrated, in which a well-confined number of ZnO nanorods are sandwiched between crossbar-type platinum and indium tin oxide electrodes (e.g. 16 nanorods in a 2×2 µm2 area). A high photocurrent/dark current ratio of 3×10(3) at a reverse bias of 1.5 V under UV illumination at room temperature, a responsivity of 4381.4 A W(-1) at 365 nm, and an ultraviolet-to-visible rejection ratio of 83 are obtained and maintained, irrespective of pixel size. A uniform photoresponse is achieved in each of the pixels, indicating the scalability with this technique for fabricating an integrated UV photodetector array circuit. PMID:21613683

Jeong, Huisu; Kim, Ki Seok; Kim, Yong Hwan; Jeong, Hyun; Song, Hui; Lee, Kwang Ho; Jeong, Mun Seok; Wang, Deli; Jung, Gun Young

2011-07-01

415

Material and device studies for the development of ultra-violet light emitting diodes (UV-LEDS) along polar, non-polar and semi-polar directions  

NASA Astrophysics Data System (ADS)

Over the past few years, significant effort was dedicated to the development of ultraviolet light emitting diodes (UV-LEDs) for a variety of applications. Such applications include chemical and biological detection, water purification and solid-state lighting. III-Nitride LEDs based on multiple quantum wells (MQWs) grown along the conventional [0001] (polar) direction suffer from the quantum confined Stark effect (QCSE), due to the existence of strong electric fields that arise from spontaneous and piezoelectric polarization. Thus, there is strong motivation to develop MQW-based III-nitride LED structures grown along non-polar and semi-polar directions. The goal of this dissertation is to develop UV-LEDs along the [0001] polar and [11 2¯ 0] non-polar directions by the method of Molecular Beam Epitaxy (MBE). The polar and non-polar LEDs were grown on the C-plane and R-plane sapphire substrates respectively. This work is a combination of materials science studies related to the nucleation, growth and n- and p-type doping of III-nitride films on these two substrates, as well as device studies related to fabrication and characterization of UV-LEDs. It was observed that the crystallographic orientation of the III-nitride films grown on R-plane sapphire depends strongly on the kinetic conditions of growth of the Aluminum Nitride (AIN) buffer. Specifically, growth of the AIN buffer under group III-rich conditions leads to nitride films having the (11 2¯ 0) non polar planes parallel to the sapphire surface, while growth of the buffer under nitrogen rich conditions leads to nitride films with the (11 2¯ 6) semi-polar planes parallel to the sapphire surface. The electron concentration and mobility for the films grown along the polar, non-polar and semi-polar directions were investigated. P-type doping of Gallium Nitride (GaN) films grown on the nonpolar (11 2¯ 0) plane do not suffer from polarity inversion and thus the material was doped p-type with a hole concentration 1 x 1018 cm-3. MQWs were grown on polar, non-polar and semi-polar planes in order to study the QCSE. It was found that the QCSE is eliminated and minimized for the MQWs grown along the non-polar and semi-polar directions respectively. UV-LEDs emitting in the wavelength regime of 330-360 nm were grown and fabricated along the polar and non-polar directions.

Chandrasekaran, Ramya

416

High-output power near-ultraviolet and violet light-emitting diodes fabricated on patterned sapphire substrates using metalorganic vapor phase epitaxy  

NASA Astrophysics Data System (ADS)

The external quantum efficiency (EQE, ?e) of conventional near-ultraviolet (NUV) light-emitting diodes (LEDs) with an InGaN multi-quantum-well (MQW) structure is limited by high dislocation density and by the narrow escape cone due to total internal reflection at the GaN/air or sapphire/air interface. We have fabricated the NUV and violet InGaN-MQW-LEDs with the high EQE on the patterned-sapphire substrate (PSS) using a single growth process by metal-organic vapor phase epitaxy (MOVPE). The PSS with parallel grooves along the <11-20>GaN direction or the <1-100>GaN direction was fabricated by a standard photolithography and subsequent reactive ion etching (RIE). In this study, fabricated the LED on the PSS with parallel grooves along the <11-20>GaN direction. The GaN layer grown by lateral epitaxy on a patterned substrate (LEPS) has dislocation density of 1.5x108 cm-2. The LEPS-NUV (or violet)-LED chips were mounted on the Si bases in a flip-chip bonding arrangement. When the LEPS-NUV-LED (the emission peak wavelength ?p: 382 nm) was operated at a forward-bias current of 20 mA at room temperature (RT), the output power (Po) and the EQE were 15.6 mW and 24%, respectively. When the LEPS-violet-LED (?p: 405 nm) was operated at a forward-bias current of 20 mA at RT, the Po and the EQE were 26.3 mW and 43%, respectively. Furthermore, we obtained the Po of approximately 61 mW at 50 mA and 111 mW at 100 mA, respectively. It was revealed that the PSS is very effective in reducing the dislocation density and for increasing the extraction efficiency due to the multiple scattering of the emission light at the GaN/patterned sapphire interface.

