Evaluation of Fiber Bragg Grating and Distributed Optical Fiber Temperature Sensors

DOE Office of Scientific and Technical Information (OSTI.GOV)

McCary, Kelly Marie

Fiber optic temperature sensors were evaluated in the High Temperature Test Lab (HTTL) to determine the accuracy of the measurements at various temperatures. A distributed temperature sensor was evaluated up to 550C and a fiber Bragg grating sensor was evaluated up to 750C. HTTL measurements indicate that there is a drift in fiber Bragg sensor over time of approximately -10C with higher accuracy at temperatures above 300C. The distributed sensor produced some bad data points at and above 500C but produced measurements with less than 2% error at increasing temperatures up to 400C

Interrogation of weak Bragg grating sensors based on dual-wavelength differential detection.

PubMed

Cheng, Rui; Xia, Li

2016-11-15

It is shown that for weak Bragg gratings the logarithmic ratio of reflected intensities at any two wavelengths within the spectrum follows a linear relationship with the Bragg wavelength shift, with a slope proportional to their wavelength spacing. This finding is exploited to develop a flexible, efficient, and cheap interrogation solution of weak fiber Bragg grating (FBGs), especially ultra-short FBGs, in distributed sensing based on dual-wavelength differential detection. The concept is experimentally studied in both single and distributed sensing systems with ultra-short FBG sensors. The work may form the basis of new and promising FBG interrogation techniques based on detecting discrete rather than continuous spectra.

Effects of tilted angle of Bragg facets on the performance of successive strips based Bragg concave diffraction grating

NASA Astrophysics Data System (ADS)

Du, Bingzheng; Zhu, Jingping; Mao, Yuzheng; Wang, Kai; Chen, Huibing; Hou, Xun

2018-03-01

The effects of the tilted angle of facets on the diffraction orders, diffraction spectra, dispersion power, and the neighbor channel crosstalk of successive etching strips based Bragg concave diffraction grating (Bragg-CDG) are studied in this paper. The electric field distribution and diffraction spectra of four Bragg-CDGs with different tilted angles are calculated by numerical simulations. With the reflection condition of Bragg facets constant, the blazing order cannot change with the titled angle. As the tilted angle increases, the number of diffraction orders of Bragg-CDG will decrease, thereby concentrating more energy on the blazing order and improving the uniformity of diffraction spectra. In addition, the dispersion power of Bragg-CDG can be improved and the neighbor channel crosstalk of devices can be reduced by increasing the tilted angle. This work is beneficial to optimize the performance of Bragg-CDG.

GaN-based flip-chip LEDs with highly reflective ITO/DBR p-type and via hole-based n-type contacts for enhanced current spreading and light extraction

NASA Astrophysics Data System (ADS)

Zhou, Shengjun; Zheng, Chenju; Lv, Jiajiang; Gao, Yilin; Wang, Ruiqing; Liu, Sheng

2017-07-01

We demonstrate GaN-based double-layer electrode flip-chip light-emitting diodes (DLE-FCLED) with highly reflective indium-tin oxide (ITO)/distributed bragg reflector (DBR) p-type contact and via hole-based n-type contacts. Transparent thin ITO in combination with TiO2/SiO2 DBR is used for reflective p-type ohmic contact, resulting in a significant reduction in absorption of light by opaque metal electrodes. The finely distributed via hole-based n-type contacts are formed on the n-GaN layer by etching via holes through p-GaN and multiple quantum well (MQW) active layer, leading to reduced lateral current spreading length, and hence alleviated current crowding effect. The forward voltage of the DLE-FCLED is 0.31 V lower than that of the top-emitting LED at 90 mA. The light output power of DLE-FCLED is 15.7% and 80.8% higher than that of top-emitting LED at 90 mA and 300 mA, respectively. Compared to top- emitting LED, the external quantum efficiency (EQE) of DLE-FCLED is enhanced by 15.4% and 132% at 90 mA and 300 mA, respectively. The maximum light output power of the DLE-FCLED obtained at 195.6 A/cm2 is 1.33 times larger than that of the top-emitting LED obtained at 93 A/cm2.

Bragg Curve, Biological Bragg Curve and Biological Issues in Space Radiation Protection with Shielding

NASA Technical Reports Server (NTRS)

Honglu, Wu; Cucinotta, F.A.; Durante, M.; Lin, Z.; Rusek, A.

2006-01-01

The space environment consists of a varying field of radiation particles including high-energy ions, with spacecraft shielding material providing the major protection to astronauts from harmful exposure. Unlike low-LET gamma or X-rays, the presence of shielding does not always reduce the radiation risks for energetic charged particle exposure. Since the dose delivered by the charged particle increases sharply as the particle approaches the end of its range, a position known as the Bragg peak, the Bragg curve does not necessarily represent the biological damage along the particle traversal since biological effects are influenced by the track structure of both primary and secondary particles. Therefore, the biological Bragg curve is dependent on the energy and the type of the primary particle, and may vary for different biological endpoints. To achieve a Bragg curve distribution, we exposed cells to energetic heavy ions with the beam geometry parallel to a monolayer of fibroblasts. Qualitative analyses of gamma-H2AX fluorescence, a known marker of DSBs, indicated increased clustering of DNA damage before the Bragg peak, enhanced homogenous distribution at the peak, and provided visual evidence of high linear energy transfer (LET) particle traversal of cells beyond the Bragg peak. A quantitative biological response curve generated for micronuclei (MN) induction across the Bragg curve did not reveal an increased yield of MN at the location of the Bragg peak. However, the ratio of mono-to bi-nucleated cells, which indicates inhibition in cell progression, increased at the Bragg peak location. These results, along with other biological concerns, show that space radiation protection with shielding can be a complicated issue.

Studies of Beam Expansion and Distributed Bragg Reflector Lasers for Fiber Optics and Optical Signal Processing.

DTIC Science & Technology

1981-03-03

described theory and experiments on the DBR laser and on the use of the Distributed Bragg Deflector ( DBD ) to act as a grating bean expander. The DBD is a...and telescope. 9 .\\pplications requiring more power can use the DBD as a power combiner for several laser stripes, as shown in Fig. 3. In design...Bragg deflector ( DBD ). This device consists of a corrugated waveguide, whose grating is slanted at an angle 6 with respect to the incident beam. The

Asymmetrical design for non-relaxed near-UV AlGaN/GaN distributed Bragg reflectors

NASA Astrophysics Data System (ADS)

Moudakir, T.; Abid, M.; Doan, B.-T.; Demarly, E.; Gautier, S.; Orsal, G.; Jacquet, J.; Ougazzaden, A.; Genty, F.

2010-10-01

Towards the development of high efficient GaN-based Vertical Cavity devices, the fabrication of cracks-free high reflective semiconductor mirrors is still an issue. For near-UV operating devices, one of the best solution is the use of AlGaN/GaN materials family. With a relatively high Al molar fraction in AlGaN, a large enough index contrast can be achieved to fabricate high reflectivity mirrors. However, the lattice mismatch between AlGaN and GaN increases with the Al molar fraction and induces a lot of cracks in the structure which affect its optical and electrical properties. Moreover, for a regrowth of an active layer on the top of the mirror, it is necessary to suppress crack generations to achieve a smooth surface. In this work, asymmetrical designs were investigated for the modeling of fully-strained AlGaN/GaN distributed Bragg Reflectors with crack-free surfaces. First, the critical thickness of MOVPE-grown AlGaN on GaN-on-sapphire templates was experimentally determined and modeled. Then, several AlGaN/GaN mirrors with various Al molar fractions and asymmetry factors were simulated demonstrating that non relaxed DBRs could be obtained with adequate parameters. Finally, it has also been shown that there is a best suited Al molar fraction in AlGaN for each DBR centering wavelength.

Efficient modeling of Bragg coherent x-ray nanobeam diffraction

DOE PAGES

Hruszkewycz, S. O.; Holt, M. V.; Allain, M.; ...

2015-07-02

X-ray Bragg diffraction experiments that utilize tightly focused coherent beams produce complicated Bragg diffraction patterns that depend on scattering geometry, characteristics of the sample, and properties of the x-ray focusing optic. In this paper, we use a Fourier-transform-based method of modeling the 2D intensity distribution of a Bragg peak and apply it to the case of thin films illuminated with a Fresnel zone plate in three different Bragg scattering geometries. Finally, the calculations agree well with experimental coherent diffraction patterns, demonstrating that nanodiffraction patterns can be modeled at nonsymmetric Bragg conditions with this approach—a capability critical for advancing nanofocused x-raymore » diffraction microscopy.« less

Optically controlled reflection modulator using GaAs-AlGaAs n-i-p-i/multiple-quantum-well structures

NASA Technical Reports Server (NTRS)

Law, K.-K.; Simes, R. J.; Coldren, L. A.; Gossard, A. C.; Maserjian, J.

1989-01-01

An optically controlled reflection modulator has been demonstrated that consists of a combination of a GaAs-AlGaAs n-i-p-i doping structure with a multiple-quantum-well structures on top of a distributed Bragg reflector, all grown by MBE. A modulation of approximately 60 percent is obtained on the test structure, corresponding to a differential change of absorption coefficient in the quantum wells of approximately 7500/cm. Changes in reflectance can be observed with a control beam power as low as 1.5 microW. This device structure has the potential of being developed as an optically addressed spatial light modulator for optical information processing.

A low-threshold high-index-contrast grating (HCG)-based organic VCSEL

NASA Astrophysics Data System (ADS)

Shayesteh, Mohammad Reza; Darvish, Ghafar; Ahmadi, Vahid

2015-12-01

We propose a low-threshold high-index-contrast grating (HCG)-based organic vertical-cavity surface-emitting laser (OVCSEL). The device has the feasibility to apply both electrical and optical excitation. The microcavity of the laser is a hybrid photonic crystal (HPC) in which the top distributed Bragg reflector (DBR) is replaced by a sub-wavelength high-contrast-grating layer, and provides a high-quality factor. The simulated quality factor of the microcavity is shown to be as high as 282,000. We also investigate the threshold behavior and the dynamics of the OVCSEL optically pumped with sub-picosecond pulses. Results from numerical simulation show that lasing threshold is 75 nJ/cm2.

Porous silicon omnidirectional mirrors and distributed Bragg reflectors for planar waveguide applications

NASA Astrophysics Data System (ADS)

Xifré-Pérez, E.; Marsal, L. F.; Ferré-Borrull, J.; Pallarès, J.

2007-09-01

The use of omnidirectional mirrors (an special case of distributed Bragg reflectors) as cladding for planar waveguides is proposed and analyzed. The proposed structure is an all-porous silicon multilayer consisting of a core layer inserted between two omnidirectional mirrors. The transfer matrix method is applied for the modal analysis. The influence of the parameters of the waveguide structure on the guided modes is analyzed. These parameters are the layer thickness and number of periods of the omnidirectional mirror, and the refractive index and thickness of the core layer. Finally, the confinement of the omnidirectional mirror cladding is analyzed with respect to two other different distributed Bragg reflector claddings.

Enhanced broadband absorption in nanowire arrays with integrated Bragg reflectors

NASA Astrophysics Data System (ADS)

Aghaeipour, Mahtab; Pettersson, Håkan

2018-05-01

A near-unity unselective absorption spectrum is desirable for high-performance photovoltaics. Nanowire (NW) arrays are promising candidates for efficient solar cells due to nanophotonic absorption resonances in the solar spectrum. The absorption spectra, however, display undesired dips between the resonance peaks. To achieve improved unselective broadband absorption, we propose to enclose distributed Bragg reflectors (DBRs) in the bottom and top parts of indium phosphide (InP) NWs, respectively. We theoretically show that by enclosing only two periods of In0.56Ga0.44As/InP DBRs, an unselective 78% absorption efficiency (72% for NWs without DBRs) is obtained at normal incidence in the spectral range from 300 nm to 920 nm. Under oblique light incidence, the absorption efficiency is enhanced up to about 85% at an incidence angle of 50°. By increasing the number of DBR periods from two to five, the absorption efficiency is further enhanced up to 95% at normal incidence. In this work, we calculated optical spectra for InP NWs, but the results are expected to be valid for other direct band gap III-V semiconductor materials. We believe that our proposed idea of integrating DBRs in NWs offers great potential for high-performance photovoltaic applications.

Distributed acoustic sensing system based on continuous wide-band ultra-weak fiber Bragg grating array

NASA Astrophysics Data System (ADS)

Tang, Jianguan; Li, Liang; Guo, Huiyong; Yu, Haihu; Wen, Hongqiao; Yang, Minghong

2017-04-01

A distributed acoustic sensing system (DAS) with low-coherence ASE and Michelson interferometer based on continuous width-band ultra-weak fiber Bragg grating (UW-FBG) array is proposed and experimentally demonstrated. The experimental result shows that the proposed system has better performance in detecting acoustic waves than the conventional hydrophone.

Miniature fiber Bragg grating sensor interrogator (FBG-Transceiver) system

NASA Astrophysics Data System (ADS)

Mendoza, Edgar A.; Kempen, Cornelia; Lopatin, Craig

2007-04-01

This paper describes recent progress conducted towards the development of a miniature fiber Bragg grating sensor interrogator (FBG-Transceiver TM) system based on multi-channel integrated optic sensor (InOSense TM) microchip technology. The hybrid InOSense TM microchip technology enables the integration of all of the functionalities, both passive and active, of conventional bench top FBG sensor interrogator systems, packaged in a miniaturized, low power operation, 2-cm x 5-cm package suitable for the long-term structural health monitoring in applications where size, weight, and power are critical for operation. The FBG-Transceiver system uses active optoelectronic components monolithically integrated to the InOSense TM microchip, a microprocessor controlled signal processing electronics board capable of processing the FBG sensors signals related to stress-strain and temperature as well as vibration and acoustics. The FBG-Transceiver TM system represents a new, reliable, highly robust technology that can be used to accurately monitor the status of an array of distributed fiber optic Bragg grating sensors installed in critical infrastructures. Its miniature package, low power operation, and state-of-the-art data communications architecture, all at a very affordable price makes it a very attractive solution for a large number of SHM/NDI applications in aerospace, naval and maritime industry, civil structures like bridges, buildings and dams, the oil and chemical industry, and for homeland security applications. The miniature, cost-efficient FBG-Transceiver TM system is poised to revolutionize the field of structural health monitoring and nondestructive inspection market. The sponsor of this program is NAVAIR under a DOD SBIR contract.

Single-mode surface plasmon distributed feedback lasers.

PubMed

Karami Keshmarzi, Elham; Tait, R Niall; Berini, Pierre

2018-03-29

Single-mode surface plasmon distributed feedback (DFB) lasers are realized in the near infrared using a two-dimensional non-uniform long-range surface plasmon polariton structure. The surface plasmon mode is excited onto a 20 nm-thick, 1 μm-wide metal stripe (Ag or Au) on a silica substrate, where the stripe is stepped in width periodically, forming a 1st order Bragg grating. Optical gain is provided by optically pumping a 450 nm-thick IR-140 doped PMMA layer as the top cladding, which covers the entire length of the Bragg grating, thus creating a DFB laser. Single-mode lasing peaks of very narrow linewidth were observed for Ag and Au DFBs near 882 nm at room temperature. The narrow linewidths are explained by the low spontaneous emission rate into the surface plasmon lasing mode as well as the high quality factor of the DFB structure. The lasing emission is exclusively TM polarized. Kinks in light-light curves accompanied by spectrum narrowing were observed, from which threshold pump power densities can be clearly identified (0.78 MW cm-2 and 1.04 MW cm-2 for Ag and Au DFB lasers, respectively). The Schawlow-Townes linewidth for our Ag and Au DFB lasers is estimated and very narrow linewidths are predicted for the lasers. The lasers are suitable as inexpensive, recyclable and highly coherent sources of surface plasmons, or for integration with other surface plasmon elements of similar structure.

Distributed Sensing of Carbon-Epoxy Composites and Filament Wound Pressure Vessels Using Fiber-Bragg Gratings

NASA Technical Reports Server (NTRS)

Grant, J.; Kaul, R.; Taylor, S.; Myer, G.; Jackson, K.; Osei, A.; Sharma, A.

2003-01-01

Multiple Fiber Bragg-gratings are embedded in carbon-epoxy laminates as well as in composite wound pressure vessel. Structural properties of such composites are investigated. The measurements include stress-strain relation in laminates and Poisson's ratio in several specimens with varying orientation of the optical fiber Bragg-sensor with respect to the carbon fiber in an epoxy matrix. Additionally, fiber Bragg gratings are bonded on the surface of these laminates and cylinders fabricated out of carbon-epoxy composites and multiple points are monitored and compared for strain measurements at several locations.

An investigation of interface transferring mechanism of surface-bonded fiber Bragg grating sensors

NASA Astrophysics Data System (ADS)

Wu, Rujun; Fu, Kunkun; Chen, Tian

2017-08-01

Surface-bonded fiber Bragg grating sensor has been widely used in measuring strain in materials. The existence of fiber Bragg grating sensor affects strain distribution of the host material, which may result in a decrease in strain measurement accuracy. To improve the measurement accuracy, a theoretical model of strain transfer from the host material to optical fiber was developed, incorporating the influence of the fiber Bragg grating sensor. Subsequently, theoretical predictions were validated by comparing with data from finite element analysis and the existing experiment [F. Ansari and Y. Libo, J. Eng. Mech. 124(4), 385-394 (1998)]. Finally, the effect of parameters of fiber Bragg grating sensors on the average strain transfer rate was discussed.

An optical microsystem based on vertical silicon-air Bragg mirror for liquid substances monitoring

NASA Astrophysics Data System (ADS)

De Stefano, Luca; Rendina, Ivo; Rea, Ilaria; Rotiroti, Lucia; De Tommasi, Edoardo; Barillaro, Giuseppe

2007-05-01

In this work, an integrated optical microsystems for the continuous detection of flammable liquids has been fabricated and characterized. The proposed system is composed of a the transducer element, which is a vertical silicon/air Bragg mirror fabricated by silicon electrochemical micromachining, sealed with a cover glass anodically bonded on its top. The device has been optically characterized in presence of liquid substances of environmental interest, such as ethanol and isopropanol. The preliminary experimental results are in good agreement with the theoretical calculations and show the possibility to use the device as an optical sensor based on the change of its reflectivity spectrum.

High-temperature-resistant distributed Bragg reflector fiber laser written in Er/Yb co-doped fiber.

PubMed

Guan, Bai-Ou; Zhang, Yang; Wang, Hong-Jun; Chen, Da; Tam, Hwa-Yaw

2008-03-03

We present a high-temperature-resistant distributed Bragg reflector fiber laser photowritten in Er/Yb codoped phosphosilicate fiber that is capable of long-term operation at 500 degrees C. Highly saturated Bragg gratings are directly inscribed into the Er/Yb fiber without hydrogen loading by using a 193 nm excimer laser and phase mask method. After annealing at elevated temperature, the remained gratings are strong enough for laser oscillation. The laser operates in robust single mode with output power more than 1 dBm and signal-to-noise ratio better than 70 dB over the entire temperature range from room temperature to 500 degrees C.

Fiber Bragg grating interrogation using wavelength modulated tunable distributed feedback lasers and a fiber-optic Mach-Zehnder interferometer.

PubMed

Roy, Anirban; Chakraborty, Arup Lal; Jha, Chandan Kumar

2017-04-20

This paper demonstrates a technique of high-resolution interrogation of two fiber Bragg gratings (FBGs) with flat-topped reflection spectra centered on 1649.55 nm and 1530.182 nm with narrow line width tunable semiconductor lasers emitting at 1651.93 nm and 1531.52 nm, respectively. The spectral shift of the reflection spectrum in response to temperature and strain is accurately measured with a fiber-optic Mach-Zehnder interferometer that has a free spectral range of 0.0523 GHz and a broadband photodetector. Laser wavelength modulation and harmonic detection techniques are used to transform the gentle edges of the flat-topped FBG into prominent leading and trailing peaks that are up to five times narrower than the FBG spectrum. Either of these peaks can be used to accurately measure spectral shifts of the FBG reflection spectrum with a resolution down to a value of 0.47 pm. A digital signal processing board is used to measure the temperature-induced spectral shifts over the range of 30°C-80°C and strain-induced spectral shifts from 0  μϵ to 12,000  μϵ. The shift is linear in both cases with a temperature sensitivity of 12.8 pm/°C and strain sensitivity of 0.12  pm/μϵ. The distinctive feature of this technique is that it does not use an optical spectrum analyzer at any stage of its design or operation. It can be readily extended to all types of tunable diode lasers and is ideally suited for compact field instruments and for biomedical applications in stroke rehabilitation monitoring.

Distributed strain measurements using fiber Bragg gratings in small-diameter optical fiber and low-coherence reflectometry.

PubMed

Coric, Dragan; Lai, Marco; Botsis, John; Luo, Aiping; Limberger, Hans G

2010-12-06

Optical low coherence reflectometry and fiber Bragg gratings written in small diameter (50 micrometer) optical fibers were used for measurements of non-homogenous internal strain fields inside an epoxy specimen with sub-grating length resolution. The results were compared with measurements using Fiber Bragg gratings in standard size (125 micrometer) single mode fibers and show that smaller fibers are less intrusive at stress heterogeneities.

Simultaneous measurement of dynamic strain and temperature distribution using high birefringence PANDA fiber Bragg grating

NASA Astrophysics Data System (ADS)

Zhu, Mengshi; Murayama, Hideaki

2017-04-01

New approach in simultaneous measurement of dynamic strain and temperature has been done by using a high birefringence PANDA fiber Bragg grating sensor. By this technique, we have succeeded in discriminating dynamic strain and temperature distribution at the sampling rate of 800 Hz and the spatial resolution of 1 mm. The dynamic distribution of strain and temperature were measured with the deviation of 5mm spatially. In addition, we have designed an experimental setup by which we can apply quantitative dynamic strain and temperature distribution to the fiber under testing without bounding it to a specimen.

Enhanced photoresponse of monolayer molybdenum disulfide (MoS2) based on microcavity structure

NASA Astrophysics Data System (ADS)

Lu, Yanan; Yang, Guofeng; Wang, Fuxue; Lu, Naiyan

2018-05-01

There is an increasing interest in using monolayer molybdenum disulfide (MoS2) for optoelectronic devices because of its inherent direct band gap characteristics. However, the weak absorption of monolayer MoS2 restricts its applications, novel concepts need to be developed to address the weakness. In this work, monolayer MoS2 monolithically integrates with plane microcavity structure, which is formed by the top and bottom chirped distributed Bragg reflector (DBR), is demonstrated to improve the absorption of MoS2. The optical absorption is 17-fold enhanced, reaching values over 70% at work wavelength. Moreover, the monolayer MoS2-based photodetector device with microcavity presents a significantly increased photoresponse, demonstrating its promising prospects in MoS2-based optoelectronic devices.

Molecular Beam Epitaxy Growth of AlGaAs/GaAs Vertical Cavity Surface Emitting Lasers and the Performance of PIN Photodetector/Vertical Cavity Surface Emitting Laser Integrated Structures

NASA Astrophysics Data System (ADS)

Wang, Y. H.; Hasnain, G.; Tai, K.; Wynn, J. D.; Weir, B. E.; Choquette, K. D.; Cho, A. Y.

1991-12-01

An all-epitaxial planar top emitting AlGaAs/GaAs multi-quantum well laser is fabricated and characterized. The constructed vertical cavity surface emitting laser (VCSEL) consists of GaAs/Al0.2Ga0.8As (100/80 Å) quantum wells sandwiched between two doped distributed Bragg reflectors characterized by a two-step composition profile. Two Ga and two Al cells are used to facilitate the growth of mirror profile. The gain-guided VCSEL is found to generate continuous wave at a characteristic temperature of 210°K up to 90°C, and can be amplitude modulated at frequencies above 5 GHz. Thresholds as low as 2 mA, and a CW power more than 1.5 mW, are obtained at room temperature. Monolithic integration of a PIN photodetector on top of the VCSEL is demonstrated and discussed. The integrated photodetector shows an effective linear responsivity to the laser emission of 0.25 A/W.

Group-III nitride VCSEL structures grown by molecular beam epitaxy

NASA Astrophysics Data System (ADS)

Ng, HockMin; Moustakas, Theodore D.

2000-07-01

III-nitride VCSEL structures designed for electron-beam pumping have been grown by molecular beam epitaxy (MBE). The structures consist of a sapphire substrate on which an AlN/GaN distributed Bragg reflector (DBR) with peak reflectance >99% at 402 nm is deposited. The active region consists of a 2-(lambda) cavity with 25 In0.1Ga0.9N/GaN multiquantum wells (MQWs) whose emission coincides with the high reflectance region of the DBR. The thicknesses of the InGaN wells and the GaN barriers are 35 angstrom and 75 angstrom respectively. The top reflector consists of a silver metallic mirror which prevents charging effects during electron-beam pumping. The structure was pumped from the top- side with a cw electron-beam using a modified cathodoluminescence (CL) system mounted on a scanning electron microscope chamber. Light output was collected from the polished sapphire substrate side. Measurements performed at 100 K showed intense emission at 407 nm with narrowing of the linewidth with increasing beam current. A narrow emission linewidth of 0.7 nm was observed indicating the onset of stimulated emission.

Fault identification and localization for Ethernet Passive Optical Network using L-band ASE source and various types of fiber Bragg grating

NASA Astrophysics Data System (ADS)

Naim, Nani Fadzlina; Bakar, A. Ashrif A.; Ab-Rahman, Mohammad Syuhaimi

2018-01-01

This paper presents a centralized and fault localization technique for Ethernet Passive Optical Access Network. This technique employs L-band Amplified Spontaneous Emission (ASE) as the monitoring source and various fiber Bragg Gratings (FBGs) as the fiber's identifier. An FBG with a unique combination of Bragg wavelength, reflectivity and bandwidth is inserted at each distribution fiber. The FBG reflection spectrum will be analyzed using an optical spectrum analyzer (OSA) to monitor the condition of the distribution fiber. Various FBGs reflection spectra is employed to optimize the limited bandwidth of monitoring source, thus allows more fibers to be monitored. Basically, one Bragg wavelength is shared by two distinct FBGs with different reflectivity and bandwidth. The experimental result shows that the system is capable to monitor up to 32 customers with OSNR value of ∼1.2 dB and monitoring power received of -24 dBm. This centralized and simple monitoring technique demonstrates a low power, cost efficient and low bandwidth requirement system.

Phase-based Bragg intragrating distributed strain sensor

NASA Astrophysics Data System (ADS)

Huang, S.; Ohn, M. M.; Measures, R. M.

1996-03-01

A strain-distribution sensing technique based on the measurement of the phase spectrum of the reflected light from a fiber-optic Bragg grating is described. When a grating is subject to a strain gradient, the grating will experience a chirp and therefore the resonant wavelength will vary along the grating, causing wavelength-dependent penetration depth. Because the group delay for each wavelength component is related to its penetration depth and the resonant wavelength is determined by strain, a measured phase spectrum can then indicate the local strain as a function of location within the grating. This phase-based Bragg grating sensing technique offers a powerful new means for studying some important effects over a few millimeters or centimeters in smart structures.

Plasmonic distributed feedback lasers at telecommunications wavelengths.

PubMed

Marell, Milan J H; Smalbrugge, Barry; Geluk, Erik Jan; van Veldhoven, Peter J; Barcones, Beatrix; Koopmans, Bert; Nötzel, Richard; Smit, Meint K; Hill, Martin T

2011-08-01

We investigate electrically pumped, distributed feedback (DFB) lasers, based on gap-plasmon mode metallic waveguides. The waveguides have nano-scale widths below the diffraction limit and incorporate vertical groove Bragg gratings. These metallic Bragg gratings provide a broad bandwidth stop band (~500 nm) with grating coupling coefficients of over 5000/cm. A strong suppression of spontaneous emission occurs in these Bragg grating cavities, over the stop band frequencies. This strong suppression manifests itself in our experimental results as a near absence of spontaneous emission and significantly reduced lasing thresholds when compared to similar length Fabry-Pérot waveguide cavities. Furthermore, the reduced threshold pumping requirements permits us to show strong line narrowing and super linear light current curves for these plasmon mode devices even at room temperature.

SU-E-T-753: Three-Dimensional Dose Distributions of Incident Proton Particle in the Polymer Gel Dosimeter and the Radiochromic Gel Dosimeter: A Simulation Study with MCNP Code

DOE Office of Scientific and Technical Information (OSTI.GOV)

Park, M; Kim, G; Ji, Y

Purpose: The purpose of this study is to estimate the three-dimensional dose distributions in the polymer and the radiochromic gel dosimeter, and to identify the detectability of both gel dosimeters by comparing with the water phantom in case of irradiating the proton particles. Methods: The normoxic polymer gel and the LCV micelle radiochromic gel were used in this study. The densities of polymer and the radiochromic gel dosimeter were 1.024 and 1.005 g/cm{sup 3}, respectively. The dose distributions of protons in the polymer and radiochromic gel were simulated using Monte Carlo radiation transport code (MCNPX, Los Alamos National Laboratory). Themore » shape of phantom irradiated by proton particles was a hexahedron with the dimension of 12.4 × 12.4 × 15.0 cm{sup 3}. The energies of proton beam were 50, 80, and 140 MeV energies were directed to top of the surface of phantom. The cross-sectional view of proton dose distribution in both gel dosimeters was estimated with the water phantom and evaluated by the gamma evaluation method. In addition, the absorbed dose(Gy) was also calculated for evaluating the proton detectability. Results: The evaluation results show that dose distributions in both gel dosimeters at intermediated section and Bragg-peak region are similar with that of the water phantom. At entrance section, however, inconsistencies of dose distribution are represented, compared with water. The relative absorbed doses in radiochromic and polymer gel dosimeter were represented to be 0.47 % and 2.26 % difference, respectively. These results show that the radiochromic gel dosimeter was better matched than the water phantom in the absorbed dose evaluation. Conclusion: The polymer and the radiochromic gel dosimeter show similar characteristics in dose distributions for the proton beams at intermediate section and Bragg-peak region. Moreover the calculated absorbed dose in both gel dosimeters represents similar tendency by comparing with that in water phantom.« less

Terahertz bandwidth photonic Hilbert transformers based on synthesized planar Bragg grating fabrication.

PubMed

Sima, Chaotan; Gates, J C; Holmes, C; Mennea, P L; Zervas, M N; Smith, P G R

2013-09-01

Terahertz bandwidth photonic Hilbert transformers are proposed and experimentally demonstrated. The integrated device is fabricated via a direct UV grating writing technique in a silica-on-silicon platform. The photonic Hilbert transformer operates at bandwidths of up to 2 THz (~16 nm) in the telecom band, a 10-fold greater bandwidth than any previously reported experimental approaches. Achieving this performance requires detailed knowledge of the system transfer function of the direct UV grating writing technique; this allows improved linearity and yields terahertz bandwidth Bragg gratings with improved spectral quality. By incorporating a flat-top reflector and Hilbert grating with a waveguide coupler, an ultrawideband all-optical single-sideband filter is demonstrated.

Novel hybrid laser modes in composite VCSEL-DFB microcavities (Conference Presentation)

NASA Astrophysics Data System (ADS)

Mischok, Andreas; Wagner, Tim; Sudzius, Markas; Brückner, Robert; Fröb, Hartmut; Lyssenko, Vadim G.; Leo, Karl

2017-02-01

Two of the most successful microcresonator concepts are the vertical cavity surface emitting laser (VCSEL), where light is confined between distributed Bragg reflectors (DBRs), and the distributed feedback (DFB) laser, where a periodic grating provides positive optical feedback to selected modes in an active waveguide (WG) layer. Our work concerns the combination of both into a composite device, facilitating coherent interaction between both regimes and giving rise to novel laser modes in the system. In a first realization, a full VCSEL stack with an organic active layer is evaporated on top of a diffraction grating with a large period (approximately 1 micron), leading to diffraction of waveguided modes into the surface emission of the device. Here, the coherent interaction between VCSEL and WG modes, as observed in an anticrossing of the dispersion lines, facilitates novel hybrid lasing modes with macroscopic in-plane coherence [1]. In further studies, we decrease the grating period of such devices to realise DFB conditions in a second-order Bragg grating which strongly couples photons via first-order light diffraction to the VCSEL. This efficient coupling can be compared to more classical cascade-coupled cavities and is successfully described by a coupled oscillator model [2]. When both resonators are non-degenerate, they are able to function as independent structures without substantial diffraction losses. The realization of such novel devices provides a promising platform for photonic circuits based on organic microlasers. [1] A. Mischok et al., Adv. Opt. Mater., early online, DOI: 10.1002/adom.201600282, (2016) [2] T. Wagner et al., Appl. Phys. Lett., accepted, in production, (2016)

DBR and DFB Lasers in Neodymium- and Ytterbium-Doped Photothermorefractive Glasses

NASA Technical Reports Server (NTRS)

Ryasnyanskiy, Aleksandr; Vorobiev, N.; Smirnov, V.; Lumeau, J.; Glebov, A.; Mokhun, O..; Spiegelberg, Ch.; Krainak, Michael A.; Glebov, A.; Glebov, L.

2014-01-01

The first demonstration, to the best of our knowledge, of distributed Bragg reflector (DBR) and monolithic distributed feedback (DFB) lasers in photothermorefractive glass doped with rare-earth ions is reported. The lasers were produced by incorporation of the volume Bragg gratings into the laser gain elements. A monolithic single-frequency solid-state laser with a line width of 250 kHz and output power of 150 mW at 1066 nm is demonstrated.

Structural Health Monitoring of Composite Materials Using Distributed Fiber Bragg Sensors

NASA Technical Reports Server (NTRS)

Grant, Joseph; Kual, Raj; Taylor, Scott; Jackson, Kurt V.; Myers, George; Wang, Y.; Sharma, A.; Burdine, Robert (Technical Monitor)

2002-01-01

Health monitoring of polymer matrix composite materials using fiber optic Bragg grating (FBG) sensors is accomplished using a tunable IR (infrared) laser via transmission mode. Results are presented from experiments of composite structures with FBG's embedded at various orientations, and surface measurements of various cryogenic composite vessels.

TU-H-CAMPUS-TeP3-03: Dose Enhancement by Gold Nanoparticles Around the Bragg Peak of Proton Beams

DOE Office of Scientific and Technical Information (OSTI.GOV)

Kwon, J; Sutherland, K; Hashimoto, T

2016-06-15

Purpose: To make clear the spatial distribution of dose enhancement around gold nanoparticles (GNPs) located near the proton Bragg peak, and to evaluate the potential of GNPs as a radio sensitizer. Methods: The dose enhancement by electrons emitted from GNPs under proton irradiation was estimated by Geant4 Monte Carlo simulation toolkit in two steps. In an initial macroscopic step, 100 and 195 MeV proton beams were incident on a water cube, 30 cm on a side. Energy distributions of protons were calculated at four depths, 50% and 75% proximal to the Bragg peak, 100% peak, and 75% distal to themore » peak (P50, P75, Peak, and D75, respectively). In a subsequent microscopic step, protons with the energy distribution calculated above were incident on a 20 nm diameter GNP in a nanometer-size water box and the spatial distribution of dose around the GNP was determined for each energy distribution. The dose enhancement factor (DEF) was also deduced. Results: The dose enhancement effect was spread to several tens of nanometers in the both depth and radial directions. The enhancement area increased in the order of P50, P75, Peak, and D75 for both cases with 100 and 195 MeV protons. In every position around the Bragg peak, the 100 MeV beam resulted in a higher dose enhancement than the 195 MeV beam. At P75, the average and maximum DEF were 3.9 and 17.0 for 100 MeV, and 3.5 and 16.2 for 195 MeV, respectively. These results indicate that lower energy protons caused higher dose enhancement in this incident proton energy range. Conclusion: The dose enhancement around GNPs spread as the position in the Bragg peak region becomes deeper and depends on proton energy. It is expected that GNPs can be used as a radio sensitizer with consideration of the location and proton beam energy.« less

Bragg superlattice for obtaining individual photoluminescence of diamond color centers in dense 3D ensembles

NASA Astrophysics Data System (ADS)

Kukushkin, V. A.

2017-10-01

A way to significantly increase the spatial resolution of the color center photoluminescence collection in chemically vapor-deposited (CVD) diamond at a fixed exciting beam focal volume is suggested. It is based on the creation of a narrow waveguide for the color center photoluminescence with a small number of allowed vertical indices of guided modes. The waveguide is formed between the top surface of a CVD diamond film and an underlaid mirror—a Bragg superlattice made of interchanging high- and low boron-doped layers of CVD diamond. The guided color center photoluminescence is extracted through the top surface of a CVD diamond film with the frustrated total internal reflection method. According to the results of simulation made for a case when color centers are nitrogen-vacancy (NV) centers, the suggested way allows to increase the maximal value of the NV center concentration still compatible with selective collection of their photoluminescence by several times at a fixed exciting beam focal volume. This increase is provided without the deterioration of the NV center photoluminescence collection efficiency.

High performance organic distributed Bragg reflector lasers fabricated by dot matrix holography.

PubMed

Wan, Wenqiang; Huang, Wenbin; Pu, Donglin; Qiao, Wen; Ye, Yan; Wei, Guojun; Fang, Zongbao; Zhou, Xiaohong; Chen, Linsen

2015-12-14

We report distributed Bragg reflector (DBR) polymer lasers fabricated using dot matrix holography. Pairs of distributed Bragg reflector mirrors with variable mirror separations are fabricated and a novel energy transfer blend consisting of a blue-emitting conjugated polymer and a red-emitting one is spin-coated onto the patterned substrate to complete the device. Under optical pumping, the device emits sing-mode lasing around 622 nm with a bandwidth of 0.41 nm. The working threshold is as low as 13.5 μJ/cm² (~1.68 kW/cm²) and the measured slope efficiency reaches 5.2%. The distributed feedback (DFB) cavity and the DBR cavity resonate at the same lasing wavelength while the DFB laser shows a much higher threshold. We further show that flexible DBR lasers can be conveniently fabricated through the UV-imprinting technique by using the patterned silica substrate as the mold. Dot matrix holography represents a versatile approach to control the number, the size, the location and the orientation of DBR mirrors, thus providing great flexibility in designing DBR lasers.

In situ three-dimensional reciprocal-space mapping during mechanical deformation.

PubMed

Cornelius, T W; Davydok, A; Jacques, V L R; Grifone, R; Schülli, T; Richard, M I; Beutier, G; Verdier, M; Metzger, T H; Pietsch, U; Thomas, O

2012-09-01

Mechanical deformation of a SiGe island epitaxically grown on Si(001) was studied by a specially adapted atomic force microscope and nanofocused X-ray diffraction. The deformation was monitored during in situ mechanical loading by recording three-dimensional reciprocal-space maps around a selected Bragg peak. Scanning the energy of the incident beam instead of rocking the sample allowed the safe and reliable measurement of the reciprocal-space maps without removal of the mechanical load. The crystal truncation rods originating from the island side facets rotate to steeper angles with increasing mechanical load. Simulations of the displacement field and the intensity distribution, based on the finite-element method, reveal that the change in orientation of the side facets of about 25° corresponds to an applied pressure of 2-3 GPa on the island top plane.

Compact RGBY light sources with high luminance for laser display applications

NASA Astrophysics Data System (ADS)

Paschke, Katrin; Blume, Gunnar; Werner, Nils; Müller, André; Sumpf, Bernd; Pohl, Johannes; Feise, David; Ressel, Peter; Sahm, Alexander; Bege, Roland; Hofmann, Julian; Jedrzejczyk, Daniel; Tränkle, Günther

2018-02-01

Watt-class visible laser light with a high luminance can be created with high-power GaAs-based lasers either directly in the red spectral region or using single-pass second harmonic generation (SHG) for the colors in the blue-yellow spectral region. The concepts and results of red- and near infrared-emitting distributed Bragg reflector tapered lasers and master oscillator power amplifier systems as well as their application for SHG bench-top experiments and miniaturized modules are presented. Examples of these high-luminance light sources aiming at different applications such as flying spot display or holographic 3D cinema are discussed in more detail. The semiconductor material allows an easy adaptation of the wavelength allowing techniques such as six-primary color 3D projection or color space enhancement by adding a fourth yellow color.

Mapping the continuous reciprocal space intensity distribution of X-ray serial crystallography.

PubMed

Yefanov, Oleksandr; Gati, Cornelius; Bourenkov, Gleb; Kirian, Richard A; White, Thomas A; Spence, John C H; Chapman, Henry N; Barty, Anton

2014-07-17

Serial crystallography using X-ray free-electron lasers enables the collection of tens of thousands of measurements from an equal number of individual crystals, each of which can be smaller than 1 µm in size. This manuscript describes an alternative way of handling diffraction data recorded by serial femtosecond crystallography, by mapping the diffracted intensities into three-dimensional reciprocal space rather than integrating each image in two dimensions as in the classical approach. We call this procedure 'three-dimensional merging'. This procedure retains information about asymmetry in Bragg peaks and diffracted intensities between Bragg spots. This intensity distribution can be used to extract reflection intensities for structure determination and opens up novel avenues for post-refinement, while observed intensity between Bragg peaks and peak asymmetry are of potential use in novel direct phasing strategies.

Distributed dual-parameter optical fiber sensor based on cascaded microfiber Fabry-Pérot interferometers

NASA Astrophysics Data System (ADS)

Xiang, Yang; Luo, Yiyang; Zhang, Wei; Liu, Deming; Sun, Qizhen

2017-04-01

We propose and demonstrate a distributed fiber sensor based on cascaded microfiber Fabry-Perot interferometers (MFPI) for simultaneous refractive index (SRI) and temperature measurement. By employing MFPI which is fabricated by taper-drawing the center of a uniform fiber Bragg grating (FBG) on standard fiber into a section of microfiber, dual parameters including SRI and temperature can be detected through demodulating the reflection spectrum of the MFPI. Further, wavelength-division-multiplexing (WDM) is applied to realize distributed dual-parameter fiber sensor by using cascaded MFPIs with different Bragg wavelengths. A prototype sensor system with 5 cascaded MFPIs is constructed to experimentally demonstrate the sensing performance.

Demonstration of a widely tunable digital supermode distributed Bragg reflector laser as a versatile source for near-infrared spectroscopy

NASA Astrophysics Data System (ADS)

Ciaffoni, L.; Hancock, G.; Hurst, P. L.; Kingston, M.; Langley, C. E.; Peverall, R.; Ritchie, G. A. D.; Whittaker, K. E.

2013-02-01

In this paper we report the characterization of a novel, widely tunable, diode laser source operating over the full telecom L-band (1563-1613 nm), namely the digital supermode distributed Bragg reflector (DS-DBR) laser, and its application to multi-wavelength gas sensing via absorption strategies. The spectroscopic performance of the laser has been assessed by investigating the ro-vibrational spectrum of CO2, and wavelength modulation spectroscopy was accomplished for proof-of-principle sensitive measurements in discrete spectral regions.

Fabrication of Extremely Short Length Fiber Bragg Gratings for Sensor Applications

NASA Technical Reports Server (NTRS)

Wu, Meng-Chou; Rogowski, Robert S.; Tedjojuwono, Ken K.

2002-01-01

A new technique and a physical model for writing extremely short length Bragg gratings in optical fibers have been developed. The model describes the effects of diffraction on the spatial spectra and therefore, the wavelength spectra of the Bragg gratings. Using an interferometric technique and a variable aperture, short gratings of various lengths and center wavelengths were written in optical fibers. By selecting the related parameters, the Bragg gratings with typical length of several hundred microns and bandwidth of several nanometers can be obtained. These short gratings can be apodized with selected diffraction patterns and hence their broadband spectra have a well-defined bell shape. They are suitable for use as miniaturized distributed strain sensors, which have broad applications to aerospace research and industry as well.

Fiber Bragg gratings for civil engineering applications

NASA Astrophysics Data System (ADS)

Maher, Mohamed H.; Tabrizi, Khosrow; Prohaska, John D.; Snitzer, Elias

1996-04-01

Fiber Bragg gratings sensors offer a unique opportunity in civil engineering. They can be configured as a low noise distributed sensor network for measuring mechanical deformations and temperature. They are ideally suited for strain measurements of high modulus structural materials such as steel and concrete. There is considerable interest in the use of these sensors for infrastructural nondestructive testing and there have been several papers on the subject. We present some results of our experiments with fiber Bragg sensors as applied to structural engineering. These include the use of fiber gratings to measure strain behavior of steel, reinforced concrete, and some preliminary results on bituminous materials, such as asphalt concrete. In nondestructive testing using fiber Bragg gratings of structural materials the packaging of the sensors is important and is discussed.

Estimation and correction of produced light from prompt gamma photons on luminescence imaging of water for proton therapy dosimetry

NASA Astrophysics Data System (ADS)

Yabe, Takuya; Komori, Masataka; Toshito, Toshiyuki; Yamaguchi, Mitsutaka; Kawachi, Naoki; Yamamoto, Seiichi

2018-02-01

Although the luminescence images of water during proton-beam irradiation using a cooled charge-coupled device camera showed almost the same ranges of proton beams as those measured by an ionization chamber, the depth profiles showed lower Bragg peak intensities than those measured by an ionization chamber. In addition, a broad optical baseline signal was observed in depths that exceed the depth of the Bragg peak. We hypothesize that this broad baseline signal originates from the interaction of proton-induced prompt gamma photons with water. These prompt gamma photons interact with water to form high-energy Compton electrons, which may cause luminescence or Cherenkov emission from depths exceeding the location of the Bragg peak. To clarify this idea, we measured the luminescence images of water during the irradiations of protons in water with minimized parallax errors, and also simulated the produced light by the interactions of prompt gamma photons with water. We corrected the measured depth profiles of the luminescence images by subtracting the simulated distributions of the produced light by the interactions of prompt gamma photons in water. Corrections were also conducted using the estimated depth profiles of the light of the prompt gamma photons, as obtained from the off-beam areas of the luminescence images of water. With these corrections, we successfully obtained depth profiles that have almost identical distributions as the simulated dose distributions for protons. The percentage relative height of the Bragg peak with corrections to that of the simulation data increased to 94% from 80% without correction. Also, the percentage relative offset heights of the deeper part of the Bragg peak with corrections decreased to 0.2%-0.4% from 4% without correction. These results indicate that the luminescence imaging of water has potential for the dose distribution measurements for proton therapy dosimetry.

Rare-earth-ion-doped ultra-narrow-linewidth lasers on a silicon chip and applications to intra-laser-cavity optical sensing

NASA Astrophysics Data System (ADS)

Bernhardi, E. H.; de Ridder, R. M.; Wörhoff, K.; Pollnau, M.

2013-03-01

We report on diode-pumped distributed-feedback (DFB) and distributed-Bragg-reflector (DBR) channel waveguide lasers in Er-doped and Yb-doped Al2O3 on standard thermally oxidized silicon substrates. Uniform surface-relief Bragg gratings were patterned by laser-interference lithography and etched into the SiO2 top cladding. The maximum grating reflectivity exceeded 99%. Monolithic DFB and DBR cavities with Q-factors of up to 1.35×106 were realized. The Erdoped DFB laser delivered 3 mW of output power with a slope efficiency of 41% versus absorbed pump power. Singlelongitudinal- mode operation at a wavelength of 1545.2 nm was achieved with an emission line width of 1.70 0.58 kHz, corresponding to a laser Q-factor of 1.14×1011. Yb-doped DFB and DBR lasers were demonstrated at wavelengths near 1020 nm with output powers of 55 mW and a slope efficiency of 67% versus launched pump power. An Yb-doped dualwavelength laser was achieved based on the optical resonances induced by two local phase shifts in the DFB structure. A stable microwave signal at ~15 GHz with a -3-dB width of 9 kHz and a long-term frequency stability of +/- 2.5 MHz was created via the heterodyne photo-detection of the two laser wavelengths. By measuring changes in the microwave beat signal as the intra-cavity evanescent laser field interacts with micro-particles on the waveguide surface, we achieved real-time detection and accurate size measurement of single micro-particles with diameters ranging between 1 μm and 20 μm, which represents the typical size of many fungal and bacterial pathogens. A limit of detection of ~500 nm was deduced.

Comparative experimental and simulation studies of high-power AlGaN-based 353 nm ultraviolet flip-chip and top-emitting LEDs

NASA Astrophysics Data System (ADS)

Liu, Mengling; Zhou, Shengjun; Liu, Xingtong; Gao, Yilin; Ding, Xinghuo

2018-03-01

Experimental and simulation studies of high-power AlGaN-based 353 nm ultraviolet (UV) flip-chip (FC) and top-emitting (TE) light-emitting diodes (LEDs) are performed here. To improve the optical and electrical properties of ultraviolet LEDs, we fabricate high-power FC-UV LEDs with Ta2O5/SiO2 distributed Bragg reflectors (DBRs) and a strip-shaped SiO2 current blocking layer (CBL). The reflectance of fourteen pairs of Ta2O5/SiO2 DBRs is 96.4% at 353 nm. The strip-shaped SiO2 CBL underneath the strip-shaped p-electrode can prevent the current concentrating in regions immediately adjacent to the p-electrode where the overlying opaque p-electrode metal layer absorbs the emitted UV light. Moreover, two-level metallization electrodes are used to improve current spreading. Our numerical results show that FC-UV LED has a more favorable current spreading uniformity than TE-UV LED. The light output power of 353 nm FC-UV LED was 23.22 mW at 350 mA, which is 24.7% higher than that of TE-UV LED.

X-ray Crystal Truncation Rod Studies of Surface Oxidation and Reduction on Pt(111)

DOE PAGES

Liu, Yihua; Barbour, Andi; Komanicky, Vladimir; ...

2016-02-26

Here, we present X-ray crystal truncation rods measurements of Pt(111) surface under electrochemical conditions. Analyses of crystal truncation rods reveal that surface oxide formation buckles the top surface layer of platinum to two different heights at the potential (0.95 V vs RHE) below the so-called place-exchange potential. While the anti-Bragg intensity, sensitive to the top surface layer, drops in response to the anodic charge transfers, its responses to the cathodic charge transfers are significantly delayed. Implications to the surface oxidation and reduction behaviors are discussed.

Distributed feedback fiber laser based on a fiber Bragg grating inscribed using the femtosecond point-by-point technique

NASA Astrophysics Data System (ADS)

Skvortsov, M. I.; Wolf, A. A.; Dostovalov, A. V.; Vlasov, A. A.; Akulov, V. A.; Babin, S. A.

2018-03-01

A distributed feedback (DFB) fiber laser based on a 32-mm long pi-phase-shifted fiber Bragg grating inscribed using the femtosecond point-by-point technique in a single-mode erbium-doped optical fiber (CorActive EDF-L 1500) is demonstrated. The lasing power of the DFB laser reaches 0.7 mW at a wavelength of 1550 nm when pumped with a laser diode at a wavelength of 976 nm and power of 525 mW. The width of the lasing spectrum is 17 kHz. It is shown that the pi-phase-shifted fiber Bragg grating fs-inscribed in a non-PM fiber provides the selection of the single polarization mode of the DFB laser. DFB laser formation in a highly doped non-photosensitive optical fiber (CoreActive SCF-ER60-8/125-12) is also demonstrated.

Fiber Bragg Grating Filter High Temperature Sensors

NASA Technical Reports Server (NTRS)

Lyons, Donald R.; Brass, Eric D.; Pencil, Eric (Technical Monitor)

2001-01-01

We present a scaled-down method for determining high temperatures using fiber-based Bragg gratings. Bragg gratings are distributed along the length of the optical fiber, and have high reflectivities whenever the optical wavelength is twice the grating spacing. These spatially distinct Bragg regions (located in the core of a fiber) are sensitive to local temperature changes. Since these fibers are silica-based they are easily affected by localized changes in temperature, which results in changes to both the grating spacing and the wavelength reflectivity. We exploit the shift in wavelength reflectivity to measure the change in the local temperature. Note that the Bragg region (sensing area) is some distance away from where the temperature is being measured. This is done so that we can measure temperatures that are much higher than the damage threshold of the fiber. We do this by affixing the fiber with the Bragg sensor to a material with a well-known coefficient of thermal expansion, and model the heat gradient from the region of interest to the actual sensor. The research described in this paper will culminate in a working device as well as be the second portion of a publication pending submission to Optics Letters.

Wide bandwidth and high resolution planar filter array based on DBR-metasurface-DBR structures

DOE PAGES

Horie, Yu; Arbabi, Amir; Arbabi, Ehsan; ...

2016-05-19

Here, we propose and experimentally demonstrate a planar array of optical bandpass filters composed of low loss dielectric metasurface layers sandwiched between two distributed Bragg reflectors (DBRs). The two DBRs form a Fabry-Perot resonator whose center wavelength is controlled by the design of the transmissive metasurface layer which functions as a phase shifting element. We demonstrate an array of bandpass filters with spatially varying center wavelengths covering a wide range of operation wavelengths of 250nm around λ = 1550nm (Δλ/λ = 16%). The center wavelengths of each filter are independently controlled only by changing the in-plane geometry of the sandwichedmore » metasurfaces, and the experimentally measured quality factors are larger than 700. The demonstrated filter array can be directly integrated on top of photodetector arrays to realize on-chip high-resolution spectrometers with free-space coupling.« less

Distributed strain measurement based on long-gauge FBG and delayed transmission/reflection ratiometric reflectometry for dynamic structural deformation monitoring.

PubMed

Nishiyama, Michiko; Igawa, Hirotaka; Kasai, Tokio; Watanabe, Naoyuki

2015-02-10

In this paper, we propose a delayed transmission/reflection ratiometric reflectometry (DTR(3)) scheme using a long-gauge fiber Bragg grating (FBG), which can be used for dynamic structural deformation monitoring of structures of between a few to tens of meters in length, such as airplane wings and helicopter blades. FBG sensors used for multipoint sensing generally employ wavelength division multiplexing techniques utilizing several Bragg central wavelengths; by contrast, the DTR(3) interrogator uses a continuous pulse array based on a pseudorandom number code and a long-gauge FBG utilizing a single Bragg wavelength and composed of simple hardware devices. The DTR(3) scheme can detect distributed strain at a 50 cm spatial resolution using a long-gauge FBG with a 100 Hz sampling rate. We evaluated the strain sensing characteristics of the long-gauge FBG when attached to a 2.5 m aluminum bar and a 5.5 m helicopter blade model, determining these structure natural frequencies in free vibration tests and their distributed strain characteristics in static tests.

Subtle design changes control the difference in colour reflection from the dorsal and ventral wing-membrane surfaces of the damselfly Matronoides cyaneipennis.

PubMed

Nixon, M R; Orr, A G; Vukusic, P

2013-01-28

The hind wings of males of the damselfly Matronoides cyaneipennis exhibit iridescence that is blue dorsally and green ventrally. These structures are used semiotically in agonistic and courtship display. Transmission electron microscopy reveals these colours are due to two near-identical 5-layer distributed Bragg reflectors, one placed either side of the wing membrane. Interestingly the thicknesses of corresponding layers in each distributed Bragg reflector are very similar for all but the second layer from each outer surface. This one key difference creates the significant disparity between the reflected spectra from the distributed Bragg reflectors and the observed colours of either side of the wing. Modelling indicates that modifications to the thickness of this layer alone create a greater change in the peak reflected wavelength than is observed for similar modifications to the thickness of any other layer. This results in an optimised and highly effective pair of semiotic reflector systems, based on extremely comparable design parameters, with relatively low material and biomechanical costs.

SU-E-T-553: Monte Carlo Calculation of Proton Bragg Peak Displacements in the Presence of Al2O3:C Dosimeters

DOE Office of Scientific and Technical Information (OSTI.GOV)

Young, L; Yang, F

2015-06-15

Purpose: The application of optically stimulated luminescence dosimeters (OSLDs) may be extended to clinical investigations verifying irradiated doses in small animal models. In proton beams, the accurate positioning of the Bragg peak is essential for tumor targeting. The purpose of this study was to estimate the displacement of a pristine Bragg peak when an Al2O3:C nanodot (Landauer, Inc.) is placed on the surface of a water phantom and to evaluate corresponding changes in dose. Methods: Clinical proton pencil beam simulations were carried out with using TOPAS, a Monte Carlo platform layered on top of GEANT4. Point-shaped beams with no energymore » spread were modeled for energies 100MV, 150MV, 200MV, and 250MV. Dose scoring for 100,000 particle histories was conducted within a water phantom (20cm × 20cm irradiated area, 40cm depth) with its surface placed 214.5cm away from the source. The modeled nanodot had a 4mm radius and 0.2mm thickness. Results: A comparative analysis of Monte Carlo depth dose profiles modeled for these proton pencil beams did not demonstrate an energy dependent in the Bragg peak shift. The shifts in Bragg Peak depth for water phantoms modeled with a nanodot on the phantom surface ranged between 2.7 to 3.2 mm. In all cases, the Bragg Peaks were shifted closer to the irradiation source. The peak dose in phantoms with an OSLD remained unchanged with percent dose differences less than 0.55% when compared to phantom doses without the nanodot. Conclusion: Monte Carlo calculations show that the presence of OSLD nanodots in proton beam therapy will not change the position of a pristine Bragg Peak by more than 3 mm. Although the 3.0 mm shift will not have a detrimental effect in patients receiving proton therapy, this effect may not be negligible in dose verification measurements for mouse models at lower proton beam energies.« less

Study of Optical Fiber Sensors for Cryogenic Temperature Measurements.

PubMed

De Miguel-Soto, Veronica; Leandro, Daniel; Lopez-Aldaba, Aitor; Beato-López, Juan Jesus; Pérez-Landazábal, José Ignacio; Auguste, Jean-Louis; Jamier, Raphael; Roy, Philippe; Lopez-Amo, Manuel

2017-11-30

In this work, the performance of five different fiber optic sensors at cryogenic temperatures has been analyzed. A photonic crystal fiber Fabry-Pérot interferometer, two Sagnac interferometers, a commercial fiber Bragg grating (FBG), and a π-phase shifted fiber Bragg grating interrogated in a random distributed feedback fiber laser have been studied. Their sensitivities and resolutions as sensors for cryogenic temperatures have been compared regarding their advantages and disadvantages. Additionally, the results have been compared with the given by a commercial optical backscatter reflectometer that allowed for distributed temperature measurements of a single mode fiber.

Efficient high-power frequency doubling of distributed Bragg reflector tapered laser radiation in a periodically poled MgO-doped lithium niobate planar waveguide.

PubMed

Jedrzejczyk, Daniel; Güther, Reiner; Paschke, Katrin; Jeong, Woo-Jin; Lee, Han-Young; Erbert, Götz

2011-02-01

We report on efficient single-pass, high-power second-harmonic generation in a periodically poled MgO-doped LiNbO3 planar waveguide using a distributed Bragg reflector tapered diode laser as a pump source. A coupling efficiency into the planar waveguide of 73% was realized, and 1.07 W of visible laser light at 532 nm was generated. Corresponding optical and electro-optical conversion efficiencies of 26% and 8.4%, respectively, were achieved. Good agreement between the experimental data and the theoretical predictions was observed.

Study of Optical Fiber Sensors for Cryogenic Temperature Measurements

PubMed Central

Leandro, Daniel; Lopez-Aldaba, Aitor; Beato-López, Juan Jesus; Pérez-Landazábal, José Ignacio; Auguste, Jean-Louis; Jamier, Raphael; Roy, Philippe; Lopez-Amo, Manuel

2017-01-01

In this work, the performance of five different fiber optic sensors at cryogenic temperatures has been analyzed. A photonic crystal fiber Fabry-Pérot interferometer, two Sagnac interferometers, a commercial fiber Bragg grating (FBG), and a π-phase shifted fiber Bragg grating interrogated in a random distributed feedback fiber laser have been studied. Their sensitivities and resolutions as sensors for cryogenic temperatures have been compared regarding their advantages and disadvantages. Additionally, the results have been compared with the given by a commercial optical backscatter reflectometer that allowed for distributed temperature measurements of a single mode fiber. PMID:29189755

Monitoring relative humidity in RPC detectors by use of fiber optic sensors

NASA Astrophysics Data System (ADS)

Caponero, M. A.; Polimadei, A.; Benussi, L.; Bianco, S.; Colafranceschi, S.; Passamonti, L.; Piccolo, D.; Pierluigi, D.; Russo, A.; Felli, F.; Saviano, G.; Vendittozzi, C.

2013-03-01

We propose to adopt Fiber Bragg Grating technology to develop an innovative sensor for monitoring relative humidity of the gas fluxed in Resistive Plate Counters. Use of Fiber Bragg Grating as sensing device makes the proposed sensor well suited to develop distributed real-time monitoring systems to be installed on large volume detectors operated in high electromagnetic fields. In fact Fiber Bragg Gratings are fully immune from electromagnetic disturbances and allow simplified wiring by in-series interconnection of tens of them along a single optical fiber. In this paper we present results intended to investigate the feasibility of our proposal.

Fabrication of gradient optical filter containing anisotropic Bragg nanostructure.

PubMed

Cho, Bomin; Um, Sungyong; Woo, Hee-Gweon; Sohn, Honglae

2011-08-01

New gradient optical filters containing asymmetric Bragg structure were prepared from the distributed Bragg reflector (DBR) porous silicon (PSi). Anisotropic DBR PSi displaying a rainbow-colored reflection was generated by using an asymmetric etching configuration. Flexible anisotropic DBR PSi composite films were obtained by casting of polymer solution onto anisotropic DBR PSi thin films. The surface and cross-sectional images images of anisotropic DBR PSi composite films obtained with cold field emission scanning electron microscope indicated that the average pore size and the thickness of porous layer decreased as the lateral distance increased. As lateral distance increased, the reflection resonance shifted to shorter wavelength.

Single-Mode, Distributed Feedback Interband Cascade Lasers

NASA Technical Reports Server (NTRS)

Frez, Clifford F. (Inventor); Borgentun, Carl E. (Inventor); Briggs, Ryan M. (Inventor); Bagheri, Mahmood (Inventor); Forouhar, Siamak (Inventor)

2016-01-01

Single-mode, distributed feedback interband cascade lasers (ICLs) using distributed-feedback gratings (e.g., lateral Bragg gratings) and methods of fabricating such ICLs are provided. The ICLs incorporate distributed-feedback gratings that are formed above the laser active region and adjacent the ridge waveguide (RWG) of the ICL. The ICLs may incorporate a double-ridge system comprising an optical confinement structure (e.g., a RWG) disposed above the laser active region that comprises the first ridge of the double ridge system, a DFB grating (e.g., lateral Bragg grating) disposed above the laser active region and adjacent the optical confinement structure, and an electric confinement structure that passes at least partially through the laser active region and that defines the boundary of the second ridge comprises and the termination of the DFB grating.

Fabrication et applications des reseaux de Bragg ultra-longs

NASA Astrophysics Data System (ADS)

Gagne, Mathieu

This thesis presents the principal accomplishments realized during the PhD project. The thesis is presented by publication format and is a collection of four published articles having fiber Bragg gratings as a central theme. First achieved in 1978, UV writing of fiber Bragg gratings is nowadays a common and mature technology being present in both industry and academia. The property of reflecting light guided by optical fibers lead to diverse applications in telecommunication, lasers as well as several types of sensors. The conventional fabrication technique is generally based on the use of generally expensive phase masks which determine the obtained characteristics of the fiber Bragg grating. The fiber being photosensitive at those wavelengths, a periodic pattern can be written into it. The maximal length, the period, the chirp, the index contrast and the apodisation are all characteristics that depend on the phase mask. The first objective of the research project is to be able to go beyond this strong dependance on the phase mask without deteriorating grating quality. This is what really sets apart the technique presented in this thesis from other long fiber Bragg grating fabrication techniques available in the literature. The fundamental approach to obtain ultra long fiber Bragg gratings of arbitrary profile is to replace the scheme of scanning a UV beam across a phase mask to expose a fixed fiber by a scheme where the UV beam and phase mask are fixed and where the fiber is moving instead. To obtain a periodic index variation, the interference pattern itself must be synchronized with the moving fiber. Two variations of this scheme were implanted: the first one using electro-optical phase modulator placed in each arm of a Talbot interferometer and the second one using a phase mask mounted on a piezo electric actuator. A new scheme that imparts fine movements of the interferometer is also implemented for the first time and showed to be essential to achieve high quality ultra long fiber Bragg gratings. High quality theory matching ultra long fiber Bragg gratings up to 1 meter long are obtained for the first time. The possibility of fabricating high quality ultra long fiber Bragg grating of more than 10 cm (approximately the maximal phase mask length) opens a variety of new applications otherwise impossible with short fiber Bragg grating technology. Ultra long fiber Bragg gratings have unique characteristics such as high reflectivity, high dispersion and ultra narrow bandwidth. Those characteristics can be used to do advanced signal processing, non linear propagation experiments, distributed feedback fiber lasers and dispersion compensator for telecommunication or optical tomography. The second objective of this project is to use these ultra-long fiber Bragg gratings as an optical cavity for fiber lasers. Alot of research in the past years have been concentrated on those lasers, particularly on distributed feedback fiber lasers where the gratings spans all the gain media. A new random fiber laser configuration is presented. It is based on passive or active insertion of phase shifts along the Bragg grating to obtained a phenomenon called light localization which is the optical equivalent of Anderson localization. This complex wave phenomenon has the unique property to mimic the reflection of a uniform photonic crystal with the random diffusion of light among the elements of a random media. Being commonly obtained in fine powders which must respect a certain set of rules, the realization of 1D structures is vastly simplified in optical fibers. Two random fiber laser schemes based on light localization, one using erbium dopant and the other one Raman scattering, are demonstrated for the first time and compared to traditional distributed feedback fiber lasers.

[Radiobiological effects of total mice irradiation with Bragg's peak protons].

PubMed

Ivanov, A A; Molokanov, A G; Ushakov, I B; Bulynina, T M; Vorozhtsova, S V; Abrosimova, A N; Kryuchkova, D M; Gaevsky, V N

2013-01-01

Outbred CD-1 female mice were irradiated in a proton beam (171 MeV, 5 Gy) on the phasotron at the Joint Institute of Nuclear Research (Dubna, Russia). Radiation was delivered in two points of the depth dose distribution: at the beam entry and on Bragg's peak. Technical requirements for studying the effects of Bragg's peak protons on organism of experimental animals were specified. It was recognized that protons with high linear energy transfer (mean LET = 1.6 keV/microm) cause a more severe damaging effect to the hemopoietic system and cytogenetic apparatus in bone marrow cells as compared with entry protons and 60Co gamma-quanta. It was shown that recovery of the main hemopoietic organs and immunity as well as elimination of chromosomal aberrations take more time following irradiation with Bragg's peak protons but not protons with the energy of 171 MeV.

Tunable Supermode Dielectric Resonators for Axion Dark-Matter Haloscopes

NASA Astrophysics Data System (ADS)

McAllister, Ben T.; Flower, Graeme; Tobar, Lucas E.; Tobar, Michael E.

