Science.gov

Sample records for grating induced thermal

  1. Four-wave mixing using polarization grating induced thermal grating in liquids exhibiting circular dichroism

    SciTech Connect

    Nunes, J.A.; Tong, W.G.; Chandler, D.W.; Rahn, L.A.

    1995-04-01

    A novel four-wave mixing technique for the detection of circular dichroism in optically active liquid samples is demonstrated. When two cross-polarized laser beams are crossed at a small angle in a circular dichroic liquid a weak thermal grating is produced with a phase depending on the sign of the circular dichroism. The authors show that the polarization of one of the beams can be modified to allow coherent interference with an intensity-grating induced thermal grating. A probe beam scattering from the composite grating results in a signal that reveals the sign and magnitude of the circular dichroism. The use of this technique to optimize the signal-to-noise ratio in the presence of scattered light and laser intensity noise is discussed.

  2. Single shot thermometry using laser induced thermal grating

    NASA Astrophysics Data System (ADS)

    Qu, Pubo; Guan, Xiaowei; Zhang, Zhenrong; Wang, Sheng; Li, Guohua; Ye, Jingfeng; Hu, Zhiyun

    2015-05-01

    With the concern of environmental protection and reducing the fossil fuel consumption, combustion processes need to be more efficient and less contaminable. Therefore, the ability to obtain important thermophysical parameters is crucial to combustion research and combustor design. Traditional surveying techniques were difficult to apply in a confined space, especially the physically intrusions of detectors can alter the combustion processes. Laser-based diagnostic techniques, like CARS, SVRS, PLIF and TDLAS, allow the in situ, non-intrusive, spatially and temporally resolved measurements of combustion parameters in hostile environments. We report here a new non-intrusive optical diagnostic technique, based on laser-induced thermal grating. Thermal gratings generated in NO2/N2 binary mixtures, arise from the nonlinear interaction between the medium and the light radiation from the interference of two pulsed, frequency-doubled Nd:YAG lasers (532 nm). This leads to the formation of a dynamic grating through the resonant absorption and the subsequent collisional relaxation. By the temporally resolved detection of a continuous wave, frequency-doubled Nd:YVO4 probe laser beam (671 nm) diffracted by LITG. The temporal behavior of the signal is a function of the local temperature and other properties of gas, various parameters of the target gas can be extracted by analyzing the signal. The accurate singleshot temperature measurements were carried out at different test conditions using a stainless steel pressurized cell, data averaged on 100 laser shots were compared with simultaneously recorded thermocouple data, and the results were consistent with each other. The LITG signal is shown to grow with increasing the gas pressure and is spatially coherent, which makes the LITG thermometry technique a promising candidate in high pressure environments.

  3. Investigation on Thermal-Induced Decay of Fiber Bragg Grating

    NASA Astrophysics Data System (ADS)

    Zhang, Peng; Ding, Pinyi; Liu, Li

    2015-06-01

    A fiber Bragg grating (FBG), with advantages such as high anti-interference ability, a simple structure, and multiplexing, is widely used as a core component in numerous applications to monitor adverse environments of high temperature and air pressure. When FBGs are exposed to these extreme conditions, especially high temperature, performance decay may occur, bringing serious impact on the stability and reliability of the instruments. Therefore, it is necessary to make a detailed analysis on the mechanism of the thermal-induced decay of a FBG. One commonly used theory is proposed by Erdogn, which is based on a power function and aging curve method. However, these empirical equations are limited in application because only one single type of FBG can be analyzed this way. This paper focuses on the mechanism of a FBG, and presents a detailed analysis on the theory of the thermal-induced decay of a FBG using the electron dipole mode. Theoretical relationships between reflectivity and time or temperature were obtained, and a corresponding thermal-induced decay testing system was designed. The experimental and theoretical reflectivity decline under different temperatures of and are plotted, and the curves of reduction derived from the theoretical model fit the experimental data well. Thus, this model can be applied to predict the performance decay of FBGs at high temperature.

  4. Investigation of the thermally induced laser beam distortion associated with vacuum compressor gratings in high energy and high average power femtosecond laser systems.

    PubMed

    Fourmaux, S; Serbanescu, C; Lecherbourg, L; Payeur, S; Martin, F; Kieffer, J C

    2009-01-01

    We report successful compensation of the thermally induced laser beam distortion associated with high energy 110 mJ and high average power femtosecond laser system of 11 Watts operated with vacuum compressor gratings. To enhance laser-based light source brightness requires development of laser systems with higher energy and higher average power. Managing the high thermal loading on vacuum optical components is a key issue in the implementation of this approach. To our knowledge this is the first time that such thermal induced distortions on the vacuum compressor gratings are characterized and compensated. PMID:19129886

  5. Investigation of the thermally induced laser beam distortion associated with vacuum compressor gratings in high energy and high average power femtosecond laser systems

    PubMed Central

    Fourmaux, S.; Serbanescu, C.; Lecherbourg, L.; Payeur, S.; Martin, F.; Kieffer, J. C.

    2009-01-01

    We report successful compensation of the thermally induced laser beam distortion associated with high energy 110 mJ and high average power femtosecond laser system of 11 Watts operated with vacuum compressor gratings. To enhance laser-based light source brightness requires development of laser systems with higher energy and higher average power. Managing the high thermal loading on vacuum optical components is a key issue in the implementation of this approach. To our knowledge this is the first time that such thermal induced distortions on the vacuum compressor gratings are characterized and compensated. PMID:19129886

  6. Temperature Measurement in Supersonic Flows by Predissociative Transient Thermal Gratings

    NASA Astrophysics Data System (ADS)

    Barker, Peter; Miles, Richard

    1998-11-01

    We present temporally resolved measurements of temperature in a range of supersonic flows by measuring the acoustic decay of laser created transient gratings. This is an extension of the LITA (Laser-Induced Thermal Acoustics) technique. A thermal density grating is created in the flow folloing absorption and thermalization of light from an interference pattern created by the crossed beams of a short-pulsed laser. Rapid thermalization occurs by collisions with energetic 0 photofragments following predissociation of O^2 in air by absorption of 193 nm light. The grating relaxes to local equilibrium by acoustic and diffusive decay. The acoustic decay launches two counter- propagating gratings traveling at the speed-of-sound. The interference of the stationary thermal grating with the two counter-propagating acoustic gratings creates a variation in grating modulation depth with time. The modulation frequency is proportional to the speed-of-sound and is used in our measurements to determine temperature. Bragg diffraction off the grating by a cw probe laser is observed as an oscillatory decay over hundreds of nanoseconds; the modulation frequency is extracted from this signal by Fourier analysis. We present single laser pulse measurements of temperature in a Mach 2.0 and 3.9 nozzle flows, and in weakly ionized flows for which this technique has been developed.

  7. Thermal annealing of tilted fiber Bragg gratings

    NASA Astrophysics Data System (ADS)

    González-Vila, Á.; Rodríguez-Cobo, L.; Mégret, P.; Caucheteur, C.; López-Higuera, J. M.

    2016-05-01

    We report a practical study of the thermal decay of cladding mode resonances in tilted fiber Bragg gratings, establishing an analogy with the "power law" evolution previously observed on uniform gratings. We examine how this process contributes to a great thermal stability, even improving it by means of a second cycle slightly increasing the annealing temperature. In addition, we show an improvement of the grating spectrum after annealing, with respect to the one just after inscription, which suggests the application of this method to be employed to improve saturation issues during the photo-inscription process.

  8. Mid-Infrared Pumped Laser-Induced Thermal Grating Spectroscopy for Detection of Acetylene in the Visible Spectral Range.

    PubMed

    Sahlberg, Anna-Lena; Kiefer, Johannes; Aldén, Marcus; Li, Zhongshan

    2016-06-01

    We present mid-infrared laser-induced thermal grating spectroscopy (IR-LITGS) using excitation radiation around 3 µm generated by a simple broadband optical parametric oscillator (OPO). Acetylene as a typical small hydrocarbon molecule is used as an example target species. A mid-infrared broadband OPO pumped by the fundamental output of a neodymium-doped yttrium aluminum garnet (Nd:YAG) laser was used to generate the pump beams, with pulse energies of 6-10 mJ depending on the wavelength. The line width of the OPO idler beam was ∼5 cm(-1), which is large enough to cover up to six adjacent acetylene lines. The probe beam was the radiation of a 532 nm cw solid state laser with 190 mW output power. Signals were generated in atmospheric pressure gas flows of N2, air, CO2 and Ar with small admixtures of C2H2 A detection limit of less than 300 ppm was found for a point measurement of C2H2 diluted in N2 As expected, the oscillation frequency of the IR-LITGS signal was found to have a large dependency on the buffer gas, which allows determination of the speed of sound. Moreover, the results reveal a very strong collisional energy exchange between C2H2 and CO2 compared to the other gases. This manifests as significant local heating. In summary, the MIR-LITGS technique enables spectroscopy of fundamental vibrational transitions in the infrared via detection in the visible spectral range. PMID:27091904

  9. Simultaneous measurement of speed of sound, thermal diffusivity, and bulk viscosity of 1-ethyl-3-methylimidazolium-based ionic liquids using laser-induced gratings.

    PubMed

    Kozlov, Dimitrii N; Kiefer, Johannes; Seeger, Thomas; Fröba, Andreas P; Leipertz, Alfred

    2014-12-11

    The technique of laser-induced gratings (LIGs) has been applied to the simultaneous determination of speed of sound and thermal diffusivity of four 1-ethyl-3-methylimidazolium ([EMIm])-based room temperature ionic liquids (RTILs)-[EMIm][N(CN)2], [EMIm][MeSO3], [EMIm][C(CN)3], and [EMIm][NTf2]-at ambient pressure (1 bar (0.1 MPa)) and temperature (28 °C (301 K)). Transient laser-induced gratings were created as a result of thermalization of a quasi-resonant excitation of highly lying combinational vibrational states of the RTIL molecules and electrostrictive compression of the liquid by radiation of a pulse-repetitive Q-switched Nd:YAG pump laser (1064 nm). The LIGs temporal evolution was recorded using Bragg diffraction of the radiation from a continuous-wave probe laser (532 nm). By fitting the temporal profiles of the LIG signals, the speed of sound and thermal diffusivity were determined, and the isentropic compressibility and thermal conductivity were calculated. Independently, the special experimental arrangement allowed the measurement of the damping of the laser-excited acoustic waves and the derivation of the RTIL bulk viscosity for the first time. PMID:25415848

  10. Electromagnetically induced grating with maximal atomic coherence

    SciTech Connect

    Carvalho, Silvania A.; Araujo, Luis E. E. de

    2011-10-15

    We describe theoretically an atomic diffraction grating that combines an electromagnetically induced grating with a coherence grating in a double-{Lambda} atomic system. With the atom in a condition of maximal coherence between its lower levels, the combined gratings simultaneously diffract both the incident probe beam as well as the signal beam generated through four-wave mixing. A special feature of the atomic grating is that it will diffract any beam resonantly tuned to any excited state of the atom accessible by a dipole transition from its ground state.

  11. Laser-induced transient grating setup with continuously tunable period

    SciTech Connect

    Vega-Flick, A.; Eliason, J. K.; Maznev, A. A.; Nelson, K. A.; Khanolkar, A.; Abi Ghanem, M.; Boechler, N.; Alvarado-Gil, J. J.

    2015-12-15

    We present a modification of the laser-induced transient grating setup enabling continuous tuning of the transient grating period. The fine control of the period is accomplished by varying the angle of the diffraction grating used to split excitation and probe beams. The setup has been tested by measuring dispersion of bulk and surface acoustic waves in both transmission and reflection geometries. The presented modification is fully compatible with optical heterodyne detection and can be easily implemented in any transient grating setup.

  12. Thermal-structural modeling of polymer Bragg grating waveguides illuminated by a light emitting diode.

    PubMed

    Joon Kim, Kyoung; Bar-Cohen, Avram; Han, Bongtae

    2012-02-20

    This study reports both analytical and numerical thermal-structural models of polymer Bragg grating (PBG) waveguides illuminated by a light emitting diode (LED). A polymethyl methacrylate (PMMA) Bragg grating (BG) waveguide is chosen as an analysis vehicle to explore parametric effects of incident optical powers and substrate materials on the thermal-structural behavior of the BG. Analytical models are verified by comparing analytically predicted average excess temperatures, and thermally induced axial strains and stresses with numerical predictions. A parametric study demonstrates that the PMMA substrate induces more adverse effects, such as higher excess temperatures, complex axial temperature profiles, and greater and more complicated thermally induced strains in the BG compared with the Si substrate. PMID:22358162

  13. Magnetomechanically induced long period fiber gratings

    SciTech Connect

    Causado-Buelvas, Jesus D.; Gomez-Cardona, Nelson D.; Torres, Pedro

    2008-04-15

    In this work, we report a simple, flexible method to create long period fiber gratings mechanically by controlling the repulsion/attraction force between two magnets that pressing a plate with a periodic array of small glass cylinders to a short length of optical fiber. Via the photoelastic effect, the pressure points induce the required periodic refractive index modulation to create the LPFG. We found that the induced device exhibits spectral characteristics similar to those of other types of LPFG. As the optical properties of LPFGs are directly related to the nature of the applied perturbations, we show, to our knowledge for the frrst time, how is the evolution of birefringence effects in mechanically induced LPFGs.

  14. Visible wavelength fiber Bragg gratings: thermal and strain sensitivities

    NASA Astrophysics Data System (ADS)

    Loren Inácio, Patrícia; Chiamenti, Ismael; Sualehe, Ivenso d. S. V.; Oliveira, Valmir; Kalinowski, Hypolito J.

    2016-05-01

    The thermal and deformation properties of fiber Bragg gratings (FBG) in the visible range were characterized for the first time in our knowledge. The FBG were written in silica single mode (cutoff in the visible and infrared range) and multimode fibers, using a phase-mask (460 nm period) illuminated by a 248 nm femtosecond laser.

  15. Properties and Applications of Laser-Induced Gratings in Rare Earth Doped Glasses.

    NASA Astrophysics Data System (ADS)

    Behrens, Edward Grady

    Scope and method of study. Four-wave-mixing techniques were used in an attempt to create permanent laser-induced grating in Pr^{3+}-, Nd ^{3+}-, Eu^ {3+}-, and Er^{3+ }-doped glasses. The permanent laser-induced grating signal intensity and build-up and erase times were investigated as function of the write beam crossing angle, write beam power, and temperature. Thermal lensing measurements were conducted on Eu^{3+} - and Nd^{3+}-doped glasses and room temperature Raman and resonant Raman spectra were obtained for Eu^{3+}-doped glasses. The permanent laser-induced grating signal intensity was studied in Eu^{3+} -doped alkali-metal glasses as a function of the alkali -metal network modifier ion and a model was developed by treating the sample as a two-level system. Optical device applications of the permanent laser-induced gratings were studied by creating some simple devices. Findings and conclusions. Permanent laser-induced gratings were created in the Pr^{3+ }- and Eu^{3+} -doped glasses. The permanent laser-induced grating is associated with a structural phase change of the glass host. The structural change is produced by high energy phonons which are emitted by radiationless relaxation processes of the rare earth ion. Nd^{3+} and Er^{3+} relax nonradiatively by the emission of phonons of much lower energy which are unable to produce the structural phase change needed to form a permanent laser-induced grating. The difference in energy of the emitted phonons is responsible for the differing characteristics of the thermal lensing experiments. The model does a good job of predicting the experimental results for the asymmetry and other parameters of the two-level system. The application of these laser -induced gratings for optical devices demonstrates their importance to optical technology.

  16. Magnetic Field Induced Changes Of Domain Structure Grating.

    NASA Astrophysics Data System (ADS)

    Maziewski, A.; Stankiewicz, A.

    1987-10-01

    A stripe domain grating (SDG) has been theoretically analysed to combine some magnetic field changeable grating parameters with a magnetic sample material parameters. The alterable grating properties were discussed for different types of fiber-optic switch device. The quality and prefered directions of SDG have been quantitatively investigated using unconventional set-up based on the light diffraction effect. The gratings have been induced by the magnetic field with different orientations and values. SDG quality was significantly improved applying nontypically oriented magnetic field. We focused our attention on SDG static properties.

  17. Observation of an electromagnetically induced grating in cold sodium atoms

    NASA Astrophysics Data System (ADS)

    Mitsunaga, Masaharu; Imoto, Nobuyuki

    1999-06-01

    We have observed diffraction signals by a grating originating from electromagnetically induced transparency (EIT) in a three-level Λ system of cold sodium atoms. Theoretical and experimental analyses of this phenomenon, called the electromagnetically induced grating (EIG), have revealed that EIG spectra exhibit background-free, Lorentzian signal profiles regardless of the pump frequencies, making a clear contrast to the case of ordinary EIT spectra.

  18. Thermally triggered fiber lasers based on secondary-type-In Bragg gratings.

    PubMed

    Feng, Fu-Rong; Ran, Yang; Liang, Yi-Zhi; Gao, Shuai; Feng, Yuan-Hua; Jin, Long; Guan, Bai-Ou

    2016-06-01

    The secondary-type-In grating formed in a small-core photosensitivity active fiber is discovered and investigated. Due to the different grating types, the transmission dip of a secondary grating structure chases and integrates with the type-In grating structure as the temperature increases, which strengthens the reflectivity of the grating. By use of these secondary-type-In gratings as Bragg reflectors, a thermally activated distributed Bragg reflector (DBR) fiber laser is proposed, which can be potentially used in high-temperature alarms and sensors. PMID:27244391

  19. FAST TRACK COMMUNICATION: An electromagnetically induced grating by microwave modulation

    NASA Astrophysics Data System (ADS)

    Xiao, Zhi-Hong; Shin, Sung Guk; Kim, Kisik

    2010-08-01

    We study the phenomenon of an electromagnetically induced phase grating in a double-dark state system of 87Rb atoms, the two closely placed lower fold levels of which are coupled by a weak microwave field. Owing to the existence of the weak microwave field, the efficiency of the phase grating is strikingly improved, and an efficiency of approximately 33% can be achieved. Under the action of the weak standing wave field, the high efficiency of the phase grating can be maintained by modulating the strength and detuning of the weak microwave field, increasing the strength of the standing wave field.

  20. Electromagnetically induced grating in asymmetric quantum wells via Fano interference.

    PubMed

    Zhou, Fengxue; Qi, Yihong; Sun, Hui; Chen, Dijun; Yang, Jie; Niu, Yueping; Gong, Shangqing

    2013-05-20

    We propose a scheme for obtaining an electromagnetically induced grating in an asymmetric semiconductor quantum well (QW) structure via Fano interference. In our structure, owing to Fano interference, the diffraction intensity of the grating, especially the first-order diffraction, can be significantly enhanced. The diffraction efficiency of the grating can be controlled efficiently by tuning the control field intensity, the interaction length, the coupling strength of tunneling, etc. This investigation may be used to develop novel photonic devices in semiconductor QW systems. PMID:23736445

  1. Thermal activation of regenerated fiber Bragg grating in few mode fibers

    NASA Astrophysics Data System (ADS)

    Lai, Man-Hong; Gunawardena, Dinusha S.; Lim, Kok-Sing; Machavaram, Venkata R.; Lee, Say-Hoe; Chong, Wu-Yi; Lee, Yen-Sian; Ahmad, Harith

    2016-03-01

    This work demonstrated for the first time, the thermal regeneration of two and four modes graded index fiber Bragg gratings using high temperature tube furnace. During the regeneration process, the seed grating is erased and a new grating with lower index contrast is formed. The thermal calibration shows that the temperature sensitivity of regenerated grating is slightly higher for fiber with larger core. On the other hand, the regeneration temperature is lower for fiber with smaller core. The temperature sustainability up to 900 °C is observed for the produced regenerated gratings in few mode fibers.

  2. Fiber Bragg Gratings for High-Temperature Thermal Characterization

    SciTech Connect

    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 Marshall Space Flight Center's Propulsion Research Center. (authors)

  3. Engineering biphoton wave packets with an electromagnetically induced grating

    SciTech Connect

    Wen Jianming; Xiao Min; Zhai Yanhua; Du Shengwang

    2010-10-15

    We propose to shape biphoton wave packets with an electromagnetically induced grating in a four-level double-{Lambda} cold atomic system. We show that the induced hybrid grating plays an essential role in directing the new fields into different angular positions, especially for the zeroth-order diffraction. A number of interesting features appears in the shaped two-photon wave forms. For example, broadening or narrowing the spectrum would be possible in the proposed scheme even without the use of a cavity.

  4. Electromagnetically induced grating in a crystal of molecular magnets system

    NASA Astrophysics Data System (ADS)

    Liu, Jibing; Liu, Na; Shan, Chuanjia; Liu, Tangkun; Li, Hong; Zheng, Anshou; Xie, Xiao-Tao

    2016-07-01

    We investigate the response of the molecular system to the magnetic field modulation. Molecular magnets are subjected to a strong standing ac magnetic field and a weak probe magnetic field. The transmission and absorption of the weak probe magnetic field can be changed due to quantum coherence and the spatially modulating of the standing field. And a electromagnetically induced grating is formed in the crystal of molecular magnets via electromagnetically induced transparency (EIT). The diffraction efficiency of the grating can be adjusted efficiently by tuning the intensity of the standing wave field and the single photon detuning.

  5. Applications of laser-induced gratings to spectroscopy and dynamics

    SciTech Connect

    Rohlfing, E.A.

    1993-12-01

    This program has traditionally emphasized two principal areas of research. The first is the spectroscopic characterization of large-amplitude motion on the ground-state potential surface of small, transient molecules. The second is the reactivity of carbonaceous clusters and its relevance to soot and fullerene formation in combustion. Motivated initially by the desire to find improved methods of obtaining stimulated emission pumping (SEP) spectra of transients, most of our recent work has centered on the use of laser-induced gratings or resonant four-wave mixing in free-jet expansions. These techniques show great promise for several chemical applications, including molecular spectroscopy and photodissociation dynamics. The author describes recent applications of two-color laser-induced grating spectroscopy (LIGS) to obtain background-free SEP spectra of transients and double resonance spectra of nonfluorescing species, and the use of photofragment transient gratings to probe photodissociation dynamics.

  6. Thermal Evaluation of Fiber Bragg Gratings at Extreme Temperatures

    NASA Technical Reports Server (NTRS)

    Juergens, Jeffrey; Adamovsky, Grigory; Bhatt, Ramakrishna; Morscher, Gregory; Floyd, Bertram

    2005-01-01

    The development of integrated fiber optic sensors for use in aerospace health monitoring systems demands that the sensors be able to perform in extreme environments. In order to use fiber optic sensors effectively in an extreme environment one must have a thorough understanding of the sensor's capabilities, limitations, and performance under extreme environmental conditions. This paper reports on our current sensor evaluation examining the performance of freestanding fiber Bragg gratings (FBG) at extreme temperatures. While the ability of FBGs to survive at extreme temperatures has been established, their performance and long term survivability is not well documented. At extreme temperatures the grating structure would be expected to dissipate, degrading the sensors performance and eventually ceasing to return a detectable signal. The fiber jacket will dissipate leaving a brittle, unprotected fiber. For FBGs to be used in aerospace systems their performance and limitations need to be thoroughly understood at extreme temperatures. As the limits of the FBGs performance are pushed the long term survivability and performance of the sensor comes into question. We will not only examine the ability of FBGs to survive extreme temperatures but also look at their performance during many thermal cycles. This paper reports on test results of the performance of thermal cycling commercially available FBGs, at temperatures up to 1000 C, seen in aerospace applications. Additionally this paper will report on the performance of commercially available FBGs held at 1000 C for hundreds of hours. Throughout the evaluation process, various parameters of the FBGs performance were monitored and recorded. Several test samples were subjected to identical test conditions to allow for statistical analysis of the data. Test procedures, calibrations, referencing techniques, performance data, and interpretations and explanations of results are presented in the paper along with directions for

  7. Performance characterization of fiber Bragg grating thermal response in space vacuum thermal environment

    NASA Astrophysics Data System (ADS)

    Jiang, Junfeng; Song, Luyao; Liu, Tiegen; Zhang, Jingchuan; Liu, Kun; Wang, Shuang; Yin, Jinde; Zhao, Peng; Xie, Jihui; Wu, Fan; Zhang, Xuezhi

    2013-12-01

    We investigated the fiber Bragg grating (FBG) thermal response in space vacuum thermal environment. The FBGs were packaged with 6061-T6 aluminum. The liquid nitrogen immersion experiment results show that its wavelength shift standard deviation is 0.76 pm for 217 h. The combination effect of vacuum and cryogenic temperature was studied by thermal cycling process in space environment simulator. The FBG sensors show accuracy better than 2% full scale, and the hysteresis errors are below 1%. It proves that these metal packaged FBG sensors can survive and meet the requirement of space measurement.