Tadatomo, Kazuyuki; Okagawa, Hiroaki; Ohuchi, Youichiro; Tsunekawa, Takashi; Kudo, Hiromitsu; Sudo, Yasuhide; Kato, Munehiro; Taguchi, Tsunemasa

2004-01-01

417

Determination of isoprene in human breath by thermal desorption gas chromatography with ultraviolet detection  

Microsoft Academic Search

We describe a new, highly sensitive and specific method for the analysis of isoprene (2-methyl-1,3-butadiene) in human breath. A known volume of expired air (150 ml) was drawn through a solid sorbent material to capture trace organic substances, followed by thermal desorption at 200°C and subsequent determination of isoprene by gas chromatography with diode-array ultraviolet detection. The calibration plot was

A. W. Jones; V. Lagesson; C. Tagesson

1995-01-01

418

Macroscopic Violation of Three Cauchy-Schwarz Inequalities Using Correlated Light Beams From an Infra-Red Emitting Semiconductor Diode Array  

NASA Technical Reports Server (NTRS)

We briefly review quantum mechanical and semi-classical descriptions of experiments which demonstrate the macroscopic violation of the three Cauchy-Schwarz inequalities: g(sup 2)(sub 11)(0) greater than or equal to 1; g(sup 2)(sub 11)(0) greater than or equal to g(sup 2)(sub 11)(t), (t approaches infinity); (the absolute value of g(sup 2)(sub 11)(0))(exp 2) less than or equal to g(sup 2)(sub 11)(0) g(sup 2)(sub 11)(0). Our measurements demonstrate the violation, at macroscopic intensities, of each of these inequalities. We show that their violation, although weak, can be demonstrated through photodetector current covariance measurements on correlated sub-Poissonian Poissonian, and super Poissonian light beams. Such beams are readily generated by a tandem array of infrared-emitting semiconductor junction diodes. Our measurements utilize an electrically coupled array of one or more infrared-emitting diodes, optically coupled to a detector array. The emitting array is operated in such a way as to generate highly correlated beams of variable photon Fano Factor. Because the measurements are made on time scales long compared with the first order coherence time and with detector areas large compared with the corresponding coherence areas, first order interference effects are negligible. The first and second inequalities are violated, as expected, when a sub-Poissonian light beam is split and the intensity fluctuations of the two split beams are measured by two photodetectors and subsequently cross-correlated. The third inequality is violated by bunched (as well as anti-bunched) beams of equal intensity provided the measured cross correlation coefficient exceeds (F - 1)/F, where F is the measured Fano Factor of each beam. We also investigate the violation for the case of unequal beams.

Edwards, P. J.; Huang, X.; Li, Y. Q. (Editor); Wang, Y. Z. (Editor)

1996-01-01

419

Coherent beam combining of high-power broad-area laser diode array in CW and pulsed modes  

Microsoft Academic Search

We present experimental results on coherent beam combining from large arrays of high power broad-area semiconductor lasers. Our laser array consists of 47 high-power anti-reflection coated broad-area semiconductor lasers and each laser emitter is capable of emitting 1.8 W when uncoated with a maximum array output power of 80W. The total available power from the AR coated array is approximately

Bo Liu; Yun Liu; Yehuda Braiman

2010-01-01

420

High-performance liquid chromatography-diode array detection of trichloroethene and aromatic and aliphatic anionic surfactants used for surfactant-enhanced aquifer remediation.  