2018-01-01

We present frequency-tuning mechanisms for dielectric resonators, which undergo "supermode" interactions as they tune. The tunable schemes are based on dielectric materials strategically placed inside traditional cylindrical resonant cavities, necessarily operating in transverse-magnetic modes for use in axion haloscopes. The first technique is based on multiple dielectric disks with radii smaller than that of the cavity. The second scheme relies on hollow dielectric cylinders similar to a Bragg resonator, but with a different location and dimension. Specifically, we engineer a significant increase in form factor for the TM030 mode utilizing a variation of a distributed Bragg reflector resonator. Additionally, we demonstrate an application of traditional distributed Bragg reflectors in TM modes which may be applied to a haloscope. Theoretical and experimental results are presented showing an increase in Q factor and tunability due to the supermode effect. The TM030 ring-resonator mode offers a between 1 and 2-order-of-magnitude improvement in axion sensitivity over current conventional cavity systems and will be employed in the forthcoming ORGAN experiment.

GaAs/GaAlAs distributed Bragg reflector laser with a focused ion beam, low dose dopant implanted grating

NASA Technical Reports Server (NTRS)

Wu, M. C.; Boenke, M. M.; Wang, S.; Clark, W. M., Jr.; Stevens, E. H.

1988-01-01

The performance of a GaAs/GaAlAs distributed Bragg reflector (DBR) laser using a focused ion beam implanted grating (FIB-DBR) is reported for the first time. Stripes of Si(2+) with a period of 2300 A and a dose about 10 to the 14th/sq cm are directly implanted into the passive large optical cavity layer to provide the distributed feedback. Surface-emitting light from the second-order grating is observed. Threshold current of 110 mA and single DBR mode operation from 20 to 40 C are obtained. The wavelength tuning rate with temperature is 0.8 A/C. The coupling coefficient is estimated to be 15/cm. The results show that FIB technology is practical for distributed feedback and DBR lasers and optoelectronic integrated circuits.

Polarization independent polymer waveguide tunable receivers incorporating a micro-optic circulator

NASA Astrophysics Data System (ADS)

Wu, Xiaoping; Park, Tae-Hyun; Park, Su-Hyun; Seo, Jun-Kyu; Oh, Min-Cheol

2018-06-01

In order to simplify the receiver configuration in a wavelength division multiplexed optical fiber network, compact wavelength tunable filters have long been expected to be used as channel selectors. Bragg reflector inherently has the most suitable reflection spectrum for filtering a single wavelength from the densely multiplexed wavelength signal. Polymer has high thermo-optic coefficient and good thermal insulation property compared to the other optical waveguide materials such as silicon and silica materials. This can be used to broadly tune the reflection spectrum of Bragg reflector using a simple micro-heater. In this work, a micro-optic circulator component and a polymeric Bragg reflector device are assembled to produce a small form factor tunable receiver. Compared to the integrated-optical versions, the micro-optics are based on well-developed manufacturing processes and can achieve competitive production yields. The device exhibits high reflectivity with a flat top passband, and a polarization dependence of 0.06 nm achieved by virtue of the low birefringence of LFR polymer, which make a significant contribution to the implementation of polarization independent tunable receiver. The wavelength tuning range of 40 nm is demonstrated by using a bottom located heater with a groove for heat isolation.

FDTD and transfer matrix methods for evaluating the performance of photonic crystal based microcavities for exciton-polaritons

NASA Astrophysics Data System (ADS)

Liu, Yi-Cheng; Byrnes, Tim

2016-11-01

We investigate alternative microcavity structures for exciton-polaritons consisting of photonic crystals instead of distributed Bragg reflectors. Finite-difference time-domain simulations and scattering transfer matrix methods are used to evaluate the cavity performance. The results are compared with conventional distributed Bragg reflectors. We find that in terms of the photon lifetime, the photonic crystal based microcavities are competitive, with typical lifetimes in the region of ∼20 ps being achieved. The photonic crystal microcavities have the advantage that they are compact and are frequency adjustable, showing that they are viable to investigate exciton-polariton condensation physics.

Monitoring of non-homogeneous strains in wood glued joints with embedded FBG optical sensors in mode I delamination tests

NASA Astrophysics Data System (ADS)

Maciel, R. S.; Frazão, O.; Morais, J. J. L.; Fernandes, J. R. A.

2013-11-01

In this work it is presented a study of the reflection spectra yielded by a Fiber Bragg Grating sensor embedded into an epoxy glue line between two wood arms, in a double cantilever beam (DCB) Mode I delamination test. The reflection spectra were obtained using a Spectral Analyzer Fibersensing Bragmeter FS2200SA in regular time intervals, as the stress applied to the laminates is continuously increased until fracture occurs. They initially show a typical Bragg grating reflection spectrum, which gradually changes into more complicated, multiple-peak spectra, resulting from a non-homogenous strain distribution along the board line. Based on these results, a model was derived for the variation of the grating effective index which fits the observed spectra when the irregular strain distribution is observed. This model consists of usual cosine description of Bragg grating effective index with linear phase variation, plus a logarithmic phase change along the fiber length, resulting in the increment of the grating wavelength with increasing distance from the load application point. Moreover, from this model the strain distribution along the grating is found, yielding the expected result.

Initial Trial using Embedded Fibre Bragg Gratings for Distributed Strain Monitoring in a Shape Adaptive Composite Foil

DTIC Science & Technology

2012-02-01

available for interrogation. Although commercially available fibre Bragg grating ( FBG ) sensors have emerged in the marketplace over the past decade...the results from a preliminary trial investigating the feasibility of using embedded FBG arrays in a shape adaptive composite foil to characterise...The response from the FBG sensors was also monitored during fabrication of the foil during the resin infusion and curing stages of the process

A reconfigurable microwave photonic filter with flexible tunability using a multi-wavelength laser and a multi-channel phase-shifted fiber Bragg grating

NASA Astrophysics Data System (ADS)

Shi, Nuannuan; Hao, Tengfei; Li, Wei; Zhu, Ninghua; Li, Ming

2018-01-01

We propose a photonic scheme to realize a reconfigurable microwave photonic filter (MPF) with flexible tunability using a multi-wavelength laser (MWL) and a multi-channel phase-shifted fiber Bragg grating (PS-FBG). The proposed MPF is capable of performing reconfigurability including single bandpass filter, two independently bandpass filter and a flat-top bandpass filter. The performance such as the central frequency and the bandwidth of passband is tuned by controlling the wavelengths of the MWL. In the MPF, The light waves from a MWL are sent to a phase modulator (PM) to generate the phase-modulated optical signals. By applying a multi-channel PS-FBG, which has a series of narrow notches in the reflection spectrum with the free spectral range (FSR) of 0.8 nm, the +1st sidebands are removed in the notches and the phased-modulated signals are converted to the intensity-modulated signals without beating signals generation between each two optical carriers. The proposed MPF is also experimentally verified. The 3-dB bandwidth of the MPF is broadened from 35 MHz to 135 MHz and the magnitude deviation of the top from the MPF is less than 0.2 dB within the frequency tunable range from 1 GHz to 5 GHz.

An efficient method to predict and include Bragg curve degradation due to lung-equivalent materials in Monte Carlo codes by applying a density modulation

NASA Astrophysics Data System (ADS)

Baumann, Kilian-Simon; Witt, Matthias; Weber, Uli; Engenhart-Cabillic, Rita; Zink, Klemens

2017-05-01

Sub-millimetre-sized heterogeneities such as lung parenchyma cause Bragg peak degradation which can lead to an underdose of the tumor and an overdose of healthy tissue when not accounted for in treatment planning. Since commonly used treatment-planning CTs do not resolve the fine structure of lungs, this degradation can hardly be considered. We present a mathematical model capable of predicting and describing Bragg peak degradation due to a lung-equivalent geometry consisting of sub-millimetre voxels filled with either lung tissue or air. The material characteristic ‘modulation power’ is introduced to quantify the Bragg peak degradation. A strategy was developed to transfer the modulating effects of such fine structures to rougher structures such as 2 mm thick CT voxels, which is the resolution of typically used CTs. This is done by using the modulation power to derive a density distribution applicable to these voxels. By replacing the previously used sub-millimetre voxels by 2 mm thick voxels filled with lung tissue and modulating the lung tissue’s density in each voxel individually, we were able to reproduce the Bragg peak degradation. Hence a solution is found to include Bragg curve degradation due to lung-equivalent materials in Monte Carlo-based treatment-planning systems.

Fiber Bragg Grating vibration sensor with DFB laser diode

NASA Astrophysics Data System (ADS)

Siska, Petr; Brozovic, Martin; Cubik, Jakub; Kepak, Stanislav; Vitasek, Jan; Koudelka, Petr; Latal, Jan; Vasinek, Vladimir

2012-01-01

The Fiber Bragg Grating (FBG) sensors are nowadays used in many applications. Thanks to its quite big sensitivity to a surrounding environment, they can be used for sensing of temperature, strain, vibration or pressure. A fiber Bragg grating vibration sensor, which is interrogated by a distributed feedback laser diode (DFB) is demonstrated in this article. The system is based on the intensity modulation of the narrow spectral bandwidth of the DFB laser, when the reflection spectrum of the FBG sensor is shifted due to the strain that is applied on it in form of vibrations caused by acoustic wave pressure from loud speaker. The sensor's response in frequency domain and strain is measured; also the factor of sensor pre-strain impact on its sensitivity is discussed.

Parity–time-symmetric circular Bragg lasers: a proposal and analysis

PubMed Central

Gu, Jiahua; Xi, Xiang; Ma, Jingwen; Yu, Zejie; Sun, Xiankai

2016-01-01

We propose a new type of semiconductor lasers by implementing the concept of parity–time symmetry in a two-dimensional circular Bragg grating structure, where both the real and imaginary parts of the refractive index are modulated along the radial direction. The laser modal properties are analyzed with a transfer-matrix method and are verified with numerical simulation of a practical design. Compared with conventional distributed-feedback lasers with modulation of only the real part of refractive index, the parity–time-symmetric circular Bragg lasers feature reduced threshold and enhanced modal discrimination, which in combination with the intrinsic circularly symmetric, large emission aperture are clear advantages in applications that require mode-hop-free, high-power, single-mode laser operation. PMID:27892933

Structural sensitivity of x-ray Bragg projection ptychography to domain patterns in epitaxial thin films

NASA Astrophysics Data System (ADS)

Hruszkewycz, S. O.; Zhang, Q.; Holt, M. V.; Highland, M. J.; Evans, P. G.; Fuoss, P. H.

2016-10-01

Bragg projection ptychography (BPP) is a coherent diffraction imaging technique capable of mapping the spatial distribution of the Bragg structure factor in nanostructured thin films. Here, we show that, because these images are projections, the structural sensitivity of the resulting images depends on the film thickness and the aspect ratio and orientation of the features of interest and that image interpretation depends on these factors. We model changes in contrast in the BPP reconstructions of simulated PbTiO3 ferroelectric thin films with meandering 180∘ stripe domains as a function of film thickness, discuss their origin, and comment on the implication of these factors on the design of BPP experiments of general nanostructured films.

Research on local resonance and Bragg scattering coexistence in phononic crystal

NASA Astrophysics Data System (ADS)

Dong, Yake; Yao, Hong; Du, Jun; Zhao, Jingbo; Jiang, Jiulong

2017-04-01

Based on the finite element method (FEM), characteristics of the local resonance band gap and the Bragg scattering band gap of two periodically-distributed vibrator structures are studied. Conditions of original anti-resonance generation are theoretically derived. The original anti-resonance effect leads to localization of vibration. Factors which influence original anti-resonance band gap are analyzed. The band gap width and the mass ratio between two vibrators are closely correlated to each other. Results show that the original anti-resonance band gap has few influencing factors. In the locally resonant structure, the Bragg scattering band gap is found. The mass density of the elastic medium and the elasticity modulus have an important impact on the Bragg band gap. The coexistence of the two mechanisms makes the band gap larger. The band gap covered 90% of the low frequencies below 2000 Hz. All in all, the research could provide references for studying the low-frequency and broad band gap of phononic crystal.

Conserving Biodiversity on Military Lands: The Commander’s Guide

DTIC Science & Technology

2010-01-01

Top: Orchid, Warren Grove Air National Guard Range, New Jersey, (© Douglas Ripley). Above left: Carnivorous pitcher plants , Fort Bragg, North...mou for Conservation of Migratory Birds (07-2006) ı mou for Federal Native Plant Conservation (09-2006) ı mou between the Department of Defense and Bat...natural resources conserva- tion by protecting large tracts of land that provide habitat for many species of plants and wildlife. The hcmp also

Nanostructured Sublayers for Improved Light Extraction of Top-Emitting and Transparent Organic Electroluminescent Devices

DTIC Science & Technology

2007-05-01

luminous efficiency and wider color gamut . In addition, organic phosphorescent light emitting materials and devices were studied. 15. SUBJECT TERMS...nanostructured Bragg mirrors provided an improved external luminous efficiency and wide color gamut , which will be an essential part of future flat-panel...layers (usually with an ultra-thin shadow mask) or the fabrication of anodes with variable thickness have been used to achieve enhanced color gamut

1.5  μm polarization-maintaining dual-wavelength single-frequency distributed Bragg reflection fiber laser with 28  GHz stable frequency difference.

PubMed

Hou, Yubin; Zhang, Qian; Qi, Shuxian; Feng, Xian; Wang, Pu

2018-03-15

We demonstrate a polarization-maintaining (PM) dual-wavelength (DW) single-frequency Er-doped distributed Bragg reflection (DBR) fiber laser with 28 GHz stable frequency difference. A homemade PM low-reflectivity superimposed fiber Bragg grating (SFBG) is employed as the output port of the DBR fiber laser. The SFBG has two reflection wavelengths located in the same grating region. The reflectivity of both DWs is around 85%. The achieved linear polarization extinction ratio is more than 20 dB. The DWs of the laser output are located at 1552.2 nm and 1552.43 nm, respectively. The optical signal-to-noise ratio (SNR) is above 60 dB. For each wavelength, only one longitudinal mode exists. The beat frequency of the two longitudinal modes is measured to be 28.4474 GHz, with the SNR of more than 65 dB and the linewidth less than 300 Hz. During a 60-min-long measurement, the standard deviation of the frequency fluctuation is 58.592 kHz.

/III-V semiconductor broadband distributed Bragg reflectors for long-wavelength VCSEL and SESAM devices

NASA Astrophysics Data System (ADS)

Koeninger, Anna; Boehm, Gerhard; Meyer, Ralf; Amann, Markus-Christian

2014-12-01

Semiconductor devices such as vertical-cavity surface-emitting lasers (VCSELs) or semiconductor-saturable absorber mirrors (SESAMs) require high-reflection mirrors. Moreover, in VCSELs, it is beneficial to have a crystalline mirror, which is as thin as possible in order to ensure a high thermal conductivity for efficient heat-sinking of the laser. On the other hand, the wavelength tuning range of a SESAM is limited by the reflection bandwidth of its distributed Bragg reflector (DBR). Thus, broadband mirrors are preferable here. This paper reports a three-pair DBR grown by molecular beam epitaxy (MBE) using BaCaF2 and GaAs on a GaAs (100) substrate. Due to the high ratio in refractive indices of GaAs and the group-IIa-fluorides, high-reflectivity mirrors and wide bandwidths can be obtained with low total thicknesses. We also investigated growth and stability of the material BaCaF2, as well as its thermal conductivity both as single layer and Bragg reflector. Observed peeling of the layers could be avoided by implementing a fluorine treatment previous to the BaCaF2 growth.

Optical Fiber Distributed Sensing Structural Health Monitoring (SHM) Strain Measurements Taken During Cryotank Y-Joint Test Article Load Cycling at Liquid Helium Temperatures

NASA Technical Reports Server (NTRS)

Allison, Sidney G.; Prosser, William H.; Hare, David A.; Moore, Thomas C.; Kenner, Winfred S.

2007-01-01

This paper outlines cryogenic Y-joint testing at Langley Research Center (LaRC) to validate the performance of optical fiber Bragg grating strain sensors for measuring strain at liquid helium temperature (-240 C). This testing also verified survivability of fiber sensors after experiencing 10 thermal cool-down, warm-up cycles and 400 limit load cycles. Graphite composite skins bonded to a honeycomb substrate in a sandwich configuration comprised the Y-joint specimens. To enable SHM of composite cryotanks for consideration to future spacecraft, a light-weight, durable monitoring technology is needed. The fiber optic distributed Bragg grating strain sensing system developed at LaRC is a viable substitute for conventional strain gauges which are not practical for SHM. This distributed sensing technology uses an Optical Frequency Domain Reflectometer (OFDR). This measurement approach has the advantage that it can measure hundreds of Bragg grating sensors per fiber and the sensors are all written at one frequency, greatly simplifying fiber manufacturing. Fiber optic strain measurements compared well to conventional strain gauge measurements obtained during these tests. These results demonstrated a high potential for a successful implementation of a SHM system incorporating LaRC's fiber optic sensing system on the composite cryotank and other future cryogenic applications.

Fiber Bragg Grating Array as a Quasi Distributed Temperature Sensor for Furnace Boiler Applications

NASA Astrophysics Data System (ADS)

Reddy, P. Saidi; Prasad, R. L. N. Sai; Sengupta, D.; Shankar, M. Sai; Srimannarayana, K.; Kishore, P.; Rao, P. Vengal

2011-10-01

This paper presents the experimental work on distributed temperature sensing making use of Fiber Bragg grating (FBG) array sensor for possible applications in the monitoring of temperature profile in high temperature boilers. A special sensor has been designed for this purpose which consists of four FBGs (of wavelengths λB1 = 1547.28 nm, λB2 = 1555.72 nm, λB3 = 1550.84 nm, λB4 = 1545.92 nm) written in hydrogen loaded fiber in line with a spacing of 15 cm between them. All the FBGs are encapsulated inside a stainless steel tube for avoiding micro cracks using rigid probe technique. The spatial distribution of temperature profile inside a prototype boiler has been measured experimentally both in horizontal and vertical directions employing the above sensor and the results are presented.

Far-field emission characteristics and linewidth measurements of surface micro-machined MEMS tunable VCSELs

NASA Astrophysics Data System (ADS)

Paul, Sujoy; Gierl, Christian; Gründl, Tobias; Zogal, Karolina; Meissner, Peter; Amann, Markus-Christian; Küppers, Franko

2013-03-01

In this paper, we demonstrate for the first time the far-field experimental results and the linewidth characteris- tics for widely tunable surface-micromachined micro-electro-mechanical system (MEMS) vertical-cavity surface- emitting lasers (VCSELs) operating at 1550 nm. The fundamental Gaussian mode emission is confirmed by optimizing the radius of curvature of top distributed Bragg reflector (DBR) membrane and by choosing an ap- propriate diameter of circular buried tunnel junctions (BTJs) so that only the fundamental Gaussian mode can sustain. For these VCSELs, a mode-hop free continuous tuning over 100 nm has already been demonstrated, which is achieved by electro-thermal tuning of the MEMS mirror. The fiber-coupled optical power of 2mW over the entire tuning range has been reported. The singlemode laser emission has more than 40 dB of side-mode suppression ratio (SMSR). The smallest linewidth achieved with these of MEMS tunable VCSELs is 98MHz which is one order of magnitude higher than that of fixed-wavelength VCSELs.

Design, manufacture and testing of an FBG-instrumented composite wing

NASA Astrophysics Data System (ADS)

Abouzeida, E.; Quinones, V.; Gowayed, Y.; Soobramaney, P.; Flowers, G.; Black, R. J.; Costa, J. M.; Faridian, F.; Moslehi, B.

2014-02-01

In this work, our research team investigated the efficacy of using optical static and dynamic strain sensing with embedded Fiber Bragg Gratings (FBGs) in structural health monitoring (SHM) of a model composite airplane wing. A one-fourth scale model of a T38 airplane wing was designed and manufactured using fabric reinforced polymer matrix composites with FBG sensors embedded under the top layer of the composite. The accuracy and durability of the sensors were evaluated at the coupon and structural levels utilizing static and dynamic testing. Strain measurements using embedded FBGs with an optical interrogator were found to be in agreement with values measured using other strain measuring devices and with results obtained using finite element analysis (ANSYS®). Preferred locations for the FBG sensors were identified in accordance with contour maps of internal strain distributions resulting from critical load cases. Manufacturing techniques used to address handling, survivability and durability of the embedded sensors during and post manufacturing of the composites were evaluated and optimized.

Metalorganic vapor phase epitaxial growth of red and infrared vertical-cavity surface-emitting laser diodes

NASA Astrophysics Data System (ADS)

Schneider, R. P.; Lott, J. A.; Lear, K. L.; Choquette, K. D.; Crawford, M. H.; Kilcoyne, S. P.; Figiel, J. J.

1994-12-01

Metalorganic vapor phase epitaxy (MOVPE) is used for the growth of vertical-cavity surface-emitting laser (VCSEL) diodes. MOVPE exhibits a number of important advantages over the more commonly-used molecular-beam epitaxial (MBE) techniques, including ease of continuous compositional grading and carbon doping for low-resistance p-type distributed Bragg reflectors (DBRs), higher growth rates for rapid throughput and greater versatility in choice of materials and dopants. Planar gain-guided red VCSELs based on AlGaInP/AlGaAs heterostructures lase continuous-wave at room temperature, with voltage thresholds between 2.5 and 3 V and maximum power outputs of over 0.3 mW. Top-emitting infra-red (IR) VCSELs exhibit the highest power-conversion (wall-plug) efficiencies (21%), lowest threshold voltage (1.47 V), and highest single mode power (4.4 mW from an 8 μm device) yet reported. These results establish MOVPE as a preferred growth technique for this important new family of photonic devices.

Thermo-spectral properties of plastic lasers

NASA Astrophysics Data System (ADS)

Dawson, Nathan J.; Aviles, Michael; Andrews, James H.; Crescimanno, Michael; Petrus, Joshua B.; Mazzocco, Anthony; Singer, Kenneth D.; Baer, Eric; Song, Hyunmin

2013-09-01

We study the effects of temperature changes on the operating wavelength of all-polymer microresonator lasers, particularly on multilayered defect distributed feedback and distributed Bragg reflector lasers. The parameters that change the operating wavelength are discussed with comparisons between experiments and simulations.

Real-Time Characterization of Aerospace Structures Using Onboard Strain Measurement Technologies and Inverse Finite Element Method

DTIC Science & Technology

2011-09-01

strain data provided by in-situ strain sensors. The application focus is on the stain data obtained from FBG (Fiber Bragg Grating) sensor arrays...sparsely distributed lines to simulate strain data from FBG (Fiber Bragg Grating) arrays that provide either single-core (axial) or rosette (tri...when the measured strain data are sparse, as it is often the case when FBG sensors are used. For an inverse element without strain-sensor data, the

Optical microphone with fiber Bragg grating and signal processing techniques

NASA Astrophysics Data System (ADS)

Tosi, Daniele; Olivero, Massimo; Perrone, Guido

2008-06-01

In this paper, we discuss the realization of an optical microphone array using fiber Bragg gratings as sensing elements. The wavelength shift induced by acoustic waves perturbing the sensing Bragg grating is transduced into an intensity modulation. The interrogation unit is based on a fixed-wavelength laser source and - as receiver - a photodetector with proper amplification; the system has been implemented using devices for standard optical communications, achieving a low-cost interrogator. One of the advantages of the proposed approach is that no voltage-to-strain calibration is required for tracking dynamic shifts. The optical sensor is complemented by signal processing tools, including a data-dependent frequency estimator and adaptive filters, in order to improve the frequency-domain analysis and mitigate the effects of disturbances. Feasibility and performances of the optical system have been tested measuring the output of a loudspeaker. With this configuration, the sensor is capable of correctly detecting sounds up to 3 kHz, with a frequency response that exhibits a top sensitivity within the range 200-500 Hz; single-frequency input sounds inducing an axial strain higher than ~10nɛ are correctly detected. The repeatability range is ~0.1%. The sensor has also been applied for the detection of pulsed stimuli generated from a metronome.

Structural sensitivity of x-ray Bragg projection ptychography to domain patterns in epitaxial thin films

DOE PAGES

Hruszkewycz, S. O.; Zhang, Q.; Holt, M. V.; ...

2016-10-04

Bragg projection ptychography (BPP) is a coherent diffraction imaging technique capable of mapping the spatial distribution of the Bragg structure factor in nanostructured thin films. Here, we show that, because these images are projections, the structural sensitivity of the resulting images depends on the film thickness and the aspect ratio and orientation of the features of interest and that image interpretation depends on these factors. Lastly, we model changes in contrast in the BPP reconstructions of simulated PbTiO 3 ferroelectric thin films with meandering 180° stripe domains as a function of film thickness, discuss their origin, and comment on themore » implication of these factors on the design of BPP experiments of general nanostructured films.« less

Germ cell loss induced by 12C6+ ion irradiation in young female mice.

PubMed

Zhang, Hong; Zhang, Xu; Yuan, Zhigang; Li, Xiaoda; Li, Wenjian; Zhou, Qingming; Min, Fengling; Xie, Yi; Liu, Bing; Duan, Xin

2006-06-01

The ovaries of Kun-Ming strain mice (3 weeks) were irradiated with different doses of 12C6+ ion in the Bragg peak or the plateau region. At 10th day after irradiation, ovarian and uterine weights were measured; normal and atretic (identified with the oocyte to be degenerating or absent) primordial, primary and preantral follicles were identified in the largest cross-section of each ovary. Percentage (%) of normal follicles of each developmental stage of oogenesis was calculated. The data showed that compared to controls, there was a dose-related decrease in percentage of normal follicles in each developmental stage. And the weights of ovary and uterus were also reduced with doses of irradiation. Moreover, these effects were much more significant in the Bragg peak region and the region close to the Bragg peak than in the beam's entrance (the plateau region). Radiosensitivity varied in different follicle maturation stages. Primordial follicles, which are thought to be extremely sensitive to ionizing irradiation, were reduced by 86.6%, while primary and preantral follicles reduced only by 72.5% and 61.8% respectively, by exposure with 6 Gy of 12C6+ ion in the Bragg peak region and the region close to the Bragg peak. The data suggested that due to their optimal depth-dose distribution in the Bragg peak region, heavy ions are ones of the best particles for radiotherapy of tumors located next of vital organs or/and surrounded by normal tissues, especially radiosensitive tissues such as gonads.

Response analysis of TLD-300 dosimeters in heavy-particle beams

NASA Astrophysics Data System (ADS)

Loncol, Th; Hamal, M.; Denis, J. M.; Vynckier, S.; Wambersie, A.; Scalliet, P.

1996-09-01

In vivo dosimetry is recommended as part of the quality control procedure for treatment verification in radiation therapy. Using thermoluminescence, such controls are planned in the p(65)+Be neutron and 85 MeV proton beams produced at the cyclotron at Louvain-La-Neuve and dedicated to therapy applications. A preliminary study of the peak 3 (C) and peak 5 (C) response of :Tm (TLD-300) to neutron and proton beams aimed to analyse the effect of different radiation qualities on the dosimetric behaviour of the detector irradiated in phantom. To broaden the range of investigation, the study was extended to an experimental C-12 heavy ion beam (95 MeV/nucleon). The peak 3 and 5 sensitivities in the neutron beam, compared to Co-60, varied little with depth. A major change of peak 5 sensitivity was observed for samples positioned under five leaves of the multi-leaf collimator. While peak 3 sensitivity was constant with depth in the unmodulated proton beam, peak 5 sensitivity increased by 15%. Near the Bragg peak, peak 3 showed the highest decrease of sensitivity. In the modulated proton beam, the sensitivity values were not significantly smaller than those measured in the unmodulated beam far from the Bragg peak region. The ratio of the heights of peak 3 and peak 5 decreased by 70% from the Co-60 reference radiation to the C-12 heavy-ion beam. This parameter was strongly correlated with the change of radiation quality.

Giant enhancement of second harmonic generation in nonlinear photonic crystals with distributed Bragg reflector mirrors.

PubMed

Ren, Ming-Liang; Li, Zhi-Yuan

2009-08-17

We theoretically investigate second harmonic generation (SHG) in one-dimensional multilayer nonlinear photonic crystal (NPC) structures with distributed Bragg reflector (DBR) as mirrors. The NPC structures have periodic modulation on both the linear and second-order susceptibility. Three major physical mechanisms, quasi-phase matching (QPM) effect, slow light effect at photonic band gap edges, and cavity effect induced by DBR mirrors can be harnessed to enhance SHG. Selection of appropriate structural parameters can facilitate coexistence of these mechanisms to act collectively and constructively to create very high SHG conversion efficiency with an enhancement by up to seven orders of magnitude compared with the ordinary NPC where only QPM works. (c) 2009 Optical Society of America

Continuous-wave dual-wavelength operation of a distributed feedback laser diode with an external cavity using a volume Bragg grating

NASA Astrophysics Data System (ADS)

Zheng, Yujin; Sekine, Takashi; Kurita, Takashi; Kato, Yoshinori; Kawashima, Toshiyuki

2018-03-01

We demonstrate continuous-wave dual-wavelength operation of a broad-area distributed feedback (DFB) laser diode with a single external-cavity configuration. This high-power DFB laser has a narrow bandwidth (<0.29 nm) and was used as a single-wavelength source. A volume Bragg grating was used as an output coupler for the external-cavity DFB laser to output another stable wavelength beam with a narrow bandwidth of 0.27 nm. A frequency difference for dual-wavelength operation of 0.88 THz was achieved and an output power of up to 415 mW was obtained. The external-cavity DFB laser showed a stable dual-wavelength operation over the practical current and temperature ranges.

Metamorphic distributed Bragg reflectors for the 1440–1600 nm spectral range: Epitaxy, formation, and regrowth of mesa structures

DOE Office of Scientific and Technical Information (OSTI.GOV)

Egorov, A. Yu., E-mail: anton@beam.ioffe.ru; Karachinsky, L. Ya.; Novikov, I. I.

It is shown that metamorphic In{sub 0.3}Ga{sub 0.7}As/In{sub 0.3}Al{sub 0.7}As distributed Bragg reflectors (DBRs) with a reflection band at 1440–1600 nm and a reflectance of no less than 0.999 can be fabricated by molecular beam epitaxy (MBE) on a GaAs substrate. It is demonstrated that mesa structures formed from metamorphic DBRs on a GaAs substrate can be regrown by MBE and microcavities can be locally formed in two separate epitaxial processes. The results obtained can find wide application in the fabrication of vertical-cavity surface-emitting lasers (VCSELs) with a buried tunnel junction.

Distributed bragg reflector using AIGaN/GaN

DOEpatents

Waldrip, Karen E.; Lee, Stephen R.; Han, Jung

2004-08-10

A supported distributed Bragg reflector or superlattice structure formed from a substrate, a nucleation layer deposited on the substrate, and an interlayer deposited on the nucleation layer, followed by deposition of (Al,Ga,B)N layers or multiple pairs of (Al,Ga,B)N/(Al,Ga,B)N layers, where the interlayer is a material selected from AlN, Al.sub.x Ga.sub.1-x N, and AlBN with a thickness of approximately 20 to 1000 angstroms. The interlayer functions to reduce or eliminate the initial tensile growth stress, thereby reducing cracking in the structure. Multiple interlayers utilized in an AlGaN/GaN DBR structure can eliminate cracking and produce a structure with a reflectivity value greater than 0.99.

Discriminating Sea Spikes in Incoherent Radar Measurements of Sea Clutter

DTIC Science & Technology

2008-03-01

het detecteren echter niet te verwachten dat bet gebruik van sea spikes te onderzoeken. Een van deze modellen zal leiden tot een Auteur (s) dergelijk...report I TNO-DV 2008 A067 6/33 Abbreviations CFAR Constant False-Alarm Rate CST Composite Surface Theory FFT Fast Fourier Transform PDF Probability Density...described by the composite surface theory (CST). This theory describes the sea surface as small Bragg-resonant capillary waves riding on top of

Thermal Characterization of a Simulated Fission Engine via Distributed Fiber Bragg Gratings

NASA Astrophysics Data System (ADS)

Duncan, Roger G.; Fielder, Robert S.; Seeley, Ryan J.; Kozikowski, Carrie L.; Raum, Matthew T.

2005-02-01

We report the use of distributed fiber Bragg gratings to monitor thermal conditions within a simulated nuclear reactor core located at the Early Flight Fission Test Facility of the NASA Marshall Space Flight Center. Distributed fiber-optic temperature measurements promise to add significant capability and advance the state-of-the-art in high-temperature sensing. For the work reported herein, seven probes were constructed with ten sensors each for a total of 70 sensor locations throughout the core. These discrete temperature sensors were monitored over a nine hour period while the test article was heated to over 700 °C and cooled to ambient through two operational cycles. The sensor density available permits a significantly elevated understanding of thermal effects within the simulated reactor. Fiber-optic sensor performance is shown to compare very favorably with co-located thermocouples where such co-location was feasible.

Shape Sensing a Morphed Wing with an Optical Fiber Bragg Grating

NASA Technical Reports Server (NTRS)

Tai, Hsiang

2005-01-01

We suggest using distributed fiber Bragg sensors systems which were developed locally at Langley Research Center carefully placed on the wing surface to collect strain component information at each location. Then we used the fact that the rate change of slope in the definition of linear strain is very small and can be treated as a constant. Thereby the strain distribution information of a morphed surface can be reduced into a distribution of local slope information of a flat surface. In other words a morphed curve surface is replaced by the collection of individual flat surface of different slope. By assembling the height of individual flat surface, the morphed curved surface can be approximated. A more sophisticated graphic routine can be utilized to restore the curved morphed surface. With this information, the morphed wing can be further adjusted and controlled. A numerical demonstration is presented.

Phase sensitive distributed vibration sensing based on ultraweak fiber Bragg grating array using double-pulse

NASA Astrophysics Data System (ADS)

Liu, Tao; Wang, Feng; Zhang, Xuping; Zhang, Lin; Yuan, Quan; Liu, Yu; Yan, Zhijun

2017-08-01

A distributed vibration sensing technique using double-optical-pulse based on phase-sensitive optical time-domain reflectometry (ϕ-OTDR) and an ultraweak fiber Bragg grating (UWFBG) array is proposed for the first time. The single-mode sensing fiber is integrated with the UWFBG array that has uniform spatial interval and ultraweak reflectivity. The relatively high reflectivity of the UWFBG, compared with the Rayleigh scattering, gains a high signal-to-noise ratio for the signal, which can make the system achieve the maximum detectable frequency limited by the round-trip time of the probe pulse in fiber. A corresponding experimental ϕ-OTDR system with a 4.5 km sensing fiber integrated with the UWFBG array was setup for the evaluation of the system performance. Distributed vibration sensing is successfully realized with spatial resolution of 50 m. The sensing range of the vibration frequency can cover from 3 Hz to 9 kHz.

Resonance energy shifts during nuclear Bragg diffraction of x rays

DOE Office of Scientific and Technical Information (OSTI.GOV)

Arthur, J.; Brown, G.S.; Brown, D.E.

1989-10-09

We have observed dramatic changes in the time distribution of synchrotron x rays resonantly scattered from {sup 57}Fe nuclei in a crystal of yttrium iron garnet, which depend on the deviation angle of the incident radiation from the Bragg angle. These changes are caused by small shifts in the effective energies of the hyperfine-split nuclear resonances, an effect of dynamical diffraction for the coherently excited nuclei in the crystal. The very high brightness of the synchro- tron x-ray source allows this effect to be observed in a 15-min measurement.

Brillouin lasing in single-mode tapered optical fiber with inscribed fiber Bragg grating array

NASA Astrophysics Data System (ADS)

Popov, S. M.; Butov, O. V.; Chamorovskiy, Y. K.; Isaev, V. A.; Kolosovskiy, A. O.; Voloshin, V. V.; Vorob'ev, I. L.; Vyatkin, M. Yu.; Mégret, P.; Odnoblyudov, M.; Korobko, D. A.; Zolotovskii, I. O.; Fotiadi, A. A.

2018-06-01

A tapered optical fiber has been manufactured with an array of fiber Bragg gratings (FBG) inscribed during the drawing process. The total fiber peak reflectivity is 5% and the reflection bandwidth is ∼3.5 nm. A coherent frequency domain reflectometry has been applied for precise profiling of the fiber core diameter and grating reflectivity both distributed along the whole fiber length. These measurements are in a good agreement with the specific features of Brillouin lasing achieved in the semi-open fiber cavity configuration.

Acousto-Optical Vector Matrix Product Processor: Implementation Issues

DTIC Science & Technology

1989-04-25

power by a factor of 3.8. The acoustic velocity in longitudinal TeO2 is 4200 m/s, almost the same as the 4100 m/s acoustic velocity in dense flint glass ...field via an Interaction Model AOD150 dense flint glass Bragg Cell. The cell’s specifications are listed in the table below. BRAGG CELL SPECIFICATIONS...39 ns intervals). Since the speed of sound in dense flint glass is 4100 m/s, the acoustic field generated in a 10 As interval is distributed over a 4.1

Orientation-Dependent Displacement Sensor Using an Inner Cladding Fiber Bragg Grating.

PubMed

Yang, Tingting; Qiao, Xueguang; Rong, Qiangzhou; Bao, Weijia

2016-09-11

An orientation-dependent displacement sensor based on grating inscription over a fiber core and inner cladding has been demonstrated. The device comprises a short piece of multi-cladding fiber sandwiched between two standard single-mode fibers (SMFs). The grating structure is fabricated by a femtosecond laser side-illumination technique. Two well-defined resonances are achieved by the downstream both core and cladding fiber Bragg gratings (FBGs). The cladding resonance presents fiber bending dependence, together with a strong orientation dependence because of asymmetrical distribution of the "cladding" FBG along the fiber cross-section.

Stimulated Brillouin scattering in ultra-long distributed feedback Bragg gratings in standard optical fiber.

PubMed

Loranger, Sébastien; Lambin-Iezzi, Victor; Wahbeh, Mamoun; Kashyap, Raman

2016-04-15

Distributed feedback (DFB) fiber Bragg gratings (FBG) are widely used as narrow-band filters and single-mode cavities for lasers. Recently, a nonlinear generation has been shown in 10-20 cm DFB gratings in a highly nonlinear fiber. First, we show in this Letter a novel fabrication technique of ultra-long DFBs in a standard fiber (SMF-28). Second, we demonstrate nonlinear generation in such gratings. A particular inscription technique was used to fabricate all-in-phase ultra-long FBG and to implement reproducible phase shift to form a DFB mode. We demonstrate stimulated Brillouin scattering (SBS) emission from this DFB mode and characterize the resulting laser. It seems that such a SBS based DFB laser stabilizes a pump's jittering and reduces its linewidth.

Study of distributed fiber-optic laser-ultrasound generation based on ghost-mode of tilted fiber Bragg gratings

NASA Astrophysics Data System (ADS)

Tian, Jiajun; Zhang, Qi; Han, Ming

2013-05-01

Fiber-optic ultrasonic transducers are an important component of an active ultrasonic testing system for structural health monitoring. Fiber-optic transducers have several advantages such as small size, light weight, and immunity to electromagnetic interference that make them much more attractive than the current available piezoelectric transducers, especially as embedded and permanent transducers in active ultrasonic testing for structural health monitoring. In this paper, a distributed fiber-optic laser-ultrasound generation based on the ghost-mode of tilted fiber Bragg gratings is studied. The influences of the laser power and laser pulse duration on the laser-ultrasound generation are investigated. The results of this paper are helpful to understand the working principle of this laser-ultrasound method and improve the ultrasonic generation efficiency.

Degradation of the Bragg peak due to inhomogeneities.

PubMed

Urie, M; Goitein, M; Holley, W R; Chen, G T

1986-01-01

The rapid fall-off of dose at the end of range of heavy charged particle beams has the potential in therapeutic applications of sparing critical structures just distal to the target volume. Here we explored the effects of highly inhomogeneous regions on this desirable depth-dose characteristic. The proton depth-dose distribution behind a lucite-air interface parallel to the beam was bimodal, indicating the presence of two groups of protons with different residual ranges, creating a step-like depth-dose distribution at the end of range. The residual ranges became more spread out as the interface was angled at 3 degrees, and still more at 6 degrees, to the direction of the beam. A second experiment showed little significant effect on the distal depth-dose of protons having passed through a mosaic of teflon and lucite. Anatomic studies demonstrated significant effects of complex fine inhomogeneities on the end of range characteristics. Monoenergetic protons passing through the petrous ridges and mastoid air cells in the base of skull showed a dramatic degradation of the distal Bragg peak. In beams with spread out Bragg peaks passing through regions of the base of skull, the distal fall-off from 90 to 20% dose was increased from its nominal 6 to well over 32 mm. Heavy ions showed a corresponding degradation in their ends of range. In the worst case in the base of skull region, a monoenergetic neon beam showed a broadening of the full width at half maximum of the Bragg peak to over 15 mm (compared with 4 mm in a homogeneous unit density medium). A similar effect was found with carbon ions in the abdomen, where the full width at half maximum of the Bragg peak (nominally 5.5 mm) was found to be greater than 25 mm behind gas-soft-tissue interfaces. We address the implications of these data for dose computation with heavy charged particles.

Structural analysis and testing of a carbon-composite wing using fiber Bragg gratings

NASA Astrophysics Data System (ADS)

Nicolas, Matthew James

The objective of this study was to determine the deflected wing shape and the out-of-plane loads of a large-scale carbon-composite wing of an ultralight aerial vehicle using Fiber Bragg Grating (FBG) technology. The composite wing was instrumented with an optical fiber on its top and bottom surfaces positioned over the main spar, resulting in approximately 780 strain sensors bonded to the wings. The strain data from the FBGs was compared to that obtained from four conventional strain gages, and was used to obtain the out-of-plane loads as well as the wing shape at various load levels using NASA-developed real-time load and displacement algorithms. The composite wing measured 5.5 meters and was fabricated from laminated carbon uniaxial and biaxial prepreg fabric with varying laminate ply patterns and wall thickness dimensions. A three-tier whiffletree system was used to load the wing in a manner consistent with an in-flight loading condition.

Designing a range modulator wheel to spread-out the Bragg peak for a passive proton therapy facility

NASA Astrophysics Data System (ADS)

Jia, S. Bijan; Romano, F.; Cirrone, Giuseppe A. P.; Cuttone, G.; Hadizadeh, M. H.; Mowlavi, A. A.; Raffaele, L.

2016-01-01

In proton beam therapy, a Spread-Out Bragg peak (SOBP) is used to establish a uniform dose distribution in the target volume. In order to create a SOBP, several Bragg peaks of different ranges, corresponding to different entrance energies, with certain intensities (weights) should be combined each other. In a passive beam scattering system, the beam is usually extracted from a cyclotron at a constant energy throughout a treatment. Therefore, a SOBP is produced by a range modulator wheel, which is basically a rotating wheel with steps of variable thicknesses, or by using the ridge filters. In this study, we used the Geant4 toolkit to simulate a typical passive scattering beam line. In particular, the CATANA transport beam line of INFN Laboratori Nazionali del Sud (LNS) in Catania has been reproduced in this work. Some initial properties of the entrance beam have been checked by benchmarking simulations with experimental data. A class dedicated to the simulation of the wheel modulators has been implemented. It has been designed in order to be easily modified for simulating any desired modulator wheel and, hence, any suitable beam modulation. By using some auxiliary range-shifters, a set of pristine Bragg peaks was obtained from the simulations. A mathematical algorithm was developed, using the simulated pristine dose profiles as its input, to calculate the weight of each pristine peak, reproduce the SOBP, and finally generate a flat dose distribution. Therefore, once the designed modulator has been realized, it has been tested at CATANA facility, comparing the experimental data with the simulation results.

Multiple nonlinear Bragg diffraction of femtosecond laser pulses in a {\\chi^{(2)}} photonic lattice with hexagonal domains

NASA Astrophysics Data System (ADS)

Vyunishev, A. M.; Arkhipkin, V. G.; Baturin, I. S.; Akhmatkhanov, A. R.; Shur, V. Ya; Chirkin, A. S.

2018-04-01

The frequency doubling of femtosecond laser pulses in a two-dimensional (2D) rectangular nonlinear photonic lattice with hexagonal domains is studied experimentally and theoretically. The broad fundamental spectrum enables frequency conversion under nonlinear Bragg diffraction for a series of transverse orders at a fixed longitudinal quasi-phase-matching order. The consistent nonstationary theory of the frequency doubling of femtosecond laser pulses is developed using the representation based on the reciprocal lattice of the structure. The calculated spatial distribution of the second-harmonic spectral intensity agrees well with the experimental data. The condition for multiple nonlinear Bragg diffraction in a 2D nonlinear photonic lattice is offered. The hexagonal shape of the domains contributes to multibeam second harmonic excitation. The maximum conversion efficiency for a series of transverse orders in the range 0.01%-0.03% is obtained.

Distributed sensing of Composite Over-wrapped Pressure Vessel using Fiber-Bragg Gratings at Ambient and Cryogenic Temperatures

NASA Technical Reports Server (NTRS)

Grant, Joseph

2005-01-01

Fiber Bragg gratings are use to monitor the structural properties of composite pressure vessels. These gratings optically inscribed into the core of a single mode fiber are used as a tool to monitor the stress strain relation in laminate structure. The fiber Bragg sensors are both embedded within the composite laminates and bonded to the surface of the vessel with varying orientations with respect to the carbon fiber in the epoxy matrix. The response of these fiber-optic sensors is investigated by pressurizing the cylinder up to its burst pressure of around 2800 psi. This is done at both ambient and cryogenic temperatures using water and liquid nitrogen. The recorded response is compared with the response from conventional strain gauge also present on the vessel. Additionally, several vessels were tested that had been damaged to simulate different type of events, such as cut tow, delimitation and impact damage.

Distributed Sensing of Composite Over-wrapped Pressure Vessel Using Fiber-Bragg Gratings at Ambient and Cryogenic Temperatures

NASA Technical Reports Server (NTRS)

Grant, Joseph

2004-01-01

Fiber Bragg gratings are use to monitor the structural properties of composite pressure vessels. These gratings optically inscribed into the core of a single mode fiber are used as a tool to monitor the stress strain relation in laminate structure. The fiber Bragg sensors are both embedded within the composite laminates and bonded to the surface of the vessel with varying orientations with respect to the carbon fiber in the epoxy matrix. The response of these fiber-optic sensors is investigated by pressurizing the cylinder up to its burst pressure of around 2800 psi. This is done at both ambient and cryogenic temperatures using water and liquid nitrogen. The recorded response is compared with the response from conventional strain gauge also present on the vessel. Additionally, several vessels were tested that had been damaged to simulate different type of events, such as cut tow, delimitation and impact damage.

Research of pressure sensor based on the fiber Bragg grating for permanent downwell monitoring application

NASA Astrophysics Data System (ADS)

Liu, Lina; Long, Pin; Liu, Tiegen

2004-11-01

Timely, accurate and reliable pressure information about how the reservoir is performing is an important component to optimizing oil yield and production rates. This paper reviews the use of fiber optical pressure sensor for downhole monitoring in the oil industry. Several types of pressure transducer with different characteristics have been introduced. Due to their multiplexing capabilities and versatility ,the use of Bragg grating sensors appears to be particularly suited for this application. A sensor for accurate and long term fluid pressure monitoring based on optical fiber Bragg gratings(FBGs) is developed. The sensor converts fluid pressure into optical fiber strain by means of a mechanical transducer to enhance its sensitivity to pressure. It can also implement distributed or multiplexed sensing. The sensor operation is studied at pressure up to 100 Mpa(1000bar) and the tested temperature to ~175°. It is possible to be used in the well.

Weakly modulated silicon-dioxide-cladding gratings for silicon waveguide Fabry-Pérot cavities.

PubMed

Grote, Richard R; Driscoll, Jeffrey B; Biris, Claudiu G; Panoiu, Nicolae C; Osgood, Richard M

2011-12-19

We show by theory and experiment that silicon-dioxide-cladding gratings for Fabry-Pérot cavities on silicon-on-insulator channel ("wire") waveguides provide a low-refractive-index perturbation, which is required for several important integrated photonics components. The underlying refractive index perturbation of these gratings is significantly weaker than that of analogous silicon gratings, leading to finer control of the coupling coefficient κ. Our Fabry-Pérot cavities are designed using the transfer-matrix method (TMM) in conjunction with the finite element method (FEM) for calculating the effective index of each waveguide section. Device parameters such as coupling coefficient, κ, Bragg mirror stop band, Bragg mirror reflectivity, and quality factor Q are examined via TMM modeling. Devices are fabricated with representative values of distributed Bragg reflector lengths, cavity lengths, and propagation losses. The measured transmission spectra show excellent agreement with the FEM/TMM calculations.

Neurosurgical applications of ion beams

NASA Astrophysics Data System (ADS)

Fabrikant, Jacob I.; Levy, Richard P.; Phillips, Mark H.; Frankel, Kenneth A.; Lyman, John T.

1989-04-01

The program at Donner Pavilion has applied nuclear medicine research to the diagnosis and radiosurgical treatment of life-threatening intracranial vascular disorders that affect more than half a million Americans. Stereotactic heavy-charged-particle Bragg peak radiosurgery, using narrow beams of heavy ions, demonstrates superior biological and physical characteristics in brain over X-and γ-rays, viz., improved dose distribution in the Bragg peak and sharp lateral and distal borders and less scattering of the beam. Examination of CNS tissue response and alteration of cerebral blood-flow dynamics related to heavy-ion Bragg peak radiosurgery is carried out using three-dimensional treatment planning and quantitative imaging utilizing cerebral angiography, computerized tomography (CT), magnetic resonance imaging (MRI), cine-CT, xenon X-ray CT and positron emission tomography (PET). Also under examination are the physical properties of narrow heavy-ion beams for improving methods of dose delivery and dose distribution and for establishing clinical RBE/LET and dose-response relationships for human CNS tissues. Based on the evaluation and treatment with stereotactically directed narrow beams of heavy charged particles of over 300 patients, with cerebral angiography, CT scanning and MRI and PET scanning of selected patients, plus extensive clinical and neuroradiological followup, it appears that Stereotactic charged-particle Bragg peak radiosurgery obliterates intracranial arteriovenous malformations or protects against rebleeding with reduced morbidity and no mortality. Discussion will include the method of evaluation, the clinical research protocol, the Stereotactic neuroradiological preparation, treatment planning, the radiosurgery procedure and the protocol for followup. Emphasis will be placed on the neurological results, including the neuroradiological and clinical response and early and late delayed injury in brain leading to complications (including vasogenic edema, arterial occlusion, venous thrombosis and radiation necrosis). Clinical results in both children and adults will be illustrated and health outcome will be related to the advantages of charged-particle treatment planning, the radiosurgical procedure, dose distribution and dose localization.

Electrical investigations of hybrid OLED microcavity structures with novel encapsulation methods

NASA Astrophysics Data System (ADS)

Meister, Stefan; Brückner, Robert; Fröb, Hartmut; Leo, Karl

2016-04-01

An electrical driven organic solid state laser is a very challenging goal which is so far well beyond reach. As a step towards realization, we monolithically implemented an Organic Light Emitting Diode (OLED) into a dielectric, high quality microcavity (MC) consisting of two Distributed Bragg Reectors (DBR). In order to account for an optimal optical operation, the OLED structure has to be adapted. Furthermore, we aim to excite the device not only electrically but optically as well. Different OLED structures with an emission layer consisting of Alq3:DCM (2 wt%) were investigated. The External Quantum Efficiencies (EQE) of this hybrid structures are in the range of 1-2 %, as expected for this material combination. Including metal layers into a MC is complicated and has a huge impact on the device performance. Using Transfer-Matrix-Algorithm (TMA) simulations, the best positions for the metal electrodes are determined. First, the electroluminescence (EL) of the adjusted OLED structure on top of a DBR is measured under nitrogen atmosphere. The modes showed quality factors of Q = 60. After the deposition of the top DBR, the EL is measured again and the quality factors increased up to Q = 600. Considering the two 25-nm-thick-silver contacts a Q-factor of 600 is very high. The realization of a suitable encapsulation method is important. Two approaches were successfully tested. The first method is based on the substitution of a DBR layer with a layer produced via Atomic Layer Deposition (ALD). The second method uses a 0.15-mm-thick cover glass glued on top of the DBR with a 0.23-μm-thick single-component glue layer. Due to the working encapsulation, it is possible to investigate the sample under ambient conditions.

Proposed linear energy transfer areal detector for protons using radiochromic film.

PubMed

Mayer, Rulon; Lin, Liyong; Fager, Marcus; Douglas, Dan; McDonough, James; Carabe, Alejandro

2015-04-01

Radiation therapy depends on predictably and reliably delivering dose to tumors and sparing normal tissues. Protons with kinetic energy of a few hundred MeV can selectively deposit dose to deep seated tumors without an exit dose, unlike x-rays. The better dose distribution is attributed to a phenomenon known as the Bragg peak. The Bragg peak is due to relatively high energy deposition within a given distance or high Linear Energy Transfer (LET). In addition, biological response to radiation depends on the dose, dose rate, and localized energy deposition patterns or LET. At present, the LET can only be measured at a given fixed point and the LET spatial distribution can only be inferred from calculations. The goal of this study is to develop and test a method to measure LET over extended areas. Traditionally, radiochromic films are used to measure dose distribution but not for LET distribution. We report the first use of these films for measuring the spatial distribution of the LET deposited by protons. The radiochromic film sensitivity diminishes for large LET. A mathematical model correlating the film sensitivity and LET is presented to justify relating LET and radiochromic film relative sensitivity. Protons were directed parallel to radiochromic film sandwiched between solid water slabs. This study proposes the scaled-normalized difference (SND) between the Treatment Planning system (TPS) and measured dose as the metric describing the LET. The SND is correlated with a Monte Carlo (MC) calculation of the LET spatial distribution for a large range of SNDs. A polynomial fit between the SND and MC LET is generated for protons having a single range of 20 cm with narrow Bragg peak. Coefficients from these fitted polynomial fits were applied to measured proton dose distributions with a variety of ranges. An identical procedure was applied to the protons deposited from Spread Out Bragg Peak and modulated by 5 cm. Gamma analysis is a method for comparing the calculated LET with the LET measured using radiochromic film at the pixel level over extended areas. Failure rates using gamma analysis are calculated for areas in the dose distribution using parameters of 25% of MC LET and 3 mm. The processed dose distributions find 5%-10% failure rates for the narrow 12.5 and 15 cm proton ranges and 10%-15% for proton ranges of 15, 17.5, and 20 cm and modulated by 5 cm. It is found through gamma analysis that the measured proton energy deposition in radiochromic film and TPS can be used to determine LET. This modified film dosimetry provides an experimental areal LET measurement that can verify MC calculations, support LET point measurements, possibly enhance biologically based proton treatment planning, and determine the polymerization process within the radiochromic film.

Health monitoring of carbon cantilever using femtosecond laser inscribed FBG array in gradient-index CYTOP polymer fibre

NASA Astrophysics Data System (ADS)

Theodosiou, Antreas; Kalli, Kyriacos; Komodromos, Michael

2017-04-01

We report on the femtosecond laser inscription of a fibre Bragg grating array in multimode, gradient-index, CYTOP polymer optical fibre and its demonstration as a quasi-distributed sensor for cantilever health monitoring measurements. We exploit the key advantage of polymer optical fibres, having a significantly lower Young's modulus compared with silica fibres, for vibration measurements. We also modify the typical multi-mode Bragg grating spectrum through control of the femtosecond laser inscription process, thereby producing gratings having single peak wavelength spectra. The sensor array is used to recover the time-dependent, wavelength response from each Bragg grating sensor and extract the mode shape of the beam. The mode shapes of the beam were used to observe "damage" introduced to the cantilever by adding masses to its surface; adjusting the level of damage by using different weights and placing them at different point across the beam. We show that health monitoring measurements are feasible with polymer based fibre Bragg gratings. The accurate and rapid detection of damage points on structural beams and the damage level is an important parameter for improved maintenance and servicing of beams under load and for the prevention of long-term damage.

An MCNPX2.7.0 study of Bragg peak degradation owing to density heterogeneity patterns for a CGMH therapeutic proton beam

NASA Astrophysics Data System (ADS)

Chao, Tsi-Chian; Tsai, Yi-Chun; Chen, Shih-Kuan; Wu, Shu-Wei; Tung, Chuan-Jong; Hong, Ji-Hong; Wang, Chun-Chieh; Lee, Chung-Chi

2017-08-01

The purpose of this study was to investigate the density heterogeneity pattern as a factor affecting Bragg peak degradation, including shifts in Bragg peak depth (ZBP), distal range (R80 and R20), and distal fall-off (R80-R20) using Monte Carlo N-Particles, eXtension (MCNPX). Density heterogeneities of different patterns with increasing complexity were placed downstream of commissioned proton beams at the Proton and Radiation Therapy Centre of Chang Gung Memorial Hospital, including one 150 MeV wobbling broad beam (10×10 cm2) and one 150 MeV proton pencil beam (FWHM of cross-plane=2.449 cm, FWHM of in-plane=2.256 cm). MCNPX 2.7.0 was used to model the transport and interactions of protons and secondary particles in density heterogeneity patterns and water using its repeated structure geometry. Different heterogeneity patterns were inserted into a 21×21×20 cm3 phantom. Mesh tally was used to track the dose distribution when the proton beam passed through the different density heterogeneity patterns. The results show that different heterogeneity patterns do cause different Bragg peak degradations owing to multiple Coulomb scattering (MCS) occurring in the density heterogeneities. A trend of increasing R20 and R80-R20 with increasing geometry complexity was observed. This means that Bragg peak degradation is mainly caused by the changes to the proton spectrum owing to MCS in the density heterogeneities. In contrast, R80 did not change considerably with different heterogeneity patterns, which indicated that the energy spectrum has only minimum effects on R80. Bragg peak degradation can occur both for a broad proton beam and a pencil beam, but is less significant for the broad beam.

Centre of mass determination based on an optical weighing machine using fiber Bragg gratings

NASA Astrophysics Data System (ADS)

Oliveira, Rui; Roriz, Paulo; Marques, Manuel B.; Frazão, Orlando

2015-09-01

The purpose of the present work was to construct a weighing machine based on fiber Bragg gratings (FBGs) for the location of the 2D coordinates of the center of gravity (COG) of objects with complex geometry and density distribution. The apparatus consisted of a rigid equilateral triangular platform mounted on three supports at its vertices, two of them having cantilevers instrumented with FBGs. As an example, two femur bone models, one with and one without a hip stem prosthesis, are used to discuss the changing of the COM caused by the implementation of the prosthesis.

Enhanced optical gain clamping for upstream packet based traffic on hybrid WDM/TDM-PON using fiber Bragg grating

NASA Astrophysics Data System (ADS)

Neto, B.; Klingler, A.; Reis, C.; Dionísio, R. P.; Nogueira, R. N.; Teixeira, A. L. J.; André, P. S.

2011-03-01

In this paper, we propose a method to mitigate the temporal power transients arising from Erbium doped fiber amplifiers (EDFAs) on packeted/bursty scenario. The technique, applicable on hybrid WDM/TDM-PON for extended reach, is based on a low power clamping provided by a distributed feedback (DFB) laser and a fiber Bragg grating (FBG). An improvement in the data signal Q factor was achieved keeping the clamping control signal with a low power, accompanied by a maximum reduction in the gain excursion of 1.12 dB.

Experimental demonstration of a ferroelectric liquid crystal tunable filter for fast demodulation of FBG sensors

NASA Astrophysics Data System (ADS)

Mathews, Sunish; Semenova, Yuliya; Rajan, Ginu; Farrell, Gerald

2009-05-01

A discretely tunable Surface-Stabilized Ferroelectric Liquid Crystal based Lyot Filter, with tuning speeds in the order of microseconds, is demonstrated experimentally as a channel dropper for the demodulation of multiple Fibre Bragg Grating sensors. The 3-stage Lyot Filter designed and experimentally verified can be used together with the high-speed ratiometric wavelength measurement system employing a fibre bend loss edge filter. Such systems can be used for the demodulation of distributed Fibre Bragg Grating sensors employed in applications such as structural monitoring, industrial sensing and haptic telerobotic surgical systems.

Circularly polarized lasing in chiral modulated semiconductor microcavity with GaAs quantum wells

NASA Astrophysics Data System (ADS)

Demenev, A. A.; Kulakovskii, V. D.; Schneider, C.; Brodbeck, S.; Kamp, M.; Höfling, S.; Lobanov, S. V.; Weiss, T.; Gippius, N. A.; Tikhodeev, S. G.

2016-10-01

We report close to circularly polarized lasing at ℏ ω = 1.473 and 1.522 eV from an AlAs/AlGaAs Bragg microcavity, with 12 GaAs quantum wells in the active region and chirally etched upper distributed Bragg refractor under optical pump at room temperature. The advantage of using the chiral photonic crystal with a large contrast of dielectric permittivities is its giant optical activity, allowing to fabricate a very thin half-wave plate, with a thickness of the order of the emitted light wavelength, and to realize the monolithic control of circular polarization.

Orientation-Dependent Displacement Sensor Using an Inner Cladding Fiber Bragg Grating

PubMed Central

Yang, Tingting; Qiao, Xueguang; Rong, Qiangzhou; Bao, Weijia

2016-01-01

An orientation-dependent displacement sensor based on grating inscription over a fiber core and inner cladding has been demonstrated. The device comprises a short piece of multi-cladding fiber sandwiched between two standard single-mode fibers (SMFs). The grating structure is fabricated by a femtosecond laser side-illumination technique. Two well-defined resonances are achieved by the downstream both core and cladding fiber Bragg gratings (FBGs). The cladding resonance presents fiber bending dependence, together with a strong orientation dependence because of asymmetrical distribution of the “cladding” FBG along the fiber cross-section. PMID:27626427

Intracore and extracore examination of fiber gratings with coherent detection

NASA Astrophysics Data System (ADS)

Froggatt, Mark Earl

2001-06-01

This thesis introduces several new methods of measurement to aid in the production and evaluation of Bragg gratings in optical fiber. Five measurements are described: UV fringe visualization for grating production, weak grating measurement for distributed sensing, strong grating measurement for telecommunication applications, second harmonic grating measurement for grating chirp assessment, and grating visualization using radiation diffraction from strong Bragg gratings. The weak grating measurement for distributed strain sensing is a summary of work published prior to beginning the thesis research, and is provided for background purposes. The UV fringe visualization is accomplished by using a phase mask very close to the plane of the fiber to diffract the incoming beams used to write the Bragg grating into nearly parallel alignment, leading to macroscopic fringes indicative of the phase, frequency, amplitude, and contrast of the microscopic fringes incident on the fiber. The weak grating measurement uses Optical Frequency Domain Reflectometry (OFDR) to measure the spatial distribution of the coupling strength of weak gratings. Included in the description of the OFDR technique are recent advances in the precision monitoring of the emission wavelength of tunable lasers. The precise monitoring of wavelength is critical to the functioning of OFDR. The strong grating measurement is based on a modified form of OFDR and an analysis of the problem in the time and frequency domains to produce accurate measurements of both the reflection and transmission Transfer Functions for Bragg gratings. This measurement technique is also applicable to a wide variety of optical fiber devices, and is shown to be scalable to multiple port devices. The second-harmonic measurement for grating chirp analysis is similar to the weak grating measurement, but it was done at a wavelength resonant with the second- harmonic grating in the fiber-780 nm for 1550 nm reflection gratings. The second-harmonic grating results from nonlinearities in the grating growth process and, due to the great sensitivity of OFDR, is detectable for almost all fiber gratings. The grating visualization also uses half-wavelength (780 nm) illumination of the grating through the core. This technique uses the diffraction of light into the radiation modes to make the grating in the fiber externally visible. By operating near the perpendicular radiation condition, and introducing coherent counter- propagating light, the spatial frequency and the amplitude of the grating as functions of distance along the fiber can be measured. To better understand the radiation from Bragg gratings, a technique known as the Volume Current Method (VCM) was used to derive an expression for the radiation from a Bragg grating for all of the LP fiber modes.

High-power green and blue electron-beam pumped surface-emitting lasers using dielectric and epitaxial distributed Bragg reflectors

DOE Office of Scientific and Technical Information (OSTI.GOV)

Klein, T., E-mail: tklein@ifp.uni-bremen.de; Klembt, S.; Institut Néel, Université Grenoble Alpes and CNRS, B.P. 166, 38042 Grenoble

2015-03-21

ZnSe-based electron-beam pumped vertical-cavity surface-emitting lasers for the green (λ = 530 nm) and blue (λ = 462 nm) spectral region have been realized. Structures with and without epitaxial bottom distributed Bragg reflector have been fabricated and characterized. The samples consist of an active region containing 20 quantum wells with a cavity length varying between an optical thickness of 10 λ to 20 λ. The active material is ZnCdSSe in case of the green devices and ZnSe for the blue ones. Room temperature single mode lasing for structures with and without epitaxial bottom mirror with a maximum output power up to 5.9 W (green) and 3.3 W (blue)more » is achieved, respectively.« less

Optical generation of millimeter-wave pulses using a fiber Bragg grating in a fiber-optics system.

PubMed

Ye, Qing; Qu, Ronghui; Fang, Zujie

2007-04-10

A scheme is proposed to transform an optical pulse into a millimeter-wave frequency modulation pulse by using a weak fiber Bragg grating (FBG) in a fiber-optics system. The Fourier transformation method is used to obtain the required spectrum response function of the FBG for the Gaussian pulse, soliton pulse, and Lorenz shape pulse. On the condition of the first-order Born approximation of the weak fiber grating, the relation of the refractive index distribution and the spectrum response function of the FBG satisfies the Fourier transformation, and the corresponding refractive index distribution forms are obtained for single-frequency modulation and linear-frequency modulation millimeter-wave pulse generation. The performances of the designed fiber gratings are also studied by a numerical simulation method for a supershort pulse transmission.

All optical mode controllable Er-doped random fiber laser with distributed Bragg gratings.

PubMed

Zhang, W L; Ma, R; Tang, C H; Rao, Y J; Zeng, X P; Yang, Z J; Wang, Z N; Gong, Y; Wang, Y S

2015-07-01

An all-optical method to control the lasing modes of Er-doped random fiber lasers (RFLs) is proposed and demonstrated. In the RFL, an Er-doped fiber (EDF) recoded with randomly separated fiber Bragg gratings (FBG) is used as the gain medium and randomly distributed reflectors, as well as the controllable element. By combining random feedback of the FBG array and Fresnel feedback of a cleaved fiber end, multi-mode coherent random lasing is obtained with a threshold of 14 mW and power efficiency of 14.4%. Moreover, a laterally-injected control light is used to induce local gain perturbation, providing additional gain for certain random resonance modes. As a result, active mode selection of the RFL is realized by changing locations of the laser cavity that is exposed to the control light.

Adsorption and desorption characteristics of gradient distributed Bragg reflector porous silicon layers.

PubMed

Um, Sungyong; Lee, Sung Gi; Woo, Hee-Gweon; Cho, Sungdong; Sohn, Honglae

2013-01-01

Adsorption and desorption characteristics of gradient distributed Bragg reflector (DBR) porous silicon (PSi) were investigated under the exposure of organic vapors. Gradient DBR PSi whose average pore size decreased as the lateral distance from the Pt electrode increased was generated by using an asymmetric etching configuration. The reflection resonances were measured as a function of lateral distance from a point closest to the plate Pt electrode to a position on the silicon surface. Two types of gradient DBR PSi (H- and HO-terminated gradient DBR PSi) were used in this study. The detection of volatile organic compounds (VOCs) using the gradient DBR PSi had been achieved. When the vapor of VOCs condensed in the nanopores, the gradient DBR PSi modified with hydrophobic and hydrophilic functionality exhibited different pore adsorption and desorption characteristics.