  8. Performance characterization of fiber Bragg grating thermal response in space vacuum thermal environment.

    PubMed

    Jiang, Junfeng; Song, Luyao; Liu, Tiegen; Zhang, Jingchuan; Liu, Kun; Wang, Shuang; Yin, Jinde; Zhao, Peng; Xie, Jihui; Wu, Fan; Zhang, Xuezhi

    2013-12-01

    We investigated the fiber Bragg grating (FBG) thermal response in space vacuum thermal environment. The FBGs were packaged with 6061-T6 aluminum. The liquid nitrogen immersion experiment results show that its wavelength shift standard deviation is 0.76 pm for 217 h. The combination effect of vacuum and cryogenic temperature was studied by thermal cycling process in space environment simulator. The FBG sensors show accuracy better than 2% full scale, and the hysteresis errors are below 1%. It proves that these metal packaged FBG sensors can survive and meet the requirement of space measurement. PMID:24387420

  9. High-precision thermal strain measurements using surface-mounted fiber Bragg grating sensors

    NASA Astrophysics Data System (ADS)

    Mueller, Uwe C.; Both, Jan; Roths, Johannes; Baier, Horst

    2010-03-01

    Thermal strain measurements by fiber Bragg grating (FBG) sensors mounted onto different host materials are demonstrated for low coefficients of thermal expansion (CTE). Such low CTEs are typically found in carbon fiber reinforced plastics (CFRP). This work has application potential for FBG sensor networks in the highprecision control of thermal deformations in structures or in curing monitoring. For this purpose, a thermal error model of the FBG sensor, which accounts for the thermo-optic coefficient and the thermal expansion of the FBG, was characterized experimentally. The error-model characterization method is based on reference measurements of FBGs bonded to ZERODUR ceramics. Using this error model, thermal strain can be measured by surface-mounted FBGs on any given host structure using an external temperature reference and the FBG's wavelength shift. This method is demonstrated successfully for unidirectional layers of CFRP with a CTE of -0.4 . 10-6 1/K in fiber direction and for steel (316 Ti), which is commonly used in cryogenic applications. Measurements are performed for temperatures from 100K to 320K and the results are verified by high-precision dilatometer measurements. Accuracy limits of the FBG-based thermal strain measurements are discussed, as well as the minimization of errors induced by the FBG's structural interface. Further, the reduction of errors in the adhesive bonding is discussed. This work expands the understanding of the separation of thermal and mechanical effects in the signals obtained by FBGs.

  10. Femtosecond-laser-inscribed sampled fiber Bragg grating with ultrahigh thermal stability.

    PubMed

    Zhang, Congzhe; Yang, Yuanhong; Wang, Chao; Liao, Changrui; Wang, Yiping

    2016-02-22

    We have successfully fabricated a series of sampled fiber Bragg gratings with easily adjustable sampling periods and duty cycles using an 800 nm femtosecond laser point-by-point inscription. The thermal stability of the fabricated fiber gratings was investigated using isochronal annealing tests, which indicated that the fiber gratings are capable of maintaining high reflectivity at temperatures of up to 1000°C for 8 h. This demonstrates the potential of the developed sampled fiber Bragg gratings for use in multi-wavelength fiber lasers and a variety of high temperature applications. PMID:26907050

  11. Laser-induced grating spectroscopy of cadmium telluride

    NASA Astrophysics Data System (ADS)

    Petrovic, Mark S.; Suchocki, Andrzej; Powell, Richard C.; Cantwell, Gene; Aldridge, Jeff

    1989-08-01

    Laser-induced transient gratings produced by two-photon absorption of picosecond pulses at 1.064 μm were used to examine the room-temperature nonlinear optical responses of CdTe crystals with different types of conductivity. Pulse-probe degenerate four-wave mixing measurements of grating dynamics on subnanosecond time scales were used to measure the ambipolar diffusion coefficient (Da) of charge carriers in the crystals. The value of Da =3.0 cm2 s-1 which was obtained is in very good agreement with theoretical estimates. A long-lived contribution to the signal consistent with a trapped charge photorefractive effect was observed at large grating spacings for n-type conductivity, and is tentatively attributed to a larger trap density in this sample. Measurements of the relative scattering efficiencies of successive diffracted orders in the Raman-Nath regime allowed for calculation of the laser-induced change in the index of refraction, due to the creation of free carriers. The value of Δn=4×10-4 which was obtained is in good agreement with theoretical estimates.

  12. Polarized thermal radiation by layer-by-layer metallic emitters with sub-wavelength grating.

    PubMed

    Lee, Jae-Hwang; Leung, Wai; Kim, Tae Guen; Constant, Kristen; Ho, Kai-Ming

    2008-06-01

    Metallic thermal emitters consisting of two layers of differently structured nickel gratings on a homogeneous nickel layer are fabricated by soft lithography and studied for polarized thermal radiation. A thermal emitter in combination with a sub-wavelength grating shows a high extinction ratio, with a maximum value close to 5, in a wide mid-infrared range from 3.2 to 7.8 mum, as well as high emissivity up to 0.65 at a wavelength of 3.7 microm. All measurements show good agreement with theoretical predictions. Numerical simulations reveal that a high electric field exists within the localized air space surrounded by the gratings and the intensified electric-field is only observed for the polarizations perpendicular to the top sub-wavelength grating. This result suggests how the emissivity of a metal can be selectively enhanced at a certain range of wavelengths for a given polarization. PMID:18545587

  13. Subwavelength-grating-induced wavefront aberrations: a case study

    NASA Astrophysics Data System (ADS)

    Crabtree, Karlton; Chipman, Russell A.

    2007-01-01

    The on-axis wavefront aberrations of a one-dimensional sub-wavelength grating anti-reflection coating on a f/1.7 lens surface is dominated by defocus, astigmatism, and piston. The astigmatism is 0.02 waves and the magnitude of the piston approaches 1 wave peak-to-valley. The difference in aberrations between orthogonally polarized wavefronts, or the retardance aberration, shows 0.01 waves of astigmatism like variation and more than 0.01 waves of retardance induced defocus like variation.

  14. Variational approach to solving the spectral Boltzmann transport equation in transient thermal grating for thin films

    NASA Astrophysics Data System (ADS)

    Chiloyan, Vazrik; Zeng, Lingping; Huberman, Samuel; Maznev, Alexei A.; Nelson, Keith A.; Chen, Gang

    2016-07-01

    The phonon Boltzmann transport equation (BTE) is widely utilized to study non-diffusive thermal transport. We find a solution of the BTE in the thin film transient thermal grating (TTG) experimental geometry by using a recently developed variational approach with a trial solution supplied by the Fourier heat conduction equation. We obtain an analytical expression for the thermal decay rate that shows excellent agreement with Monte Carlo simulations. We also obtain a closed form expression for the effective thermal conductivity that demonstrates the full material property and heat transfer geometry dependence, and recovers the limits of the one-dimensional TTG expression for very thick films and the Fuchs-Sondheimer expression for very large grating spacings. The results demonstrate the utility of the variational technique for analyzing non-diffusive phonon-mediated heat transport for nanostructures in multi-dimensional transport geometries, and will assist the probing of the mean free path distribution of materials via transient grating experiments.

  15. Laser induced damage in multilayer dielectric gratings due to ultrashort laser pulses. Revision 1

    SciTech Connect

    Shore, B.W.; Stuart, B.C.; Feit, M.D.; Rubenchik, A.M.; Perry, M.D.

    1995-07-11

    Chirped pulse amplification is increasingly used to produce intense ultrashort laser pulses. When high-efficiency gratings are the dispersive element, as in the LLNL Petawatt laser, their susceptibility to laser induced damage constitutes a limitation on the peak intensities that can be reached. To obtain robust gratings, it is necessary to understand the causes of short-pulse damage, and to recognize the range of design options for high efficiency gratings. Metal gratings owe their high efficiency to their high conductivity. To avoid the inevitable light absorption that accompanies conductivity, we have developed designs for high efficiency rejection gratings that use only transparent dielectric materials. These combine the reflectivity of a multi-layer dielectric stack with a diffraction grating. We report here our present understanding of short-pulse laser induced damage, as it applies to dielectric gratings.

  16. Laser induced damage in multilayer dielectric gratings due to ultrashort laser pulses

    SciTech Connect

    Shore, B.W.; Stuart, B.C.; Feit, M.D.; Rubenchik, A.M.; Perry, M.D.

    1995-05-26

    Chirped pulse amplification is increasingly used to produce intense ultrashort laser pulses. When high-efficiency gratings are the dispersive element, as in the LLNL Petawatt laser, their susceptibility to laser induced damage constitutes a limitation on the peak intensities that can be reached. To obtain robust gratings, it is necessary to understand the causes of short-pulse damage, and to recognize the range of design options for high efficiency gratings. Metal gratings owe their high efficiency to their high conductivity. To avoid the inevitable light absorption that accompanies conductivity, we have developed designs for high efficiency reflection gratings that use only transparent dielectric materials. These combine the reflectivity of a multilayer dielectric stack with a diffraction grating. We report here our present understanding of short-pulse laser induced damage, as it applies to dielectric gratings.

  17. Thermally tunable integrated planar Bragg-grating stabilized diode laser

    NASA Astrophysics Data System (ADS)

    Lynch, S. G.; Gates, J. C.; Berry, S. A.; Holmes, C.; Smith, P. G. R.

    2015-03-01

    A pair of external cavity diode lasers are fabricated using an integrated planar Bragg grating. The planar waveguide and Bragg reflector is UV-written within a glass-on-silicon chip. Intensity isolated, continuous wavelength tuning at > 1kHz modulation rate is acheived using micro-heating elements fabricated directly over the Bragg grating. Low RIN (<140dB) and low linewidth (δν ~ 200 kHz) operation is found using a heterodyne measurement. We demonstrate the lasers operating in phase-locked loop configuration where one laser is frequency-offset locked to the other.

  18. Trace species concentration and temperature measurements at high pressure using laser-induced grating spectroscopy

    NASA Astrophysics Data System (ADS)

    Brown, Michael S.; DeBarber, Peter A.; Cummings, Eric B.; Hornung, Hans G.

    1995-09-01

    We have recorded laser-induced grating signals from mixtures of NO2 and air over a pressure range extending from less that 100 kPa (1 atm) to 10 MPa (100 atm). Signals generated from concentrations of NO2 at the part-per-million level have been successfully detected with high signal-to-noise rations. The measurements were made using the technique of laser-induced thermal acoustics (LITA). Analysis of the acquired data was made using a comprehensive theory which includes the hydrodynamic response of the fluid and finite beam-size effects. The observed pressure dependence of the peak amplitude signals is consistent with the theory. Additionally, least squares fits between the theory and the temporally resolved signal yield accurate values of the local sound speed and thermal diffusivity. Determination of the local sound speed provides a measurement of the local temperature.

  19. Laser-Induced Thermal Acoustics

    NASA Astrophysics Data System (ADS)

    Cummings, Eric Bryant

    1995-01-01

    Laser-induced thermal acoustics (LITA) is a new technique for remote nonintrusive measurement of thermophysical gas properties. LITA involves forming, via opto-acoustic effects, grating-shaped perturbations of gas properties by the use of intersecting beams from a short-pulse laser. A third beam scatters coherently into a signal beam off the perturbation grating via acousto-optical effects. The evolution of the gas perturbations modulates the scattered signal beam. Accurate values of the sound speed, transport properties, and composition of the gas can be extracted by analyzing the signal beam. An analytical expression for the spectrum, absolute magnitude, and time history of the LITA signal is derived. The optoacoustic effects of thermalization and electrostriction are treated. Finite beam-diameter, beam-duration, and thermalization-rate effects are included in the analysis. The expression accurately models experimental signals over a wide range of gas conditions. Experimental tests using LITA have been conducted on pure and NO_2-seeded air and helium at pressures ranging from {~ }0.1 kPa-14 MPa. Carbon dioxide has been explored near its liquid-vapor critical point. Accuracies of 0.1% in sound speed measurements have been achieved in these tests. Accuracies of {~}1% have been achieved in measurements of thermal diffusivity, although beam misalignment effects have typically degraded this accuracy by a factor of {~} 10-20. Using LITA, susceptibility spectra have been taken of approximately a femtogram of NO_2 . The effects of fluid motion and turbulence have been explored. LITA velocimetry has been demonstrated, in which the Doppler shift of light scattered from a flowing fluid is measured. LITA velocimetry requires no particle seeding, has a coherent signal beam, and can be applied to pulsed flows. LITA has also been applied to measure single-shot |chi^{(1) }|^2 or "Rayleigh scattering" spectra of a gas by the use of a technique of wavelength -division multiplexing

  20. Laser-induced thermal acoustics

    NASA Astrophysics Data System (ADS)

    Cummings, Eric B.

    Laser-induced thermal acoustics (LITA) is a new technique for remote nonintrusive measurement of thermophysical gas properties. LITA involves forming, via opto-acoustic effects, grating-shaped perturbations of gas properties using intersecting beams from a short-pulse laser. A third beam scatters coherently into a signal beam off the perturbation grating via acousto-optical effects. The evolution of the gas perturbations modulates the scattered signal beam. Accurate values of the sound speed, transport properties, and composition of the gas can be extracted by analyzing the signal beam.An analytical expression for the spectrum, absolute magnitude, and time history of the LITA signal is derived. The optoacoustic effects of thermalization and electrostriction are treated. Finite beam-diameter, beam-duration, and thermalization-rate effects are included in the analysis. The expression accurately models experimental signals over a wide range of gas conditions.Experimental tests using LITA have been conducted on pure and [...]-seeded air and helium at pressures ranging from ~0.1 kPa-14 MPa. Carbon dioxide has been explored near its liquid-vapor critical point. Accuracies of 0.1% in sound speed measurements have been achieved in these tests. Accuracies of ~1% have been achieved in measurements of thermal diffusivity, although beam misalignment effects have typically degraded this accuracy by a factor of ~10-20. Using LITA, susceptibility spectra have been taken of approximately a femtogram of [...]. The effects of fluid motion and turbulence have been explored. LITA velocimetry has been demonstrated, in which the Doppler shift of light scattered from a flowing fluid is measured. LITA velocimetry requires no particle seeding, has a coherent signal beam, and can be applied to pulsed flows. LITA has also been applied to measure single-shot [...] or "Rayleigh scattering" spectra of a gas using a technique of wavelength-division multiplexing, called multiplex LITA. The LITA

  1. Generation of High-Density Electrons Based on Plasma Grating Induced Bragg Diffraction in Air

    SciTech Connect

    Shi Liping; Li Wenxue; Wang Yongdong; Lu Xin; Ding Liang'en; Zeng Heping

    2011-08-26

    Efficient nonlinear Bragg diffraction was observed as an intense infrared femtosecond pulse was focused on a plasma grating induced by interference between two ultraviolet femtosecond laser pulses in air. The preformed electrons inside the plasma grating were accelerated by subsequent intense infrared laser pulses, inducing further collisional ionization and significantly enhancing the local electron density.

  2. Kinetic of Long Period Gratings UV-Induced and Sensing Characteristics

    NASA Astrophysics Data System (ADS)

    Costa, Rita Zanlorensi Visneck; Kamikawachi, Ricardo Canute; Muller, Marcia; Fabris, José Luís

    2008-04-01

    This work presents results concerning to the production and characterization of long-period gratings in optical fibres using the point-to-point writing technique with an ultraviolet laser. Long-period gratings, with a nominal period of 407 μm, were engraved in the core of hydrogen loaded photosensitive single-mode optical fibres. The loading was carried out by submitting the fibre to a pressure of 130 atm at room temperature along time intervals up to 20 days. During the writing process, long-period grating growth was monitored recording the transmission spectrum after each engraved point. After the end of the inscription process, the grating attenuation, resonant wavelength and bandwidth were still monitored along the time. Spectral changes were recorded during time intervals as longer as 595 hours, and an analysis of the grating's growth kinetic is presented. The long-period grating thermal and strain sensitivities were also determined and the results are presented. Long-period grating was also characterized for temperature changes within the range from 25 °C to 425 °C in consecutive up-and-down thermal cycles and hysteresis effects are discussed. The analysis of the grating strain response was done with the device submitted to longitudinal mechanical stress resulting in relative deformations ranging from 0 to 125 μɛ in incremental steps of 25 μɛ. The interplay between the cross-sensitivity is discussed as well as its role in the grating performance as a sensor.

  3. Spectral enhancement of thermal radiation by laser fabricating grating structure on nickel surface

    NASA Astrophysics Data System (ADS)

    Liu, Song; Liu, Shi-Bing

    2015-05-01

    Previous studies have shown some correlations between the optical properties of objects and their surface patterns. We fabricate tens of micrometer period gratings by femtosecond laser direct writing technology on polished nickel targets and measure their thermal radiation spectra at a temperature of 623 K by Fourier transform infrared (FTIR) spectrometry. The results show an obvious major enhanced peak in which the wavelength is slightly larger than the grating period. Surface plasmon resonance (SPR) and Kirchhoff’s law of thermal radiation are applied to give this phenomenon a preliminary explanation. In addition, we utilized rigorous coupled wave analysis (RCWA) to simulate the absorption spectrum of the grating surface. The experiment results show good agreement with the simulation results. Project supported by the National Natural Science Foundation of China (Grant No. 51275012).

  4. Subwavelength-grating-induced wavefront aberrations: a case study

    NASA Astrophysics Data System (ADS)

    Crabtree, Karlton; Chipman, Russell A.

    2007-07-01

    The on-axis wavefront aberrations of a one-dimensional subwavelength-grating antireflection coating on an f/1.7 lens surface are shown to be small with noticeable contributions of defocus, astigmatism, and piston. The astigmatism is 0.02 wave, and the magnitude of the piston approaches one wave peak-to-valley. The difference in aberrations between orthogonally polarized wavefronts, or the retardance aberration, shows 0.01 wave of astigmatismlike variation and more than 0.01 wave of retardance-induced defocuslike variation. A small coupling between polarization states occurs in the form of the familiar Maltese cross, yielding a maximum of 3% coupling in the four diagonal edges of the pupil.

  5. Temporal thermal response of Type II-IR fiber Bragg gratings

    SciTech Connect

    Liao Changrui; Wang Dongning; Li Yuhua; Sun Tong; Grattan, Kenneth T. V.

    2009-06-01

    We use the phase mask method to investigate both experimentally and theoretically the temporal thermal response of Type II-IR fiber Bragg gratings inscribed by a femtosecond laser. A fast testing system is developed to measure the thermal response time by means of periodic CO2 laser irradiation, which creates a rapid temperature change environment. The temporal thermal response is found to be independent of the heat power and the heat direction, although the grating produced destroys the axial symmetry of the fiber. The measured values of the temporal thermal response are {approx}230 ms for heating and {approx}275 ms for cooling, which different from the simulation results obtained from a lumped system equation. The causes of such differences are investigated in detail.

  6. Concentration measurements with Laser-Induced Thermal Acoustics

    NASA Astrophysics Data System (ADS)

    Schlamp, Stefan; Sobota, Thomas H.

    2001-03-01

    Laser-induced thermal acoustics (LITA) is used to measure the concentration of iodine vapor (40-150 ppm) in air instantaneously (1 μs), remotely, and non-intrusively. Two focused, pulsed intersecting laser beams inscribe a density grating in the fluid. A cw interrogation beam directed at the Bragg angle on the grating is scattered into a coherent signal beam whose intensity depends on the instantaneous density grating magnitude. The signal beam is detected by a photomultiplier tube and its history recorded by a digital storage oscilloscope. The species in question (e.g., I_2) and the dilution species are excited resonantly (by thermalization) and non-resonantly (by electrostriction), respectively. The signals show oscillations at (twice) the grating's Brillouin frequency for the case of thermalization (electrostriction). The ratio of the thermalization to the electrostriction grating magnitudes is proportional to the resonant species concentration. They are extracted by a least-squares fitting scheme. For good accuracy, the ratio must be of order unity. For this case, the standard error is 5%. The speed of sound (error <1%) and flow velocity (error <1%) can be measured simultaneously.

  7. Monte Carlo study of non-diffusive relaxation of a transient thermal grating in thin membranes

    NASA Astrophysics Data System (ADS)

    Zeng, Lingping; Chiloyan, Vazrik; Huberman, Samuel; Maznev, Alex A.; Peraud, Jean-Philippe M.; Hadjiconstantinou, Nicolas G.; Nelson, Keith A.; Chen, Gang

    2016-02-01

    The impact of boundary scattering on non-diffusive thermal relaxation of a transient grating in thin membranes is rigorously analyzed using the multidimensional phonon Boltzmann equation. The gray Boltzmann simulation results indicate that approximating models derived from previously reported one-dimensional relaxation model and Fuchs-Sondheimer model fail to describe the thermal relaxation of membranes with thickness comparable with phonon mean free path. Effective thermal conductivities from spectral Boltzmann simulations free of any fitting parameters are shown to agree reasonably well with experimental results. These findings are important for improving our fundamental understanding of non-diffusive thermal transport in membranes and other nanostructures.

  8. Negative-index gratings formed by femtosecond laser overexposure and thermal regeneration

    PubMed Central

    He, Jun; Wang, Yiping; Liao, Changrui; Wang, Chao; Liu, Shen; Yang, Kaiming; Wang, Ying; Yuan, Xiaocong; Wang, Guo Ping; Zhang, Wenjing

    2016-01-01

    We demonstrate a method for the preparation of negative-index fibre Bragg gratings (FBGs) using 800 nm femtosecond laser overexposure and thermal regeneration. A positive-index type I-IR FBG was first inscribed in H2-free single-mode fibre using a femtosecond laser directed through a phase mask, and then a highly polarization dependant phase-shifted FBG (P-PSFBG) was fabricated from the type I-IR FBG by overexposure to the femtosecond laser. Subsequently, the P-PSFBG was thermally annealed at 800 °C for 12 hours. Grating regeneration was observed during thermal annealing, and a negative-index FBG was finally obtained with a high reflectivity of 99.22%, an ultra-low insertion loss of 0.08 dB, a blueshift of 0.83 nm in the Bragg wavelength, and an operating temperature of up to 1000 °C for more than 10 hours. Further annealing tests showed that the thermal stability of the negative-index FBG was lower than that of a type II-IR FBG, but much higher than that of a type I-IR FBG. Moreover, the formation of such a negative-index grating may result from thermally regenerated type IIA photosensitivity. PMID:26979090

  9. Study of laser induced plasma grating dynamics in gases

    NASA Astrophysics Data System (ADS)

    Jarnac, A.; Durand, M.; Liu, Y.; Prade, B.; Houard, A.; Tikhonchuk, V.; Mysyrowicz, A.

    2014-02-01

    The relaxation of a plasma grating resulting from the interference of two crossing laser filaments in molecular and atomic gases is studied experimentally. Dissipation of the grating fringes is dominated by ambipolar diffusion in atomic gases and by a combination of ambipolar diffusion and collision-assisted free electron recombination in molecular gases. A theoretical model of the grating evolution is developed and compared to experimental results. Good agreement with simulations allows extracting plasma properties such as electron density, diffusion and recombination coefficients in Ne, Ar, Kr, Xe, N2, O2, CO2 and air at atmospheric pressure.

  10. Thermal Stability of Photosensitive Bragg Gratings in Sputter-Deposited Germanosilicate Glass

    SciTech Connect

    POTTER JR.,BARRETT G.; POTTER,KELLY SIMMONS; DUNBAR,TIMOTHY D.