PubMed

A method utilizing direct aqueous injection with high-performance liquid chromatography and diode array detection (HPLC-DAD) is presented for the quantitation determination of trichloroethene (TCE) in the presence of anionic surfactants that are used to enhance the recovery of dense non-aqueous phase liquids from contaminated groundwater aquifers. The anionic surfactants investigated in this study including alkyl diphenyloxide disulfonate (Dowfax 8390) and dihexylsulfosuccinate (Aerosol MA 80-1) are used to enhance the solubility, and hence recovery, of TCE. In this type of environmental engineering application, the levels of surfactants and TCE encountered are very high (part per million to part per thousand). The anionic surfactants and TCE are quantitatively determined by direct aqueous injection onto a reversed-phase HPLC column with diode array detection. The quantitation limits of the method obtained using 100 microl injections are 0.1 mg/l for alkyl diphenyloxide disulfonates, 20 mg/l for dihexylsulfosuccinate, and 0.05 mg/l for TCE. This approach is advantageous over using gas chromatography for TCE and HPLC for the surfactants because the use of a single analytical instrument reduces sample preparation and analysis times, which increases sample throughput. PMID:11073296

Field, J A; Sawyer, T E

2000-10-01

421

Integrating qualitative and quantitative characterization of traditional Chinese medicine injection by high-performance liquid chromatography with diode array detection and tandem mass spectrometry.  

PubMed

The present study aims to describe and exemplify an integrated strategy of the combination of qualitative and quantitative characterization of a multicomponent mixture for the quality control of traditional Chinese medicine injections with the example of Danhong injection (DHI). The standardized chemical profile of DHI has been established based on liquid chromatography with diode array detection. High-performance liquid chromatography coupled with time-of-flight mass spectrometry and high-performance liquid chromatography with electrospray multistage tandem ion-trap mass spectrometry have been developed to identify the major constituents in DHI. The structures of 26 compounds including nucleotides, phenolic acids, and flavonoid glycosides were identified or tentatively characterized. Meanwhile, the simultaneous determination of seven marker constituents, including uridine, adenosine, danshensu, protocatechuic aldehyde, p-coumaric acid, rosmarinic acid, and salvianolic acid B, in DHI was performed by multiwavelength detection based on high-performance liquid chromatography with diode array detection. The integrated qualitative and quantitative characterization strategy provided an effective and reliable pattern for the comprehensive and systematic characterization of the complex traditional Chinese medicine system. PMID:24723550

Xie, Yuan-Yuan; Xiao, Xue; Luo, Juan-Min; Fu, Chan; Wang, Qiao-Wei; Wang, Yi-Ming; Liang, Qiong-Lin; Luo, Guo-An

2014-06-01

422

A Pt/TiO(2)/Ti Schottky-type selection diode for alleviating the sneak current in resistance switching memory arrays.  

PubMed

This study examined the properties of Schottky-type diodes composed of Pt/TiO(2)/Ti, where the Pt/TiO(2) and TiO(2)/Ti junctions correspond to the blocking and ohmic contacts, respectively, as the selection device for a resistive switching cross-bar array. An extremely high forward-to-reverse current ratio of approximately 10(9) was achieved at 1 V when the TiO(2) film thickness was 19 nm. TiO(2) film was grown by atomic layer deposition at a substrate temperature of 250 degrees C. Conductive atomic force microscopy revealed that the forward current flew locally, which limits the maximum forward current density to < 10 A cm(-2) for a large electrode (an area of approximately 60 000 microm(2)). However, the local current measurement showed a local forward current density as high as approximately 10(5) A cm(-2). Therefore, it is expected that this type of Schottky diode effectively suppresses the sneak current without adverse interference effects in a nano-scale resistive switching cross-bar array with high block density. PMID:20400821

Park, Woo Young; Kim, Gun Hwan; Seok, Jun Yeong; Kim, Kyung Min; Song, Seul Ji; Lee, Min Hwan; Hwang, Cheol Seong

2010-05-14

423

III-nitride blue and UV photonic-crystal light-emitting diodes  

Microsoft Academic Search

We report on the successful nano-fabrication and characterization of III-nitride blue and ultraviolet (UV) photonic crystal light emitting diodes (PC-LEDs) using electron beam lithography and inductively coupled plasma dry etching. Triangular arrays of holes with different diameters\\/periodicities were etched on the LEDs. Optical measurements on the photonic crystals (PCs) performed using near-field scanning optical microscopy (NSOM) showed a 60° periodic

Jagat B. Shakya; Kyoung Hoon Kim; Tom N. Oder; Jing Yu Lin; Hong Xing Jiang

2004-01-01

424

III-nitride blue and UV photonic crystal light-emitting diodes  

Microsoft Academic Search

We report on the successful nano-fabrication and characterization of III-nitride blue and ultraviolet (UV) photonic crystal light emitting diodes (PC-LEDs) using electron beam lithography and inductively coupled plasma dry etching. Triangular arrays of holes with different diameters\\/periodicities were etched on the LEDs. Optical measurements on the photonic crystals (PCs) performed using near-field scanning optical microscopy (NSOM) showed a 60 o