All-nitride AlxGa1−xN:Mn/GaN distributed Bragg reflectors for the near-infrared

PubMed Central

Capuzzo, Giulia; Kysylychyn, Dmytro; Adhikari, Rajdeep; Li, Tian; Faina, Bogdan; Tarazaga Martín-Luengo, Aitana; Bonanni, Alberta

2017-01-01

Since the technological breakthrough prompted by the inception of light emitting diodes based on III-nitrides, these material systems have emerged as strategic semiconductors not only for the lighting of the future, but also for the new generation of high-power electronic and spintronic devices. While III-nitride optoelectronics in the visible and ultraviolet spectral range is widely established, all-nitride efficient devices in the near-infrared (NIR) are still wanted. Here, through a comprehensive protocol of design, modeling, epitaxial growth and in-depth characterization, we develop AlxGa1−xN:Mn/GaN NIR distributed Bragg reflectors and we show their efficiency in combination with GaN:(Mn,Mg) layers containing Mn-Mgk complexes optically active in the near-infrared range of wavelengths. PMID:28198432

RETRACTED ARTICLE: Quasi-distributed fiber bragg grating array sensor for furnace applications

NASA Astrophysics Data System (ADS)

Reddy, P. Saidi; Sai Prasad, R. L. N.; Sen Gupta, D.; Sai Shankar, M.; Srimannarayana, K.; Ravinder Reddy, P.

2012-05-01

An experimental work on distributed temperature sensing making use of the fiber Bragg grating (FBG) array sensor for possible applications in the monitoring of the temperature profile in high temperature boilers is presented. A special sensor has been designed for this purpose which consists of four FBGs (of wavelengths λ B1 =1545.8 nm, λ B2 =1547 nm, λ B3 =1550.8 nm, λ B4 =1555.5 nm at 30 °C) written in the hydrogen-loaded fiber in line. All the FBGs are encapsulated inside a stainless steel tube using the rigid probe technique for avoiding micro cracks. The spatial distribution of the temperature profile inside a prototype boiler was measured experimentally both in horizontal and vertical directions employing the above sensor, and the results are presented. Further, the finite element simulation has been carried out by using ANSYS R11 software to predict temperature contours in the boiler, and the experimental and predicted results were found to be closely matching.

Optical Characterizations of VCSEL for Emission at 850 nm with Al Oxide Confinement Layers

NASA Astrophysics Data System (ADS)

Mokhtari, Merwan; Pagnod-Rossiaux, Philippe; Laruelle, Francois; Landesman, Jean-Pierre; Moreac, Alain; Levallois, Christophe; Cassidy, Daniel T.

2018-03-01

In-plane micro-photoluminescence (μ-PL) and micro-reflectivity measurements have been performed at room temperature by optical excitation perpendicular to the surface of two different structures: a complete vertical surface-emitting laser (VCSEL) structure and a VCSEL without the upper p-type distributed Bragg reflector (P-DBR). The two structures were both laterally oxidized and measurements were made on the top of oxidized and unoxidized regions. We show that, since the photoluminescence (PL) spectra consist of the cumulative effect of InGaAs/AlGaAs multi-quantum wells (MQWs) luminescence and interferences in the DBR, the presence or not of the P-DBR and oxide layers can significantly modify the spectrum. μ-PL mapping performed on full VCSEL structures clearly shows oxidized and unoxidized regions that are not resolved with visible light optical microscopy. Finally, preliminary measurements of the degree of polarization (DOP) of the PL have been made on a complete VCSEL structure before and after an oxidation process. We obtain an image of DOP measured by polarization-resolved μ-PL. These measurements allow us to evaluate the main components of strain.

Resonant-enhanced full-color emission of quantum-dot-based micro LED display technology.

PubMed

Han, Hau-Vei; Lin, Huang-Yu; Lin, Chien-Chung; Chong, Wing-Cheung; Li, Jie-Ru; Chen, Kuo-Ju; Yu, Peichen; Chen, Teng-Ming; Chen, Huang-Ming; Lau, Kei-May; Kuo, Hao-Chung

2015-12-14

Colloidal quantum dots which can emit red, green, and blue colors are incorporated with a micro-LED array to demonstrate a feasible choice for future display technology. The pitch of the micro-LED array is 40 μm, which is sufficient for high-resolution screen applications. The method that was used to spray the quantum dots in such tight space is called Aerosol Jet technology which uses atomizer and gas flow control to obtain uniform and controlled narrow spots. The ultra-violet LEDs are used in the array to excite the red, green and blue quantum dots on the top surface. To increase the utilization of the UV photons, a layer of distributed Bragg reflector was laid down on the device to reflect most of the leaked UV photons back to the quantum dot layers. With this mechanism, the enhanced luminous flux is 194% (blue), 173% (green) and 183% (red) more than that of the samples without the reflector. The luminous efficacy of radiation (LER) was measured under various currents and a value of 165 lm/Watt was recorded.

Upstream vertical cavity surface-emitting lasers for fault monitoring and localization in WDM passive optical networks

NASA Astrophysics Data System (ADS)

Wong, Elaine; Zhao, Xiaoxue; Chang-Hasnain, Connie J.

2008-04-01

As wavelength division multiplexed passive optical networks (WDM-PONs) are expected to be first deployed to transport high capacity services to business customers, real-time knowledge of fiber/device faults and the location of such faults will be a necessity to guarantee reliability. Nonetheless, the added benefit of implementing fault monitoring capability should only incur minimal cost associated with upgrades to the network. In this work, we propose and experimentally demonstrate a fault monitoring and localization scheme based on a highly-sensitive and potentially low-cost monitor in conjunction with vertical cavity surface-emitting lasers (VCSELs). The VCSELs are used as upstream transmitters in the WDM-PON. The proposed scheme benefits from the high reflectivity of the top distributed Bragg reflector (DBR) mirror of optical injection-locked (OIL) VCSELs to reflect monitoring channels back to the central office for monitoring. Characterization of the fault monitor demonstrates high sensitivity, low bandwidth requirements, and potentially low output power. The added advantage of the proposed fault monitoring scheme incurs only a 0.5 dB penalty on the upstream transmissions on the existing infrastructure.

Measurement of strain distribution in bonded joints by fiber Bragg gratings

NASA Astrophysics Data System (ADS)

Guemes, J. Alfredo; Diaz-Carrillo, Sebastian; Menendez, Jose M.

1998-07-01

Due to the small dimensions of the adhesive layer, the high non-uniformity of the strain field and the non linear elastic behavior of the adhesive material, the strain distribution at an adhesive joint can be predicted by FEM, but can not be experimentally obtained with classical approaches; only non standard procedures like Moire interferometry, or special artifacts like KGR extensometers may afford some insights on the behavior of the adhesive. Due to their small size, ensuring low perturbation of the strain field, and their innate ability to measure strain and strain gradient along the sensor, fiber Bragg gratings offer a good opportunity to solve this problem, and it is a good example of situations that may benefit from these new sensors. Fiber Bragg gratings may be placed or at the interface, within the adhesive layer, or embedded at the adherents, if these were made of composite material. Tests may be run at different temperatures, changing the adhesive characteristics from brittle to pseudoplastic without additional difficulties. When loading the joint, the strain field is obtained by analyzing the distorted spectrum of the reflected light pulse; the algorithm for doing it has already been published. A comparison with theoretical results is done, and the validity and utility of these sensors for this and similar applications is demonstrated.

Ultra-compact, flat-top demultiplexer using anti-reflection contra-directional couplers for CWDM networks on silicon.

PubMed

Shi, Wei; Yun, Han; Lin, Charlie; Greenberg, Mark; Wang, Xu; Wang, Yun; Fard, Sahba Talebi; Flueckiger, Jonas; Jaeger, Nicolas A F; Chrostowski, Lukas

2013-03-25

Wavelength-division-multiplexing (WDM) networks with wide channel grids and bandwidths are promising for low-cost, low-power optical interconnects. Wide-bandwidth, single-band (i.e., no free-spectral range) add-drop filters have been developed on silicon using anti-reflection contra-directional couplers with out-of-phase Bragg gratings. Using such filter components, we demonstrate a 4-channel, coarse-WDM demultiplexer with flat passbands of up to 13 nm and an ultra-compact size of 1.2 × 10(-3) mm(2).

Temporal Response of Dilute Nitride Multi-Quantum-Well Vertical Cavity Enhanced Photodetector

NASA Astrophysics Data System (ADS)

Nordin, M. S.; Sarcan, F.; Gunes, M.; Boland-Thoms, A.; Erol, A.; Vickers, A. J.

2018-01-01

The temporal response characteristics of a GaInNAs-based vertical resonant cavity enhanced photodetector device are presented for operation at λ ≈ 1.3 μm. The absorption layers of the device are composed of nine 7-nm-thick Ga0.65In0.35N0.02As0.98 quantum wells and are sandwiched between top and bottom AlGaAs/GaAs distributed Bragg reflectors (DBRs). The temperature dependence of the transient photoconductivity (TPC) under different light intensities and bias voltages is reported. Photoluminescence measurements were also performed on structures with and without the top DBR to determine their optical response under continuous illumination. The response time was measured using excitation from a 1047-nm pulsed neodymium-doped yttrium lithium fluoride laser with pulse width of 500 ps and repetition rate of 1 kHz. The rise time of the TPC was 2.27 ns at T = 50 K, decreasing to 1.79 ns at T = 300 K. The TPC decay time was 25.44 ns at T = 50 K, decreasing to 16.58 ns at T = 300 K. With detectivity of 2.28 × 10^{10} {cm}√ {Hz} / {W} and noise-equivalent power of 2.45 × 10^{ - 11} {W/}√ {Hz} , the proposed device is faster and more sensitive with better signal-to-noise ratio compared with other GaInNAs-based resonant cavity enhanced photodetectors (RCEPDs) for operation at 1.3 μm.

SU-E-T-121: Analyzing the Broadening Effect On the Bragg Peak Due to Heterogeneous Geometries and Implementing User-Routines in the Monte-Carlo Code FLUKA in Order to Reduce Computation Time

DOE Office of Scientific and Technical Information (OSTI.GOV)

Baumann, K; Weber, U; Simeonov, Y

2015-06-15

Purpose: Aim of this study was to analyze the modulating, broadening effect on the Bragg Peak due to heterogeneous geometries like multi-wire chambers in the beam path of a particle therapy beam line. The effect was described by a mathematical model which was implemented in the Monte-Carlo code FLUKA via user-routines, in order to reduce the computation time for the simulations. Methods: The depth dose curve of 80 MeV/u C12-ions in a water phantom was calculated using the Monte-Carlo code FLUKA (reference curve). The modulating effect on this dose distribution behind eleven mesh-like foils (periodicity ∼80 microns) occurring in amore » typical set of multi-wire and dose chambers was mathematically described by optimizing a normal distribution so that the reverence curve convoluted with this distribution equals the modulated dose curve. This distribution describes a displacement in water and was transferred in a probability distribution of the thickness of the eleven foils using the water equivalent thickness of the foil’s material. From this distribution the distribution of the thickness of one foil was determined inversely. In FLUKA the heterogeneous foils were replaced by homogeneous foils and a user-routine was programmed that varies the thickness of the homogeneous foils for each simulated particle using this distribution. Results: Using the mathematical model and user-routine in FLUKA the broadening effect could be reproduced exactly when replacing the heterogeneous foils by homogeneous ones. The computation time was reduced by 90 percent. Conclusion: In this study the broadening effect on the Bragg Peak due to heterogeneous structures was analyzed, described by a mathematical model and implemented in FLUKA via user-routines. Applying these routines the computing time was reduced by 90 percent. The developed tool can be used for any heterogeneous structure in the dimensions of microns to millimeters, in principle even for organic materials like lung tissue.« less

Russian Activities in Space Photovoltaic Power Modules with Concentrators

NASA Technical Reports Server (NTRS)

Andreev, Vyacheslav M.; Rumyantsev, Valeri D.

2004-01-01

Space concentrator modules with point-and line-focus Fresnel lenses and with reflective parabolic troughs have been developed recently at Ioffe Physico-Technical Institute. PV receivers for these modules are based: on the single junction LPE and MOCVD AlGaAs/GaAs solar cells characterized by AM0 efficiencies of 23.5 - 24% at 20 - 50 suns and 24 - 24.75 at 50 - 200 suns; on the mechanically stacked tandem AlGaAs/GaAs-GaSb cells with efficiency of 27 - 28 at 20 - 100 suns. MOCVD AlGaAs/GaAs cells with internal Bragg reflector have shown a higher radiation resistance as compared to a traditional structure. Monolithic two-terminal tandems AlGaAs (top)-GaAs (bottom) for space application and GaSb (top) - InGaAsSb (bottom) for TRV application are under development as well.

Spatial distributions of dose enhancement around a gold nanoparticle at several depths of proton Bragg peak

NASA Astrophysics Data System (ADS)

Kwon, Jihun; Sutherland, Kenneth; Hashimoto, Takayuki; Shirato, Hiroki; Date, Hiroyuki

2016-10-01

Gold nanoparticles (GNPs) have been recognized as a promising candidate for a radiation sensitizer. A proton beam incident on a GNP can produce secondary electrons, resulting in an enhancement of the dose around the GNP. However, little is known about the spatial distribution of dose enhancement around the GNP, especially in the direction along the incident proton. The purpose of this study is to determine the spatial distribution of dose enhancement by taking the incident direction into account. Two steps of calculation were conducted using the Geant4 Monte Carlo simulation toolkit. First, the energy spectra of 100 and 195 MeV protons colliding with a GNP were calculated at the Bragg peak and three other depths around the peak in liquid water. Second, the GNP was bombarded by protons with the obtained energy spectra. Radial dose distributions were computed along the incident beam direction. The spatial distributions of the dose enhancement factor (DEF) and subtracted dose (Dsub) were then evaluated. The spatial DEF distributions showed hot spots in the distal radial region from the proton beam axis. The spatial Dsub distribution isotropically spread out around the GNP. Low energy protons caused higher and wider dose enhancement. The macroscopic dose enhancement in clinical applications was also evaluated. The results suggest that the consideration of the spatial distribution of GNPs in treatment planning will maximize the potential of GNPs.

Light trapping in thin film solar cells using textured photonic crystal

DOEpatents

Yi, Yasha [Somerville, MA; Kimerling, Lionel C [Concord, MA; Duan, Xiaoman [Amesbury, MA; Zeng, Lirong [Cambridge, MA

2009-01-27

A solar cell includes a photoactive region that receives light. A photonic crystal is coupled to the photoactive region, wherein the photonic crystal comprises a distributed Bragg reflector (DBR) for trapping the light.

Determination of the depth dose distribution of proton beam using PRESAGE TM dosimeter

NASA Astrophysics Data System (ADS)

Zhao, L.; Das, I. J.; Zhao, Q.; Thomas, A.; Adamovics, J.; Oldman, M.

2010-11-01

PRESAGETM dosimeter dosimeter has been proved useful for 3D dosimetry in conventional photon therapy and IMRT [1-5]. Our objective is to examine the use of PRESAGETM dosimeter for verification of depth dose distribution in proton beam therapy. Three PRESAGETM samples were irradiated with a 79 MeV un-modulated proton beam. Percent depth dose profile measured from the PRESAGETM dosimeter is compared with data obtained in a water phantom using a parallel plate Advanced Markus chamber. The Bragg-peak position determined from the PRESAGETM is within 2 mm compared to measurements in water. PRESAGETM shows a highly linear response to proton dose. However, PRESAGETM also reveals an underdosage around the Bragg peak position due to LET effects. Depth scaling factor and quenching correction factor need further investigation. Our initial result shows that PRESAGETM has promising dosimetric characteristics that could be suitable for proton beam dosimetry.

A contact vibration measurement sensor based on a distributed Bragg reflector fiber laser

NASA Astrophysics Data System (ADS)

Jin, Jie; Fang, Gan; Lyu, Chengang; Zhang, Shuai

2017-12-01

A new contact method to measure vibrations with a frequency range of about 30-110 Hz by a distributed Bragg reflector (DBR) fiber laser sensor, based on a beat frequency modulation, has been proposed. In order to demonstrate the plausibility for a DBR fiber sensor to detect vibrations lower than 110 Hz without any complex structures, it is encapsulated in a rectangular slice composed of an epoxy resin glue, with a Young’s modulus of about 2.9 GPa. In experiments, the packaged DBR fiber sensor is placed on a vibration platform to sense the vibration, with a commercial magnet-electrical vibration velocity transducer as a reference. Experimental results indicate that the single DBR fiber laser is able to measure the low-frequency vibration with a few tens of Hertz and several microns of amplitude, offering potential for a low-frequency vibration measurement.

Transport properties of doped AlP for the development of conductive AlP/GaP distributed Bragg reflectors and their integration into light-emitting diodes

NASA Astrophysics Data System (ADS)

Hestroffer, Karine; Sperlich, Dennis; Dadgostar, Shabnam; Golz, Christian; Krumland, Jannis; Masselink, William Ted; Hatami, Fariba

2018-05-01

The transport properties of n- and p-doped AlP layers grown by gas-source molecular beam epitaxy are investigated. n- and p-types of conductivities are achieved using Si and Be with peak room-temperature mobilities of 59.6 cm2/Vs and 65.0 cm2/Vs for electrons and holes, respectively. Si-doping results are then used for the design of n-doped AlP/GaP distributed Bragg reflectors (DBRs) with an ohmic resistance of about 7.5 ± 0.1 Ω. The DBRs are integrated as bottom mirrors in GaP-based light-emitting diodes (LEDs) containing InGaP/GaP quantum dots. The functionality of the LED structure and the influence of the DBRs on the InGaP/GaP electroluminescence spectra are demonstrated.

Suspended light-emitting diode featuring a bottom dielectric distributed Bragg reflector

NASA Astrophysics Data System (ADS)

Cai, Wei; Wang, Wei; Zhu, Bingcheng; Gao, Xumin; Zhu, Guixia; Yuan, Jialei; Wang, Yongjin

2018-01-01

Here, we propose, fabricate and characterize the light manipulation of a suspended-membrane InGaN/GaN multiple-quantum-well light-emitting diode (MQW-LED) with a dielectric distributed Bragg reflector (DBR) positioned at the bottom, implemented on a GaN-on-silicon platform. Silicon removal is conducted to obtain the suspended MQW-LED architecture, and back wafer thinning of the epitaxial film is performed to improve the device performance. A 6-pair SiO2/Ta2O5 DBR is deposited on the backside to manipulate the emitted light. The experimental results demonstrate that the bottom dielectric DBR exhibits high reflectivity and distinctly changes the light emission, which are consistent with the performed simulation results. This work represents a significant step towards the realization of inexpensive, electrically driven and simply fabricated GaN VCSELs for potential use in number of applications.

Efficient generation of 1.9  W yellow light by cascaded frequency doubling of a distributed Bragg reflector tapered diode.

PubMed

Hansen, A K; Christensen, M; Noordegraaf, D; Heist, P; Papastathopoulos, E; Loyo-Maldonado, V; Jensen, O B; Skovgaard, P M W

2016-11-10

Watt-level yellow emitting lasers are interesting for medical applications, due to their high hemoglobin absorption, and for efficient detection of certain fluorophores. In this paper, we demonstrate a compact and robust diode-based laser system in the yellow spectral range. The system generates 1.9 W of single-frequency light at 562.4 nm by cascaded single-pass frequency doubling of the 1124.8 nm emission from a distributed Bragg reflector (DBR) tapered laser diode. The absence of a free-space cavity makes the system stable over a base-plate temperature range of 30 K. At the same time, the use of a laser diode enables the modulation of the pump wavelength by controlling the drive current. This is utilized to achieve a power modulation depth above 90% for the second harmonic light, with a rise time below 40  μs.

Photonic integrated circuits based on sampled-grating distributed-Bragg-reflector lasers

NASA Astrophysics Data System (ADS)

Barton, Jonathon S.; Skogen, Erik J.; Masanovic, Milan L.; Raring, James; Sysak, Matt N.; Johansson, Leif; DenBaars, Steven P.; Coldren, Larry A.

2003-07-01

The Sampled-Grating Distributed-Bragg-Reflector laser(SGDBR) provides wide tunability (>40nm), and high output power (>10mW). Driven by the demand for network reconfigurability and ease of implementation, the SGDBR has moved from the research lab to be commercially viable in the marketplace. The SGDBR is most often implemented using an offset-quantum well epitaxial structure in which the quantum wells are etched off in the passive sections. Alternatively, quantum well intermixing has been used recently to achieve the same goal - resulting in improved optical gain and the potential for multiple bandgaps along the device structure. These epitaxial "platforms" provide the basis for more exotic opto-electronic device functionality exhibiting low chirp for digital applications and enhanced linearity for analog applications. This talk will cover state-of-the-art opto-electronic devices based on the SGDBR platform including: integrated Mach-Zehnder modulators, and integrated electro-absorption modulators.

High-Quality Crystal Growth and Characteristics of AlGaN-Based Solar-Blind Distributed Bragg Reflectors with a Tri-layer Period Structure

PubMed Central

Chang, Jianjun; Chen, Dunjun; Yang, Lianhong; Liu, Yanli; Dong, Kexiu; Lu, Hai; Zhang, Rong; Zheng, Youdou

2016-01-01

To realize AlGaN-based solar-blind ultraviolet distributed Bragg reflectors (DBRs), a novel tri-layer AlGaN/AlInN/AlInGaN periodical structure that differs from the traditional periodically alternating layers of high- and low-refractive-index materials was proposed and grown on an Al0.5Ga0.5N template via metal-organic chemical vapour deposition. Because of the intentional design of the AlInGaN strain transition layer, a state-of-the-art DBR structure with atomic-level-flatness interfaces was achieved using an AlGaN template. The fabricated DBR exhibits a peak reflectivity of 86% at the centre wavelength of 274 nm and a stopband with a full-width at half-maximum of 16 nm. PMID:27381651

1.55-μm InGaAs/InGaAlAs MQW vertical-cavity surface-emitting lasers with InGaAlAs/InP distributed Bragg reflectors

NASA Astrophysics Data System (ADS)

Xia, Jinan; Hoan O, Beom; Gol Lee, Seung; Hang Lee, El

2005-03-01

High-performance InGaAs/InGaAlAs multiple-quantum-well vertical-cavity surface-emitting lasers (VCSELs) with InGaAlAs/InP distributed Bragg reflectors are proposed for operation at the wavelength of 1.55 μm. The lasers have good heat diffusion characteristic, large index contrast in DBRs, and weak temperature sensitivity. They could be fabricated either by metal-organic chemical vapor deposition (MOCVD) or by molecular beam epitaxy (MBE) growth. The laser light-current characteristics indicate that a suitable reflectivity of the DBR on the light output side in a laser makes its output power increase greatly and its lasing threshold current reduce significantly, and that a small VCSEL could output the power around its maximum for the output mirror at the reflectivity varying in a broader range than a large VCSEL does.

Record-level quantum efficiency from a high polarization strained GaAs/GaAsP superlattice photocathode with distributed Bragg reflector

DOE PAGES

Liu, Wei; Chen, Yiqiao; Lu, Wentao; ...

2016-12-19

Photocathodes that provide high polarization and high quantum efficiency (QE) can significantly enhance the physics capabilities of electron accelerators. We report record-level QE from a high-polarization strained GaAs/GaAsP superlattice photocathode fabricated with a Distributed Bragg Reflector (DBR). The DBR photocathode technique enhances the absorption of incident laser light thereby enhancing QE, but as literature suggests, it is very challenging to optimize all of the parameters associated with the fabrication of complicated photocathode structures composed of many distinct layers. Past reports of DBR photocathodes describe high polarization but typically QE of only ~ 1%, which is comparable to QE of highmore » polarization photocathodes grown without a DBR structure. As a result, this work describes a new strained GaAs/GaAsP superlattice DBR photocathode exhibiting polarization of 84% and QE of 6.4%.« less

Record-level quantum efficiency from a high polarization strained GaAs/GaAsP superlattice photocathode with distributed Bragg reflector

DOE Office of Scientific and Technical Information (OSTI.GOV)

Liu, Wei; Chen, Yiqiao; Lu, Wentao

Photocathodes that provide high polarization and high quantum efficiency (QE) can significantly enhance the physics capabilities of electron accelerators. We report record-level QE from a high-polarization strained GaAs/GaAsP superlattice photocathode fabricated with a Distributed Bragg Reflector (DBR). The DBR photocathode technique enhances the absorption of incident laser light thereby enhancing QE, but as literature suggests, it is very challenging to optimize all of the parameters associated with the fabrication of complicated photocathode structures composed of many distinct layers. Past reports of DBR photocathodes describe high polarization but typically QE of only ~ 1%, which is comparable to QE of highmore » polarization photocathodes grown without a DBR structure. As a result, this work describes a new strained GaAs/GaAsP superlattice DBR photocathode exhibiting polarization of 84% and QE of 6.4%.« less

Long fiber Bragg grating sensor interrogation using discrete-time microwave photonic filtering techniques.

PubMed

Ricchiuti, Amelia Lavinia; Barrera, David; Sales, Salvador; Thevenaz, Luc; Capmany, José

2013-11-18

A novel technique for interrogating photonic sensors based on long fiber Bragg gratings (FBGs) is presented and experimentally demonstrated, dedicated to detect the presence and the precise location of several spot events. The principle of operation is based on a technique used to analyze microwave photonics (MWP) filters. The long FBGs are used as quasi-distributed sensors. Several hot-spots can be detected along the FBG with a spatial accuracy under 0.5 mm using a modulator and a photo-detector (PD) with a modest bandwidth of less than 1 GHz. The proposed interrogation system is intrinsically robust against environmental changes.

Separation of Time Scales in a Quantum Newton’s Cradle

DOE PAGES

van den Berg, R.; Wouters, B.; Eliëns, S.; ...

2016-06-01

For strongly repulsive bosons in one dimension, we provide detailed modeling of the Bragg pulse used in quantum Newton's cradle-like settings or in Bragg spectroscopy experiments. By employing the Fermi-Bose mapping for a nite harmonically trapped gas and the Quench Action approach for a thermodynamic system on a ring, we reconstruct the exact post-pulse many-body time evolution of Lieb-Liniger gases in the Tonks-Girardeau limit, together with their changing local density pro le and momentum distribution. Our results display a clear separation of timescales between rapid and trap-insensitive relaxation immediately after the pulse, followed by slow in-trap periodic behaviour.

Strain Imaging of Nanoscale Semiconductor Heterostructures with X-Ray Bragg Projection Ptychography

NASA Astrophysics Data System (ADS)

Holt, Martin V.; Hruszkewycz, Stephan O.; Murray, Conal E.; Holt, Judson R.; Paskiewicz, Deborah M.; Fuoss, Paul H.

2014-04-01

We report the imaging of nanoscale distributions of lattice strain and rotation in complementary components of lithographically engineered epitaxial thin film semiconductor heterostructures using synchrotron x-ray Bragg projection ptychography (BPP). We introduce a new analysis method that enables lattice rotation and out-of-plane strain to be determined independently from a single BPP phase reconstruction, and we apply it to two laterally adjacent, multiaxially stressed materials in a prototype channel device. These results quantitatively agree with mechanical modeling and demonstrate the ability of BPP to map out-of-plane lattice dilatation, a parameter critical to the performance of electronic materials.

Asymmetry in serial femtosecond crystallography data.

PubMed

Sharma, Amit; Johansson, Linda; Dunevall, Elin; Wahlgren, Weixiao Y; Neutze, Richard; Katona, Gergely

2017-03-01

Serial crystallography is an increasingly important approach to protein crystallography that exploits both X-ray free-electron laser (XFEL) and synchrotron radiation. Serial crystallography recovers complete X-ray diffraction data by processing and merging diffraction images from thousands of randomly oriented non-uniform microcrystals, of which all observations are partial Bragg reflections. Random fluctuations in the XFEL pulse energy spectrum, variations in the size and shape of microcrystals, integrating over millions of weak partial observations and instabilities in the XFEL beam position lead to new types of experimental errors. The quality of Bragg intensity estimates deriving from serial crystallography is therefore contingent upon assumptions made while modeling these data. Here it is observed that serial femtosecond crystallography (SFX) Bragg reflections do not follow a unimodal Gaussian distribution and it is recommended that an idealized assumption of single Gaussian peak profiles be relaxed to incorporate apparent asymmetries when processing SFX data. The phenomenon is illustrated by re-analyzing data collected from microcrystals of the Blastochloris viridis photosynthetic reaction center and comparing these intensity observations with conventional synchrotron data. The results show that skewness in the SFX observations captures the essence of the Wilson plot and an empirical treatment is suggested that can help to separate the diffraction Bragg intensity from the background.

One-dimensional Tamm plasmons: Spatial confinement, propagation, and polarization properties

NASA Astrophysics Data System (ADS)

Chestnov, I. Yu.; Sedov, E. S.; Kutrovskaya, S. V.; Kucherik, A. O.; Arakelian, S. M.; Kavokin, A. V.

2017-12-01

Tamm plasmons are confined optical states at the interface of a metal and a dielectric Bragg mirror. Unlike conventional surface plasmons, Tamm plasmons may be directly excited by an external light source in both TE and TM polarizations. Here we consider the one-dimensional propagation of Tamm plasmons under long and narrow metallic stripes deposited on top of a semiconductor Bragg mirror. The spatial confinement of the field imposed by the stripe and its impact on the structure and energy of Tamm modes are investigated. We show that the Tamm modes are coupled to surface plasmons arising at the stripe edges. These plasmons form an interference pattern close to the bottom surface of the stripe that involves modification of both the energy and loss rate for the Tamm mode. This phenomenon is pronounced only in the case of TE polarization of the Tamm mode. These findings pave the way to application of laterally confined Tamm plasmons in optical integrated circuits as well as to engineering potential traps for both Tamm modes and hybrid modes of Tamm plasmons and exciton polaritons with meV depth.

Bragg reflection band width and optical rotatory dispersion of cubic blue-phase liquid crystals

NASA Astrophysics Data System (ADS)

Yoshida, Hiroyuki; Anucha, Konkanok; Ogawa, Yasuhiro; Kawata, Yuto; Ozaki, Masanori; Fukuda, Jun-ichi; Kikuchi, Hirotsugu

2016-10-01

The Bragg reflection band width and optical rotatory dispersion of liquid crystalline cholesteric blue phases (BPs) I and II are compared by numerical simulations. Attention is paid to the wavelength regions for which the reflection bands with lowest photon energies appear, i.e., the [110 ] direction for BP I and the [100 ] direction for BP II. Finite difference time domain and 4 ×4 matrix calculations performed on the theoretical director tensor distribution of BPs with the same material parameters show that BP II, which has simple cubic symmetry, has a wider photonic band gap than BP I, which has body centered cubic symmetry, possibly due to the fact that the density of the double-twist cylinders in BP II are twice that in BP I. The theoretical results on the Bragg reflection band width are supported by reflectance measurements performed on BPs I and II for light incident along the [110 ] and [100 ] directions, respectively.

Intrinsic Fabry-Perot Sensors for Magnetic Field Detection

NASA Astrophysics Data System (ADS)

Broadway, Christian; Descamps, Frédéric; Kinet, Damien; Caucheteur, Christophe; Mégret, Patrice

2018-01-01

Within the context of ensuring stable nuclear fusion, it is important to monitor and control a number of parametersincluding the magnetic field associated with plasma circulation. Optical fibre sensing techniques have seen a surge in promulgation and research advances in recent years, due to their immunity to electromagnetic radiation and compact dimensions. Prior work has shown that fibre Bragg gratings are one method of recovering the induced magnetic field, with the main point of interest being their use as distributed point sensors. However, Bragg grating inscription leads to the creation of linear birefringence that increases detector noise and could obscure a given signal. We have hypothesised that by using an intrinsic Fabry-Perot cavity comprised of two identical Bragg gratings, we could obtain a more accurate detector with the removal of photo-induced birefringence in the detection region. We present a proof of concept optical fibre sensor based on an intrinsic Fabry-Perot cavity that shows spectrally visible amplitude modulation. Finally, we demonstrate faster data processing that allows real time monitoring of a given scenario.

Monitoring on internal temperature of composite insulator with embedding fiber Bragg grating for early diagnosis

NASA Astrophysics Data System (ADS)

Chen, Wen; Tang, Ming

2017-04-01

The abnormal temperature rise is the precursor of the defective composite insulator in power transmission line. However no consolidated techniques or methodologies can on line monitor its internal temperature now. Thus a new method using embedding fiber Bragg grating (FBG) in fiber reinforced polymer (FRP) rod is adopted to monitor its internal temperature. To correctly demodulate the internal temperature of FRP rod from the Bragg wavelength shift of FBG, the conversion coefficient between them is deduced theoretically based on comprehensive investigation on the thermal stresses of the metal-composite joint, as well as its material and structural properties. Theoretical model shows that the conversion coefficients of FBG embedded in different positions will be different because of non-uniform thermal stress distribution, which is verified by an experiment. This work lays the theoretical foundation of monitoring the internal temperature of composite insulator with embedding FBG, which is of great importance to its health structural monitoring, especially early diagnosis.

Proposed linear energy transfer areal detector for protons using radiochromic film

DOE Office of Scientific and Technical Information (OSTI.GOV)

Mayer, Rulon; Lin, Liyong; Fager, Marcus

2015-04-15

Radiation therapy depends on predictably and reliably delivering dose to tumors and sparing normal tissues. Protons with kinetic energy of a few hundred MeV can selectively deposit dose to deep seated tumors without an exit dose, unlike x-rays. The better dose distribution is attributed to a phenomenon known as the Bragg peak. The Bragg peak is due to relatively high energy deposition within a given distance or high Linear Energy Transfer (LET). In addition, biological response to radiation depends on the dose, dose rate, and localized energy deposition patterns or LET. At present, the LET can only be measured atmore » a given fixed point and the LET spatial distribution can only be inferred from calculations. The goal of this study is to develop and test a method to measure LET over extended areas. Traditionally, radiochromic films are used to measure dose distribution but not for LET distribution. We report the first use of these films for measuring the spatial distribution of the LET deposited by protons. The radiochromic film sensitivity diminishes for large LET. A mathematical model correlating the film sensitivity and LET is presented to justify relating LET and radiochromic film relative sensitivity. Protons were directed parallel to radiochromic film sandwiched between solid water slabs. This study proposes the scaled-normalized difference (SND) between the Treatment Planning system (TPS) and measured dose as the metric describing the LET. The SND is correlated with a Monte Carlo (MC) calculation of the LET spatial distribution for a large range of SNDs. A polynomial fit between the SND and MC LET is generated for protons having a single range of 20 cm with narrow Bragg peak. Coefficients from these fitted polynomial fits were applied to measured proton dose distributions with a variety of ranges. An identical procedure was applied to the protons deposited from Spread Out Bragg Peak and modulated by 5 cm. Gamma analysis is a method for comparing the calculated LET with the LET measured using radiochromic film at the pixel level over extended areas. Failure rates using gamma analysis are calculated for areas in the dose distribution using parameters of 25% of MC LET and 3 mm. The processed dose distributions find 5%–10% failure rates for the narrow 12.5 and 15 cm proton ranges and 10%–15% for proton ranges of 15, 17.5, and 20 cm and modulated by 5 cm. It is found through gamma analysis that the measured proton energy deposition in radiochromic film and TPS can be used to determine LET. This modified film dosimetry provides an experimental areal LET measurement that can verify MC calculations, support LET point measurements, possibly enhance biologically based proton treatment planning, and determine the polymerization process within the radiochromic film.« less

Sub-wavelength grating structure on the planar waveguide (Conference Presentation)

NASA Astrophysics Data System (ADS)

Qing-Song, Zhu; Sheng-Hui, Chen

2016-10-01

Making progress in recent years, with the technology of the grating, the grating period can be reduced to shrink the size of the light coupler on a waveguide. The working wavelength of the light coupler can be in the range from the near-infrared to visible. In this study , we used E-gun evaporation system with ion-beam-assisted deposition system to fabricate bottom cladding (SiO2), guiding layer (Ta2O5) and Distributed Bragg Reflector(DBR) of the waveguide on the silicon substrate. Electron-beam lithography is used to make sub-wavelength gratings and reflector grating on the planar waveguide which is a coupling device on the guiding layer. The best fabrication parameters were analyzed to deposit the film. The exposure and development times also influenced to fabricate the grating quality. The purpose is to reduce the device size and enhance coupling efficiency which maintain normal incidence of the light . We designed and developed the device using the Finite-Difference Time-Domain (FDTD) method. The grating period, depth, fill factor, film thickness, Distributed Bragg Reflector(DBR) numbers and reflector grating period have been discussed to enhance coupling efficiency and maintained normal incidence of the light. According to the simulation results, when the wavelength is 1300 nm, the coupling grating period is 720 nm and the Ta2O5 film is 460 nm with 360 nm of reflector grating period and 2 layers of Distributed Bragg Reflector, which had the optimum coupling efficiency and normal incidence angle. In the measurement, We successfully measured the TE wave coupling efficiency of the photoresist grating coupling device.

A combined molecular dynamics and Monte Carlo simulation of the spatial distribution of energy deposition by proton beams in liquid water.

PubMed

Garcia-Molina, Rafael; Abril, Isabel; Heredia-Avalos, Santiago; Kyriakou, Ioanna; Emfietzoglou, Dimitris

2011-10-07

We have evaluated the spatial distribution of energy deposition by proton beams in liquid water using the simulation code SEICS (Simulation of Energetic Ions and Clusters through Solids), which combines molecular dynamics and Monte Carlo techniques and includes the main interaction phenomena between the projectile and the target constituents: (i) the electronic stopping force due to energy loss to target electronic excitations, including fluctuations due to the energy-loss straggling, (ii) the elastic scattering with the target nuclei, with their corresponding energy loss and (iii) the dynamical changes in projectile charge state due to electronic capture and loss processes. An important feature of SEICS is the accurate account of the excitation spectrum of liquid water, based on a consistent solid-state description of its energy-loss-function over the whole energy and momentum space. We analyse how the above-mentioned interactions affect the depth distribution of the energy delivered in liquid water by proton beams with incident energies of the order of several MeV. Our simulations show that the position of the Bragg peak is determined mainly by the stopping power, whereas its width can be attributed to the energy-loss straggling. Multiple elastic scattering processes contribute slightly only at the distal part of the Bragg peak. The charge state of the projectiles only changes when approaching the end of their trajectories, i.e. near the Bragg peak. We have also simulated the proton-beam energy distribution at several depths in the liquid water target, and found that it is determined mainly by the fluctuation in the energy loss of the projectile, evaluated through the energy-loss straggling. We conclude that a proper description of the target excitation spectrum as well as the inclusion of the energy-loss straggling is essential in the calculation of the proton beam depth-dose distribution.

Ionoacoustic characterization of the proton Bragg peak with submillimeter accuracy

DOE Office of Scientific and Technical Information (OSTI.GOV)

Assmann, W., E-mail: walter.assmann@lmu.de; Reinhardt, S.; Lehrack, S.

2015-02-15

Purpose: Range verification in ion beam therapy relies to date on nuclear imaging techniques which require complex and costly detector systems. A different approach is the detection of thermoacoustic signals that are generated due to localized energy loss of ion beams in tissue (ionoacoustics). Aim of this work was to study experimentally the achievable position resolution of ionoacoustics under idealized conditions using high frequency ultrasonic transducers and a specifically selected probing beam. Methods: A water phantom was irradiated by a pulsed 20 MeV proton beam with varying pulse intensity and length. The acoustic signal of single proton pulses was measuredmore » by different PZT-based ultrasound detectors (3.5 and 10 MHz central frequencies). The proton dose distribution in water was calculated by Geant4 and used as input for simulation of the generated acoustic wave by the matlab toolbox k-WAVE. Results: In measurements from this study, a clear signal of the Bragg peak was observed for an energy deposition as low as 10{sup 12} eV. The signal amplitude showed a linear increase with particle number per pulse and thus, dose. Bragg peak position measurements were reproducible within ±30 μm and agreed with Geant4 simulations to better than 100 μm. The ionoacoustic signal pattern allowed for a detailed analysis of the Bragg peak and could be well reproduced by k-WAVE simulations. Conclusions: The authors have studied the ionoacoustic signal of the Bragg peak in experiments using a 20 MeV proton beam with its correspondingly localized energy deposition, demonstrating submillimeter position resolution and providing a deep insight in the correlation between the acoustic signal and Bragg peak shape. These results, together with earlier experiments and new simulations (including the results in this study) at higher energies, suggest ionoacoustics as a technique for range verification in particle therapy at locations, where the tumor can be localized by ultrasound imaging. This acoustic range verification approach could offer the possibility of combining anatomical ultrasound and Bragg peak imaging, but further studies are required for translation of these findings to clinical application.« less

Distributed feedback acoustic surface wave oscillator

NASA Technical Reports Server (NTRS)

Elachi, C. (Inventor)

1977-01-01

An acoustic surface wave oscillator is constructed from a semiconductor piezoelectric acoustic surface wave amplifier by providing appropriate perturbations at the piezoelectric boundary. The perturbations cause Bragg order reflections that maintain acoustic wave oscillation under certain conditions of gain and feedback.

WE-H-BRA-01: BEST IN PHYSICS (THERAPY): Nano-Dosimetric Kinetic Model for Variable Relative Biological Effectiveness of Proton and Ion Beams

DOE Office of Scientific and Technical Information (OSTI.GOV)

Abolfath, R; Bronk, L; Titt, U.

2016-06-15

Purpose: Recent clonogenic cell survival and γH2AX studies suggest proton relative biological effectiveness (RBE) may be a non-linear function of linear energy transfer (LET) in the distal edge of the Bragg peak and beyond. We sought to develop a multiscale model to account for non-linear response phenomena to aid in the optimization of intensity-modulated proton therapy. Methods: The model is based on first-principle simulations of proton track structures, including secondary ions, and an analytical derivation of the dependence on particle LET of the linear-quadratic (LQ) model parameters α and β. The derived formulas are an extension of the microdosimetric kineticmore » (MK) model that captures dissipative track structures and non-Poissonian distribution of DNA damage at the distal edge of the Bragg peak and beyond. Monte Carlo simulations were performed to confirm the non-linear dose-response characteristics arising from the non-Poisson distribution of initial DNA damage. Results: In contrast to low LET segments of the proton depth dose, from the beam entrance to the Bragg peak, strong deviations from non-dissipative track structures and Poisson distribution in the ionization events in the Bragg peak distal edge govern the non-linear cell response and result in the transformation α=(1+c-1 L) α-x+2(c-0 L+c-2 L^2 )(1+c-1 L) β-x and β=(1+c-1 L)^2 β-x. Here L is the charged particle LET, and c-0,c-1, and c-2 are functions of microscopic parameters and can be served as fitting parameters to the cell-survival data. In the low LET limit c-1, and c-2 are negligible hence the linear model proposed and used by Wilkins-Oelfke for the proton treatment planning system can be retrieved. The present model fits well the recent clonogenic survival data measured recently in our group in MDACC. Conclusion: The present hybrid method provides higher accuracy in calculating the RBE-weighted dose in the target and normal tissues.« less

Quantum confinement of zero-dimensional hybrid organic-inorganic polaritons at room temperature

NASA Astrophysics Data System (ADS)

Nguyen, H. S.; Han, Z.; Abdel-Baki, K.; Lafosse, X.; Amo, A.; Lauret, J.-S.; Deleporte, E.; Bouchoule, S.; Bloch, J.

2014-02-01

We report on the quantum confinement of zero-dimensional polaritons in perovskite-based microcavity at room temperature. Photoluminescence of discrete polaritonic states is observed for polaritons localized in symmetric sphere-like defects which are spontaneously nucleated on the top dielectric Bragg mirror. The linewidth of these confined states is found much sharper (almost one order of magnitude) than that of photonic modes in the perovskite planar microcavity. Our results show the possibility to study organic-inorganic cavity polaritons in confined microstructure and suggest a fabrication method to realize integrated polaritonic devices operating at room temperature.

Fiber Bragg Gratings for High-Temperature Thermal Characterization

DOE Office of Scientific and Technical Information (OSTI.GOV)

Stinson-Bagby, Kelly L.; Fielder, Robert S.

2004-07-01

Fiber Bragg grating (FBG) sensors were used as a characterization tool to study the SAFE-100 thermal simulator at the Nasa Marshal Space Flight Center. The motivation for this work was to support Nasa space nuclear power initiatives through the development of advanced fiber optic sensors for space-based nuclear power applications. Distributed high temperature measurements, up to 1150 deg. C, were made with FBG temperature sensors. Additionally, FBG strain measurements were taken at elevated temperatures to provide a strain profile of the core during operation. This paper will discuss the contribution of these measurements to meet the goals of Nasa Marshallmore » Space Flight Center's Propulsion Research Center. (authors)« less

Fine tuning of the dichroic behavior of Bragg reflectors based on anisotropically nanostructured silicon

NASA Astrophysics Data System (ADS)

Diener, J.; Künzner, N.; Kovalev, D.; Gross, E.; Koch, F.; Fujii, M.

2003-05-01

Electro-chemical etching of heavily doped, (110) oriented, p+ (boron) doped silicon wafers results in porous silicon (PSi) layers which exhibit a strong in-plane anisotropy of the refractive index (birefringence). Single- and multiple layers of anisotropically nanostructured silicon (Si) have been fabricated and studied by polarization-resolved reflection and transmission measurements. Dielectric stacks of birefringent PSi acting as distributed Bragg reflectors have two distinct reflection bands depending on the polarization of the incident linearly polarized light. This effect is caused by a three-dimensional (in plane and in-depth) variation of the refraction index. The possibility of fine tuning the two orthogonally polarized reflection bands and their spectral splitting is demonstrated.

High-power, cladding-pumped all-fiber laser with selective transverse mode generation property.

PubMed

Li, Lei; Wang, Meng; Liu, Tong; Leng, Jinyong; Zhou, Pu; Chen, Jinbao

2017-06-10

We demonstrate, to the best of our knowledge, the first cladding-pumped all-fiber oscillator configuration with selective transverse mode generation based on a mode-selective fiber Bragg grating pair. Operating in the second-order (LP 11 ) mode, maximum output power of 4.2 W is obtained with slope efficiency of about 38%. This is the highest reported output power of single higher-order transverse mode generation in an all-fiber configuration. The intensity distribution profile and spectral evolution have also been investigated in this paper. Our work suggests the potential of realizing higher power with selective transverse mode operation based on a mode-selective fiber Bragg grating pair.

Deterministic Bragg Coherent Diffraction Imaging.

PubMed

Pavlov, Konstantin M; Punegov, Vasily I; Morgan, Kaye S; Schmalz, Gerd; Paganin, David M

2017-04-25

A deterministic variant of Bragg Coherent Diffraction Imaging is introduced in its kinematical approximation, for X-ray scattering from an imperfect crystal whose imperfections span no more than half of the volume of the crystal. This approach provides a unique analytical reconstruction of the object's structure factor and displacement fields from the 3D diffracted intensity distribution centred around any particular reciprocal lattice vector. The simple closed-form reconstruction algorithm, which requires only one multiplication and one Fourier transformation, is not restricted by assumptions of smallness of the displacement field. The algorithm performs well in simulations incorporating a variety of conditions, including both realistic levels of noise and departures from ideality in the reference (i.e. imperfection-free) part of the crystal.

Quasi-distributed fiber sensor using active mode locking laser cavity with multiple FBG reflections

NASA Astrophysics Data System (ADS)

Park, Chang Hyun; Kim, Gyeong Hun; Kim, Chang-Seok; Lee, Hwi Don; Chung, Youngjoo

2017-04-01

We have demonstrated a quasi-distributed sensor using an active mode-locking (AML) laser with multiple fiber Bragg grating (FBG) reflections of the same center wavelength. We found that variations in the multiple cavity segment lengths between FBGs can be measured by simply sweeping the modulation frequency, because the modulation frequency of the AML laser is proportionally affected by cavity length.

Numerical simulation and experimental investigation of GaN-based flip-chip LEDs and top-emitting LEDs.

PubMed

Liu, Xingtong; Zhou, Shengjun; Gao, Yilin; Hu, Hongpo; Liu, Yingce; Gui, Chengqun; Liu, Sheng

2017-12-01

We demonstrate a GaN-based flip-chip LED (FC-LED) with a highly reflective indium-tin oxide (ITO)/distributed Bragg reflector (DBR) ohmic contact. A transparent ITO current spreading layer combined with Ta 2 O 5 /SiO 2 double DBR stacks is used as a reflective p-type ohmic contact in the FC-LED. We develop a strip-shaped SiO 2 current blocking layer, which is well aligned with a p-electrode, to prevent the current from crowding around the p-electrode. Our combined numerical simulation and experimental results revealed that the FC-LED with ITO/DBR has advantages of better current spreading and superior heat dissipation performance compared to top-emitting LEDs (TE-LEDs). As a result, the light output power (LOP) of the FC-LED with ITO/DBR was 7.6% higher than that of the TE-LED at 150 mA, and the light output saturation current was shifted from 130.9  A/cm 2 for the TE-LED to 273.8  A/cm 2 for the FC-LED with ITO/DBR. Owing to the high reflectance of the ITO/DBR ohmic contact, the LOP of the FC-LED with ITO/DBR was 13.0% higher than that of a conventional FC-LED with Ni/Ag at 150 mA. However, because of the better heat dissipation of the Ni/Ag ohmic contact, the conventional FC-LED with Ni/Ag exhibited higher light output saturation current compared to the FC-LED with ITO/DBR.

Electrically driven hybrid Si/III-V Fabry-Pérot lasers based on adiabatic mode transformers.

PubMed

Ben Bakir, B; Descos, A; Olivier, N; Bordel, D; Grosse, P; Augendre, E; Fulbert, L; Fedeli, J M

2011-05-23

We report the first demonstration of an electrically driven hybrid silicon/III-V laser based on adiabatic mode transformers. The hybrid structure is formed by two vertically superimposed waveguides separated by a 100-nm-thick SiO2 layer. The top waveguide, fabricated in an InP/InGaAsP-based heterostructure, serves to provide optical gain. The bottom Si-waveguides system, which supports all optical functions, is constituted by two tapered rib-waveguides (mode transformers), two distributed Bragg reflectors (DBRs) and a surface-grating coupler. The supermodes of this hybrid structure are controlled by an appropriate design of the tapers located at the edges of the gain region. In the middle part of the device almost all the field resides in the III-V waveguide so that the optical mode experiences maximal gain, while in regions near the III-V facets, mode transformers ensure an efficient transfer of the power flow towards Si-waveguides. The investigated device operates under quasi-continuous wave regime. The room temperature threshold current is 100 mA, the side-mode suppression ratio is as high as 20 dB, and the fiber-coupled output power is ~7 mW.

A comparative study of thermal characteristics of GaN-based VCSELs with three different typical structures

NASA Astrophysics Data System (ADS)

Mei, Yang; Xu, Rong-Bin; Xu, Huan; Ying, Lei-Ying; Zheng, Zhi-Wei; Zhang, Bao-Ping; Li, Mo; Zhang, Jian

2018-01-01

Thermal characteristics of GaN-based vertical cavity surface emitting lasers (VCSELs) with three typical structures were investigated both theoretically and experimentally. The simulation results based on a steady state quasi three-dimensional cylindrical model show that the thermal resistance (R th) is affected by cavity length, mesa size, as well as the bottom distributed Bragg reflector (DBR) size, and the detail further depends on different structures. Among different devices, GaN VCSEL with a hybrid cavity formed by one nitride bottom DBR and another dielectric top DBR is featured with lower R th, which is meanwhile affected strongly by the materials of the epitaxial bottom DBR. The main issues affecting the thermal dissipation in VCSELs with double dielectric DBRs are the bottom dielectric DBR and the dielectric current-confinement layer. To validate the simulation results, GaN-based VCSEL bonded on a copper plate was fabricated. R th of this device was measured and the results agreed well with the simulation. This work provides a better understanding of the thermal characteristics of GaN-based VCSELs and is useful in optimizing the structure design and improving the device performance.

SU-F-T-129: Impact of Radial Fluctuations in RBE for Therapeutic Proton Beams

DOE Office of Scientific and Technical Information (OSTI.GOV)

Butkus, M; Palmer, T

Purpose: To evaluate the off axis relative biological effectiveness (RBE) for actively scanned proton beams and determine if a constant radial RBE can be assumed. Methods: The PHITS Monte Carlo code paired with a microscopic analytical function was used to determine probability distribution functions of the lineal energy in 0.3µm diameter spheres throughout a water phantom. Twenty million primary protons were simulated for a 0.6cm diameter pencil beam. Beam energies corresponding to Bragg Peak depths of 50, 100, 150, 200, 250, and 300mm were used and evaluated transversely every millimeter and radially for annuli of 1.0, 2.0, 3.0, 3.2, 3.4,more » 3.6, 4.0, 5.0, 10.0, 15.0, 20.0 and 25.0mm outer radius. The acquired probability distributions were reduced to dose-mean lineal energies and applied to the modified microdosimetric kinetic model, for human submandibular gland (HSG) cells, to calculate relative biological effectiveness (RBE) compared to 60Co beams at the 10% survival threshold. Results: RBE was generally seen to increase as distance from the central axis (CAX) increased. However, this increase was only seen in low dose regions and its overall effects on the transverse biological dose remains low. In the entrance region of the phantom (10mm depth), minimum and maximum calculated RBEs varied between 15.22 and 18.88% for different energies. At the Bragg peak, this difference ranged from 3.15 to 26.77%. Despite these rather large variations the dose-weighted RBE and the CAX RBE varied by less than 0.14% at 10mm depth and less than 0.16% at the Bragg peak. Similarly small variations were found at all depths proximal of the Bragg peak. Conclusion: Although proton RBE does vary radially, its overall effect on biological dose is minimal and the use of a radially constant RBE in treatment planning for scanned proton beams would not produce large errors.« less

Effect of Rayleigh-scattering distributed feedback on multiwavelength Raman fiber laser generation.

PubMed

El-Taher, A E; Harper, P; Babin, S A; Churkin, D V; Podivilov, E V; Ania-Castanon, J D; Turitsyn, S K

2011-01-15

We experimentally demonstrate a Raman fiber laser based on multiple point-action fiber Bragg grating reflectors and distributed feedback via Rayleigh scattering in an ~22-km-long optical fiber. Twenty-two lasing lines with spacing of ~100 GHz (close to International Telecommunication Union grid) in the C band are generated at the watt level. In contrast to the normal cavity with competition between laser lines, the random distributed feedback cavity exhibits highly stable multiwavelength generation with a power-equalized uniform distribution, which is almost independent on power.

SU-E-J-201: Investigation of MRI Guided Proton Therapy

DOE Office of Scientific and Technical Information (OSTI.GOV)

Li, JS

2015-06-15

Purpose: Image-guided radiation therapy has been employed for cancer treatment to improve the tumor localization accuracy. Radiation therapy with proton beams requires more on this accuracy because the proton beam has larger uncertainty and dramatic dose variation along the beam direction. Among all the image modalities, magnetic-resonance image (MRI) is the best for soft tissue delineation and real time motion monitoring. In this work, we investigated the behavior of the proton beam in magnetic field with Monte Carlo simulations. Methods: A proton Monte Carlo platform, TOPAS, was used for this investigation. Dose calculations were performed with this platform in amore » 30cmx30cmx30cm water phantom for both pencil and broad proton beams with different energies (120, 150 and 180MeV) in different magnetic fields (0.5T, 1T and 3T). The isodose distributions, dose profiles in lateral and beam direction were evaluated. The shifts of the Bragg peak in different magnetic fields for different proton energies were compared and the magnetic field effects on the characters of the dose distribution were analyzed. Results: Significant effects of magnetic field have been observed on the proton beam dose distributions, especially for magnetic field of 1T and up. The effects are more significant for higher energy proton beam because higher energy protons travel longer distance in the magnetic field. The Bragg peak shift in the lateral direction is about 38mm for 180MeV and 11mm for 120MeV proton beams in 3T magnetic field. The peak positions are retracted back for 6mm and 2mm, respectively. The effect on the beam penumbra and dose falloff at the distal edge of the Bragg peak is negligible. Conclusion: Though significant magnetic effects on dose distribution have been observed for proton beams, MRI guided proton therapy is feasible because the magnetic effects on dose is predictable and can be considered in patient dose calculation.« less

ERS-1 and Seasat scatterometer measurements of ocean winds: Model functions and the directional distribution of short waves

NASA Technical Reports Server (NTRS)

Freilich, Michael H.; Dunbar, R. Scott

1993-01-01

Calculation of accurate vector winds from scatterometers requires knowledge of the relationship between backscatter cross-section and the geophysical variable of interest. As the detailed dynamics of wind generation of centimetric waves and radar-sea surface scattering at moderate incidence angles are not well known, empirical scatterometer model functions relating backscatter to winds must be developed. Less well appreciated is the fact that, given an accurate model function and some knowledge of the dominant scattering mechanisms, significant information on the amplitudes and directional distributions of centimetric roughness elements on the sea surface can be inferred. accurate scatterometer model functions can thus be used to investigate wind generation of short waves under realistic conditions. The present investigation involves developing an empirical model function for the C-band (5.3 GHz) ERS-1 scatterometer and comparing Ku-band model functions with the C-band model to infer information on the two-dimensional spectrum of centimetric roughness elements in the ocean. The C-band model function development is based on collocations of global backscatter measurements with operational surface analyses produced by meteorological agencies. Strengths and limitations of the method are discussed, and the resulting model function is validated in part through comparison with the actual distributions of backscatter cross-section triplets. Details of the directional modulation as well as the wind speed sensitivity at C-band are investigated. Analysis of persistent outliers in the data is used to infer the magnitudes of non-wind effects (such as atmospheric stratification, swell, etc.). The ERS-1 C-band instrument and the Seasat Ku-band (14.6 GHz) scatterometer both imaged waves of approximately 3.4 cm wavelength assuming that Bragg scattering is the dominant mechanism. Comparisons of the C-band and Ku-band model functions are used both to test the validity of the postulated Bragg mechanism and to investigate the directional distribution of the imaged waves under a variety of conditions where Bragg scatter is dominant.

Remote coding scheme based on waveguide Bragg grating in PLC splitter chip for PON monitoring.

PubMed

Zhang, Xuan; Lu, Fengjun; Chen, Si; Zhao, Xingqun; Zhu, Min; Sun, Xiaohan

2016-03-07

A distributing arranged waveguide Bragg gratings (WBGs) in PLC splitter chip based remote coding scheme is proposed and analyzed for passive optical network (PON) monitoring, by which the management system can identify each drop fiber link through the same reflector in the terminal of each optical network unit, even though there exist several equidistant users. The corresponding coding and capacity models are respectively established and investigated so that we can obtain a minimum number of the WBGs needed under the condition of the distributed structure. Signal-to-noise ratio (SNR) model related to the number of equidistant users is also developed to extend the analyses for the overall performance of the system. Simulation results show the proposed scheme is feasible and allow the monitoring of a 64 users PON with SNR range of 7.5~10.6dB. The scheme can solve some of difficulties of construction site at the lower user cost for PON system.

Etched distributed Bragg reflectors as three-dimensional photonic crystals: photonic bands and density of states.

PubMed

Pavarini, E; Andreani, L C

2002-09-01

The photonic band dispersion and density of states (DOS) are calculated for the three-dimensional (3D) hexagonal structure corresponding to a distributed Bragg reflector patterned with a 2D triangular lattice of circular holes. Results for the Si/SiO(2) and GaAs/Al(x)Ga(1-x)As systems determine the optimal parameters for which a gap in the 2D plane occurs and overlaps the 1D gap of the multilayer. The DOS is considerably reduced in correspondence with the overlap of 2D and 1D gaps. Also, the local density of states (i.e., the DOS weighted with the squared electric field at a given point) has strong variations depending on the position. Both results imply substantial changes of spontaneous emission rates and patterns for a local emitter embedded in the structure and make this system attractive for the fabrication of a 3D photonic crystal with controlled radiative properties.

A high-precision, distributed geodetic strainmeter based on dual coaxial cable Bragg gratings

NASA Astrophysics Data System (ADS)

Fu, J.; Wei, T.; Wei, M.; Shen, Y.

2014-12-01

Observations of surface deformation are essential for understanding a wide range of geophysical problems, including earthquakes, volcanoes, landslides, and glaciers. Current geodetic technologies, such as GPS, InSAR, borehole and laser strainmeters, are costly and limited in their temporal or spatial resolution. Here we present a new type of strainmeter based on coaxial cable Bragg grating (CCBG) sensing technology that provides high-precision, distributed strain measurements at a moderate cost. The coaxial-cable-based strainmeter is designed to cover a long distance (~ km) under harsh environmental conditions such as extreme temperatures. To minimize the environmental noises, two CCBGs are introduced into the geodetic strainmeter: one is used to measure the strain applied on it, and the other acts as a reference only to detect the environmental noises. The environmental noises are removed using the inputs from the strained CCBG and the reference CCBG in a frequency mixer. The test results show that the geodetic strainmeter with dual CCBGs has micron-strain accuracy in the lab.

Comparison of Fiber Optic Strain Demodulation Implementations

NASA Technical Reports Server (NTRS)

Quach, Cuong C.; Vazquez, Sixto L.

2005-01-01

NASA Langley Research Center is developing instrumentation based upon principles of Optical Frequency-Domain Reflectometry (OFDR) for the provision of large-scale, dense distribution of strain sensors using fiber optics embedded with Bragg gratings. Fiber Optic Bragg Grating technology enables the distribution of thousands of sensors immune to moisture and electromagnetic interference with negligible weight penalty. At Langley, this technology provides a key component for research and development relevant to comprehensive aerospace vehicle structural health monitoring. A prototype system is under development that includes hardware and software necessary for the acquisition of data from an optical network and conversion of the data into strain measurements. This report documents the steps taken to verify the software that implements the algorithm for calculating the fiber strain. Brief descriptions of the strain measurement system and the test article are given. The scope of this report is the verification of software implementations as compared to a reference model. The algorithm will be detailed along with comparison results.

Efficiency enhancement and angle-dependent color change in see-through organic photovoltaics using distributed Bragg reflectors

NASA Astrophysics Data System (ADS)

Dong, Wan Jae; Lo, Nhat-Truong; Jung, Gwan Ho; Ham, Juyoung; Lee, Jong-Lam

2016-03-01

A distributed Bragg reflector (DBR) is conducted as a bottom reflector in see-through organic photovoltaics (OPVs) with an active layer of poly(3-hexylthiophene) and phenyl-C61-butyric acid methyl ester (P3HT:PCBM). The DBR consists of alternative layers of the high- and low-refractive index materials of Ta2O5 (n = 2.16) and SiO2 (n = 1.46). The DBR selectively reflects the light within a specific wavelength region (490 nm-630 nm) where the absorbance of P3HT:PCBM is maximum. The see-through OPVs fabricated on DBR exhibit efficiency enhancement by 31% compared to the device without DBR. Additionally, the angle-dependent transmittance of DBR is analysed using optical simulation and verified by experimental results. As the incident angle of light increases, peak of reflectance shifts to shorter wavelength and the bandwidth gets narrower. This unique angle-dependent optical properties of DBR allows the facile color change of see-through OPVs.

Wafer-scale Fabrication of Non-Polar Mesoporous GaN Distributed Bragg Reflectors via Electrochemical Porosification.

PubMed

Zhu, Tongtong; Liu, Yingjun; Ding, Tao; Fu, Wai Yuen; Jarman, John; Ren, Christopher Xiang; Kumar, R Vasant; Oliver, Rachel A

2017-03-27

Distributed Bragg reflectors (DBRs) are essential components for the development of optoelectronic devices. For many device applications, it is highly desirable to achieve not only high reflectivity and low absorption, but also good conductivity to allow effective electrical injection of charges. Here, we demonstrate the wafer-scale fabrication of highly reflective and conductive non-polar gallium nitride (GaN) DBRs, consisting of perfectly lattice-matched non-polar (11-20) GaN and mesoporous GaN layers that are obtained by a facile one-step electrochemical etching method without any extra processing steps. The GaN/mesoporous GaN DBRs exhibit high peak reflectivities (>96%) across the entire visible spectrum and wide spectral stop-band widths (full-width at half-maximum >80 nm), while preserving the material quality and showing good electrical conductivity. Such mesoporous GaN DBRs thus provide a promising and scalable platform for high performance GaN-based optoelectronic, photonic, and quantum photonic devices.

Unassisted photoelectrochemical water splitting exceeding 7% solar-to-hydrogen conversion efficiency using photon recycling

PubMed Central

Shi, Xinjian; Jeong, Hokyeong; Oh, Seung Jae; Ma, Ming; Zhang, Kan; Kwon, Jeong; Choi, In Taek; Choi, Il Yong; Kim, Hwan Kyu; Kim, Jong Kyu; Park, Jong Hyeok

2016-01-01

Various tandem cell configurations have been reported for highly efficient and spontaneous hydrogen production from photoelectrochemical solar water splitting. However, there is a contradiction between two main requirements of a front photoelectrode in a tandem cell configuration, namely, high transparency and high photocurrent density. Here we demonstrate a simple yet highly effective method to overcome this contradiction by incorporating a hybrid conductive distributed Bragg reflector on the back side of the transparent conducting substrate for the front photoelectrochemical electrode, which functions as both an optical filter and a conductive counter-electrode of the rear dye-sensitized solar cell. The hybrid conductive distributed Bragg reflectors were designed to be transparent to the long-wavelength part of the incident solar spectrum (λ>500 nm) for the rear solar cell, while reflecting the short-wavelength photons (λ<500 nm) which can then be absorbed by the front photoelectrochemical electrode for enhanced photocurrent generation. PMID:27324578

Fabrication of high reflectivity nanoporous distributed Bragg reflectors by controlled electrochemical etching of GaN

NASA Astrophysics Data System (ADS)

Lee, Seung-Min; Kang, Jin-Ho; Lee, June Key; Ryu, Sang-Wan

2016-09-01

The nanoporous medium is a valuable feature of optical devices because of its variable optical refractive index with porosity. One important application is in a GaN-based vertical cavity surface emitting laser having a distributed Bragg reflector (DBR) composed of alternating nanoporous and bulk GaNs. However, optimization of the fabrication process for high reflectivity DBRs having wellcontrolled high reflection bands has not been studied yet. We used electrochemical etching to study the fabrication process of a nanoporous GaN DBR and analyzed the relationship between the morphology and optical reflectivity. Several electrolytes were examined for the formation of the optimized nanoporous structure. A highly reflective DBRs having reflectivity of ~100% were obtained over a wide wavelength range of 450-750 nm. Porosification of semiconductors into nanoporous layers could provide a high reflectivity DBR due to controlled index-contrast, which would be advantages for the construction of a high-Q optical cavity.