    2000-07-24

    The thermal stability of photo-imprinted Bragg gratings formed in reactive-atmosphere, RF-magnetron sputtered germanosilicate thin films was evaluated in terms of point defect modifications observed during isochronal annealing. Optical and magnetic spectroscopes were utilized to evaluate structural relaxation in these sputtered glasses on both a local and medium-range size scale. Depending upon the substrate temperature used during deposition, significant structural rearrangement was found to occur with increasing post-deposition anneal temperature to 600 C. This resulted in changes in the photobleaching response of the material itself as the identity of optically active structural defects evolved. Based on a color center model for photosensitivity in these materials and measured changes in optical absorption with annealing, the thermal stability of a photo-imprinted Bragg grating was modeled. Good qualitative agreement with experiment was observed.

  11. Temperature-insensitive compact phase-shifted long-period gratings induced by surface deformation in single-mode fiber

    NASA Astrophysics Data System (ADS)

    Zheng, Shijie; Lei, Xiaohua; Zhu, Yinian

    2015-12-01

    We present a temperature-insensitive compact phase-shifted long-period grating (PS-LPG) induced by using focused pulse CO2 laser via point-by-point technique. By introducing a phase shift with 1800° ( π shift) in the center of the long-period grating (~420 µm per period, 20 periodicity in total), the original coupling resonance at 1318.55 nm splits into two symmetrical spectral peaks at 1283 and 1348 nm. FWHM between those two peaks is 36.55 nm, and the power intensities of two peaks are the same as -10.2 dB. The thermal characteristic of the PS-LPGs is around 8.8 pm/°C that is less than that of fiber Bragg grating (12 pm/°C). As a result, such fiber grating devices can be applied in a laser cavity as an all-fiber filter. Variation of phase shifts in LPGs give rise to different spectral peaks of coupled resonance, which makes the proposed PS-LPGs as a good candidate for the applications in sensing networks and optical telecommunications.

  12. Influence of pre-annealing on the thermal regeneration of fiber Bragg gratings in standard optical fibers.

    PubMed

    Holmberg, Patrik; Laurell, Fredrik; Fokine, Michael

    2015-10-19

    A detailed study of the dynamics during thermal regeneration of fiber Bragg gratings, written in hydrogen-loaded standard single-mode fibers using a ns pulsed 213 nm UV laser, is reported. Isothermal pre-annealing performed in the range 85 °C to 1100 °C, with subsequent grating regeneration at 1100 °C, resulted in a maximum refractive index modulation, Δn(m) ~1.4⋅10(-4), for gratings pre-annealed near 900 °C while a minimum value of Δn(m) ~2⋅10(-5) was achieved irrespective of pre-annealing temperature. This optimum denote an inflection point between opposing thermally triggered processes, which we ascribe to the reaction-diffusion mechanism of molecular water and hydroxyl species in silica. The results shed new light on the mechanisms underlying thermal grating regeneration in optical fibers. PMID:26480412

  13. Trace species concentration and temperature measurements at high pressure using laser-induced grating spectroscopy

    SciTech Connect

    Brown, M.S.; DeBarber, P.A.; Cummings, E.B.; Hornung, H.G.

    1995-12-31

    Ongoing development by NASA and engine manufacturers of the next generation of aircraft engines for civil transport calls for combustors that will operate at pressures up to 60 atm and 2,000 K. Diagnostic measurements of this combustion environment are required to address the many engineering and modeling questions. While a variety of laser-based optical techniques have been developed over the last 20 years to detect trace species in reacting flows, few measurements have been made at pressures above 10 atm. Here, the authors have recorded laser-induced grating signals from mixtures of NO{sub x} and air over a pressure range extending from less than 100 kPa (1 atm) to 10 MPa (100 atm). Signals generated from concentrations of NO{sub 2} at the part-per-million level have been successfully detected with high signal-to-noise ratios. The measurements were made using the technique of laser-induced thermal acoustics (LITA). Analysis of the acquired data was made using a comprehensive theory which includes the hydrodynamic response of the fluid and finite beam-size effects. The observed pressure dependence of the peak amplitude signals is consistent with the theory. Additionally, least squares fits between the theory and the temporally resolved signal yield accurate values of the local sound speed and thermal diffusivity. Determination of the local sound speed provides a measurement of the local temperature.

  14. Design of a high voltage source to fabricate fiber optic arc induced gratings

    NASA Astrophysics Data System (ADS)

    Mata-Chavez, R. I.; Estudillo-Ayala, J. M.; Hernández-Garcia, J. C.; Rojas-Laguna, R.; Anzueto-Sanchez, G.; Martínez-Ríos, A.; Trejo-Duran, M.; Alvarado-Méndez, E. A.; Andrade-Lucio, J. A.

    2007-03-01

    In this paper we propose a high voltage source which is controlled by a communication port I/O of a data acquisition card. The graphical programming language LabView is employed for this task. We make use of this source to produce optical fiber gratings by inducing an electric arc with the point by point procedure. It has a control section to modify the arc duration time and thus the voltage and current applied to the fiber by means of two electrodes. The experimental setup by which we characterized the gratings is depicted and we also present the transmitting spectrum. The gratings were fabricated with SMF-28 fiber but microstructured fiber can be exploited too. These gratings can be used with optical fiber lasers as optical filters and in the implementation of optical sensors.

  15. Dynamics of surface thermal expansion and diffusivity using two-color reflection transient gratings

    SciTech Connect

    Pennington, D.M.; Harris, C.B.

    1993-02-01

    We report ultrafast measurements of the dynamic thermal expansion of a surface and the temperature dependent surface thermal diffusivity using a two-color reflection transient grating technique. Studies were performed on p-type, n-type, and undoped GaAs(100) samples at several temperatures. Using a 75 fs ultraviolet probe with visible excitation beams, the electronic effects that dominate single color experiments become negligible; thus surface expansion due to heating and the subsequent contraction caused by cooling provide the dominant influence on the diffracted probe. The diffracted signal was composed of two components, thermal expansion of the surface and heat flow away from the surface, allowing the determination of the rate of expansion as well as the surface thermal diffusivity. At room temperature a signal rise due to thermal expansion was observed, corresponding to a maximum average displacement of {approx} 1 {angstrom} at 32 ps. Large fringe spacings were used, thus the dominant contributions to the signal were expansion and diffusion perpendicular to the surface. Values for the surface thermal diffusivity of GaAs were measured and found to be in reasonable agreement with bulk values above 50{degrees}K. Below 50{degrees}K, the diffusivity at the surface was more than an order of magnitude slower than in the bulk due to increased phonon boundary scattering. Comparison of the results with a straightforward thermal model yields good agreement over a range of temperatures (12--300{degrees}K). The applicability and advantages of the transient grating technique for studying photothermal and photoacoustic phenomena are discussed.

  16. Simultaneous regeneration of seed FBGs during the HFCVD diamond-grating coating process and its thermal monitoring

    NASA Astrophysics Data System (ADS)

    Alberto, Nélia J.; Kalinowski, Hypolito J.; Neto, Victor F.; Nogueira, Rogério N.

    2015-09-01

    In this work, the simultaneous regeneration of seed fibre Bragg gratings (FBGs) during the diamond-grating coating and the thermal monitoring of that process is presented. The diamond was deposited through the hot filament chemical vapour deposition (HFCVD) process, and due to the high temperatures characteristics of this method (above 800 ºC), regenerated FBGs are suitable samples to be coated. The advantages of this study are the possibility to regenerate the seed gratings during the coating process, becoming the fibre more resistant and the procedure less time consuming, and to control the temperature, a critical parameter for the morphology of the deposited layers.

  17. Bending induced self-organized switchable gratings on polymeric substrates.

    PubMed

    Parra-Barranco, Julian; Oliva-Ramirez, Manuel; Gonzalez-Garcia, Lola; Alcaire, Maria; Macias-Montero, Manuel; Borras, Ana; Frutos, Fabian; Gonzalez-Elipe, Agustin R; Barranco, Angel

    2014-08-13

    We present a straightforward procedure of self-surface patterning with potential applications as large area gratings, invisible labeling, optomechanical transducers, or smart windows. The methodology is based in the formation of parallel micrometric crack patterns when polydimethylsiloxane foils coated with tilted nanocolumnar SiO2 thin films are manually bent. The SiO2 thin films are grown by glancing angle deposition at room temperature. The results indicate that crack spacing is controlled by the film nanostructure independently of the film thickness and bending curvature. They also show that the in-plane microstructural anisotropy of the SiO2 films due to column association perpendicular to the growth direction determines the anisotropic formation of parallel cracks along two main axes. These self-organized patterned foils are completely transparent and work as customized reversible diffraction gratings under mechanical activation. PMID:25007108

  18. Gamma radiation-induced blue shift of resonance peaks of Bragg gratings in pure silica fibres

    NASA Astrophysics Data System (ADS)

    Faustov, A. V.; Gusarov, A. I.; Mégret, P.; Wuilpart, M.; Kinet, D.; Zhukov, A. V.; Novikov, S. G.; Svetukhin, V. V.; Fotiadi, A. A.

    2016-02-01

    We report the first observation of a significant gamma radiation-induced blue shift of the reflection/transmission peak of fibre Bragg gratings inscribed into pure-silica core fibres via multiphoton absorption of femtosecond pulses. At a total dose of ~100 kGy, the shift is ~20 pm. The observed effect is attributable to the ionising radiation-induced decrease in the density of the silica glass when the rate of colour centre formation is slow. We present results of experimental measurements that provide the key parameters of the dynamics of the gratings for remote dosimetry and temperature sensing.

  19. Development of Laser-induced Grating Spectroscopy for Underwater Temperature Measurement in Shock Wave Focusing Regions

    NASA Technical Reports Server (NTRS)

    Gojani, Ardian B.; Danehy, Paul M.; Alderfer, David W.; Saito, Tsutomu; Takayama, Kazuyoshi

    2003-01-01

    In Extracorporeal Shock Wave Lithotripsy (ESWL) underwater shock wave focusing generates high pressures at very short duration of time inside human body. However, it is not yet clear how high temperatures are enhanced at the spot where a shock wave is focused. The estimation of such dynamic temperature enhancements is critical for the evaluation of tissue damages upon shock loading. For this purpose in the Interdisciplinary Shock Wave Research Center a technique is developed which employs laser induced thermal acoustics or Laser Induced Grating Spectroscopy. Unlike most of gasdynamic methods of measuring physical quantities this provides a non-invasive one having spatial and temporal resolutions of the order of magnitude of 1.0 mm3 and 400 ns, respectively. Preliminary experiments in still water demonstrated that this method detected sound speed and hence temperature in water ranging 283 K to 333 K with errors of 0.5%. These results may be used to empirically establish the equation of states of water, gelatin or agar cells which will work as alternatives of human tissues.

  20. Development of laser-induced grating spectroscopy for underwater temperature measurement in shock wave focusing regions

    NASA Astrophysics Data System (ADS)

    Gojani, Ardian B.; Danehy, Paul M.; Alderfer, David W.; Saito, Tsutomu; Takayama, Kazuyoshi

    2004-02-01

    In Extracorporeal Shock Wave Lithotripsy (ESWL) underwater shock wave focusing generates high pressures at very short duration of time inside human body. However, it is not yet clear how high temperatures are enhanced at the spot where a shock wave is focused. The estimation of such dynamic temperature enhancements is critical for the evaluation of tissue damages upon shock loading. For this purpose in the Interdisciplinary Shock Wave Research Center a technique is developed which employs laser induced thermal acoustics or Laser Induced Grating Spectroscopy. Unlike most of gas-dynamic methods of measuring physical quantities this provides a non-invasive one having spatial and temporal resolutions of the order of magnitude of 1.0 mm 3 and 400 ns, respectively. Preliminary experiments in still water demonstrated that this method detected sound speed and hence temperature in water ranging 283 K to 333 K with errors of 0.5%. These results are used to empirically establish the equation of states of water, gelatin or agar cell which will work as alternatives of human tissues.

  1. Coherent manipulation of the Raman-induced gratings in atomic media

    NASA Astrophysics Data System (ADS)

    Arkhipkin, V. G.; Myslivets, S. A.

    2016-01-01

    We consider dynamically controllable periodic structures (gratings), resulting from Raman interaction of a weak probe field with a standing-wave pump and a second control laser field in four-level atomic media of N type. The gratings under study are induced due to periodic spatial modulation of the Raman gain in a standing pump field and fundamentally differ from the ones based on electromagnetically induced transparency. We show that spectral and transmission properties of these gratings can be controlled with the help of an additional weak field (control field) by varying its intensity or frequency. Small variations of the control field intensity can change the system from opaque to transparent and vice versa and this structure can operate as an all-optical transistor. Such a structure can also be used as a tunable nonlinear mirror with amplification.

  2. Asymmetric mode coupling in arc-induced long-period fiber gratings

    NASA Astrophysics Data System (ADS)

    Martinez-Rios, A.; Torres-Gomez, I.; Anzueto-Sanchez, G.; Selvas-Aguilar, R.; Duran-Ramirez, V. M.; Guerrero-Viramontes, J. A.; Toral-Acosta, D.; Salceda Delgado, G.; Castillo-Guzman, A.

    2016-04-01

    An extensive experimental study of the transverse modal field characteristics of mircrobend arc-induced long-period fiber gratings is presented. A wavelength scanning of the near-field intensity pattern inside each loss band in the transmission spectrum, shows a clear asymmetry in the transverse intensity distribution resulting from the fabrication method. This asymmetry reflects as a 10.7 dB difference in the notch depths for two orthogonal polarizations. Though a one year study, it was found that that environmental conditions during fabrication strongly affects the gratings characteristics. The best performance was obtained during the autumn season, where microbend arc-induced long-period fiber gratings produce wavelength filters with short lengths (between 10 and 30 periods for depths in excess of 20 dB) and the insertion loss may be as low as 0.12 dB.

  3. CO2 laser induced long period gratings in optical microfibers.

    PubMed

    Xuan, Haifeng; Jin, Wei; Zhang, Min

    2009-11-23

    Long period gratings (LPGs) are fabricated by use of focused high frequency CO(2) laser pulses to periodically modify the transverse dimension of silica microfibers. A 20-period LPG with a 27 dB attenuation dip is realized in a microfiber with a diameter of approximately 6.3 microm. The resonant wavelength has a negative temperature coefficient and a high sensitivity to external refractive index. The microfiber LPGs may be useful in micron scale in-fiber devices and sensors. PMID:19997432

  4. Thermal stability of ferroelectric domain gratings in Rb-doped KTP

    NASA Astrophysics Data System (ADS)

    Lindgren, Gustav; Peña, Alexandra; Zukauskas, Andrius; Liljestrand, Charlotte; Ménaert, Bertrand; Boulanger, Benoît.; Canalias, Carlota

    2015-08-01

    We study the thermal stability of domain walls in periodically poled Rb-doped KTP crystals. Domain-wall motion is observed after annealing the crystals above 550 °C. This motion is highly anisotropic along the a- and b- crystallographic axes. Along the b-axis domain wall motion is in the order of tens of micrometers. In the a-direction, it results in either three orders of magnitude smaller domain wall displacement or in domain merging, depending on the initial domain configuration. We show that the thermal stability of the domain gratings depends on their periodicity, resulting in complete backswitching for sub-micrometer domains annealed at 730 °C.

  5. Measurement of the thermal expansion of melt-textured YBCO using optical fibre grating sensors

    NASA Astrophysics Data System (ADS)

    Zeisberger, M.; Latka, I.; Ecke, W.; Habisreuther, T.; Litzkendorf, D.; Gawalek, W.

    2005-02-01

    In this paper we present measurements of the thermal expansion of melt-textured YBaCuO in the temperature range 30-300 K by means of optical fibre sensors. The sample, which had a size of 38 × 38 × 18 mm3, was prepared by our standard melt-texturing process using SmBaCuO seeds. One fibre containing three Bragg gratings which act as strain sensors was glued to the sample surface with two sensors parallel to the ab-plane and one sensor parallel to the c-axis. The sample was cooled down to a minimum temperature of 30 K in a vacuum chamber using a closed cycle refrigerator. In the temperature range we used, the thermal expansion coefficients are in the range of (3-9) × 10-6 K-1 (ab-direction) and (5-13) × 10-6 K-1 (c-direction).

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

    SciTech Connect

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

    2005-02-06

    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 deg. 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.

  7. Laser-induced thermal-acoustic velocimetry with heterodyne detection

    SciTech Connect

    Schlamp, Stefan; Cummings, Eric B.; Sobota, Thomas H.

    2000-02-15

    Laser-induced thermal acoustics (LITA) was used with heterodyne detection to measure simultaneously and in a single laser pulse the sound speed and flow velocity of NO{sub 2} -seeded air in a low-speed wind tunnel up to Mach number M=0.1 . The uncertainties of the velocity and the sound speed measurements were {approx}0.2 m/s and 0.5%, respectively. Measurements were obtained through a nonlinear least-squares fit to a general, analytic closed-form solution for heterodyne-detected LITA signals from thermal gratings. Agreement between theory and experiment is exceptionally good. (c) 2000 Optical Society of America.

  8. Magnetically driven microconvective instability of optically induced concentration grating in ferrofluids.

    PubMed

    Zablotsky, Dmitry; Blums, Elmars

    2011-08-01

    In this paper, we consider a concentration grating of magnetic nanoparticles optically induced by thermodiffusion in a layer of ferrofluid in the presence of the external homogeneous magnetic field. The applied field is directed along the concentration gradient and leads to the appearance of the internal nonhomogeneous demagnetizing fields. When the system reaches equilibrium, the optical pumping is switched off, and the grating is allowed to relax. We carry out a stability analysis using the Galerkin approach and numerical simulations of the full system of equations to determine the growth rates and the mode amplitudes of the hydrodynamic and concentration perturbations during the relaxation stage. PMID:21929102

  9. Compact fiber Bragg grating dynamic strain sensor cum broadband thermometer for thermally unstable ambience

    NASA Astrophysics Data System (ADS)

    Sreekumar, K.; Asokan, S.

    2010-01-01

    An instrument for simultaneous measurement of dynamic strain and temperature in a thermally unstable ambience has been proposed, based on fiber Bragg grating technology. The instrument can function as a compact and stand-alone broadband thermometer and a dynamic strain gauge. It employs a source wavelength tracking procedure for linear dependence of the output on the measurand, offering high dynamic range. Two schemes have been demonstrated with their relative merits. As a thermometer, the present instrumental configuration can offer a linear response in excess of 500 °C that can be easily extended by adding a suitable grating and source without any alteration in the procedure. Temperature sensitivity is about 0.06 °C for a bandwidth of 1 Hz. For the current grating, the upper limit of strain measurement is about 150 µɛ with a sensitivity of about 80 nɛ Hz-1/2. The major source of uncertainty associated with dynamic strain measurement is the laser source intensity noise, which is of broad spectral band. A low noise source device or the use of optical power regulators can offer improved performance. The total harmonic distortion is less than 0.5% up to about 50 µɛ,1.2% at 100 µɛ and about 2.3% at 150 µɛ. Calibrated results of temperature and strain measurement with the instrument have been presented. Traces of ultrasound signals recorded by the system at 200 kHz, in an ambience of 100-200 °C temperature fluctuation, have been included. Also, the vibration spectrum and engine temperature of a running internal combustion engine has been recorded as a realistic application of the system.

  10. Compartmentalized liquid crystal alignment induced by sparse polymer ribbons with surface relief gratings.

    PubMed

    Ji, Zhichao; Zhang, Xinzheng; Shi, Bin; Li, Wei; Luo, Weiwei; Drevensek-Olenik, Irena; Wu, Qiang; Xu, Jingjun

    2016-01-15

    We report on the liquid crystal (LC) alignment induced by sparse polymer ribbons fabricated by the two-photon polymerization-based direct laser writing method. Each ribbon is fabricated by a single scan of the laser through the photoresist and possesses surface relief gratings on both sides. The relief gratings are caused by the optical interference between the incident and reflected laser beams. With the aid of these relief gratings, LC molecules can be well aligned along the selected direction of the ribbons. LC cells with the Z-shaped and checkerboard-type microstructures are constructed based on the sparse out-of-plane polymeric ribbons. Our results show that with such polymer ribbons a compartmentalized LC alignment in the arbitrary microstructures can be realized. PMID:26766708

  11. The determination of the elastic constants of isotropic solids by means of transient thermal surface gratings

    NASA Astrophysics Data System (ADS)

    Fivez, J.

    2016-01-01

    Starting from the coupled thermoelastic equations, an analytic formula is obtained for the surface deformation of a semi-infinite homogeneous and isotropic solid in an impulsive stimulated scattering (ISS) experiment. The surface ripple consists of a transient diffusive grating and a standing Rayleigh wave. The time evolution of the diffusive part directly reveals the thermal diffusivity. The oscillatory part then reveals the elastic properties, and explicit formulae are presented for retrieving the elastic moduli as a function of the frequency and amplitude of the standing Rayleigh wave. The analytic formulae not only allow to avoid time-consuming and delicate numerical integration but they also demonstrate the uniqueness of the inversion from signal to material parameters and offer direct insight into the error propagation. The formulae are applied to real experimental data, illustrating the strength and the limitations of the ISS technique.

  12. Thermal image encryption obtained with a SiO2 space-variant subwavelength grating supporting surface phonon-polaritons.

    PubMed

    Dahan, Nir; Niv, Avi; Biener, Gabriel; Kleiner, Vladimir; Hasman, Erez

    2005-12-01

    Space-variant partially polarized thermal emission is investigated. We show that by coupling surface phonon-polaritons to a propagating field, large anisotropy of the emissivity is obtained within a narrow spectral range. We experimentally demonstrate this effect by fabricating a space-variant subwavelength grating on a SiO2 substrate to encrypt an image in the polarization state of a thermal radiation field. PMID:16342718

  13. Femtosecond laser-induced subwavelength ripples formed by asymmetrical grating splitting

    NASA Astrophysics Data System (ADS)

    Feng, Pin; Jiang, Lan; Li, Xin; Zhang, Kaihu; Shi, Xuesong; Li, Bo; Lu, Yongfeng

    2016-05-01

    The formation process and mechanism of subwavelength ripples were studied upon irradiation of ZnO by a femtosecond laser (800 nm, 50 fs, 1 kHz). An abnormally asymmetrical grating-splitting phenomenon was discovered. At relatively high laser fluences (F = 0.51-0.63 J/cm2), near-wavelength ripples were split asymmetrically to create subwavelength laser-induced periodic surface structures (LIPSS) with dual gaps (∼230 nm and ∼430 nm) on the primary grooves. At relatively low laser fluences (F = 0.4-0.45 J/cm2), near-wavelength ripples were split symmetrically, leading to the formation of uniform subwavelength structures with a period of ∼340 nm. The splitting phenomena are related to the varying laser beam dose induced by the overlapping during line scanning. The two grating-splitting types further imply that the dominated mechanism for LIPSS formation may be changed under different processing conditions.

  14. Behavior of femtosecond laser-induced eccentric fiber Bragg gratings at very high temperatures.

    PubMed

    Chikh-Bled, Hicham; Chah, Karima; González-Vila, Álvaro; Lasri, Boumediène; Caucheteur, Christophe

    2016-09-01

    In this work, eccentric Bragg gratings are photoinscribed in telecommunication-grade optical fibers. They are localized close to the core-cladding interface, yielding strong cladding mode resonance couplings and high photoinduced birefringence. Their transmitted amplitude spectrum is measured with polarized light while they are exposed to temperature changes up to 900°C. Despite the gratings' overall good thermal stability that confirms their robustness for high-temperature refractometry, we report an interesting polarization effect depending on both the cladding mode resonance family and mode order. While the core mode birefringence decreases with growing temperatures, certain cladding mode resonances show an increase in wavelength splitting between their orthogonally polarized components. This differential behavior is of high interest in developing high-resolution, multiparametric sensing platforms. PMID:27607969

  15. Impact of index change saturation on the growth behavior of higher-order type I ultrafast induced fiber Bragg gratings

    SciTech Connect

    Smelser, Christopher W.; Mihailov, Stephen J.; Grobnic, Dan

    2008-05-15

    Ultrafast infrared induced fiber Bragg gratings in a hydrogen-loaded SMF-28 fiber are shown to exhibit complex and, what we believe to be, novel spectral evolutions. It is believed that the induced grating peak profile in the fiber is nonsinusoidal as a result of the nonlinear absorption required to modify the material. Rouard's method is used to show that the observed spectral evolution is a consequence of the saturation of the nonsinusoidal index change profile.