J. Shakya; K. H. Kim; T. N. Oder; J. Y. Lina; H. X. Jiang

425

Far ultraviolet sensitivity of silicon CMOS sensors  

NASA Astrophysics Data System (ADS)

We describe vacuum ultraviolet sensitivity measurements of a new high performance silicon-based CMOS sensor from Teledyne Imaging Sensors. These sensors do not require the high voltages of MCP detectors, making them a lower mass and power alternative to the more mature MCP technology. These devices demonstrate up to 40 percent quantum efficiency at vacuum ultraviolet wavelengths, either meeting or greatly exceeding 10 percent quantum efficiency across the entire 100-200 nm wavelength region. As with similar visible sensitive devices, backside illumination results in a higher quantum efficiency than frontside illumination. Measurements of the vacuum ultraviolet sensitivity of the Teledyne silicon PIN detectors were made by directing a known intensity of ultraviolet light at discrete wavelengths onto the test detectors and reading out the resulting photocurrent. The sensitivity of the detector at a given wavelength was then calculated from the intensity and wavelength of the incoming light and the relative photodiode to NIST-traceable calibration diode active areas. A custom electromechanical interface was developed to make these measurements within the SwRI Vacuum Radiometric Calibration Chamber. While still in the single pixel stage, full 1K × 1K focal plane arrays are possible using existing CMOS readout electronics and hold great promise for inclusion in future spaceflight instrument concepts.

Davis, Michael W.; Greathouse, Thomas K.; Retherford, Kurt D.; Winters, Gregory S.; Bai, Yibin; Beletic, James W.

2012-07-01

426

Arrays  

NSDL National Science Digital Library

This interactive Flash applet helps students develop the concept of equal groups as a foundation for multiplication and division. The applet displays an array of dots, some of which are covered by a card. Student use the visible number of rows and columns to determine the total number of dots. Clicking on the card reveals the full array, and a voice announces the total.

2011-01-01

427

The feasibility study and characterization of a two-dimensional diode array in “magic phantom” for high dose rate brachytherapy quality assurance  

SciTech Connect

Purpose: High dose rate (HDR) brachytherapy is a radiation treatment technique capable of delivering large dose rates to the tumor. Radiation is delivered using remote afterloaders to drive highly active sources (commonly {sup 192}Ir with an air KERMA strength range between 20 000 and 40 000 U, where 1 U = 1 ?Gy m{sup 2}/h in air) through applicators directly into the patient's prescribed region of treatment. Due to the obvious ramifications of incorrect treatment while using such an active source, it is essential that there are methods for quality assurance (QA) that can directly and accurately verify the treatment plan and the functionality of the remote afterloader. This paper describes the feasibility study of a QA system for HDR brachytherapy using a phantom based two-dimensional 11 × 11 epitaxial diode array, named “magic phantom.”Methods: The HDR brachytherapy treatment plan is translated to the phantom with two rows of 10 (20 in total) HDR source flexible catheters, arranged above and below the diode array “magic plate” (MP). Four-dimensional source tracking in each catheter is based upon a developed fast iterative algorithm, utilizing the response of the diodes in close proximity to the {sup 192}Ir source, sampled at 100 ms intervals by a fast data acquisition (DAQ) system. Using a {sup 192}Ir source in a solid water phantom, the angular response of the developed epitaxial diodes utilized in the MP and also the variation of the MP response as a function of the source-to-detector distance (SDD) were investigated. These response data are then used by an iterative algorithm for source dwelling position determination. A measurement of the average transit speed between dwell positions was performed using the diodes and a fast DAQ.Results: The angular response of the epitaxial diode showed a variation of 15% within 360°, with two flat regions above and below the detector face with less than 5% variation. For SDD distances of between 5 and 30 mm the relative response of the epitaxial diodes used in the MP is in good agreement (within 8%) with radial dose function measurements found within the TG-43 protocol, with SDD of up to 70 mm showing a 40% over response. A method for four-dimensional localization of the HDR source was developed, allowing the source dwell position to be derived within 0.50 mm of the expected position. An estimation of the average transit speed for varying step sizes was determined and was found to increase from (12.8 ± 0.3) up to (38.6 ± 0.4) cm/s for a step size of 2.5 and 50 mm, respectively.Conclusions: Our characterization of the designed QA “magic phantom” with MP in realistic HDR photon fields demonstrates the promising performance for real-time source position tracking in four dimensions and measurements of transit times. Further development of this system will allow a full suite for QA in HDR brachytherapy and analysis, and for future in vivo tracking.