Electrically-Tunable Group Delays Using Quantum Wells in a Distributed Bragg Reflector

NASA Technical Reports Server (NTRS)

Nelson, Thomas R., Jr.; Loehr, John P.; Fork, Richard L.; Cole, Spencer; Jones, Darryl K.; Keys, Andrew

1999-01-01

There is a growing interest in the fabrication of semiconductor optical group delay lines for the development of phased arrays of Vertical-Cavity Surface-Emitting Lasers (VCSELs). We present a novel structure incorporating In(x)GA(1-x)As quantum wells in the GaAs quarter-wave layers of a GaAs/AlAs distributed Bragg reflector (DBR). Application of an electric field across the quantum wells leads to red shifting and peak broadening of the el-hhl exciton peak via the quantum-confined Stark effect. Resultant changes in the index of refraction thereby provide a means for altering the group delay of an incident laser pulse. We discuss the tradeoffs between the maximum amount of change in group delay versus absorption losses for such a device. We also compare a simple theoretical model to experimental results, and discuss both angle and position tuning of the BDR band edge resonance relative to the exciton absorption peak. The advantages of such monolithically grown devices for phased-array VCSEL applications will be detailed.

XFEL diffraction: Developing processing methods to optimize data quality

DOE PAGES

Sauter, Nicholas K.

2015-01-29

Serial crystallography, using either femtosecond X-ray pulses from free-electron laser sources or short synchrotron-radiation exposures, has the potential to reveal metalloprotein structural details while minimizing damage processes. However, deriving a self-consistent set of Bragg intensities from numerous still-crystal exposures remains a difficult problem, with optimal protocols likely to be quite different from those well established for rotation photography. Here several data processing issues unique to serial crystallography are examined. It is found that the limiting resolution differs for each shot, an effect that is likely to be due to both the sample heterogeneity and pulse-to-pulse variation in experimental conditions. Shotsmore » with lower resolution limits produce lower-quality models for predicting Bragg spot positions during the integration step. Also, still shots by their nature record only partial measurements of the Bragg intensity. An approximate model that corrects to the full-spot equivalent (with the simplifying assumption that the X-rays are monochromatic) brings the distribution of intensities closer to that expected from an ideal crystal, and improves the sharpness of anomalous difference Fourier peaks indicating metal positions.« less

Narrow-band generation in random distributed feedback fiber laser.

PubMed

Sugavanam, Srikanth; Tarasov, Nikita; Shu, Xuewen; Churkin, Dmitry V

2013-07-15

Narrow-band emission of spectral width down to ~0.05 nm line-width is achieved in the random distributed feedback fiber laser employing narrow-band fiber Bragg grating or fiber Fabry-Perot interferometer filters. The observed line-width is ~10 times less than line-width of other demonstrated up to date random distributed feedback fiber lasers. The random DFB laser with Fabry-Perot interferometer filter provides simultaneously multi-wavelength and narrow-band (within each line) generation with possibility of further wavelength tuning.

A Theoretical Study and Numerical Simulation of a Quasi-Distributed Sensor Based on the Low-Finesse Fabry-Perot Interferometer: Frequency-Division Multiplexing

PubMed Central

Guillen Bonilla, José Trinidad; Guillen Bonilla, Alex; Rodríguez Betancourtt, Verónica M.; Guillen Bonilla, Héctor; Casillas Zamora, Antonio

2017-01-01

The application of the sensor optical fibers in the areas of scientific instrumentation and industrial instrumentation is very attractive due to its numerous advantages. In the industry of civil engineering for example, quasi-distributed sensors made with optical fiber are used for reliable strain and temperature measurements. Here, a quasi-distributed sensor in the frequency domain is discussed. The sensor consists of a series of low-finesse Fabry-Perot interferometers where each Fabry-Perot interferometer acts as a local sensor. Fabry-Perot interferometers are formed by pairs of identical low reflective Bragg gratings imprinted in a single mode fiber. All interferometer sensors have different cavity length, provoking frequency-domain multiplexing. The optical signal represents the superposition of all interference patterns which can be decomposed using the Fourier transform. The frequency spectrum was analyzed and sensor’s properties were defined. Following that, a quasi-distributed sensor was numerically simulated. Our sensor simulation considers sensor properties, signal processing, noise system, and instrumentation. The numerical results show the behavior of resolution vs. signal-to-noise ratio. From our results, the Fabry-Perot sensor has high resolution and low resolution. Both resolutions are conceivable because the Fourier Domain Phase Analysis (FDPA) algorithm elaborates two evaluations of Bragg wavelength shift. PMID:28420083

Distributed Weak Fiber Bragg Grating Vibration Sensing System Based on 3 × 3 Fiber Coupler

NASA Astrophysics Data System (ADS)

Li, Wei; Zhang, Jian

2018-06-01

A novel distributed weak fiber Bragg gratings (FBGs) vibration sensing system has been designed to overcome the disadvantages of the conventional methods for optical fiber sensing networking, which are: low signal intensity in the usually adopted time-division multiplexing (TDM) technology, insufficient quantity of multiplexed FBGs in the wavelength-division multiplexing (WDM) technology, and that the mixed WDM/TDM technology measures only the physical parameters of the FBG locations but cannot perform distributed measurement over the whole optical fiber. This novel system determines vibration events in the optical fiber line according to the intensity variation of the interference signals between the adjacent weak FBG reflected signals and locates the vibration points accurately using the TDM technology. It has been proven by tests that this system performs vibration signal detection and demodulation in a way more convenient than the conventional methods for the optical fiber sensing system. It also measures over the whole optical fiber, therefore, distributed measurement is fulfilled, and the system locating accuracy is up to 20 m, capable of detecting any signals of whose drive signals lower limit voltage is 0.2 V while the frequency range is 3 Hz‒1 000 Hz. The system has the great practical significance and application value for perimeter surveillance systems.

A Theoretical Study and Numerical Simulation of a Quasi-Distributed Sensor Based on the Low-Finesse Fabry-Perot Interferometer: Frequency-Division Multiplexing.

PubMed

Guillen Bonilla, José Trinidad; Guillen Bonilla, Alex; Rodríguez Betancourtt, Verónica M; Guillen Bonilla, Héctor; Casillas Zamora, Antonio

2017-04-14

The application of the sensor optical fibers in the areas of scientific instrumentation and industrial instrumentation is very attractive due to its numerous advantages. In the industry of civil engineering for example, quasi-distributed sensors made with optical fiber are used for reliable strain and temperature measurements. Here, a quasi-distributed sensor in the frequency domain is discussed. The sensor consists of a series of low-finesse Fabry-Perot interferometers where each Fabry-Perot interferometer acts as a local sensor. Fabry-Perot interferometers are formed by pairs of identical low reflective Bragg gratings imprinted in a single mode fiber. All interferometer sensors have different cavity length, provoking frequency-domain multiplexing. The optical signal represents the superposition of all interference patterns which can be decomposed using the Fourier transform. The frequency spectrum was analyzed and sensor's properties were defined. Following that, a quasi-distributed sensor was numerically simulated. Our sensor simulation considers sensor properties, signal processing, noise system, and instrumentation. The numerical results show the behavior of resolution vs. signal-to-noise ratio. From our results, the Fabry-Perot sensor has high resolution and low resolution. Both resolutions are conceivable because the Fourier Domain Phase Analysis (FDPA) algorithm elaborates two evaluations of Bragg wavelength shift.

Compact SOI optimized slot microring coupled phase-shifted Bragg grating resonator for sensing

NASA Astrophysics Data System (ADS)

Zhao, Chao Ying; Zhang, Lei; Zhang, Cheng Mei

2018-05-01

We propose a novel sensor structure composed of a slot microring and a phase-shifted sidewall Bragg gratings in a slot waveguide. We first present a theoretical analysis of transmission by using the transfer matrix. Then, the mode-field distributions of transmission spectrum obtained from 3D simulations based on FDTD method demonstrates that our sensor exhibit theoretical sensitivity of 297 . 13 nm / RIU, a minimum detection limit of 1 . 1 × 10-4 RIU, the maximum extinction ratio of 20 dB, the quality factor of 2 × 103 and a compact dimension-theoretical structure of 15 μm × 8 . 5 μm. Finally, the sensor's performance is simulated for NaCl solution.

In situ study of annealing-induced strain relaxation in diamond nanoparticles using Bragg coherent diffraction imaging

NASA Astrophysics Data System (ADS)

Hruszkewycz, S. O.; Cha, W.; Andrich, P.; Anderson, C. P.; Ulvestad, A.; Harder, R.; Fuoss, P. H.; Awschalom, D. D.; Heremans, F. J.

2017-02-01

We observed changes in morphology and internal strain state of commercial diamond nanocrystals during high-temperature annealing. Three nanodiamonds were measured with Bragg coherent x-ray diffraction imaging, yielding three-dimensional strain-sensitive images as a function of time/temperature. Up to temperatures of 800 °C, crystals with Gaussian strain distributions with a full-width-at-half-maximum of less than 8 × 10 - 4 were largely unchanged, and annealing-induced strain relaxation was observed in a nanodiamond with maximum lattice distortions above this threshold. X-ray measurements found changes in nanodiamond morphology at temperatures above 600 °C that are consistent with graphitization of the surface, a result verified with ensemble Raman measurements.

Wigner analysis of three dimensional pupil with finite lateral aperture

PubMed Central

Chen, Hsi-Hsun; Oh, Se Baek; Zhai, Xiaomin; Tsai, Jui-Chang; Cao, Liang-Cai; Barbastathis, George; Luo, Yuan

2015-01-01

A three dimensional (3D) pupil is an optical element, most commonly implemented on a volume hologram, that processes the incident optical field on a 3D fashion. Here we analyze the diffraction properties of a 3D pupil with finite lateral aperture in the 4-f imaging system configuration, using the Wigner Distribution Function (WDF) formulation. Since 3D imaging pupil is finite in both lateral and longitudinal directions, the WDF of the volume holographic 4-f imager theoretically predicts distinct Bragg diffraction patterns in phase space. These result in asymmetric profiles of diffracted coherent point spread function between degenerate diffraction and Bragg diffraction, elucidating the fundamental performance of volume holographic imaging. Experimental measurements are also presented, confirming the theoretical predictions. PMID:25836443

Fiber Bragg grating based temperature profiling in ferromagnetic nanoparticles-enhanced radiofrequency ablation

NASA Astrophysics Data System (ADS)

Jelbuldina, Madina; Korobeinyk, Alina V.; Korganbayev, Sanzhar; Inglezakis, Vassilis J.; Tosi, Daniele

2018-07-01

In this work, we report the real-time temperature profiling performed with a fiber Bragg grating (FBG) sensing system, applied to a ferromagnetic nanoparticles (NP)-enhanced radiofrequency ablation (RFA) for interventional cancer care. A minimally invasive RFA setup has been prepared and applied ex vivo on a liver phantom; NPs (with concentrations of 5 and 10 mg/mL) have been synthesized and injected within the tissue prior to ablation, in order to facilitate the heat distribution to the peripheral sides of the treated tissue. A network of 15 FBG sensors has been deployed in situ in order to detect the parenchymal temperature distribution and estimate the thermal profiles in real time during the ablation, highlighting the impact of the NPs on the RFA mechanism. The results confirm that NP-enhanced ablation with 5 mg/mL density shows a better heat penetration that a standard RFA achieving an almost double-sized lesion, while a higher density (10 mg/mL) does not improve the heat distribution. Thermal data are reported highlighting both spatial and temporal gradients, evaluating the capability of NPs to deliver sufficient heating to the peripheral sides of the tumor borders.

Numerical analyses for thinned fiber Bragg grating under uneven surrounding refractive index environment

NASA Astrophysics Data System (ADS)

Luo, Bin-bin; Zhao, Ming-fu; Zhou, Xiao-jun; Huang, De-yi; Wang, Shao-fei; Cao, Xue-mei

2011-12-01

Based on the fiber waveguide models, a modified transfer matrix method was utilized to calculate the reflection spectrum of the thinned fiber Bragg grating (ThFBG) under the uneven surrounding refractive index (SRI) environment. Tow SRI ranges, including the high SRI region (from 1.42 to the fiber cladding index) and the low ones (from 1.33 to about 1.36), were considered. Numerical results showed that the responsive characteristics of the reflectance spectrum of the ThFBG were closely related to the properties of the SRI distribution, first, the original reflection spectrum of the ThFBG would split into many tinny resonant peaks and the reflectance spectrums are asymmetric since the uneven SRI distributions, second, the number of the resonant peaks, the decline of the amplitude, and the degree of the asymmetric of the reflectance spectrums would increase as the increase in the SRI gradient and the D-value of the SRI between the tow ends of the ThFBG. The same numerical approach could be used to analyze the responsive characteristics of the ThFBG under the uneven medium environment where the SRI distribution was any other functions.

Feasibility of RACT for 3D dose measurement and range verification in a water phantom.

PubMed

Alsanea, Fahed; Moskvin, Vadim; Stantz, Keith M

2015-02-01

The objective of this study is to establish the feasibility of using radiation-induced acoustics to measure the range and Bragg peak dose from a pulsed proton beam. Simulation studies implementing a prototype scanner design based on computed tomographic methods were performed to investigate the sensitivity to proton range and integral dose. Derived from thermodynamic wave equation, the pressure signals generated from the dose deposited from a pulsed proton beam with a 1 cm lateral beam width and a range of 16, 20, and 27 cm in water using Monte Carlo methods were simulated. The resulting dosimetric images were reconstructed implementing a 3D filtered backprojection algorithm and the pressure signals acquired from a 71-transducer array with a cylindrical geometry (30 × 40 cm) rotated over 2π about its central axis. Dependencies on the detector bandwidth and proton beam pulse width were performed, after which, different noise levels were added to the detector signals (using 1 μs pulse width and a 0.5 MHz cutoff frequency/hydrophone) to investigate the statistical and systematic errors in the proton range (at 20 cm) and Bragg peak dose (of 1 cGy). The reconstructed radioacoustic computed tomographic image intensity was shown to be linearly correlated to the dose within the Bragg peak. And, based on noise dependent studies, a detector sensitivity of 38 mPa was necessary to determine the proton range to within 1.0 mm (full-width at half-maximum) (systematic error < 150 μm) for a 1 cGy Bragg peak dose, where the integral dose within the Bragg peak was measured to within 2%. For existing hydrophone detector sensitivities, a Bragg peak dose of 1.6 cGy is possible. This study demonstrates that computed tomographic scanner based on ionizing radiation-induced acoustics can be used to verify dose distribution and proton range with centi-Gray sensitivity. Realizing this technology into the clinic has the potential to significantly impact beam commissioning, treatment verification during particle beam therapy and image guided techniques.

Investigation of Carbon-Polymer Structures with Embedded Fiber-Optic Bragg Gratings

NASA Technical Reports Server (NTRS)

Grant, Joseph; Kaul, R.; Taylor, S.; Myers, G.; Sharma, A.

2003-01-01

Several Bragg-grating sensors fabricated within the same optical fiber are buried within multiple-ply carbon-epoxy planar and cylindrical structures. Effect of different orientation of fiber-sensors with respect to carbon fibers in the composite structure is investigated. This is done for both fabric and uni-tape material samples. Response of planar structures to axial and transverse strain up to 1 millistrain is investigated with distributed Bragg-grating sensors. Material properties like Young's Modulus and Poisson ratio is measured. A comparison is made between response measured by sensors in different ply-layers and those bonded on the surface. The results from buried fiber- sensors do not completely agree with surface bonded conventional strain gauges. A plausible explanation is given for observed differences. The planar structures are subjected to impacts with energies up to 10 ft-lb. Effect of this impact on the material stiffness is also investigated with buried fiber-optic Bragg sensors. The strain response of such optical sensors is also measured for cylindrical carbon-epoxy composite structures. The sensors are buried within the walls of the cylinder as well as surface bonded in both the axial as well as hoop directions. The response of these fiber-optic sensors is investigated by pressurizing the cylinder up to its burst pressure of around 1500 psi. This is done at both room temperature as well as cryogenic temperatures. The recorded response is compared with that from a conventional strain gauge.

A new theory for X-ray diffraction.

PubMed

Fewster, Paul F

2014-05-01

This article proposes a new theory of X-ray scattering that has particular relevance to powder diffraction. The underlying concept of this theory is that the scattering from a crystal or crystallite is distributed throughout space: this leads to the effect that enhanced scatter can be observed at the `Bragg position' even if the `Bragg condition' is not satisfied. The scatter from a single crystal or crystallite, in any fixed orientation, has the fascinating property of contributing simultaneously to many `Bragg positions'. It also explains why diffraction peaks are obtained from samples with very few crystallites, which cannot be explained with the conventional theory. The intensity ratios for an Si powder sample are predicted with greater accuracy and the temperature factors are more realistic. Another consequence is that this new theory predicts a reliability in the intensity measurements which agrees much more closely with experimental observations compared to conventional theory that is based on `Bragg-type' scatter. The role of dynamical effects (extinction etc.) is discussed and how they are suppressed with diffuse scattering. An alternative explanation for the Lorentz factor is presented that is more general and based on the capture volume in diffraction space. This theory, when applied to the scattering from powders, will evaluate the full scattering profile, including peak widths and the `background'. The theory should provide an increased understanding of the reliability of powder diffraction measurements, and may also have wider implications for the analysis of powder diffraction data, by increasing the accuracy of intensities predicted from structural models.

Design and fabrication of one-dimensional and two- dimensional photonic bandgap devices

NASA Astrophysics Data System (ADS)

Lim, Kuo-Yi

1999-10-01

One-dimensional and two-dimensional photonic bandgap devices have been designed and fabricated using III-V compound semiconductors. The one-dimensional photonic bandgap devices consist of monorail and air-bridge waveguide microcavities, while the two-dimensional photonic bandgap devices consist of light-emitting devices with enhanced extraction efficiency. Fabrication techniques such as gas source molecular beam epitaxy, direct-write electron-beam lithography, reactive ion etching and thermal oxidation of AlxGa1- xAs have been employed. The III-V thermal oxide, in particular, is used as an index confinement material, as a sacrificial material for micromechanical fabrication of the air-bridge microcavity, and in the realization of a wide-bandwidth distributed Bragg reflector. The one-dimensional photonic bandgap waveguide microcavities have been designed to operate in the wavelength regimes of 4.5 m m and 1.55 m m. The devices designed to operate in the 1.55 m m wavelength regime have been optically characterized. The transmission spectra exhibit resonances at around 1.55 m m and cavity quality factors (Q's) ranging from 136 to 334. The resonant modal volume is calculated to be about 0.056 m m3. Tunability in the resonance wavelengths has also been demonstrated by changing the size of the defect in the one-dimensional photonic crystal. The two-dimensional photonic bandgap light-emitting device consists of a In0.51Ga0.49P/In0.2Ga0.8As/In 0.51Ga0.49P quantum well emitting at 980nm with a triangular photonic lattice of holes in the top cladding layer of the quantum well. The photonic crystal prohibits the propagation of guided modes in the semiconductor, thus enhancing the extraction of light vertical to the light-emitting device. A wide-bandwidth GaAs/AlxOy distributed Bragg reflector mirror under the quantum well structure further enhances the extraction of light from the devices. The extraction efficiency of the two-dimensional photonic bandgap light-emitting device is expected to be at least 5 times that of a device without the two-dimensional photonic crystal. A photoluminescence measurement setup has been modified to optically characterize these devices. (Copies available exclusively from MIT Libraries, Rm. 14-0551, Cambridge, MA 02139-4307. Ph. 617-253-5668; Fax 617-253-1690.)

Novel thermal annealing methodology for permanent tuning polymer optical fiber Bragg gratings to longer wavelengths.

PubMed

Pospori, A; Marques, C A F; Sagias, G; Lamela-Rivera, H; Webb, D J

2018-01-22

The Bragg wavelength of a polymer optical fiber Bragg grating can be permanently shifted by utilizing the thermal annealing method. In all the reported fiber annealing cases, the authors were able to tune the Bragg wavelength only to shorter wavelengths, since the polymer fiber shrinks in length during the annealing process. This article demonstrates a novel thermal annealing methodology for permanently tuning polymer optical fiber Bragg gratings to any desirable spectral position, including longer wavelengths. Stretching the polymer optical fiber during the annealing process, the period of Bragg grating, which is directly related with the Bragg wavelength, can become permanently longer. The methodology presented in this article can be used to multiplex polymer optical fiber Bragg gratings at any desirable spectral position utilizing only one phase-mask for their photo-inscription, reducing thus their fabrication cost in an industrial setting.

In situ study of annealing-induced strain relaxation in diamond nanoparticles using Bragg coherent diffraction imaging

DOE PAGES

Hruszkewycz, S. O.; Cha, W.; Andrich, P.; ...

2017-02-14

Here, we observed changes in morphology and internal strain state of commercial diamond nanocrystals during high-temperature annealing. Three nanodiamonds were measured with Bragg coherent x-ray diffraction imaging, yielding three-dimensional strain-sensitive images as a function of time/temperature. Up to temperatures of 800 °C, crystals with Gaussian strain distributions with a full-width-at-half-maximum of less than 8 × 10 –4 were largely unchanged, and annealing-induced strain relaxation was observed in a nanodiamond with maximum lattice distortions above this threshold. X-ray measurements found changes in nanodiamond morphology at temperatures above 600 °C that are consistent with graphitization of the surface, a result verified withmore » ensemble Raman measurements.« less

Bloch oscillations in the absence of a lattice

NASA Astrophysics Data System (ADS)

Meinert, Florian; Knap, Michael; Kirilov, Emil; Jag-Lauber, Katharina; Zvonarev, Mikhail B.; Demler, Eugene; Nägerl, Hanns-Christoph

2017-06-01

The interplay of strong quantum correlations and far-from-equilibrium conditions can give rise to striking dynamical phenomena. We experimentally investigated the quantum motion of an impurity atom immersed in a strongly interacting one-dimensional Bose liquid and subject to an external force. We found that the momentum distribution of the impurity exhibits characteristic Bragg reflections at the edge of an emergent Brillouin zone. Although Bragg reflections are typically associated with lattice structures, in our strongly correlated quantum liquid they result from the interplay of short-range crystalline order and kinematic constraints on the many-body scattering processes in the one-dimensional system. As a consequence, the impurity exhibits periodic dynamics, reminiscent of Bloch oscillations, although the quantum liquid is translationally invariant. Our observations are supported by large-scale numerical simulations.

Analysis and design of tunable wideband microwave photonics phase shifter based on Fabry-Perot cavity and Bragg mirrors in silicon-on-insulator waveguide.

PubMed

Qu, Pengfei; Zhou, Jingran; Chen, Weiyou; Li, Fumin; Li, Haibin; Liu, Caixia; Ruan, Shengping; Dong, Wei

2010-04-20

We designed a microwave (MW) photonics phase shifter, consisting of a Fabry-Perot filter, a phase modulation region (PMR), and distributed Bragg reflectors, in a silicon-on-insulator rib waveguide. The thermo-optics effect was employed to tune the PMR. It was theoretically demonstrated that the linear MW phase shift of 0-2pi could be achieved by a refractive index variation of 0-9.68x10(-3) in an ultrawideband (about 38?GHz-1.9?THz), and the corresponding tuning resolution was about 6.92 degrees / degrees C. The device had a very compact size. It could be easily integrated in silicon optoelectronic chips and expected to be widely used in the high-frequency MW photonics field.

Tunable Bragg filters with a phase transition material defect layer

DOE PAGES

Wang, Xi; Gong, Zilun; Dong, Kaichen; ...

2016-01-01

We propose an all-solid-state tunable Bragg filter with a phase transition material as the defect layer. Bragg filters based on a vanadium dioxide defect layer sandwiched between silicon dioxide/titanium dioxide Bragg gratings are experimentally demonstrated. Temperature dependent reflection spectroscopy shows the dynamic tunability and hysteresis properties of the Bragg filter. Temperature dependent Raman spectroscopy reveals the connection between the tunability and the phase transition of the vanadium dioxide defect layer. This work paves a new avenue in tunable Bragg filter designs and promises more applications by combining phase transition materials and optical cavities.

Tunable Bragg filters with a phase transition material defect layer

DOE Office of Scientific and Technical Information (OSTI.GOV)

Wang, Xi; Gong, Zilun; Dong, Kaichen

We propose an all-solid-state tunable Bragg filter with a phase transition material as the defect layer. Bragg filters based on a vanadium dioxide defect layer sandwiched between silicon dioxide/titanium dioxide Bragg gratings are experimentally demonstrated. Temperature dependent reflection spectroscopy shows the dynamic tunability and hysteresis properties of the Bragg filter. Temperature dependent Raman spectroscopy reveals the connection between the tunability and the phase transition of the vanadium dioxide defect layer. This work paves a new avenue in tunable Bragg filter designs and promises more applications by combining phase transition materials and optical cavities.

Experimental depth dose curves of a 67.5 MeV proton beam for benchmarking and validation of Monte Carlo simulation

PubMed Central

Faddegon, Bruce A.; Shin, Jungwook; Castenada, Carlos M.; Ramos-Méndez, José; Daftari, Inder K.

2015-01-01

Purpose: To measure depth dose curves for a 67.5 ± 0.1 MeV proton beam for benchmarking and validation of Monte Carlo simulation. Methods: Depth dose curves were measured in 2 beam lines. Protons in the raw beam line traversed a Ta scattering foil, 0.1016 or 0.381 mm thick, a secondary emission monitor comprised of thin Al foils, and a thin Kapton exit window. The beam energy and peak width and the composition and density of material traversed by the beam were known with sufficient accuracy to permit benchmark quality measurements. Diodes for charged particle dosimetry from two different manufacturers were used to scan the depth dose curves with 0.003 mm depth reproducibility in a water tank placed 300 mm from the exit window. Depth in water was determined with an uncertainty of 0.15 mm, including the uncertainty in the water equivalent depth of the sensitive volume of the detector. Parallel-plate chambers were used to verify the accuracy of the shape of the Bragg peak and the peak-to-plateau ratio measured with the diodes. The uncertainty in the measured peak-to-plateau ratio was 4%. Depth dose curves were also measured with a diode for a Bragg curve and treatment beam spread out Bragg peak (SOBP) on the beam line used for eye treatment. The measurements were compared to Monte Carlo simulation done with geant4 using topas. Results: The 80% dose at the distal side of the Bragg peak for the thinner foil was at 37.47 ± 0.11 mm (average of measurement with diodes from two different manufacturers), compared to the simulated value of 37.20 mm. The 80% dose for the thicker foil was at 35.08 ± 0.15 mm, compared to the simulated value of 34.90 mm. The measured peak-to-plateau ratio was within one standard deviation experimental uncertainty of the simulated result for the thinnest foil and two standard deviations for the thickest foil. It was necessary to include the collimation in the simulation, which had a more pronounced effect on the peak-to-plateau ratio for the thicker foil. The treatment beam, being unfocussed, had a broader Bragg peak than the raw beam. A 1.3 ± 0.1 MeV FWHM peak width in the energy distribution was used in the simulation to match the Bragg peak width. An additional 1.3–2.24 mm of water in the water column was required over the nominal values to match the measured depth penetration. Conclusions: The proton Bragg curve measured for the 0.1016 mm thick Ta foil provided the most accurate benchmark, having a low contribution of proton scatter from upstream of the water tank. The accuracy was 0.15% in measured beam energy and 0.3% in measured depth penetration at the Bragg peak. The depth of the distal edge of the Bragg peak in the simulation fell short of measurement, suggesting that the mean ionization potential of water is 2–5 eV higher than the 78 eV used in the stopping power calculation for the simulation. The eye treatment beam line depth dose curves provide validation of Monte Carlo simulation of a Bragg curve and SOBP with 4%/2 mm accuracy. PMID:26133619

A highly distributed Bragg stack with unique geometry provides effective camouflage for Loliginid squid eyes

PubMed Central

Holt, Amanda L.; Sweeney, Alison M.; Johnsen, Sönke; Morse, Daniel E.

2011-01-01

Cephalopods possess a sophisticated array of mechanisms to achieve camouflage in dynamic underwater environments. While active mechanisms such as chromatophore patterning and body posturing are well known, passive mechanisms such as manipulating light with highly evolved reflectors may also play an important role. To explore the contribution of passive mechanisms to cephalopod camouflage, we investigated the optical and biochemical properties of the silver layer covering the eye of the California fishery squid, Loligo opalescens. We discovered a novel nested-spindle geometry whose correlated structure effectively emulates a randomly distributed Bragg reflector (DBR), with a range of spatial frequencies resulting in broadband visible reflectance, making it a nearly ideal passive camouflage material for the depth at which these animals live. We used the transfer-matrix method of optical modelling to investigate specular reflection from the spindle structures, demonstrating that a DBR with widely distributed thickness variations of high refractive index elements is sufficient to yield broadband reflectance over visible wavelengths, and that unlike DBRs with one or a few spatial frequencies, this broadband reflectance occurs from a wide range of viewing angles. The spindle shape of the cells may facilitate self-assembly of a random DBR to achieve smooth spatial distributions in refractive indices. This design lends itself to technological imitation to achieve a DBR with wide range of smoothly varying layer thicknesses in a facile, inexpensive manner. PMID:21325315

Mutual Injection Locking of Monolithically Integrated Coupled-Cavity DBR Lasers

DOE PAGES

Tauke-Pedretti, Anna; Vawter, G. Allen; Skogen, Erik J.; ...

2011-07-01

We present a photonic integrated circuit (PIC) composed of two strongly coupled distributed Bragg reflector (DBR) lasers. This PIC utilizes the dynamics of mutual injection locking to increase the relaxation resonance frequency from 3 GHz to beyond 30 GHz. Mutual injection-locking and external injection-locking operation are then compared.

Experimental study of dual polarized radar return from the sea surface

NASA Astrophysics Data System (ADS)

Ermakov, S. A.; Kapustin, I. A.; Lavrova, O. Yu.; Molkov, A. A.; Sergievskaya, I. A.; Shomina, O. V.

2017-10-01

Dual-polarized microwave radars are of particular interest nowadays as perspective tool of ocean remote sensing. Microwave radar backscattering at moderate and large incidence angles according to conventional models is determined by resonance (Bragg) surface waves typically of cm-scale wavelength range. Some recent experiments have indicated, however, that an additional, non Bragg component (NBC) contributes to the radar return. The latter is considered to occur due to wave breaking. At present our understanding of the nature of different components of radar return is still poor. This paper presents results of field experiment using an X-/C-/S-band Doppler radar operating at HH- and VVpolarizations. The intensity and radar Doppler shifts for Bragg and non Bragg components are retrieved from measurements of VV and HH radar returns. Analysis of a ratio of VV and HH radar backscatter - polarization ratio (PR) has demonstrated a significant role of a non Bragg component. NBC contributes significantly to the total radar backscatter, in particular, at moderate incidence angles (about 50-70 deg.) it is 2-3 times smaller than VV Bragg component and several times larger that HH Bragg component. Both NBC and BC depend on azimuth angle, being minimal for cross wind direction, but NBC is more isotropic than BC. It is obtained that velocities of scatterers retrieved from radar Doppler shifts are different for Bragg waves and for non Bragg component; NBC structures are "faster" than Bragg waves particularly for upwind radar observations. Bragg components propagate approximately with phase velocities of linear gravity-capillary waves (when accounting for wind drift). Velocities of NBC scatterers depend on radar band, being the largest for S-band and the smallest at X-band, this means that different structures on the water surface are responsible for non Bragg scattering in a given radar band.

Fiber Bragg grating filter using evaporated induced self assembly of silica nano particles

NASA Astrophysics Data System (ADS)

Hammarling, Krister; Zhang, Renyung; Manuilskiy, Anatoliy; Nilsson, Hans-Erik

2014-03-01

In the present work we conduct a study of fiber filters produced by evaporation of silica particles upon a MM-fiber core. A band filter was designed and theoretically verified using a 2D Comsol simulation model of a 3D problem, and calculated in the frequency domain in respect to refractive index. The fiber filters were fabricated by stripping and chemically etching the middle part of an MM-fiber until the core was exposed. A mono layer of silica nano particles were evaporated on the core using an Evaporation Induced Self-Assembly (EISA) method. The experimental results indicated a broader bandwidth than indicated by the simulations which can be explained by the mismatch in the particle size distributions, uneven particle packing and finally by effects from multiple mode angles. Thus, there are several closely connected Bragg wavelengths that build up the broader bandwidth. The experimental part shows that it is possible by narrowing the particle size distributing and better control of the particle packing, the filter effectiveness can be greatly improved.

Ultra-thin distributed Bragg reflectors via stacked single-crystal silicon nanomembranes

DOE Office of Scientific and Technical Information (OSTI.GOV)

Cho, Minkyu; Seo, Jung-Hun; Lee, Jaeseong

2015-05-04

In this paper, we report ultra-thin distributed Bragg reflectors (DBRs) via stacked single-crystal silicon (Si) nanomembranes (NMs). Mesh hole-free single-crystal Si NMs were released from a Si-on-insulator substrate and transferred to quartz and Si substrates. Thermal oxidation was applied to the transferred Si NM to form high-quality SiO{sub 2} and thus a Si/SiO{sub 2} pair with uniform and precisely controlled thicknesses. The Si/SiO{sub 2} layers, as smooth as epitaxial grown layers, minimize scattering loss at the interface and in between the layers. As a result, a reflection of 99.8% at the wavelength range from 1350 nm to 1650 nm can be measuredmore » from a 2.5-pair DBR on a quartz substrate and 3-pair DBR on a Si substrate with thickness of 0.87 μm and 1.14 μm, respectively. The high reflection, ultra-thin DBRs developed here, which can be applied to almost any devices and materials, holds potential for application in high performance optoelectronic devices and photonics applications.« less

Nanoporous distributed Bragg reflectors on free-standing nonpolar m-plane GaN

NASA Astrophysics Data System (ADS)

Mishkat-Ul-Masabih, Saadat; Luk, Ting Shan; Rishinaramangalam, Ashwin; Monavarian, Morteza; Nami, Mohsen; Feezell, Daniel

2018-01-01

We report the fabrication of m-plane nanoporous distributed Bragg reflectors (DBRs) on free-standing GaN substrates. The DBRs consist of 15 pairs of alternating undoped and highly doped n-type ([Si] = ˜3.7 × 1019 cm-3) GaN. Electrochemical (EC) etching was performed to convert the highly doped regions into a porous material, consequently reducing the effective refractive index of the layers. We demonstrate a DBR with peak reflectance greater than 98% at 450 nm with a stopband width of ˜72 nm. The polarization ratio of an incident polarized light source remains identical after reflection from the DBR, verifying that there is no drop in the polarization ratio due to the interfaces between the porous layers. We also quantify the porosity under various EC bias conditions for layers with different doping concentrations. The bias voltage controls the average pore diameter, while the pore density is primarily determined by the doping concentration. The results show that nanoporous DBRs on nonpolar free-standing GaN are promising candidates for high-reflectance, lattice-matched DBR mirrors for GaN-based resonant cavity devices.

Broadband and wide-angle distributed Bragg reflectors based on amorphous germanium films by glancing angle deposition.

PubMed

Leem, Jung Woo; Yu, Jae Su

2012-08-27

We fabricated the distributed Bragg reflectors (DBRs) with amorphous germanium (a-Ge) films consisted of the same materials at a center wavelength (λc) of 1.33 μm by the glancing angle deposition. Their optical reflectance properties were investigated in the infrared wavelength region of 1-1.9 μm at incident light angles (θ inc) of 8-70°, together with the theoretical analysis using a rigorous coupled-wave analysis simulation. The two alternating a-Ge films at the incident vapor flux angles of 0 and 75° were formed as the high and low refractive index materials, respectively. The a-Ge DBR with only 5 periods exhibited a normalized stop bandwidth (∆λ/λ c) of ~24.1%, maintaining high reflectance (R) values of > 99%. Even at a high θ inc of 70°, the ∆λ/λ c was ~21.9%, maintaining R values of > 85%. The a-Ge DBR with good uniformity was obtained over the area of a 2 inch Si wafer. The calculated reflectance results showed a similar tendency to the measured data.

Strain Modal Analysis of Small and Light Pipes Using Distributed Fibre Bragg Grating Sensors

PubMed Central

Huang, Jun; Zhou, Zude; Zhang, Lin; Chen, Juntao; Ji, Chunqian; Pham, Duc Truong

2016-01-01

Vibration fatigue failure is a critical problem of hydraulic pipes under severe working conditions. Strain modal testing of small and light pipes is a good option for dynamic characteristic evaluation, structural health monitoring and damage identification. Unique features such as small size, light weight, and high multiplexing capability enable Fibre Bragg Grating (FBG) sensors to measure structural dynamic responses where sensor size and placement are critical. In this paper, experimental strain modal analysis of pipes using distributed FBG sensors ispresented. Strain modal analysis and parameter identification methods are introduced. Experimental strain modal testing and finite element analysis for a cantilever pipe have been carried out. The analysis results indicate that the natural frequencies and strain mode shapes of the tested pipe acquired by FBG sensors are in good agreement with the results obtained by a reference accelerometer and simulation outputs. The strain modal parameters of a hydraulic pipe were obtained by the proposed strain modal testing method. FBG sensors have been shown to be useful in the experimental strain modal analysis of small and light pipes in mechanical, aeronautic and aerospace applications. PMID:27681728

Wide forbidden band induced by the interference of different transverse acoustic standing-wave modes

NASA Astrophysics Data System (ADS)

Tao, Zhiyong; He, Weiyu; Xiao, Yumeng; Wang, Xinlong

2008-03-01

A non-Bragg nature forbidden band is experimentally observed in an axially symmetric hard-walled duct with a periodically varying cross section. Unlike the familiar Bragg ones, the observed bandgap is found to result from the interference of sound wave modes having different transverse standing-wave profiles, the so-called non-Bragg resonance. The experiments also show that the non-Bragg band can be comparably wider than the Bragg one; furthermore, the sound transmission loss within the band can be much more effective, exhibiting the great significance of the non-Bragg resonance in wave propagation in periodic waveguides.

A new theory for X-ray diffraction

PubMed Central

Fewster, Paul F.

2014-01-01

This article proposes a new theory of X-ray scattering that has particular relevance to powder diffraction. The underlying concept of this theory is that the scattering from a crystal or crystallite is distributed throughout space: this leads to the effect that enhanced scatter can be observed at the ‘Bragg position’ even if the ‘Bragg condition’ is not satisfied. The scatter from a single crystal or crystallite, in any fixed orientation, has the fascinating property of contributing simultaneously to many ‘Bragg positions’. It also explains why diffraction peaks are obtained from samples with very few crystallites, which cannot be explained with the conventional theory. The intensity ratios for an Si powder sample are predicted with greater accuracy and the temperature factors are more realistic. Another consequence is that this new theory predicts a reliability in the intensity measurements which agrees much more closely with experimental observations compared to conventional theory that is based on ‘Bragg-type’ scatter. The role of dynamical effects (extinction etc.) is discussed and how they are suppressed with diffuse scattering. An alternative explanation for the Lorentz factor is presented that is more general and based on the capture volume in diffraction space. This theory, when applied to the scattering from powders, will evaluate the full scattering profile, including peak widths and the ‘background’. The theory should provide an increased understanding of the reliability of powder diffraction measurements, and may also have wider implications for the analysis of powder diffraction data, by increasing the accuracy of intensities predicted from structural models. PMID:24815975

Fabrication and characterization of TiO2/SiO2 based Bragg reflectors for light trapping applications

NASA Astrophysics Data System (ADS)

Dubey, R. S.; Ganesan, V.

Distributed Bragg reflectors (DBRs) have received an intensive attention due to their increasing demand in optoelectronic and photonic devices. Such reflectors are capable to prohibit the light propagation within the specified wavelength range of interest. In this paper, we present the fabrication of TiO2/SiO2 stacks based Bragg reflectors by using a simple and in-expensive sol-gel spin coating technique. The prepared single-layer thin films of TiO2 and SiO2 onto glass substrates were characterized for their optical constants. By tuning the process parameters, one-seven DBR stacks of TiO2/SiO2 were prepared. The corresponding shift of the Bragg reflection peak was observed with the increased number of DBR stacks and as much as about 90% reflectance is observed from the 7DBR stacks. The experimentally measured reflectance was compared with the simulated one, which showed good in agreement. FESEM measurement has confirmed the formation of bright and dark strips of TiO2 and SiO2 films with their thicknesses 80 and 115 nm respectively. The simulation study was explored to a design of thin film silicon solar cell using 7DBR stacks. An enhancement in light absorption in the visible wavelength range is observed which coincides with the experimental result of the reflectance. The use of DBR at the bottom of the solar cell could felicitate the better light harvesting with the occurrence of Fabry-Perot resonances in the absorbing layer.

A distributed fluid level sensor suitable for monitoring fuel load on board a moving fuel tank

NASA Astrophysics Data System (ADS)

Arkwright, John W.; Parkinson, Luke A.; Papageorgiou, Anthony W.

2018-02-01

A temperature insensitive fiber Bragg grating sensing array has been developed for monitoring fluid levels in a moving tank. The sensors are formed from two optical fibers twisted together to form a double helix with pairs of fiber Bragg gratings located above one another at the points where the fibers are vertically disposed. The sensing mechanism is based on a downwards deflection of the section of the double helix containing the FBGs which causes the tension in the upper FBG to decrease and the tension in the lower FBG to increase with concomitant changes in Bragg wavelength in each FBG. Changes in ambient temperature cause a common mode increase in Bragg wavelength, thus monitoring the differential change in wavelength provides a temperature independent measure of the applied pressure. Ambient temperature can be monitored simultaneously by taking the average wavelength of the upper and lower FBGs. The sensors are able to detect variations in pressure with resolutions better than 1 mmH2O and when placed on the bottom of a tank can be used to monitor fluid level based on the recorded pressure. Using an array of these sensors located along the bottom of a moving tank it was possible to monitor the fluid level at multiple points and hence dynamically track the total fluid volume in the tank. The outer surface of the sensing array is formed from a thin continuous Teflon sleeve, making it suitable for monitoring the level of volatile fluids such as aviation fuel and gasoline.

Long-gauge FBGs interrogated by DTR3 for dynamic distributed strain measurement of helicopter blade model

NASA Astrophysics Data System (ADS)

Nishiyama, M.; Igawa, H.; Kasai, T.; Watanabe, N.

2014-05-01

In this paper, we describe characteristics of distributed strain sensing based on a Delayed Transmission/Reflection Ratiometric Reflectometry (DTR3) scheme with a long-gauge Fiber Bragg Grating (FBG), which is attractive to dynamic structural deformation monitoring such as a helicopter blade and an airplane wing. The DTR3 interrogator using the longgauge FBG has capability of detecting distributed strain with 50 cm spatial resolution in 100 Hz sampling rate. We evaluated distributed strain sensing characteristics of the long-gauge FBG attached on a 5.5 m helicopter blade model in static tests and free vibration dynamic tests.

Visible light emitting vertical cavity surface emitting lasers

DOEpatents

Bryan, Robert P.; Olbright, Gregory R.; Lott, James A.; Schneider, Jr., Richard P.

1995-01-01

A vertical cavity surface emitting laser that emits visible radiation is built upon a substrate, then having mirrors, the first mirror on top of the substrate; both sets of mirrors being a distributed Bragg reflector of either dielectrics or other materials which affect the resistivity or of semiconductors, such that the structure within the mirror comprises a plurality of sets, each having a thickness of .lambda./2n where n is the index of refraction of each of the sets; each of the mirrors adjacent to spacers which are on either side of an optically active bulk or quantum well layer; and the spacers and the optically active layer are from one of the following material systems: In.sub.z (Al.sub.y Ga.sub.1-y).sub.1-z P, InAlGaAs, AlGaAs, InGaAs, or AlGaP/GaP, wherein the optically active region having a length equal to m .lambda./2n.sub.eff where m is an integer and n.sub.eff is the effective index of refraction of the laser cavity, and the spacer layer and one of the mirrors being transmissive to radiation having a wavelength of .lambda./n, typically within the green to red portion of the visible spectrum.

Visible light emitting vertical cavity surface emitting lasers

DOEpatents

Bryan, R.P.; Olbright, G.R.; Lott, J.A.; Schneider, R.P. Jr.

1995-06-27

A vertical cavity surface emitting laser that emits visible radiation is built upon a substrate, then having mirrors, the first mirror on top of the substrate; both sets of mirrors being a distributed Bragg reflector of either dielectrics or other materials which affect the resistivity or of semiconductors, such that the structure within the mirror comprises a plurality of sets, each having a thickness of {lambda}/2n where n is the index of refraction of each of the sets; each of the mirrors adjacent to spacers which are on either side of an optically active bulk or quantum well layer; and the spacers and the optically active layer are from one of the following material systems: In{sub z}(Al{sub y}Ga{sub 1{minus}y}){sub 1{minus}z}P, InAlGaAs, AlGaAs, InGaAs, or AlGaP/GaP, wherein the optically active region having a length equal to m {lambda}/2n{sub eff} where m is an integer and n{sub eff} is the effective index of refraction of the laser cavity, and the spacer layer and one of the mirrors being transmissive to radiation having a wavelength of {lambda}/n, typically within the green to red portion of the visible spectrum. 10 figs.

Photopumped infrared vertical-cavity surface-emitting laser

NASA Astrophysics Data System (ADS)

Hadji, E.; Bleuse, J.; Magnea, N.; Pautrat, J. L.

1996-04-01

The feasibility of a photopumped infrared vertical-cavity surface-emitting laser (VCSEL) based on CdHgTe alloys is demonstrated. The structure of the VCSEL consists of a 16.5-period Cd0.4Hg0.6Te/Cd0.75Hg0.25Te bottom Bragg reflector and a 3λ/4 thick Cd0.75Hg0.25Te cavity, containing a 100-nm-thick well, grown by molecular beam epitaxy. The top mirror is a 7-period YF3/ZnS dielectric stack. The cavity quality factor is Q=350. This heterostructure VCSEL operates at 3.06 μm with a measured power density threshold of 45 kW/cm2 at 10 K.

Chromatic X-ray magnifying method and apparatus by Bragg reflective planes on the surface of Abbe sphere

DOEpatents

Thoe, Robert S.

1991-01-01

Method and apparatus for producing sharp, chromatic, magnified images of X-ray emitting objects, are provided. The apparatus, which constitutes an X-ray microscope or telescope, comprises a connected collection of Bragg reflecting planes, comprised of either a bent crystal or a synthetic multilayer structure, disposed on and adjacent to a locus determined by a spherical surface. The individual Bragg planes are spatially oriented to Bragg reflect radiation from the object location toward the image location. This is accomplished by making the Bragg planes spatially coincident with the surfaces of either a nested series of prolate ellipsoids of revolution, or a nested series of spheres. The spacing between the Bragg reflecting planes can be tailored to control the wavelengths and the amount of the X-radiation that is Bragg reflected to form the X-ray image.

Bragg coherent diffractive imaging of single-grain defect dynamics in polycrystalline films

NASA Astrophysics Data System (ADS)

Yau, Allison; Cha, Wonsuk; Kanan, Matthew W.; Stephenson, G. Brian; Ulvestad, Andrew

2017-05-01

Polycrystalline material properties depend on the distribution and interactions of their crystalline grains. In particular, grain boundaries and defects are crucial in determining their response to external stimuli. A long-standing challenge is thus to observe individual grains, defects, and strain dynamics inside functional materials. Here we report a technique capable of revealing grain heterogeneity, including strain fields and individual dislocations, that can be used under operando conditions in reactive environments: grain Bragg coherent diffractive imaging (gBCDI). Using a polycrystalline gold thin film subjected to heating, we show how gBCDI resolves grain boundary and dislocation dynamics in individual grains in three-dimensional detail with 10-nanometer spatial and subangstrom displacement field resolution. These results pave the way for understanding polycrystalline material response under external stimuli and, ideally, engineering particular functions.

Tunable ultranarrow spectrum selective absorption in a graphene monolayer at terahertz frequency

NASA Astrophysics Data System (ADS)

Wu, Jun

2016-06-01

Complete absorption in a graphene monolayer at terahertz frequency through the critical coupling effect is investigated. It is achieved by sandwiching the graphene monolayer between a dielectric grating and a Bragg grating. The designed graphene absorber exhibits near-unity absorption at resonance but with an ultranarrow spectrum and antenna-like response, which is attributed to the combined effects of guided mode resonance with dielectric grating and the photonic band gap with Bragg grating. In addition to numerical simulation, the electric field distributions are also illustrated to provide a physical understanding of the perfect absorption effect. Furthermore, the absorption performance can be tuned by only changing the Fermi level of graphene, which is beneficial for real application. It is believed that this study may be useful for designing next-generation graphene-based optoelectronic devices.

A Fiber Bragg Grating Temperature Sensor for 2-400 K

DOE Office of Scientific and Technical Information (OSTI.GOV)

Zaynetdinov, Madrakhim; See, Erich M.; Geist, Brian

2015-03-01

We demonstrate fiber optic, multiplexible temperature sensing using a fiber Bragg grating (FBG) with an operational range of 2-400 K, and a temperature resolution better than 10 mK for temperatures < 12 K. This represents a significant reduction in the lowest usable temperature as well as a significant increase in sensitivity at cryogenic temperatures compared with previously reported multiplexible solutions. This is accomplished by mounting the section of the fiber with a FBG on a polytetrafluoroethylene coupon, which has a non-negligible coefficient of thermal expansion down to < 4 K. The sensors exhibit a good stability over multiple temperature cyclesmore » and acceptable sensor-to-sensor repeatability. Possible applications for this sensor include distributed temperature sensing across superconducting elements and cryogenic temperature measurements in environments where electrical measurements are impractical or unsafe.« less

Multi-resonance peaks fiber Bragg gratings based on largely-chirped structure

NASA Astrophysics Data System (ADS)

Chen, Chao; Zhang, Xuan-Yu; Wei, Wei-Hua; Chen, Yong-Yi; Qin, Li; Ning, Yong-Qiang; Yu, Yong-Sen

2018-04-01

A composite fiber Bragg grating (FBG) with multi-resonance peaks (MRPs) has been realized by using femtosecond (fs) laser point-by-point inscription in single-mode fiber. This device contains a segment of largely-chirped gratings with the ultrahigh chirp coefficients and a segment of uniform high-order gratings. The observed MRPs are distributed in an ultra-broadband wavelength range from 1200 nm to 1700 nm in the form of quasi-period or multi-peak-group. For the 8th-order MRPs-FBG, we studied the axial strain and high-temperature sensing characteristics of different resonance peaks experimentally. Moreover, we have demonstrated a multi-wavelength fiber lasers with three-wavelength stable output by using a 9th-order MRPs-FBG as the wavelength selector. This work is significant for the fabrication and functionalization of FBGs with complicated spectra characteristics.

Numerical model of tapered fiber Bragg gratings for comprehensive analysis and optimization of their sensing and strain-induced tunable dispersion properties.

PubMed

Osuch, Tomasz; Markowski, Konrad; Jędrzejewski, Kazimierz

2015-06-10

A versatile numerical model for spectral transmission/reflection, group delay characteristic analysis, and design of tapered fiber Bragg gratings (TFBGs) is presented. This approach ensures flexibility with defining both distribution of refractive index change of the gratings (including apodization) and shape of the taper profile. Additionally, sensing and tunable dispersion properties of the TFBGs were fully examined, considering strain-induced effects. The presented numerical approach, together with Pareto optimization, were also used to design the best tanh apodization profiles of the TFBG in terms of maximizing its spectral width with simultaneous minimization of the group delay oscillations. Experimental verification of the model confirms its correctness. The combination of model versatility and possibility to define the other objective functions of Pareto optimization creates a universal tool for TFBG analysis and design.

Bragg coherent diffractive imaging of single-grain defect dynamics in polycrystalline films

DOE PAGES

Yau, Allison; Cha, Wonsuk; Kanan, Matthew W.; ...

2017-05-19

Polycrystalline material properties depend on the distribution and interactions of their crystalline grains. In particular, grain boundaries and defects are crucial in determining their response to external stimuli. A long-standing challenge is thus to observe individual grains, defects, and strain dynamics inside functional materials. Here we report a technique capable of revealing grain heterogeneity, including strain fields and individual dislocations, that can be used under operando conditions in reactive environments: grain Bragg coherent diffractive imaging (gBCDI). Using a polycrystalline gold thin film subjected to heating, we show how gBCDI resolves grain boundary and dislocation dynamics in individual grains in three-dimensionalmore » detail with 10-nanometer spatial and subangstrom displacement field resolution. Finally, these results pave the way for understanding polycrystalline material response under external stimuli and, ideally, engineering particular functions.« less

Linear, Low Noise Microwave Photonic Systems using Phase and Frequency Modulation

DTIC Science & Technology

2012-05-11

modulation experiments 65 5.1 Review of FM lasers . . . . . . . . . . . . . . . . . . . . . . . . . . . 65 5.1.1 Fabry - Perot lasers...asymmetrical Mach Zehnder interferometers (a-MZI) [17, 34], Fabry - Perot filters [35], fiber Bragg gratings [36] and tunable integrated filters [37, 38...transmitting subcarrier-multiplexed, analog signals for applications in cable television distribution. Experimental results for a Fabry - Perot

Fiber Bragg grating inscription in optical multicore fibers

NASA Astrophysics Data System (ADS)

Becker, Martin; Elsmann, Tino; Lorenz, Adrian; Spittel, Ron; Kobelke, Jens; Schuster, Kay; Rothhardt, Manfred; Latka, Ines; Dochow, Sebastian; Bartelt, Hartmut

2015-09-01

Fiber Bragg gratings as key components in telecommunication, fiber lasers, and sensing systems usually rely on the Bragg condition for single mode fibers. In special applications, such as in biophotonics and astrophysics, high light coupling efficiency is of great importance and therefore, multimode fibers are often preferred. The wavelength filtering effect of Bragg gratings in multimode fibers, however is spectrally blurred over a wide modal spectrum of the fiber. With a well-designed all solid multicore microstructured fiber a good light guiding efficiency in combination with narrow spectral filtering effect by Bragg gratings becomes possible.

Fiber optic security seal including plural Bragg gratings

DOEpatents

Forman, Peter R.

1994-01-01

An optical security system enables the integrity of a container seal to be remotely interrogated. A plurality of Bragg gratings is written holographically into the core of at least one optical fiber placed about the container seal, where each Bragg grating has a predetermined location and a known frequency for reflecting incident light. A time domain reflectometer is provided with a variable frequency light output that corresponds to the reflecting frequencies of the Bragg gratings to output a signal that is functionally related to the location and reflecting frequency of each of the Bragg gratings.

TiO2 surface functionalization of COC based planar waveguide Bragg gratings for refractive index sensing

NASA Astrophysics Data System (ADS)

Rosenberger, M.; Girschikofsky, M.; Förthner, M.; Belle, S.; Rommel, M.; Frey, L.; Schmauss, B.; Hellmann, R.

2018-01-01

We demonstrate the applicability of a planar waveguide Bragg grating in cyclo-olefin copolymer (COC) for refractive index sensing. The polymer planar waveguide Bragg grating fabricated using a single writing step technique is coated with a high-index layer of titanium dioxide (TiO2) leading to a distinct birefringence. This in turn results in the splitting of the Bragg reflection into two distinct Bragg wavelengths, which strongly differ regarding their refractive index sensitivities. Where one wavelength is only slightly affected by the ambient refractive index, the second Bragg peak shows a strong sensitivity. Furthermore, we investigate the temperature behaviour of the functionalized sensor and discuss it with respect to applications in refractive index sensing.

Dose- and LET-painting with particle therapy.

PubMed

Bassler, Niels; Jäkel, Oliver; Søndergaard, Christian Skou; Petersen, Jørgen B

2010-10-01

Tumour hypoxia is one of the limiting factors in obtaining tumour control in radiotherapy. The high-LET region of a beam of heavy charged particles such as carbon ions is located in the distal part of the Bragg peak. A modulated or spread out Bragg peak (SOBP) is a weighted function of several Bragg peaks at various energies, which however results in a dilution of the dose-average LET in the target volume. Here, we investigate the possibility to redistribute the LET by dedicated treatment plan optimisation, in order to maximise LET in the target volume. This may be a strategy to potentially overcome hypoxia along with dose escalation or dose painting. The high-LET region can be shaped in very different ways, while maintaining the distribution of the absorbed dose or biological effective dose. Treatment plans involving only carbon ion beams, show very different LET distributions depending on how the fields are arranged. Alternatively, a LET boost can be applied in multi-modal treatment planning, such as combining carbon ions with protons and/or photons. For such mixed radiation modalities, significant "LET boosts" can be achieved at nearly arbitrary positions within the target volume. Following the general understanding of the relationship between hypoxia, LET and the oxygen enhancement ratio (OER), we conclude, that an additional therapeutic advantage can be achieved by confining the high-LET part of the radiation in hypoxic compartments of the tumour, and applying low-LET radiation to the normoxic tissue. We also anticipate that additional advantages may be achieved by deliberate sparing of normal tissue from high LET regions. Consequently, treatment planning based on simultaneous dose and LET optimisation has a potential to achieve higher tumour control and/or reduced normal tissue control probability (NTCP).

Induction of micronuclei in human fibroblasts across the Bragg curve of energetic heavy ions

NASA Technical Reports Server (NTRS)

Hada, Megumi; Rusek, Adam; Cucinotta, Francis A.; Wu, Honglu

2006-01-01

The space environment consists of a varying field of radiation particles including high energy ions, with spacecraft shielding material providing the major protection to astronauts from harmful exposure. Unlike low-L or X-rays, the presence of shielding does not always reduce the radiation risks for energetic charged particle exposure. Although the dose delivered by the charged particle increases sharply as the particle approaches the Bragg peak, the Bragg curve does not necessarily represent the biological damage along the particle traversal. The "biological Bragg curve" is dependent on the energy and the type of the primary particle, and may vary for different biological endpoints. To investigate "biological Bragg curves", we analyzed micronuclei (MN) induction along the particle traversal of Si and Fe ions at incident energies of 300 MeV/nucleon and 1 GeV/nucleon. A quantitative biological response curve did not reveal an increased yield of MN at the location of the Bragg peak. However, the ratio of mono-to bi-nucleated cells, which indicates inhibition in cell progression, increased at the Bragg peak location. These results confirm the hypothesis that "over kill" at the Bragg peak will affect the outcome of other biological endpoints.

Design of a compact and high sensitive refractive index sensor base on metal-insulator-metal plasmonic Bragg grating.

PubMed

Binfeng, Yun; Guohua, Hu; Ruohu, Zhang; Yiping, Cui

2014-11-17

A nanometric and high sensitive refractive index sensor based on the metal-insulator-metal plasmonic Bragg grating is proposed. The wavelength encoded sensing characteristics of the refractive index sensor were investigated by analyzing its transmission spectrum. The numerical results show that a good linear relationship between the Bragg wavelength and the refractive index of the sensing material can be obtained, which is in accordance with the analytical results very well. A high refractive index sensitivity of 1,488 nm/RIU around Bragg resonance wavelength of 1,550 nm was obtained. Besides, the simulation results show that the sensitivity is depended on the Bragg resonance wavelength and the longer the Bragg resonance wavelength, the higher sensitivity can be obtained. Furthermore, the figure of merit of the refractive index sensor can be greatly increased by introducing a nano-cavity in the proposed plasmonic Bragg grating structure. This work pave the way for high sensitive nanometric refractive index sensor design and application.

The significance of Bragg's law in electron diffraction and microscopy, and Bragg's second law.

PubMed

Humphreys, C J

2013-01-01

Bragg's second law, which deserves to be more widely known, is recounted. The significance of Bragg's law in electron diffraction and microscopy is then discussed, with particular emphasis on differences between X-ray and electron diffraction. As an example of such differences, the critical voltage effect in electron diffraction is described. It is then shown that the lattice imaging of crystals in high-resolution electron microscopy directly reveals the Bragg planes used for the imaging process, exactly as visualized by Bragg in his real-space law. Finally, it is shown how in 2012, for the first time, on the centennial anniversary of Bragg's law, single atoms have been identified in an electron microscope using X-rays emitted from the specimen. Hence atomic resolution X-ray maps of a crystal in real space can be formed which give the positions and identities of the different atoms in the crystal, or of a single impurity atom in the crystal.

Fiber optic security seal including plural Bragg gratings

DOEpatents

Forman, P.R.

1994-09-27

An optical security system enables the integrity of a container seal to be remotely interrogated. A plurality of Bragg gratings is written holographically into the core of at least one optical fiber placed about the container seal, where each Bragg grating has a predetermined location and a known frequency for reflecting incident light. A time domain reflectometer is provided with a variable frequency light output that corresponds to the reflecting frequencies of the Bragg gratings to output a signal that is functionally related to the location and reflecting frequency of each of the Bragg gratings. 2 figs.

Tunable Optical Assembly with Vibration Dampening

NASA Technical Reports Server (NTRS)

Shams, Qamar A.; Allison, Sidney G.; Fox, Robert L.

2008-01-01

Since their market introduction in 1995, fiber Bragg gratings (FBGs) have emerged as excellent means of measuring such parameters as strain and temperature. Distributed-grating sensing is particularly beneficial for such structural-health monitoring applications such as those of 'smart' structures or integrated vehicle health management in aerospace vehicles. Because of the variability of their output wavelengths, tunable lasers have become widely used as means of measuring FBGs. Several versions of a lightweight assembly for strain-tuning an FBG and dampening its vibrations have been constructed. The main components of such an assembly are one or more piezoelectric actuators, an optical fiber containing one or more Bragg grating(s), a Bragg-grating strain-measurement system, and a voltage source for actuation. The piezoelectric actuators are, more specifically, piezoceramic fiber composite actuators and, can be, still more specifically, of a type known in the art as macro-fiber composite (MFC) actuators. In fabrication of one version of the assembly, the optical fiber containing the Bragg grating(s) is sandwiched between the piezoelectric actuators along with an epoxy that is used to bond the optical fiber to both actuators, then the assembly is placed in a vacuum bag and kept there until the epoxy is cured. Bonding an FBG directly into an MFC actuator greatly reduces the complexity, relative to assemblies, that include piezoceramic fiber composite actuators, hinges, ferrules, and clamp blocks with setscrews. Unlike curved actuators, MFC actuators are used in a flat configuration and are less bulky. In addition, the MFC offers some vibration dampening and support for the optical fiber whereas, in a curved piezoelectric actuator assembly, the optical fiber is exposed, and there is nothing to keep the exposed portion from vibrating.

SU-E-T-146: Beam Energy Spread Estimate Based On Bragg Peak Measurement

DOE Office of Scientific and Technical Information (OSTI.GOV)

Anferov, V; Derenchuk, V; Moore, R

2015-06-15

Purpose: ProNova is installing and commissioning a two room proton therapy system in Knoxville, TN. Beam energy out of the 230MeV cyclotron was measured on Jan 24, 2015. Cyclotron beam was delivered into a Zebra multi layered IC detector calibrated in terms of penetration range in water. The analysis of the measured Bragg peak determines penetration range in water which can be subsequently converted into proton beam energy. We extended this analysis to obtain an estimate of the beam energy spread out of the cyclotron. Methods: Using Monte Carlo simulations we established the correlation between Bragg peak shape parameters (widthmore » at 50% and 80% dose levels, distal falloff) and penetration range for a monoenergetic proton beam. For large uniform field impinging on a small area detector, we observed linear dependence of each Bragg peak parameter on beam penetration range as shown in Figure A. Then we studied how this correlation changes when the shape of Bragg peak is distorted by the beam focusing conditions. As shown in Figure B, small field size or diverging beam cause Bragg peak deformation predominantly in the proximal region. The distal shape of the renormalized Bragg peaks stays nearly constant. This excludes usage of Bragg peak width parameters for energy spread estimates. Results: The measured Bragg peaks had an average distal falloff of 4.86mm, which corresponds to an effective range of 35.5cm for a monoenergetic beam. The 32.7cm measured penetration range is 2.8cm less. Passage of a 230MeV proton beam through a 2.8cm thick slab of water results in a ±0.56MeV energy spread. As a final check, we confirmed agreement between shapes of the measured Bragg peak and one generated by Monte-Carlo code for proton beam with 0.56 MeV energy spread. Conclusion: Proton beam energy spread can be estimated using Bragg peak analysis.« less

Fine tuning of transmission features in nanoporous anodic alumina distributed Bragg reflectors

NASA Astrophysics Data System (ADS)

Lim, Siew Yee; Law, Cheryl Suwen; Santos, Abel

2018-01-01

This study introduces an innovative apodisation strategy to tune the filtering features of distributed Bragg reflectors based on nanoporous anodic alumina (NAA-DBRs). The effective medium of NAA-DBRs, which is modulated in a stepwise fashion by a pulse-like anodisation approach, is apodised following a logarithmic negative function to engineer the transmission features of NAA-DBRs. We investigate the effect of various apodisation parameters such as apodisation amplitude difference, anodisation period, current density offset and pore widening time, to tune and optimise the optical properties of NAA-DBRs in terms of central wavelength position, full width at half maximum and quality of photonic stop band. The transmission features of NAA-DBRs are shown to be fully controllable with precision across the spectral regions by means of the apodisation parameters. Our study demonstrates that an apodisation strategy can significantly narrow the width and enhance the quality of the characteristic photonic stop band of NAA-DBRs. This rationally designed anodisation approach based on the combination of apodisation and stepwise pulse anodisation enables the development of optical filters with tuneable filtering features to be integrated into optical technologies acting as essential photonic elements in devices such as optical sensors and biosensors.

Observation of Significant Quantum Efficiency Enhancement from a Polarized Photocathode with Distributed Bragg Reflector

DOE Office of Scientific and Technical Information (OSTI.GOV)

Zhang, Shukui; Poelker, Matthew; Stutzman, Marcy L.

2015-09-01

Polarized photocathodes with higher Quantum efficiency (QE) would help to reduce the technological challenge associated with producing polarized beams at milliampere levels, because less laser light would be required, which simplifies photocathode cooling requirements. And for a given amount of available laser power, higher QE would extend the photogun operating lifetime. The distributed Bragg reflector (DBR) concept was proposed to enhance the QE of strained-superlattice photocathodes by increasing the absorption of the incident photons using a Fabry-Perot cavity formed between the front surface of the photocathode and the substrate that includes a DBR, without compromising electron polarization. Here we presentmore » recent results showing QE enhancement of a GaAs/GaAsP strained-superlattice photocathode made with a DBR structure. Typically, a GaAs/GaAsP strained-superlattice photocathode without DBR provides a QE of 1%, at a laser wavelength corresponding to peak polarization. In comparison, the GaAs/GaAsP strained-superlattice photocathodes with DBR exhibited an enhancement of over 2 when the incident laser wavelength was tuned to meet the resonant condition for the Fabry-Perot resonator.« less

A Cascaded Approach for Correcting Ionospheric Contamination with Large Amplitude in HF Skywave Radars

PubMed Central

Wei, Yinsheng; Guo, Rujiang; Xu, Rongqing; Tang, Xiudong

2014-01-01

Ionospheric phase perturbation with large amplitude causes broadening sea clutter's Bragg peaks to overlap each other; the performance of traditional decontamination methods about filtering Bragg peak is poor, which greatly limits the detection performance of HF skywave radars. In view of the ionospheric phase perturbation with large amplitude, this paper proposes a cascaded approach based on improved S-method to correct the ionospheric phase contamination. This approach consists of two correction steps. At the first step, a time-frequency distribution method based on improved S-method is adopted and an optimal detection method is designed to obtain a coarse ionospheric modulation estimation from the time-frequency distribution. At the second correction step, based on the phase gradient algorithm (PGA) is exploited to eliminate the residual contamination. Finally, use the measured data to verify the effectiveness of the method. Simulation results show the time-frequency resolution of this method is high and is not affected by the interference of the cross term; ionospheric phase perturbation with large amplitude can be corrected in low signal-to-noise (SNR); such a cascade correction method has a good effect. PMID:24578656

Generation of spectrally stable continuous-wave emission and ns pulses with a peak power of 4 W using a distributed Bragg reflector laser and a ridge-waveguide power amplifier.