  16. Length and Width Effects of Metal Films on Stress-Induced Bending of Surface Micromachined Cantilever Curved Grating

    NASA Astrophysics Data System (ADS)

    Kuo, Ju-Nan

    2012-02-01

    In this study, the length and width effects of metal films on the stress-induced bending of a surface micromachined cantilever curved grating are systematically investigated. A characterization of cantilever curved gratings with various lengths and widths was conducted to observe out-of-plane deformation. A finite element model was established to analyze the deformation. Finite element analysis and experimental results indicate that the commonly used beam theory formula for predicting the deformation of surface micromachined cantilever curved gratings is not valid for these devices. Experiments show that the shape of a cantilever curved grating and residual stress have a close relationship. As the length increases, the residual stress of the metal increases, resulting in a larger out-of-plane deformation of the cantilever curved grating. The tip deflection gradually decreases as the length-to-width ratio of the cantilever curved grating increases. A more reliable shape design of metal films on the stress-induced bending of surface micromachined cantilever curved gratings can thus be achieved.

  17. Thermal stress modification in regenerated fiber Bragg grating via manipulation of glass transition temperature based on CO₂-laser annealing.

    PubMed

    Lai, Man-Hong; Lim, Kok-Sing; Gunawardena, Dinusha S; Yang, Hang-Zhou; Chong, Wu-Yi; Ahmad, Harith

    2015-03-01

    In this work, we have demonstrated thermal stress relaxation in regenerated fiber Bragg gratings (RFBGs) by using direct CO₂-laser annealing technique. After the isothermal annealing and slow cooling process, the Bragg wavelength of the RFBG has been red-shifted. This modification is reversible by re-annealing and rapid cooling. It is repeatable with different cooling process in the subsequent annealing treatments. This phenomenon can be attributed to the thermal stress modification in the fiber core by means of manipulation of glass transition temperature with different cooling rates. This finding in this investigation is important for accurate temperature measurement of RFBG in dynamic environment. PMID:25723423

  18. Optical vortex generation with wavelength tunability based on an acoustically-induced fiber grating.

    PubMed

    Zhang, Wending; Wei, Keyan; Huang, Ligang; Mao, Dong; Jiang, Biqiang; Gao, Feng; Zhang, Guoquan; Mei, Ting; Zhao, Jianlin

    2016-08-22

    We presented a method to actualize the optical vortex generation with wavelength tunability via an acoustically-induced fiber grating (AIFG) driven by a radio frequency source. The circular polarization fundamental mode could be converted to the first-order optical vortex through the AIFG, and its topological charges were verified by the spiral pattern of coaxial interference between the first-order optical vortex and a Gaussian-reference beam. A spectral tuning range from 1540 nm to 1560 nm was demonstrated with a wavelength tunability slope of 4.65 nm/kHz. The mode conversion efficiency was 95% within the whole tuning spectral range. PMID:27557207

  19. Excited and enhanced twinborn acoustic-induced mutual forces in oblique grating structures

    NASA Astrophysics Data System (ADS)

    Lu, Shuifang; Zhang, Xin; Wu, Fugen; Yao, Yuanwei; Chen, Zongwang

    2016-07-01

    We propose a water-immersed geometrically oblique grating structure patterned with a 1D periodic array of oblique rhombuses. Twin acoustic-induced mutual forces (both repulsive and attractive) between coupled steel plates were realized in this system when the external plane wave normally impacted the plates. Calculations showed that the emerging forces are more than an order of magnitude larger than the corresponding induced force of a conventional grating structure. We also found that the strong acoustic-induced mutual forces stem from the resonant excitation of nonleaky flexural Lamb modes in the coupled plates, and that these forces couple more strongly with the external incident acoustic waves. Furthermore, the amplitudes and resonant wavelengths of these forces can be coarsely controlled by changing the symmetry of the system and finely adjusted by varying the slant angle and the edge-length of the oblique rhombus. The proposed acoustic system could potentially be applied in sensors and in the ultrasonic detection of weak signals in water.

  20. Neural network data analysis for laser-induced thermal acoustics

    NASA Astrophysics Data System (ADS)

    Schlamp, Stefan; Hornung, Hans G.; Cummings, Eric B.

    2000-06-01

    A general, analytical closed-form solution for laser-induced thermal acoustic (LITA) signals using homodyne or heterodyne detection and using electrostrictive and thermal gratings is derived. A one-hidden-layer feed-forward neural network is trained using back-propagation learning and a steepest descent learning rule to extract the speed of sound and flow velocity from a heterodyne LITA signal. The effect of the network size on the performance is demonstrated. The accuracy is determined with a second set of LITA signals that were not used during the training phase. The accuracy is found to be better than that of a conventional frequency decomposition technique while being computationally as efficient. This data analysis method is robust with respect to noise, numerically stable and fast enough for real-time data analysis.

  1. Laser-induced grating spectroscopy of rare earth ions in solids

    SciTech Connect

    French, V.A.

    1992-01-01

    The characteristics of energy transfer and migration processes important in the optical dynamics of Tm,Ho:YAG and Tm:YAG laser crystals were investigated using both time-resolved fluorescence spectroscopy and laser-induced grating spectroscopy. Four-wave mixing techniques were used to produce permanent laser-induced refractive index gratings in Eu-doped silicate glasses. The effects on the characteristics of these permanent gratings produced by changing the divalent modifier ions of the glass host are reported. Efficient long-range energy migration was found to take place in the [sup 3]F[sub 4] level of the Tm ions, which enhances the energy transfer to Ho ions. The parameters describing excitation migration were determined experimentally and used to calculate an overall Tm-Ho energy transfer rate. This was found to be in close agreement with the rate determined by the results of fluorescence spectral dynamics measurements. Theoretical estimates were made of the fundamental ion-ion interaction rates responsible for each of the physical processes investigated here and the results were all found to be in close agreement with the experimentally determined values. The author extends previous investigations on the Eu-doped silicate glasses by describing the variation of the four-wave-mixing signal intensity of a series of glasses with different divalent alkaline network modifier ions. The temperature dependence of the signal from one of the samples was measured and a theoretical explanation for the change in the refractive index associated with the double-minimum potential well model is developed.

  2. Micro-strain sensing using wrinkled stiff thin films on soft substrates as tunable optical grating.

    PubMed

    Ma, Teng; Liang, Hanshuang; Chen, George; Poon, Benny; Jiang, Hanqing; Yu, Hongbin

    2013-05-20

    We report a strain sensing approach that utilizes wrinkled patterns on poly (dimethylsiloxane) (PDMS) as an optical grating to measure thermally-induced strain of different materials. The mechanism for the strain sensing and the effect of PDMS grating on strain sensing are discussed. By bonding the PDMS grating onto a copper or silicon substrate, the coefficient of thermal expansion (CTE) of the substrates can be deduced by measuring the diffraction angle change due to the change in PDMS grating periodicity when thermal strain is introduced. The measured CTEs agree well with the known reference values. PMID:23736421

  3. Mechanically induced long period fiber gratings on single mode tapered optical fiber for structure sensing applications

    NASA Astrophysics Data System (ADS)

    Pulido-Navarro, María. G.; Marrujo-García, Sigifredo; Álvarez-Chávez, José A.; Velázquez-González, Jesús S.; Martínez-Piñón, Fernando; Escamilla-Ambrosio, Ponciano J.

    2015-08-01

    The modal characteristics of tapered single mode optical fibers and its strain sensing characteristics by using mechanically induced long period fiber gratings are presented in this work. Both Long Period Fiber Gratings (LPFG) and fiber tapers are fiber devices that couple light from the core fiber into the fiber cladding modes. The mechanical LPFG is made up of two plates, one flat and the other grooved. For this experiment the grooved plate was done on an acrylic slab with the help of a computer numerical control machine. The manufacturing of the tapered fiber is accomplished by applying heat using an oxygen-propane flame burner and stretching the fiber, which protective coating has been removed. Then, a polymer-tube-package is added in order to make the sensor sufficiently stiff for the tests. The mechanical induced LPFG is accomplished by putting the tapered fiber in between the two plates, so the taper acquires the form of the grooved plate slots. Using a laser beam the transmission spectrum showed a large peak transmission attenuation of around -20 dB. The resultant attenuation peak wavelength in the transmission spectrum shifts with changes in tension showing a strain sensitivity of 2pm/μɛ. This reveals an improvement on the sensitivity for structure monitoring applications compared with the use of a standard optical fiber. In addition to the experimental work, the supporting theory and numerical simulation analysis are also included.

  4. All-optical beam control with high speed using image-induced blazed gratings in coherent media

    SciTech Connect

    Zhao, L.; Duan Wenhui; Yelin, S. F.

    2010-07-15

    Based on the theory of electromagnetically induced transparency, we study the formation of all-optical blazed transmission gratings in a coherently driven three-level atomic system using intensity-modulated images in coupling fields. Also, we analyze the feasibility of high-speed (megahertz) modulation for the induced gratings by means of image-bearing flat-top pulse trains. Consequently, continuous-wave probe fields can be efficiently and rapidly deflected in free space. When more sophisticated images are adopted, our scheme can provide further possibilities of all-optical beam splitting and fanning.

  5. Thermal characterization of nanofluids using laser induced thermal lens technique

    NASA Astrophysics Data System (ADS)

    Kurian, Achamma; Kumar, Rajesh B.; George, Sajan D.

    2009-08-01

    A laser induced thermal lens technique has been employed to evaluate the dynamic thermal parameter, the thermal diffusivity, of gold nanofluids. Gold nanoparticles were synthesized by citrate reduction of HAuCl4 in water. The UVVIS optical absorption spectra show an absorption peak around 540 nm owing to surface Plasmon resonance band of the gold particles. The thermal diffusivity of gold nanoparticles was evaluated by knowing the time constant of transient thermal lens obtained by fitting the experimental curve to the theoretical model of the mode-matched thermal lens. Analyses of the results show that the nanofluid exhibits lower thermal diffusivity value in comparison to the host medium, water. Further investigations also reveal that the concentration of nanoparticles in the fluid have influence on the measured thermal diffusivity value. Results are interpreted in terms of interfacial thermal resistance around the nanoparticles as well as on the clustering of nanoparticles.

  6. Quantification of Protein-Induced Membrane Remodeling Kinetics In Vitro with Lipid Multilayer Gratings

    PubMed Central

    Lowry, Troy W.; Hariri, Hanaa; Prommapan, Plengchart; Kusi-Appiah, Aubrey; Vafai, Nicholas; Bienkiewicz, Ewa A.; Van Winkle, David H.; Stagg, Scott M.

    2016-01-01

    The dynamic self-organization of lipids in biological systems is a highly regulated process that enables the compartmentalization of living systems at micro- and nanoscopic scales. Consequently, quantitative methods for assaying the kinetics of supramolecular remodeling such as vesicle formation from planar lipid bilayers or multilayers are needed to understand cellular self-organization. Here, a new nanotechnology-based method for quantitative measurements of lipid–protein interactions is presented and its suitability for quantifying the membrane binding, inflation, and budding activity of the membrane-remodeling protein Sar1 is demonstrated. Lipid multilayer gratings are printed onto surfaces using nanointaglio and exposed to Sar1, resulting in the inflation of lipid multilayers into unilamellar structures, which can be observed in a label-free manner by monitoring the diffracted light. Local variations in lipid multilayer volume on the surface is used to vary substrate availability in a microarray format. A quantitative model is developed that allows quantification of binding affinity (KD) and kinetics (kon and koff). Importantly, this assay is uniquely capable of quantifying membrane remodeling. Upon Sar1-induced inflation of single bilayers from surface supported multilayers, the semicylindrical grating lines are observed to remodel into semispherical buds when a critical radius of curvature is reached. PMID:26649649

  7. Two-dimensional electromagnetically induced grating via gain and phase modulation in a two-level system

    NASA Astrophysics Data System (ADS)

    Cheng, Guang-Ling; Cong, Lu; Chen, Ai-Xi

    2016-04-01

    A scheme for two-dimensional (2D) electromagnetically induced grating via spatial gain and phase modulation is presented in a two-level atomic system. Based on the interactions of two orthogonal standing-wave fields, the atom could diffract the weak probe beam into high-order directions and a 2D diffraction grating is generated. It is shown that the diffraction efficiency of the grating can be efficiently manipulated by controlling the Rabi frequencies of control fields, the detunings of the control and probe fields, and interaction length. Different from 2D cross-grating via electromagnetically induced transparency in a four-level atomic system, the present scheme results from the spatial modulation of gain and phase in a simple two-level system, which could lead to 2D gain-phase grating with larger diffraction intensities in the diffraction directions. The studies we present may have potential applications in developing photon devices for optical-switching, optical imaging and quantum information processing.

  8. Amplitude and phase gratings based on spatially modulated densities of optically generated polarons in thermally reduced LiNbO3

    NASA Astrophysics Data System (ADS)

    Bruening, Hauke; Imlau, Mirco

    2011-03-01

    In thermally reduced, nominally pure LiNb O3 a variety of small polarons can be observed, being responsible for the distinct photochromic properties of this material. In this contribution we use a spatially modulated excitation of polarons for the recording of holographic gratings. These gratings inherit some of the pronounced features of the polarons like a stretched-exponential relaxation behavior with a lifetime in the ms-range. Beside amplitude gratings we also find phase gratings leading to a high diffraction efficiency in some recording and readout geometries. The origin of these phase gratings can't be explained by the classic photorefractive effect due to Fe Li or other photorefractive dopants. In contrast, our findings are discussed in the frame of a model taking into account a local change of the refractive index by the polaronic distortion of the crystal lattice. Measurements of activation energies also indicate that these gratings can be attributed to the small bound (NbLi4 +)-polaron. Financial support by Deutsche Forschungsgemeinschaft (IM 37/5-1) is gratefully acknowledged.

  9. Flexible modulation of plasmon-induced transparency in a strongly coupled graphene grating-sheet system.

    PubMed

    Luo, Weiwei; Cai, Wei; Xiang, Yinxiao; Wang, Lei; Ren, Mengxin; Zhang, Xinzheng; Xu, Jingjun

    2016-03-21

    General actively tunable near-field plasmon-induced transparency (PIT) systems based on couplings between localized plasmon resonances of graphene nanostructures not only suffer from interantenna separations of smaller than 20 nm, but also lack switchable effect about the transparency window. Here, the performance of an active PIT system based on graphene grating-sheet with near-field coupling distance of more than 100 nm is investigated in mid-infrared. The transparency window in spectrum is analyzed objectively and proved to be more likely stemmed from Aulter-Townes splitting. The proposed system exhibits flexible tunability in slow-light and electro-optical switches, promising for practical active photonic devices. PMID:27136776

  10. Laser-induced damage of multilayer dielectric gratings with picosecond laser pulses under vacuum and air

    NASA Astrophysics Data System (ADS)

    Kong, Fanyu; Jin, Yunxia; Huang, Haopeng; Zhang, Hong; Liu, Shijie; He, Hongbo

    2015-10-01

    In this study, laser damage tests of multilayer dielectric gratings (MDGs) are performed in vacuum (5×10-4 Pa) and in air at a wavelength of 1053 nm with pulse widths of 0.56 ps ~9.7 ps. The laser-induced damage threshold (LIDT) of MDGs in vacuum/air ranges from 2.1/2.2 J/cm2 to 4.4/4.8 J/cm2 for laser beams of normal incidence. The LIDT of MDGs follows a τ0.26 scaling in the pulse width regime considered. The typical damage morphologies in the two environments caused by the near threshold pulse were observed using a scanning electron microscope (SEM); the results indicate that the damage features of MDGs in vacuum are the same as those in air. The testing results reveal that a clean vacuum environment neither changes the laser damage mechanism nor lowers the LIDT of MDGs.

  11. Temperature sensing on tapered single mode fiber using mechanically induced long period fiber gratings

    NASA Astrophysics Data System (ADS)

    Marrujo-García, Sigifredo; Velázquez-González, Jesús Salvador; Pulido-Navarro, María. Guadalupe; González-Ocaña, Ernesto; Mújica-Ascencio, Saúl; Martínez-Piñón, Fernando

    2015-09-01

    The modeling of a temperature optical fiber sensor is proposed and experimentally demonstrated in this work. The suggested structure to obtain the sensing temperature characteristics is by the use of a mechanically induced Long Period Fiber Grating (LPFG) on a tapered single mode optical fiber. A biconical fiber optic taper is made by applying heat using an oxygen-propane flame burner while stretching the single mode fiber (SMF) whose coating has been removed. The resulting geometry of the device is important to analyze the coupling between the core mode to the cladding modes, and this will determine whether the optical taper is adiabatic or non-adiabatic. On the other hand, the mechanical LPFG is made up of two plates, one grooved and other flat, the grooved plate was done on an acrylic slab with the help of a computerized numerical control machine (CNC). In addition to the experimental work, the supporting theory is also included.

  12. Tailoring thermal radiative properties with film-coupled concave grating metamaterials

    NASA Astrophysics Data System (ADS)

    Wang, Hao; Wang, Liping

    2015-06-01

    This work numerically investigates the radiative properties of film-coupled metamaterials made of a two-dimensional metallic concave grating on a continuous metal film separated by an ultrathin dielectric spacer. Spectrally-selective absorption is demonstrated in the visible and near-infrared regime, and underlying mechanisms are elucidated to be either localized magnetic polaritons (MPs) or surface plasmon polaritons (SPPs). The unique behaviors of MPs and SPPs are explained with the help of electromagnetic field distributions at respective resonance frequencies. An inductor-capacitor model is utilized to further confirm the excitation of MP, while dispersion relation is used to understand the behaviors of different SPP modes. Geometric effects of ridge width and grating period on the resonance absorption peaks are discussed. Moreover, directional responses at oblique incidences for different polarization states are studied. Fundamental understanding gained here will facilitate the design of novel metamaterials in energy harvesting and sensing applications.

  13. Thermal effects on an embedded grating sensor in an FRP structure

    NASA Astrophysics Data System (ADS)

    Lau, Kin-tak; Yuan, Libo; Zhou, Li-min

    2001-08-01

    Much research has been carried out in the field of using optical fibre sensors as internal strain and temperature measuring devices for advanced composite structures in recent years. The specific application is the use of embedded optical fibre sensors for smart composite reinforcement for strain monitoring in an innovative civil engineering structure, particularly for the structure after rehabilitation. Researchers have also paid attention to using the optical fibre sensor for monitoring the condition of composite materials during manufacturing and curing processes. However, heat induced in the curing process may influence the accuracy of measurement and eventuate in causing damage at the bond interface between the optical fibre and the surrounding matrix material because of the different thermal properties of silica fibre and composite materials. In this paper, a simple theoretical model is introduced to determine the interfacial properties of the embedded optical fibre system in composite laminates with different values of the coefficient of thermal expansion under different temperature environments. A finite-element method is used to compare the result from the theoretical prediction. The results show that the maximum shear stress in the coating layer decreases with increasing surrounding temperature when the optical fibre is embedded into carbon and Kevlar fibre composites. In contrast, increasing the temperature when the optical fibre is embedded into glass fibre composite results in the increase of maximum shear stress of the material. The compaction pressure distribution along the circumference of the coating layer also varies with temperature.

  14. Corrosion detection of steel reinforced concrete using combined carbon fiber and fiber Bragg grating active thermal probe

    NASA Astrophysics Data System (ADS)

    Li, Weijie; Ho, Siu Chun Michael; Song, Gangbing

    2016-04-01

    Steel reinforcement corrosion is one of the dominant causes for structural deterioration for reinforced concrete structures. This paper presents a novel corrosion detection technique using an active thermal probe. The technique takes advantage of the fact that corrosion products have poor thermal conductivity, which will impede heat propagation generated from the active thermal probe. At the same time, the active thermal probe records the temperature response. The presence of corrosion products can thus be detected by analyzing the temperature response after the injection of heat at the reinforcement-concrete interface. The feasibility of the proposed technique was firstly analyzed through analytical modeling and finite element simulation. The active thermal probe consisted of carbon fiber strands to generate heat and a fiber optic Bragg grating (FBG) temperature sensor. Carbon fiber strands are used due to their corrosion resistance. Wet-dry cycle accelerated corrosion experiments were performed to study the effect of corrosion products on the temperature response of the reinforced concrete sample. Results suggest a high correlation between corrosion severity and magnitude of the temperature response. The technique has the merits of high accuracy, high efficiency in measurement and excellent embeddability.

  15. 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. PMID:26974608

  16. Temperature and Pressure Dependence of Signal Amplitudes for Electrostriction Laser-Induced Thermal Acoustics

    NASA Technical Reports Server (NTRS)

    Herring, Gregory C.

    2015-01-01

    The relative signal strength of electrostriction-only (no thermal grating) laser-induced thermal acoustics (LITA) in gas-phase air is reported as a function of temperature T and pressure P. Measurements were made in the free stream of a variable Mach number supersonic wind tunnel, where T and P are varied simultaneously as Mach number is varied. Using optical heterodyning, the measured signal amplitude (related to the optical reflectivity of the acoustic grating) was averaged for each of 11 flow conditions and compared to the expected theoretical dependence of a pure-electrostriction LITA process, where the signal is proportional to the square root of [P*P /( T*T*T)].

  17. Distributed strain and temperature mapping in the Safe Affordable Fission Engine (SAFE-100) thermal simulator using fiber Bragg gratings

    NASA Astrophysics Data System (ADS)

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

    2004-07-01

    The motivation for the reported research was to support NASA space nuclear power initiatives through the development of advanced fiber Bragg grating (FBG) sensors for the SAFE-100 non-nuclear core simulator. The purpose of the combined temperature and strain mapping was to obtain a correlation between power distribution and core shape within the simulator. In a nuclear reactor, core dimension affects local reactivity and therefore power distribution. 20 FBG temperature sensors were installed in the SAFE-100 thermal simulator at the NASA Marshal Space Flight Center in an interstitial location approximately 2.3mm in diameter. The simulator was heated during two separate experiments using graphite resistive heating elements. The first experiment reached a maximum temperature of approximately 800°C, while the second experiment reached 1150°C. A detailed profile of temperature vs. time and location within the simulator was generated. During a second test, highly distributed fiber Bragg grating strain sensors were arrayed about the circumference and along the length of the heated core region. The maximum temperature during this test was approximately 300°C. A radial and longitudinal strain distribution was obtained that correlated well with known power distribution. Work continues to increase the strain sensor operating temperature and sensor multiplexing to allow high-resolution mapping.

  18. Transient grating-induced phase inhomogeneity in FeRh studied by time-resolved hard x-ray nanodiffraction

    NASA Astrophysics Data System (ADS)

    Zhu, Yi; Zhang, Qingteng; Chen, Pice; Walko, D. A.; Dufresne, E. M.; Thiele, J. U.; Fullerton, E. E.; Cai, Zhonghou; Evans, P. G.; Wen, Haidan

    2014-03-01

    The photo-induced antiferromagnetic to ferromagnetic phase transition of FeRh at room temperature has important technological applications in the magnetic recording industry. This first-order phase transition is accompanied by a large, abrupt lattice expansion. In this study, spatially periodic phase modulation in a FeRh thin film was induced by an optical transient grating; the temporal and spatial evolution of the resulting lattice profile was probed by ultrafast hard x-ray nanodiffraction. We found that the transient grating induced lattice profile deviates from the initial sinusoidal spatial modulation during the recovery process, which allows us to quantitatively measure the in-plane propagation of the phase boundary. Work at Argonne was supported by the Argonne LDRD grant (2013-036-R1).

  19. Degenerate four-wave mixing and two-photon induced gratings in colloidal quantum dots CdSe/ZnS

    NASA Astrophysics Data System (ADS)

    Smirnov, A. M.; Kozlova, M. V.; Dneprovskii, V. S.