Espinoza, A.; Beeksma, B.; Petasecca, M.; Fuduli, I.; Porumb, C.; Cutajar, D.; Lerch, M. L. F.; Rosenfeld, A. B. [Centre for Medical Radiation Physics, University of Wollongong, New South Wales 2522 (Australia)] [Centre for Medical Radiation Physics, University of Wollongong, New South Wales 2522 (Australia); Corde, S.; Jackson, M. [Department of Radiation Oncology, Prince of Wales Hospital, New South Wales 2031 (Australia)] [Department of Radiation Oncology, Prince of Wales Hospital, New South Wales 2031 (Australia)

2013-11-15

428

Determination of brilliant green from fish pond water using carbon nanotube assisted pseudo-stir bar solid/liquid microextraction combined with UV-vis spectroscopy-diode array detection  

NASA Astrophysics Data System (ADS)

This paper describes the development of a new design of hollow fiber solid/liquid phase microextraction (HF-SLPME) for determination of brilliant green (BG) residues in water fish ponds. This method consists of an aqueous donor phase and carbon nanotube reinforced organic solvent (acceptor phase) operated in direct immersion sampling mode. The multi-walled carbon nanotube dispersed in the organic solvent is held in the pores and lumen of a porous polypropylene hollow fiber. It is in contact directly with the aqueous donor phase. In this method the solid/liquid extractor phase is supported using a polypropylene hollow fiber membrane. Both ends of the hollow fiber segment are sealed with magnetic stoppers. This device is placed inside the donor solution and plays the rule of a pseudo-stir bar. It is disposable, so single use of the fiber reduces the risk of carry-over problems. Brilliant green (BG) after extraction from the aqueous samples with mentioned HF-SLPME device was determined by ultraviolet-visible spectroscopy with diode array detection (UV-vis/DAD). The absorption wavelength was set to 625 nm ( ?max). The effect of different variables on the extraction was evaluated and optimized to enhance the sensitivity and extraction efficiency of the proposed method. The calibration curve was linear in the range of 1.00-10,000 ?g L -1 of BG in the initial solution with R2 = 0.979. Detection limit, based on three times the standard deviation of the blank, was 0.55 ?g L -1. All experiments were carried out at room temperature (25 ± 0.5 °C).

Es'haghi, Zarrin; Khooni, Maliheh Ahmadi-Kalateh; Heidari, Tahereh

2011-08-01

429

Individually Addressable AlInGaN Micro-LED Arrays With CMOS Control and Subnanosecond Output Pulses  

Microsoft Academic Search

We report the fabrication and characterization of an ultraviolet (370 nm) emitting AlInGaN-based micro-light- emitting diode (micro-LED) array integrated with complementary metal-oxide-semiconductor control electronics. This configuration allows an 8 × 8 array of micro-LED pixels, each of 72-mum diameter, to be individually addressed. The micro-LED pixels can be driven in direct current (dc), square wave, or pulsed operation, with linear

Jonathan J. D. McKendry; Bruce R. Rae; Zheng Gong; Keith R. Muir; Benoit Guilhabert; David Massoubre; Erdan Gu; David Renshaw; Martin D. Dawson; Robert K. Henderson

2009-01-01

430

Time evolution of pulsed far-field patterns of GaAlAs phase-locked laser-diode arrays  

NASA Astrophysics Data System (ADS)

The time evolution of pulsed far fields from commercially available gain-guided phase-locked arrays has been studied and compared to experimental results previously obtained by streak camera measurements, and to predictions of coupled-mode theories developed for index- and gain-guided arrays. Although phase locking is evident by 100 ps into the drive pulse, stable operation in a fixed superposition of array modes is not achieved until 1-2 ns after the drive pulse has stabilized.

Forrest, Kathrine A.; Abshire, James B.