PubMed

Klehr, A; Wenzel, H; Fricke, J; Bugge, F; Erbert, G

2014-10-06

We have developed a diode-laser based master oscillator power amplifier (MOPA) light source which emits high-power spectrally stabilized and nearly-diffraction limited optical pulses in the nanoseconds range as required by many applications. The MOPA consists of a distributed Bragg reflector (DBR) laser as master oscillator driven by a constant current and a ridge waveguide power amplifier (PA) which can be driven by a constant current (DC) or by rectangular current pulses with a width of 5 ns at a repetition frequency of 200 kHz. Under pulsed operation the amplifier acts as an optical gate, converting the CW input beam emitted by the DBR laser into a train of short amplified optical pulses. With this experimental MOPA arrangement no relaxation oscillations occur. A continuous wave power of 1 W under DC injection and a pulse power of 4 W under pulsed operation are reached. For both operational modes the optical spectrum of the emission of the amplifier exhibits a peak at a constant wavelength of 973.5 nm with a spectral width < 10 pm.

Detection of thermal gradients through fiber-optic Chirped Fiber Bragg Grating (CFBG): Medical thermal ablation scenario

NASA Astrophysics Data System (ADS)

Korganbayev, Sanzhar; Orazayev, Yerzhan; Sovetov, Sultan; Bazyl, Ali; Schena, Emiliano; Massaroni, Carlo; Gassino, Riccardo; Vallan, Alberto; Perrone, Guido; Saccomandi, Paola; Arturo Caponero, Michele; Palumbo, Giovanna; Campopiano, Stefania; Iadicicco, Agostino; Tosi, Daniele

2018-03-01

In this paper, we describe a novel method for spatially distributed temperature measurement with Chirped Fiber Bragg Grating (CFBG) fiber-optic sensors. The proposed method determines the thermal profile in the CFBG region from demodulation of the CFBG optical spectrum. The method is based on an iterative optimization that aims at minimizing the mismatch between the measured CFBG spectrum and a CFBG model based on coupled-mode theory (CMT), perturbed by a temperature gradient. In the demodulation part, we simulate different temperature distribution patterns with Monte-Carlo approach on simulated CFBG spectra. Afterwards, we obtain cost function that minimizes difference between measured and simulated spectra, and results in final temperature profile. Experiments and simulations have been carried out first with a linear gradient, demonstrating a correct operation (error 2.9 °C); then, a setup has been arranged to measure the temperature pattern on a 5-cm long section exposed to medical laser thermal ablation. Overall, the proposed method can operate as a real-time detection technique for thermal gradients over 1.5-5 cm regions, and turns as a key asset for the estimation of thermal gradients at the micro-scale in biomedical applications.

Characteristics research on self-amplified distributed feedback fiber laser

NASA Astrophysics Data System (ADS)

Song, Zhiqiang; Qi, Haifeng; Guo, Jian; Wang, Chang; Peng, Gangding

2014-09-01

A distributed feedback (DFB) fiber laser with a ratio of the backward to forward output power of 1:100 was composed by a 45-mm-length asymmetrical phase-shifted fiber grating fabricated on the 50-mm erbium-doped photosensitive fiber. Forward output laser was amplified using a certain length of Nufern EDFL-980-Hp erbium-doped fiber to absorb the surplus pump power after the active phase-shifted fiber grating and get population inversion. By using OptiSystem software, the best fiber length of the EDFL to get the highest gain was simulated. In order to keep the amplified laser with the narrow line-width and low noise, a narrow-band light filter consisting of a fiber Bragg grating (FBG) with the same Bragg wavelength as the laser and an optical circulator was used to filter the amplified spontaneous emission (ASE) noise of the out-cavity erbium-doped fiber. The designed laser structure sufficiently utilized the pump power, and a DFB fiber laser with the 32.5-mW output power, 11.5-kHz line width, and -87-dB/Hz relative intensity noise (RIN) at 300 mW of 980 nm pump power was brought out.

100-mW high-power three-section tunable distributed Bragg reflector laser diodes with a real refractive-index-guided self-aligned structure

NASA Astrophysics Data System (ADS)

Takayama, Toru; Mochida, Atsunori; Orita, Kenji; Tamura, Satoshi; Ohnishi, Toshikazu; Yuri, Masaaki; Shimizu, Hirokazu

2002-05-01

High-power (>100mW) 820 nm-band distributed Bragg reflector (DBR) laser diodes (LDs) with stable fundamental transverse mode operation and continuous wavelength tuning characteristics have been developed. To obtain high-power LDs with a stable fundamental transverse mode in 820 nm wavelength range, an AlGaAs narrow stripe (2.0 micrometers ) real refractive-index-guided self-aligned (RISA) structure is utilized. In the RISA structure, the index step between inside and outside the stripe region ((Delta) n) can be precisely controlled in the order of 10-3). To maintain a stable fundamental transverse mode up to an output power over 100 mW, (Delta) n is designed to be 4x10-3. Higher-order transverse modes are effectively suppressed by a narrow stripe geometry. Further, to achieve continuous wavelength tuning capability, the three-section LD structure, which consists of the active (700micrometers ), phase control (300micrometers ), and DBR(500micrometers ) sections, is incorporated. Our DBR LDs show a maximum output power over 200mW with a stable fundamental transverse mode, and wavelength tuning characteristics ((Delta) (lambda) ~2nm) under 100 mW CW operation.

Effect of SiO 2/Si 3N 4 dielectric distributed Bragg reflectors (DDBRs) for Alq 3/NPB thin-film resonant cavity organic light emitting diodes

NASA Astrophysics Data System (ADS)

Lei, Po-Hsun; Wang, Shun-Hsi; Juang, Fuh Shyang; Tseng, Yung-Hsin; Chung, Meng-Jung

2010-05-01

In this article, we report on the effect of SiO 2/Si 3N 4 dielectric distributed Bragg reflectors (DDBRs) for Alq 3/NPB thin-film resonant cavity organic light emitting diode (RCOLED) in increasing the light output intensity and reducing the linewidth of spontaneous emission spectrum. The optimum DDBR number is found as 3 pairs. The device performance will be bad by further increasing or decreasing the number of DDBR. As compared to the conventional Alq 3/NPB thin-film organic light emitting diode (OLED), the Alq 3/NPB thin-film RCOLED with 3-pair DDBRs has the superior electrical and optical characteristics including a forward voltage of 6 V, a current efficiency of 3.4 cd/A, a luminance of 2715 cd/m 2 under the injection current density of 1000 A/m 2, and a full width at half maximum (FWHM) of 12 nm for emission spectrum over the 5-9 V bias range. These results represent that the Alq 3/NPB thin-film OLED with DDBRs shows a potential as the light source for plastic optical fiber (POF) communication system.

High-sensitivity stress sensor based on Bragg grating in BDK-doped photosensitive polymer optical fiber

NASA Astrophysics Data System (ADS)

Wang, Tongxin; Luo, Yanhua; Peng, Gang-Ding; Zhang, Qijin

2012-02-01

Bragg grating in a single-mode photosensitive polymer optical fiber (POF) with benzil dimethyl ketal (BDK)-doped in core has been inscribed through the Sagnac ring interference method. The Bragg wavelength of grating is about 1570nm. The stress and strain response of fiber Bragg grating (FBG) has been studied respectively. By fitting the experimental result, the strain sensitivity of FBG in POF has been found to be almost same to that of conventional silica fiber Bragg gratings. However, the stress sensitivity of FBG in POF is measured to be 421pm/MPa, which is 28 times higher than FBG in silica fiber. And such high stress sensitivity makes Bragg grating in a single-mode BDK-doped POF appear to be very attractive for constructing stress sensor with high resolution.

In Situ Three-Dimensional Reciprocal-Space Mapping of Diffuse Scattering Intensity Distribution and Data Analysis for Precursor Phenomenon in Shape-Memory Alloy

NASA Astrophysics Data System (ADS)

Cheng, Tian-Le; Ma, Fengde D.; Zhou, Jie E.; Jennings, Guy; Ren, Yang; Jin, Yongmei M.; Wang, Yu U.

2012-01-01

Diffuse scattering contains rich information on various structural disorders, thus providing a useful means to study the nanoscale structural deviations from the average crystal structures determined by Bragg peak analysis. Extraction of maximal information from diffuse scattering requires concerted efforts in high-quality three-dimensional (3D) data measurement, quantitative data analysis and visualization, theoretical interpretation, and computer simulations. Such an endeavor is undertaken to study the correlated dynamic atomic position fluctuations caused by thermal vibrations (phonons) in precursor state of shape-memory alloys. High-quality 3D diffuse scattering intensity data around representative Bragg peaks are collected by using in situ high-energy synchrotron x-ray diffraction and two-dimensional digital x-ray detector (image plate). Computational algorithms and codes are developed to construct the 3D reciprocal-space map of diffuse scattering intensity distribution from the measured data, which are further visualized and quantitatively analyzed to reveal in situ physical behaviors. Diffuse scattering intensity distribution is explicitly formulated in terms of atomic position fluctuations to interpret the experimental observations and identify the most relevant physical mechanisms, which help set up reduced structural models with minimal parameters to be efficiently determined by computer simulations. Such combined procedures are demonstrated by a study of phonon softening phenomenon in precursor state and premartensitic transformation of Ni-Mn-Ga shape-memory alloy.

Simultaneous measurement of temperature and strain using a phase-shifted fiber Bragg grating inscribed by femtosecond laser

NASA Astrophysics Data System (ADS)

Jiang, Yajun; Liu, Chi; Li, Dong; Yang, Dexing; Zhao, Jianlin

2018-04-01

A novel method for simultaneous measurement of temperature and strain using a single phase-shifted fiber Bragg grating (PS-FBG) is proposed. The PS-FBG is produced by exposing the fusion-spliced fiber with a femtosecond laser and uniform phase mask. Due to the non-uniform structure and strain distribution in the fusion-spliced region, the phase-shift changes with different responses during increases to the temperature and strain; by measuring the central wavelengths and the loss difference of two transmission dips, temperature and strain can be determined simultaneously. The resolutions of this particular sensor in measuring temperature and strain are estimated to be  ±1.5 °C and  ±12.2 µɛ in a range from  -50 °C to 150 °C and from 0 µɛ to 2070 µɛ.

Lateral cavity photonic crystal surface emitting lasers with ultralow threshold and large power

NASA Astrophysics Data System (ADS)

Wang, Yufei; Qu, Hongwei; Zhou, Wenjun; Jiang, Bin; Zhang, Jianxin; Qi, Aiyi; Liu, Lei; Fu, Feiya; Zheng, Wanhua

2012-03-01

The Bragg diffraction condition of surface-emitting lasing action is analyzed and Γ2-1 mode is chosen for lasing. Two types of lateral cavity photonic crystal surface emitting lasers (LC-PCSELs) based on the PhC band edge mode lateral resonance and vertical emission to achieve electrically driven surface emitting laser without distributed Bragg reflectors in the long wavelength optical communication band are designed and fabricated. Deep etching techniques, which rely on the active layer being or not etched through, are adopted to realize the LC-PCSELs on the commercial AlGaInAs/InP multi-quantum-well (MQW) epitaxial wafer. 1553.8 nm with ultralow threshold of 667 A/cm2 and 1575 nm with large power of 1.8 mW surface emitting lasing actions are observed at room temperature, providing potential values for mass production with low cost of electrically driven PCSELs.

Three-dimensional imaging of crystalline inclusions embedded in intact maize stalks.

PubMed

Badger, John; Lal, Jyotsana; Harder, Ross; Inouye, Hideyo; Gleber, S Charlotte; Vogt, Stefan; Robinson, Ian; Makowski, Lee

2013-10-03

Mineral inclusions in biomass are attracting increased scrutiny due to their potential impact on processing methods designed to provide renewable feedstocks for the production of chemicals and fuels. These inclusions are often sculpted by the plant into shapes required to support functional roles that include the storage of specific elements, strengthening of the plant structure, and providing a defense against pathogens and herbivores. In situ characterization of these inclusions faces substantial challenges since they are embedded in an opaque, complex polymeric matrix. Here we describe the use of Bragg coherent diffraction imaging (BCDI) to study mineral inclusions within intact maize stalks. Three-dimensional BCDI data sets were collected and used to reconstruct images of mineral inclusions at 50-100 nm resolution. Asymmetries in the intensity distributions around the Bragg peaks provided detailed information about the deformation fields within these crystal particles revealing lattice defects that result in distinct internal crystal domains.

Bragg Reflector-Induced Increased Nonradiative Lifetime in Gallium Arsenide (GaAs)/Aluminum Gallium Arsenide (AlGaAs) Double Heterostructures

DTIC Science & Technology

2015-09-01

ARL-TR-7473 ● SEP 2015 US Army Research Laboratory Bragg Reflector-Induced Increased Nonradiative Lifetime in Gallium Arsenide...return it to the originator. ARL-TR-7473 ● SEP 2015 US Army Research Laboratory Bragg Reflector-Induced Increased Nonradiative ...3. DATES COVERED (From - To) 4. TITLE AND SUBTITLE Bragg Reflector-Induced Increased Nonradiative Lifetime in Gallium Arsenide (GaAs)/Aluminum

Book Review:

NASA Astrophysics Data System (ADS)

Borcherds, P.

2005-03-01

This book achieves what its subtitle indicates. The author skilfully weaves together the story of Bragg's life and of the scientific developments with which he was most closely involved. The author has a good understanding of Bragg's scientific work which he explains in considerable detail, with a number of diagrams reproduced from Bragg's papers, and manages to convey the excitement generated by Bragg's discoveries. The salient points of Bragg's life are well known. He was born and brought up in Australia and is still the youngest ever winner of a Nobel prize (though Josephson did his seminal work at a comparable age, it took many years for him to get his Prize). From 1914 to 1918 Bragg was involved with acoustic methods of detecting enemy guns. From 1919 to 1938 he was Professor of Physics in Manchester, and for about a year he was Director of the National Physical Laboratory. He then went to Cambridge as Cavendish Professor until 1953, when he moved to the Royal Institution (where his father had been). While an undergraduate at Cambridge 'Bragg's most influential teacher was...C T R Wilson [Nobel Laureate, 1927]...[whose] lectures "were the best, and delivery the worst, of any lectures to which I have ever been. He mumbled facing the board, he was very hesitant in his delivery, and yet the way he presented the subject was quite brilliant'' '. One wonders how long Wilson's inspirational teaching would survive today, with continual inspections and the requirement to satisfy the demands of the jobsworths. Bragg's comments on this would make interesting reading! Bragg was a very successful public lecturer on science. He made use of vivid analogies, many of which are quoted by Hunter. Since this book is published by Oxford University Press, I hope that some of them may appear in future editions of The Oxford Dictionary of Quotations. (Bragg is included in Mackay's A Dictionary of Scientific Quotations (Bristol: Institute of Physics Publishing)). There are too many superb quotations to include all of them in this review, but one of Bragg's Golden Rules for newcomers to his laboratory should be on the door of every experimental laboratory: 'Never be afraid to carry on an experiment which is declared stupid by the theorists [sic] of the laboratory'. This book is, as its subtitle implies, about Bragg and about his science. Hunter has skilfully and seamlessly interwoven the two strands. At one minute you are reading about the man and at the next you realize you are reading about the science. In writing about the science, Hunter writes knowledgeably and expects the reader to make an effort to understand. In this he is following the precept of Bragg who, when advised to avoid technical terms when lecturing to a lay audience, ridiculed this attitude with a telling metaphor: 'What could be more technical than a description of a football match? To picture the scientist's plight, one must imagine the sports expert being told to describe the match using as little as possible such terms as "ball'' or "goal'', and of course avoiding the very complex ideas involved in "try'' or "offside'' '. Bragg made several major contributions to crystallography and these are described, as already mentioned. One has to concentrate quite hard to follow but the effort is worthwhile and Hunter manages not only to convey the excitement felt by Bragg and his colleagues but also to let the reader feel it too. Bragg interacted strongly with other crystallographers, not least with his father, but also with Pauling. At times there was a close race between Bragg and Pauling, which is fully discussed. Bragg succeeded Rutherford at Cambridge. The appointment was controversial. Under Rutherford the Cavendish Laboratory concentrated on nuclear physics, while Bragg was a crystallographer, with little interest in nuclear physics. However the crystallographic work Bragg encouraged on haemoglobin and DNA led to several Nobel prizes. Bragg's activities in canvassing for Nobel prizes are described: an impressive number were awarded to those closely associated with Bragg. For many years past, one of the highlights of television in Britain over Christmas has been the series of Royal Institution Christmas Lectures, aimed at children. In the days before video recorders, the lectures were broadcast at about 5 pm and many of my colleagues in the Physics Department at the University of Birmingham would rush home to watch them. They were fascinating, and had marvellous demonstrations, organized by the memorable Mr Coates, who is mentioned in this book. Mr Coates has retired, but the lectures and the demonstrations continue, and long may they do so. The Christmas Lectures have a long tradition. Bragg himself gave them in 1934, and when he became Director of the RI he strongly encouraged them. What I had not realized until reading this book was the drama associated with Bragg's appointment to the RI. The author has had access to Bragg's papers, and quotes from them very effectively. This is a book I have enjoyed reading and reviewing. I have been tempted to reproduce even more of the quotations of Bragg's own words, but I leave the pleasure of finding them to you when you read the book. I strongly recommend it as essential reading for all physicists and crystallographers, and indeed for all scientists at all stages in their careers. Every university library must buy a copy.

Steep and flat bandpass filter using linearly chirped and apodized fiber Bragg grating

NASA Astrophysics Data System (ADS)

Wu, Xunqi; Jacquet, Jo"l.; Duan, Guanghua

2010-02-01

The development of new optical systems requires the design of novel components that fulfill the market constraints. In particular, low loss, high optical rejection and low cost narrowband filters can play an important role for the introduction of the Wavelength Division Multiplexing (WDM) technology in the local network. So, a novel fiber filter is proposed in this article, with a special combined apodized Linearly Chirped Fiber Bragg Grating (LCFBG) which presents the preferable flat-top and steep-edge characteristics. In the design, we use a continuum cavity condition which is obtained when the effective round-trip phase of oscillated wavelength band is kept identical over the whole Bragg wavelength range. And the transmission spectra are calculated by the reconstruction of the matrixes with the continuum oscillation condition. Therefore, our works show that the ideal square shaped filter is obtained with a lower chirp value relatively together with symmetric reflectivity on both mirrors. The coupling coefficient of the FBG is adjusted to get the same reflectivity values and then to get a transmission filter close to unity. We have then introduced an apodization function of the filter to get a flatter transfer function. Various apodizations schemes have been tested. In this paper, we design and analyze a type of continuum fiber filter with the cavity formed between mirror and apodized LCFBG as reflectors. We calculate firstly the reflectivity, the transmissivity and the group time delay of LCFBG modeled by a simple and practical Transfer Matrix Method (TMM), and then the cavity is reconstructed by TMM, the length of the oscillated cavity is calculated by the continuum oscillation condition, so the output of transmission from the side of LCFBG is continuous in the corresponded reflected bandwidth of LCFBG. We obtain the results and discuss some characteristics of this type of continuum fiber filter.

High-Power Single-Mode 2.65-micron InGaAsSb/AlInGaAsSb Diode Lasers

NASA Technical Reports Server (NTRS)

Frez, Clifford F.; Briggs, Ryan M.; Forouhar, Siamak; Borgentun, Carl E.; Gupta, James

2013-01-01

Central to the advancement of both satellite and in-situ science are improvements in continuous-wave and pulsed infrared laser systems coupled with integrated miniaturized optics and electronics, allowing for the use of powerful, single-mode light sources aboard both satellite and unmanned aerial vehicle platforms. There is a technological gap in supplying adequate laser sources to address the mid-infrared spectral window for spectroscopic characterization of important atmospheric gases. For high-power applications between 2 to 3 micron, commercial laser technologies are unsuitable because of limitations in output power. For instance, existing InP-based laser systems developed for fiber-based telecommunications cannot be extended to wavelengths longer than 2 micron. For emission wavelengths shorter than 3 micron, intersubband devices, such as infrared quantum cascade lasers, become inefficient due to band-offset limitations. To date, successfully demonstrated singlemode GaSb-based laser diodes emitting between 2 and 3 micron have employed lossy metal Bragg gratings for distributed- feedback coupling, which limits output power due to optical absorption. By optimizing both the quantum well design and the grating fabrication process, index-coupled distributed-feedback 2.65-micron lasers capable of emitting in excess of 25 mW at room temperature have been demonstrated. Specifically, lasers at 3,777/cm (2.65 micron) have been realized to interact with strong absorption lines of HDO and other isotopologues of H2O. With minor modifications of the optical cavity and quantum well designs, lasers can be fabricated at any wavelength within the 2-to-3-micron spectral window with similar performance. At the time of this reporting, lasers with this output power and wavelength accuracy are not commercially available. Monolithic ridge-waveguide GaSb lasers were fabricated that utilize secondorder lateral Bragg gratings to generate single-mode emission from InGaAsSb/ AlInGaAsSb multi-quantum well structures. The device fabrication utilizes etched index-coupled gratings in the top AlGaAsSb cladding of the laser chip along the ridge waveguide, whereas commercial lasers that emit close to this wavelength include loss-coupled metal gratings that limit the output power of the laser. Semiconductor-laser-based spectrometers can be used to replace gas sensors currently used in industry and government. With the availability of high-power laser sources at mid-infrared wavelengths, sensors can target strong fundamental gas absorption lines to maximize instrument sensitivity.

Reconstruction of fiber grating period profiles by use of Wigner-Ville distributions and spectrograms.

PubMed

Azaña, J; Muriel, M A

2000-12-01

The grating-period profile and length of an arbitrary fiber Bragg grating structure can be reconstructed from the structure's reflection response by use of a time-frequency signal representation based on the well-known Wigner-Ville distribution and spectrogram. We present a detailed description of this synthesis technique. By means of numerical simulations, the technique is tested with several fiber grating structures. In general, our results show good agreement between exact and reconstructed functions. The technique's advantages and limitations are discussed. We propose and demonstrate the application of the proposed synthesis technique to distributed mechanical strain or temperature sensing.

Grating-assisted polarization optical time-domain reflectometry for distributed fiber-optic sensing.

PubMed

Han, Ming; Wang, Yunjing; Wang, Anbo

2007-07-15

We report a novel type of polarization optical time-domain reflectometry (POTDR) for fully distributed fiber-optic sensing, in which the reflected optical signal is from a series of fiber Bragg gratings that are uniformly distributed along the fiber. Compared with a conventional POTDR that uses the Rayleigh backscattering, this grating-assisted POTDR can have a much better signal-to-noise ratio and consequently a better measurement resolution and a larger measurement range of the fiber birefringence. Experimental results have shown that the measurement resolution of the grating-assisted POTDR is almost an order of magnitude better than that of a conventional POTDR.

News

NASA Astrophysics Data System (ADS)

2002-03-01

UK Awards: Teacher of Physics Awards Institute Matters: Institute of Physics Education Conference UK Awards: Top SHAP students win prizes Competition: International creative essay competition UK Awards: Kelvin Medal Particle Physics Resources: New poster from PPARC Australia: Physics Students's Day at Adventure World UK Awards: Bragg Medal winners in a FLAP ASE Annual Meeting: Particle Physics at ASE 2002 UK Grants: PPARC Awards AAPT Winter Meeting: Physics First - but do you need maths? UK In-Service Training: The Particle Physics Institutes for A-level teachers Physics on Stage 2: Not too entertaining this time, please! Scotland: A reasoned approach wins reasonable funding Institute Matters: New education manager Germany: Physics gets real: curriculum change for better teaching Research Frontiers: Let there be light - if you hang on a minute

Application of fiber grating-based acoustic sensor in progressive failure testing of e-glass/vinylester curve composites

NASA Astrophysics Data System (ADS)

Azmi, Asrul Izam; Raju, Raju; Peng, Gang-Ding

2012-02-01

This paper reports an application of phase shifted fiber Bragg grating (PS-FBG) intensity-type acoustic sensor in a continuous and in-situ failure testing of an E-glass/vinylester top hat stiffener (THS). The narrow transmission channel of the PS-FBG is highly sensitive to small perturbation, hence suitable to be used in an effective acoustic emission (AE) assessment technique. The progressive failure of THS was tested under transverse loading to experimentally simulate the actual loading in practice. Our experimental tests have demonstrated, in good agreement with the commercial piezoelectric sensors, that the important failures information of the THS was successfully recorded by the simple intensity-type PS-FBG sensor.

Failure monitoring of E-glass/vinylester composites using fiber grating acoustic sensor

NASA Astrophysics Data System (ADS)

Azmi, A. I.; Raju; Peng, G. D.

2013-06-01

This paper reports an application of an optical fiber sensor in a continuous and in situ failure testing of an E-glass/vinylester top hat stiffener (THS). The sensor head was constructed from a compact phase-shifted fiber Bragg grating (PS-FBG). The narrow transmission channel of the PS-FBG is highly sensitive to small perturbation, hence suitable to be used in acoustic emission (AE) assessment technique. The progressive failure of THS was tested under transverse loading to experimentally simulate the actual loading in practice. Our experimental tests have demonstrated, in good agreement with the commercial piezoelectric sensors, that the important failures information of the THS was successfully recorded by the simple intensity-type PS-FBG sensor.

Summary of the Topical Workshop on Top Quark Differential Distributions 2014

NASA Astrophysics Data System (ADS)

Czakon, Michal; Mitov, Alexander; Rojo, Juan

2016-01-01

We summarize the Topical Workshop on Top Quark Differential Distributions 2014, which took place in Cannes immediately before the annual Top2014 conference. The workshop was motivated by the availability of top quark differential distributions at next-to-next-to-leading order and the forthcoming Large Hadron Collider (LHC) 13 TeV data. The main goal of the workshop was to explore the impact of improved calculations of top quark production on precision LHC measurements, PDF determinations and searches for physics beyond the Standard Model, as well as finding ways in which the high precision data from ATLAS, CMS and LHCb can be used to further refine theoretical predictions for top production.

Light is a Messenger - The Life and Science of William Lawrence Bragg

NASA Astrophysics Data System (ADS)

Hunter, Graeme K.

2004-10-01

Light is a Messenger , is the first biography of William Lawrence Bragg, who was only 25 when he won the 1915 Nobel Prize in Physics-the youngest person ever to win a Nobel Prize. It describes how bragg discovered how to use X-rays to determine the arrangement of atoms in crystals and his pivotal role in developing this technique to the point that the structures of the most complex molecules known to man-the proteins and nucelic acids-could be solved. Although Bragg's Nobel Prize was for Physics, his research profoundly affected chemistry and the new field of molecular biology, of which he became a founding figure. This book explains how these revolutionary scientific events occurred while Bragg struggled to emerge from the shadow of his father, Sir William Bragg, and amidst a career-long rivalry with the brilliant American chemist, Linus Pauling.

A magnetically tunable non-Bragg defect mode in a corrugated waveguide filled with liquid crystals

NASA Astrophysics Data System (ADS)

Zhang, Lu; Fan, Ya-Xian; Liu, Huan; Han, Xu; Lu, Wen-Qiang; Tao, Zhi-Yong

2018-04-01

A magnetically tunable, non-Bragg defect mode (NBDM) was created in the terahertz frequency range by inserting a defect in the middle of a periodically corrugated waveguide filled with liquid crystals (LCs). In the periodic waveguide, non-Bragg gaps beyond the Bragg ones, which appear in the transmission spectra, are created by different transverse mode resonances. The transmission spectra of the waveguide containing a defect showed that a defect mode was present inside the non-Bragg gap. The NBDM has quite different features compared to the Bragg defect mode, which includes more complex, high-order guided wave modes. In our study, we filled the corrugated waveguide with LCs to realize the tunability of the NBDM. The simulated results showed that the NBDM in a corrugated waveguide filled with LCs can be used in filters, sensors, switches, and other terahertz integrated devices.

Measuring top-quark polarization in top-pair + missing-energy events.

PubMed

Berger, Edmond L; Cao, Qing-Hong; Yu, Jiang-Hao; Zhang, Hao

2012-10-12

The polarization of a top quark can be sensitive to new physics beyond the standard model. Since the charged lepton from top-quark decay is maximally correlated with the top-quark spin, it is common to measure the polarization from the distribution in the angle between the charged lepton and the top-quark directions. We propose a novel method based on the charged lepton energy fraction and illustrate the method with a detailed simulation of top-quark pairs produced in supersymmetric top squark pair production. We show that the lepton energy ratio distribution that we define is very sensitive to the top-quark polarization but insensitive to the precise measurement of the top-quark energy.

The Bragg gap vanishing phenomena in one-dimensional photonic crystals.

PubMed

Zhang, Hui; Chen, Xi; Li, Youquan; Fu, Yunqi; Yuan, Naichang

2009-05-11

We theoretically deduce the Bragg gap vanishing conditions in one-dimensional photonic crystals and experimentally demonstrate the m=0 band-gap vanishing phenomena at microwave frequencies. In the case of mismatched impedance, the Bragg gap will vanish as long as the discrete modes appear in photonic crystals containing dispersive materials, while for the matched impedance cases, Bragg gaps will always disappear. The experimental results and the simulations agree extremely well with the theoretical expectation.

Optical Fiber Thermometer Based on Fiber Bragg Gratings

NASA Astrophysics Data System (ADS)

Rosli, Ekbal Bin; Mohd. Noor, Uzer

2018-03-01

Fiber Bragg grating has generated much interest in use as sensors to measure strain, temperature, and other physical parameters. It also the most common component used to develop this sensor with the advantages of simple, intrinsic sensing elements, electrically passive operation, EMI immunity, high sensitivity, compact size and potentially low cost [6]. This paper reports the design of an optical fiber thermometer based on fiber Bragg gratings. The system was developed for detecting temperature and strain by monitoring the shift of Bragg wavelength. The shifting of Bragg wavelength is used to indicate the temperature and strain due to the change in the surrounding temperature and strain. When the temperature and strain reach the exact wavelength level of the system, the temperature and strain value will display on the Arduino liquid crystal display (LCD). The optical fiber will provide the broadband light source and after passing the FBG the Bragg wavelength into the optical spectrum analyzer (OSA). The system is based on FBG as a physical quantity sensor. The temperatures measured is taken from the water bath and that of the strain is provided by amount of slotted mass used. The outcome of this project is to characterize the Bragg wavelength shifting from the fiber Bragg grating output. As the conclusion, this project provides an efficient optical fiber thermometer in measuring temperature and strain in order to replace the use of conventional electrical instruments.

Induction of Micronuclei in Human Fibroblasts across the Bragg Curve of Energetic Si and Fe Ions

NASA Technical Reports Server (NTRS)

Wu, H.; Rusek, A.; Hada, M.

2006-01-01

The space environment consists of a varying field of radiation particles including high-energy ions, with spacecraft shielding material providing the major protection to astronauts from harmful exposure. Unlike low-LET gamma or X-rays, the presence of shielding does not always reduce the radiation risks for energetic charged particle exposure. Since the dose delivered by the charged particle increases sharply as the particle approaches the end of its range, a position known as the Bragg peak, the Bragg curve does not necessarily represent the biological damage along the particle traversal since biological effects are influenced by the track structure of both primary and secondary particles. Therefore, the biological Bragg curve is dependent on the energy and the type of the primary particle, and may vary for different biological endpoints. We studied micronuclei (MN) induction across the Bragg curve of Si and Fe ions at incident energies of 300 MeV/nucleon and 1 GeV/nucleon. A quantitative biological response curve did not reveal an increased yield of MN at the location of the Bragg peak. However, the ratio of mono- to bi-nucleated cells, which indicates inhibition in cell progression, increased at the Bragg peak location. These results confirm the hypothesis that severely damaged cells at the Bragg peak are likely to go through reproduction death.

Validation of the physical and RBE-weighted dose estimator based on PHITS coupled with a microdosimetric kinetic model for proton therapy.

PubMed

Takada, Kenta; Sato, Tatsuhiko; Kumada, Hiroaki; Koketsu, Junichi; Takei, Hideyuki; Sakurai, Hideyuki; Sakae, Takeji

2018-01-01

The microdosimetric kinetic model (MKM) is widely used for estimating relative biological effectiveness (RBE)-weighted doses for various radiotherapies because it can determine the surviving fraction of irradiated cells based on only the lineal energy distribution, and it is independent of the radiation type and ion species. However, the applicability of the method to proton therapy has not yet been investigated thoroughly. In this study, we validated the RBE-weighted dose calculated by the MKM in tandem with the Monte Carlo code PHITS for proton therapy by considering the complete simulation geometry of the clinical proton beam line. The physical dose, lineal energy distribution, and RBE-weighted dose for a 155 MeV mono-energetic and spread-out Bragg peak (SOBP) beam of 60 mm width were evaluated. In estimating the physical dose, the calculated depth dose distribution by irradiating the mono-energetic beam using PHITS was consistent with the data measured by a diode detector. A maximum difference of 3.1% in the depth distribution was observed for the SOBP beam. In the RBE-weighted dose validation, the calculated lineal energy distributions generally agreed well with the published measurement data. The calculated and measured RBE-weighted doses were in excellent agreement, except at the Bragg peak region of the mono-energetic beam, where the calculation overestimated the measured data by ~15%. This research has provided a computational microdosimetric approach based on a combination of PHITS and MKM for typical clinical proton beams. The developed RBE-estimator function has potential application in the treatment planning system for various radiotherapies. © The Author 2017. Published by Oxford University Press on behalf of The Japan Radiation Research Society and Japanese Society for Radiation Oncology.

Validation of the physical and RBE-weighted dose estimator based on PHITS coupled with a microdosimetric kinetic model for proton therapy

PubMed Central

Sato, Tatsuhiko; Kumada, Hiroaki; Koketsu, Junichi; Takei, Hideyuki; Sakurai, Hideyuki; Sakae, Takeji

2018-01-01

Abstract The microdosimetric kinetic model (MKM) is widely used for estimating relative biological effectiveness (RBE)-weighted doses for various radiotherapies because it can determine the surviving fraction of irradiated cells based on only the lineal energy distribution, and it is independent of the radiation type and ion species. However, the applicability of the method to proton therapy has not yet been investigated thoroughly. In this study, we validated the RBE-weighted dose calculated by the MKM in tandem with the Monte Carlo code PHITS for proton therapy by considering the complete simulation geometry of the clinical proton beam line. The physical dose, lineal energy distribution, and RBE-weighted dose for a 155 MeV mono-energetic and spread-out Bragg peak (SOBP) beam of 60 mm width were evaluated. In estimating the physical dose, the calculated depth dose distribution by irradiating the mono-energetic beam using PHITS was consistent with the data measured by a diode detector. A maximum difference of 3.1% in the depth distribution was observed for the SOBP beam. In the RBE-weighted dose validation, the calculated lineal energy distributions generally agreed well with the published measurement data. The calculated and measured RBE-weighted doses were in excellent agreement, except at the Bragg peak region of the mono-energetic beam, where the calculation overestimated the measured data by ~15%. This research has provided a computational microdosimetric approach based on a combination of PHITS and MKM for typical clinical proton beams. The developed RBE-estimator function has potential application in the treatment planning system for various radiotherapies. PMID:29087492

Development of an Automated Impact Hammer for Modal Analysis of Structures

DTIC Science & Technology

2012-02-01

6 3.5 Integration with FBG interrogation system . . . . . . . . . . . . . . . . . 7 4 Experimental...distributed Fibre Bragg Gratings ( FBGs ) in optical fibres. The modified approach to SIDER has been given the name iSIDER or inverse SIDER to reflect the...response is measured at many locations using a large array of surface mounted FBG strain sensors [2]. FBGs are ideally suited to the roving response approach

Frequency-Modulated Microwave Photonic Links with Direct Detection: Review and Theory

DTIC Science & Technology

2010-12-15

create large amounts of signal distortion. Alternatives to MZIs have been pro- posed, including Fabry - Perot interferometers, ber Bragg gratings (FBGs...multiplexed, analog signals for applications in cable television distribution. Experimental results for a Fabry - Perot discriminated, FM subcarrier...multiplexed system were presented by [17]. An array of optical frequency modulated DFB lasers and a Fabry - Perot discriminator were used to transmit and

Writing and applications of fiber Bragg grating arrays

NASA Astrophysics Data System (ADS)

LaRochelle, Sophie; Cortes, Pierre-Yves; Fathallah, H.; Rusch, Leslie A.; Jaafar, H. B.

2000-12-01

Multiple Bragg gratings are written in a single fibre strand with accurate positioning to achieve predetermined time delays between optical channels. Applications of fibre Bragg grating arrays include encoders/decoders with series of identical gratings for optical code-division multiple access.

Single- and two-phase flow characterization using optical fiber bragg gratings.

PubMed

Baroncini, Virgínia H V; Martelli, Cicero; da Silva, Marco José; Morales, Rigoberto E M

2015-03-17

Single- and two-phase flow characterization using optical fiber Bragg gratings (FBGs) is presented. The sensor unit consists of the optical fiber Bragg grating positioned transversely to the flow and fixed in the pipe walls. The hydrodynamic pressure applied by the liquid or air/liquid flow to the optical fiber induces deformation that can be detected by the FBG. Given that the applied pressure is directly related to the mass flow, it is possible to establish a relationship using the grating resonance wavelength shift to determine the mass flow when the flow velocity is well known. For two phase flows of air and liquid, there is a significant change in the force applied to the fiber that accounts for the very distinct densities of these substances. As a consequence, the optical fiber deformation and the correspondent grating wavelength shift as a function of the flow will be very different for an air bubble or a liquid slug, allowing their detection as they flow through the pipe. A quasi-distributed sensing tool with 18 sensors evenly spread along the pipe is developed and characterized, making possible the characterization of the flow, as well as the tracking of the bubbles over a large section of the test bed. Results show good agreement with standard measurement methods and open up plenty of opportunities to both laboratory measurement tools and field applications.

TH-CD-201-10: Highly Efficient Synchronized High-Speed Scintillation Camera System for Measuring Proton Range, SOBP and Dose Distributions in a 2D-Plane

DOE Office of Scientific and Technical Information (OSTI.GOV)

Goddu, S; Sun, B; Grantham, K

2016-06-15

Purpose: Proton therapy (PT) delivery is complex and extremely dynamic. Therefore, quality assurance testing is vital, but highly time-consuming. We have developed a High-Speed Scintillation-Camera-System (HS-SCS) for simultaneously measuring multiple beam characteristics. Methods: High-speed camera was placed in a light-tight housing and dual-layer neutron shield. HS-SCS is synchronized with a synchrocyclotron to capture individual proton-beam-pulses (PBPs) at ∼504 frames/sec. The PBPs from synchrocyclotron trigger the HS-SCS to open its shutter for programmed exposure-time. Light emissions within 30×30×5cm3 plastic-scintillator (BC-408) were captured by a CCD-camera as individual images revealing dose-deposition in a 2D-plane with a resolution of 0.7mm for range andmore » SOBP measurements and 1.67mm for profiles. The CCD response as well as signal to noise ratio (SNR) was characterized for varying exposure times, gains for different light intensities using a TV-Optoliner system. Software tools were developed to analyze ∼5000 images to extract different beam parameters. Quenching correction-factors were established by comparing scintillation Bragg-Peaks with water scanned ionization-chamber measurements. Quenching corrected Bragg-peaks were integrated to ascertain proton-beam range (PBR), width of Spared-Out-Bragg-Peak (MOD) and distal.« less

Experimental investigation on mass flow rate measurements using fibre Bragg grating sensors

NASA Astrophysics Data System (ADS)

Thekkethil, S. R.; Thomas, R. J.; Neumann, H.; Ramalingam, R.

2017-02-01

Flow measurement and control of cryogens is one of the major requirements of systems such as superconductor magnets for fusion reactors, MRI magnets etc. They can act as an early diagnostic tool for detection of any faults and ensure correct distribution of cooling load while also accessing thermal performance of the devices. Fibre Bragg Grating (FBG) sensors provide compact and accurate measurement systems which have added advantages such as immunity towards electrical and magnetic interference, low attenuation losses and remote sensing. This paper summarizes the initial experimental investigations and calibration of a novel FBG based mass flow meter. This design utilizes the viscous drag due to the flow to induce a bending strain on the fibre. The strain experienced by the fibre will be proportional to the flowrate and can be measured in terms of Bragg wavelength shift. The flowmeter is initially tested at atmospheric conditions using helium. The results are summarized and the performance parameters of the sensor are estimated. The results were also compared to a numerical model and further results for liquid helium is also reported. An overall sensitivity of 29 pm.(g.s-1)-1 was obtained for a helium flow, with a resolution of 0.2 g.s-1. A hysteresis error of 8 pm was also observed during load-unload cycles. The sensor is suitable for further tests using cryogens.

Energy-selective Neutron Imaging for Three-dimensional Non-destructive Probing of Crystalline Structures

NASA Astrophysics Data System (ADS)

Peetermans, S.; Bopp, M.; Vontobel, P.; Lehmann, E. H.

Common neutron imaging uses the full polychromatic neutron beam spectrum to reveal the material distribution in a non-destructive way. Performing it with a reduced energy band, i.e. energy-selective neutron imaging, allows access to local variation in sample crystallographic properties. Two sample categories can be discerned with different energy responses. Polycrystalline materials have an energy-dependent cross-section featuring Bragg edges. Energy-selective neutron imaging can be used to distinguish be- tween crystallographic phases, increase material sensitivity or penetration, improve quantification etc. An example of the latter is shown by the examination of copper discs prior to machining them into linear accelerator cavity structures. The cross-section of single crystals features distinct Bragg peaks. Based on their pattern, one can determine the orientation of the crystal, as in a Laue pattern, but with the tremendous advantage that the operation can be performed for each pixel, yielding crystal orientation maps at high spatial resolution. A wholly different method to investigate such samples is also introduced: neutron diffraction imaging. It is based on projections formed by neutrons diffracted from the crystal lattice out of the direct beam. The position of these projections on the detector gives information on the crystal orientation. The projection itself can be used to reconstruct the crystal shape. A three-dimensional mapping of local Bragg reflectivity or a grain orientation mapping can thus be obtained.

William Henry Bragg, man and scientist, Nobel Laureate and First Professor of Physics, University of Adelaide 1886-1909.

PubMed

Patterson, John; George, Robert

2018-03-01

In London, November 1915, a telegram was received at the home of William Henry Bragg from the secretary of the Academy of Science in Stockholm announcing the award of the Nobel Prize in Physics for "the analysis of crystal structures by means of X-rays". A second similar telegram was addressed to his 25 year old son William Lawrence Bragg (Jenkin, 2008). This article commemorates the centenary of that event and the unveiling of a bust of Sir William Bragg alongside that of his son, Sir Lawrence Bragg, on North Terrace in Adelaide where he spent 23 years of his early career. Copyright © 2018. Published by Elsevier Ltd.

Microfabricated bragg waveguide

DOEpatents

Fleming, James G.; Lin, Shawn-Yu; Hadley, G. Ronald

2004-10-19

A microfabricated Bragg waveguide of semiconductor-compatible material having a hollow core and a multilayer dielectric cladding can be fabricated by integrated circuit technologies. The microfabricated Bragg waveguide can comprise a hollow channel waveguide or a hollow fiber. The Bragg fiber can be fabricated by coating a sacrificial mandrel or mold with alternating layers of high- and low-refractive-index dielectric materials and then removing the mandrel or mold to leave a hollow tube with a multilayer dielectric cladding. The Bragg channel waveguide can be fabricated by forming a trench embedded in a substrate and coating the inner wall of the trench with a multilayer dielectric cladding. The thicknesses of the alternating layers can be selected to satisfy the condition for minimum radiation loss of the guided wave.

Performance evaluation of Bragg coherent diffraction imaging

NASA Astrophysics Data System (ADS)

Öztürk, H.; Huang, X.; Yan, H.; Robinson, I. K.; Noyan, I. C.; Chu, Y. S.

2017-10-01

In this study, we present a numerical framework for modeling three-dimensional (3D) diffraction data in Bragg coherent diffraction imaging (Bragg CDI) experiments and evaluating the quality of obtained 3D complex-valued real-space images recovered by reconstruction algorithms under controlled conditions. The approach is used to systematically explore the performance and the detection limit of this phase-retrieval-based microscopy tool. The numerical investigation suggests that the superb performance of Bragg CDI is achieved with an oversampling ratio above 30 and a detection dynamic range above 6 orders. The observed performance degradation subject to the data binning processes is also studied. This numerical tool can be used to optimize experimental parameters and has the potential to significantly improve the throughput of Bragg CDI method.

D-shaped fiber grating refractive index sensor induced by an ultrashort pulse laser.

PubMed

Liao, Changrui; Wang, Qiao; Xu, Lei; Liu, Shen; He, Jun; Zhao, Jing; Li, Zhengyong; Wang, Yiping

2016-03-01

The fabrication of fiber Bragg gratings was here demonstrated using ultrashort pulse laser point-by-point inscription. This is a very convenient means of creating fiber Bragg gratings with different grating periods and works by changing the translation speed of the fiber. The laser energy was first optimized in order to improve the spectral properties of the fiber gratings. Then, fiber Bragg gratings were formed into D-shaped fibers for use as refractive index sensors. A nonlinear relationship was observed between the Bragg wavelength and liquid refractive index, and a sensitivity of ∼30  nm/RIU was observed at 1.450. This shows that D-shaped fiber Bragg gratings might be used to develop promising biochemical sensors.

Continuous wave and modulation performance of 1550nm band wafer-fused VCSELs with MBE-grown InP-based active region and GaAs-based DBRs

NASA Astrophysics Data System (ADS)

Babichev, A. V.; Karachinsky, L. Ya.; Novikov, I. I.; Gladyshev, A. G.; Mikhailov, S.; Iakovlev, V.; Sirbu, A.; Stepniak, G.; Chorchos, L.; Turkiewicz, J. P.; Agustin, M.; Ledentsov, N. N.; Voropaev, K. O.; Ionov, A. S.; Egorov, A. Yu.

2017-02-01

We report for the first time on wafer-fused InGaAs-InP/AlGaAs-GaAs 1550 nm vertical-cavity surface-emitting lasers (VCSELs) incorporating a InAlGaAs/InP MQW active region with re-grown tunnel junction sandwiched between top and bottom undoped AlGaAs/GaAs distributed Bragg reflectors (DBRs) all grown by molecular beam epitaxy. InP-based active region includes seven compressively strained quantum wells (2.8 nm) optimized to provide high differential gain. Devices with this active region demonstrate lasing threshold current < 2.5 mA and output optical power > 2 mW in the temperature range of 10-70°C. The wall-plug efficiency (WPE) value-reaches 20 %. Lasing spectra show single mode CW operation with a longitudinal side mode suppression ratio (SMSR) up to 45 dB at > 2 mW output power. Small signal modulation response measurements show a 3-dB modulation bandwidth of 9 GHz at pump current of 10 mA and a D-factor value of 3 GHz/(mA)1/2. Open-eye diagram at 30 Gb/s of standard NRZ is demonstrated. Achieved CW and modulation performance is quite sufficient for fiber to the home (FTTH) applications where very large volumes of low-cost lasers are required.

Negative axial strain sensitivity in gold-coated eccentric fiber Bragg gratings

PubMed Central

Chah, Karima; Kinet, Damien; Caucheteur, Christophe

2016-01-01

New dual temperature and strain sensor has been designed using eccentric second-order fiber Bragg gratings produced in standard single-mode optical fiber by point-by-point direct writing technique with tight focusing of 800 nm femtosecond laser pulses. With thin gold coating at the grating location, we experimentally show that such gratings exhibit a transmitted amplitude spectrum composed by the Bragg and cladding modes resonances that extend in a wide spectral range exceeding one octave. An overlapping of the first order and second order spectrum is then observed. High-order cladding modes belonging to the first order Bragg resonance coupling are close to the second order Bragg resonance, they show a negative axial strain sensitivity (−0.55 pm/με) compared to the Bragg resonance (1.20 pm/με) and the same temperature sensitivity (10.6 pm/°C). With this well conditioned system, temperature and strain can be determined independently with high sensitivity, in a wavelength range limited to a few nanometers. PMID:27901059

Cross-fiber Bragg grating transducer

NASA Technical Reports Server (NTRS)

Albin, Sacharia (Inventor); Zheng, Jianli (Inventor); Lavarias, Arnel (Inventor)

2000-01-01

A transducer has been invented that uses specially-oriented gratings in waveguide a manner that allows the simultaneous measurement of physical phenomena (such as shear force, strain and temperature) in a single sensing element. The invention has a highly sensitive, linear response and also has directional sensitivity with regard to strain. The transducer has a waveguide with a longitudinal axis as well as two Bragg gratings. The transducer has a first Bragg grating associated with the waveguide that has an angular orientation .theta..sub.a relative to a perpendicular to the longitudinal axis such that 0.degree.<.theta..sub.a <.theta..sub.max. The second Bragg grating is associated with the waveguide in such a way that the angular orientation .theta..sub.b of the grating relative to a perpendicular to the longitudinal axis is (360.degree.-.theta..sub.max)<.theta..sub.b <360.degree.. The first Bragg grating can have a periodicity .LAMBDA..sub.a and the second Bragg grating can have a periodicity .LAMBDA..sub.b such that the periodicity .LAMBDA..sub.a of the first Bragg grating does not equal the periodicity .LAMBDA..sub.b of the second Bragg grating. The angle of the gratings can be such that .theta..sub.a =360.degree.-.theta..sub.b. The waveguide can assume a variety of configurations, including an optical fiber, a rectangular waveguide and a planar waveguide. The waveguide can be fabricated of a variety of materials, including silica and polymer material.

Wideband Waveguide Acousto-Optic Bragg Cell.

DTIC Science & Technology

The results of an effort to improve the performance specifications of acousto - optic Bragg cells are reported. Various configurations of multiple...would provide a 700 MHz acousto - optic bandwidth. Investigated were Bragg cells fabricated on Ti diffused LiNb03 waveguides as well as Ti diffused LiNb03

INTERNATIONAL CONFERENCE ON SEMICONDUCTOR INJECTION LASERS SELCO-87: Continuous-wave distributed-feedback InGaAsP (λ = 1.55 μm) injection heterolasers

NASA Astrophysics Data System (ADS)

Baryshev, V. I.; Golikova, E. G.; Duraev, V. P.; Kuchinskiĭ, V. I.; Kizhaev, K. Yu; Kuksenkov, D. V.; Portnoĭ, E. L.; Smirnitskiĭ, V. B.

1988-11-01

A study was made of stimulated emission from mesa-stripe distributed-feedback lasers in the form of double heterostructures with separate electron and optical confinement. A diffraction grating with a period Λ = 0.46 μm, formed on the surface of the upper waveguide layer by holographic lithography, ensured distributed feedback in the second order. The threshold current for cw operation at room temperature was 35-70 mA, the shift of the emission wavelength with temperature was ~ 0.08 nm/K, and the feedback coefficient deduced from the width of a "Bragg gap" was 110-150 cm- 1.

Application of a Fiber Optic Distributed Strain Sensor System to Woven E-Glass Composite

NASA Technical Reports Server (NTRS)

Anastasi, Robert F.; Lopatin, Craig

2001-01-01

A distributed strain sensing system utilizing a series of identically written Bragg gratings along an optical fiber is examined for potential application to Composite Armored Vehicle health monitoring. A vacuum assisted resin transfer molding process was used to fabricate a woven fabric E-glass/composite panel with an embedded fiber optic strain sensor. Test samples machined from the panel were mechanically tested in 4-point bending. Experimental results are presented that show the mechanical strain from foil strain gages comparing well to optical strain from the embedded sensors. Also, it was found that the distributed strain along the sample length was consistent with the loading configuration.

High-Precision Differential Predictions for Top-Quark Pairs at the LHC

NASA Astrophysics Data System (ADS)

Czakon, Michal; Heymes, David; Mitov, Alexander

2016-02-01

We present the first complete next-to-next-to-leading order (NNLO) QCD predictions for differential distributions in the top-quark pair production process at the LHC. Our results are derived from a fully differential partonic Monte Carlo calculation with stable top quarks which involves no approximations beyond the fixed-order truncation of the perturbation series. The NNLO corrections improve the agreement between existing LHC measurements [V. Khachatryan et al. (CMS Collaboration), Eur. Phys. J. C 75, 542 (2015)] and standard model predictions for the top-quark transverse momentum distribution, thus helping alleviate one long-standing discrepancy. The shape of the top-quark pair invariant mass distribution turns out to be stable with respect to radiative corrections beyond NLO which increases the value of this observable as a place to search for physics beyond the standard model. The results presented here provide essential input for parton distribution function fits, implementation of higher-order effects in Monte Carlo generators, as well as top-quark mass and strong coupling determination.

High-Precision Differential Predictions for Top-Quark Pairs at the LHC.

PubMed

Czakon, Michal; Heymes, David; Mitov, Alexander

2016-02-26

We present the first complete next-to-next-to-leading order (NNLO) QCD predictions for differential distributions in the top-quark pair production process at the LHC. Our results are derived from a fully differential partonic Monte Carlo calculation with stable top quarks which involves no approximations beyond the fixed-order truncation of the perturbation series. The NNLO corrections improve the agreement between existing LHC measurements [V. Khachatryan et al. (CMS Collaboration), Eur. Phys. J. C 75, 542 (2015)] and standard model predictions for the top-quark transverse momentum distribution, thus helping alleviate one long-standing discrepancy. The shape of the top-quark pair invariant mass distribution turns out to be stable with respect to radiative corrections beyond NLO which increases the value of this observable as a place to search for physics beyond the standard model. The results presented here provide essential input for parton distribution function fits, implementation of higher-order effects in Monte Carlo generators, as well as top-quark mass and strong coupling determination.

Study of phase-locked diode laser array and DFB/DBR surface emitting laser diode

NASA Astrophysics Data System (ADS)

Hsin, Wei

New types of phased-array and surface-emitting lasers are designed. The importance and approaches (or structures) of different phased array and surface emitting laser diodes are reviewed. The following are described: (1) a large optical cavity channel substrate planar laser array with layer thickness chirping; (2) a vertical cavity surface emitter with distributed feedback (DFB) optical cavity and a transverse junction buried heterostructure; (3) a microcavity distributed Bragg reflector (DBR) surface emitter; and (4) two surface emitting laser structures which utilized lateral current injection schemes to overcome the problems occurring in the vertical injection scheme.

Understanding temperature tuning of the all polymer co-extruded laser

NASA Astrophysics Data System (ADS)

Crescimanno, Michael; Andrews, Jim; Aviles, Michael; Dawson, Nathan; Petrus, Joshua; Mazzocco, Anthony; Singer, Ken; Baer, Eric; Song, Hyunmin

2012-10-01

We investigate the effects of elevated temperatures on a few types of all-polymer multilayer films that were fabricated using a co-extrusion melt-process technique. We report on the anisotropic thermal expansion of the multilayer films, which affects the photonic crystal structure via constituent wise induced anisotropic strains and a change in the relative refractive indices. In addition to the characterization of these films in the temperature range of approximately 20-95 degrees C, we show the application to non-contact temperature sensing and wavelength tuning of all polymer Distributed FeedBack (DFB) lasers and Distributed Bragg Reflector (DBR) lasers.

Investigation of Structural Properties of Carbon-Epoxy Composites Using Fiber-Bragg Gratings

NASA Technical Reports Server (NTRS)

Grant, J.; Kaul, R.; Taylor, S.; Jackson, K.; Sharma, A.; Burdine, Robert V. (Technical Monitor)

2002-01-01

Fiber Bragg-gratings are embedded in carbon-epoxy laminates as well as bonded on the surface of cylindrical structures fabricated out of such composites. Structural properties of such composites is investigated. The measurements include stress-strain relation in laminates and Poisson's ratio in several specimens with varying orientation of the optical fiber Bragg-sensor with respect to the carbon fiber in an epoxy matrix. Additionally, Bragg gratings are bonded on the surface of cylinders fabricated out of carbon-epoxy composites and longitudinal and hoop strain on the surface is measured.

Excitation of surface electromagnetic waves in a graphene-based Bragg grating

PubMed Central

Sreekanth, Kandammathe Valiyaveedu; Zeng, Shuwen; Shang, Jingzhi; Yong, Ken-Tye; Yu, Ting

2012-01-01

Here, we report the fabrication of a graphene-based Bragg grating (one-dimensional photonic crystal) and experimentally demonstrate the excitation of surface electromagnetic waves in the periodic structure using prism coupling technique. Surface electromagnetic waves are non-radiative electromagnetic modes that appear on the surface of semi-infinite 1D photonic crystal. In order to fabricate the graphene-based Bragg grating, alternating layers of high (graphene) and low (PMMA) refractive index materials have been used. The reflectivity plot shows a deepest, narrow dip after total internal reflection angle corresponds to the surface electromagnetic mode propagating at the Bragg grating/air boundary. The proposed graphene based Bragg grating can find a variety of potential surface electromagnetic wave applications such as sensors, fluorescence emission enhancement, modulators, etc. PMID:23071901

Performance evaluation of Bragg coherent diffraction imaging

DOE PAGES

Ozturk, Hande; Huang, X.; Yan, H.; ...

2017-10-03

In this study, we present a numerical framework for modeling three-dimensional (3D) diffraction data in Bragg coherent diffraction imaging (Bragg CDI) experiments and evaluating the quality of obtained 3D complex-valued real-space images recovered by reconstruction algorithms under controlled conditions. The approach is used to systematically explore the performance and the detection limit of this phase-retrieval-based microscopy tool. The numerical investigation suggests that the superb performance of Bragg CDI is achieved with an oversampling ratio above 30 and a detection dynamic range above 6 orders. The observed performance degradation subject to the data binning processes is also studied. Furthermore, this numericalmore » tool can be used to optimize experimental parameters and has the potential to significantly improve the throughput of Bragg CDI method.« less

Excitation of surface electromagnetic waves in a graphene-based Bragg grating.

PubMed

Sreekanth, Kandammathe Valiyaveedu; Zeng, Shuwen; Shang, Jingzhi; Yong, Ken-Tye; Yu, Ting

2012-01-01

Here, we report the fabrication of a graphene-based Bragg grating (one-dimensional photonic crystal) and experimentally demonstrate the excitation of surface electromagnetic waves in the periodic structure using prism coupling technique. Surface electromagnetic waves are non-radiative electromagnetic modes that appear on the surface of semi-infinite 1D photonic crystal. In order to fabricate the graphene-based Bragg grating, alternating layers of high (graphene) and low (PMMA) refractive index materials have been used. The reflectivity plot shows a deepest, narrow dip after total internal reflection angle corresponds to the surface electromagnetic mode propagating at the Bragg grating/air boundary. The proposed graphene based Bragg grating can find a variety of potential surface electromagnetic wave applications such as sensors, fluorescence emission enhancement, modulators, etc.

Wide angle and narrow-band asymmetric absorption in visible and near-infrared regime through lossy Bragg stacks

PubMed Central

Shu, Shiwei; Zhan, Yawen; Lee, Chris; Lu, Jian; Li, Yang Yang

2016-01-01

Absorber is an important component in various optical devices. Here we report a novel type of asymmetric absorber in the visible and near-infrared spectrum which is based on lossy Bragg stacks. The lossy Bragg stacks can achieve near-perfect absorption at one side and high reflection at the other within the narrow bands (several nm) of resonance wavelengths, whereas display almost identical absorption/reflection responses for the rest of the spectrum. Meanwhile, this interesting wavelength-selective asymmetric absorption behavior persists for wide angles, does not depend on polarization, and can be ascribed to the lossy characteristics of the Bragg stacks. Moreover, interesting Fano resonance with easily tailorable peak profiles can be realized using the lossy Bragg stacks. PMID:27251768

Electrically injected visible vertical cavity surface emitting laser diodes

DOEpatents

Schneider, Richard P.; Lott, James A.

1994-01-01

Visible laser light output from an electrically injected vertical cavity surface emitting laser (VSCEL) diode is enabled by the addition of phase-matching spacer layers on either side of the active region to form the optical cavity. The spacer layers comprise InAlP which act as charge carrier confinement means. Distributed Bragg reflector layers are formed on either side of the optical cavity to act as mirrors.

Electrically injected visible vertical cavity surface emitting laser diodes

DOEpatents

Schneider, R.P.; Lott, J.A.

1994-09-27

Visible laser light output from an electrically injected vertical cavity surface emitting laser (VSCEL) diode is enabled by the addition of phase-matching spacer layers on either side of the active region to form the optical cavity. The spacer layers comprise InAlP which act as charge carrier confinement means. Distributed Bragg reflector layers are formed on either side of the optical cavity to act as mirrors. 5 figs.

Widely tunable mid-infrared quantum cascade lasers using sampled grating reflectors.

PubMed

Mansuripur, Tobias S; Menzel, Stefan; Blanchard, Romain; Diehl, Laurent; Pflügl, Christian; Huang, Yong; Ryou, Jae-Hyun; Dupuis, Russell D; Loncar, Marko; Capasso, Federico

2012-10-08

We demonstrate a three-section, electrically pulsed quantum cascade laser which consists of a Fabry-Pérot section placed between two sampled grating distributed Bragg reflectors. The device is current-tuned between ten single modes spanning a range of 0.46 μm (63 cm(-1)), from 8.32 to 8.78 μm. The peak optical output power exceeds 280 mW for nine of the modes.

Cancellation of birefringence in DBR laser through principal axis offset by a rotation of 90°

NASA Astrophysics Data System (ADS)

Zaini, M. K. A.; Lai, M. H.; Islam, M. R.; Lim, K. S.; Ahmad, H.

2018-04-01

The cancellation of birefringence in the distributed Bragg reflector based on 90° rotation offset method is demonstrated. It is found that the birefringence, which causes the peak bifurcation has been eliminated and a single peak is produced at each resonance in the output spectrum. This modification is an economic solution for eliminating the birefringence of the optical fibre devices.

Dealloying in Individual Nanoparticles and Thin Film Grains: A Bragg Coherent Diffractive Imaging Study

DOE Office of Scientific and Technical Information (OSTI.GOV)

Cha, Wonsuk; Liu, Yihua; You, Hoydoo

Dealloying is a process whereby selective dissolution results in a porous, strained structure often with new properties. The process is of both intrinsic and applied interest, and recently has been used to make highly active catalysts. The porosity has been studied using electron microscopy while the dealloying-induced strain has been studied at the ensemble level using X-ray diffraction. Despite the importance of local, for example, at the individual particle or grain level, strain in controlling the properties of the dealloyed material, it remains unresolved due to the difficulty of imaging 3D strain distributions with nanometer resolution in reactive environments. Thismore » information could play an integral role in understanding and controlling lattice strain for a variety of applications. Here, 3D strain distributions in individual nanoparticles and thin film grains in silver-gold alloys undergoing nitric acid-induced dealloying are imaged by Bragg coherent diffractive imaging. Particles exhibit dramatic changes in their local strains due to dealloying but grains do not. Furthermore, the average lattice in both grains and particles contracts during dealloying. In general, the results reveal significant dealloying-induced strain heterogeneity at the nanoscale in both isolated and extended samples, which may be utilized to develop advanced nanostructures for a variety of important applications.« less

Detection, Localization and Quantification of Impact Events on a Stiffened Composite Panel with Embedded Fiber Bragg Grating Sensor Networks

PubMed Central

Lamberti, Alfredo; Luyckx, Geert; Van Paepegem, Wim; Rezayat, Ali; Vanlanduit, Steve

2017-01-01

Nowadays, it is possible to manufacture smart composite materials with embedded fiber optic sensors. These sensors can be exploited during the composites’ operating life to identify occurring damages such as delaminations. For composite materials adopted in the aviation and wind energy sector, delaminations are most often caused by impacts with external objects. The detection, localization and quantification of such impacts are therefore crucial for the prevention of catastrophic events. In this paper, we demonstrate the feasibility to perform impact identification in smart composite structures with embedded fiber optic sensors. For our analyses, we manufactured a carbon fiber reinforced plate in which we embedded a distributed network of fiber Bragg grating (FBG) sensors. We impacted the plate with a modal hammer and we identified the impacts by processing the FBG data with an improved fast phase correlation (FPC) algorithm in combination with a variable selective least squares (VS-LS) inverse solver approach. A total of 164 impacts distributed on 41 possible impact locations were analyzed. We compared our methodology with the traditional P-Inv based approach. In terms of impact localization, our methodology performed better in 70.7% of the cases. An improvement on the impact time domain reconstruction was achieved in 95.1% of the cases. PMID:28368319

Detection, Localization and Quantification of Impact Events on a Stiffened Composite Panel with Embedded Fiber Bragg Grating Sensor Networks.

PubMed

Lamberti, Alfredo; Luyckx, Geert; Van Paepegem, Wim; Rezayat, Ali; Vanlanduit, Steve

2017-04-01

Nowadays, it is possible to manufacture smart composite materials with embedded fiber optic sensors. These sensors can be exploited during the composites' operating life to identify occurring damages such as delaminations. For composite materials adopted in the aviation and wind energy sector, delaminations are most often caused by impacts with external objects. The detection, localization and quantification of such impacts are therefore crucial for the prevention of catastrophic events. In this paper, we demonstrate the feasibility to perform impact identification in smart composite structures with embedded fiber optic sensors. For our analyses, we manufactured a carbon fiber reinforced plate in which we embedded a distributed network of fiber Bragg grating (FBG) sensors. We impacted the plate with a modal hammer and we identified the impacts by processing the FBG data with an improved fast phase correlation (FPC) algorithm in combination with a variable selective least squares (VS-LS) inverse solver approach. A total of 164 impacts distributed on 41 possible impact locations were analyzed. We compared our methodology with the traditional P-Inv based approach. In terms of impact localization, our methodology performed better in 70.7% of the cases. An improvement on the impact time domain reconstruction was achieved in 95 . 1 % of the cases.

Laterally coupled distributed feedback lasers emitting at 2 μm with quantum dash active region and high-duty-cycle etched semiconductor gratings

NASA Astrophysics Data System (ADS)

Papatryfonos, Konstantinos; Saladukha, Dzianis; Merghem, Kamel; Joshi, Siddharth; Lelarge, Francois; Bouchoule, Sophie; Kazazis, Dimitrios; Guilet, Stephane; Le Gratiet, Luc; Ochalski, Tomasz J.; Huyet, Guillaume; Martinez, Anthony; Ramdane, Abderrahim

2017-02-01

Single-mode diode lasers on an InP(001) substrate have been developed using InAs/In0.53Ga0.47As quantum dash (Qdash) active regions and etched lateral Bragg gratings. The lasers have been designed to operate at wavelengths near 2 μm and exhibit a threshold current of 65 mA for a 600 μm long cavity, and a room temperature continuous wave output power per facet >5 mW. Using our novel growth approach based on the low ternary In0.53Ga0.47As barriers, we also demonstrate ridge-waveguide lasers emitting up to 2.1 μm and underline the possibilities for further pushing the emission wavelength out towards longer wavelengths with this material system. By introducing experimentally the concept of high-duty-cycle lateral Bragg gratings, a side mode suppression ratio of >37 dB has been achieved, owing to an appreciably increased grating coupling coefficient of κ ˜ 40 cm-1. These laterally coupled distributed feedback (LC-DFB) lasers combine the advantage of high and well-controlled coupling coefficients achieved in conventional DFB lasers, with the regrowth-free fabrication process of lateral gratings, and exhibit substantially lower optical losses compared to the conventional metal-based LC-DFB lasers.