    2015-05-01

    The features of nonlinear and electro-optical processes has been discovered in the case of two-photon resonant excitation of the excitons in colloidal CdSe/ZnS quantum dots. Self-diffraction arises for two laser beams intersecting in the cell with colloidal CdSe/ZnS quantum dots (QDs) due to the dynamic phase grating formatting. The calculated induced change in the refractive is sufficient to form a phase diffraction grating. Such a large value of χ(3) as compared to the third-order nonlinear susceptibility for the solvent (hexane) is due to the increase in χ(3) occurring when the intermediate resonance is attained in a medium transparent for laser radiation. In order to identify physical processes responsible for the induced grating formation and the diffraction efficiency self-diffracted pulse intensity dependences on the incident pulse intensity were measured for two samples of colloidal QD CdSe/ZnS, which frequency of the fundamental exciton transition is tuned to the high-frequency and low-frequency region from the double laser frequency. The discovered cubic dependence of the self-diffracted pulse intensity on the incident pulse intensity was explained by four-wave mixing process. Discovered above 5-th index of power dependence of the self-diffracted pulse intensity on the excitation pulses intensity we explained by the increasing magnitude of two-photon absorption (due to shifting of two photons energy of laser radiation to the exact exciton absorption resonance by red Stark shift of the exciton absorption), accompanied by the growth absorption by two-photon excited carriers that leads to the induced amplitude grating formation in addition to the phase grating.

  20. Specific features of formation of self-induced gratings on metal foils during scanning by a tightly focused femtosecond laser beam

    SciTech Connect

    Dostovalov, A V; Korolkov, V P; Golubtsov, S K; Kondrat'ev, V I

    2014-04-28

    Formation of self-induced gratings on a metal surface scanned by a focused femtosecond laser beam has been investigated. It is experimentally shown that application of femtosecond IR radiation allows one to form more ordered self-induced gratings as compared with the gratings formed by visible light. The dependence of the tilt of grating lines with respect to the beam polarisation direction on the distance between tracks and the beam motion direction in adjacent tracks is analysed. Formation of two-dimensional periodic gratings during double laser beam passage along the same trajectory but with a small difference in the beam polarisation directions has been found for the first time. (interaction of laser radiation with matter)

  1. Casimir-Lifshitz force out of thermal equilibrium between dielectric gratings

    NASA Astrophysics Data System (ADS)

    Noto, Antonio; Messina, Riccardo; Guizal, Brahim; Antezza, Mauro

    2014-08-01

    We calculate the Casimir-Lifshitz pressure in a system consisting of two different one-dimensional dielectric lamellar gratings having two different temperatures and immersed in an environment having a third temperature. The calculation of the pressure is based on the knowledge of the scattering operators, deduced using the Fourier modal method. The behavior of the pressure is characterized in detail as a function of the three temperatures of the system as well as the geometrical parameters of the two gratings. We show that the interplay between nonequilibrium effects and geometrical periodicity offers a rich scenario for the manipulation of the force. In particular, we find regimes where the force can be strongly reduced for large ranges of temperatures. Moreover, a repulsive pressure can be obtained, whose features can be tuned by controlling the degrees of freedom of the system. Remarkably, the transition distance between attraction and repulsion can be decreased with respect to the case of two slabs, implying an experimental interest for the observation of repulsion.

  2. Widely tunable LP11 cladding-mode resonance in a twisted mechanically induced long-period fiber grating.

    PubMed

    Nair, Anitha S; Sudeep Kumar, V P; Joe, Hubert

    2015-03-10

    A record tunability of 35 nm for the LP(11) cladding-mode resonance in a twisted mechanically induced long-period fiber grating using standard single-mode communication fiber is demonstrated. By forming the LP(11) resonance far away from its cut-off wavelength and modifying the grooves of the grating in the form of smooth semicircular humps, a high twist sensitivity of 8.75 nm/(rad/cm) and a controlled tunability of 35 nm is achieved. The fiber with its lacquer coating is not broken even at a severe twist rate of 5.44 rad/cm. The present design can be used as a novel variable optical selective wavelength attenuator since the bandwidth, rejection efficiency, and center wavelength can be controlled by changing the grating length, pressure over the grating, and fiber twist, respectively. Using the results, a cost-effective tunable variable optical attenuator for selective channel-blanking applications is also demonstrated. A fine tunability of 1.5 nm is achieved for a twist rate change of 0.1 rad/cm. PMID:25968376

  3. Alternative radiative and dark mode-induced multi-broadband transmission in asymmetrical metallic grating

    NASA Astrophysics Data System (ADS)

    Li, Yue; Fei, Guang Tao; Xu, Shao Hui; Shang, Guo Liang; De Zhang, Li

    2016-01-01

    The phenomenon of extraordinary and multi-broadband optical transmission through sub-wavelength metallic grating with symmetry breaking has been theoretically investigated. Under normal incident light, the radiative and dark modes appear in adjacent slits of the grating with asymmetric heights. Through the destructive interference of alternative radiative and dark modes, multiple broadband transmission and enhanced light propagation is realized. The counter-propagating light circulation results in sharp dips in the transmission spectrum. These characteristics of the asymmetric grating could provide highly controllable ways to design novel devices.

  4. Continuous monitoring of mining induced strain in a road pavement using fiber Bragg grating sensors

    NASA Astrophysics Data System (ADS)

    Nosenzo, Giorgio; Whelan, B. E.; Brunton, M.; Kay, Daryl; Buys, Henk

    2013-06-01

    This paper describes the application of fiber Bragg grating (FBG) based sensors for monitoring road pavement strains caused by mining induced ground subsidence as a result of underground longwall coal mining beneath a major highway in New South Wales, Australia. After a lengthy planning period, the risks to the highway pavement were successfully managed by the highway authority and the mining company through a technical committee. The technical committee comprised representatives of the mining company, the highway authority and specialists in the fields of pavement engineering, geotechnical engineering and subsidence. An important component of the management strategy is the installation of a total of 840 strain and temperature sensors in the highway pavement using FBG arrays encapsulated in glass-fiber composite cables. The sensors and associated demodulation equipment provide continuous strain measurements along the pavement, enabling on-going monitoring of the effects of mining subsidence on the pavement and timely implementation of planned mitigation and response measures to ensure the safety and serviceability of the highway throughout the mining period.

  5. Continuous monitoring of mining induced strain in a road pavement using fibre Bragg grating sensors

    NASA Astrophysics Data System (ADS)

    Whelan, B. E.; Brunton, M.; Nosenzo, Giorgio; Kay, Daryl; Buys, Henk

    2012-02-01

    This paper describes the application of Fibre Bragg Grating (FBG) based sensors for monitoring road pavement strains caused by mining induced ground subsidence as a result of underground longwall coal mining beneath a major highway in New South Wales, Australia. After a lengthy planning period, the risks to the highway pavement were successfully managed by the highway authority and the mining company through a technical committee. The technical committee comprised representatives of the mining company, the highway authority and specialists in the fields of pavement engineering, geotechnical engineering and subsidence. An important component of the management strategy is the installation of a total of 840 strain and temperature sensors in the highway pavement using FBG arrays encapsulated in glass-fibre composite cables. The sensors and associated demodulation equipment provide continuous strain measurements along the pavement, enabling on-going monitoring of the effects of mining subsidence on the pavement and timely implementation of planned mitigation and response measures to ensure the safety and serviceability of the highway throughout the mining period.

  6. Cuspal Displacement Induced by Bulk Fill Resin Composite Polymerization: Biomechanical Evaluation Using Fiber Bragg Grating Sensors

    PubMed Central

    Ramos, João; Alves, Sofia; Nogueira, Rogério

    2016-01-01

    Polymerization shrinkage is a major concern to the clinical success of direct composite resin restorations. The aim of this study was to compare the effect of polymerization shrinkage strain of two resin composites on cuspal movement based on the use of fiber Bragg grating (FBG) sensors. Twenty standardized Class II cavities prepared in upper third molars were allocated into two groups (n = 10). Restorations involved the bulk fill placement of conventional microhybrid resin composite (Esthet•X® HD, Dentsply DeTrey) (Group 1) or flowable “low-shrinkage” resin composite (SDR™, Dentsply DeTrey) (Group 2). Two FBG sensors were used per restoration for real-time measurement of cuspal linear deformation and temperature variation. Group comparisons were determined using ANCOVA (α = 0.05) considering temperature as the covariate. A statistically significant correlation between cuspal deflection, time, and material was observed (p < 0.01). Cuspal deflection reached 8.8 μm (0.23%) and 7.8 μm (0.20%) in Groups 1 and 2, respectively. When used with bulk fill technique, flowable resin composite SDR™ induced significantly less cuspal deflection than the conventional resin composite Esthet•X® HD (p = 0.015) and presented a smoother curve slope during the polymerization. FBG sensors appear to be a valid tool for accurate real-time monitoring of cuspal deformation. PMID:27190517

  7. Cuspal Displacement Induced by Bulk Fill Resin Composite Polymerization: Biomechanical Evaluation Using Fiber Bragg Grating Sensors.

    PubMed

    Vinagre, Alexandra; Ramos, João; Alves, Sofia; Messias, Ana; Alberto, Nélia; Nogueira, Rogério

    2016-01-01

    Polymerization shrinkage is a major concern to the clinical success of direct composite resin restorations. The aim of this study was to compare the effect of polymerization shrinkage strain of two resin composites on cuspal movement based on the use of fiber Bragg grating (FBG) sensors. Twenty standardized Class II cavities prepared in upper third molars were allocated into two groups (n = 10). Restorations involved the bulk fill placement of conventional microhybrid resin composite (Esthet•X® HD, Dentsply DeTrey) (Group 1) or flowable "low-shrinkage" resin composite (SDR™, Dentsply DeTrey) (Group 2). Two FBG sensors were used per restoration for real-time measurement of cuspal linear deformation and temperature variation. Group comparisons were determined using ANCOVA (α = 0.05) considering temperature as the covariate. A statistically significant correlation between cuspal deflection, time, and material was observed (p < 0.01). Cuspal deflection reached 8.8 μm (0.23%) and 7.8 μm (0.20%) in Groups 1 and 2, respectively. When used with bulk fill technique, flowable resin composite SDR™ induced significantly less cuspal deflection than the conventional resin composite Esthet•X® HD (p = 0.015) and presented a smoother curve slope during the polymerization. FBG sensors appear to be a valid tool for accurate real-time monitoring of cuspal deformation. PMID:27190517

  8. Mechanically induced long period fiber gratings in Er3+ fiber for structural health monitoring

    NASA Astrophysics Data System (ADS)

    Pulido-Navarro, M. G.; Alvarez-Chavez, J. A.; Ceballos-Herrera, D. E.; Escamilla-Ambrosio, P. J.

    2013-09-01

    This work presents preliminary results on wavelength sensitivity due to mechanically induced long period fiber grating (LPFG) on both standard single-mode and Er-doped fibers. The work presents and compares results for both types of fibers under different torsion conditions. In order to apply the torsion one of the fiber ends is fixed while torsion is applied on the other end. A LPFG whose period is 503μm is used to press on the fiber after the torsion, this will allow for micro curvatures to be formed on the fiber, which will in turn generate a periodical index perturbation on it. Here, it was noted that the rejection band shifts to shorter wavelengths for Er-doped fibers. It was detected that for torsion of 6 turns applied to 10cm doped fiber the wavelength peaks can shift up to 25nm, which is longer than similar results reported on standard fibers. Therefore, by using Er-doped fibers this technique will give more sensitive and accurate results on the real conditions of the structure under study. These results can be employed for sensing applications, especially for small to medium size structures, being these structures mechanical, civil or aeronautical. Theoretical calculations and simulations are employed for experimental results validation.

  9. Synthesis of chirped apodized fiber Bragg grating parameters using Direct Tabu Search algorithm: Application to the determination of thermo-optic and thermal expansion coefficients

    NASA Astrophysics Data System (ADS)

    Karim, Fethallah; Seddiki, Omar

    2010-05-01

    In this paper, Direct Tabu Search (DTS) is proposed to synthesize the physical parameters of a fiber Bragg grating (FBG) numerically from its reflection response. A reflected spectrum is being calculated by using the Transfer Matrix Method (TMM). Direct search based strategies are used to direct a tabu search. These strategies are based on a new pattern search procedure called Adaptive Pattern Search (APS). In addition, the well-known Nelder-Mead (NME) algorithm is used as a local search method at the final stage of the optimization process. Direct Tabu Search (DTS) is applied for reconstruction of a raised cosine chirped fiber Bragg grating (CFBG) and a Gaussian multi channel fiber grating. The method is then used to synthesize a CFBG from its reflectivity taken at different temperatures. It gives a good estimate of the thermal expansion coefficient and the thermo-optic coefficient of the fiber.

  10. Using the laser-induced Marangoni effect for the recording of diffraction gratings

    NASA Astrophysics Data System (ADS)

    Rastopov, S. F.; Sukhodol'Skii, A. T.

    1987-08-01

    A method for recording diffraction gratings is proposed which uses the photoinduced Marangoni effect occurring during the evaporation of a thin absorbing liquid layer on a solid substrate. The dynamics of mass transfer processes is analyzed using results of experiments with a concentrated solution of Rhodamine in ethyl alcohol in which the diffraction efficiency of the grating was determined directly in the process of its recording.

  11. Thermally induced alkylation of diamond.

    PubMed

    Hoeb, Marco; Auernhammer, Marianne; Schoell, Sebastian J; Brandt, Martin S; Garrido, Jose A; Stutzmann, Martin; Sharp, Ian D

    2010-12-21

    We present an approach for the thermally activated formation of alkene-derived self-assembled monolayers on oxygen-terminated single and polycrystalline diamond surfaces. Chemical modification of the oxygen and hydrogen plasma-treated samples was achieved by heating in 1-octadecene. The resulting layers were characterized using X-ray photoelectron spectroscopy, thermal desorption spectroscopy, atomic force microscopy, Fourier transform infrared spectroscopy, and water contact angle measurements. This investigation reveals that alkenes selectively attach to the oxygen-terminated sites via covalent C-O-C bonds. The hydrophilic oxygen-terminated diamond is rendered strongly hydrophobic following this reaction. The nature of the process limits the organic layer growth to a single monolayer, and FTIR measurements reveal that such monolayers are dense and well ordered. In contrast, hydrogen-terminated diamond sites remain unaffected by this process. This method is thus complementary to the UV-initiated reaction of alkenes with diamond, which exhibits the opposite reactivity contrast. Thermal alkylation increases the range of available diamond functionalization strategies and provides a means of straightforwardly forming single organic layers in order to engineer the surface properties of diamond. PMID:21090790

  12. Holographically formed, acoustically switchable gratings based on polymer-dispersed liquid crystals.

    PubMed

    Liu, Yan Jun; Lu, Mengqian; Ding, Xiaoyun; Leong, Eunice S P; Lin, Sz-Chin Steven; Shi, Jinjie; Teng, Jing Hua; Wang, Lin; Bunning, Timothy J; Huang, Tony Jun

    2013-08-01

    We report holographic polymer-dispersed liquid crystal (H-PDLC) gratings driven by surface acoustic waves (SAWs). Our experiments show that upon applying SAWs, the H-PDLC grating exhibited switchable properties: The diffraction of the H-PDLC grating decreased, whereas the transmission increased. This acoustically switchable behavior is due to the acoustic streaming-induced realignment of liquid crystals as well as absorption-resulted thermal diffusion. Such SAW-driven H-PDLC gratings are potentially useful in many photonic applications, such as optical switches, spatial light modulators, and switchable add/drop filters. PMID:22909448

  13. Thermal behavior of resonant waveguide-grating mirrors in Yb:YAG thin-disk lasers.

    PubMed

    Rumpel, Martin; Dannecker, Benjamin; Voss, Andreas; Moeller, Michael; Moormann, Christian; Graf, Thomas; Ahmed, Marwan Abdou

    2013-11-15

    We present the experimental investigations of different designs of resonant waveguide-grating (RWG) mirrors, used as intracavity folding mirrors in an Yb:YAG thin-disk laser (TDL). The investigation was focused on the rise of the surface temperature due to the coupling of the incident radiation to a waveguide mode as well as on laser efficiency, polarization, and wavelength selectivity. It was found that the damage threshold and efficiency can be increased significantly with a proper design of the structure in comparison to the simplest design with a single waveguide layer. So far, the presented RWG allow the generation of linear polarization with a narrow spectral linewidth down to 25 pm FWHM in a fundamental mode Yb:YAG TDL. Damage thresholds of 60 kW/cm(2) have been reached where only 63 K of surface temperature increase was observed. This showed that the improved mirrors are suitable for the generation of kW-class narrow linewidth, linearly polarized Yb:YAG TDL. PMID:24322127

  14. Wavelength tunability of L-band fiber ring lasers using mechanically induced long-period fiber gratings

    NASA Astrophysics Data System (ADS)

    Sakata, Hajime; Yoshimi, Hitoshi; Otake, Yuki

    2009-03-01

    We report on oscillation wavelength control in erbium-doped fiber ring lasers by adjusting the period of a mechanically induced long-period fiber grating (LPFG) inserted into the fiber ring resonator. Pump light is provided by a 974 nm laser diode (LD), the emission of which is coupled into the fiber ring resonator through a wavelength-division multiplexing coupler. Laser oscillation occurs with a threshold pump LD current of 40 mA, corresponding to a threshold pump power of 5 mW. When a periodic pressure of 0.81 N/mm is applied to form the LPFG, the fiber ring laser exhibits the tunable range of 40.9 nm, i.e., from 1563.1 to 1604 nm, by changing the grating period.

  15. Thermally induced fracturing of Ula water injectors

    SciTech Connect

    Svendsen, A.P.; Wright, M.S. ); Clifford, P.J.; Berry, P.J. )

    1991-11-01

    This paper describes the impact that thermally induced fracturing (TIF) has had on the North Sea Ula field injection wells, allowing higher than anticipated water injection rates to be achieved. This work also discusses how thermal stress reduced fracture propagation pressures by 2,000 psi and how a 3D simulation code developed to model TIF was used. Injection-water-quality specifications and techniques to optimize TIF are presented.

  16. Investigation of ultrafast photothermal surface expansion and diffusivity in GaAs via laser-induced dynamic gratings

    SciTech Connect

    Pennington, D.M.

    1992-04-01

    This thesis details the first direct ultrafast measurements of the dynamic thermal expansion of a surface and the temperature dependent surface thermal diffusivity using a two-color reflection transient grating technique. Studies were performed on p-type, n-type, and undoped GaAs(100) samples over a wide range of temperatures. By utilizing a 90 fs ultraviolet probe with visible excitation beams, the effects of interband saturation and carrier dynamics become negligible; thus lattice expansion due to heating and subsequent contraction caused by cooling provided the dominant influence on the probe. At room temperature a rise due to thermal expansion was observed, corresponding to a maximum net displacement of {approximately} 1 {Angstrom} at 32 ps. The diffracted signal was composed of two components, thermal expansion of the surface and heat flow away from the surface, thus allowing a determination of the rate of expansion as well as the surface thermal diffusivity, D{sub S}. By varying the fringe spacing of the grating, this technique has the potential to separate the signal contributions to the expansion of the lattice in the perpendicular and parallel directions. In the data presented here a large fringe spacing was used, thus the dominant contribution to the rising edge of the signal was expansion perpendicular to the surface. Comparison of he results with a straightforward thermal model yields good agreement over a range of temperatures (20--300{degrees}K). Values for D{sub S} in GaAs were measured and found to be in reasonable agreement with bulk values above 50{degrees}K. Below 50{degrees}K, D{sub S} were determined to be up to an order of magnitude slower than the bulk diffusivity due to increased phonon boundary scattering. The applicability and advantages of the TG technique for studying photothermal and photoacoustic phenomena are discussed.

  17. Thermally induced microstrain broadening in hexagonal zinc

    SciTech Connect

    Lawson, Andrew C; Valdez, James A; Roberts, Joyce A; Leineweber, Andreas; Mittemeijer, E J; Kreher, W

    2008-01-01

    Neutron powder-diffraction experiments on polycrystalline hexagonal zinc show considerable temperature-dependent line broadening. Whereas as-received zinc at 300 K exhibits narrow reflections, during cooling to a minimum temperature of 10K considerable line-broadening appears, which largely disappears again during reheating. The line broadening may be ascribed to microstrains induced by thermal microstresses due to the anisotropy of the thermal expansion (shrinkage) of hexagonal zinc. Differences between the thermal microstrains and theoretical predictions considering elastic deformation of the grains can be explained by plastic deformation and surface effects.

  18. GISAXS study of Au-coated light-induced polymer gratings

    SciTech Connect

    Castro-Colin, M. Korolkov, D.; Yadavalli, N. S.; Mayorova, M.; Kentzinger, M.; Santer, S.

    2015-07-23

    Surface Relief Gratings (SRGs) are inscribed in the Au-coated azobenzene containing photosensitive polymer films on a glass substrate. The structures consist of micrometer-period sinusoidal patterns of sub-micron amplitudes, formed by photo-isomerization and molecular reorientation processes in the polymer film during exposure to the light interference pattern that drove the formation of a SRG; the precursor is a stack sequence of Au, polymer, and glass. The SRG structures were exposed in GISAXS geometry to high-intensity X-ray radiation from a liquid Ga source (0.134 nm). Scattered photons were registered by a 2D detector, and their intensity distribution enabled us to characterize the structures. Analysis of the 2D patterns yielded information about the pitch of the gratings as well as the thickness of the films forming the gratings. The GISAXS experiments were carried out at the Research Center Juelich.

  19. Surface plasmon resonance in eccentric femtosecond-laser-induced fiber Bragg gratings.

    PubMed

    Chah, Karima; Voisin, Valérie; Kinet, Damien; Caucheteur, Christophe

    2014-12-15

    Highly localized refractive index modulations are photo-written in the core of pure silica fiber using point-by-point focused UV femtosecond pulses. These specific gratings exhibit a comb-like transmitted amplitude spectrum, with polarization-dependent narrowband cladding mode resonances. In this work, eccentric gratings are surrounded by a gold sheath, allowing the excitation of surface plasmon polaritons (SPP) for radially-polarized light modes. The spectral response is studied as a function of the surrounding refractive index and a maximum sensitivity of 50  nm/RIU (refractive index unit) is reported for a well-defined cladding-mode resonance among the spectral comb. This novel kind of plasmonic fiber grating sensor offers rapidity of production, design flexibility, and high temperature stability. PMID:25503022

  20. Direct UV written planar Bragg gratings that feature zero fluence induced birefringence

    NASA Astrophysics Data System (ADS)

    Holmes, Christopher; Cooper, Peter A.; Fernando, Harendra N. J.; Stroll, Andreas; Gates, James C.; Krishnan, Chirenjeevi; Haynes, Roger; Mennea, Paolo L.; Carpenter, Lewis G.; Gawith, Corin B. E.; Roth, Martin M.; Charlton, Martin D.; Smith, Peter G. R.

    2015-12-01

    Direct UV writing is a planar fabrication process capable of simultaneously defining waveguides and Bragg gratings. The technique is fully computer controlled and uniquely uses a small focused spot ~7 μm in diameter for direct writing exposure. This work investigates its use to achieve phase trimming and Bragg grating definition in silica-on-silicon lithographic waveguides. It is observed that birefringence control using direct UV writing can be made independent of exposure fluence with this technique through tailoring substrate stress. The result is demonstrated experimentally and supported theoretically using finite element analysis.

  1. Realistic Testing of the Safe Affordable Fission Engine (SAFE-100) Thermal Simulator Using Fiber Bragg Gratings

    NASA Astrophysics Data System (ADS)

    Stinson-Bagby, Kelly L.; Fielder, Robert S.; van Dyke, Melissa K.; Wong, Wayne A.

    2004-02-01

    The motivation for the reported research 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 were made with 20 FBG temperature sensors installed in the SAFE-100 thermal simulator at the NASA Marshal Space Flight Center. Experiments were performed at temperatures approaching 800°C and 1150°C for characterization studies of the SAFE-100 core. Temperature profiles were successfully generated for the core during temperature increases and decreases. Related tests in the SAFE-100 successfully provided strain measurement data.

  2. Realistic Testing of the Safe Affordable Fission Engine (SAFE-100) Thermal Simulator Using Fiber Bragg Gratings

    SciTech Connect

    Stinson-Bagby, Kelly L.; Fielder, Robert S.; Van Dyke, Melissa K.; Wong, Wayne A.