1987-08-01

431

Dosimetric verification for intensity-modulated arc therapy plans by use of 2D diode array, radiochromic film and radiosensitive polymer gel  

PubMed Central

Several tools are used for the dosimetric verification of intensity-modulated arc therapy (IMAT) treatment delivery. However, limited information is available for composite on-line evaluation of these tools. The purpose of this study was to evaluate the dosimetric verification of IMAT treatment plans using a 2D diode array detector (2D array), radiochromic film (RCF) and radiosensitive polymer gel dosimeter (RPGD). The specific verification plans were created for IMAT for two prostate cancer patients by use of the clinical treatment plans. Accordingly, the IMAT deliveries were performed with the 2D array on a gantry-mounting device, RCF in a cylindrical acrylic phantom, and the RPGD in two cylindrical phantoms. After the irradiation, the planar dose distributions from the 2D array and the RCFs, and the 3D dose distributions from the RPGD measurements were compared with the calculated dose distributions using the gamma analysis method (3% dose difference and 3-mm distance-to-agreement criterion), dose-dependent dose difference diagrams, dose difference histograms, and isodose distributions. The gamma passing rates of 2D array, RCFs and RPGD for one patient were 99.5%, 96.5% and 93.7%, respectively; the corresponding values for the second patient were 97.5%, 92.6% and 92.9%. Mean percentage differences between the RPGD measured and calculated doses in 3D volumes containing PTVs were –0.29 ± 7.1% and 0.97 ± 7.6% for the two patients, respectively. In conclusion, IMAT prostate plans can be delivered with high accuracy, although the 3D measurements indicated less satisfactory agreement with the treatment plans, mainly due to the dosimetric inaccuracy in low-dose regions of the RPGD measurements.

Hayashi, Naoki; Malmin, Ryan L.; Watanabe, Yoichi

2014-01-01

432

Dosimetric verification for intensity-modulated arc therapy plans by use of 2D diode array, radiochromic film and radiosensitive polymer gel.  

PubMed

Several tools are used for the dosimetric verification of intensity-modulated arc therapy (IMAT) treatment delivery. However, limited information is available for composite on-line evaluation of these tools. The purpose of this study was to evaluate the dosimetric verification of IMAT treatment plans using a 2D diode array detector (2D array), radiochromic film (RCF) and radiosensitive polymer gel dosimeter (RPGD). The specific verification plans were created for IMAT for two prostate cancer patients by use of the clinical treatment plans. Accordingly, the IMAT deliveries were performed with the 2D array on a gantry-mounting device, RCF in a cylindrical acrylic phantom, and the RPGD in two cylindrical phantoms. After the irradiation, the planar dose distributions from the 2D array and the RCFs, and the 3D dose distributions from the RPGD measurements were compared with the calculated dose distributions using the gamma analysis method (3% dose difference and 3-mm distance-to-agreement criterion), dose-dependent dose difference diagrams, dose difference histograms, and isodose distributions. The gamma passing rates of 2D array, RCFs and RPGD for one patient were 99.5%, 96.5% and 93.7%, respectively; the corresponding values for the second patient were 97.5%, 92.6% and 92.9%. Mean percentage differences between the RPGD measured and calculated doses in 3D volumes containing PTVs were -0.29 ± 7.1% and 0.97 ± 7.6% for the two patients, respectively. In conclusion, IMAT prostate plans can be delivered with high accuracy, although the 3D measurements indicated less satisfactory agreement with the treatment plans, mainly due to the dosimetric inaccuracy in low-dose regions of the RPGD measurements. PMID:24449714

Hayashi, Naoki; Malmin, Ryan L; Watanabe, Yoichi

2014-05-01

433

High-power near-resonant 1.55 micrometer-emitting InGaAsP/InP antiguided diode laser arrays  

NASA Astrophysics Data System (ADS)

This dissertation discusses design aspects, materials growth issues, device fabrication and characterization of high-power phase locked arrays of diode lasers and describes a series of experiments with progressive improvements in output power and beam quality from the first high-power 1.55mum-wavelength near-resonant antiguided arrays. Also presented are results and discussion of the first above-threshold analysis of the effect of element width on the modal behaviour of resonant antiguided arrays. Two appendices give experimental details of the MOCVD growth of InGaAsP on InP and the fabrication procedures for the broad-area type and self-aligned array devices. The best results obtained from strained-layer quaternary-quantum-well InGaAsP/InP 1.55mum-emitting near-resonant antiguided arrays include 2.5W front-facet peak-power in a 2.6sp° wide beam (6×diffraction-limit, D.L.), with 1.2W in the central lobe, from 40-element, 250mum aperture devices. The width of the central lobe remains constant from 4 to 15×threshold. Devices with improved temperature characteristics and closer to the resonance condition provide 1W power in a beam 1.15sp° wide (2.7×D.L.), with 61% of the energy in the central lobe; and 1.75W peak-power in a 1.5sp° wide beam (3.5×D.L.) at heatsink temperatures between 15sp°C and 45sp°C.