Dealloying in Individual Nanoparticles and Thin Film Grains: A Bragg Coherent Diffractive Imaging Study

DOE PAGES

Cha, Wonsuk; Liu, Yihua; You, Hoydoo; ...

2017-05-09

Dealloying is a process whereby selective dissolution results in a porous, strained structure often with new properties. The process is of both intrinsic and applied interest, and recently has been used to make highly active catalysts. The porosity has been studied using electron microscopy while the dealloying-induced strain has been studied at the ensemble level using X-ray diffraction. Despite the importance of local, for example, at the individual particle or grain level, strain in controlling the properties of the dealloyed material, it remains unresolved due to the difficulty of imaging 3D strain distributions with nanometer resolution in reactive environments. Thismore » information could play an integral role in understanding and controlling lattice strain for a variety of applications. Here, 3D strain distributions in individual nanoparticles and thin film grains in silver-gold alloys undergoing nitric acid-induced dealloying are imaged by Bragg coherent diffractive imaging. Particles exhibit dramatic changes in their local strains due to dealloying but grains do not. Furthermore, the average lattice in both grains and particles contracts during dealloying. In general, the results reveal significant dealloying-induced strain heterogeneity at the nanoscale in both isolated and extended samples, which may be utilized to develop advanced nanostructures for a variety of important applications.« less

NNLO QCD predictions for fully-differential top-quark pair production at the Tevatron

NASA Astrophysics Data System (ADS)

Czakon, Michal; Fiedler, Paul; Heymes, David; Mitov, Alexander

2016-05-01

We present a comprehensive study of differential distributions for Tevatron top-pair events at the level of stable top quarks. All calculations are performed in NNLO QCD with the help of a fully differential partonic Monte-Carlo and are exact at this order in perturbation theory. We present predictions for all kinematic distributions for which data exists. Particular attention is paid on the top-quark forward-backward asymmetry which we study in detail. We compare the NNLO results with existing approximate NNLO predictions as well as differential distributions computed with different parton distribution sets. Theory errors are significantly smaller than current experimental ones with overall agreement between theory and data.

A Method for Obtaining High Frequency, Global, IR-Based Convective Cloud Tops for Studies of the TTL

NASA Technical Reports Server (NTRS)

Pfister, Leonhard; Ueyama, Rei; Jensen, Eric; Schoeberl, Mark

2017-01-01

Models of varying complexity that simulate water vapor and clouds in the Tropical Tropopause Layer (TTL) show that including convection directly is essential to properly simulating the water vapor and cloud distribution. In boreal winter, for example, simulations without convection yield a water vapor distribution that is too uniform with longitude, as well as minimal cloud distributions. Two things are important for convective simulations. First, it is important to get the convective cloud top potential temperature correctly, since unrealistically high values (reaching above the cold point tropopause too frequently) will cause excessive hydration of the stratosphere. Second, one must capture the time variation as well, since hydration by convection depends on the local relative humidity (temperature), which has substantial variation on synoptic time scales in the TTL. This paper describes a method for obtaining high frequency (3-hourly) global convective cloud top distributions which can be used in trajectory models. The method uses rainfall thresholds, standard IR brightness temperatures, meteorological temperature analyses, and physically realistic and documented corrections IR brightness temperature corrections to derive cloud top altitudes and potential temperatures. The cloud top altitudes compare well with combined CLOUDSAT and CALIPSO data, both in time-averaged overall vertical and horizontal distributions and in individual cases (correlations of .65-.7). An important finding is that there is significant uncertainty (nearly .5 km) in evaluating the statistical distribution of convective cloud tops even using lidar. Deep convection whose tops are in regions of high relative humidity (such as much of the TTL), will cause clouds to form above the actual convection. It is often difficult to distinguish these clouds from the actual convective cloud due to the uncertainties of evaluating ice water content from lidar measurements. Comparison with models show that calculated cloud top altitudes are generally higher than those calculated by global analyses (e.g., MERRA). Interannual variability in the distribution of convective cloud top altitudes is also investigated.

FIBER AND INTEGRATED OPTICS: Bandgap modes in a coupled waveguide array

NASA Astrophysics Data System (ADS)

Usievich, B. A.; Nurligareev, D. Kh; Svetikov, V. V.; Sychugov, V. A.

2009-08-01

This work examines a waveguide array that consists of ten Nb2O5/SiO2 double layers and supports a 0.63-μm surface wave. The deposition of a Nb2O5 capping layer on top of the waveguide array enables a marked increase in the wave field intensity on its surface. The efficiency of surface-wave excitation in the Kretschmann configuration can be optimised by adjusting the number of double layers. We analyse the behaviour of the Bragg mode in relation to the thickness of the layer exposed to air and the transition of this mode from the second allowed band to the first through the bandgap of the system. In addition, the conventional leaky mode converts to a surface mode and then to a guided mode.

SU-E-T-671: Range-Modulation Effects of Carbon Ion Beams in Lung Tissue

DOE Office of Scientific and Technical Information (OSTI.GOV)

Witt, M; Weber, U; Simeonov, Y

Purpose: When particles traversing inhomogeneous materials like lung they show a characteristic range modulation which cannot be observed in homogeneous materials. It is possible to describe the range modulation by a convolution of an unperturbed Bragg-Curve and a normal distribution. The sigma of the normal distribution is a parameter for the strength of the modulation effect. A new material parameter (modulation power, P-mod) is introduced which is independent of the material thickness. It is defined as the square of sigma divided by the mean water equivalent thickness of the target (µ). Methods: The modulation power of lung tissue was determinedmore » by actual Bragg-peak measurements after traversing an ex-vivo porcine lung and by Monte-Carlo simulations with micro-CT data of human lung tissue. The determined modulation powers were used to show the effect of range modulation effects in a simplified treatment situation. A four centimeter spread-out Bragg-peak after traversing eight centimeter of lung tissue was simulated in FLUKA. The SOBP with and without consideration of range modulation effects were compared. Results: As well in the measurements as in the MC simulations range modulation effects of lung tissue were observed. The determined modulation powers showed a great range from 0.05 mm, in the micro-CT data, to 0.7 mm in the lung measurements. The SOBP comparison showed that range modulation effects Result in over- and underdosages at the distal and proximal edge of the SOBP. In the investigated case, the last 0.5 cm of the SOBP showed an underdosage of up to 50% at the distal edge, while 0.5 cm distal to the SOBP an overdosage of up to 50% was observed. Conclusion: Range modulation effects occur in inhomogeneous materials like lung. These modulation effects may Result in clinically relevant over- and underdosages but are currently not considered in commercially available treatment planning systems.« less

Tunable and reconfigurable microwave filter by use of a Bragg-grating-based acousto-optic superlattice modulator.

PubMed

Delgado-Pinar, M; Mora, J; Díez, A; Andrés, M V; Ortega, B; Capmany, J

2005-01-01

We present an all-optical novel configuration for implementing multitap transversal filters by use of a broadband source sliced by fiber Bragg grating arrays generated by propagating an acoustic wave along a strong uniform fiber Bragg grating. The tunability and reconfigurability of the microwave filter are demonstrated.

Cascaded Bragg scattering in fiber optics.

PubMed

Xu, Y Q; Erkintalo, M; Genty, G; Murdoch, S G

2013-01-15

We report on a theoretical and experimental study of cascaded Bragg scattering in fiber optics. We show that the usual energy-momentum conservation of Bragg scattering can be considerably relaxed via cascade-induced phase-matching. Experimentally we demonstrate frequency translation over six- and 11-fold cascades, in excellent agreement with derived phase-matching conditions.

Crystallography: To Infinity and Beyond…

ERIC Educational Resources Information Center

Bond, Charles

2014-01-01

William Henry Bragg moved from Cambridge in Britain to South Australia to take up a professorship at the University of Adelaide in 1885. He brought with him a broad interest in many areas of physics, but when Wilhelm Roentgen discovered X-rays in the 1890s, Bragg's interest was stimulated. William's Australian-born son, Lawrence (WL Bragg), began…

Wave power focusing due to the Bragg resonance

NASA Astrophysics Data System (ADS)

Tao, Ai-feng; Yan, Jin; Wang, Yi; Zheng, Jin-hai; Fan, Jun; Qin, Chuan

2017-08-01

Wave energy has drawn much attention as an achievable way to exploit the renewable energy. At present, in order to enhance the wave energy extraction, most efforts have been concentrated on optimizing the wave energy convertor and the power take-off system mechanically and electrically. However, focusing the wave power in specific wave field could also be an alternative to improve the wave energy extraction. In this experimental study, the Bragg resonance effect is applied to focus the wave energy. Because the Bragg resonance effect of the rippled bottom largely amplifies the wave reflection, leading to a significant increase of wave focusing. Achieved with an energy conversion system consisting of a point absorber and a permanent magnet single phase linear motor, the wave energy extracted in the wave flume with and without Bragg resonance effect was measured and compared quantitatively in experiment. It shows that energy extraction by a point absorber from a standing wave field resulted from Bragg resonance effect can be remarkably increased compared with that from a propagating wave field (without Bragg resonance effect).

Bragg-Fresnel optics: New field of applications

DOE Office of Scientific and Technical Information (OSTI.GOV)

Snigirev, A.

Bragg-Fresnel Optics shows excellent compatibility with the third generation synchrotron radiation sources such as ESRF and is capable of obtaining monochromatic submicron focal spots with 10{sup 8}-10{sup 9} photons/sec in an energy bandwidth of 10{sup -4}-10{sup -6} and in a photon energy range between 2-100 keV. New types of Bragg-Fresnel lenses like modified, ion implanted, bent and acoustically modulated were tested. Microprobe techniques like microdiffraction and microfluorescence based on Bragg-Fresnel optics were realised at the ESRF beamlines. Excellent parameters of the X-ray beam at the ESRF in terms of low emittance and quite small angular source size allow for Bragg-Fresnelmore » optics to occupy new fields of applications such as high resolution diffraction, holography, interferometry and phase contrast imaging.« less

Use of 3000 Bragg Grating Strain Sensors Distributed on Four Eight-meter Optical Fibers During Static Load Tests of a Composite Structure

NASA Technical Reports Server (NTRS)

Childers, Brooks A.; Froggatt, Mark E.; Allison, Sidney G.; Moore, Thomas C., Sr.; Hare, David A.; Batten, Christopher F.; Jegley, Dawn C.

2001-01-01

This paper describes the use of a fiber optic system to measure strain at thousands of locations along optical fibers where weakly reflecting Bragg gratings have been photoetched. The optical fibers were applied to an advanced composite transport wing along with conventional foil strain gages. A comparison of the fiber optic and foil gage systems used for this test will be presented including: a brief description of both strain data systems; a discussion of the process used for installation of the optical fiber; comparative data from the composite wing test; the processes used for the location and display of the high density fiber optic data. Calibration data demonstrating the potential accuracy of the fiber optic system will also be presented. The opportunities for industrial and commercial applications will be discussed. The fiber optic technique is shown to be a valuable augmentation to foil strain gages providing insight to structural behavior previously requiring reliance on modeling.

3D Bragg coherent diffractive imaging of five-fold multiply twinned gold nanoparticle

DOE Office of Scientific and Technical Information (OSTI.GOV)

Kim, Jong Woo; Ulvestad, Andrew; Manna, Sohini

The formation mechanism of five-fold multiply twinned nanoparticles has been a long-term topic because of their geometrical incompatibility. So, various models have been proposed to explain how the internal structure of the multiply twinned nanoparticles accommodates the constraints of the solid-angle deficiency. Here, we investigate the internal structure, strain field and strain energy density of 600 nm sized five-fold multiply twinned gold nanoparticles quantitatively using Bragg coherent diffractive imaging, which is suitable for the study of buried defects and three-dimensional strain distribution with great precision. Our study reveals that the strain energy density in five-fold multiply twinned gold nanoparticles ismore » an order of magnitude higher than that of the single nanocrystals such as an octahedron and triangular plate synthesized under the same conditions. This result indicates that the strain developed while accommodating an angular misfit, although partially released through the introduction of structural defects, is still large throughout the crystal.« less

The influence of grating shape formation fluctuation on DFB laser diode threshold condition

NASA Astrophysics Data System (ADS)

Bao, Shiwei; Song, Qinghai; Xie, Chunmei

2018-03-01

Not only the grating material refractive index itself but also the Bragg grating physical shape formation affects the coupling strength greatly. The Bragg grating shape includes three factors, namely grating depth, duty ratio and grating angle. During the lithography and wet etching process, there always will be some fluctuation between the target and real grating shape formation after fabrication process. This grating shape fluctuation will affect the DFB coupling coefficient κ , and then consequently threshold current and corresponding wavelength. This paper studied the grating shape formation fluctuation influence to improve the DFB fabrication yield. A truncated normal random distribution fluctuation is considered in this paper. The simulation results conclude that it is better to choose relative thicker grating depth with lower refractive index to obtain a better fabrication tolerance, while not quite necessary to spend too much effort on improving lithography and wet etching process to get a precisely grating duty ratio and grating angle.

3D Bragg coherent diffractive imaging of five-fold multiply twinned gold nanoparticle

DOE PAGES

Kim, Jong Woo; Ulvestad, Andrew; Manna, Sohini; ...

2017-08-11

The formation mechanism of five-fold multiply twinned nanoparticles has been a long-term topic because of their geometrical incompatibility. So, various models have been proposed to explain how the internal structure of the multiply twinned nanoparticles accommodates the constraints of the solid-angle deficiency. Here, we investigate the internal structure, strain field and strain energy density of 600 nm sized five-fold multiply twinned gold nanoparticles quantitatively using Bragg coherent diffractive imaging, which is suitable for the study of buried defects and three-dimensional strain distribution with great precision. Our study reveals that the strain energy density in five-fold multiply twinned gold nanoparticles ismore » an order of magnitude higher than that of the single nanocrystals such as an octahedron and triangular plate synthesized under the same conditions. This result indicates that the strain developed while accommodating an angular misfit, although partially released through the introduction of structural defects, is still large throughout the crystal.« less

The influence of grating shape formation fluctuation on DFB laser diode threshold condition

NASA Astrophysics Data System (ADS)

Bao, Shiwei; Song, Qinghai; Xie, Chunmei

2018-06-01

Not only the grating material refractive index itself but also the Bragg grating physical shape formation affects the coupling strength greatly. The Bragg grating shape includes three factors, namely grating depth, duty ratio and grating angle. During the lithography and wet etching process, there always will be some fluctuation between the target and real grating shape formation after fabrication process. This grating shape fluctuation will affect the DFB coupling coefficient κ, and then consequently threshold current and corresponding wavelength. This paper studied the grating shape formation fluctuation influence to improve the DFB fabrication yield. A truncated normal random distribution fluctuation is considered in this paper. The simulation results conclude that it is better to choose relative thicker grating depth with lower refractive index to obtain a better fabrication tolerance, while not quite necessary to spend too much effort on improving lithography and wet etching process to get a precisely grating duty ratio and grating angle.

All-fiber optoelectronic sensor with Bragg gratings for in-situ cure monitoring

NASA Astrophysics Data System (ADS)

Cusano, Andrea; Breglio, Giovanni; Cutolo, Antonello; Calabro, Antonio M.; Giordano, Michele; Nicolais, Luigi, II

2000-08-01

Real-time, in situ monitoring for quality control of the polymer cure process is of high interest, since thermoset polymer-matrix composite are widely used in large industrial areas: aeronautical, aerospace, automotive and civil due to their low cost/low weight features. However, their final properties are strongly dependence on the processing parameters, such as temperature and pressure sequence. The key-point for advanced composite materials is the possibility to have distributed and simultaneous monitoring of chemoreological and physical properties during the cure process. To this aim, we have developed and tested an optoelectronic fiber optic sensor based on the Fresnel principle able to monitor the variations of the refractive index due to the cure process of an epoxy based resin. Experimental results have been obtained on sensor capability to monitor the cure kinetics by assuming the refractive index as reaction co-ordinate. The integration with in-fiber Bragg grating in order to measure the local temperature has been discussed and tested.

SU-FF-T-668: A Simple Algorithm for Range Modulation Wheel Design in Proton Therapy

DOE Office of Scientific and Technical Information (OSTI.GOV)

Nie, X; Nazaryan, Vahagn; Gueye, Paul

2009-06-01

Purpose: To develop a simple algorithm in designing the range modulation wheel to generate a very smooth Spread-Out Bragg peak (SOBP) for proton therapy.Method and Materials: A simple algorithm has been developed to generate the weight factors in corresponding pristine Bragg peaks which composed a smooth SOBP in proton therapy. We used a modified analytical Bragg peak function based on Monte Carol simulation tool-kits of Geant4 as pristine Bragg peaks input in our algorithm. A simple METLAB(R) Quad Program was introduced to optimize the cost function in our algorithm. Results: We found out that the existed analytical function of Braggmore » peak can't directly use as pristine Bragg peak dose-depth profile input file in optimization of the weight factors since this model didn't take into account of the scattering factors introducing from the range shifts in modifying the proton beam energies. We have done Geant4 simulations for proton energy of 63.4 MeV with a 1.08 cm SOBP for variation of pristine Bragg peaks which composed this SOBP and modified the existed analytical Bragg peak functions for their peak heights, ranges of R{sub 0}, and Gaussian energies {sigma}{sub E}. We found out that 19 pristine Bragg peaks are enough to achieve a flatness of 1.5% of SOBP which is the best flatness in the publications. Conclusion: This work develops a simple algorithm to generate the weight factors which is used to design a range modulation wheel to generate a smooth SOBP in protonradiation therapy. We have found out that a medium number of pristine Bragg peaks are enough to generate a SOBP with flatness less than 2%. It is potential to generate data base to store in the treatment plan to produce a clinic acceptable SOBP by using our simple algorithm.« less

Design and performance investigation of a highly accurate apodized fiber Bragg grating-based strain sensor in single and quasi-distributed systems.

PubMed

Ali, Taha A; Shehata, Mohamed I; Mohamed, Nazmi A

2015-06-01

In this work, fiber Bragg grating (FBG) strain sensors in single and quasi-distributed systems are investigated, seeking high-accuracy measurement. Since FBG-based strain sensors of small lengths are preferred in medical applications, and that causes the full width at half-maximum (FWHM) to be larger, a new apodization profile is introduced for the first time, to the best of our knowledge, with a remarkable FWHM at small sensor lengths compared to the Gaussian and Nuttall profiles, in addition to a higher mainlobe slope at these lengths. A careful selection of apodization profiles with detailed investigation is performed-using sidelobe analysis and the FWHM, which are primary judgment factors especially in a quasi-distributed configuration. A comparison between the elite selection of apodization profiles (extracted from related literature) and the proposed new profile is carried out covering the reflectivity peak, FWHM, and sidelobe analysis. The optimization process concludes that the proposed new profile with a chosen small length (L) of 10 mm and Δn_ac of 1.4×10^-4 is the optimum choice for single stage and quasi-distributed strain-sensor networks, even better than the Gaussian profile at small sensor lengths. The proposed profile achieves the smallest FWHM of 15 GHz (suitable for UDWDM), and the highest mainlobe slope of 130 dB/nm. For the quasi-distributed scenario, a noteworthy high isolation of 6.953 dB is achieved while applying a high strain value of 1500 μstrain (με) for a five-stage strain-sensing network. Further investigation was undertaken, proving that consistency in choosing the apodization profile in the quasi-distributed network is mandatory. A test was made of the inclusion of a uniform apodized sensor among other apodized sensors with the proposed profile in an FBG strain-sensor network.

Reflectivity of linear and nonlinear gamma radiated apodized chirped Bragg grating under ocean

DOE Office of Scientific and Technical Information (OSTI.GOV)

Hamdalla, Taymour A.; Faculty of Science, Tabuk University, Tabuk

In this paper, the effect Co{sup 60} gamma radiation is investigated on the effective refractive index of apodized chirped Bragg grating. Nine apodization profiles are considered. Comparison between the reflectivity of the gamma radiated and non radiated fiber Bragg grating has been carried out. The electric field of signals propagating through the apodized chirped fiber Bragg grating (ACFBG) is first calculated from which, new values for the refractive index are determined. The nonlinear effects appear on the ACFBG reflectivity. The effect of nonlinearity and undersea temperature and pressure on the grating is also studied.

Observation of the standing wave effect in large-area, very-high-frequency capacitively coupled plasmas by using a fiber Bragg grating sensor

NASA Astrophysics Data System (ADS)

Han, Dao-Man; Liu, Yong-Xin; Gao, Fei; Wang, Xiang-Yu; Li, Ang; Xu, Jun; Jing, Zhen-Guo; Wang, You-Nian

2018-06-01

The large-area capacitive discharges driven at very high frequencies have been attracting much attention due to their wide applications in material etching and thin film deposition. However, in the regime, the standing wave effect (SWE) becomes a major limitation for plasma material processing uniformity. In this work, a fiber Bragg grating sensor was utilized for the observation of the SWE in a large-area capacitive discharge reactor by measuring the radial distribution of the neutral gas temperature T g. The influences of the RF power and the working pressure on the radial profiles of T g were studied. At a higher frequency (100 MHz) and a lower pressure (5 Pa), T g presents a center-peaked radial distribution, indicating a significant SWE. As the RF power increases, the central peak of T g becomes more evident due to the enhanced SWE. By contrast, at 100 MHz and a higher pressure (40 Pa), the radial distribution of T g shows an evident peak at the electrode edge and T g decays dramatically towards the discharge center because the electromagnetic waves are strongly damped as they are propagating from the edge to the center. At a lower frequency (27 MHz), only edge-high profiles of T g are observed for various pressures. For the sake of a comparison, a hairpin resonance probe was used to measure the radial distributions of the plasma density n p under the same condition. The radial profiles of T g are found to generally resemble those of n p under various conditions. Based on the experimental results, the neutral gas heating mechanism was analyzed.

Climate Change Impacts on Fort Bragg, NC

DTIC Science & Technology

2013-10-15

28 5.8 Soil erosion at Fort Bragg...Rust fungi that attack the plant appear worse during wet sum- mers. Since the summers may be wetter at Fort Bragg, it may become more difficult to...drop zones. This plant requires frequent fires on its sandy soils . All of these species are associated with the Longleaf pine forests of the

Mesoporous TiO2 Bragg Stack Templated by Graft Copolymer for Dye-sensitized Solar Cells

PubMed Central

Park, Jung Tae; Chi, Won Seok; Kim, Sang Jin; Lee, Daeyeon; Kim, Jong Hak

2014-01-01

Organized mesoporous TiO2 Bragg stacks (om-TiO2 BS) consisting of alternating high and low refractive index organized mesoporous TiO2 (om-TiO2) films were prepared to enhance dye loading, light harvesting, electron transport, and electrolyte pore-infiltration in dye-sensitized solar cells (DSSCs). The om-TiO2 films were synthesized via a sol-gel reaction using amphiphilic graft copolymers consisting of poly(vinyl chloride) backbones and poly(oxyethylene methacrylate) side chains, i.e., PVC-g-POEM as templates. To generate high and low index films, the refractive index of om-TiO2 film was tuned by controlling the grafting ratio of PVC-g-POEM via atomic transfer radical polymerization (ATRP). A polymerized ionic liquid (PIL)-based DSSC fabricated with a 1.2-μm-thick om-TiO2 BS-based photoanode exhibited an efficiency of 4.3%, which is much higher than that of conventional DSSCs with a nanocrystalline TiO2 layer (nc-TiO2 layer) (1.7%). A PIL-based DSSC with a heterostructured photoanode consisting of 400-nm-thick organized mesoporous TiO2 interfacial (om-TiO2 IF) layer, 7-μm-thick nc-TiO2, and 1.2-μm-thick om-TiO2 BS as the bottom, middle and top layers, respectively, exhibited an excellent efficiency of 7.5%, which is much higher than that of nanocrystaline TiO2 photoanode (3.5%). PMID:24980936

Narrow linewidth short cavity Brillouin random laser based on Bragg grating array fiber and dynamical population inversion gratings

NASA Astrophysics Data System (ADS)

Popov, S. M.; Butov, O. V.; Chamorovski, Y. K.; Isaev, V. A.; Mégret, P.; Korobko, D. A.; Zolotovskii, I. O.; Fotiadi, A. A.

2018-06-01

We report on random lasing observed with 100-m-long fiber comprising an array of weak FBGs inscribed in the fiber core and uniformly distributed over the fiber length. Extended fluctuation-free oscilloscope traces highlight power dynamics typical for lasing. An additional piece of Er-doped fiber included into the laser cavity enables a stable laser generation with a linewidth narrower than 10 kHz.

SU-E-T-161: SOBP Beam Analysis Using Light Output of Scintillation Plate Acquired by CCD Camera.

PubMed

Cho, S; Lee, S; Shin, J; Min, B; Chung, K; Shin, D; Lim, Y; Park, S

2012-06-01

To analyze Bragg-peak beams in SOBP (spread-out Bragg-peak) beam using CCD (charge-coupled device) camera - scintillation screen system. We separated each Bragg-peak beam using light output of high sensitivity scintillation material acquired by CCD camera and compared with Bragg-peak beams calculated by Monte Carlo simulation. In this study, CCD camera - scintillation screen system was constructed with a high sensitivity scintillation plate (Gd2O2S:Tb) and a right-angled prismatic PMMA phantom, and a Marlin F-201B, EEE-1394 CCD camera. SOBP beam irradiated by the double scattering mode of a PROTEUS 235 proton therapy machine in NCC is 8 cm width, 13 g/cm 2 range. The gain, dose rate and current of this beam is 50, 2 Gy/min and 70 nA, respectively. Also, we simulated the light output of scintillation plate for SOBP beam using Geant4 toolkit. We evaluated the light output of high sensitivity scintillation plate according to intergration time (0.1 - 1.0 sec). The images of CCD camera during the shortest intergration time (0.1 sec) were acquired automatically and randomly, respectively. Bragg-peak beams in SOBP beam were analyzed by the acquired images. Then, the SOBP beam used in this study was calculated by Geant4 toolkit and Bragg-peak beams in SOBP beam were obtained by ROOT program. The SOBP beam consists of 13 Bragg-peak beams. The results of experiment were compared with that of simulation. We analyzed Bragg-peak beams in SOBP beam using light output of scintillation plate acquired by CCD camera and compared with that of Geant4 simulation. We are going to study SOBP beam analysis using more effective the image acquisition technique. © 2012 American Association of Physicists in Medicine.

High-speed two-dimensional laser scanner based on Bragg gratings stored in photothermorefractive glass.

PubMed

Yaqoob, Zahid; Arain, Muzammil A; Riza, Nabeel A

2003-09-10

A high-speed free-space wavelength-multiplexed optical scanner with high-speed wavelength selection coupled with narrowband volume Bragg gratings stored in photothermorefractive (PTR) glass is reported. The proposed scanner with no moving parts has a modular design with a wide angular scan range, accurate beam pointing, low scanner insertion loss, and two-dimensional beam scan capabilities. We present a complete analysis and design procedure for storing multiple tilted Bragg-grating structures in a single PTR glass volume (for normal incidence) in an optimal fashion. Because the scanner design is modular, many PTR glass volumes (each having multiple tilted Bragg-grating structures) can be stacked together, providing an efficient throughput with operations in both the visible and the infrared (IR) regions. A proof-of-concept experimental study is conducted with four Bragg gratings in independent PTR glass plates, and both visible and IR region scanner operations are demonstrated.

Three-dimensional light bullets in a Bragg medium with carbon nanotubes

NASA Astrophysics Data System (ADS)

Zhukov, Alexander V.; Bouffanais, Roland; Belonenko, Mikhail B.; Dvuzhilov, Ilya S.; Nevzorova, Yulia V.

2017-07-01

We present a theoretical study of the propagation of three-dimensional extremely short electromagnetic pulses (a.k.a. light bullets) through a Bragg medium containing an immersed array of carbon nanotubes. We demonstrate the possible stable propagation of such light bullets. In particular, our results suggest these light bullets can carry information about the Bragg medium itself.

Effects of thermal loading and hydrostatic pressure on reflecting wavelengths of double-coated fiber Bragg grating with different coating-layer thickness

NASA Astrophysics Data System (ADS)

Seraji, Faramarz E.; Toutian, Golnoush

2017-10-01

Fiber Bragg grating (FBG) of different configurations used as sensing devices are vulnerable to environmental factors, such as static pressures and thermal loading, which cause their characteristic Bragg reflecting wavelengths to up/down-shift. In this paper, by considering double-coated FBG with different primary and secondary coating materials, the effects of thermal loading and hydrostatic pressure on FBG with different coating-layer thicknesses are analyzed to find design criteria for controlling the Bragg wavelength shift. The obtained results of the analysis may be employed as criteria to design pressure and temperature sensors when using double-coated FBGs.

Bragg spectroscopy of strongly interacting Fermi gases

NASA Astrophysics Data System (ADS)

Lingham, M. G.; Fenech, K.; Peppler, T.; Hoinka, S.; Dyke, P.; Hannaford, P.; Vale, C. J.

2016-10-01

This article provides an overview of recent developments and emerging topics in the study of two-component Fermi gases using Bragg spectroscopy. Bragg scattering is achieved by exposing a gas to two intersecting laser beams with a slight frequency difference and measuring the momentum transferred to the atoms. By varying the Bragg laser detuning, it is possible to measure either the density or spin response functions which characterize the basic excitations present in the gas. Specifically, one can measure properties such as the dynamic and static structure factors, Tan's universal contact parameter and observe signatures for the onset of pair condensation locally within a gas.

A high-temperature fiber sensor using a low cost interrogation scheme.

PubMed

Barrera, David; Sales, Salvador

2013-09-04

Regenerated Fibre Bragg Gratings have the potential for high-temperature monitoring. In this paper, the inscription of Fibre Bragg Gratings (FBGs) and the later regeneration process to obtain Regenerated Fiber Bragg Gratings (RFBGs) in high-birefringence optical fiber is reported. The obtained RFBGs show two Bragg resonances corresponding to the slow and fast axis that are characterized in temperature terms. As the temperature increases the separation between the two Bragg resonances is reduced, which can be used for low cost interrogation. The proposed interrogation setup is based in the use of optical filters in order to convert the wavelength shift of each of the Bragg resonances into optical power changes. The design of the optical filters is also studied in this article. In first place, the ideal filter is calculated using a recursive method and defining the boundary conditions. This ideal filter linearizes the output of the interrogation setup but is limited by the large wavelength shift of the RFBG with temperature and the maximum attenuation. The response of modal interferometers as optical filters is also analyzed. They can be easily tuned shifting the optical spectrum. The output of the proposed interrogation scheme is simulated in these conditions improving the sensitivity.

A High-Temperature Fiber Sensor Using a Low Cost Interrogation Scheme

PubMed Central

Barrera, David; Sales, Salvador

2013-01-01

Regenerated Fibre Bragg Gratings have the potential for high-temperature monitoring. In this paper, the inscription of Fibre Bragg Gratings (FBGs) and the later regeneration process to obtain Regenerated Fiber Bragg Gratings (RFBGs) in high-birefringence optical fiber is reported. The obtained RFBGs show two Bragg resonances corresponding to the slow and fast axis that are characterized in temperature terms. As the temperature increases the separation between the two Bragg resonances is reduced, which can be used for low cost interrogation. The proposed interrogation setup is based in the use of optical filters in order to convert the wavelength shift of each of the Bragg resonances into optical power changes. The design of the optical filters is also studied in this article. In first place, the ideal filter is calculated using a recursive method and defining the boundary conditions. This ideal filter linearizes the output of the interrogation setup but is limited by the large wavelength shift of the RFBG with temperature and the maximum attenuation. The response of modal interferometers as optical filters is also analyzed. They can be easily tuned shifting the optical spectrum. The output of the proposed interrogation scheme is simulated in these conditions improving the sensitivity. PMID:24008282

Effects of Coating and Diametric Load on Fiber Bragg Gratings as Cryogenic Temperature Sensors

NASA Technical Reports Server (NTRS)

Wu, meng-Chou; Pater, Ruth H.; DeHaven, Stanton L.

2008-01-01

Cryogenic temperature sensing was demonstrated using pressurized fiber Bragg gratings (PFBGs) with polymer coating of various thicknesses. The PFBG was obtained by applying a small diametric load to a regular fiber Bragg grating (FBG). The Bragg wavelengths of FBGs and PFBG were measured at temperatures from 295 K to 4.2 K. The temperature sensitivities of the FBGs were increased by the polymer coating. A physical model was developed to relate the Bragg wavelength shifts to the thermal expansion coefficients, Young's moduli, and thicknesses of the coating polymers. When a diametric load of no more than 15 N was applied to a FBG, a pressure-induced transition occurred at 200 K during the cooling cycle. The pressure induced transition yielded PFBG temperature sensitivities three times greater than conventional FBGs for temperatures ranging from 80 to 200 K, and ten times greater than conventional fibers for temperatures below 80 K. PFBGs were found to produce an increased Bragg wavelength shift of 2.2 nm compared to conventional FBGs over the temperature range of 4.2 to 300 K. This effect was independent of coating thickness and attributed to the change of the fiber thermo-optic coefficient.

System Construction for the Measurement of Bragg Grating Characteristics in Optical Fibers

NASA Technical Reports Server (NTRS)

West, Douglas P.

1995-01-01

Bragg gratings are used to measure strain in optical fibers. To measure strain they are sometimes used as a smart structure. They must be characterized after they are written to determine their spectral response. This paper deals with the test setup to characterize Bragg grating spectral responses.Bragg gratings are a photo-induced phenomena in optical fibers. The gratings can be used to measure strain by measuring the shift in wavelength. They placed the fibers into a smart structure to measure the stress and strain produced on support columns placed in bridges. As the cable is subjected to strain the grating causes a shift to a longer wavelength if the fiber is stretched and a shift to a shorter wavelength shift if the fiber is compacted. Our applications involve using the fibers to measure stress and strain on airborne systems. There are many ways to write Bragg gratings into optical fibers. Our focus is on side writing the grating. Our capabilities are limited in the production rate of the gratings. The Bragg grating is written into a fiber and becomes a permanent fixture. We are writing the grating to be centered at 1300 nm because that is the standard phase mask wavelength.

Thermoacoustic range verification using a clinical ultrasound array provides perfectly co-registered overlay of the Bragg peak onto an ultrasound image

NASA Astrophysics Data System (ADS)

Patch, S. K.; Kireeff Covo, M.; Jackson, A.; Qadadha, Y. M.; Campbell, K. S.; Albright, R. A.; Bloemhard, P.; Donoghue, A. P.; Siero, C. R.; Gimpel, T. L.; Small, S. M.; Ninemire, B. F.; Johnson, M. B.; Phair, L.

2016-08-01

The potential of particle therapy due to focused dose deposition in the Bragg peak has not yet been fully realized due to inaccuracies in range verification. The purpose of this work was to correlate the Bragg peak location with target structure, by overlaying the location of the Bragg peak onto a standard ultrasound image. Pulsed delivery of 50 MeV protons was accomplished by a fast chopper installed between the ion source and the cyclotron inflector. The chopper limited the train of bunches so that 2 Gy were delivered in 2 μ \\text{s} . The ion pulse generated thermoacoustic pulses that were detected by a cardiac ultrasound array, which also produced a grayscale ultrasound image. A filtered backprojection algorithm focused the received signal to the Bragg peak location with perfect co-registration to the ultrasound images. Data was collected in a room temperature water bath and gelatin phantom with a cavity designed to mimic the intestine, in which gas pockets can displace the Bragg peak. Phantom experiments performed with the cavity both empty and filled with olive oil confirmed that displacement of the Bragg peak due to anatomical change could be detected. Thermoacoustic range measurements in the waterbath agreed with Monte Carlo simulation within 1.2 mm. In the phantom, thermoacoustic range estimates and first-order range estimates from CT images agreed to within 1.5 mm.

Quality assurance of proton beams using a multilayer ionization chamber system

DOE Office of Scientific and Technical Information (OSTI.GOV)

Dhanesar, Sandeep; Sahoo, Narayan; Kerr, Matthew

2013-09-15

Purpose: The measurement of percentage depth-dose (PDD) distributions for the quality assurance of clinical proton beams is most commonly performed with a computerized water tank dosimetry system with ionization chamber, commonly referred to as water tank. Although the accuracy and reproducibility of this method is well established, it can be time-consuming if a large number of measurements are required. In this work the authors evaluate the linearity, reproducibility, sensitivity to field size, accuracy, and time-savings of another system: the Zebra, a multilayer ionization chamber system.Methods: The Zebra, consisting of 180 parallel-plate ionization chambers with 2 mm resolution, was used tomore » measure depth-dose distributions. The measurements were performed for scattered and scanned proton pencil beams of multiple energies delivered by the Hitachi PROBEAT synchrotron-based delivery system. For scattered beams, the Zebra-measured depth-dose distributions were compared with those measured with the water tank. The principal descriptors extracted for comparisons were: range, the depth of the distal 90% dose; spread-out Bragg peak (SOBP) length, the region between the proximal 95% and distal 90% dose; and distal-dose fall off (DDF), the region between the distal 80% and 20% dose. For scanned beams, the Zebra-measured ranges were compared with those acquired using a Bragg peak chamber during commissioning.Results: The Zebra demonstrated better than 1% reproducibility and monitor unit linearity. The response of the Zebra was found to be sensitive to radiation field sizes greater than 12.5 × 12.5 cm; hence, the measurements used to determine accuracy were performed using a field size of 10 × 10 cm. For the scattered proton beams, PDD distributions showed 1.5% agreement within the SOBP, and 3.8% outside. Range values agreed within −0.1 ± 0.4 mm, with a maximum deviation of 1.2 mm. SOBP length values agreed within 0 ± 2 mm, with a maximum deviation of 6 mm. DDF values agreed within 0.3 ± 0.1 mm, with a maximum deviation of 0.6 mm. For the scanned proton pencil beams, Zebra and Bragg peak chamber range values demonstrated agreement of 0.0 ± 0.3 mm with a maximum deviation of 1.3 mm. The setup and measurement time for all Zebra measurements was 3 and 20 times less, respectively, compared to the water tank measurements.Conclusions: Our investigation shows that the Zebra can be useful not only for fast but also for accurate measurements of the depth-dose distributions of both scattered and scanned proton beams. The analysis of a large set of measurements shows that the commonly assessed beam quality parameters obtained with the Zebra are within the acceptable variations specified by the manufacturer for our delivery system.« less

Operation JANGLE, Nevada Proving Ground. Project 1(8)b. Air Weather Service Participation in Operation JANGLE

DTIC Science & Technology

1951-12-31

AVAIL AND/OR SPECIAL DISTRIBUTION STAMP UNANNOUNCED DATE RECEIVED IN DTIC DISTRIBUTION STATF.MFNT Ä Approved lot public releasej Distribution...es (countirio prelininary pafes) Ho. -A* AW ^q^l^^^grles A OIEUTION JINCHJB *.*?** " **** **** mOJWI l(8)b AIR WEATHER SERVICE PiRTICIPATICK Hi...Top Figh Right MediuB Top Mediua Left Medina Right Medina Top High Botton High Right High Left High PROJECT l(8)b o i M h P 9 e •a. (O

Pinning down the large- x gluon with NNLO top-quark pair differential distributions

NASA Astrophysics Data System (ADS)

Czakon, Michał; Hartland, Nathan P.; Mitov, Alexander; Nocera, Emanuele R.; Rojo, Juan

2017-04-01

Top-quark pair production at the LHC is directly sensitive to the gluon PDF at large x. While total cross-section data is already included in several PDF determinations, differential distributions are not, because the corresponding NNLO calculations have become available only recently. In this work we study the impact on the large- x gluon of top-quark pair differential distributions measured by ATLAS and CMS at √{s}=8 TeV. Our analysis, performed in the NNPDF3.0 framework at NNLO accuracy, allows us to identify the optimal combination of LHC top-quark pair measurements that maximize the constraints on the gluon, as well as to assess the compatibility between ATLAS and CMS data. We find that differential distributions from top-quark pair production provide significant constraints on the large- x gluon, comparable to those obtained from inclusive jet production data, and thus should become an important ingredient for the next generation of global PDF fits.

Top Quark Production Asymmetries A FB t and A FB l

DOE Office of Scientific and Technical Information (OSTI.GOV)

Berger, Edmond L.; Cao, Qing-Hong; Chen, Chuan-Ren

2012-02-14

A large forward-backward asymmetry is seen in both the top quark rapidity distribution A FB t and in the rapidity distribution of charged leptons A FB l from top quarks produced at the Tevatron. We study the kinematic and dynamic aspects of the relationship of the two observables arising from the spin correlation between the charged lepton and the top quark with different polarization states. We emphasize the value of both measurements, and we conclude that a new physics model which produces more right-handed than left-handed top quarks is favored by the present data.

Top quark production asymmetries A(FB)t and A(FB)ℓ.

PubMed

Berger, Edmond L; Cao, Qing-Hong; Chen, Chuan-Ren; Yu, Jiang-Hao; Zhang, Hao

2012-02-17

A large forward-backward asymmetry is seen in both the top quark rapidity distribution A(FB)(t) and in the rapidity distribution of charged leptons A(FB)(ℓ) from top quarks produced at the Tevatron. We study the kinematic and dynamic aspects of the relationship of the two observables arising from the spin correlation between the charged lepton and the top quark with different polarization states. We emphasize the value of both measurements, and we conclude that a new physics model which produces more right-handed than left-handed top quarks is favored by the present data.

Experimental Realization of Efficient, Room Temperature Single-Photon Sources with Definite Circular and Linear Polarizations

NASA Astrophysics Data System (ADS)

Boutsidis, Christos

In this thesis I present experimental demonstrations of room-temperature, single-photon sources with definite linear and circular polarizations. Definite photon polarization increases the efficiency of quantum communication systems. In contrast with cryogenic-temperature single-photon sources based on epitaxial quantum dots requiring expensive MBE and nanofabrication, my method utilizes a mature liquid crystal technology, which I made consistent with single-emitter fluorescence microscopy. The structures I have prepared are planar-aligned cholesteric liquid crystals forming 1-D photonic bandgaps for circularly-polarized light, which were used to achieve definite circularly-polarized fluorescence of single emitters doped in this environment. I also used planar-aligned nematic liquid crystals to align single molecules with linear dipole moments and achieved definite linearly-polarized fluorescence. I used single nanocrystal quantum dots, single nanodiamond color-centers, rare-earth-doped nanocrystals, and single terrylene and DiIC18(3) dye molecules as emitters. For nanocrystal quantum dots I observed circular polarization dissymmetry factors as large as ge = --1.6. In addition, I observed circularly-polarized resonances in the fluorescence of emitters within a cholesteric microcavity, with cavity quality factors of up to Q ˜ 250. I also showed that the fluorescence of DiIC18(3) dye molecules in planar-aligned nematic cells exhibits definite linear polarization, with a degree of polarization of rho = --0.58 +/- 0.03. Distributed Bragg reflectors form another type of microcavity that can be used to realize a single-photon source. I characterized the fluorescence from nanocrystal quantum dots doped in the defect layers of such microcavites, both organic and inorganic. Finally, to demonstrate the single-photon properties of single-emitter-doped cholesteric and nematic liquid crystal structures and distributed Bragg reflector microcavities, I present observations of photon antibunching from emitters doped in each of these structures. These experimental observations include photon antibunching from: nanocrystal quantum dots and nanodiamond color-centers doped in a cholesteric microcavity; terrylene and DiIC 18(3) dye molecules doped in nematic structures, and nanocrystal quantum dots doped in the distributed Bragg reflector microcavity. A value of the zero-time second-order coherence as low as g(2)(0) = 0.001 +/- 0.03 was measured. These results represent an important step forward in the realization of room temperature single-photon sources with definite polarization for secure quantum communication.

Damage Detection of CFRP Plates by Full-Spectral Analysis of a Fibre Bragg Grating Sensor Signal

DOE Office of Scientific and Technical Information (OSTI.GOV)

Mizutani, Yoshihiro; Solid and Structures Engineering Laboratory, Department of Mechanical Sciences and Engineering, Tokyo Institute of Technology, Japan, 2-12-1-I1-70, Ookayama, Meguro-ku, Tokyo 152-8552; Groves, Roger M.

2010-05-28

This paper describes the measurement of average strain, strain distribution and vibration of cantilever beam made of Carbon Fiber Reinforced Plastics (CFRP), using a single Fibre Bragg Grating (FBG) sensor mounted on the beam surface. Average strain is determined from the displacement of the peak wavelength of reflected light from the FBG sensor. Unstrained reference FBG sensors were used to compensate for temperature drift and the photoelastic coefficient (P{sub e}), which was used to calculate the gauge factor. Measured strains agree with those measured by a resistance foil strain gauge attached to the sample. Stress distributions are measured by monitoringmore » the variation in the full width half maximum (FWHM) values of the reflected spectrum, using a proposed optical analytical model, described in the paper. FWHM values were measured for both the cantilever test beam and a for a reference beam, loaded using a four-point bending rig. The trend of the stress distribution for the test beam matches with our analytical model, however with a relatively large noise present in the experimentally determined data. The vibration of cantilever beam was measured by temporal analysis of the peak reflection wavelength. This technique is very stable as measurements are not affected by variations in the signal amplitude. Finally an application of FBG sensors for damage detection of CFRP plates is demonstrated, by measuring the average strain and natural frequency. With small defects of different sizes applied to the CFRP plate, average strains were seen to increase with damage size and the natural frequency decreased with damage size.« less

Biogeography of top predators - seabirds and cetaceans - along four latitudinal transects in the Atlantic Ocean

NASA Astrophysics Data System (ADS)

Jungblut, Simon; Nachtsheim, Dominik A.; Boos, Karin; Joiris, Claude R.

2017-07-01

The distribution, abundance, and species assemblage of top predators - seabirds and cetaceans - can be correlated to water masses as defined by hydrological parameters. In comparison to other oceans, information about the structuring effects of water masses on top predators in the Atlantic Ocean is limited. The present study aims 1) to provide baseline distributional data of top predators for future comparisons, for instance in the course of climate change, and 2) to test how water masses and seasons affect distributional patterns of seabirds and cetaceans in the temperate and tropical Atlantic. During four trans-equatorial expeditions of the RV Polarstern between 2011 and 2014, at-sea observation data of seabirds, cetaceans and other megafauna were collected. Counts of top predators were generally low in the surveyed regions. Statistical analyses for the eight most abundant seabird species and the pooled number of cetaceans revealed water masses and seasons to account for differences in counts and thus also distribution. In most cases, borders between water masses were not very distinct due to gradual changes in surface water properties. Thus, top predator counts were correlated to water masses but, in contrast to polar waters, not strongly linked to borders between water masses. Additional factors, e.g. distance to locally productive areas (upwelling), competition effects, and seabird associations to prey-accumulating subsurface predators may be similarly important in shaping distributional patterns of top predators in the tropical and temperate Atlantic, but could not be specifically tested for here.

Data Mining the Corporate Dental System of USA DENTAC Fort Bragg

DTIC Science & Technology

2016-06-10

Data Mining the Corporate Dental System of USA DENTAC Fort Bragg FREDWIN HOLOMON, D.D.S. B.S. University of...AEGD Program Director ABSTRACT Statement of the problem: Dental wellness has not reached optimum levels at Fort Bragg after implementation of...the Go First Class Program. Purpose: To examine the Go First Class Program’s influence upon dental wellness and readiness. Materials and Methods

Turbulence hierarchy in a random fibre laser

PubMed Central

González, Iván R. Roa; Lima, Bismarck C.; Pincheira, Pablo I. R.; Brum, Arthur A.; Macêdo, Antônio M. S.; Vasconcelos, Giovani L.; de S. Menezes, Leonardo; Raposo, Ernesto P.; Gomes, Anderson S. L.; Kashyap, Raman

2017-01-01

Turbulence is a challenging feature common to a wide range of complex phenomena. Random fibre lasers are a special class of lasers in which the feedback arises from multiple scattering in a one-dimensional disordered cavity-less medium. Here we report on statistical signatures of turbulence in the distribution of intensity fluctuations in a continuous-wave-pumped erbium-based random fibre laser, with random Bragg grating scatterers. The distribution of intensity fluctuations in an extensive data set exhibits three qualitatively distinct behaviours: a Gaussian regime below threshold, a mixture of two distributions with exponentially decaying tails near the threshold and a mixture of distributions with stretched-exponential tails above threshold. All distributions are well described by a hierarchical stochastic model that incorporates Kolmogorov’s theory of turbulence, which includes energy cascade and the intermittence phenomenon. Our findings have implications for explaining the remarkably challenging turbulent behaviour in photonics, using a random fibre laser as the experimental platform. PMID:28561064

Vibration monitoring of a helicopter blade model using the optical fiber distributed strain sensing technique.

PubMed

Wada, Daichi; Igawa, Hirotaka; Kasai, Tokio

2016-09-01

We demonstrate a dynamic distributed monitoring technique using a long-length fiber Bragg grating (FBG) interrogated by optical frequency domain reflectometry (OFDR) that measures strain at a speed of 150 Hz, spatial resolution of 1 mm, and measurement range of 20 m. A 5 m FBG is bonded to a 5.5 m helicopter blade model, and vibration is applied by the step relaxation method. The time domain responses of the strain distributions are measured, and the blade deflections are calculated based on the strain distributions. Frequency response functions are obtained using the time domain responses of the calculated deflection induced by the preload release, and the modal parameters are retrieved. Experimental results demonstrated the dynamic monitoring performances and the applicability to the modal analysis of the OFDR-FBG technique.

Spatiotemporal dynamics and optical vortices in a photorefractive phase-conjugate resonator

NASA Technical Reports Server (NTRS)

Liu, Siuying Raymond; Indebetouw, Guy

1992-01-01

A truncated modal expansion approach is used to study the spatiotemporal dynamics of a phase-conjugate resonator as a function of Bragg detuning. The numerical results reveal a rich variety of behaviors. Emphasis is given to the spatial distribution of optical vortices, their trajectories and their relationship to the beam's spatial coherence. The limitations of the model are discussed and experimental results are presented for comparison with the model's predictions and assessment of its soundness.

Simulation of Optical Resonators for Vertical-Cavity Surface-Emitting Lasers (vcsel)

NASA Astrophysics Data System (ADS)

Mansour, Mohy S.; Hassen, Mahmoud F. M.; El-Nozahey, Adel M.; Hafez, Alaa S.; Metry, Samer F.

2010-04-01

Simulation and modeling of the reflectivity and transmissivity of the multilayer DBR of VCSEL, as well as inside the active region quantum well are analyzed using the characteristic matrix method. The electric field intensity distributions inside such vertical-cavity structure are calculated. A software program under MATLAB environment is constructed for the simulation. This study was performed for two specific Bragg wavelengths 980 nm and 370 nm for achieving a resonant periodic gain (RPG)

Acceleration Strain Transducer

DTIC Science & Technology

2007-11-05

accelerometer 10 includes a fiber laser 12. Fiber laser 12 can be either a Fabry - Perot type cavity fiber laser or a distributed feedback fiber laser. In a... Fabry - Perot type fiber laser, the laser cavity is a length of erbium- doped optical fiber with a Bragg grating written in the fiber core at either end of...the phase shifted signal. Receiver 26 is capable of demodulating and detecting the signal from the fiber laser by various methods well known in the

Continuous diffraction of molecules and disordered molecular crystals

PubMed Central

Yefanov, Oleksandr M.; Ayyer, Kartik; White, Thomas A.; Barty, Anton; Morgan, Andrew; Mariani, Valerio; Oberthuer, Dominik; Pande, Kanupriya

2017-01-01

The intensities of far-field diffraction patterns of orientationally aligned molecules obey Wilson statistics, whether those molecules are in isolation (giving rise to a continuous diffraction pattern) or arranged in a crystal (giving rise to Bragg peaks). Ensembles of molecules in several orientations, but uncorrelated in position, give rise to the incoherent sum of the diffraction from those objects, modifying the statistics in a similar way as crystal twinning modifies the distribution of Bragg intensities. This situation arises in the continuous diffraction of laser-aligned molecules or translationally disordered molecular crystals. This paper develops the analysis of the intensity statistics of such continuous diffraction to obtain parameters such as scaling, beam coherence and the number of contributing independent object orientations. When measured, continuous molecular diffraction is generally weak and accompanied by a background that far exceeds the strength of the signal. Instead of just relying upon the smallest measured intensities or their mean value to guide the subtraction of the background, it is shown how all measured values can be utilized to estimate the background, noise and signal, by employing a modified ‘noisy Wilson’ distribution that explicitly includes the background. Parameters relating to the background and signal quantities can be estimated from the moments of the measured intensities. The analysis method is demonstrated on previously published continuous diffraction data measured from crystals of photosystem II [Ayyer et al. (2016 ▸), Nature, 530, 202–206]. PMID:28808434

Fabrication of locally micro-structured fiber Bragg gratings by fs-laser machining

NASA Astrophysics Data System (ADS)

Dutz, Franz J.; Stephan, Valentin; Marchi, Gabriele; Koch, Alexander W.; Roths, Johannes; Huber, Heinz P.

2018-06-01

Here, we describe a method for producing locally micro-structured fiber Bragg gratings (LMFGB) by fs-laser machining. This technique enables the precise and reproducible ablation of cladding material to create circumferential grooves inside the claddings of optical fibers. From initial ablation experiments we acquired optimized process parameters. The fabricated grooves were located in the middle of uniform type I fiber Bragg gratings. LMFBGs with four different groove widths of 48, 85, 135 and 205 μ { {m}} were produced. The grooves exhibited constant depths of about 30 μ {m} and steep sidewall angles. With the combination of micro-structures and fiber Bragg gratings, fiber optic sensor elements with enhanced functionalities can be achieved.

Top-pair production at the LHC through NNLO QCD and NLO EW

NASA Astrophysics Data System (ADS)

Czakon, Michał; Heymes, David; Mitov, Alexander; Pagani, Davide; Tsinikos, Ioannis; Zaro, Marco

2017-10-01

In this work we present for the first time predictions for top-quark pair differential distributions at the LHC at NNLO QCD accuracy and including EW corrections. For the latter we include not only contributions of O({α}_s^2α ) , but also those of order O({α}_s{α}^2) and O({α}^3) . Besides providing phenomenological predictions for all main differential distributions with stable top quarks, we also study the following issues. 1) The effect of the photon PDF on top-pair spectra: we find it to be strongly dependent on the PDF set used — especially for the top p T distribution. 2) The difference between the additive and multiplicative approaches for combining QCD and EW corrections: with our scale choice, we find relatively small differences between the central predictions, but reduced scale dependence within the multiplicative approach. 3) The potential effect from the radiation of heavy bosons on inclusive top-pair spectra: we find it to be, typically, negligible.

Differential distributions for t-channel single top-quark production and decay at next-to-next-to-leading order in QCD

DOE Office of Scientific and Technical Information (OSTI.GOV)

Berger, Edmond L.; Gao, Jun; Zhu, Hua Xing

We present a detailed phenomenological study of the next-to-next-to-leading order (NNLO) QCD corrections for t-channel single top (anti-)quark production and its semi-leptonic decay at the CERN Large Hadron Collider (LHC). We find the NNLO corrections for the total inclusive rates at the LHC with different center of mass energies are generally smaller than the NLO corrections, indicative of improved convergence. However, they can be large for differential distributions, reaching a level of 10% or more in certain regions of the transverse momentum distributions of the top (anti-)quark and the pseudo-rapidity distributions of the leading jet in the event. In allmore » cases the perturbative hard-scale uncertainties are greatly reduced after the NNLO corrections are included. We also show a comparison of the normalized parton-level distributions to recent data from the 8 TeV measurement of the ATLAS collaboration. The NNLO corrections tend to shift the theoretical predictions closer to the measured transverse momentum distribution of the top (anti)-quark. Importantly, for the LHC at 13 TeV, we present NNLO cross sections in a fiducial volume with decays of the top quark included.« less

High-sensitivity cryogenic temperature sensors using pressurized fiber Bragg gratings

NASA Technical Reports Server (NTRS)

Wu, Meng-Chou; DeHaven, Stanton L.

2006-01-01

Cryogenic temperature sensing was studied using a pressurized fiber Bragg grating (PFBG). The PFBG was obtained by simply applying a small diametric load to a regular fiber Bragg grating (FBG), which was coated with polyimide of a thickness of 11 micrometers. The Bragg wavelength of the PFBG was measured at temperatures from 295 to 4.2 K. A pressure-induced transition occurred at 200 K during the cooling cycle. As a result the temperature sensitivity of the PFBG was found to be nonlinear but reach 24 pm/K below 200 K, more than three times the regular FBG. For the temperature change from 80 K to 10 K, the PFBG has a total Bragg wavelength shift of about 470 pm, 10 times more than the regular FBG. From room temperature to liquid helium temperature the PFBG gives a total wavelength shift of 3.78 nm, compared to the FBG of 1.51 nm. The effect of the coating thickness on the temperature sensitivity of the gratings is also discussed.

High-sensitivity Cryogenic Temperature Sensors using Pressurized Fiber Bragg Gratings

NASA Technical Reports Server (NTRS)

Wu, Meng-Chou; DeHaven, Stanton L.

2006-01-01

Cryogenic temperature sensing was studied using a pressurized fiber Bragg grating (PFBG). The PFBG was obtained by simply applying a small diametric load to a regular fiber Bragg grating (FBG), which was coated with polyimide of a thickness of 11 micrometers. The Bragg wavelength of the PFBG was measured at temperatures from 295 to 4.2 K. A pressure-induced transition occurred at 200 K during the cooling cycle. As a result the temperature sensitivity of the PFBG was found to be nonlinear but reach 24 pm/K below 200 K, more than three times the regular FBG. For the temperature change from 80 K to 10 K, the PFBG has a total Bragg wavelength shift of about 470 pm, 10 times more than the regular FBG. From room temperature to liquid helium temperature the PFBG gives a total wavelength shift of 3.78 nm, compared to the FBG of 1.51 nm. The effect of the coating thickness on the temperature sensitivity of the gratings is also discussed.

Stability test of the silicon Fiber Bragg Grating embroidered on textile for joint angle measurement

NASA Astrophysics Data System (ADS)

Apiwattanadej, Thanit; Chun, Byung Jae; Lee, Hyub; Li, King Ho Holden; Kim, Young-Jin

2017-06-01

Recently, Fiber Bragg Grating (FBG) sensors are being used for motion tracking applications. However, the sensitivity, linearity and stability of the systems have not been fully studied. Herein, an embroidered optical Fiber Bragg Grating (FBG) on a stretchable supportive textile for elbow movement measurement was developed. The sensing principle of this system is based on the alteration of Bragg wavelength due to strain from the elbow movements. The relationship between elbow movements and reflected Bragg wavelength was found to be linear. The dynamic range of FBG sensor on elbow support is between 0 and 120 degree. Finally, the stability of the FBG sensor on the supportive textile was tested during the exercise and the cleaning process with water. The sensitivity of FBG sensors for joint angle measurement and the effect of the movement and cleaning process to signals from FBG sensors after using in the real activity will be the basis knowledge for design and actual implementation of future optical fiber based wearable devices.

Reflectors and tuning elements for widely-tunable GaAs-based sampled grating DBR lasers

NASA Astrophysics Data System (ADS)

Brox, O.; Wenzel, H.; Della Case, P.; Tawfieq, M.; Sumpf, B.; Weyers, M.; Knigge, A.

2018-02-01

Widely-tunable lasers without moving parts are attractive light sources for sensors in industry and biomedicine. In contrast to InP based sampled grating (SG) distributed Bragg reflector (DBR) diode lasers which are commercially available, shorter wavelength GaAs SG-DBR lasers are still under development. One reason is the difficulty to integrate gratings with coupling coefficients that are high enough for functional grating bursts with lengths below 10 μm. Recently we have demonstrated > 20 nm wide quasi-continuous tuning with a GaAs based SG-DBR laser emitting around 975 nm. Wavelength selective reflectors are realized with SGs having different burst periods for the front and back mirrors. Thermal tuning elements (resistors) which are placed on top of the SG allow the control of the spectral positions of the SG reflector combs and hence to adjust the Vernier mode. In this work we characterize subsections of the developed SG-DBR laser to further improve its performance. We study the impact of two different vertical structures (with vertical far field FWHMs of 41° and 24°) and two grating orders on the coupling coefficient. Gratings with coupling coefficients above 350 cm-1 have been integrated into SG-DBR lasers. We also examine electronic tuning elements (a technique which is typically applied in InP based SG-DBR lasers and allows tuning within nanoseconds) and discuss the limitations in the GaAs material system

Holographically Encoded Volume Phase Masks

DTIC Science & Technology

2015-07-13

Lu et al., “Coherent beam combination of fiber laser arrays via multiplexed volume Bragg gratings,” in Conf. on Lasers and Electro- Optics: Science...combining of fiber lasers using multiplexed volume Bragg gratings,” in Conf. on Lasers and Electro- Optics: Science and Innovations, OSA Technical Digest...satisfying the Bragg condition of the hologram. Moreover, this approach enables the capability to encode and multiplex several phase masks into a single

Strain Measurement during Stress Rupture of Composite Over-Wrapped Pressure Vessel with Fiber Bragg Gratings Sensors

NASA Technical Reports Server (NTRS)

Banks, Curtis E.; Grant, Joseph; Russell, Sam; Arnett, Shawn

2008-01-01

Fiber optic Bragg gratings were used to measure strain fields during Stress Rupture (SSM) test of Kevlar Composite Over-Wrapped Pressure Vessels (COPV). The sensors were embedded under the over-wrapped attached to the liner released from the Kevlar and attached to the Kevlar released from the liner. Additional sensors (foil gages and fiber bragg gratings) were surface mounted on the COPY liner.

Bragg projection ptychography on niobium phase domain

DOE PAGES

Burdet, Nicolas; Shi, Xiaowen; Huang, Xiaojing; ...

2016-08-10

Here, we demonstrate that the highly sensitive phase-contrast properties of Bragg coherent diffraction measurements combined with the translational diversity of ptychography can provide a Bragg “dark field” imaging method capable of revealing the finger print of domain structure in metallic thin films. Experimental diffraction data was taken from a epitaxially grown niobium metallic thin film on sapphire; and analyzed with the help of a careful combination of implemented refinement mechanisms.

Clear as Crystal: The Story of the Braggs--How X-Ray Crystallography Has Contributed to Science

ERIC Educational Resources Information Center

George, Robert; Patterson, John

2014-01-01

Here is a brief history of the work of two of Australia's most famous scientists, Sir William Bragg and his son Sir Lawrence Bragg. Jointly awarded the Nobel Prize in 1915 for their groundbreaking research into the use of X-rays to study the chemical structure and function of molecules, they have contributed to our heritage and to science at an…

Detection of Ammonia-Oxidizing Bacteria (AOB) Using a Porous Silicon Optical Biosensor Based on a Multilayered Double Bragg Mirror Structure.

PubMed

Zhang, Hongyan; Lv, Jie; Jia, Zhenhong

2018-01-01

We successfully demonstrate a porous silicon (PS) double Bragg mirror by electrochemical etching at room temperature as a deoxyribonucleic acid (DNA) label-free biosensor for detecting ammonia-oxidizing bacteria (AOB). Compared to various other one-dimension photonic crystal configurations of PS, the double Bragg mirror structure is quite easy to prepare and exhibits interesting optical properties. The width of high reflectivity stop band of the PS double Bragg mirror is about 761 nm with a sharp and deep resonance peak at 1328 nm in the reflectance spectrum, which gives a high sensitivity and distinguishability for sensing performance. The detection sensitivity of such a double Bragg mirror structure is illustrated through the investigation of AOB DNA hybridization in the PS pores. The redshifts of the reflectance spectra show a good linear relationship with both complete complementary and partial complementary DNA. The lowest detection limit for complete complementary DNA is 27.1 nM and the detection limit of the biosensor for partial complementary DNA is 35.0 nM, which provides the feasibility and effectiveness for the detection of AOB in a real environment. The PS double Bragg mirror structure is attractive for widespread biosensing applications and provides great potential for the development of optical applications.

Symmetry investigations on the incompressible stationary axisymmetric Euler equations with swirl

NASA Astrophysics Data System (ADS)

Frewer, M.; Oberlack, M.; Guenther, S.

2007-08-01

We discuss the incompressible stationary axisymmetric Euler equations with swirl, for which we derive via a scalar stream function an equivalent representation, the Bragg-Hawthorne equation [Bragg, S.L., Hawthorne, W.R., 1950. Some exact solutions of the flow through annular cascade actuator discs. J. Aero. Sci. 17, 243]. Despite this obvious equivalence, we will show that under a local Lie point symmetry analysis the Bragg-Hawthorne equation exposes itself as not being fully equivalent to the original Euler equations. This is reflected in the way that it possesses additional symmetries not being admitted by its counterpart. In other words, a symmetry of the Bragg-Hawthorne equation is in general not a symmetry of the Euler equations. Not the differential Euler equations but rather a set of integro-differential equations attains full equivalence to the Bragg-Hawthorne equation. For these intermediate Euler equations, it is interesting to note that local symmetries of the Bragg-Hawthorne equation transform to local as well as to nonlocal symmetries. This behaviour, on the one hand, is in accordance with Zawistowski's result [Zawistowski, Z.J., 2001. Symmetries of integro-differential equations. Rep. Math. Phys. 48, 269; Zawistowski, Z.J., 2004. General criterion of invariance for integro-differential equations. Rep. Math. Phys. 54, 341] that it is possible for integro-differential equations to admit local Lie point symmetries. On the other hand, with this transformation process we collect symmetries which cannot be obtained when carrying out a usual local Lie point symmetry analysis. Finally, the symmetry classification of the Bragg-Hawthorne equation is used to find analytical solutions for the phenomenon of vortex breakdown.

Cloud-top height retrieval from polarizing remote sensor POLDER

NASA Astrophysics Data System (ADS)

He, Xianqiang; Pan, Delu; Yan, Bai; Mao, Zhihua

2006-10-01

A new cloud-top height retrieval method is proposed by using polarizing remote sensing. In cloudy conditions, it shows that, in purple and blue bands, linear polarizing radiance at the top-of-atmosphere (TOA) is mainly contributed by Rayleigh scattering of the atmosphere's molecules above cloud, and the contribution by cloud reflection and aerosol scattering can be neglected. With such characteristics, the basis principle and method of cloud-top height retrieval using polarizing remote sensing are presented in detail, and tested by the polarizing remote sensing data of POLDER. The satellite-derived cloud-top height product can not only show the distribution of global cloud-top height, but also obtain the cloud-top height distribution of moderate-scale meteorological phenomena like hurricanes and typhoons. This new method is promising to become the operational algorithm for cloud-top height retrieval for POLDER and the future polarizing remote sensing satellites.