    2004-02-04

    The motivation for the reported research 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 were made with 20 FBG temperature sensors installed in the SAFE-100 thermal simulator at the NASA Marshal Space Flight Center. Experiments were performed at temperatures approaching 800 deg. C and 1150 deg. C for characterization studies of the SAFE-100 core. Temperature profiles were successfully generated for the core during temperature increases and decreases. Related tests in the SAFE-100 successfully provided strain measurement data.

  3. Propagation effect in inhomogeneous media, including media with light-induced and fixed gratings

    NASA Astrophysics Data System (ADS)

    Tsai, Chang-Ching

    Optical waves propagation in various types of volume gratings, materials with constant impendence and optical fibers are studied. Instability of cross-phase modulation and of Energy transfer via GRON-type (Grating-type Orientational Nonlinearity in Liquid Crystal) Stimulated Scattering is numerically observed. Two diffractive optical elements made of volume gratings are suggested and analyzed. A transmission hologram based on the analogy with Stimulated Raman Adiabatic Passage (STIRAP) in nonlinear optics is proposed. This transmission hologram demonstrates high diffraction efficiency and low sensitivity to polarization and hologram strength. The other is a reflection hologram with two crossed-gratings. It features good angular selectivity in comparison with the poor angular selectivity of conventional Bragg grating mirror. This defense also contains the approximation of Maxwell equations for the description of depolarized light sources and polarization-insensitive detectors. A scalar wave equation, Z-Helmholtz equation, is proposed and discussed in the approximation of constant impedance media. As examples, this equation successfully describes (a) Fresnel transmission coefficient, and (b) Goose-Hanschen shift in total internal reflection, for depolarized incident light and, at the same time, polarization-insensitive detectors. Evolution of polarization during light propagation in an inhomogeneous locally isotropic medium, and also in a single-mode fiber is described by Rytov's non-rotation equation. With arbitrary chosen real unit vector, the complete description of polarization change can be described in a single rotation angle obtained from the integral of rotation rate. Based on introduction of this reference frame, a device is suggested as rigid body's rotation sensor due to polarization change in a twisted fiber.

  4. Ultraviolet induced absorption and Bragg grating inscription in RbCdF{sub 3}:Mn{sup 2+}

    SciTech Connect

    Williams, G. V. M.; Dotzler, C.; Edgar, A.; Raymond, S. G.

    2007-12-01

    The effects of ultraviolet (UV) irradiation on the optical absorption, optically stimulated luminescence (OSL), and thermoluminescence (TL) properties of RbCdF{sub 3}:Mn{sup 2+} are reported. There is a UV induced optical absorption at {approx}4 eV, together with OSL and TL that are attributed to a distribution of carrier traps, as well as isolated or disconnected traps. We show that the time-integrated OSL for samples with different Mn{sup 2+} concentrations is correlated with the UV-induced change in the absorption coefficient, which we attribute to a higher trap concentration in samples with high Mn{sup 2+} concentrations. The UV-induced changes in the optical properties can be completely bleached, which leads to the possibility of holographic storage. We show that stable and rewritable thick Bragg gratings can be made in RbCdF{sub 3}:Mn{sup 2+} single crystals after UV irradiation at 254 nm where the gratings were made by two beam interference at 364 nm.

  5. Photo-induced refractive index and topographical surface gratings in functionalized nanocarbon solid film

    SciTech Connect

    McGee, David J.; Ferrie, John; Plachy, Aljoscha; Joo, Yongho; Choi, Jonathan; Kanimozhi, Catherine; Gopalan, Padma

    2015-11-02

    We demonstrate that a single-walled carbon nanotube network noncovalently coupled with a pyrene-modified azo-benzene chromophore functions as a host matrix for a broad range of photo-orientation and photomechanical effects. The chromophore could be efficiently reoriented through repeated trans-cis-trans isomerization under linearly polarized 480 nm light, with Δn of 0.012 at 650 nm and fast characteristic rise-times of 0.12 s. Erasable phase diffraction gratings could also be written, with permanent surface relief gratings forming at sufficiently long irradiation times. In addition to demonstrating a mechanism for photo-manipulation of single-walled carbon nanotubes, these results show photo-orientation of chromophores in azo-functionalized single-walled carbon nanotube networks as a path towards the photosensitive tuning of the electrostatic environment of the nanotube.

  6. Ultrasonic Sensitivity of Strain-Insensitive Fiber Bragg Grating Sensors and Evaluation of Ultrasound-Induced Strain

    PubMed Central

    Tsuda, Hiroshi; Kumakura, Kenji; Ogihara, Shinji

    2010-01-01

    In conventional ultrasound detection in structures, a fiber Bragg grating (FBG) is glued on or embedded in the structure. However, application of strain to the structure can influence the sensitivity of the FBG toward ultrasound and can prevent its effective detection. An FBG can work as a strain-insensitive ultrasound sensor when it is not directly glued to the monitored structure, but is instead applied to a small thin plate to form a mobile sensor. Another possible configuration is to affix an FBG-inscribed optical fiber without the grating section attached to the monitored structure. In the present study, sensitivity to ultrasound propagated through an aluminum plate was compared for a strain-insensitive FBG sensor and an FBG sensor installed in a conventional manner. Strains induced by ultrasound from a piezoelectric transducer and by quasi-acoustic emission of a pencil lead break were also quantitatively evaluated from the response amplitude of the FBG sensor. Experimental results showed that the reduction in the signal-to-noise ratio for ultrasound detection with strain-insensitive FBG sensors, relative to traditionally-installed FBG sensors, was only 6 dB, and the ultrasound-induced strain varied within a range of sub-micron strains. PMID:22163523

  7. Generation of self-induced-transparency gap solitons by modulational instability in uniformly doped fiber Bragg gratings

    SciTech Connect

    Kalithasan, B.; Porsezian, K.; Senthilnathan, K.; Tchofo Dinda, P.

    2010-05-15

    We consider the continuous-wave (cw) propagation through a fiber Bragg grating that is uniformly doped with two-level resonant atoms. Wave propagation is governed by a system of nonlinear coupled-mode Maxwell-Bloch (NLCM-MB) equations. We identify modulational instability (MI) conditions required for the generation of ultrashort pulses in both anomalous and normal dispersion regimes. From a detailed linear stability analysis, we find that the atomic detuning frequency has a strong influence on the MI. That is, the atomic detuning frequency induces nonconventional MI sidebands at the photonic band gap (PBG) edges and near the PBG edges. Especially in the normal dispersion regime, MI occurs without any threshold condition, which is in contrast with that of conventional fiber Bragg gratings. We also perform a numerical analysis to solve the NLCM-MB equations. The numerical results of the prediction of both the optimum modulation wave number and the optimum gain agree well with that of the linear stability analysis. Another main result of the present work is the prediction of the existence of both bright and dark self-induced transparency gap solitons at the PBG edges.

  8. Optical high temperature sensor based on fiber Bragg grating

    NASA Astrophysics Data System (ADS)

    Zhang, Bowei

    The aim of this thesis is to fabricate a fiber Bragg grating (FBG) temperature sensor that is capable to measure temperatures in excess of 1100°C. For this purpose, two topics have been studied and investigated during this project. One of them is the development of a high temperature resistant molecular-water induced FBGs; and the other is to investigate the effect of microwave-irradiation on the hydrogen-loaded FBG. The molecular-water induced FBGs are different from the other types of FBG. In these devices the refractive index is modulated by the periodic changes of molecular-water concentration within the grating. The device was developed using thermal annealing technology based on hydrogen-load FBG. Thermal stability of these devices was studied by measuring the grating reflectivity from room temperature to 1000°C. The stability of the device was tested by examining the FBG reflectivity for a period of time at certain temperatures. The results show that these devices are extremely stable at temperatures in excess of 1000°C. The hydroxyl concentration in the grating has been also investigated during this thesis. Based on the knowledge of hydroxyl groups inside FBG, a microwave treatment was designed to increase the hydroxyl concentration in the FBG area. The results show that the molecular-water induced grating, which was fabricated using microwave radiated hydrogen-loaded FBI, are stable at temperatures above 1100°C.

  9. In situ detection and analysis of laser-induced damage on a 1.5-m multilayer-dielectric grating compressor for high-energy, petawatt-class laser systems.

    PubMed

    Qiao, J; Schmid, A W; Waxer, L J; Nguyen, T; Bunkenburg, J; Kingsley, C; Kozlov, A; Weiner, D

    2010-05-10

    A grating-inspection system and a damage-analysis method have been developed to measure in situ laser-induced damage on a 1.5-m tiled-grating assembly of the OMEGA EP pulse compressor during a 15-ps, 2.2-kJ energy ramp. The beam fluence at which significant damage growth occurred was determined. This is the first report on beam fluence versus laser-induced-damage growth of meter-sized multilayer-dielectric-diffraction gratings. This result was correlated to the damage-probability measurement conducted on a small grating sample and is consistent with the fluence, corresponding to 100% damage probability. PMID:20588897

  10. Picosecond-pulse-induced two-photon fluorescence enhancement in biological material by application of grating waveguide structures

    NASA Astrophysics Data System (ADS)

    Selle, André; Kappel, Christoph; Bader, Mark Andreas; Marowsky, Gerd; Winkler, Kathrin; Alexiev, Ulrike

    2005-07-01

    We report enhancement of two-photon fluorescence (TPF) excitation in fluorescent dyes and fluorescently labeled biomolecules by exploiting the optical properties of double grating waveguide structures (DGWSs). Picosecond laser pulses generate a large evanescent field based on the guided mode phenomenon in the resonant DGWSs, which induces strong TPF signals from fluorescent dyes at the waveguide surface. By recording enhanced TPF signals of Rhodamine B and Lucifer Yellow under resonance conditions, a detection sensitivity of concentrations of approximately one dye molecule per 0.1 μm2 was achieved. For the first time to our knowledge, enhanced TPF signals of a Lucifer Yellow-labeled biomolecule (human self-peptide) in an aqueous environment are demonstrated. These results strongly encourage the use of DGWSs as enhancement platforms in modern biophysics and biotechnology for investigations of biological membranes and cells.

  11. Temperature-Insensitive Fibre-Optic Acceleration Sensor Based on Intensity-Referenced Fibre Bragg Gratings

    NASA Astrophysics Data System (ADS)

    Sun, Li-Qun; Dong, Bo; Wang, Yong-Xin; Evan, LALLY; Wang, An-Bo

    2008-10-01

    A temperature-insensitive acceleration sensor using two fibre Bragg gratings (FBGs), based on reflection spectrum intensity modulation and optical power detection, is proposed and demonstrated. A cantilever beam is used to generate acceleration-induced axial strain along two sensing gratings, which are glued on the two opposite surfaces of the beam. Because the two gratings operate within the linear spectral range of a light source, formed by a thermally-tunable extrinsic Fabry-Perot optical filter, the intensity difference of the two reflections from the gratings is proportional to the acceleration applied. This eliminates the need for sophisticated wavelength interrogation of the gratings, and it also endows the sensor with immunity to temperature variation. Compared with a commercial micromachined accelerometer, the sensor is proven to be capable of accurately detecting acceleration.

  12. Diffraction pattern of gratings with erosion

    NASA Astrophysics Data System (ADS)

    Olivares-Pérez, Arturo; Fuentes-Tapia, Israel

    2015-03-01

    We present a theoretical study of amplitude diffraction gratings using computer simulating, which consists of a random sampling of points on the image grating to determine the points to be plotted and the points to remove, to simulate erosion in amplitude on the grating. We show their behavior in the diffraction patterns and the induced noise by limiting the number of points that representing the image of the eroded gratings and their symmetry.

  13. Laser-induced thermal acoustic velocimetry

    NASA Astrophysics Data System (ADS)

    Schlamp, Stefan

    2000-11-01

    Laser-Induced Thermal Acoustics (LITA) is a non- intrusive, remote, four-wave mixing laser diagnostic technique for measurements of the speed of sound and of the thermal diffusivity in gases. If the gas composition is known, then its temperature and density can be inferred. Beam misalignments and bulk fluid velocities can influence the time history and intensity of LITA signals. A closed-form analytic expression for LITA signals incorporating these effects is derived. The magnitude of beam misalignment and the flow velocity can be inferred from the signal shape using a least-squares fit of this model to the experimental data. High-speed velocimetry using homodyne detection is demonstrated with NO2-seeded air in a supersonic blow-down nozzle. The measured speed of sound deviates less than 2% from the theoretical value assuming isentropic quasi-1D flow. Boundary layer effects degrade the velocity measurements to errors of 20%. Heterodyne detection is used for low-speed velocimetry up to Mach number M = 0.1. The uncertainty of the velocity measurements was ~0.2 m/s. The sound speed measurements were repeatable to 0.5%. The agreement between theory and experiments is very good. A one-hidden-layer feed-forward neural network is trained using back-propagation learning and a steepest descent learning rule to extract the speed of sound and flow velocity from a heterodyne LITA signal. The effect of the network size on the performance is demonstrated. The accuracy is determined with a second set of LITA signals that were not used during the training phase. The accuracy is found to be better than that of a conventional frequency decomposition technique while being computationally as efficient. This data analysis method is robust with respect to noise, numerically stable, and fast enough for real-time data analysis. The accuracy and uncertainty of non-resonant LITA measurements is investigated. The error in measurements of the speed of sound and of the thermal diffusivity

  14. Grating lobes

    NASA Technical Reports Server (NTRS)

    1981-01-01

    The radiation patterns characteristic of an indefinite planar array of isotropic antennas was investigated. Particular emphasis was given to the grating lobe scatter from the rectenna. It is shown that an idealy arrayed rectenna of indefinite extent would produce grating lobes which are impulsive. It is further shown that a shift to finite extent or introduction of typical variations in element placement should generate more typical patterns.

  15. Investigation on thermal behavior of resonant waveguide-grating mirrors in an Yb:YAG thin-disk laser

    NASA Astrophysics Data System (ADS)

    Rumpel, Martin; Dannecker, Benjamin; Voss, Andreas; Möller, Michael; Moormann, Christian; Graf, Thomas; Abdou Ahmed, Marwan

    2014-05-01

    We present the experimental investigations of different designs of resonant waveguide-grating mirrors (RWG) which are used as intracavity folding mirror in an Yb:YAG thin-disk laser. The studied mirrors combine structured fused silica substrates, a thin-layer waveguide (Ta2O5), a buffer layer (SiO2) and partial reflectors. The grating period was chosen to be 510 nm to allow resonances at an angle of incidence of ~10° for TE polarization. The waveguide layer has a thickness of 236 nm. It is followed by the buffer layer with a thickness of 580 nm and the subsequent alternating Ta2O5/SiO2 layers. The exact coating sequence depends on the two design approaches which were investigated in this work: either introducing different partial reflectors, i.e. stacks of quarter-wave layers on top of the waveguide while keeping the groove depth of the grating constant, or increasing the grating depth, while keeping an identical partial reflector. The investigation was focused on the rise of the surface temperature due to the coupling of the incident radiation to a waveguide mode, as well as on the laser efficiency, polarization and wavelength selectivity. It is found that, when compared to the simplest RWG design which consists of only a single Ta2O5 waveguide layer, damage threshold as well as laser efficiency can be significantly increased, while the laser performances in terms of polarization- and wavelength selectivity are maintained. So far, the presented RWG allow the generation of linear polarization with a narrow spectral linewidth down to 25 pm FWHM in a fundamental mode Yb:YAG thin-disk laser. Damage thresholds of 60kW/cm2 have been reached where only 63K of surface temperature increase was observed. This shows that the improved mirrors are suitable for the generation of kW-class narrow linewidth, linearly polarized Yb:YAG thin-disk lasers.

  16. Study on thermally induced vibration of flexible boom in various thermal environments of vacuum chamber

    NASA Astrophysics Data System (ADS)

    Kong, Changduk; Oh, Kyung-Won; Park, Hyun-Bum; Sugiyama, Y.

    2005-02-01

    In order to simulate the thermally-induced vibration phenomenon of the flexible thin boom structure of the spacecraft such as the thin solar panel and the flexible cantilever with the attached tip mass in space, the thermally-induced vibration including thermal flutter of the flexible thin boom with the concentrated tip mass was experimentally investigated at various thermal environments using a heat lamp and both vacuum and air condition using the vacuum chamber. In this experimental study, divergence speed, natural frequency and thermal strains of the thermally-induced vibration were comparatively evaluated at various thermal environment conditions. Finally the thermally-induced vibration of the flexible boom structure of the earth orbit satellite in solar radiation environment from the earth eclipse region including umbra and penumbra was simulated using the vacuum chamber and power control of the heating lamp.

  17. Coaxial Dual-wavelength Interferometric Method for a Thermal Infrared Focal-plane-array with Integrated Gratings.

    PubMed

    Shang, Yuanfang; Ye, Xiongying; Cao, Liangcai; Song, Pengfei; Feng, Jinyang

    2016-01-01

    Uncooled infrared (IR) focal-plane-array (FPA) with both large sensing range and high sensitivity is a great challenge due to the limited dynamic range of the detected signals. A coaxial dual-wavelength interferometric system was proposed here to detect thermal-induced displacements of an ultrasensitive FPA based on polyvinyl-chloride(PVC)/gold bimorph cantilevers and carbon nanotube (CNT)-based IR absorbing films. By alternately selecting the two displacement measurements performed by λ1 (=640 nm) and λ2 (=660 nm), the temperature measuring range with greater than 50% maximum sensitivity can be extended by eight-fold in comparison with the traditional single-wavelength mode. Meanwhile, the relative measurement error over the full measuring range is below 0.4%. In addition, it offers a feasible approach for on-line and on-wafer FPA characterization with great convenience and high efficiency. PMID:27193803

  18. Coaxial Dual-wavelength Interferometric Method for a Thermal Infrared Focal-plane-array with Integrated Gratings

    NASA Astrophysics Data System (ADS)

    Shang, Yuanfang; Ye, Xiongying; Cao, Liangcai; Song, Pengfei; Feng, Jinyang

    2016-05-01

    Uncooled infrared (IR) focal-plane-array (FPA) with both large sensing range and high sensitivity is a great challenge due to the limited dynamic range of the detected signals. A coaxial dual-wavelength interferometric system was proposed here to detect thermal-induced displacements of an ultrasensitive FPA based on polyvinyl-chloride(PVC)/gold bimorph cantilevers and carbon nanotube (CNT)-based IR absorbing films. By alternately selecting the two displacement measurements performed by λ1 (=640 nm) and λ2 (=660 nm), the temperature measuring range with greater than 50% maximum sensitivity can be extended by eight-fold in comparison with the traditional single-wavelength mode. Meanwhile, the relative measurement error over the full measuring range is below 0.4%. In addition, it offers a feasible approach for on-line and on-wafer FPA characterization with great convenience and high efficiency.

  19. Coaxial Dual-wavelength Interferometric Method for a Thermal Infrared Focal-plane-array with Integrated Gratings

    PubMed Central

    Shang, Yuanfang; Ye, Xiongying; Cao, Liangcai; Song, Pengfei; Feng, Jinyang

    2016-01-01

    Uncooled infrared (IR) focal-plane-array (FPA) with both large sensing range and high sensitivity is a great challenge due to the limited dynamic range of the detected signals. A coaxial dual-wavelength interferometric system was proposed here to detect thermal-induced displacements of an ultrasensitive FPA based on polyvinyl-chloride(PVC)/gold bimorph cantilevers and carbon nanotube (CNT)-based IR absorbing films. By alternately selecting the two displacement measurements performed by λ1 (=640 nm) and λ2 (=660 nm), the temperature measuring range with greater than 50% maximum sensitivity can be extended by eight-fold in comparison with the traditional single-wavelength mode. Meanwhile, the relative measurement error over the full measuring range is below 0.4%. In addition, it offers a feasible approach for on-line and on-wafer FPA characterization with great convenience and high efficiency. PMID:27193803

  20. pH induced switching in hydrogel coated fiber Bragg grating sensor

    NASA Astrophysics Data System (ADS)

    Shivananju, B. N.; Priydarshi, Manish K.; Roy Mahapatra, D.; Hegde, G. M.; Asokan, S.

    In this paper we report a novel hydrogel functionalized optical Fiber Bragg Grating (FBG) sensor based on chemo-mechanical- optical sensing, and demonstrate its specific application in pH activated process monitoring. The sensing mechanism is based on the stress due to ion diffusion and polymer phase transition which produce strain in the FBG. This results in shift in the Bragg wavelength which is detected by an interrogator system. A simple dip coating method to coat a thin layer of hydrogel on the FBG has been established. The gel consists of sodium alginate and calcium chloride. Gel formation is observed in real-time by continuously monitoring the Bragg wavelength shift. We have demonstrated pH sensing in the range of pH of 2 to 10. Another interesting phenomenon is observed by swelling and deswelling of FBG functionalized with hydrogel by a sequence of alternate dipping between acidic and base solutions. It is observed that the Bragg wavelength undergoes reversible and repeatable pH dependent switching.

  1. Fiber Bragg Grating Temperature Sensors in a 6.5-MW Generator Exciter Bridge and the Development and Simulation of Its Thermal Model

    PubMed Central

    de Morais Sousa, Kleiton; Probst, Werner; Bortolotti, Fernando; Martelli, Cicero; da Silva, Jean Carlos Cardozo

    2014-01-01

    This work reports the thermal modeling and characterization of a thyristor. The thyristor is used in a 6.5-MW generator excitation bridge. Temperature measurements are performed using fiber Bragg grating (FBG) sensors. These sensors have the benefits of being totally passive and immune to electromagnetic interference and also multiplexed in a single fiber. The thyristor thermal model consists of a second order equivalent electric circuit, and its power losses lead to an increase in temperature, while the losses are calculated on the basis of the excitation current in the generator. Six multiplexed FBGs are used to measure temperature and are embedded to avoid the effect of the strain sensitivity. The presented results show a relationship between field current and temperature oscillation and prove that this current can be used to determine the thermal model of a thyristor. The thermal model simulation presents an error of 1.5 °C, while the FBG used allows for the determination of the thermal behavior and the field current dependence. Since the temperature is a function of the field current, the corresponding simulation can be used to estimate the temperature in the thyristors. PMID:25198007

  2. Fiber Bragg grating temperature sensors in a 6.5-MW generator exciter bridge and the development and simulation of its thermal model.

    PubMed

    de Morais Sousa, Kleiton; Probst, Werner; Bortolotti, Fernando; Martelli, Cicero; da Silva, Jean Carlos Cardozo

    2014-01-01

    This work reports the thermal modeling and characterization of a thyristor. The thyristor is used in a 6.5-MW generator excitation bridge. Temperature measurements are performed using fiber Bragg grating (FBG) sensors. These sensors have the benefits of being totally passive and immune to electromagnetic interference and also multiplexed in a single fiber. The thyristor thermal model consists of a second order equivalent electric circuit, and its power losses lead to an increase in temperature, while the losses are calculated on the basis of the excitation current in the generator. Six multiplexed FBGs are used to measure temperature and are embedded to avoid the effect of the strain sensitivity. The presented results show a relationship between field current and temperature oscillation and prove that this current can be used to determine the thermal model of a thyristor. The thermal model simulation presents an error of 1.5 °C, while the FBG used allows for the determination of the thermal behavior and the field current dependence. Since the temperature is a function of the field current, the corresponding simulation can be used to estimate the temperature in the thyristors. PMID:25198007

  3. Electromagnetically induced grating via coherently driven the n-doped In0.47Ga0.53As semiconductor quantum well nanostructure

    NASA Astrophysics Data System (ADS)

    Naseri, Tayebeh

    2016-06-01

    A new scheme for investigating electromagnetically induced grating (EIG) in the vanishing two-photon absorption condition in a three-level ladder-configuration n-doped semiconductor quantum well is presented. By applying a standing-wave field interacting with the system, the absorption and dispersion of the probe field will change with the spatial periodical modulation. It is shown that the first-order diffraction intensity sensitively depends on the intensity of coupling fields, detuning of applied laser fields and interaction length. Moreover, it can reach its maximum on varying the system parameters. A novel result shows the considerable efficiency of higher order diffractions is significantly improved via relative phase between applied laser fields. Furthermore, it is found that the intensity of the switching and coupling fields can increase the efficiency of the phase grating in the present model. Such a unique feature of the cooperative Electromagnetic Induced Grating may be extended to further develop diffraction based new photonic devices in quantum information networks and new photonic devices in all-optical switching and optical imaging.