Bhattacharya, Arnab

434

ZnO homojunction photodiodes based on Sb-doped p-type nanowire array and n-type film for ultraviolet detection  

NASA Astrophysics Data System (ADS)

ZnO p-n homojunctions based on Sb-doped p-type nanowire array and n-type film were grown by combining chemical vapor deposition (for nanowires) with molecular-beam epitaxy (for film). Indium tin oxide and Ti/Au were used as contacts to the ZnO nanowires and film, respectively. Characteristics of field-effect transistors using ZnO nanowires as channels indicate p-type conductivity of the nanowires. Electron beam induced current profiling confirmed the existence of ZnO p-n homojunction. Rectifying I-V characteristic showed a turn-on voltage of around 3 V. Very good response to ultraviolet light illumination was observed from photocurrent measurements.

Wang, Guoping; Chu, Sheng; Zhan, Ning; Lin, Yuqing; Chernyak, Leonid; Liu, Jianlin

2011-01-01

435

Chemically synthesized nanowire TiO2/ZnO core-shell p-n junction array for high sensitivity ultraviolet photodetector  

NASA Astrophysics Data System (ADS)

A sol-gel-based ultrathin TiO2 lamination coating was adapted to a hydrothermally grown ZnO nanowire array to realize an all-oxide ultra-sensitive p-n photodiode. The core-shell heterojunction—the key component of the device—is composed of a 5-10 nm thick p-type Cr-doped TiO2 nanoshell and n-type single-crystalline ZnO nanowires (50 nm radius). Owing to the enhanced light scattering and carrier separation in the core-shell architecture, this device exhibits the highest performance among the ZnO nanowire-based photodetectors. At a moderate reverse bias of -5 V and under ultraviolet light illumination at 104 ?W, it shows a switch current ratio of 140 and a responsivity as large as 250 A/W, while it shows nearly no response to the infrared and visible light.

Dao, T. D.; Dang, C. T. T.; Han, G.; Hoang, C. V.; Yi, W.; Narayanamurti, V.; Nagao, T.

2013-11-01

436

Light transmission enhancement from hybrid ZnO micro-mesh and nanorod arrays with application to GaN-based light-emitting diodes.  

PubMed

A hybrid ZnO micro-mesh and nanorod arrays (MMNR) was fabricated as a light output window for GaN-based light-emitting diodes (LEDs) to enhance the light extraction efficiency. The light output power of GaN-based LEDs with the ZnO MMNR is improved by 95% compared to the original planar LEDs. The ZnO MMNR is manufactured by photolithography techniques and a two-step wet chemical growth process. The incident angle-resolved light transmission of the ZnO MMNR beyond the critical angle of total internal reflection is greatly enhanced. The light diffraction pattern of the ZnO MMNR shows that it possesses both the two-dimensional diffraction grating effect of a ZnO micro-mesh and the light scattering effect of a ZnO nanorod array. LEDs with the ZnO MMNR have greater light extraction efficiency than those with only a ZnO micro-mesh or a ZnO nanorod array. The local optical field patterns of the ZnO micro-mesh and the ZnO MMNR are investigated using confocal scanning electroluminescence microscopy. The microscopic light extraction mechanism of the ZnO MMNR is analyzed in-depth. PMID:24514365

Yin, Zhengmao; Liu, Xiaoyan; Wang, Huining; Wu, Yongzhong; Hao, Xiaopeng; Ji, Ziwu; Xu, Xiangang

2013-11-18

437

Monitoring of environmental arsenic by cultures of the photosynthetic bacterial sensor illuminated with a near-infrared light emitting diode array.  

PubMed

Recombinant Rhodopseudomonas palustris, harboring the carotenoid-metabolizing gene crtI (CrtIBS), and whose color changes from greenish yellow to red in response to inorganic As(III), was cultured in transparent microplate wells illuminated with a light emitting diode (LED) array. The cells were seen to grow better under near-infrared light, when compared with cells illuminated with blue or green LEDs. The absorbance ratio of 525 to 425 nm after cultivation for 24 h, which reflects red carotenoid accumulation, increased with an increase in As(III) concentrations. The detection limit of cultures illuminated with near-infrared LED was 5 microgram/l, which was equivalent to that of cultures in test tubes illuminated with an incandescent lamp. A near-infrared LED array, in combination with a microplate, enabled the simultaneous handling of multiple cultures, including CrtIBS and a control strain, for normalization by the illumination of those with equal photon flux densities. Thus, the introduction of a near-infrared LED array to the assay is advantageous for the monitoring of arsenic in natural water samples that may contain a number of unknown factors and, therefore, need normalization of the reporter event. PMID:22210618

Maeda, Isamu; Sakurai, Hirokazu; Yoshida, Kazuyuki; Siddiki, Mohammad; Shimizu, Tokuo; Fukami, Motohiro; Ueda, Shunsaku

2011-12-01

438

Structural characterization of phenolics and betacyanins in Gomphrena globosa by high-performance liquid chromatography-diode array detection/electrospray ionization multi-stage mass spectrometry.  