Determination of Algorithm Parallelism in NP Complete Problems for Distributed Architectures

DTIC Science & Technology

1990-03-05

12 structure STACK declare OpenStack (S-.NODE **TopPtr) -+TopPtrI FlushStack(S.-NODE **TopPtr) -*TopPtr PushOnStack(S-.NODE **TopPtr, ITEM *NewltemPtr...OfCoveringSets, CoveringSets, L, Best CoverTime, Vertex, Set3end SCND ADT B.26 structure STACKI declare OpenStack (S-NODE **TopPtr) -+TopPtr FlushStack(S

Optical Interarray Processing.

DTIC Science & Technology

1980-03-01

of around 30 frames/sec. One dimensional input transducers such as acousto-optic Bragg cells have much higher frame rates. For example, a TeO2 Bragg...Conventional manufacturing processes such as grinding and polish- ing a glass piece would be difficult if not impossible to apply to the fabrication of such...time-bandwidth product (TBW). An acoustic shear wave in a TeO2 Bragg cell will propagate with a speed of 617 meters/ sec, while the practical physical

Pressure Effects on the Temperature Sensitivity of Fiber Bragg Gratings

NASA Technical Reports Server (NTRS)

Wu, Meng-Chou

2012-01-01

A 3-dimensional physical model was developed to relate the wavelength shifts resulting from temperature changes of fiber Bragg gratings (FBGs) to the thermal expansion coefficients, Young s moduli of optical fibers, and thicknesses of coating polymers. Using this model the Bragg wavelength shifts were calculated and compared with the measured wavelength shifts of FBGs with various coating thickness for a finite temperature range. There was a discrepancy between the calculated and measured wavelength shifts. This was attributed to the refractive index change of the fiber core by the thermally induced radial pressure. To further investigate the pressure effects, a small diametric load was applied to a FBG and Bragg wavelength shifts were measured over a temperature range of 4.2 to 300K.

Free-electron maser with high-selectivity Bragg resonator using coupled propagating and trapped modes

NASA Astrophysics Data System (ADS)

Ginzburg, N. S.; Golubev, I. I.; Golubykh, S. M.; Zaslavskii, V. Yu.; Zotova, I. V.; Kaminsky, A. K.; Kozlov, A. P.; Malkin, A. M.; Peskov, N. Yu.; Perel'Shteĭn, É. A.; Sedykh, S. N.; Sergeev, A. S.

2010-10-01

A free-electron maser (FEM) with a double-mirror resonator involving a new modification of Bragg structures operating on coupled propagating and quasi-cutoff (trapped) modes has been studied. The presence of trapped waves in the feedback chain improves the selectivity of Bragg resonators and ensures stable single-mode generation regime at a considerable superdimensionality of the interaction space. The possibility of using the new feedback mechanism has been confirmed by experiments with a 30-GHz FEM pumped by the electron beam of LIU-3000 (JINR) linear induction accelerator, in which narrow-band generation was obtained at a power of ˜10 MW and a frequency close to the cutoff frequency of the trapped mode excited in the input Bragg reflector.

Bragg peak prediction from quantitative proton computed tomography using different path estimates

PubMed Central

Wang, Dongxu; Mackie, T Rockwell

2015-01-01

This paper characterizes the performance of the straight-line path (SLP) and cubic spline path (CSP) as path estimates used in reconstruction of proton computed tomography (pCT). The GEANT4 Monte Carlo simulation toolkit is employed to simulate the imaging phantom and proton projections. SLP, CSP and the most-probable path (MPP) are constructed based on the entrance and exit information of each proton. The physical deviations of SLP, CSP and MPP from the real path are calculated. Using a conditional proton path probability map, the relative probability of SLP, CSP and MPP are calculated and compared. The depth dose and Bragg peak are predicted on the pCT images reconstructed using SLP, CSP, and MPP and compared with the simulation result. The root-mean-square physical deviations and the cumulative distribution of the physical deviations show that the performance of CSP is comparable to MPP while SLP is slightly inferior. About 90% of the SLP pixels and 99% of the CSP pixels lie in the 99% relative probability envelope of the MPP. Even at an imaging dose of ~0.1 mGy the proton Bragg peak for a given incoming energy can be predicted on the pCT image reconstructed using SLP, CSP, or MPP with 1 mm accuracy. This study shows that SLP and CSP, like MPP, are adequate path estimates for pCT reconstruction, and therefore can be chosen as the path estimation method for pCT reconstruction, which can aid the treatment planning and range prediction of proton radiation therapy. PMID:21212472

Broad-area detection of structural irregularities in composites using fibre Bragg gratings

NASA Astrophysics Data System (ADS)

Davis, Claire E.; Norman, Patrick; Moss, Scott; Ratcliffe, Colin; Crane, Roger

2010-04-01

The Structural Irregularity and Damage Evaluation Routine (SIDER) is a broadband vibration-based technique that uses features in complex curvature operating shapes to locate damage and other areas with structural stiffness variations. It is designed for the inspection of large-scale composite structures not amenable to more conventional inspection methods. The current SIDER methodology relies on impact excitation at a series of grid points on the structure and records the response using a small number of accelerometers to determine the operational curvature shapes. This paper reports on a modification to the SIDER technique whereby the acceleration measurements are replaced with in-plane strain measurements using Fibre Bragg Gratings (FBGs). One of the major challenges associated with using Bragg gratings for this type of response measurement is that the strains induced by structural vibrations tend to be low, particularly at higher frequencies. This paper also reports on the development of an intensity-based, swept wavelength interrogation system to facilitate these measurements. The modified SIDER system was evaluated on an E-glass/vinyl ester composite test beam containing a machined notch. The measurements accurately detected the presence and location of the notch. The distributive capacity of FBGs means that these sensors have the potential to replace the excitation grid with a measurement grid, allowing for single point or environmental excitation. The spatially separated measurements of strain can be used to provide the curvature shapes directly. This change in approach could potentially transition SIDER from an interval-based, broad-area inspection tool to an in-service structural health monitoring system.

Crystallographic Analysis of a Japanese Sword by using Bragg Edge Transmission Spectroscopy

NASA Astrophysics Data System (ADS)

Shiota, Yoshinori; Hasemi, Hiroyuki; Kiyanagi, Yoshiaki

Neutron imaging using a pulsed neutron source can give crystallographic information over wide area of a sample by analysing position dependent transmission spectra. With the use of a Bragg edge imaging method we non-destructively obtained crystallographic information of a Japanese sword, signed by Bishu Osafune Norimitsu, in order to know position dependent crystallographic characteristics and to check usefulness of the method for the Japanese sword investigation. Strong texture appeared on the back side. On the other hand in the middle area almost isotropic feature appeared and edge side showed feature between them. Rather isotropic area in the centre area gradually reduced from the grip side to the tip side. The crystallite size was smaller near the edge and became larger towards the back side. The smaller crystallite size will be due to quenching around the edge and this trend disappeared in the grip (nakago) area. The larger crystallite size will be due to strong hammering. Coarse grains were also observed directly as transmission images with the use of a high spatial resolution detector. The spatial distribution of the grains was not uniform but the reason have not been understood. Furthermore, a white area around a tip area was proved to be a void by looking at the Brag edge transmission spectra. This void may be formed during forging process of two kinds of steel. It is suggested that consideration on differences in the texture and the crystallite size depending on position will give information to clarify the manufacturing process, and Bragg edge analysis will be a profitable tool for research of Japanese sword.

Using response time distributions to examine top-down influences on attentional capture.

PubMed

Burnham, Bryan R

2013-02-01

Three experiments examined contingent attentional capture, which is the finding that cuing effects are larger when cues are perceptually similar to a target than when they are dissimilar to the target. This study also analyzed response times (RTs) in terms of the underlying distributions for valid cues and invalid cues. Specifically, an ex-Gaussian analysis and a vincentile analysis examined the influence of top-down attentional control settings on the shift and skew of RT distributions and how the shift and the skew contributed to the cuing effects in the mean RTs. The results showed that cue/target similarity influenced the size of cuing effects. The RT distribution analyses showed that the cuing effects reflected only a shifting effect, not a skewing effect, in the RT distribution between valid cues and invalid cues. That is, top-down attentional control moderated the cuing effects in the mean RTs through distribution shifting, not distribution skewing. The results support the contingent orienting hypothesis (Folk, Remington, & Johnston, Journal of Experimental Psychology: Human Perception and Performance, 18, 1030-1044, 1992) over the attentional disengagement account (Theeuwes, Atchley, & Kramer, 2000) as an explanation for when top-down attentional settings influence the selection of salient stimuli.

Optical fiber Bragg grating-instrumented silicone liner for interface pressure measurement within prosthetic sockets of lower-limb amputees

NASA Astrophysics Data System (ADS)

Al-Fakih, Ebrahim; Arifin, Nooranida; Pirouzi, Gholamhossein; Mahamd Adikan, Faisal Rafiq; Shasmin, Hanie Nadia; Abu Osman, Noor Azuan

2017-08-01

This paper presents a fiber Bragg grating (FBG)-instrumented prosthetic silicone liner that provides cushioning for the residual limb and can successfully measure interface pressures inside prosthetic sockets of lower-limb amputees in a simple and practical means of sensing. The liner is made of two silicone layers between which 12 FBG sensors were embedded at locations of clinical interest. The sensors were then calibrated using a custom calibration platform that mimics a real-life situation. Afterward, a custom gait simulating machine was built to test the liner performance during an amputee's simulated gait. To validate the findings, the results were compared to those obtained by the commonly used F-socket mats. As the statistical findings reveal, both pressure mapping methods measured the interface pressure in a consistent way, with no significant difference (P-values ≥0.05). This pressure mapping technique in the form of a prosthetic liner will allow prosthetics professionals to quickly and accurately create an overall picture of the interface pressure distribution inside sockets in research and clinical settings, thereby improving the socket fit and amputee's satisfaction.

Revealing the effect of edge contamination on vortex matter structure in a Nb single crystal with neutron diffraction techniques

NASA Astrophysics Data System (ADS)

Hanson, Helen; Wang, Xi; Luk, Michael; Shi, Jing; Ling, Xinsheng; Maranville, Brian; Majkrzak, Charles

2011-03-01

The vortex matter of type II superconductors provides a model system to study the effect of quenched random disorder on an elastic lattice, particularly in the framework of Bragg glass theory. Neutron scattering techniques are used to examine the structure of the vortex matter and to quantify the phase diagram. After measuring various thermal-magnetic histories, our data provided evidence for the edge contamination model in a Nb single crystal. Since surface oxidation is known to suppress the Bean-Livingston Surface barrier and the inhomogeneous distribution of surface impurities in Nb, we oxidize our sample surface and repeat our measurements. By comparing the data, we are able isolate the dynamic impact of the edge disorder from the static influence of bulk pinning. We discuss the various experimental obstacles in measuring the predicted Bragg glass state. We also report on Reverse Monte Carlo Refinement simulations modeling possible structures of our vortex matter. This research was supported by the U.S. DOE under grant DE- FG 02 - 07 ER46458.

Advances in Bio-Tactile Sensors for Minimally Invasive Surgery Using the Fibre Bragg Grating Force Sensor Technique:A Survey

PubMed Central

Abushagur, Abdulfatah A.G.; Arsad, Norhana; Ibne Reaz, Mamun; Ashrif, A.; Bakar, A.

2014-01-01

The large interest in utilising fibre Bragg grating (FBG) strain sensors for minimally invasive surgery (MIS) applications to replace conventional electrical tactile sensors has grown in the past few years. FBG strain sensors offer the advantages of optical fibre sensors, such as high sensitivity, immunity to electromagnetic noise, electrical passivity and chemical inertness, but are not limited by phase discontinuity or intensity fluctuations. FBG sensors feature a wavelength-encoding sensing signal that enables distributed sensing that utilises fewer connections. In addition, their flexibility and lightness allow easy insertion into needles and catheters, thus enabling localised measurements inside tissues and blood. Two types of FBG tactile sensors have been emphasised in the literature: single-point and array FBG tactile sensors. This paper describes the current design, development and research of the optical fibre tactile techniques that are based on FBGs to enhance the performance of MIS procedures in general. Providing MIS or microsurgery surgeons with accurate and precise measurements and control of the contact forces during tissues manipulation will benefit both surgeons and patients. PMID:24721774

High-speed demodulation of weak fiber Bragg gratings based on microwave photonics and chromatic dispersion

NASA Astrophysics Data System (ADS)

Zhou, Lei; Li, Zhengying; Xiang, Na; Bao, Xiaoyi

2018-06-01

A high speed quasi-distributed demodulation method based on the microwave photonics and the chromatic dispersion effect is designed and implemented for weak fiber Bragg gratings (FBGs). Due to the effect of dispersion compensation fiber (DCF), FBG wavelength shift leads to the change of the difference frequency signal at the mixer. With the way of crossing microwave sweep cycle, all wavelengths of cascade FBGs can be high speed obtained by measuring the frequencies change. Moreover, through the introduction of Chirp-Z and Hanning window algorithm, the analysis of difference frequency signal is achieved very well. By adopting the single-peak filter as a reference, the length disturbance of DCF caused by temperature can be also eliminated. Therefore, the accuracy of this novel method is greatly improved, and high speed demodulation of FBGs can easily realize. The feasibility and performance are experimentally demonstrated using 105 FBGs with 0.1% reflectivity, 1 m spatial interval. Results show that each grating can be distinguished well, and the demodulation rate is as high as 40 kHz, the accuracy is about 8 pm.

A high speed, portable, multi-function, weigh-in-motion (WIM) sensing system and a high performance optical fiber Bragg grating (FBG) demodulator

NASA Astrophysics Data System (ADS)

Zhang, Hongtao; Wei, Zhanxiong; Fan, Lingling; Yang, Shangming; Wang, Pengfei; Cui, Hong-Liang

2010-04-01

A high speed, portable, multi-function WIM sensing system based on Fiber Bragg Grating (FBG) technology is reported in this paper. This system is developed to measure the total weight, the distribution of weight of vehicle in motion, the distance of wheel axles and the distance between left and right wheels. In this system, a temperature control system and a real-time compensation system are employed to eliminate the drifts of optical fiber Fabry-Pérot tunable filter. Carbon Fiber Laminated Composites are used in the sensor heads to obtain high reliability and sensitivity. The speed of tested vehicles is up to 20 mph, the full scope of measurement is 4000 lbs, and the static resolution of sensor head is 20 lbs. The demodulator has high speed (500 Hz) data collection, and high stability. The demodulator and the light source are packed into a 17'' rack style enclosure. The prototype has been tested respectively at Stevens' campus and Army base. Some experiences of avoiding the pitfalls in developing this system are also presented in this paper.

New generation all-silica based optical elements for high power laser systems

NASA Astrophysics Data System (ADS)

Tolenis, T.; GrinevičiÅ«tÄ--, L.; Melninkaitis, A.; Selskis, A.; Buzelis, R.; MažulÄ--, L.; Drazdys, R.

2017-08-01

Laser resistance of optical elements is one of the major topics in photonics. Various routes have been taken to improve optical coatings, including, but not limited by, materials engineering and optimisation of electric field distribution in multilayers. During the decades of research, it was found, that high band-gap materials, such as silica, are highly resistant to laser light. Unfortunately, only the production of anti-reflection coatings of all-silica materials are presented to this day. A novel route will be presented in materials engineering, capable to manufacture high reflection optical elements using only SiO2 material and GLancing Angle Deposition (GLAD) method. The technique involves the deposition of columnar structure and tailoring the refractive index of silica material throughout the coating thickness. A numerous analysis indicate the superior properties of GLAD coatings when compared with standard methods for Bragg mirrors production. Several groups of optical components are presented including anti-reflection coatings and Bragg mirrors. Structural and optical characterisation of the method have been performed and compared with standard methods. All researches indicate the possibility of new generation coatings for high power laser systems.

Size–strain separation in diffraction line profile analysis

DOE Office of Scientific and Technical Information (OSTI.GOV)

Scardi, P.; Ermrich, M.; Fitch, A.

Separation of size and strain effects on diffraction line profiles has been studied in a round robin involving laboratory instruments and synchrotron radiation beamlines operating with different radiation, optics, detectors and experimental configurations. The studied sample, an extensively ball milled iron alloy powder, provides an ideal test case, as domain size broadening and strain broadening are of comparable size. The high energy available at some synchrotron radiation beamlines provides the best conditions for an accurate analysis of the line profiles, as the size–strain separation clearly benefits from a large number of Bragg peaks in the pattern; high counts, reliable intensitymore » values in low-absorption conditions, smooth background and data collection at different temperatures also support the possibility to include diffuse scattering in the analysis, for the most reliable assessment of the line broadening effect. However, results of the round robin show that good quality information on domain size distribution and microstrain can also be obtained using standard laboratory equipment, even when patterns include relatively few Bragg peaks, provided that the data are of good quality in terms of high counts and low and smooth background.« less

Shape memory polymeric composites sensing by optic fibre Bragg gratings: A very first approach

NASA Astrophysics Data System (ADS)

Quadrini, Fabrizio; Santo, Loredana; Ciminello, Monica; Concilio, Antonio; Volponi, Ruggero; Spena, Paola

2016-05-01

Shape memory polymer composites (SMPCs) have the potential for many applications in aerospace, spanning from self-repairing of structures to self-deploying of antennas, solar sails, or functional devices (e.g. for grabbing small space debris). In all these cases, it may be essential to have information about their configuration at different stages of shape recovery. In this study, the strain history of a prepreg carbon fibre system, cured with a shape memory polymer (SMP) interlayer, is monitored through a Fibre Bragg Grating (FBG), a fibre optic sensor device. SMPC has been manufactured by using traditional technologies for aerospace. After manufacturing cylindrical shape samples, an external fibre optic system is added to the composite structure; this system is especially suited for high temperatures which are necessary for SMP recovery and composite softening. Sensor functionality is checked before and after each strain history path. Optic fibre arrangement is optimized to avoid unwanted breakings whereas strains are limited by fibre collapsing, i.e. within nominal 2% of deformation. Dynamic information about shape recovery gives fundamental insights about strain evolution during time as well as its spatial distribution.

Size–strain separation in diffraction line profile analysis

DOE PAGES

Scardi, P.; Ermrich, M.; Fitch, A.; ...

2018-05-29

Separation of size and strain effects on diffraction line profiles has been studied in a round robin involving laboratory instruments and synchrotron radiation beamlines operating with different radiation, optics, detectors and experimental configurations. The studied sample, an extensively ball milled iron alloy powder, provides an ideal test case, as domain size broadening and strain broadening are of comparable size. The high energy available at some synchrotron radiation beamlines provides the best conditions for an accurate analysis of the line profiles, as the size–strain separation clearly benefits from a large number of Bragg peaks in the pattern; high counts, reliable intensitymore » values in low-absorption conditions, smooth background and data collection at different temperatures also support the possibility to include diffuse scattering in the analysis, for the most reliable assessment of the line broadening effect. However, results of the round robin show that good quality information on domain size distribution and microstrain can also be obtained using standard laboratory equipment, even when patterns include relatively few Bragg peaks, provided that the data are of good quality in terms of high counts and low and smooth background.« less

Heating and Cooling Master Plan for Fort Bragg, NC, Fiscal Years 2005 to 2030

DTIC Science & Technology

2009-02-01

Pacific Northwest National Labora- tory ( PNNL ) performed an energy use analysis on these buildings in 2005. These buildings are located in 33 specific...electrical equipment the electrical use is provided in the PNNL analysis .* The central chilled water system energy use is reported in cooling chilled...February 2009 C on st ru ct io n E n gi n ee ri n g R es ea rc h L ab or at or y Approved for public release; distribution is unlimited

Second-harmonic generation from a positive-negative index material heterostructure.

PubMed

Mattiucci, Nadia; D'Aguanno, Giuseppe; Bloemer, Mark J; Scalora, Michael

2005-12-01

Resonant cavities have been widely used in the past to enhance material, nonlinear response. Traditional mirrors include metallic films and distributed Bragg reflectors. In this paper we propose negative index material mirrors as a third alternative. With the help of a rigorous Green function approach, we investigate second harmonic generation from single and coupled cavities, and theoretically prove that negative index material mirrors can raise the nonlinear conversion efficiency of a bulk material by at least four orders of magnitude compared to a bulk medium.

Fabrication and characterization of the Si-photonics-integrated vertical resonant-cavity light-emitting diode

NASA Astrophysics Data System (ADS)

Kong, Duanhua; Kim, Taek; Kim, Sihan; Hong, Hyungi; Shcherbatko, Igor; Park, Youngsoo; Shin, Dongjae; Ha, Kyoung-Ho; Jeong, Gitae

2014-03-01

We designed and fabricated a 1.3-um hybrid vertical Resonant-Cavity Light-Emitting Diode for optical interconnect by using direct III-V wafer bonding on silicon on insulator (SOI). The device included InP based front distributed Bragg reflector (DBR), InGaAlAs based active layer, and SOI-based high-contrast-grating (HCG) as a back reflector. 42-uW continuous wave optical power was achieved at 20mA at room temperature.

A scanning microcavity for in situ control of single-molecule emission

NASA Astrophysics Data System (ADS)

Toninelli, C.; Delley, Y.; Stöferle, T.; Renn, A.; Götzinger, S.; Sandoghdar, V.

2010-07-01

We report on the fabrication and characterization of a scannable Fabry-Perot microcavity, consisting of a curved micromirror at the end of an optical fiber and a planar distributed Bragg reflector. Furthermore, we demonstrate the coupling of single organic molecules embedded in a thin film to well-defined resonator modes. We discuss the choice of cavity parameters that will allow sufficiently high Purcell factors for enhancing the zero-phonon transition between the vibrational ground levels of the electronic excited and ground states.

Lateral electrochemical etching of III-nitride materials for microfabrication

DOE Office of Scientific and Technical Information (OSTI.GOV)

Han, Jung

Conductivity-selective lateral etching of III-nitride materials is described. Methods and structures for making vertical cavity surface emitting lasers with distributed Bragg reflectors via electrochemical etching are described. Layer-selective, lateral electrochemical etching of multi-layer stacks is employed to form semiconductor/air DBR structures adjacent active multiple quantum well regions of the lasers. The electrochemical etching techniques are suitable for high-volume production of lasers and other III-nitride devices, such as lasers, HEMT transistors, power transistors, MEMs structures, and LEDs.

Development of Advanced Laser Diode Sources

NASA Technical Reports Server (NTRS)

Coleman, J. J.; Papen, G. C.

1998-01-01

The design and operation of InGaAs-GaAs-AlGaAs asymmetric cladding ridge waveguide distributed Bragg reflector lasers is presented. Targeted for the remote sensing of water vapor with absorption lines in the lambda approximately 930 nm region, these devices operate CW with threshold currents as low as 11 MA and slope efficiencies as high as 0.37 W/A. Tbey also operate with over 30-dB side-mode suppression, and the typical CW characteristic temperature, T(sub o), is 95 K.

Comparison of Model Calculations of Biological Damage from Exposure to Heavy Ions with Measurements

NASA Technical Reports Server (NTRS)

Kim, Myung-Hee Y.; Hada, Megumi; Cucinotta, Francis A.; Wu, Honglu

2014-01-01

The space environment consists of a varying field of radiation particles including high-energy ions, with spacecraft shielding material providing the major protection to astronauts from harmful exposure. Unlike low-LET gamma or X rays, the presence of shielding does not always reduce the radiation risks for energetic charged-particle exposure. Dose delivered by the charged particle increases sharply at the Bragg peak. However, the Bragg curve does not necessarily represent the biological damage along the particle path since biological effects are influenced by the track structures of both primary and secondary particles. Therefore, the ''biological Bragg curve'' is dependent on the energy and the type of the primary particle and may vary for different biological end points. Measurements of the induction of micronuclei (MN) have made across the Bragg curve in human fibroblasts exposed to energetic silicon and iron ions in vitro at two different energies, 300 MeV/nucleon and 1 GeV/nucleon. Although the data did not reveal an increased yield of MN at the location of the Bragg peak, the increased inhibition of cell progression, which is related to cell death, was found at the Bragg peak location. These results are compared to the calculations of biological damage using a stochastic Monte-Carlo track structure model, Galactic Cosmic Ray Event-based Risk Model (GERM) code (Cucinotta, et al., 2011). The GERM code estimates the basic physical properties along the passage of heavy ions in tissue and shielding materials, by which the experimental set-up can be interpreted. The code can also be used to describe the biophysical events of interest in radiobiology, cancer therapy, and space exploration. The calculation has shown that the severely damaged cells at the Bragg peak are more likely to go through reproductive death, the so called "overkill".

Depth Dose Measurement using a Scintillating Fiber Optic Dosimeter for Proton Therapy Beam of the Passive-Scattering Mode Having Range Modulator Wheel

NASA Astrophysics Data System (ADS)

Hwang, Ui-Jung; Shin, Dongho; Lee, Se Byeong; Lim, Young Kyung; Jeong, Jong Hwi; Kim, Hak Soo; Kim, Ki Hwan

2018-05-01

To apply a scintillating fiber dosimetry system to measure the range of a proton therapy beam, a new method was proposed to correct for the quenching effect on measuring an spread out Bragg peak (SOBP) proton beam whose range is modulated by a range modulator wheel. The scintillating fiber dosimetry system was composed of a plastic scintillating fiber (BCF-12), optical fiber (SH 2001), photo multiplier tube (H7546), and data acquisition system (PXI6221 and SCC68). The proton beam was generated by a cyclotron (Proteus-235) in the National Cancer Center in Korea. It operated in the double-scattering mode and the spread out of the Bragg peak was achieved by a spinning range modulation wheel. Bragg peak beams and SOBP beams of various ranges were measured, corrected, and compared to the ion chamber data. For the Bragg peak beam, quenching equation was used to correct the quenching effect. On the proposed process of correcting SOBP beams, the measured data using a scintillating fiber were separated by the Bragg peaks that the SOBP beam contained, and then recomposed again to reconstruct an SOBP after correcting for each Bragg peak. The measured depth-dose curve for the single Bragg peak beam was well corrected by using a simple quenching equation. Correction for SOBP beam was conducted with a newly proposed method. The corrected SOBP signal was in accordance with the results measured with an ion chamber. We propose a new method to correct for the SOBP beam from the quenching effect in a scintillating fiber dosimetry system. This method can be applied to other scintillator dosimetry for radiation beams in which the quenching effect is shown in the scintillator.

InxAl1-xN chiral nanorods mimicking the polarization features of scarab beetles

NASA Astrophysics Data System (ADS)

Magnusson, R.; Birch, J.; Hsiao, C.-L.; Sandström, P.; Arwin, H.; Järrendahl, K.

2015-03-01

The scarab beetle Cetonia aurata is known to reflect light with brilliant colors and a high degree of circular polarization. Both color and polarization effects originate from the beetles exoskeleton and have been attributed to a Bragg reflection of the incident light due to a twisted laminar structure. Our strategy for mimicking the optical properties of the Cetonia aurata was therefore to design and fabricate transparent, chiral films. A series of films with tailored transparent structures of helicoidal InxAl1-xN nanorods were grown on sapphire substrates using UHV magnetron sputtering. The value of x is tailored to gradually decrease from one side to the other in each nanorod normal to its growth direction. This introduces an in-plane anisotropy with different refractive indices in the direction of the gradient and perpendicular to it. By rotating the sample during film growth the in-plane optical axis will be rotated from bottom to top and thereby creating a chiral film. Based on Muellermatrix ellipsometry, optical modeling has been done suggesting that both the exoskeleton of Cetonia aurata and our artificial material can be modeled by an anisotropic film made up of a stack of thin layers, each one with its in-plane optical axis slightly rotated with respect to the previous layer. Simulations based on the optical modeling were used to investigate how pitch and thickness of the film together with the optical properties of the constitutive materials affects the width and spectral position of the Bragg reflection band.

Relaxation of ferroelectric states in 2D distributions of quantum dots: EELS simulation

NASA Astrophysics Data System (ADS)

Cortés, C. M.; Meza-Montes, L.; Moctezuma, R. E.; Carrillo, J. L.

2016-06-01

The relaxation time of collective electronic states in a 2D distribution of quantum dots is investigated theoretically by simulating EELS experiments. From the numerical calculation of the probability of energy loss of an electron beam, traveling parallel to the distribution, it is possible to estimate the damping time of ferroelectric-like states. We generate this collective response of the distribution by introducing a mean field interaction among the quantum dots, and then, the model is extended incorporating effects of long-range correlations through a Bragg-Williams approximation. The behavior of the dielectric function, the energy loss function, and the relaxation time of ferroelectric-like states is then investigated as a function of the temperature of the distribution and the damping constant of the electronic states in the single quantum dots. The robustness of the trends and tendencies of our results indicate that this scheme of analysis can guide experimentalists to develop tailored quantum dots distributions for specific applications.

Review of Session 6: Medical Physics

PubMed Central

Fukuda, Shigekazu

2014-01-01

Medical physics is very important in carbon ion radiotherapy, as it is in conventional radiotherapy using X-rays and in estimation of exposed dose in the space environment. High-energy ion beams such as carbon beams have physical characteristics such as the Bragg curve, high LET, and nuclear reactions producing fragmentations. Therefore, understanding these properties well is essential for further development of carbon radiotherapy and manned space activity. We invited, therefore, the following six presentations relevant to issues ranging from the measurement of fragmentations, lineal energy distributions using the microdosimetric approach, and neutron dose with active beam delivery of carbon-ion therapy, to the depth–dose distribution of various ions inside a human head phantom.

Coherent X-Ray Imaging of Collagen Fibril Distributions within Intact Tendons

PubMed Central

Berenguer, Felisa; Bean, Richard J.; Bozec, Laurent; Vila-Comamala, Joan; Zhang, Fucai; Kewish, Cameron M.; Bunk, Oliver; Rodenburg, John M.; Robinson, Ian K.

2014-01-01

The characterization of the structure of highly hierarchical biosamples such as collagen-based tissues at the scale of tens of nanometers is essential to correlate the tissue structure with its growth processes. Coherent x-ray Bragg ptychography is an innovative imaging technique that gives high resolution images of the ordered parts of such samples. Herein, we report how we used this method to image the collagen fibrillar ultrastructure of intact rat tail tendons. The images show ordered fibrils extending over 10–20 μm in length, with a quantifiable D-banding spacing variation of 0.2%. Occasional defects in the fibrils distribution have also been observed, likely indicating fibrillar fusion events. PMID:24461021

Finite element modeling to determine thermal residual strain distribution of bonded composite repairs for structural health monitoring design

NASA Astrophysics Data System (ADS)

Baker, Wayne; Jones, Rhys; Davis, Claire; Galea, Stephen C.

2002-11-01

The economic implication of fleet upgrades, particularly in Australia with military aircraft such as the F-111 and F/A-18, has led to an increasing reliance on composite repair technology to address fatigue and corrosion-affected aircraft components. The increasing use of such repairs has led to a research effort to develop various in-situ health monitoring systems that may be incorporated with a repair. This paper reports on the development of a theoretical methodology that uses finite element analysis (FEA) to model the strain profiles which optical sensors, on or within the patch, will be exposed to under various operational scenarios, including load and disbond. Numerical techniques are then used to predict the fibre Bragg grating (FBG) reflections which occur with these strain profiles. The quality of these reflection are a key consideration when designing FBG based structural health monitoring (SHM) systems. This information can be used to optimise the location of both surface mounted, and embedded sensors, and determine feasibility of SHM system design. Research was conducted into the thermal residual strain (TRS) within the patch. A finite element study revealed the presence of significant thermal residual strain gradients along the surface of the tapered region of the patch. As Bragg gratings are particularly sensitive to strain gradients, (producing a result similar to a chirped grating) the strain gradient on the composite at potential sensor locations both under load, and in the event of disbond was considered. A sufficiently high gradient leads to an altered Bragg reflection. These spurious reflections need to be considered, and theoretically obtained reflections can provide information to allow for load scenarios where the Bragg shift is not a smooth, well defined peak. It can also be shown that embedded fibres offer a higher average thermal residual strain reading, while being subject to a much lower strain gradient. This particularly favors the optical disbond detection system that is being developed. While certification concerns exist with embedding sensors in repairs, this study shows that embedded optical fibre sensors may provide for a health monitoring system with enhanced reliability and sensitivity.

Perovskite/c-Si tandem solar cell with inverted nanopyramids: realizing high efficiency by controllable light trapping

PubMed Central

Shi, Dai; Zeng, Yang; Shen, Wenzhong

2015-01-01

Perovskite/c-Si tandem solar cells (TSCs) have become a promising candidate in recent years for achieving efficiency over 30%. Although general analysis has shown very high upper limits for such TSCs, it remains largely unclear what specific optical structures could best approach these limits. Here we propose the combination of perovskite/c-Si tandem structure with inverted nanopyramid morphology as a practical way of achieving efficiency above 31% based on realistic solar cell parameters. By full-field simulation, we have shown that an ultra-low surface reflectance can be achieved by tuning the pyramid geometry within the range of experimental feasibility. More importantly, we have demonstrated that the index-guided modes can be excited within the top cell layer by introducing a TCO interlayer that prevents coupling of guided light energy into the bottom cell. This light trapping scheme has shown superior performance over the Bragg stack intermediate reflector utilized in previous micropyramid-based TSCs. Finally, by controlling the coupling between the top and bottom cell through the thickness of the interlayer, current generation within the tandem can be optimized for both two- and four-terminal configurations, yielding efficiencies of 31.9% and 32.0%, respectively. These results have provided useful guidelines for the fabrication of perovskite/c-Si TSCs. PMID:26566176

Perovskite/c-Si tandem solar cell with inverted nanopyramids: realizing high efficiency by controllable light trapping.

PubMed

Shi, Dai; Zeng, Yang; Shen, Wenzhong

2015-11-13

Perovskite/c-Si tandem solar cells (TSCs) have become a promising candidate in recent years for achieving efficiency over 30%. Although general analysis has shown very high upper limits for such TSCs, it remains largely unclear what specific optical structures could best approach these limits. Here we propose the combination of perovskite/c-Si tandem structure with inverted nanopyramid morphology as a practical way of achieving efficiency above 31% based on realistic solar cell parameters. By full-field simulation, we have shown that an ultra-low surface reflectance can be achieved by tuning the pyramid geometry within the range of experimental feasibility. More importantly, we have demonstrated that the index-guided modes can be excited within the top cell layer by introducing a TCO interlayer that prevents coupling of guided light energy into the bottom cell. This light trapping scheme has shown superior performance over the Bragg stack intermediate reflector utilized in previous micropyramid-based TSCs. Finally, by controlling the coupling between the top and bottom cell through the thickness of the interlayer, current generation within the tandem can be optimized for both two- and four-terminal configurations, yielding efficiencies of 31.9% and 32.0%, respectively. These results have provided useful guidelines for the fabrication of perovskite/c-Si TSCs.

High-resolution three-dimensional structural microscopy by single-angle Bragg ptychography

DOE PAGES

Hruszkewycz, S. O.; Allain, M.; Holt, M. V.; ...

2016-11-21

Coherent X-ray microscopy by phase retrieval of Bragg diffraction intensities enables lattice distortions within a crystal to be imaged at nanometre-scale spatial resolutions in three dimensions. While this capability can be used to resolve structure–property relationships at the nanoscale under working conditions, strict data measurement requirements can limit the application of current approaches. Here, in this work, we introduce an efficient method of imaging three-dimensional (3D) nanoscale lattice behaviour and strain fields in crystalline materials with a methodology that we call 3D Bragg projection ptychography (3DBPP). This method enables 3D image reconstruction of a crystal volume from a series ofmore » two-dimensional X-ray Bragg coherent intensity diffraction patterns measured at a single incident beam angle. Structural information about the sample is encoded along two reciprocal-space directions normal to the Bragg diffracted exit beam, and along the third dimension in real space by the scanning beam. Finally, we present our approach with an analytical derivation, a numerical demonstration, and an experimental reconstruction of lattice distortions in a component of a nanoelectronic prototype device.« less

Non-invasive timing of gas gun-launched projectiles using external surface-mounted optical fiber-Bragg grating strain gauges

NASA Astrophysics Data System (ADS)

Goodwin, Peter M.; Marshall, Bruce R.; Stevens, Gerald D.; Dattelbaum, Dana M.

2013-03-01

Non-invasive detection methods for tracking gun-launched projectiles are important not only for assessment of gun performance but are also essential for timing a variety of diagnostics, for example, to investigate plate-impact events for shock compression experiments. Measurement of the time of passage of a projectile moving inside of the gun barrel can be achieved by detection of the transient hoop strain induced in the barrel of a light-gas gun by the passage of the projectile using external, barrel surface-mounted optical fiber-Bragg grating strain gauges. Optical fiber-Bragg gratings have been implemented and their response characterized on single-stage and two-stage light gas guns routinely used for dynamic experimentation at Los Alamos National Laboratory. Two approaches, using either broadband or narrowband illumination, were used to monitor changes in the Bragg wavelength of the fiber-Bragg gratings. The second approach, using narrowband laser illumination, offered the highest sensitivity. The feasibility of using these techniques to generate early, pre-event signals useful for triggering high-latency diagnostics was demonstrated.

Non-invasive timing of gas gun-launched projectiles using external surface-mounted optical fiber-Bragg grating strain gauges.

PubMed

Goodwin, Peter M; Marshall, Bruce R; Stevens, Gerald D; Dattelbaum, Dana M

2013-03-01

Non-invasive detection methods for tracking gun-launched projectiles are important not only for assessment of gun performance but are also essential for timing a variety of diagnostics, for example, to investigate plate-impact events for shock compression experiments. Measurement of the time of passage of a projectile moving inside of the gun barrel can be achieved by detection of the transient hoop strain induced in the barrel of a light-gas gun by the passage of the projectile using external, barrel surface-mounted optical fiber-Bragg grating strain gauges. Optical fiber-Bragg gratings have been implemented and their response characterized on single-stage and two-stage light gas guns routinely used for dynamic experimentation at Los Alamos National Laboratory. Two approaches, using either broadband or narrowband illumination, were used to monitor changes in the Bragg wavelength of the fiber-Bragg gratings. The second approach, using narrowband laser illumination, offered the highest sensitivity. The feasibility of using these techniques to generate early, pre-event signals useful for triggering high-latency diagnostics was demonstrated.

Dynamic interrogator for elastic wave sensing using Fabry Perot filters based on fiber Bragg gratings.

PubMed

Harish, Achar V; Varghese, Bibin; Rao, Babu; Balasubramaniam, Krishnan; Srinivasan, Balaji

2015-07-01

Use of in-fiber Fabry-Perot (FP) filters based on fiber Bragg gratings as both sensor as well as an interrogator for enhancing the detection limit of elastic wave sensing is investigated in this paper. The sensitivity of such a demodulation scheme depends on the spectral discrimination of the sensor and interrogator gratings. Simulations have shown that the use of in-fiber FP filters with high finesse provide better performance in terms of sensitivity compared to the demodulation using fiber Bragg gratings. Based on these results, a dynamic interrogator capable of sensing acoustic waves with amplitude of less than 1 micro-strain over frequencies of 10 kHz to several 100 kHz has been implemented. Frequency response of the fiber Bragg gratings in the given experimental setup has been compared to that of the conventional piezo sensors demonstrating that fiber Bragg gratings can be used over a relatively broad frequency range. Dynamic interrogator has been packaged in a compact box without any degradation in its performance. Copyright © 2015 Elsevier B.V. All rights reserved.

Optimal design of radial Bragg cavities and lasers.

PubMed

Ben-Bassat, Eyal; Scheuer, Jacob

2015-07-01

We present a new and optimal design approach for obtaining maximal confinement of the field in radial Bragg cavities and lasers for TM polarization. The presented approach outperforms substantially the previously employed periodic and semi-periodic design schemes of such lasers. We show that in order to obtain maximal confinement, it is essential to consider the complete reflection properties (amplitude and phase) of the propagating radial waves at the interfaces between Bragg layers. When these properties are taken into account, we find that it is necessary to introduce a wider ("half-wavelength") layer at a specific radius in the "quarter-wavelength" radial Bragg stack. It is shown that this radius corresponds to the cylindrical equivalent of Brewster's angle. The confinement and field profile are calculated numerically by means of transfer matrix method.

Control of propagation of spatially localized polariton wave packets in a Bragg mirror with embedded quantum wells

NASA Astrophysics Data System (ADS)

Sedova, I. E.; Chestnov, I. Yu.; Arakelian, S. M.; Kavokin, A. V.; Sedov, E. S.

2018-01-01

We considered the nonlinear dynamics of Bragg polaritons in a specially designed stratified semiconductor structure with embedded quantum wells, which possesses a convex dispersion. The model for the ensemble of single periodically arranged quantum wells coupled with the Bragg photon fields has been developed. In particular, the generalized Gross-Pitaevskii equation with the non-parabolic dispersion has been obtained for the Bragg polariton wave function. We revealed a number of dynamical regimes for polariton wave packets resulting from competition of the convex dispersion and the repulsive nonlinearity effects. Among the regimes are spreading, breathing and soliton propagation. When the control parameters including the exciton-photon detuning, the matter-field coupling and the nonlinearity are manipulated, the dynamical regimes switch between themselves.

Special types of FBG and CoaxBG structures for telecommunication and monitoring systems

NASA Astrophysics Data System (ADS)

Morozov, Oleg G.; Nasybullin, Aidar R.; Morozov, Gennady A.; Danilaev, Maxim P.; Zastela, Mikhail Y.; Farkhutdinov, Rafael V.; Faskhutdinov, Lenar M.

2015-03-01

The technology of fiber Bragg gratings is used as one of the most applicable technologies for construction of fiber optic sensors and telecommunication systems. Periodic irregular wave resistance located in the guiding waveguide can be regarded as analog of the fiber Bragg grating structure in the field of radio-frequency. Coaxial waveguide can be used as a guide system, so a special case of this structure is the Bragg grating on coaxial cable. Recently, the special structure of sensors were beginning to be used with heterogeneity as a discrete phase π-shift. Based on the properties analysis of the Bragg reflection characteristics of structures with a phase shift in the optical and microwave range shown advantage of using these devices in measuring systems.

Stimulated Rayleigh-Bragg scattering in two-photon absorbing media

NASA Astrophysics Data System (ADS)

He, Guang S.; Lu, Changgui; Zheng, Qingdong; Prasad, Paras N.; Zerom, Petros; Boyd, Robert W.; Samoc, Marek

2005-06-01

The origin and mechanism of backward stimulated Rayleigh scattering in two-photon absorbing media are studied theoretically and experimentally. This type of stimulated scattering has the unusual features of no frequency shift and low pump threshold requirement compared to all other known stimulated scattering effects. This frequency-unshifted stimulated Rayleigh scattering effect can be well explained by a two-photon-excitation-enhanced Bragg grating reflection model. The reflection of the forward pump beam from this stationary Bragg grating may substantially enhance the backward Rayleigh scattering beam, providing a positive feedback mechanism without causing any frequency shift. A two-counterpropagating-beam-formed grating experiment in a two-photon absorbing dye solution is conducted. The measured dynamic behavior of Bragg grating formation and reflectivity properties are basically consistent with the predictions from the proposed model.

Thermal and chemical treatment of polymer optical fiber Bragg grating sensors for enhanced mechanical sensitivity

NASA Astrophysics Data System (ADS)

Pospori, A.; Marques, C. A. F.; Sáez-Rodríguez, D.; Nielsen, K.; Bang, O.; Webb, D. J.

2017-07-01

An investigation of the thermal annealing effects on the strain, stress, and force sensitivities of polymer optical fiber Bragg grating sensors is performed. We demonstrate for the first time that the fiber annealing can enhance both stress and force sensitivities of Bragg grating sensors, with the possible cause being the molecular relaxation of the polymer when fiber is raised above the β -transition temperature. A simple, cost-effective, but well controlled method for fiber annealing is also presented in this work. In addition, the effects of chemical etching on the strain, stress, and force sensitivities have been investigated. Results show that fiber etching too can increase the force sensitivity, and it can also affect the strain and stress sensitivities of the Bragg grating sensors.

Etched Polymer Fibre Bragg Gratings and Their Biomedical Sensing Applications

PubMed Central

Rajan, Ginu; Bhowmik, Kishore; Xi, Jiangtao; Peng, Gang-Ding

2017-01-01

Bragg gratings in etched polymer fibres and their unique properties and characteristics are discussed in this paper. Due to the change in material and mechanical properties of the polymer fibre through etching, Bragg gratings inscribed in such fibres show high reflectivity and enhanced intrinsic sensitivity towards strain, temperature, and pressure. The short-term and long-term stability of the gratings and the effect of hysteresis on the dynamic characteristics are also discussed. The unique properties and enhanced intrinsic sensitivity of etched polymer fibre Bragg grating are ideal for the development of high-sensitivity sensors for biomedical applications. To demonstrate their biomedical sensing capabilities, a high-sensitivity pressure transducer that operates in the blood pressure range, and a breathing rate monitoring device are developed and presented. PMID:29027945

Coherent Bragg nanodiffraction at the hard X-ray Nanoprobe beamline.

PubMed

Hruszkewycz, S O; Holt, M V; Maser, J; Murray, C E; Highland, M J; Folkman, C M; Fuoss, P H

2014-03-06

Bragg coherent diffraction with nanofocused hard X-ray beams provides unique opportunities for quantitative in situ studies of crystalline structure in nanoscale regions of complex materials and devices by a variety of diffraction-based techniques. In the case of coherent diffraction imaging, a major experimental challenge in using nanoscale coherent beams is maintaining a constant scattering volume such that coherent fringe visibility is maximized and maintained over the course of an exposure lasting several seconds. Here, we present coherent Bragg diffraction patterns measured from different nanostructured thin films at the Sector 26 Nanoprobe beamline at the Advanced Photon Source and demonstrate that with nanoscale positional control, coherent diffraction patterns can be measured with source-limited fringe visibilities more than 50% suitable for imaging by coherent Bragg ptychography techniques.

Coherent Bragg nanodiffraction at the hard X-ray Nanoprobe beamline

PubMed Central

Hruszkewycz, S. O.; Holt, M. V.; Maser, J.; Murray, C. E.; Highland, M. J.; Folkman, C. M.; Fuoss, P. H.

2014-01-01

Bragg coherent diffraction with nanofocused hard X-ray beams provides unique opportunities for quantitative in situ studies of crystalline structure in nanoscale regions of complex materials and devices by a variety of diffraction-based techniques. In the case of coherent diffraction imaging, a major experimental challenge in using nanoscale coherent beams is maintaining a constant scattering volume such that coherent fringe visibility is maximized and maintained over the course of an exposure lasting several seconds. Here, we present coherent Bragg diffraction patterns measured from different nanostructured thin films at the Sector 26 Nanoprobe beamline at the Advanced Photon Source and demonstrate that with nanoscale positional control, coherent diffraction patterns can be measured with source-limited fringe visibilities more than 50% suitable for imaging by coherent Bragg ptychography techniques. PMID:24470418

Effect of titanium dental implants on proton therapy delivered for head tumors: experimental validation using an anthropomorphic head phantom

NASA Astrophysics Data System (ADS)

Oancea, C.; Shipulin, K.; Mytsin, G.; Molokanov, A.; Niculae, D.; Ambrožová, I.; Davídková, M.

2017-03-01

A dosimetric experiment was performed at the Medico-Technical Complex in the Joint Institute for Nuclear Research, Dubna, to investigate the effects of metallic dental implants in the treatment of head and neck tumours with proton therapy. The goal of the study was to evaluate the 2D dose distributions of different clinical treatment plans measured in an anthropomorphic phantom, and compare them to predictions from a treatment planning system. The anthropomorphic phantom was sliced into horizontal segments. Two grade 4 Titanium implants were inserted between 2 slices, corresponding to a maxillary area. GafChromic EBT2 films were placed between the segments containing the implants to measure the 2D delivered dose. Two different targets were designed: the first target includes the dental implants in the isocentre, and in the second target, the proton beam is delivered through the implants, which are located at the entrance region of the Bragg curve. The experimental results were compared to the treatment plans made using our custom 3D Treatment Planning System, named RayTreat. To quantitatively determine differences in the isodose distributions (measured and calculated), the gamma index (3 mm, 3%) was calculated for each target for the matrix value in the region of high isodose (> 90%): for the experimental setup, which includes the implants in the SOBP region, the result obtained was 84.3%. When the implants were localised in the entrance region of the Bragg curve, the result obtained was 86.4%. In conclusion, the uncertainties introduced by the clinically planned dose distribution are beyond reasonable limits. The linear energy transfer spectra in close proximity to the implants were investigated using solid state nuclear track detectors (TED). Scattered particles outside the target were detected.

Subwavelength and directional control of flexural waves in zone-folding induced topological plates

NASA Astrophysics Data System (ADS)

Chaunsali, Rajesh; Chen, Chun-Wei; Yang, Jinkyu

2018-02-01

Inspired by the quantum spin Hall effect shown by topological insulators, we propose a plate structure that can be used to demonstrate the pseudospin Hall effect for flexural waves. The system consists of a thin plate with periodically arranged resonators mounted on its top surface. We extend a technique based on the plane-wave expansion method to identify a double Dirac cone emerging due to the zone-folding in frequency band structures. This particular design allows us to move the double Dirac cone to a lower frequency than the resonating frequency of local resonators. We then manipulate the pattern of local resonators to open subwavelength Bragg band gaps that are topologically distinct. Building on this method, we verify numerically that a waveguide at an interface between two topologically distinct resonating plate structures can be used for guiding low-frequency, spin-dependent one-way flexural waves along a desired path with bends.

Highly selective and compact tunable MOEMS photonic crystal Fabry-Perot filter.

PubMed

Boutami, S; Ben Bakir, B; Leclercq, J-L; Letartre, X; Rojo-Romeo, P; Garrigues, M; Viktorovitch, P; Sagnes, I; Legratiet, L; Strassner, M

2006-04-17

The authors report a compact and highly selective tunable filter using a Fabry-Perot resonator combining a bottom micromachined 3-pair-InP/air-gap Bragg reflector with a top photonic crystal slab mirror. It is based on the coupling between radiated vertical cavity modes and waveguided modes of the photonic crystal. The full-width at half maximum (FWHM) of the resonance, as measured by microreflectivity experiments, is close to 1.5nm (around 1.55 microm). The presence of the photonic crystal slab mirror results in a very compact resonator, with a limited number of layers. The demonstrator was tuned over a 20nm range for a 4V tuning voltage, the FWHM being kept below 2.5nm. Bending of membranes is a critical issue, and better results (FWHM=0.5nm) should be obtained on the same structure if this technological point is fixed.

Solid-state laser source of narrowband ultraviolet B light for skin disease care with advanced performance

NASA Astrophysics Data System (ADS)

Tarasov, Aleksandr A.; Chu, Hong; Buchwald, Kristian

2015-02-01

Two years ago we reported about the development of solid state laser source for medical skin treatment with wavelength 310.6 nm and average power 200 mW. Here we describe the results of investigation of the advanced version of the laser, which is a more compact device with increased output power and flat top beam profile. Ti: Sapphire laser, the main module of our source, was modified and optimized such, that UV average power of the device was increased 1.7 times. Fiber optic homogenizer was replaced by articulated arm with diffraction diffuser, providing round spot with flat profile at the skin. We investigated and compare characteristics of Ti: Sapphire lasers with volume Bragg grating and with fused silica transmission grating, which was used first time for Ti: Sapphire laser spectral selection and tuning. Promising performance of last gratings is demonstrated.

Imprint control of BaTiO 3 thin films via chemically induced surface polarization pinning

DOE PAGES

Lee, Hyungwoo; Kim, Tae Heon; Patzner, Jacob J.; ...

2016-02-22

Surface-adsorbed polar molecules can significantly alter the ferroelectric properties of oxide thin films. Thus, fundamental understanding and controlling the effect of surface adsorbates are crucial for the implementation of ferroelectric thin film devices, such as ferroelectric tunnel junctions. Herein, we report an imprint control of BaTiO 3 (BTO) thin films by chemically induced surface polarization pinning in the top few atomic layers of the water-exposed BTO films. Our studies based on synchrotron X-ray scattering and coherent Bragg rod analysis demonstrate that the chemically induced surface polarization is not switchable but reduces the polarization imprint and improves the bistability of ferroelectricmore » phase in BTO tunnel junctions. Here, we conclude that the chemical treatment of ferroelectric thin films with polar molecules may serve as a simple yet powerful strategy to enhance functional properties of ferroelectric tunnel junctions for their practical applications.« less

Full-Scale Measurement and Prediction of the Dynamics of High-Speed Helicopter Tow Cables

DTIC Science & Technology

2014-02-14

fairing at tow speeds up to 17 knots. The technique for measuring vibration amplitudes along the cable is based on fiber Bragg grating ( FBG ) sensors...cm long. As light propagates through a FBG , it is partially reflected at each interface between the bands of high and low refractive index. If the...slightly, which can be measured by a change in the Bragg wavelength. State-of-the-art FBG interrogators can resolve Bragg wavelength shifts down to 0.001 nm

Double Bragg Interferometry

NASA Astrophysics Data System (ADS)

Ahlers, H.; Müntinga, H.; Wenzlawski, A.; Krutzik, M.; Tackmann, G.; Abend, S.; Gaaloul, N.; Giese, E.; Roura, A.; Kuhl, R.; Lämmerzahl, C.; Peters, A.; Windpassinger, P.; Sengstock, K.; Schleich, W. P.; Ertmer, W.; Rasel, E. M.

2016-04-01

We employ light-induced double Bragg diffraction of delta-kick collimated Bose-Einstein condensates to create three symmetric Mach-Zehnder interferometers. They rely on (i) first-order, (ii) two successive first-order, and (iii) second-order processes which demonstrate the scalability of the corresponding momentum transfer. With respect to devices based on conventional Bragg scattering, these symmetric interferometers double the scale factor and feature a better suppression of noise and systematic uncertainties intrinsic to the diffraction process. Moreover, we utilize these interferometers as tiltmeters for monitoring their inclination with respect to gravity.

Job Order Contracting: A Procurement Success Story

DTIC Science & Technology

1988-02-01

Engineering/Procurement processing time 279 CI4 TABLE C-2 JOC DELIVERY ORDER PROCESSING TIME Contract size and location Amount Elapsed time- ($000) days...Bragg 2.1 68 Monroe 2.1 196 Sill 2.2 3 bragg 2.3 32 C-5 Ii ~A¶A~.AL&A .LiA..hLI TABLE C-2 JOC DELIVERY ORDER PROCESSING TIME (Continued) Conrat szean...DEUVERY ORDER PROCESSING TIME (Continued) Amount Elapsed time- Contract size and location Amou daps($000) days Bragg S 14.7 11 Monroe 14.8 30 Monroe

Design and fabrication of inverted rib waveguide Bragg grating

NASA Astrophysics Data System (ADS)

Huang, Cheng-Sheng; Wang, Wei-Chih

2009-03-01

A polymeric SU8 rib waveguide Bragg grating filterfabricated using reactive ion etching (RIE) and solvent assisted microcontact molding (SAMIM) is presented. SAMIM is one kind of soft lithography. The technique is unique in which that a composite hPDMS/PDMS stamp was used to transfer the grating pattern onto an inverted SU8 rib waveguide system. The composite grating stamp can be used repeatedly several times with degradation. Using this stamp and inverter rib waveguide structure, the Bragg grating filter fabrication can be significantly simplified.

Moiré phase-shifted fiber Bragg gratings in polymer optical fibers

NASA Astrophysics Data System (ADS)

Min, Rui; Marques, Carlos; Bang, Ole; Ortega, Beatriz

2018-03-01

We demonstrate a simple way to fabricate phase-shifted fiber Bragg grating in polymer optical fibers as a narrowband transmission filter for a variety of applications at telecom wavelengths. The filters have been fabricated by overlapping two uniform fiber Bragg gratings with slightly different periods to create a Moiré grating with only two pulses (one pulse is 15 ns) of UV power. Experimental characterization of the filter is provided under different conditions where the strain and temperature sensitivities were measured.

Compact fiber CPA system based on a CFBG stretcher and CVBG compressor with matched dispersion profile.

PubMed

Bartulevicius, Tadas; Frankinas, Saulius; Michailovas, Andrejus; Vasilyeu, Ruslan; Smirnov, Vadim; Trepanier, Francois; Rusteika, Nerijus

2017-08-21

In this work, a compact fiber chirped pulse amplification system exploiting a tandem of a chirped fiber Bragg grating stretcher and a chirped volume Bragg grating compressor with matched chromatic dispersion is presented. Chirped pulses of 230 ps duration were amplified in a Yb-doped fiber amplifier and re-compressed to 208 fs duration with good fidelity. The compressed pulse duration was fine-tuned by temperature gradient along the fiber Bragg grating stretcher.

Error Measurements in an Acousto-Optic Tunable Filter Fiber Bragg Grating Sensor System

DTIC Science & Technology

1994-05-01

for an ideal AOTF, at 833 and 838 nm using a TeO2 crystal ............................ 33 Figure 3.12. Frequency characteristics of Equation (3.43...multiple channels in an AOTF requires the presence of multiple RF frequencies to establish the complex grating. Since the crystal used in the AOTF ( TeO2 ) is...in germano- silicate glass . This index modulation, Bragg grating, acts as an optical band rejection filter for those wavelengths that meet the Bragg

Silicon single mode waveguide modulator based upon switchable Bragg reflector

NASA Astrophysics Data System (ADS)

Azogui, Jonathan; Ramon, Yonathan; Businaro, Luca; Ciasca, Gabriele; Gerardino, Annamaria; Zalevsky, Zeev

2018-02-01

In this paper we present the development of an electro optical "Bragg" modulator for telecommunication, in both design and fabrication. The device consists from a regular single mode silicon waveguide (WG) in which an effective Bragg reflector is "turned on" within the WG by means of external bias, due to the plasma dispersion effect, in which the (complexed) refractive index is affected by carrier concentration within the Silicon. Three different strategies are presented for both design and fabrication.

Photonic spectra of a Bragg microresonator with a ferroelectric resonator layer

NASA Astrophysics Data System (ADS)

Fedorova, Irina V.; Eliseeva, Svetlana V.; Sementsov, Dmitrij I.

2018-05-01

Transmission spectra of a photonic crystal resonator structure have been obtained where the Bragg dielectric mirrors contain a finite number of periods with an inverted order of layers and the resonator layer is made of a ferroelectric with a permittivity many times exceeding the permittivity of the layers in Bragg mirrors. Almost a complete transmission suppression was detected not only in the photonic band gap (except for a narrow region of the defect mode), but also outside the forbidden band.

Distributed Bragg reflector tapered diode lasers emitting more than 10 W at 1154 nm

NASA Astrophysics Data System (ADS)

Feise, D.; Bugge, F.; Matalla, M.; Thies, A.; Ressel, P.; Blume, G.; Hofmann, J.; Paschke, K.

2018-02-01

Distributed Bragg reflector tapered diode lasers (DBR-TPL) emitting at 1154 nm are ideal light sources to be implemented into medical devices and hand-held tools for treatment in dermatology and ophthalmology at 577 nm due to their high spectral radiance enabling second harmonic generation from near infrared to yellow. In this work, we present DBR-TPLs which are able to emit more than 10 W in continuous-wave operation with a narrow spectral emission at 1154 nm and a very good beam quality providing excellent spectral radiance. The investigated DBRTPLs are based on three different epitaxial structures with varying vertical far field angles of 35°, 26°, and 17°. To optimize the coupling efficiency into non-linear crystals we studied DBR-TPL with a vertical far field angle of approx. 17° based on an asymmetrical super large optical cavity epitaxial structure. At a pump current of 18 A these devices are able to emit more than 9 W at 25°C and nearly 11 W at 10°C. The spectral emission is very narrow (ΔλFWHM = 18 pm) and single mode over the entire current range. While the beam quality factor M2 according to the 1/e2-level remains 1.1, the M2 according to second order moments deteriorates when the laser is pumped with higher currents. Therefore, the power content in the central lobe increases somewhat less rapidly than the total power.

Comparison of distributed Bragg reflector ridge waveguide diode lasers and monolithic master oscillator power amplifiers

NASA Astrophysics Data System (ADS)

Werner, Nils; Wegemund, Jan; Gerke, Sebastian; Feise, David; Bugge, Frank; Paschke, Katrin; Tränkle, Günther

2018-02-01

Diode lasers with ridge waveguide structures and wavelength stabilization by a distributed Bragg-reflector (DBR) are key components for many different applications. These lasers provide diffraction limited laser emission in a single spectral mode, while an arbitrary emission wavelength can be chosen as long as the semiconductor allows for amplification. Furthermore, the DBR grating can be fabricated during the lateral structuring of the device which makes them well suited for mass production. A variety of different concepts can be used for the actual realization of the laser. While standard DBR ridge waveguide lasers (DBR-RWL) with a DBR as reflection grating provide up to 1W optical output power, the DBR can be also used as transmission grating for improved efficiency. Furthermore, more complex structures like monolithic master oscillator power amplifiers (MOPA), which show less spectral mode hops than DBR-RWLs, have been fabricated. The wide range of possible applications have different requirements on the emission characteristic of the used lasers. While the lasers can fulfill the requirements on the emission spectrum and the optical output power, the effects due to optical feedback from optical elements of the setup may limit their practical use in the respective application. Thus, it is of high importance to analyze the emission behavior of the different laser designs at various operation conditions with and without optical feedback. Here, the detailed investigation of the emission characteristics of lasers at an exemplary emission wavelength of 1120 nm is be presented.

Simultaneous frequency stabilization and high-power dense wavelength division multiplexing (HP-DWDM) using an external cavity based on volume Bragg gratings (VBGs)

NASA Astrophysics Data System (ADS)

Hengesbach, Stefan; Klein, Sarah; Holly, Carlo; Witte, Ulrich; Traub, Martin; Hoffmann, Dieter

2016-03-01

Multiplexing technologies enable the development of high-brightness diode lasers for direct industrial applications. We present a High-Power Dense Wavelength Division Multiplexer (HP-DWDM) with an average channel spacing of 1.7 (1.5) nm and a subsequent external cavity mirror to provide feedback for frequency stabilization and multiplexing in one step. The "self-optimizing" multiplexing unit consists of four reflective Volume Bragg Gratings (VBGs) with 99% diffraction efficiency and seven dielectric mirrors to overlay the radiation of five input channels with an adjustable channel spacing of 1-2 nm. In detail, we focus on the analysis of the overall optical efficiency, the change of the beam parameter product and the spectral width. The performance is demonstrated using five 90 μm multimode 9xx single emitters with M2<=17. Because of the feedback the lateral (multimodal) spatial and angular intensity distribution changes strongly and the beam parameter product decreases by a factor of 1.2 to 1.9. Thereby the angular intensity distribution is more affected than the width of the beam waist. The spectral width per emitter decreases to 3-200 pm (FWHM) depending on the injection current and the reflectance of the feedback mirror (0.75%, 1.5%, 4%, 6% or 8%). The overall optical multiplexing efficiency ranges between 77% and 86%. With some modifications (e.g. enhanced AR-coatings) we expect 90-95%.

Experimental and numerical study on refractive index sensors based on fibre Bragg gratings inscribed in multimode fibre

NASA Astrophysics Data System (ADS)

Filipe Kuhne, Jean; Rocha, Ana Maria; de Oliveira, Valmir; José Kalinowski, Hypolito; Canute Kamikawachi, Ricardo

2018-02-01

In this work is reported the experimental and numerical results of the refractive index response of etched fibre Bragg gratings written in a graded index multimode fibre. The responses of the modes coupled by the grating inscribed in a multimode fibre are compared with the mode coupled by a grating inscribed in single mode fibre. The results of this study show that the refractive index sensitivity and the dynamical range of etched fibre Bragg gratings written in multimode fibres are higher than the ones verified in single-mode fibres. The determination of oil-biodiesel blend concentrations are also compared as an example of practical applications. It is shown that a greater core diameter of the multimode fibre enables the Bragg gratings to exhibit enhanced sensitivity without requiring further fibre diameter reduction.

Multi-Stress Monitoring System with Fiber-Optic Mandrels and Fiber Bragg Grating Sensors in a Sagnac Loop

PubMed Central

Kim, Hyunjin; Sampath, Umesh; Song, Minho

2015-01-01

Fiber Bragg grating sensors are placed in a fiber-optic Sagnac loop to combine the grating temperature sensors and the fiber-optic mandrel acoustic emission sensors in single optical circuit. A wavelength-scanning fiber-optic laser is used as a common light source for both sensors. A fiber-optic attenuator is placed at a specific position in the Sagnac loop in order to separate buried Bragg wavelengths from the Sagnac interferometer output. The Bragg wavelength shifts are measured with scanning band-pass filter demodulation and the mandrel output is analyzed by applying a fast Fourier transform to the interference signal. This hybrid-scheme could greatly reduce the size and the complexity of optical circuitry and signal processing unit, making it suitable for low cost multi-stress monitoring of large scale power systems. PMID:26230700

Development of In-Fiber Reflective Bragg Gratings as Shear Stress Monitors in Aerodynamic Facilities

NASA Technical Reports Server (NTRS)

Parmar, Devendra S.; Sprinkle, Danny R.; Singh, Jag J.

1998-01-01

Bragg gratings centered at nominal wavelengths of 1290 nm and 1300 run were inscribed in a 9/125 microns germano-silicate optical fiber, using continuous wave frequency doubled Ar+ laser radiation at 244 nm. Such gratings have been used extensively as temperature and strain monitors in smart structures. They have, however, never been used for measuring aerodynamic shear stresses. As a test of their sensitivity as shear stress monitors, a Bragg fiber attached to a metal plate was subjected to laminar flows in a glass pipe. An easily measurable large flow-induced wavelength shift (Delta Lambda(sub B)) was observed in the Bragg reflected wavelength. Thereafter, the grating was calibrated by making one time, simultaneous measurements of Delta Lambda(sub B) and the coefficient of skin friction (C(sub f)) with a skin friction balance, as a function of flow rates in a subsonic wind tunnel. Onset of fan-induced transition in the tunnel flow provided a unique flow rate for correlating Delta Lambda(sub B) and (C(sub f) values needed for computing effective modulus of rigidity (N(sub eff)) of the fiber attached to the metal plate. This value Of N(sub eff) is expected to remain constant throughout the elastic stress range expected during the Bragg grating aerodynamic tests. It has been used for calculating the value of Cf at various tunnel speeds, on the basis of measured values of Bragg wavelength shifts at those speeds.