  4. 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. PMID:26192856

  5. Thermally-induced structural motions of satellite solar arrays

    NASA Astrophysics Data System (ADS)

    Johnston, John Dennis

    1999-11-01

    Satellites have experienced attitude disturbances resulting from thermally. induced structural motions of flexible appendages since the early days of the space program. Thermally-induced structural motions are typically initiated during orbital eclipse transitions when a satellite exits from or enters into the Earth's shadow. The accompanying rapid changes in thermal loading may lead to time-varying temperature differences through the cross-section of appendages resulting in differential thermal expansion and corresponding structural deformations. Since the total angular momentum of the system must be conserved, motions of flexible appendages such as booms and solar arrays result in rigid body rotations of the entire satellite. These potentially large attitude disturbances may violate satellite pointing and jitter requirements. This research investigates thermally-induced structural motions of rigid panel solar arrays (solar panels) through analytical and experimental studies. Orbital eclipse transition heating and thermal analyses were completed to study solar panel thermal behavior and provide results for input to dynamics analyses. A hybrid coordinate dynamical model was utilized to study the planar dynamics of a simple satellite consisting of a rigid hub with a cantilevered flexible solar panel undergoing thermally-induced structural motions. Laboratory experimental studies were carried out to gain new insight into thermal-structural behavior and to validate analytical models. The experimental studies investigated the thermal-structural performance of honeycomb sandwich panels and satellite solar panel hardware subject to simulated eclipse transition heating. Results from the analytical and experimental studies illustrate the importance of the through-the-thickness temperature difference and its time derivatives as well as the ratio of the characteristic thermal and structural response times in solar panel thermally-induced structural motions. The thermal

  6. Prediction of thermal cycling induced matrix cracking

    NASA Technical Reports Server (NTRS)

    Mcmanus, Hugh L.

    1992-01-01

    Thermal fatigue has been observed to cause matrix cracking in laminated composite materials. A method is presented to predict transverse matrix cracks in composite laminates subjected to cyclic thermal load. Shear lag stress approximations and a simple energy-based fracture criteria are used to predict crack densities as a function of temperature. Prediction of crack densities as a function of thermal cycling is accomplished by assuming that fatigue degrades the material's inherent resistance to cracking. The method is implemented as a computer program. A simple experiment provides data on progressive cracking of a laminate with decreasing temperature. Existing data on thermal fatigue is also used. Correlations of the analytical predictions to the data are very good. A parametric study using the analytical method is presented which provides insight into material behavior under cyclical thermal loads.

  7. Analogy of transistor function with modulating photonic band gap in electromagnetically induced grating

    PubMed Central

    Wang, Zhiguo; Ullah, Zakir; Gao, Mengqin; Zhang, Dan; Zhang, Yiqi; Gao, Hong; Zhang, Yanpeng

    2015-01-01

    Optical transistor is a device used to amplify and switch optical signals. Many researchers focus on replacing current computer components with optical equivalents, resulting in an optical digital computer system processing binary data. Electronic transistor is the fundamental building block of modern electronic devices. To replace electronic components with optical ones, an equivalent optical transistor is required. Here we compare the behavior of an optical transistor with the reflection from a photonic band gap structure in an electromagnetically induced transparency medium. A control signal is used to modulate the photonic band gap structure. Power variation of the control signal is used to provide an analogy between the reflection behavior caused by modulating the photonic band gap structure and the shifting of Q-point (Operation point) as well as amplification function of optical transistor. By means of the control signal, the switching function of optical transistor has also been realized. Such experimental schemes could have potential applications in making optical diode and optical transistor used in quantum information processing. PMID:26349444

  8. Analogy of transistor function with modulating photonic band gap in electromagnetically induced grating

    NASA Astrophysics Data System (ADS)

    Wang, Zhiguo; Ullah, Zakir; Gao, Mengqin; Zhang, Dan; Zhang, Yiqi; Gao, Hong; Zhang, Yanpeng

    2015-09-01

    Optical transistor is a device used to amplify and switch optical signals. Many researchers focus on replacing current computer components with optical equivalents, resulting in an optical digital computer system processing binary data. Electronic transistor is the fundamental building block of modern electronic devices. To replace electronic components with optical ones, an equivalent optical transistor is required. Here we compare the behavior of an optical transistor with the reflection from a photonic band gap structure in an electromagnetically induced transparency medium. A control signal is used to modulate the photonic band gap structure. Power variation of the control signal is used to provide an analogy between the reflection behavior caused by modulating the photonic band gap structure and the shifting of Q-point (Operation point) as well as amplification function of optical transistor. By means of the control signal, the switching function of optical transistor has also been realized. Such experimental schemes could have potential applications in making optical diode and optical transistor used in quantum information processing.

  9. Continuous wave ultraviolet light-induced fiber Bragg gratings in few- and single-mode microstructured polymer optical fibers.

    PubMed

    Dobb, Helen; Webb, David J; Kalli, Kyriacos; Argyros, Alexander; Large, Maryanne C J; van Eijkelenborg, Martijn A

    2005-12-15

    We report observations and measurements of the inscription of fiber Bragg gratings (FBGs) in two different types of microstructured polymer optical fiber: few-mode and an endlessly single mode. Contrary to the FBG inscription in silica microstructured fiber, where high-energy laser pulses are a prerequisite, we have successfully used a low-power cw laser source operating at 325 nm to produce 1 cm long gratings with a reflection peak at 1570 nm. Peak reflectivities of more than 10% have been observed. PMID:16389810

  10. Fiber Grating Environmental Sensing System

    DOEpatents

    Schulz, Whitten L.; Udd, Eric

    2003-07-29

    Fiber grating environmental measurement systems are comprised of sensors that are configured to respond to changes in moisture or chemical content of the surrounding medium through the action of coatings and plates inducing strain that is measured. These sensors can also be used to monitor the interior of bonds for degradation due to aging, cracking, or chemical attack. Means to multiplex these sensors at high speed and with high sensitivity can be accomplished by using spectral filters placed to correspond to each fiber grating environmental sensor. By forming networks of spectral elements and using wavelength division multiplexing arrays of fiber grating sensors may be processed in a single fiber line allowing distributed high sensitivity, high bandwidth fiber optic grating environmental sensor systems to be realized.

  11. Diffraction gratings for optical sensing

    NASA Astrophysics Data System (ADS)

    Lu, Patrick P.

    The following document summarizes a journey through the world of diffraction gratings, covering topics such as their history, fabrication, metrology, and uses in some of the most precise scientific experiments ever proposed. Though diffraction gratings have long been used for spectroscopy and pulse compression, it was not until recently that researchers have explored their ability to split and recombine single-frequency CW laser sources for high-precision interferometry. Gravitational-wave detection, one of the most challenging sensing applications to date, is being investigated by the Laser Interferometer Gravitational-Wave Observatory (LIGO) and Laser Interferometer Space Antenna (LISA) projects. Future generations of LIGO and LISA detectors may incorporate gratings as key optical components. This thesis describes the ways gratings can improve interferometer performance by simplifying thermal management and discusses the essential challenges that must be overcome before they can be adopted. The use of gratings requires new interferometer geometries. We show cases where these can be implemented simply and compactly. Gravitational-wave interferometry imposes many requirements on grating components. Using improved metrology methods, we demonstrate that large dielectric gratings with uniformly high efficiency can be fabricated and validated. In particular, we measure the diffraction efficiency of two 20-cm-scale gratings over their entire apertures. The values taken from across their surfaces collectively had means and standard deviations of mu = 99.293% and sigma = 0.164%, and mu =99.084% and sigma =0.079%. We also present simplified models of thermal distortions in gratings, and show them to be in good agreement with measurements conducted by a wavefront sensor. Special focus is given to experimental demonstrations that have achieved highly precise measurements of translational and rotational motion, also known as displacement and angular sensing. For the former

  12. Stretchable diffraction gratings for spectrometry

    NASA Astrophysics Data System (ADS)

    Simonov, Aleksey N.; Grabarnik, Semen; Vdovin, Gleb

    2007-07-01

    We have investigated the possibility of using transparent stretchable diffraction gratings for spectrometric applications. The gratings were fabricated by replication of a triangular-groove master into a transparent viscoelastic. The sample length, and hence the spatial period, can be reversibly changed by mechanical stretching. When used in a monochromator with two slits, the stretchable grating permits scanning the spectral components over the output slit, converting the monochromator into a scanning spectrometer. The spectral resolution of such a spectrometer was found to be limited mainly by the wave-front aberrations due to the grating deformation. A model relating the deformation-induced aberrations in different diffraction orders is presented. In the experiments, a 12-mm long viscoelastic grating with a spatial frequency of 600 line pairs/mm provided a full-width at half-maximum resolution of up to ~1.2 nm in the 580-680 nm spectral range when slowly stretched by a micrometer screw and ~3 nm when repeatedly stretched by a voice coil at 15 Hz. Comparison of aberrations in transmitted and diffracted beams measured by a Shack- Hartmann wave-front sensor showed that astigmatisms caused by stretch-dependent wedge deformation are the main factors limiting the resolution of the viscoelastic-grating-based spectrometer.

  13. Induced natural convection thermal cycling device

    DOEpatents

    Heung, Leung Kit

    2002-08-13

    A device for separating gases, especially isotopes, by thermal cycling of a separation column using a pressure vessel mounted vertically and having baffled sources for cold and heat. Coils at the top are cooled with a fluid such as liquid nitrogen. Coils at the bottom are either electrical resistance coils or a tubular heat exchange. The sources are shrouded with an insulated "top hat" and simultaneously opened and closed at the outlets to cool or heat the separation column. Alternatively, the sources for cold and heat are mounted separately outside the vessel and an external loop is provided for each circuit.

  14. Factors Affecting Thermally Induced Furan Formation

    Technology Transfer Automated Retrieval System (TEKTRAN)

    Furan, a potential carcinogen, can be induced by heat from sugars and fatty acids. However, factors that contribute to its formation in foods are unclear. The objective of this research was to investigate the effects of pH, presence of phosphate, heating time and heating temperature on furan forma...

  15. Fiber Bragg gratings as a candidate technology for satellite optical communication payloads: radiation-induced spectral effects

    NASA Astrophysics Data System (ADS)

    Gusarov, Andrei I.; Doyle, Dominic B.; Karafolas, Nikos; Berghmans, Francis

    2000-10-01

    Intra-core Fiber Bragg Gratings is a candidate technology for a number of future applications in satellite payloads that plan to use multi-wavelength optical links for communicating with other satellites or with ground stations. Applications include wavelength multiplexing and demultiplexing units in multi- wavelength inter-satellite links as well as Add/Drop Multiplexers in the context of broadband satellite constellations using optical networking with on board optical routing. The main advantages of fiber Bragg gratings is that these devices are passive requiring no electric al power, have low mass, and can be compactly packaged. When considered for applications in space the main parameters of concern to be controlled are the stability in wavelength selectivity and throughput loss.

  16. Fiber Bragg grating based spatially resolved characterization of flux-pinning-induced strain of disk-shaped bulk YBCO samples

    NASA Astrophysics Data System (ADS)

    Latka, Ines; Habisreuther, Tobias; Zeisberger, Matthias

    2009-07-01

    A new optical method for the characterization of magnetostrictive effects in bulk superconductors will be presented. Several of wavelength encoded fiber Bragg gratings can be inscribed in one fiber with small spatial distances, which gives the possibility to measure magnetostrictive effects spatially resolved. To demonstrate the performance, samples with Bragg grating arrays glued onto the surface of an YBCO disk where tested in a superconducting solenoid at temperatures of 60 K and magnetic inductances of 6.5 T. For the first time the radius position dependent strain and not only sum effects could be measured. It was stated that in the remnant state both, elongating and compressive strain, occur. This is in agreement with our simulations.

  17. Thermal diffusion by Brownian-motion-induced fluid stress

    NASA Astrophysics Data System (ADS)

    Kreft, Jennifer; Chen, Yeng-Long

    2007-08-01

    The Ludwig-Soret effect, the migration of a species due to a temperature gradient, has been extensively studied without a complete picture of its cause emerging. Here we investigate the dynamics of DNA and spherical particles subjected to a thermal gradient using a combination of Brownian dynamics and the lattice Boltzmann method. We observe that the DNA molecules will migrate to colder regions of the channel, an observation also made in experiments. In fact, the thermal diffusion coefficient found agrees quantitatively with the experimentally measured value. We also observe that the thermal diffusion coefficient decreases as the radius of the studied spherical particles increases. Furthermore, we observe that the thermal-fluctuation-fluid-momentum-flux coupling induces a gradient in the stress which leads to thermal migration in both systems.

  18. Research on tunable phase shift induced by piezoelectric transducer in linearly chirped fiber Bragg grating with the V-I transmission matrix formalism

    NASA Astrophysics Data System (ADS)

    Wu, Liangying; Pei, Li; Liu, Chao; Wang, Jianshuai

    2016-05-01

    In this study, the V-I transmission matrix (V-I TM) is proposed to analyze the tunable single phase shift (SPS) and multiple phase shifts (MPS) inserted in a linearly chirped fiber Bragg grating (LCFBG). According to the simulation results, the peaks appear on the transmission spectrum, when the phase shifts are induced in the LCFBG. With the increase of the phase shift, the center wavelength of the peak moves toward long wavelength region. A remarkable degree of bilateral symmetry can be found as characteristic of the depth of peaks. The maximum depth caused by inserted π-shift is the symmetric axis. Moreover, when MPS are inserted simultaneously, the appeared peaks are independent and the variation tendency of each peak is the same with that caused by SPS. The experiment of phase shift induced by a piezoelectric transducer (PZT) verifies the correctness of the simulation, and a narrow bandwidth of 0.028 nm is acquired.

  19. Cardiac induced localised motion of the human torso detected by a long period grating fibre optic sensing scheme

    NASA Astrophysics Data System (ADS)

    Allsop, T.; Lloyd, G.; Bhamber, R. S.; Hadzievski, L.; Halliday, M.; Webb, D. J.

    2014-05-01

    Cardiovascular health of the human population is a major concern for medical clinicians, with cardiovascular diseases responsible for 48% of all deaths worldwide, according to the World Health Organisation. Therefore the development of new practicable and economical diagnostic tools to scrutinise the cardiovascular health of humans is a major driver for clinicians. We offer a new technique to obtain seismocardiographic signals covering both ballistocardiography (below 20Hz) and audible heart sounds (20Hz upwards). The detection scheme is based upon an array of curvature/displacement sensors using fibre optic long period gratings interrogated using a variation of the derivative spectroscopy interrogation technique.

  20. Multilayer diffraction grating

    DOEpatents

    Barbee, Jr., Troy W.

    1990-01-01

    This invention is for a reflection diffraction grating that functions at X-ray to VUV wavelengths and at normal angles of incidence. The novel grating is comprised of a laminar grating of period D with flat-topped grating bars. A multiplicity of layered synthetic microstructures, of period d and comprised of alternating flat layers of two different materials, are disposed on the tops of the grating bars of the laminar grating. In another embodiment of the grating, a second multiplicity of layered synthetic microstructures are also disposed on the flat faces, of the base of the grating, between the bars. D is in the approximate range from 3,000 to 50,000 Angstroms, but d is in the approximate range from 10 to 400 Angstroms. The laminar grating and the layered microstructures cooperatively interact to provide many novel and beneficial instrumentational advantages.

  1. Multilayer diffraction grating

    DOEpatents

    Barbee, T.W. Jr.

    1990-04-10

    This invention is for a reflection diffraction grating that functions at X-ray to VUV wavelengths and at normal angles of incidence. The novel grating is comprised of a laminar grating of period D with flat-topped grating bars. A multiplicity of layered synthetic microstructures, of period d and comprised of alternating flat layers of two different materials, are disposed on the tops of the grating bars of the laminar grating. In another embodiment of the grating, a second multiplicity of layered synthetic microstructures are also disposed on the flat faces, of the base of the grating, between the bars. D is in the approximate range from 3,000 to 50,000 Angstroms, but d is in the approximate range from 10 to 400 Angstroms. The laminar grating and the layered microstructures cooperatively interact to provide many novel and beneficial instrumentational advantages. 2 figs.

  2. Holographic grating formation in a colloidal suspension of silver nanoparticles.

    PubMed

    Adleman, James R; Eggert, Helge A; Buse, Karsten; Psaltis, Demetri

    2006-02-15

    Holographic gratings are recorded in colloidal suspensions of silver nanoparticles by utilizing interfering nanosecond pulses. The diffraction efficiency is measured with continuous-wave light. An instantaneous response together with a transient grating are observed: the nanoparticles absorb the pump light and heat up. Heat is transferred to the solvent, and a delayed thermal grating appears. The final decay time constant of this grating depends quadratically on the period length and has a typical value of 1 micros for grating spacings of several micrometers. PMID:16496882

  3. A Fe-C coated long-period fiber grating sensor for corrosion-induced mass loss measurement.

    PubMed

    Chen, Yizheng; Tang, Fujian; Bao, Yi; Tang, Yan; Chen, Genda

    2016-05-15

    This Letter reports a Fe-C coated long period fiber gratings sensor with a grating period of 387±0.1  μm for corrosion monitoring of low carbon steel in a 3.5 wt. % NaCl solution. An LPFG sensor was first deposited with a 0.8 μm thick layer of silver (Ag) and then electroplated with a 20 μm thick Fe-C coating. The chemical composition of the Fe-C coating was designed to include the main elements of low carbon steel. The resonant wavelength of the coated sensor was correlated with the mass loss of steel over time. Test results indicated a corrosion sensitivity of 0.0423 nm per 1% mass loss up to 80% Fe-C mass loss and 0.576 nm per 1% mass loss between 80% and 95% Fe-C mass loss. The corrosion sensitivity of such a Fe-C coated LPFG sensor was a trade-off for the service life of the sensor, both depending on thicknesses of the inner silver layer and the outer Fe-C coating. PMID:27176989

  4. Laser-Induced Transient Grating Analysis of Dynamics of Interaction between Sensory Rhodopsin II D75N and the HtrII Transducer

    PubMed Central

    Inoue, Keiichi; Sasaki, Jun; Spudich, John L.; Terazima, Masahide

    2007-01-01

    The interaction between sensory rhodopsin II (SRII) and its transducer HtrII was studied by the time-resolved laser-induced transient grating method using the D75N mutant of SRII, which exhibits minimal visible light absorption changes during its photocycle, but mediates normal phototaxis responses. Flash-induced transient absorption spectra of transducer-free D75N and D75N joined to 120 amino-acid residues of the N-terminal part of the SRII transducer protein HtrII (ΔHtrII) showed only one spectrally distinct K-like intermediate in their photocycles, but the transient grating method resolved four intermediates (K1–K4) distinct in their volumes. D75N bound to HtrII exhibited one additional slower kinetic species, which persists after complete recovery of the initial state as assessed by absorption changes in the UV-visible region. The kinetics indicate a conformationally changed form of the transducer portion (designated Tr*), which persists after the photoreceptor returns to the unphotolyzed state. The largest conformational change in the ΔHtrII portion was found to cause a ΔHtrII-dependent increase in volume rising in 8 μs in the K4 state and a drastic decrease in the diffusion coefficient (D) of K4 relatively to those of the unphotolyzed state and Tr*. The magnitude of the decrease in D indicates a large structural change, presumably in the solvent-exposed HAMP domain of ΔHtrII, where rearrangement of interacting molecules in the solvent would substantially change friction between the protein and the solvent. PMID:17189313

  5. Er3+-doped fiber-based Mach-Zehnder interferometer with mechanically induced long-period fiber gratings

    NASA Astrophysics Data System (ADS)

    Pérez-Sánchez, G.; Alvarez-Chavez, J. A.

    2013-09-01

    There are a few semi-conductor, multiple-wavelength, high-performance sources already available for ITU-T channel generation in DWDM systems. The 200 Ghz barrier has imposed a limitation to such sources. An option for overcoming such a limitation is a super-continuum, all fibre source working in the amplified spontaneous emission regime. Furthermore, in this work we propose an Er-doped fiber based Mach-Zehnder interferometer, made with mechanicallyinduced, long-period fiber gratings, which generate a fringe pattern ranging from 1450 to 1650 nm. These characteristics are of great interest for the development of all-fiber devices that could produce and even select a few channels in the 1550nm region, the transmission window of interest for ultra-long haul optical communication systems. A full set of optical characterization and results will be included in the presentation.

  6. Thermally induced natural convection effects in Yucca Mountain drifts.

    PubMed

    Webb, Stephen W; Francis, Nicholas D; Dunn, Sandra Dalvit; Itamura, Michael T; James, Darryl L

    2003-01-01

    Thermally induced natural convection from the heat produced by emplaced waste packages is an important heat and mass transfer mechanism within the Yucca Mountain Project (YMP) drifts. Various models for analyzing natural convection have been employed. The equivalent porous medium approach using Darcy's law has been used in many YMP applications. However, this approach has questionable fidelity, especially for turbulent flow conditions. Computational fluid dynamics (CFD), which is based on the fundamental Navier-Stokes equations, is currently being evaluated as a technique to calculate thermally induced natural convection in YMP. Data-model comparisons for turbulent flow conditions show good agreement of CFD predictions with existing experiments including YMP-specific data. PMID:12714318

  7. Renewable liquid reflection grating

    DOEpatents

    Ryutov, Dmitri D.; Toor, Arthur

    2003-10-07

    A renewable liquid reflection grating. Electrodes are operatively connected to a conducting liquid in an arrangement that produces a reflection grating and driven by a current with a resonance frequency. In another embodiment, the electrodes create the grating by a resonant electrostatic force acting on a dielectric liquid.

  8. Multilayer dielectric diffraction gratings

    DOEpatents

    Perry, Michael D.; Britten, Jerald A.; Nguyen, Hoang T.; Boyd, Robert; Shore, Bruce W.

    1999-01-01

    The design and fabrication of dielectric grating structures with high diffraction efficiency used in reflection or transmission is described. By forming a multilayer structure of alternating index dielectric materials and placing a grating structure on top of the multilayer, a diffraction grating of adjustable efficiency, and variable optical bandwidth can be obtained. Diffraction efficiency into the first order in reflection varying between 1 and 98 percent has been achieved by controlling the design of the multilayer and the depth, shape, and material comprising the grooves of the grating structure. Methods for fabricating these gratings without the use of ion etching techniques are described.

  9. Multilayer dielectric diffraction gratings

    DOEpatents

    Perry, M.D.; Britten, J.A.; Nguyen, H.T.; Boyd, R.; Shore, B.W.

    1999-05-25

    The design and fabrication of dielectric grating structures with high diffraction efficiency used in reflection or transmission is described. By forming a multilayer structure of alternating index dielectric materials and placing a grating structure on top of the multilayer, a diffraction grating of adjustable efficiency, and variable optical bandwidth can be obtained. Diffraction efficiency into the first order in reflection varying between 1 and 98 percent has been achieved by controlling the design of the multilayer and the depth, shape, and material comprising the grooves of the grating structure. Methods for fabricating these gratings without the use of ion etching techniques are described. 7 figs.

  10. Effects of ply thickness on thermal cycle induced damage and thermal strain

    NASA Technical Reports Server (NTRS)

    Tompkins, Stephen S.

    1994-01-01

    An experimental study was conducted to determine the effects of ply thickness in composite laminates on thermally induced cracking and changes in the coefficient of thermal expansion, CTE. A graphite-epoxy composite material, P75/ERL 1962, in thin (1 mil) and thick (5 mils) prepregs was used to make cross-ply laminates, ((0/90)(sub n))s, with equal total thickness (n=2, n=10) and cross-ply laminates with the same total number of plies (n=2). Specimens of each laminate configuration were cycled up to 1500 times between -250 and 250 F. Thermally induced microdamage was assessed as a function of the number of cycles as was the change in CTE. The results showed that laminates fabricated with thin-plies microcracked at significantly different rates and reached significantly different equilibrium crack densities than the laminate fabricated with thick-ply and n=2. The CTE of thin-ply laminates was less affected by thermal cycling and damage than the CTE of thick-ply laminates. These differences are attributed primarily to differences in interply constraints. Observed effects of ply thickness on crack density was qualitatively predicted by a combined shear-lag stress/energy method.