PubMed

The metabolite profiling of Gomphrena globosa inflorescences was performed by high-performance liquid chromatography-diode array detection/electrospray ionization multi-stage mass spectrometry (HPLC-DAD/ESI-MS(n)). Based on the fragmentation patterns, 24 phenolic compounds were characterized. The identified phenolics include p-coumaric and ferulic acids, quercetin, kaempferol, isorhamnetin, and hydroxylated 6,7-methylenedioxyflavone derivatives, as well as their aglycones, none of them reported before in the species. This is also the first time that tetrahydroxy-methylenedioxyflavone derivatives and acetylglycosides are described in nature. Betacyanins were also found. This study significantly extends the knowledge of the G. globosa metabolome, by providing further insights into its phenolic composition. PMID:22002699

Ferreres, Federico; Gil-Izquierdo, Angel; Valentão, Patrícia; Andrade, Paula B

2011-11-30

439

Liquid chromatography with diode array detection and multivariate curve resolution for the selective and sensitive quantification of estrogens in natural waters.  

PubMed

Following the green analytical chemistry principles, an efficient strategy involving second-order data provided by liquid chromatography (LC) with diode array detection (DAD) was applied for the simultaneous determination of estriol, 17?-estradiol, 17?-ethinylestradiol and estrone in natural water samples. After a simple pre-concentration step, LC-DAD matrix data were rapidly obtained (in less than 5min) with a chromatographic system operating isocratically. Applying a second-order calibration algorithm based on multivariate curve resolution with alternating least-squares (MCR-ALS), successful resolution was achieved in the presence of sample constituents that strongly coelute with the analytes. The flexibility of this multivariate model allowed the quantification of the four estrogens in tap, mineral, underground and river water samples. Limits of detection in the range between 3 and 13ngL(-1), and relative prediction errors from 2 to 11% were achieved. PMID:24952625

Pérez, Rocío L; Escandar, Graciela M

2014-07-01

440

High efficiency 2 micrometer laser utilizing wing-pumped Tm.sup.3+ and a laser diode array end-pumping architecture  

DOEpatents

Wing pumping a Tm.sup.3+ doped, end pumped solid state laser generates 2 .mu.m laser radiation at high average powers with high efficiency. Using laser diode arrays to end-pump the laser rod or slab in the wing of the Tm.sup.3+ absorption band near 785 nm results in 2-for-1 quantum efficiency in Tm.sup.3+ because high Tm.sup.3+ concentrations can be used. Wing pumping allows the thermal power generated in the rod or slab to be distributed over a large enough volume to make thermal management practical in the laser gain medium even at high average power operation. The approach is applicable to CW, Q-switched, and rep-pulsed free-laser operation.

Beach, Raymond J. (Livermore, CA)

1997-01-01

441

Fast separation and determination of phenolic compounds by capillary electrophoresis-diode array detection. Application to the characterisation of alperujo after ultrasound-assisted extraction.  

PubMed

A dynamic approach has been proposed for the ultrasound-assisted extraction of twenty phenolic compounds from alperujo, a semisolid waste from the olive oil industry, that is a representative example of samples with a complex matrix. Multivariate methodology was used to carry out a detailed optimisation study of both the separation-determination and extraction steps in terms of resolution-analysis time and extraction efficiency, respectively. Consequently, the proposed method was able to extract the target analytes in 13 min; then, after dilution and centrifugation, the extract was injected into the capillary electrophoresis-diode array detection system for individual separation determination in 11 min. No cleanup of the extract was required. This method is less time-consuming, more selective and provides a larger information level than the Folin-Ciocalteau spectrophotometric method. Alperujo was demonstrated to be a powerful source of phenolic compounds, particularly as compared with olive oil--8680 versus 50-1200 microg/g. PMID:15378901

Priego-Capote, F; Ruiz-Jiménez, J; de Castro, M D Luque

2004-08-01