Improved Phase-Mask Fabrication of Fiber Bragg Gratings

NASA Technical Reports Server (NTRS)

Grant, Joseph; Wang, Ying; Sharma, Anup

2004-01-01

An improved method of fabrication of Bragg gratings in optical fibers combines the best features of two prior methods: one that involves the use of a phase mask and one that involves interference between the two coherent laser beams. The improved method affords flexibility for tailoring Bragg wavelengths and bandwidths over wide ranges. A Bragg grating in an optical fiber is a periodic longitudinal variation in the index of refraction of the fiber core. The spatial period (Bragg wavelength) is chosen to obtain enhanced reflection of light of a given wavelength that would otherwise propagate relatively unimpeded along the core. Optionally, the spatial period of the index modulation can be made to vary gradually along the grating (such a grating is said to be chirped ) in order to obtain enhanced reflection across a wavelength band, the width of which is determined by the difference between the maximum and minimum Bragg wavelengths. In the present method as in both prior methods, a Bragg grating is formed by exposing an optical fiber to an ultraviolet-light interference field. The Bragg grating coincides with the pattern of exposure of the fiber core to ultraviolet light; in other words, the Bragg grating coincides with the interference fringes. Hence, the problem of tailoring the Bragg wavelength and bandwidth is largely one of tailoring the interference pattern and the placement of the fiber in the interference pattern. In the prior two-beam interferometric method, a single laser beam is split into two beams, which are subsequently recombined to produce an interference pattern at the location of an optical fiber. In the prior phase-mask method, a phase mask is used to diffract a laser beam mainly into two first orders, the interference between which creates the pattern to which an optical fiber is exposed. The prior two-beam interferometric method offers the advantage that the period of the interference pattern can be adjusted to produce gratings over a wide range of Bragg wavelengths, but offers the disadvantage that success depends on precise alignment and high mechanical stability. The prior phase-mask method affords the advantages of compactness of equipment and relative insensitivity to both misalignment and vibration, but does not afford adjustability of the Bragg wavelength. The present method affords both the flexibility of the prior two-beam interferometric method and the compactness and stability of the prior phase-mask method. In this method (see figure), a laser beam propagating along the x axis is normally incident on a phase mask that lies in the (y,z) plane. The phase of light propagating through the mask is modulated with a spatial periodicity, p, along the y axis chosen to diffract the laser light primarily to first order at the angle . (The zero-order laser light propagating along the x axis can be used for alignment and thereafter suppressed during exposure of the fiber.) The diffracted light passes through a concave cylindrical lens, which converts the flat diffracted wave fronts to cylindrical ones, as though the light emanated from a line source. Then two parallel flat mirrors recombine the diffracted beams to form an interference field equivalent to that of two coherent line sources at positions A and B (virtual sources). The interference pattern is a known function of the parameters of the apparatus and of position (x,y) in the interference field. Hence, the tilt, wavelength, and chirp of the Bragg grating can be chosen through suitable adjustments of the apparatus and/or of the position and orientation of the optical fiber. In particular, the Bragg wavelength can be adjusted by moving the fiber along the x axis, and the bandwidth can be modified over a wide range by changing the fiber tilt angle or by moving the phase mask and/or the fiber. Alignment is easy because the zero-order beam defines the x axis. The interference is relatively stable and insensitive to the mechanical vibration because of the gh symmetry and compactness of the apparatus, the fixed positions of the mirrors and lens, and the consequent fixed positions of the two virtual line sources, which are independent of the translations of the phase mask and the laser relative to the lens.

Performance of a distributed simultaneous strain and temperature sensor based on a Fabry-Perot laser diode and a dual-stage FBG optical demultiplexer.

PubMed

Kim, Suhwan; Kwon, Hyungwoo; Yang, Injae; Lee, Seungho; Kim, Jeehyun; Kang, Shinwon

2013-11-12

A simultaneous strain and temperature measurement method using a Fabry-Perot laser diode (FP-LD) and a dual-stage fiber Bragg grating (FBG) optical demultiplexer was applied to a distributed sensor system based on Brillouin optical time domain reflectometry (BOTDR). By using a Kalman filter, we improved the performance of the FP-LD based OTDR, and decreased the noise using the dual-stage FBG optical demultiplexer. Applying the two developed components to the BOTDR system and using a temperature compensating algorithm, we successfully demonstrated the simultaneous measurement of strain and temperature distributions under various experimental conditions. The observed errors in the temperature and strain measured using the developed sensing system were 0.6 °C and 50 με, and the spatial resolution was 1 m, respectively.

Measurement of the top quark mass using template methods on dilepton events in p anti-p collisions at s**(1/2) = 1.96-TeV

DOE Office of Scientific and Technical Information (OSTI.GOV)

Abulencia, A.; Acosta, D.; Adelman, Jahred A.

2006-02-01

The authors describe a measurement of the top quark mass from events produced in p{bar p} collisions at a center-of-mass energy of 1.96 TeV, using the Collider Detector at Fermilab. They identify t{bar t} candidates where both W bosons from the top quarks decay into leptons (e{nu}, {mu}{nu}, or {tau}{nu}) from a data sample of 360 pb{sup -1}. The top quark mass is reconstructed in each event separately by three different methods, which draw upon simulated distributions of the neutrino pseudorapidity, t{bar t} longitudinal momentum, or neutrino azimuthal angle in order to extract probability distributions for the top quark mass.more » For each method, representative mass distributions, or templates, are constructed from simulated samples of signal and background events, and parameterized to form continuous probability density functions. A likelihood fit incorporating these parameterized templates is then performed on the data sample masses in order to derive a final top quark mass. Combining the three template methods, taking into account correlations in their statistical and systematic uncertainties, results in a top quark mass measurement of 170.1 {+-} 6.0(stat.) {+-} 4.1(syst.) GeV/c{sup 2}.« less

The fully differential top decay distribution

DOE Office of Scientific and Technical Information (OSTI.GOV)

Aguilar-Saavedra, J. A.; Boudreau, J.; Escobar, C.

We write down the four-dimensional fully differential decay distribution for the top quark decay t → Wb → ℓνb. We discuss how its eight physical parameters can be measured, either with a global fit or with the use of selected one-dimensional distributions and asymmetries. We give expressions for the top decay amplitudes for a general tbW interaction, and show how the untangled measurement of the two components of the fraction of longitudinal W bosons – those with b quark helicities of 1/2 and –1/2, respectively – could improve the precision of a global fit to the tbW vertex.

The fully differential top decay distribution

DOE PAGES

Aguilar-Saavedra, J. A.; Boudreau, J.; Escobar, C.; ...

2017-03-29

We write down the four-dimensional fully differential decay distribution for the top quark decay t → Wb → ℓνb. We discuss how its eight physical parameters can be measured, either with a global fit or with the use of selected one-dimensional distributions and asymmetries. We give expressions for the top decay amplitudes for a general tbW interaction, and show how the untangled measurement of the two components of the fraction of longitudinal W bosons – those with b quark helicities of 1/2 and –1/2, respectively – could improve the precision of a global fit to the tbW vertex.

Corrugated grating on organic multilayer Bragg reflector

NASA Astrophysics Data System (ADS)

Jaquet, Sylvain; Scharf, Toralf; Herzig, Hans Peter

2007-08-01

Polymeric multilayer Bragg structures are combined with diffractive gratings to produce artificial visual color effects. A particular effect is expected due to the angular reflection dependence of the multilayer Bragg structure and the dispersion caused by the grating. The combined effects can also be used to design particular filter functions and various resonant structures. The multilayer Bragg structure is fabricated by spin-coating of two different low-cost polymer materials in solution on a cleaned glass substrate. These polymers have a refractive index difference of about 0.15 and permit multilayer coatings without interlayer problems. Master gratings of different periods are realized by laser beam interference and replicated gratings are superimposed on the multilayer structure by soft embossing in a UV curing glue. The fabrication process requires only polymer materials. The obtained devices are stable and robust. Angular dependent reflection spectrums for the visible are measured. These results show that it is possible to obtain unexpected reflection effects. A rich variety of color spectra can be generated, which is not possible with a single grating. This can be explained by the coupling of transmission of grating orders and the Bragg reflection band. A simple model permits to explain some of the spectral vs angular dependence of reflected light.

Development of variable-magnification X-ray Bragg optics.

PubMed

Hirano, Keiichi; Yamashita, Yoshiki; Takahashi, Yumiko; Sugiyama, Hiroshi

2015-07-01

A novel X-ray Bragg optics is proposed for variable-magnification of an X-ray beam. This X-ray Bragg optics is composed of two magnifiers in a crossed arrangement, and the magnification factor, M, is controlled through the azimuth angle of each magnifier. The basic properties of the X-ray optics such as the magnification factor, image transformation matrix and intrinsic acceptance angle are described based on the dynamical theory of X-ray diffraction. The feasibility of the variable-magnification X-ray Bragg optics was verified at the vertical-wiggler beamline BL-14B of the Photon Factory. For X-ray Bragg magnifiers, Si(220) crystals with an asymmetric angle of 14° were used. The magnification factor was calculated to be tunable between 0.1 and 10.0 at a wavelength of 0.112 nm. At various magnification factors (M ≥ 1.0), X-ray images of a nylon mesh were observed with an air-cooled X-ray CCD camera. Image deformation caused by the optics could be corrected by using a 2 × 2 transformation matrix and bilinear interpolation method. Not only absorption-contrast but also edge-contrast due to Fresnel diffraction was observed in the magnified images.

Frequency shift of the Bragg and Non-Bragg backscattering from periodic water wave

NASA Astrophysics Data System (ADS)

Wen, Biyang; Li, Ke

2016-08-01

Doppler effect is used to measure the relative speed of a moving target with respect to the radar, and is also used to interpret the frequency shift of the backscattering from the ocean wave according to the water-wave phase velocity. The widely known relationship between the Doppler shift and the water-wave phase velocity was deduced from the scattering measurements data collected from actual sea surface, and has not been verified under man-made conditions. Here we show that this ob- served frequency shift of the scattering data from the Bragg and Non-Bragg water wave is not the Doppler shift corresponding to the water-wave phase velocity as commonly believed, but is the water-wave frequency and its integral multiple frequency. The power spectrum of the backscatter from the periodic water wave consists of serials discrete peaks, which is equally spaced by water wave frequency. Only when the water-wave length is the integer multiples of the Bragg wave, and the radar range resolution is infinite, does the frequency shift of the backscattering mathematically equal the Doppler shift according to the water-wave phase velocity.

Further Improvement of the RITS Code for Pulsed Neutron Bragg-edge Transmission Imaging

NASA Astrophysics Data System (ADS)

Sato, H.; Watanabe, K.; Kiyokawa, K.; Kiyanagi, R.; Hara, K. Y.; Kamiyama, T.; Furusaka, M.; Shinohara, T.; Kiyanagi, Y.

The RITS code is a unique and powerful tool for a whole Bragg-edge transmission spectrum fitting analysis. However, it has had two major problems. Therefore, we have proposed methods to overcome these problems. The first issue is the difference in the crystallite size values between the diffraction and the Bragg-edge analyses. We found the reason was a different definition of the crystal structure factor. It affects the crystallite size because the crystallite size is deduced from the primary extinction effect which depends on the crystal structure factor. As a result of algorithm change, crystallite sizes obtained by RITS drastically approached to crystallite sizes obtained by Rietveld analyses of diffraction data; from 155% to 110%. The second issue is correction of the effect of background neutrons scattered from a specimen. Through neutron transport simulation studies, we found that the background components consist of forward Bragg scattering, double backward Bragg scattering, and thermal diffuse scattering. RITS with the background correction function which was developed through the simulation studies could well reconstruct various simulated and experimental transmission spectra, but refined crystalline microstructural parameters were often distorted. Finally, it was recommended to reduce the background by improving experimental conditions.

Shock absorption ability of laminate mouth guards in two different malocclusions using fiber Bragg grating (FBG) sensor.

PubMed

Bhalla, Ashish; Grewal, Navneet; Tiwari, Umesh; Mishra, Vandana; Mehla, Nahar Singh; Raviprakash, Suryanarain; Kapur, Pawan

2013-06-01

The majority of orofacial injuries affect the upper jaw, with the maxillary incisors being most prone to injury, often accounting for as many as 80% of all cases. Children with malocclusion in the anterior segment of the maxilla are more prone to traumatic injuries than those exhibiting normal occlusion, because most often the damaging force impacts directly against the maxillary anterior teeth. Hence, because of the difference of dissipation of the impact force because of the presence or absence of malocclusion, the mouthguard's shock absorption capacity would be influenced by certain factors. In the present study, a unique in vitro experiment utilizing fiber Bragg Grating (FBG) as distributed strain sensors was carried out to evaluate the shock absorption ability of laminate customized mouthguards in two different malocclusions compared with normal occlusion. The impact was produced using a customized pendulum device with three interchangeable impact objects on typhodont models with two different malocclusions and normal occlusion from different heights. Response of gratings was monitored using an optical spectrum analyzer. Strain induced because each impact was determined from the Bragg's wavelength shifts for each grating. For every model, 12 impact strikes were measured using three different impact objects on the two specified sites by releasing the object from two different heights. The laminated mouthguards showed significant variation in shock absorption ability when different malocclusions were compared. Hence, modifications in the original design of the laminated mouthguards should be considered for athletic competitors with malocclusion to provide adequate protection against impact. FBG sensor has shown the unique advantage of high sensitivity to strain measurement and can be used in further studies. The height of the impact is an important variable in determining the shock absorption ability of mouthguards. © 2012 John Wiley & Sons A/S.

Structural characterization of the phospholipid stabilizer layer at the solid-liquid interface of dispersed triglyceride nanocrystals with small-angle x-ray and neutron scattering

NASA Astrophysics Data System (ADS)

Schmiele, Martin; Schindler, Torben; Unruh, Tobias; Busch, Sebastian; Morhenn, Humphrey; Westermann, Martin; Steiniger, Frank; Radulescu, Aurel; Lindner, Peter; Schweins, Ralf; Boesecke, Peter

2013-06-01

Dispersions of crystalline nanoparticles with at least one sufficiently large unit cell dimension can give rise to Bragg reflections in the small-angle scattering range. If the nanocrystals possess only a small number of unit cells along these particular crystallographic directions, the corresponding Bragg reflections will be broadened. In a previous study of phospholipid stabilized dispersions of β-tripalmitin platelets [Unruh, J. Appl. Crystallogr.JACGAR0021-889810.1107/S0021889807044378 40, 1008 (2007)], the x-ray powder pattern simulation analysis (XPPSA) was developed. The XPPSA method facilitates the interpretation of the rather complicated small-angle x-ray scattering (SAXS) curves of such dispersions of nanocrystals. The XPPSA method yields the distribution function of the platelet thicknesses and facilitates a structural characterization of the phospholipid stabilizer layer at the solid-liquid interface between the nanocrystals and the dispersion medium from the shape of the broadened 001 Bragg reflection. In this contribution an improved and extended version of the XPPSA method is presented. The SAXS and small-angle neutron scattering patterns of dilute phospholipid stabilized tripalmitin dispersions can be reproduced on the basis of a consistent simulation model for the particles and their phospholipid stabilizer layer on an absolute scale. The results indicate a surprisingly flat arrangement of the phospholipid molecules in the stabilizer layer with a total thickness of only 12 Å. The stabilizer layer can be modeled by an inner shell for the fatty acid chains and an outer shell including the head groups and additional water. The experiments support a dense packing of the phospholipid molecules on the nanocrystal surfaces rather than isolated phospholipid domains.

Single-longitudinal mode distributed-feedback fiber laser with low-threshold and high-efficiency

NASA Astrophysics Data System (ADS)

Jiang, Man; Zhou, Pu; Gu, Xijia

2018-01-01

Single-frequency fiber laser has attracted a lot of interest in recent years due to its numerous application potentials in telecommunications, LIDAR, high resolution sensing, atom frequency standard, etc. Phosphate glass fiber is one of the candidates for building compact high gain fiber lasers because of its capability of high-concentration of rare-earth ions doping in fiber core. Nevertheless, it is challenging for the integration of UV-written intra-core fiber Bragg gratings into the fiber laser cavity due to the low photosensitivity of phosphate glass fiber. The research presented in this paper will focus on demonstration of UV-written Bragg gratings in phosphate glass fiber and its application in direct-written short monolithic single-frequency fiber lasers. Strong π-phase shift Bragg grating structure is direct-inscribed into the Er/Yb co-doped gain fiber using an excimer laser, and a 5-cm-long phase mask is used to inscribe a laser cavity into the Er/Yb co-doped phosphate glass fibers. The phase mask is a uniform mask with a 50 μm gap in the middle. The fiber laser device emits output power of 10.44 mW with a slope efficiency of 21.5% and the threshold power is about 42.8 mW. Single-longitudinal mode operation is validated by radio frequency spectrum measurement. Moreover, the output spectrum at the highest power shows an excellent optical signal to noise ratio of about 70 dB. These results, to the best of our knowledge, show the lowest power threshold and highest efficiency among the reports that using the same structure to achieve single-longitudinal mode laser output.

Quasi-interferometric scheme improved by fiber Bragg grating written on macrostructure defect in silica multimode optical fiber operating in a few-mode regime

NASA Astrophysics Data System (ADS)

Evtushenko, Alexander S.; Faskhutdinov, Lenar M.; Kafarova, Anastasia M.; Kuznetzov, Artem A.; Minaeva, Alina Yu.; Sevruk, Nikita L.; Nureev, Ilnur I.; Vasilets, Alexander A.; Andreev, Vladimir A.; Morozov, Oleg G.; Burdin, Vladimir A.; Bourdine, Anton V.

2017-04-01

This work presents results of experimental approbation of earlier on proposed modified fiber optic stress sensor based on a few-mode effects occurring during laser-excited optical signal propagation over silica multimode optical fiber (MMF). Modification is concerned with a passage to quasi-interferometric scheme realized by two multimode Y-couplers with equalized arm lengths improved by fiber Bragg grating (FBG) written on preliminary formed precision macrostructure defects in silica multimode graded-index optical fibers and special offset launching conditions providing laser-based excitation of higher-order modes. The "arms" of quasi-interferometer are two equalized lengths of MMF Cat. OM2 with great central dip of refractive index profile and strong pulse splitting due to high differential mode delay (DMD). We tested FBGs with Bragg wavelength both 1310 nm and 1550 nm written over tapers or up-tapers preliminary formed in short pieces of MMF Cat. OM2+/OM3 and further jointed to the end of one of the arms before output Y-coupler. Researches were focused on comparison analysis of pulse responses under changing of selected excited mode mixing and power diffusion processes due to stress distributed action to sensor fiber depending. Here we considered FBGs not only as particular wavelength reflector during spectral response measurement but also as local periodic microstructure defect which strongly effects on few-mode signal components mixing process also improved by combination with macro-defect like taper or up-taper that should provide response variation. Some results pulse response measurements produced for different scheme configuration and their comparison analysis are represented.

Measurements of top quark properties in top pair production and decay at the LHC using the CMS detector

DOE PAGES

Jindariani, Sergo

2016-05-31

Measurements are presented of the properties of top quarks in pair production and decay from proton-proton collisions at the LHC. The data were collected at centre-of-mass energies of 7 and 8 TeV by the CMS experiment during the years 2011 and 2012. The top quark-antiquark charge asymmetry is measured using the difference of the absolute rapidities of the reconstructed top and anti-top kinematics, as well as from distributions of the top quark decay products. The measurements are performed in the decay channels of the tt¯ pair into both one and two leptons in the final state. The polarization of topmore » quarks and top pair spin correlations are measured from the angular distributions of top quark decay products. The W-boson helicity fractions and angular asymmetries are extracted and limits on anomalous contributions to the Wtb vertex are determined. The flavor content in top-quark pair events is measured using the fraction of top quarks decaying into a W-boson and a b -quark relative to all top quark decays, R=B(t→Wb)/B(t→Wq) , and the result is used to determine the CKM matrix element Vtb as well as the width of the top quark resonance. Finally, all of the results are found to be in good agreement with standard model predictions.« less

Diameter measurement of optical nanofiber based on high-order Bragg reflections using a ruled grating.

PubMed

Zhu, Ming; Wang, Yao-Ting; Sun, Yi-Zhi; Zhang, Lijian; Ding, Wei

2018-02-01

A convenient method using a commercially available ruled grating for precise and overall diameter measurement of optical nanofibers (ONFs) is presented. We form a composite Bragg reflector with a micronscale period by dissolving aluminum coating, slicing the grating along ruling lines, and mounting it on an ONF. The resonant wavelengths of high-order Bragg reflections possess fiber diameter dependence, enabling nondestructive measurement of the ONF diameter profile. This method provides an easy and economic diagnostic tool for wide varieties of ONF-based applications.

Strain measurements by fiber Bragg grating sensors for in situ pile loading tests

NASA Astrophysics Data System (ADS)

Schmidt-Hattenberger, Cornelia; Straub, Tilmann; Naumann, Marcel; Borm, Günter; Lauerer, Robert; Beck, Christoph; Schwarz, Wolfgang

2003-07-01

A fiber Bragg grating (FBG) sensor network has been installed into a large diameter concrete pile on a real construction site. The intention was to monitor its deformation behavior during several quasi-static loading cycles. The skin friction between pile and subsoil affecting the ultimate bearing capacity of the pile as well as the settlement behavior of the structure under investigation has been derived from our measurements. A comparison between the results of the fiber Bragg grating sensors and conventional concrete strain gages (CSG) has shown excellent correspondence.

Arrays of Regenerated Fiber Bragg Gratings in Non-Hydrogen-Loaded Photosensitive Fibers for High-Temperature Sensor Networks

PubMed Central

Lindner, Eric; Chojetztki, Christoph; Brueckner, Sven; Becker, Martin; Rothhardt, Manfred; Vlekken, Johan; Bartelt, Hartmut

2009-01-01

We report about the possibility of using regenerated fiber Bragg gratings generated in photosensitive fibers without applying hydrogen loading for high temperature sensor networks. We use a thermally induced regenerative process which leads to a secondary increase in grating reflectivity. This refractive index modification has shown to become more stable after the regeneration up to temperatures of 600 °C. With the use of an interferometric writing technique, it is possible also to generate arrays of regenerated fiber Bragg gratings for sensor networks. PMID:22408510

Electro-optical tunable waveguide embedded multiscan Bragg gratings in lithium niobate by direct femtosecond laser writing.

PubMed

Kroesen, Sebastian; Horn, Wolfgang; Imbrock, Jörg; Denz, Cornelia

2014-09-22

optical tunable Bragg gratings in lithium niobate fabricated by direct femtosecond laser writing. The hybrid design that consists of a circular type-II waveguide and a multiscan type-I Bragg grating exhibits low loss ordinary and extraordinary polarized guiding as well as narrowband reflections in the c-band of optical communications. High bandwidth tunability of more than a peak width and nearly preserved electro-optic coefficients of r(13) = 7.59 pm V(-1) and r(33) = 23.21 pm V(-1) are demonstrated.

A lithium niobate electro-optic tunable Bragg filter fabricated by electron beam lithography

NASA Astrophysics Data System (ADS)

Pierno, L.; Dispenza, M.; Secchi, A.; Fiorello, A.; Foglietti, V.

2008-06-01

We have designed and fabricated a lithium niobate tunable Bragg filter patterned by electron beam lithography and etched by reactive ion etching. Devices with 1 mm, 2 mm and 4 mm length and 360 and 1080 nm Bragg period, with 5 pm V-1 tuning efficiency, have been characterized. Some applications were identified. Optical simulation based on finite element model (FEM) software showing the optical filtering curve and the coupling factor dependence on the manufacturing parameter is reported. The tuning of the filter window position is electro-optically controlled.

The Harp probe - An in situ Bragg scattering sensor

NASA Technical Reports Server (NTRS)

Mollo-Christensen, E.; Huang, N. E.; Long, S. R.; Bliven, L. F.

1984-01-01

A wave sensor, consisting of parallel, evenly spaced capacitance wires, whose output is the sum of the water surface deflections at the wires, has been built and tested in a wave tank. The probe output simulates Bragg scattering of electromagnetic waves from a water surface with waves; it can be used to simulate electromagnetic probing of the sea surface by radar. The study establishes that the wave probe, called the 'Harp' for short, will simulate Bragg scattering and that it can also be used to study nonlinear wave processes.

Framework for three-dimensional coherent diffraction imaging by focused beam x-ray Bragg ptychography.

PubMed

Hruszkewycz, Stephan O; Holt, Martin V; Tripathi, Ash; Maser, Jörg; Fuoss, Paul H

2011-06-15

We present the framework for convergent beam Bragg ptychography, and, using simulations, we demonstrate that nanocrystals can be ptychographically reconstructed from highly convergent x-ray Bragg diffraction. The ptychographic iterative engine is extended to three dimensions and shown to successfully reconstruct a simulated nanocrystal using overlapping raster scans with a defocused curved beam, the diameter of which matches the crystal size. This object reconstruction strategy can serve as the basis for coherent diffraction imaging experiments at coherent scanning nanoprobe x-ray sources.

Precision top-quark mass measurement at CDF.

PubMed

Aaltonen, T; Alvarez González, B; Amerio, S; Amidei, D; Anastassov, A; Annovi, A; Antos, J; Apollinari, G; Appel, J A; Arisawa, T; Artikov, A; Asaadi, J; Ashmanskas, W; Auerbach, B; Aurisano, A; Azfar, F; Badgett, W; Bae, T; Barbaro-Galtieri, A; Barnes, V E; Barnett, B A; Barria, P; Bartos, P; Bauce, M; Bedeschi, F; Behari, S; Bellettini, G; Bellinger, J; Benjamin, D; Beretvas, A; Bhatti, A; Bisello, D; Bizjak, I; Bland, K R; Blumenfeld, B; Bocci, A; Bodek, A; Bortoletto, D; Boudreau, J; Boveia, A; Brigliadori, L; Bromberg, C; Brucken, E; Budagov, J; Budd, H S; Burkett, K; Busetto, G; Bussey, P; Buzatu, A; Calamba, A; Calancha, C; Camarda, S; Campanelli, M; Campbell, M; Canelli, F; Carls, B; Carlsmith, D; Carosi, R; Carrillo, S; Carron, S; Casal, B; Casarsa, M; Castro, A; Catastini, P; Cauz, D; Cavaliere, V; Cavalli-Sforza, M; Cerri, A; Cerrito, L; Chen, Y C; Chertok, M; Chiarelli, G; Chlachidze, G; Chlebana, F; Cho, K; Chokheli, D; Chung, W H; Chung, Y S; Ciocci, M A; Clark, A; Clarke, C; Compostella, G; Convery, M E; Conway, J; Corbo, M; Cordelli, M; Cox, C A; Cox, D J; Crescioli, F; Cuevas, J; Culbertson, R; Dagenhart, D; d'Ascenzo, N; Datta, M; de Barbaro, P; Dell'Orso, M; Demortier, L; Deninno, M; Devoto, F; d'Errico, M; Di Canto, A; Di Ruzza, B; Dittmann, J R; D'Onofrio, M; Donati, S; Dong, P; Dorigo, M; Dorigo, T; Ebina, K; Elagin, A; Eppig, A; Erbacher, R; Errede, S; Ershaidat, N; Eusebi, R; Farrington, S; Feindt, M; Fernandez, J P; Field, R; Flanagan, G; Forrest, R; Frank, M J; Franklin, M; Freeman, J C; Funakoshi, Y; Furic, I; Gallinaro, M; Garcia, J E; Garfinkel, A F; Garosi, P; Gerberich, H; Gerchtein, E; Giagu, S; Giakoumopoulou, V; Giannetti, P; Gibson, K; Ginsburg, C M; Giokaris, N; Giromini, P; Giurgiu, G; Glagolev, V; Glenzinski, D; Gold, M; Goldin, D; Goldschmidt, N; Golossanov, A; Gomez, G; Gomez-Ceballos, G; Goncharov, M; González, O; Gorelov, I; Goshaw, A T; Goulianos, K; Grinstein, S; Grosso-Pilcher, C; Group, R C; Guimaraes da Costa, J; Hahn, S R; Halkiadakis, E; Hamaguchi, A; Han, J Y; Happacher, F; Hara, K; Hare, D; Hare, M; Harr, R F; Hatakeyama, K; Hays, C; Heck, M; Heinrich, J; Herndon, M; Hewamanage, S; Hocker, A; Hopkins, W; Horn, D; Hou, S; Hughes, R E; Hurwitz, M; Husemann, U; Hussain, N; Hussein, M; Huston, J; Introzzi, G; Iori, M; Ivanov, A; James, E; Jang, D; Jayatilaka, B; Jeon, E J; Jindariani, S; Jones, M; Joo, K K; Jun, S Y; Junk, T R; Kamon, T; Karchin, P E; Kasmi, A; Kato, Y; Ketchum, W; Keung, J; Khotilovich, V; Kilminster, B; Kim, D H; Kim, H S; Kim, J E; Kim, M J; Kim, S B; Kim, S H; Kim, Y K; Kim, Y J; Kimura, N; Kirby, M; Klimenko, S; Knoepfel, K; Kondo, K; Kong, D J; Konigsberg, J; Kotwal, A V; Kreps, M; Kroll, J; Krop, D; Kruse, M; Krutelyov, V; Kuhr, T; Kurata, M; Kwang, S; Laasanen, A T; Lami, S; Lammel, S; Lancaster, M; Lander, R L; Lannon, K; Lath, A; Latino, G; LeCompte, T; Lee, E; Lee, H S; Lee, J S; Lee, S W; Leo, S; Leone, S; Lewis, J D; Limosani, A; Lin, C-J; Lindgren, M; Lipeles, E; Lister, A; Litvintsev, D O; Liu, C; Liu, H; Liu, Q; Liu, T; Lockwitz, S; Loginov, A; Lucchesi, D; Lueck, J; Lujan, P; Lukens, P; Lungu, G; Lys, J; Lysak, R; Madrak, R; Maeshima, K; Maestro, P; Malik, S; Manca, G; Manousakis-Katsikakis, A; Margaroli, F; Marino, C; Martínez, M; Mastrandrea, P; Matera, K; Mattson, M E; Mazzacane, A; Mazzanti, P; McFarland, K S; McIntyre, P; McNulty, R; Mehta, A; Mehtala, P; Mesropian, C; Miao, T; Mietlicki, D; Mitra, A; Miyake, H; Moed, S; Moggi, N; Mondragon, M N; Moon, C S; Moore, R; Morello, M J; Morlock, J; Movilla Fernandez, P; Mukherjee, A; Muller, Th; Murat, P; Mussini, M; Nachtman, J; Nagai, Y; Naganoma, J; Nakano, I; Napier, A; Nett, J; Neu, C; Neubauer, M S; Nielsen, J; Nodulman, L; Noh, S Y; Norniella, O; Oakes, L; Oh, S H; Oh, Y D; Oksuzian, I; Okusawa, T; Orava, R; Ortolan, L; Pagan Griso, S; Pagliarone, C; Palencia, E; Papadimitriou, V; Paramonov, A A; Patrick, J; Pauletta, G; Paulini, M; Paus, C; Pellett, D E; Penzo, A; Phillips, T J; Piacentino, G; Pianori, E; Pilot, J; Pitts, K; Plager, C; Pondrom, L; Poprocki, S; Potamianos, K; Prokoshin, F; Pranko, A; Ptohos, F; Punzi, G; Rahaman, A; Ramakrishnan, V; Ranjan, N; Redondo, I; Renton, P; Rescigno, M; Riddick, T; Rimondi, F; Ristori, L; Robson, A; Rodrigo, T; Rodriguez, T; Rogers, E; Rolli, S; Roser, R; Ruffini, F; Ruiz, A; Russ, J; Rusu, V; Safonov, A; Sakumoto, W K; Sakurai, Y; Santi, L; Sato, K; Saveliev, V; Savoy-Navarro, A; Schlabach, P; Schmidt, A; Schmidt, E E; Schwarz, T; Scodellaro, L; Scribano, A; Scuri, F; Seidel, S; Seiya, Y; Semenov, A; Sforza, F; Shalhout, S Z; Shears, T; Shepard, P F; Shimojima, M; Shochet, M; Shreyber-Tecker, I; Simonenko, A; Sinervo, P; Sliwa, K; Smith, J R; Snider, F D; Soha, A; Sorin, V; Song, H; Squillacioti, P; Stancari, M; St Denis, R; Stelzer, B; Stelzer-Chilton, O; Stentz, D; Strologas, J; Strycker, G L; Sudo, Y; Sukhanov, A; Suslov, I; Takemasa, K; Takeuchi, Y; Tang, J; Tecchio, M; Teng, P K; Thom, J; Thome, J; Thompson, G A; Thomson, E; Toback, D; Tokar, S; Tollefson, K; Tomura, T; Tonelli, D; Torre, S; Torretta, D; Totaro, P; Trovato, M; Ukegawa, F; Uozumi, S; Varganov, A; Vázquez, F; Velev, G; Vellidis, C; Vidal, M; Vila, I; Vilar, R; Vizán, J; Vogel, M; Volpi, G; Wagner, P; Wagner, R L; Wakisaka, T; Wallny, R; Wang, S M; Warburton, A; Waters, D; Wester, W C; Whiteson, D; Wicklund, A B; Wicklund, E; Wilbur, S; Wick, F; Williams, H H; Wilson, J S; Wilson, P; Winer, B L; Wittich, P; Wolbers, S; Wolfe, H; Wright, T; Wu, X; Wu, Z; Yamamoto, K; Yamato, D; Yang, T; Yang, U K; Yang, Y C; Yao, W-M; Yeh, G P; Yi, K; Yoh, J; Yorita, K; Yoshida, T; Yu, G B; Yu, I; Yu, S S; Yun, J C; Zanetti, A; Zeng, Y; Zhou, C; Zucchelli, S

2012-10-12

We present a precision measurement of the top-quark mass using the full sample of Tevatron √s = 1.96 TeV proton-antiproton collisions collected by the CDF II detector, corresponding to an integrated luminosity of 8.7 fb(-1). Using a sample of tt¯ candidate events decaying into the lepton+jets channel, we obtain distributions of the top-quark masses and the invariant mass of two jets from the W boson decays from data. We then compare these distributions to templates derived from signal and background samples to extract the top-quark mass and the energy scale of the calorimeter jets with in situ calibration. The likelihood fit of the templates from signal and background events to the data yields the single most-precise measurement of the top-quark mass, M(top)=172.85±0.71(stat)±0.85(syst) GeV/c(2).

20 Gbit/s error free transmission with ~850 nm GaAs-based vertical cavity surface emitting lasers (VCSELs) containing InAs-GaAs submonolayer quantum dot insertions

NASA Astrophysics Data System (ADS)

Lott, J. A.; Shchukin, V. A.; Ledentsov, N. N.; Stinz, A.; Hopfer, F.; Mutig, A.; Fiol, G.; Bimberg, D.; Blokhin, S. A.; Karachinsky, L. Y.; Novikov, I. I.; Maximov, M. V.; Zakharov, N. D.; Werner, P.

2009-02-01

We report on the modeling, epitaxial growth, fabrication, and characterization of 830-845 nm vertical cavity surface emitting lasers (VCSELs) that employ InAs-GaAs quantum dot (QD) gain elements. The GaAs-based VCSELs are essentially conventional in design, grown by solid-source molecular beam epitaxy, and include top and bottom gradedheterointerface AlGaAs distributed Bragg reflectors, a single selectively-oxidized AlAs waveguiding/current funneling aperture layer, and a quasi-antiwaveguiding microcavity. The active region consists of three sheets of InAs-GaAs submonolayer insertions separated by AlGaAs matrix layers. Compared to QWs the InAs-GaAs insertions are expected to offer higher exciton-dominated modal gain and improved carrier capture and retention, thus resulting in superior temperature stability and resilience to degradation caused by operating at the larger switching currents commonly employed to increase the data rates of modern optical communication systems. We investigate the robustness and temperature performance of our QD VCSEL design by fabricating prototype devices in a high-frequency ground-sourceground contact pad configuration suitable for on-wafer probing. Arrays of VCSELs are produced with precise variations in top mesa diameter from 24 to 36 μm and oxide aperture diameter from 1 to 12 μm resulting in VCSELs that operate in full single-mode, single-mode to multi-mode, and full multi-mode regimes. The single-mode QD VCSELs have room temperature threshold currents below 0.5 mA and peak output powers near 1 mW, whereas the corresponding values for full multi-mode devices range from about 0.5 to 1.5 mA and 2.5 to 5 mW. At 20°C we observe optical transmission at 20 Gb/s through 150 m of OM3 fiber with a bit error ratio better than 10-12, thus demonstrating the great potential of our QD VCSELs for applications in next-generation short-distance optical data communications and interconnect systems.

Bragg gratings: Optical microchip sensors

NASA Astrophysics Data System (ADS)

Watts, Sam

2010-07-01

A direct UV writing technique that can create multiple Bragg gratings and waveguides in a planar silica-on-silicon chip is enabling sensing applications ranging from individual disposable sensors for biotechnology through to multiplexed sensor networks in pharmaceutical manufacturing.

Self-Evaluation of PANDA-FBG Based Sensing System for Dynamic Distributed Strain and Temperature Measurement.

PubMed

Zhu, Mengshi; Murayama, Hideaki; Wada, Daichi

2017-10-12

A novel method is introduced in this work for effectively evaluating the performance of the PANDA type polarization-maintaining fiber Bragg grating (PANDA-FBG) distributed dynamic strain and temperature sensing system. Conventionally, the errors during the measurement are unknown or evaluated by using other sensors such as strain gauge and thermocouples. This will make the sensing system complicated and decrease the efficiency since more than one kind of sensor is applied for the same measurand. In this study, we used the approximately constant ratio of primary errors in strain and temperature measurement and realized the self-evaluation of the sensing system, which can significantly enhance the applicability, as well as the reliability in strategy making.

Distributed fiber sensing system with wide frequency response and accurate location

NASA Astrophysics Data System (ADS)

Shi, Yi; Feng, Hao; Zeng, Zhoumo

2016-02-01

A distributed fiber sensing system merging Mach-Zehnder interferometer and phase-sensitive optical time domain reflectometer (Φ-OTDR) is demonstrated for vibration measurement, which requires wide frequency response and accurate location. Two narrow line-width lasers with delicately different wavelengths are used to constitute the interferometer and reflectometer respectively. A narrow band Fiber Bragg Grating is responsible for separating the two wavelengths. In addition, heterodyne detection is applied to maintain the signal to noise rate of the locating signal. Experiment results show that the novel system has a wide frequency from 1 Hz to 50 MHz, limited by the sample frequency of data acquisition card, and a spatial resolution of 20 m, according to 200 ns pulse width, along 2.5 km fiber link.

Quantum dash based single section mode locked lasers for photonic integrated circuits.

PubMed

Joshi, Siddharth; Calò, Cosimo; Chimot, Nicolas; Radziunas, Mindaugas; Arkhipov, Rostislav; Barbet, Sophie; Accard, Alain; Ramdane, Abderrahim; Lelarge, Francois

2014-05-05

We present the first demonstration of an InAs/InP Quantum Dash based single-section frequency comb generator designed for use in photonic integrated circuits (PICs). The laser cavity is closed using a specifically designed Bragg reflector without compromising the mode-locking performance of the self pulsating laser. This enables the integration of single-section mode-locked laser in photonic integrated circuits as on-chip frequency comb generators. We also investigate the relations between cavity modes in such a device and demonstrate how the dispersion of the complex mode frequencies induced by the Bragg grating implies a violation of the equi-distance between the adjacent mode frequencies and, therefore, forbids the locking of the modes in a classical Bragg Device. Finally we integrate such a Bragg Mirror based laser with Semiconductor Optical Amplifier (SOA) to demonstrate the monolithic integration of QDash based low phase noise sources in PICs.

Femtosecond laser-inscribed fiber Bragg gratings for strain monitoring in power cables of offshore wind turbines.

PubMed

Burgmeier, Jörg; Schippers, Wolfgang; Emde, Nico; Funken, Peter; Schade, Wolfgang

2011-05-01

A fiber Bragg grating sensor system used for monitoring the effects of strain on the power cable of an offshore wind turbine is presented. The Bragg grating structure was inscribed into coated nonphotosensitive standard telecommunication fibers using an IR femtosecond laser and the point-by-point writing technique. Because of the presence of the protective coating of the fiber, the mechanical stability of the resultant sensor device is better than that of a sensor consisting of a bare fiber. A system containing this sensing element was to our knowledge for the first time successfully installed and tested in an offshore wind turbine prototype (REpower 6M, REpower Systems, AG, Germany) in February 2010, near Ellhöft (Germany). The fabrication process of the fiber Bragg gratings, measurement results of the online monitoring, and a comparison between the sensor signal and commonly used sensing techniques are presented.

A Bragg beam splitter for hard x-ray free-electron lasers.

PubMed

Osaka, Taito; Yabashi, Makina; Sano, Yasuhisa; Tono, Kensuke; Inubushi, Yuichi; Sato, Takahiro; Matsuyama, Satoshi; Ishikawa, Tetsuya; Yamauchi, Kazuto

2013-02-11

We report a Bragg beam splitter developed for utilization of hard x-ray free-electron lasers. The splitter is based on an ultrathin silicon crystal operating in the symmetric Bragg geometry to provide high reflectivity and transmissivity simultaneously. We fabricated frame-shaped Si(511) and (110) crystals with thicknesses below 10 μm by a reactive dry etching method using atmospheric-pressure plasma. The thickness variation over an illuminated area is less than 300 nm peak-to-valley. High crystalline perfection was verified by topographic and diffractometric measurements. The crystal thickness was evaluated from the period of the Pendellösung beats measured with a highly monochromatic and collimated x-ray probe. The crystals provide two replica pulses with uniform wavefront [(<1/50)λ] and low spatial intensity variation (<5%). These Bragg beam splitters will play an important role in innovating XFEL applications.

A fully reconfigurable waveguide Bragg grating for programmable photonic signal processing.

PubMed

Zhang, Weifeng; Yao, Jianping

2018-04-11

Since the discovery of the Bragg's law in 1913, Bragg gratings have become important optical devices and have been extensively used in various systems. In particular, the successful inscription of a Bragg grating in a fiber core has significantly boosted its engineering applications. However, a conventional grating device is usually designed for a particular use, which limits general-purpose applications since its index modulation profile is fixed after fabrication. In this article, we propose to implement a fully reconfigurable grating, which is fast and electrically reconfigurable by field programming. The concept is verified by fabricating an integrated grating on a silicon-on-insulator platform, which is employed as a programmable signal processor to perform multiple signal processing functions including temporal differentiation, microwave time delay, and frequency identification. The availability of ultrafast and reconfigurable gratings opens new avenues for programmable optical signal processing at the speed of light.

Fabrication of Fiber-Optic Tilted Bragg Grating Filter in 40 nm Range with A Single Phase Mask

NASA Technical Reports Server (NTRS)

Grant, Joseph; Wang, Y.; Sharma, A.; Burdine, Robert V. (Technical Monitor)

2002-01-01

Fiber-optic Bragg grating filters are fabricated with a range of Bragg wavelength between 1296 and 1336 nm, using a single phase mask. 30 mW of continuous-wave light at 244 nm is used from a frequency-doubled argon-ion laser having an intracavity etalon. Gratings are fabricated by tilting the photosensitive fiber with respect to the phase mask up to an angle of 15 degrees. The variation of Bragg wavelength with the fiber-tilt is explained with a simple formula. High spatial coherence of 244 nm light makes it possible to displace the fiber as much as 6 mm in front of the phase mask and tilt the fiber by as much as 15 degrees. This results in nearly constant band-width and near 100% reflectively for all gratings throughout the 40 nm range.

Dynamical effects in Bragg coherent x-ray diffraction imaging of finite crystals

NASA Astrophysics Data System (ADS)

Shabalin, A. G.; Yefanov, O. M.; Nosik, V. L.; Bushuev, V. A.; Vartanyants, I. A.

2017-08-01

We present simulations of Bragg coherent x-ray diffractive imaging (CXDI) data from finite crystals in the frame of the dynamical theory of x-ray diffraction. The developed approach is based on a numerical solution of modified Takagi-Taupin equations and can be applied for modeling of a broad range of x-ray diffraction experiments with finite three-dimensional crystals of arbitrary shape also in the presence of strain. We performed simulations for nanocrystals of a cubic and hemispherical shape of different sizes and provided a detailed analysis of artifacts in the Bragg CXDI reconstructions introduced by the dynamical diffraction. Based on our theoretical analysis we developed an analytical procedure to treat effects of refraction and absorption in the reconstruction. Our results elucidate limitations for the kinematical approach in the Bragg CXDI and suggest a natural criterion to distinguish between kinematical and dynamical cases in coherent x-ray diffraction on a finite crystal.

Wavelength-spacing-tunable multichannel filter incorporating a sampled chirped fiber Bragg grating based on a symmetrical chirp-tuning technique without center wavelength shift

NASA Astrophysics Data System (ADS)

Han, Young-Geun; Dong, Xinyong; Lee, Ju Han; Lee, Sang Bae

2006-12-01

We propose and experimentally demonstrate a simple and flexible scheme for a wavelength-spacing-tunable multichannel filter exploiting a sampled chirped fiber Bragg grating based on a symmetrical modification of the chirp ratio. Symmetrical bending along a sampled chirped fiber Bragg grating attached to a flexible cantilever beam induces a variation of the chirp ratio and a reflection chirp bandwidth of the grating without a center wavelength shift. Accordingly, the wavelength spacing of a sampled chirped fiber Bragg grating is continuously controlled by the reflection chirp bandwidth variation of the grating corresponding to the bending direction, which allows for realization of an effective wavelength-spacing-tunable multichannel filter. Based on the proposed technique, we achieve the continuous tunability of the wavelength spacing in a range from 1.51 to 6.11 nm, depending on the bending direction of the cantilever beam.

Passive cavity surface-emitting lasers: option of temperature-insensitive lasing wavelength for uncooled dense wavelength division multiplexing systems

NASA Astrophysics Data System (ADS)

Shchukin, V. A.; Ledentsov, N. N.; Slight, T.; Meredith, W.; Gordeev, N. Y.; Nadtochy, A. M.; Payusov, A. S.; Maximov, M. V.; Blokhin, S. A.; Blokhin, A. A.; Zadiranov, Yu. M.; Maleev, N. A.; Ustinov, V. M.; Choquette, K. D.

2016-03-01

A concept of passive cavity surface-emitting laser is proposed aimed to control the temperature shift of the lasing wavelength. The device contains an all-semiconductor bottom distributed Bragg reflector (DBR), in which the active medium is placed, a dielectric resonant cavity and a dielectric top DBR, wherein at least one of the dielectric materials has a negative temperature coefficient of the refractive index, dn/dT < 0. This is shown to be the case for commonly used dielectric systems SiO2/TiO2 and SiO2/Ta2O5. Two SiO2/TiO2 resonant structures having a cavity either of SiO2 or TiO2 were deposited on a substrate, their optical power reflectance spectra were measured at various temperatures, and refractive index temperature coefficients were extracted, dn/dT = 0.0021 K-1 for SiO2 and dn/dT = -0.0092 K-1 for TiO2. Using such dielectric materials allows designing passive cavity surface-emitting lasers having on purpose either positive, or zero, or negative temperature shift of the lasing wavelength dλ/dT. A design for temperature-insensitive lasing wavelength (dλ/dT = 0) is proposed. Employing devices with temperature-insensitive lasing wavelength in wavelength division multiplexing systems may allow significant reducing of the spectral separation between transmission channels and an increase in number of channels for a defined spectral interval enabling low cost energy efficient uncooled devices.

Single-Photon Emission from InAs/AlGaAs Quantum Dots

NASA Astrophysics Data System (ADS)

Rakhlin, M. V.; Belyaev, K. G.; Klimko, G. V.; Mukhin, I. S.; Ivanov, S. V.; Toropov, A. A.

2018-04-01

The results of investigation of the radiative characteristics of heterostructures with InAs/AlGaAs quantum dots (QDs) grown by molecular beam epitaxy have been presented. The properties of single QDs were determined by spectroscopy of micro-photoluminescence in cylindrical mesa-structures with a diameter of 200-1000 nm or columnar microresonators with distributed Bragg mirrors. The single-photon nature of the radiation is confirmed by measurements and analysis of the second-order correlation function g 2(τ) in a wide spectral range from 630 to 730 nm.

IV-VI compound midinfrared high-reflectivity mirrors and vertical-cavity surface-emitting lasers grown by molecular-beam epitaxy

NASA Astrophysics Data System (ADS)

Shi, Z.; Xu, G.; McCann, P. J.; Fang, X. M.; Dai, N.; Felix, C. L.; Bewley, W. W.; Vurgaftman, I.; Meyer, J. R.

2000-06-01

Midinfrared broadband high-reflectivity Pb1-xSrxSe/BaF2 distributed Bragg reflectors and vertical-cavity surface-emitting lasers (VCSELs) with PbSe as the active material were grown by molecular-beam epitaxy. Because of an extremely high index contrast, mirrors with only three quarter-wave layer pairs had reflectivities exceeding 99%. For pulsed optical pumping, a lead salt VCSEL emitting at the cavity wavelength of 4.5-4.6 μm operated nearly to room temperature (289 K).

Measurement of the Top Quark Mass in the All Hadronic Channel at the Tevatron

DOE Office of Scientific and Technical Information (OSTI.GOV)

Lungu, Gheorghe

2007-01-01

This study presents a measurement of the top quark mass in the all hadronic channel of the top quark pair production mechanism, using 1 fb -1 of pmore » $$\\bar{p}$$ collisions at √s =1.96 TeV collected at the Collider Detector at Fermilab (CDF). Few novel techniques have been used in this measurement. A template technique was used to simultaneously determine the mass of the top quark and the energy scale of the jets. Two sets of distributions have been parameterized as a function of the top quark mass and jet energy scale. One set of distributions is built from the event-by-event reconstructed top masses, determined using the Standard Model matrix element for the t$$\\bar{t}$$ all hadronic process. This set is sensitive to changes in the value of the top quark mass. The other set of distributions is sensitive to changes in the scale of jet energies and is built from the invariant mass of pairs of light flavor jets, providing an in situ calibration of the jet energy scale. The energy scale of the measured jets in the final state is expressed in units of its uncertainty, sigmac. The measured mass of the top quark is 171.1±3.7(stat.unc.)±2.1(syst.unc.) GeV/ c 2 and to the date represents the most precise mass measurement in the all hadronic channel and third best overall.« less

Using single top rapidity to measure V{sub td}, V{sub ts}, V{sub tb} at hadron colliders

DOE Office of Scientific and Technical Information (OSTI.GOV)

Aguilar-Saavedra, J. A.; Onofre, A.; Departamento de Fisica, Universidade do Minho, P-4710-057 Braga

2011-04-01

Single top production processes are usually regarded as the ones in which V{sub tb} can be directly measured at hadron colliders. We show that the analysis of the single top rapidity distribution in t-channel and tW production can also set direct limits on V{sub td}. At LHC with 10 fb{sup -1} at 14 TeV, the combined limits on V{sub td} may be reduced by almost a factor of 2 when the top rapidity distribution is used. This also implies that the limits on V{sub tb} can also be reduced by 15%, since both parameters, as well as V{sub ts}, mustmore » be simultaneously obtained from a global fit to data. At Tevatron, the exploitation of this distribution would require very high statistics.« less

Optical body fat measurement might contribute to the search for a predictor of type-2 diabetes mellitus

NASA Astrophysics Data System (ADS)

Tafeit, Erwin; Horejsi, Renate; Sudi, Karl; Berg, Aloys; Reibnegger, Gilbert; Moeller, Reinhard

2001-10-01

The optical device LIPOMETER allows for non-invasive, quick, precise and safe determination of subcutaneous fat distribution, so-called subcutaneous adipose tissue topography (SAT-Top). Previously we showed how the high-dimensional SAT-Top information of women with type-2 diabetes mellitus (NIDDM) and a health control group can be analysed and represented in low-dimensional plots by applying special artificial neural networks (ANNs). Three top-down sorted subcutaneous adipose tissue compartments were determined (upper trunk, lower trunk, legs). NIDDM women provided significantly higher upper trunk obesity and significantly lower leg obesity (apple type), as compared with their healthy control group. Now we apply those ANN results on SAT-Top measurements of young and healthy women, comparing their individual subcutaneous fat pattern to the body fat distribution of NIDDM women and to the normal fat development of healthy women. Some of these young and healthy women provide a subcutaneous fat distribution very similar to the SAT-Top results of NIDDM women, which might increase their risk for this disease later in life.

Using Custom Fiber Bragg Grating-Based Sensors to Monitor Artificial Landslides.

PubMed

Zhang, Qinghua; Wang, Yuan; Sun, Yangyang; Gao, Lei; Zhang, Zhenglin; Zhang, Wenyuan; Zhao, Pengchong; Yue, Yin

2016-09-02

Four custom fiber Bragg grating (FBG)-based sensors are developed to monitor an artificial landslide located in Nanjing, China. The sensors are composed of a rod and two FBGs. Based on the strength of the rods, two sensors are referred to as "hard sensors" (Sensor 1 and Sensor 2), the other two are referred to as "soft sensors" (Sensor 3 and Sensor 4). The two FBGs are fixed on each sensor rod at distances of 50 cm and 100 cm from the top of the rod (an upper FBG and a lower FBG). In the experiment presented in this paper, the sensors are installed on a slope on which an artificial landslide is generated through both machine-based and manual excavation. The fiber sensing system consists of the four custom FBG-based sensors, optical fiber, a static fiber grating demodulation instrument (SM125), and a PC with the necessary software. Experimental data was collected in the presence of an artificial landslide, and the results show that the lower FBGs are more sensitive than the upper FBGs for all four of the custom sensors. It was also found that Sensor 2 and Sensor 4 are more capable of monitoring small-scale landslides than Sensor 1 and Sensor 3, and this is mainly due to their placement location with respect to the landslide. The stronger rods used in the hard sensors make them more adaptable to the harsh environments of large landslides. Thus, hard sensors should be fixed near the landslide, while soft sensors should be placed farther away from the landslide. In addition, a clear tendency of strain variation can be detected by the soft sensors, which can be used to predict landslides and raise a hazard alarm.

Using Custom Fiber Bragg Grating-Based Sensors to Monitor Artificial Landslides

PubMed Central

Zhang, Qinghua; Wang, Yuan; Sun, Yangyang; Gao, Lei; Zhang, Zhenglin; Zhang, Wenyuan; Zhao, Pengchong; Yue, Yin

2016-01-01

Four custom fiber Bragg grating (FBG)-based sensors are developed to monitor an artificial landslide located in Nanjing, China. The sensors are composed of a rod and two FBGs. Based on the strength of the rods, two sensors are referred to as “hard sensors” (Sensor 1 and Sensor 2), the other two are referred to as “soft sensors” (Sensor 3 and Sensor 4). The two FBGs are fixed on each sensor rod at distances of 50 cm and 100 cm from the top of the rod (an upper FBG and a lower FBG). In the experiment presented in this paper, the sensors are installed on a slope on which an artificial landslide is generated through both machine-based and manual excavation. The fiber sensing system consists of the four custom FBG-based sensors, optical fiber, a static fiber grating demodulation instrument (SM125), and a PC with the necessary software. Experimental data was collected in the presence of an artificial landslide, and the results show that the lower FBGs are more sensitive than the upper FBGs for all four of the custom sensors. It was also found that Sensor 2 and Sensor 4 are more capable of monitoring small-scale landslides than Sensor 1 and Sensor 3, and this is mainly due to their placement location with respect to the landslide. The stronger rods used in the hard sensors make them more adaptable to the harsh environments of large landslides. Thus, hard sensors should be fixed near the landslide, while soft sensors should be placed farther away from the landslide. In addition, a clear tendency of strain variation can be detected by the soft sensors, which can be used to predict landslides and raise a hazard alarm. PMID:27598163

Optical fiber Bragg grating-instrumented silicone liner for interface pressure measurement within prosthetic sockets of lower-limb amputees.

PubMed

Al-Fakih, Ebrahim; Arifin, Nooranida; Pirouzi, Gholamhossein; Mahamd Adikan, Faisal Rafiq; Shasmin, Hanie Nadia; Abu Osman, Noor Azuan

2017-08-01

This paper presents a fiber Bragg grating (FBG)-instrumented prosthetic silicone liner that provides cushioning for the residual limb and can successfully measure interface pressures inside prosthetic sockets of lower-limb amputees in a simple and practical means of sensing. The liner is made of two silicone layers between which 12 FBG sensors were embedded at locations of clinical interest. The sensors were then calibrated using a custom calibration platform that mimics a real-life situation. Afterward, a custom gait simulating machine was built to test the liner performance during an amputee's simulated gait. To validate the findings, the results were compared to those obtained by the commonly used F-socket mats. As the statistical findings reveal, both pressure mapping methods measured the interface pressure in a consistent way, with no significant difference (P-values ≥0.05). This pressure mapping technique in the form of a prosthetic liner will allow prosthetics professionals to quickly and accurately create an overall picture of the interface pressure distribution inside sockets in research and clinical settings, thereby improving the socket fit and amputee's satisfaction. (2017) COPYRIGHT Society of Photo-Optical Instrumentation Engineers (SPIE).

An Approach for the Dynamic Measurement of Ring Gear Strains of Planetary Gearboxes Using Fiber Bragg Gratings

PubMed Central

Zhang, Xiaodong; Hou, Chenggang

2017-01-01

The strain of the ring gear can reflect the dynamic characteristics of planetary gearboxes directly, which makes it an ideal signal to monitor the health condition of the gearbox. To overcome the disadvantages of traditional methods, a new approach for the dynamic measurement of ring gear strains using fiber Bragg gratings (FBGs) is proposed in this paper. Firstly, the installation of FBGs is determined according to the analysis for the strain distribution of the ring gear. Secondly, the parameters of the FBG are determined in consideration of the accuracy and sensitivity of the measurement as well as the size of the ring gear. The strain measured by the FBG is then simulated under non-uniform strain field conditions. Thirdly, a dynamic measurement system is built and tested. Finally, the strains of the ring gear are measured in a planetary gearbox under normal and faulty conditions. The experimental results showed good agreement with the theoretical results in values, trends, and the fault features can be seen from the time domain of the measured strain signal, which proves that the proposed method is feasible for the measurement of the ring gear strains of planetary gearboxes. PMID:29258164

An Approach for the Dynamic Measurement of Ring Gear Strains of Planetary Gearboxes Using Fiber Bragg Gratings.

PubMed

Niu, Hang; Zhang, Xiaodong; Hou, Chenggang

2017-12-16

The strain of the ring gear can reflect the dynamic characteristics of planetary gearboxes directly, which makes it an ideal signal to monitor the health condition of the gearbox. To overcome the disadvantages of traditional methods, a new approach for the dynamic measurement of ring gear strains using fiber Bragg gratings (FBGs) is proposed in this paper. Firstly, the installation of FBGs is determined according to the analysis for the strain distribution of the ring gear. Secondly, the parameters of the FBG are determined in consideration of the accuracy and sensitivity of the measurement as well as the size of the ring gear. The strain measured by the FBG is then simulated under non-uniform strain field conditions. Thirdly, a dynamic measurement system is built and tested. Finally, the strains of the ring gear are measured in a planetary gearbox under normal and faulty conditions. The experimental results showed good agreement with the theoretical results in values, trends, and the fault features can be seen from the time domain of the measured strain signal, which proves that the proposed method is feasible for the measurement of the ring gear strains of planetary gearboxes.

Insole optical fiber Bragg grating sensors network for dynamic vertical force monitoring

NASA Astrophysics Data System (ADS)

Domingues, Maria Fátima; Tavares, Cátia; Leitão, Cátia; Frizera-Neto, Anselmo; Alberto, Nélia; Marques, Carlos; Radwan, Ayman; Rodriguez, Jonathan; Postolache, Octavian; Rocon, Eduardo; André, Paulo; Antunes, Paulo

2017-09-01

In an era of unprecedented progress in technology and increase in population age, continuous and close monitoring of elder citizens and patients is becoming more of a necessity than a luxury. Contributing toward this field and enhancing the life quality of elder citizens and patients with disabilities, this work presents the design and implementation of a noninvasive platform and insole fiber Bragg grating sensors network to monitor the vertical ground reaction forces distribution induced in the foot plantar surface during gait and body center of mass displacements. The acquired measurements are a reliable indication of the accuracy and consistency of the proposed solution in monitoring and mapping the vertical forces active on the foot plantar sole, with a sensitivity up to 11.06 pm/N. The acquired measurements can be used to infer the foot structure and health condition, in addition to anomalies related to spine function and other pathologies (e.g., related to diabetes); also its application in rehabilitation robotics field can dramatically reduce the computational burden of exoskeletons' control strategy. The proposed technology has the advantages of optical fiber sensing (robustness, noninvasiveness, accuracy, and electromagnetic insensitivity) to surpass all drawbacks verified in traditionally used sensing systems (fragility, instability, and inconsistent feedback).

Smart fiber-reinforced polymer anchorage system with optical fiber Bragg grating sensors

NASA Astrophysics Data System (ADS)

Huang, Minghua; Zhou, Zhi; He, Jianping; Chen, Genda; Ou, Jinping

2010-03-01

Civil Engineers have used fiber reinforced polymer (FRP) with high axial strength as an effective and economical alternative to steel in harsh corrosion environments. However, the practical applications of FRP are limited by the tendency of FRP materials to fail suddenly under lateral pressure and surface injury. For example, shear stresses result from the bonding effect between the FRP material and the structure of the anchorage system due to the lower shear strength of FRP. This paper proposes a novel smart FRP anchorage system with embedded optical fiber Bragg grating (FBG) sensors to monitor the axial strain state and accordingly the interfacial shear stress, as well as the interfacial damage characteristics of FRP anchorage. One FBG sensor was embedded in an FRP rod outside the anchorage region to evaluate the properties of the material, and seven FBG sensors were distributed along the rod in the anchor to monitor the axial strain variations and study the interfacial mechanical behaviors of the smart FRP anchorage under a static pulling load. The experimental results agreed well with theoretical predictions. The smart FRP anchorage system with optical FBG sensors proves effective and practical for monitoring the long-term mechanical behavior of FRP anchorage systems.

Insole optical fiber Bragg grating sensors network for dynamic vertical force monitoring.

PubMed

Domingues, Maria Fátima; Tavares, Cátia; Leitão, Cátia; Frizera-Neto, Anselmo; Alberto, Nélia; Marques, Carlos; Radwan, Ayman; Rodriguez, Jonathan; Postolache, Octavian; Rocon, Eduardo; André, Paulo; Antunes, Paulo

2017-09-01

In an era of unprecedented progress in technology and increase in population age, continuous and close monitoring of elder citizens and patients is becoming more of a necessity than a luxury. Contributing toward this field and enhancing the life quality of elder citizens and patients with disabilities, this work presents the design and implementation of a noninvasive platform and insole fiber Bragg grating sensors network to monitor the vertical ground reaction forces distribution induced in the foot plantar surface during gait and body center of mass displacements. The acquired measurements are a reliable indication of the accuracy and consistency of the proposed solution in monitoring and mapping the vertical forces active on the foot plantar sole, with a sensitivity up to 11.06 ?? pm / N . The acquired measurements can be used to infer the foot structure and health condition, in addition to anomalies related to spine function and other pathologies (e.g., related to diabetes); also its application in rehabilitation robotics field can dramatically reduce the computational burden of exoskeletons’ control strategy. The proposed technology has the advantages of optical fiber sensing (robustness, noninvasiveness, accuracy, and electromagnetic insensitivity) to surpass all drawbacks verified in traditionally used sensing systems (fragility, instability, and inconsistent feedback).

An improved genetic algorithm for increasing the addressing accuracy of encoding fiber Bragg grating sensor network

NASA Astrophysics Data System (ADS)

Liu, Huanlin; Wang, Chujun; Chen, Yong

2018-01-01

Large-capacity encoding fiber Bragg grating (FBG) sensor network is widely used in modern long-term health monitoring system. Encoding FBG sensors have greatly improved the capacity of distributed FBG sensor network. However, the error of addressing increases correspondingly with the enlarging of capacity. To address the issue, an improved algorithm called genetic tracking algorithm (GTA) is proposed in the paper. In the GTA, for improving the success rate of matching and reducing the large number of redundant matching operations generated by sequential matching, the individuals are designed based on the feasible matching. Then, two kinds of self-crossover ways and a dynamic variation during mutation process are designed to increase the diversity of individuals and to avoid falling into local optimum. Meanwhile, an assistant decision is proposed to handle the issue that the GTA cannot solve when the variation of sensor information is highly overlapped. The simulation results indicate that the proposed GTA has higher accuracy compared with the traditional tracking algorithm and the enhanced tracking algorithm. In order to address the problems of spectrum fragmentation and low sharing degree of spectrum resources in survivable.

Alternative solution model for the ternary carbonate system CaCO3 - MgCO3 - FeCO3 - II. Calibration of a combined ordering model and mixing model

USGS Publications Warehouse

McSwiggen, P.L.

1993-01-01

Earlier attempts at solution models for the ternary carbonate system have been unable to adequately accommodate the cation ordering which occurs in some of the carbonate phases. The carbonate solution model of this study combines a Margules type of interaction model with a Bragg-Williams type of ordering model. The ordering model determines the equilibrium state of order for a crystal, from which the cation distribution within the lattice can be obtained. The interaction model addresses the effect that mixing different cation species within a given cation layer has on the total free energy of the system. An ordering model was derived, based on the Bragg-Williams approach; it is applicable to ternary systems involving three cations substituting on two sites, and contains three ordering energy parameters (WCaMg, WCaFe, and WCaMgFe). The solution model of this study involves six Margules-type interaction parameters (W12, W21, W13, W31, W23, and W32). Values for the two sets of energy parameters were calculated from experimental data and from compositional relationships in natural assemblages. ?? 1993 Springer-Verlag.

An adaptive wing for a small-aircraft application with a configuration of fibre Bragg grating sensors

NASA Astrophysics Data System (ADS)

Mieloszyk, M.; Krawczuk, M.; Zak, A.; Ostachowicz, W.

2010-08-01

In this paper a concept of an adaptive wing for small-aircraft applications with an array of fibre Bragg grating (FBG) sensors has been presented and discussed. In this concept the shape of the wing can be controlled and altered thanks to the wing design and the use of integrated shape memory alloy actuators. The concept has been tested numerically by the use of the finite element method. For numerical calculations the commercial finite element package ABAQUS® has been employed. A finite element model of the wing has been prepared in order to estimate the values of the wing twisting angles and distributions of the twist for various activation scenarios. Based on the results of numerical analysis the locations and numbers of the FBG sensors have also been determined. The results of numerical calculations obtained by the authors confirmed the usefulness of the assumed wing control strategy. Based on them and the concept developed of the adaptive wing, a wing demonstration stand has been designed and built. The stand has been used to verify experimentally the performance of the adaptive wing and the usefulness of the FBG sensors for evaluation of the wing condition.

Temperature dependence of the distribution of the thermally activated energy barriers in Tl2Ba2CaCu2O8 film

NASA Astrophysics Data System (ADS)

Ren, C.; Lin, F. Y.; Ding, S. Y.; Li, Z. M.; Aruna, S. A.; Qiu, L.; Yao, X. X.; Yan, S. L.; Si, M. S.

1999-06-01

The effects of frequency and ac amplitude on ac susceptibility have been measured for a thin Tl2Ba2CaCu2O8 film in the range 100 Hz-100 kHz in magnetic field 0.52 T. A phenomenological equation with an asymmetrical distribution of thermally activated energy barriers has been used to analyse these frequency and amplitude dependences of the ac susceptibility icons/Journals/Common/chi" ALT="chi" ALIGN="TOP"/>(icons/Journals/Common/omega" ALT="omega" ALIGN="TOP"/>,hac) in the vicinity of the peak temperature of icons/Journals/Common/chi" ALT="chi" ALIGN="TOP"/>´´. We obtain the effective energy barrier U against amplitude hac (current density j): Uicons/Journals/Common/propto" ALT="propto" ALIGN="TOP"/> hac-0.38. This U(j) relationship shows that the flux lines are in the 3D collective creep regime. Therefore, we conclude that the effective energy barrier is in fact an average of the barrier's distribution, and the distribution function is a distinguished asymmetrical one in this 3D collective creep regime.