  11. Prediction of thermal cycling induced cracking in polmer matrix composites

    NASA Technical Reports Server (NTRS)

    Mcmanus, Hugh L.

    1994-01-01

    The work done in the period August 1993 through February 1994 on the 'Prediction of Thermal Cycling Induced Cracking In Polymer Matrix Composites' program is summarized. Most of the work performed in this period, as well as the previous one, is described in detail in the attached Master's thesis, 'Analysis of Thermally Induced Damage in Composite Space Structures,' by Cecelia Hyun Seon Park. Work on a small thermal cycling and aging chamber was concluded in this period. The chamber was extensively tested and calibrated. Temperatures can be controlled very precisely, and are very uniform in the test chamber. Based on results obtained in the previous period of this program, further experimental progressive cracking studies were carried out. The laminates tested were selected to clarify the differences between the behaviors of thick and thin ply layers, and to explore other variables such as stacking sequence and scaling effects. Most specimens tested were made available from existing stock at Langley Research Center. One laminate type had to be constructed from available prepreg material at Langley Research Center. Specimens from this laminate were cut and prepared at MIT. Thermal conditioning was carried out at Langley Research Center, and at the newly constructed MIT facility. Specimens were examined by edge inspection and by crack configuration studies, in which specimens were sanded down in order to examine the distribution of cracks within the specimens. A method for predicting matrix cracking due to decreasing temperatures and/or thermal cycling in all plies of an arbitrary laminate was implemented as a computer code. The code also predicts changes in properties due to the cracking. Extensive correlations between test results and code predictions were carried out. The computer code was documented and is ready for distribution.

  12. Phased-array grating compression for high-energy chirped pulse amplification lasers.

    PubMed

    Cotel, A; Castaing, M; Pichon, P; Le Blanc, C

    2007-03-01

    The development of phased-array grating compressor is a crucial issue for high-energy, ultra-short pulse petawatt-class lasers. We present a theoretical and experimental analysis of two-grating phasing in a broadband pulse mosaic compressor. The phase defaults induced by misaligned gratings are studied. Monochromatic grating phasing is experimentally achieved with an interferometric technique and pulse compression is demonstrated with a two-phased-array grating system. PMID:19532511

  13. A physical model for measuring thermally-induced block displacements

    NASA Astrophysics Data System (ADS)

    Bakun-Mazor, Dagan; Feldhiem, Aviran; Keissar, Yuval; Hatzor, Yossef H.

    2016-04-01

    A new model for thermally-induced block displacement in discontinuous rock slopes has been recently suggested. The model consists of a discrete block that is separated from the rock mass by a tension crack and rests on an inclined plane. The tension crack is filled with a wedge block or rock fragments. Irreversible block sliding is assumed to develop in response to climatic thermal fluctuations and consequent contraction and expansion of the sliding block material. While a tentative analytical solution for this model is already available, we are exploring here the possibility of obtaining such a permanent, thermally-induced, rock block displacement, under fully controlled conditions at the laboratory, and the sensitivity of the mechanism to geometry, mechanical properties, and temperature fluctuations. A large scale concrete physical model (50x150x60 cm^3) is being examined in a Climate-Controlled Room (CCR). The CCR permits accurate control of ambient temperature from 5 to 45 Celsius degrees. The permanent plastic displacement is being measured using four displacement transducers and a high resolution (29M pixel) visual range camera. A series of thermocouples measure the heating front inside the sliding block, hence thermal diffusivity is evaluated from the measured thermal gradient and heat flow. In order to select the appropriate concrete mixture, the mechanical and thermo-physical properties of concrete samples are determined in the lab. Friction angle and shear stiffness of the sliding interface are determined utilizing a hydraulic, servo-controlled direct shear apparatus. Uniaxial compression tests are performed to determine the uniaxial compressive strength, Young's modulus and Poison's ratio of the intact block material using a stiff triaxial load frame. Thermal conductivity and linear thermal expansion coefficient are determined experimentally using a self-constructed measuring system. Due to the fact that this experiment is still in progress, preliminary

  14. Thermally Induced Osteocyte Damage Initiates a Remodelling Signaling Cascade

    PubMed Central

    Dolan, Eimear B.; McNamara, Laoise M.

    2015-01-01

    Thermal elevations experienced by bone during orthopaedic procedures, such as cutting and drilling, exothermal reactions from bone cement, and thermal therapies such as tumor ablation, can result in thermal damage leading to death of native bone cells (osteocytes, osteoblasts, osteoclasts and mesenchymal stem cells). Osteocytes are believed to be the orchestrators of bone remodeling, which recruit nearby osteoclast and osteoblasts to control resorption and bone growth in response to mechanical stimuli and physical damage. However, whether heat-induced osteocyte damage can directly elicit bone remodelling has yet to be determined. This study establishes the link between osteocyte thermal damage and the remodeling cascade. We show that osteocytes directly exposed to thermal elevations (47°C for 1 minute) become significantly apoptotic and alter the expression of osteogenic genes (Opg and Cox2). The Rankl/Opg ratio is consistently down-regulated, at days 1, 3 and 7 in MLO-Y4s heat-treated to 47°C for 1 minute. Additionally, the pro-osteoblastogenic signaling marker Cox2 is significantly up-regulated in heat-treated MLO-Y4s by day 7. Furthermore, secreted factors from heat-treated MLO-Y4s administered to MSCs using a novel co-culture system are shown to activate pre-osteoblastic MSCs to increase production of the pro-osteoblastic differentiation marker, alkaline phosphatase (day 7, 14), and calcium deposition (day 21). Most interestingly, an initial pro-osteoclastogenic signaling response (increase Rankl and Rankl/Opg ratio at day 1) followed by later stage pro-osteoblastogenic signaling (down-regulation in Rankl and the Rankl/Opg ratio and an up-regulation in Opg and Cox2 by day 7) was observed in non-heat-treated MLO-Y4s in co-culture when these were exposed to the biochemicals produced by heat-treated MLO-Y4s. Taken together, these results elucidate the vital role of osteocytes in detecting and responding to thermal damage by means of thermally induced apoptosis

  15. Thermally induced osteocyte damage initiates a remodelling signaling cascade.

    PubMed

    Dolan, Eimear B; Haugh, Matthew G; Voisin, Muriel C; Tallon, David; McNamara, Laoise M

    2015-01-01

    Thermal elevations experienced by bone during orthopaedic procedures, such as cutting and drilling, exothermal reactions from bone cement, and thermal therapies such as tumor ablation, can result in thermal damage leading to death of native bone cells (osteocytes, osteoblasts, osteoclasts and mesenchymal stem cells). Osteocytes are believed to be the orchestrators of bone remodeling, which recruit nearby osteoclast and osteoblasts to control resorption and bone growth in response to mechanical stimuli and physical damage. However, whether heat-induced osteocyte damage can directly elicit bone remodelling has yet to be determined. This study establishes the link between osteocyte thermal damage and the remodeling cascade. We show that osteocytes directly exposed to thermal elevations (47°C for 1 minute) become significantly apoptotic and alter the expression of osteogenic genes (Opg and Cox2). The Rankl/Opg ratio is consistently down-regulated, at days 1, 3 and 7 in MLO-Y4s heat-treated to 47°C for 1 minute. Additionally, the pro-osteoblastogenic signaling marker Cox2 is significantly up-regulated in heat-treated MLO-Y4s by day 7. Furthermore, secreted factors from heat-treated MLO-Y4s administered to MSCs using a novel co-culture system are shown to activate pre-osteoblastic MSCs to increase production of the pro-osteoblastic differentiation marker, alkaline phosphatase (day 7, 14), and calcium deposition (day 21). Most interestingly, an initial pro-osteoclastogenic signaling response (increase Rankl and Rankl/Opg ratio at day 1) followed by later stage pro-osteoblastogenic signaling (down-regulation in Rankl and the Rankl/Opg ratio and an up-regulation in Opg and Cox2 by day 7) was observed in non-heat-treated MLO-Y4s in co-culture when these were exposed to the biochemicals produced by heat-treated MLO-Y4s. Taken together, these results elucidate the vital role of osteocytes in detecting and responding to thermal damage by means of thermally induced apoptosis

  16. Ultrafast transient grating radiation to optical image converter

    DOEpatents

    Stewart, Richard E; Vernon, Stephen P; Steel, Paul T; Lowry, Mark E

    2014-11-04

    A high sensitivity transient grating ultrafast radiation to optical image converter is based on a fixed transmission grating adjacent to a semiconductor substrate. X-rays or optical radiation passing through the fixed transmission grating is thereby modulated and produces a small periodic variation of refractive index or transient grating in the semiconductor through carrier induced refractive index shifts. An optical or infrared probe beam tuned just below the semiconductor band gap is reflected off a high reflectivity mirror on the semiconductor so that it double passes therethrough and interacts with the radiation induced phase grating therein. A small portion of the optical beam is diffracted out of the probe beam by the radiation induced transient grating to become the converted signal that is imaged onto a detector.

  17. Laser-induced thermal acoustics (LITA) signals from finite beams

    NASA Astrophysics Data System (ADS)

    Cummings, E. B.; Leyva, I. A.; Hornung, H. G.

    1995-06-01

    Laser-induced thermal acoustics (LITA) is a four-wave mixing technique that may be employed to measure sound speeds, transport properties, velocities, and susceptibilities of fluids. It is particularly effective in high-pressure gases ( greater than 1 bar). An analytical expression for LITA signals is derived by the use of linearized equations of hydrodynamics and light scattering. This analysis, which includes full finite-beam-size effects and the optoacoustic effects of thermalization and electrostriction, predicts the amplitude and the time history of narrow-band time-resolved LITA and broadband spectrally resolved (mulitplex) LITA signals. The time behavior of the detected LITA signal depends significantly on the detection solid angle, with implications for the measurement of diffusivities by the use of LITA and the proper physical picture of LITA scattering. This and other elements of the physics of LITA that emerge from the analysis are discussed. Theoretical signals are compared with experimental LITA data.

  18. Thermally induced optical nonlinearity during transient heating of thin films

    SciTech Connect

    Chen, G. ); Tien, C.L. )

    1994-05-01

    This work studies the temperature field and the optical response of weakly absorbing thin films with thermally induced optical nonlinearity during picosecond to nanosecond pulsed-laser heating. A one-dimensional model is presented that examines the effects of the temperature dependent optical constants and the nonuniform absorption caused by interference. The energy equation is solved numerically, coupled with the matrix method in optical multilayer theory. Both cadmium sulfide (CdS) thin films and a zinc selenide (ZnSe) interference filter are considered. The computational results compare favorably with available experimental data on the ZnSe interference filter. This study shows that the transient temperature distributions in the films are highly nonuniform. Such nonuniformity yields Airy's formulae for calculating the thin-film reflectance and transmittance inapplicable. Applications of the work include optical bistability, localized change of the film structure, and measurement of the thermal diffusivity of thin films. 31 refs., 7 figs., 1 tab.

  19. Controlling the thermally induced focal shift in laser processing heads

    NASA Astrophysics Data System (ADS)

    Negel, Jan-Philipp; Abt, Felix; Blázquez-Sánchez, David; Austerschulte, Armin; Hafner, Margit; Liebig, Thomas; von Strobl-Albeg, Philipp; Weber, Rudolf; Abdou Ahmed, Marwan; Voss, Andreas; Graf, Thomas

    2012-03-01

    A system being able to in situ measure and control not simply the distance between the workpiece and the focusing optics, but the true focal position on the workpiece including the thermally induced focal shift in a laser processing head is presented. In order to achieve this, a bundle of astigmatic measurement beams is used following the same optical path as the welding beam. A camera and a software algorithm allow to keep the focal position constant within a range of 4 mm and with a resolution between 150 μm and 500 μm.

  20. Thermally induced birefringence in Nd:YAG slab lasers

    SciTech Connect

    Ostermeyer, Martin; Mudge, Damien; Veitch, Peter J.; Munch, Jesper

    2006-07-20

    We study thermally induced birefringence in crystalline Nd:YAG zigzag slab lasers and the associated depolarization losses. The optimum crystallographic orientation of the zigzag slab within the Nd:YAG boule and photoelastic effects in crystalline Nd:YAG slabs are briefly discussed. The depolarization is evaluated using the temperature and stress distributions, calculated using a finite element model, for realistically pumped and cooled slabs of finite dimensions. Jones matrices are then used to calculate the depolarization of the zigzag laser mode. We compare the predictions with measurements of depolarization, and suggest useful criteria for the design of the gain media for such lasers.

  1. Morphogenesis and propagation of complex cracks induced by thermal shocks.

    PubMed

    Bourdin, Blaise; Marigo, Jean-Jacques; Maurini, Corrado; Sicsic, Paul

    2014-01-10

    We study the genesis and the selective propagation of complex crack networks induced by thermal shock or drying of brittle materials. We use a quasistatic gradient damage model to perform large-scale numerical simulations showing that the propagation of fully developed cracks follows Griffith criterion and depends only on the fracture toughness, while crack morphogenesis is driven by the material's internal length. Our numerical simulations feature networks of parallel cracks and selective arrest in two dimensions and hexagonal columnar joints in three dimensions, without any hypotheses on cracks geometry, and are in good agreement with available experimental results. PMID:24483901

  2. Nonresonant Referenced Laser-Induced Thermal Acoustics Thermometry in Air

    NASA Astrophysics Data System (ADS)

    Hart, Roger C.; Balla, R. Jeffrey; Herring, Gregory C.

    1999-01-01

    We report a detailed investigation of nonresonant laser-induced thermal acoustics (LITA) for the single-shot measurement of the speed of sound ( v S ) in an oven containing room air. A model for the speed of sound that includes important acoustic relaxation effects is used to convert the speed of sound into temperature. A reference LITA channel is used to reduce uncertainties in v S . Comparing thermocouple temperatures with temperatures deduced from our v S measurements and model, we find the mean temperature difference from 300 to 650 K to be 1% ( 2 ). The advantages of using a reference LITA channel are discussed.

  3. Compensation for thermally induced birefringence in polycrystalline ceramic active elements

    SciTech Connect

    Kagan, M A; Khazanov, E A

    2003-10-31

    Polycrystalline ceramics differ significantly from single crystals in that the crystallographic axes (and hence of the axes of thermally induced birefringence) are oriented randomly in each granule of the ceramic. The quaternion formalism is employed to calculate the depolarisation in the ceramics and the efficiency of its compensation. The obtained analytic expressions are in good agreement with the numerical relations. It is shown that the larger the ratio of the sample length to the granule size, the closer the properties of the ceramics to those of a single crystal with the [111] orientation (in particular, the uncompensated depolarisation is inversely proportional to this ratio). (active media)

  4. Thermal spike model of ion-induced grain growth

    SciTech Connect

    Alexander, D.E. ); Was, G.S. . Dept. of Nuclear Engineering)

    1990-11-01

    A thermal spike model has been developed to describe the phenomenon of ion irradiation-induced grain growth in metal alloy thin films. In single phase films where the driving force for grain growth is the reduction of grain boundary curvature, the model shows that ion-induced grain boundary mobility, M{sub ion}, is proportional to the quantity F{sub D}{sup 2}/{Delta}H{sub coh}{sup 3}, where F{sub D} is the deposited ion damage energy and {Delta}H{sub coh} is the cohesive energy of the element or alloy. Experimental strain growth results from ion irradiated coevaporated binary alloy films compare favorably with model predictions. 11 refs., 1 fig., 1 tab.

  5. Laser-induced photo-thermal magnetic imaging

    NASA Astrophysics Data System (ADS)

    Thayer, David A.; Lin, Yuting; Luk, Alex; Gulsen, Gultekin

    2012-08-01

    Due to the strong scattering nature of biological tissue, optical imaging beyond the diffusion limit suffers from low spatial resolution. In this letter, we present an imaging technique, laser-induced photo-thermal magnetic imaging (PMI), which uses laser illumination to induce temperature increase in a medium and magnetic resonance imaging to map the spatially varying temperature, which is proportional to absorbed energy. This technique can provide high-resolution images of optical absorption and can potentially be used for small animal as well as breast cancer and lymph node imaging. First, we describe the theory of PMI, including the modeling of light propagation and heat transfer in tissue. We also present experimental data with corresponding predictions from theoretical models, which show excellent agreement.

  6. First order Bragg grating filters in silicon on insulator waveguides

    NASA Astrophysics Data System (ADS)

    Waugh, Peter Michael

    2008-08-01

    The subject of this project is the design; analysis, fabrication and characterisation of first order Bragg Grating optical filters in Silicon-on-Insulator (SOI) planar waveguides. It is envisaged that this work will result in the possibility of Bragg Grating filters for use in Silicon Photonics. It is the purpose of the work to create as far as is possible flat surface waveguides so as to facilitate Thermo-Optic tuning and also the incorporation into rib-waveguide Silicon Photonics. The spectral response of the shallow Bragg Gratings was modelled using Coupled Mode Theory (CMT) by way of RSoft Gratingmod TM. Also the effect of having a Bragg Grating with alternate layers of refractive index of 1.5 and 3.5 was simulated in order to verify that Silica and Silicon layered Bragg Gratings could be viable. A series of Bragg Gratings were patterned on 1.5 micron SOI at Philips in Eindhoven, Holland to investigate the variation of grating parameters with a) the period of the gratings b) the mark to space ratio of the gratings and c) the length of the region converted to Bragg Gratings (i.e. the number of grating period repetitions). One set of gratings were thermally oxidised at Philips in Eindhoven and another set were ion implanted with Oxygen ions at the Ion Beam Facility, University of Surrey, England. The gratings were tested and found to give transmission minima at approximately 1540 nanometres and both methods of creating flat surfaces were found to give similar minima. Atomic Force Microscopy was applied to the grating area of the as-implanted samples in the Advanced Technology Institute, University of Surrey, which were found to have surface undulations in the order of 60 nanometres.

  7. Compact and tunable silicon nitride Bragg grating filters in polymer

    NASA Astrophysics Data System (ADS)

    Zhang, Ziyang; Novo, Alejandro Maese; Liu, Dongliang; Keil, Norbert; Grote, Norbert

    2014-06-01

    A series of tunable filters based on silicon nitride waveguide Bragg gratings buried in polymer are studied, fabricated and analyzed. The gratings are etched completely through the waveguides to improve the peak reflectivity at short grating lengths. Reflectivity from 1% to 70% can be reached when the third-order grating length varies from 16 µm to 160 µm. The experimental results are in good agreement with numerical simulations. Due to its compact size and the thermal advantages of polymer, the filter can be tuned very efficiently by a micro heater buried beneath. A tuning range of 34.5 nm is demonstrated at a heat power of only 22 mW.

  8. Reflective diffraction grating

    DOEpatents

    Lamartine, Bruce C.

    2003-06-24

    Reflective diffraction grating. A focused ion beam (FIB) micromilling apparatus is used to store color images in a durable medium by milling away portions of the surface of the medium to produce a reflective diffraction grating with blazed pits. The images are retrieved by exposing the surface of the grating to polychromatic light from a particular incident bearing and observing the light reflected by the surface from specified reception bearing.

  9. Thermally Induced And Base Catalyzed Reactions Of Naphthoquinone Diazides

    NASA Astrophysics Data System (ADS)

    Koshiba, Mitsunobu; Murata, Makoto; Matsui, Mariko; Harita, Yoshiyuki

    1988-01-01

    Thermally induced and base catalyzed reactions of a phenol ester of 1,2-naphthoquinone-diazide-5-sulfonic acid (DAM) with p-cresol were investigated. In total seven reaction products were obtained for the thermally induced reaction. The three major products, TR--F4, TR-F6 and TR-F7, were isolated and their structures were determined by means of several advanced spectroscopic techniques like Fourier transform nuclear magnetic resonance (FTNMR) and field desorption mass spectroscopy (FD-MS). Besides a cresol ester of indenecarboxylic acid (TR-F6) and an azo compound which contains two DAM originated moieties and cresol (TR-F7), the formation of a novel compound was found; a phenol ester of 2-cresyl-l-naphthol-5-sulfonic acid. On the other hand, four reaction products were found in the base (a 2.38wt% tetramethylammonium hydroxide aq. solution) catalyzed reaction products of DAM with p-cresol, and two major products, BC-Fl and BC-F3, which appeared at the initial stage of the reaction were isolated. The structure determination of the two major products was carried out in the same manner as described above. It was discovered that BC-Fl was a cresol ester of 1-naphthol while BC-F3 was an azoxy compound. Brief discussions will be made on those reactions of naphthoquinone diazides with a matrix novolak resin with reference to the results obtained by the present study.

  10. Temperature insensitive refractive index sensor based on concatenated long period fiber gratings

    NASA Astrophysics Data System (ADS)

    Tripathi, Saurabh M.; Bock, Wojtek J.; Mikulic, Predrag

    2013-10-01

    We propose and demonstrate a temperature immune biosensor based on two concatenated LPGs incorporating a suitable inter-grating-space (IGS). Compensating the thermal induced phase changes in the grating region by use of an appropriate length of the IGS the temperature insensitivity has been achieved. Using standard telecommunication grade single-mode fibers we show that a length ratio of ~8.2 is sufficient to realize the proposed temperature insensitivity. The resulting sensor shows a refractive index sensitivity of 423.28 nm/RIU displaying the capability of detecting an index variation of 2.36 × 10-6 RIU in the bio-samples. The sensor can also be applied as a temperature insensitive WMD channel isolation filter in the optical communication systems, removing the necessity of any external thermal insulation packaging.

  11. Manipulation of plasma grating by impulsive molecular alignment

    SciTech Connect

    Lu, Peifen; Wu, Jian; Zeng, Heping

    2013-11-25

    We experimentally demonstrated that multiphoton-ionization-induced plasma grating in air could be precisely manipulated by impulsive molecular alignment. In the linear region, the impulsively aligned molecules modulated the diffraction efficiency of the plasma grating for a time-delayed femtosecond laser pulse. In the nonlinear region, the third harmonic generation from the plasma grating was either enhanced or suppressed by following the alignment of the molecules.

  12. Non-diffusive thermal conductivity in semiconductors at room temperature

    NASA Astrophysics Data System (ADS)

    Maznev, Alexei; Johnson, Jeremy; Eliason, Jeffrey; Nelson, Keith; Minnich, Austin; Collins, Kimberlee; Chen, Gang; Cuffe, John; Kehoe, Timothy; Sotomayor Torres, Clivia

    2012-02-01

    The ``textbook'' value of phonon mean free path (MFP) in silicon at room temperature is ˜40 nm. However, a large contribution to thermal conductivity comes from low-frequency phonons with much longer MFPs. We find that heat transport in semiconductors such as Si and GaAs significantly deviates from the Fourier law at distances much longer than previously thought, >=1 μm at room temperature and above. We use the laser-induced transient thermal grating technique in which absorption of crossed laser pulses in a sample sets up a sinusoidal temperature profile monitored via diffraction of a probe laser beam. By changing the period of the thermal grating we vary the thermal transport distance within the range ˜1-10 μm. In measurements performed on thin free-standing Si membranes and on bulk GaAs the thermal grating decay time deviates from the expected quadratic dependence on the grating period, thus providing model-independent evidence of non-diffusive transport. The simplicity of the experimental configuration permits analytical treatment of non-equilibrium phonon transport with the Boltzmann transport equation. Our analysis shows that at small grating periods the effective thermal conductivity is reduced due to diminishing contributions of ``ballistic'' low-frequency phonons with long MFPs.

  13. Bidirectional grating compressors

    NASA Astrophysics Data System (ADS)

    Wang, Cheng; Li, Zhaoyang; Li, Shuai; Liu, Yanqi; Leng, Yuxin; Li, Ruxin

    2016-07-01

    A bidirectional grating compressor for chirped pulse amplifiers is presented. It compresses a laser beam simultaneously in two opposite directions. The pulse compressor is shown to promote chirped pulse amplifiers' output energy without grating damages. To verify the practicability, an experiment is carried out. In addition, a crosscorrelation instrument is designed and set up to test the time synchronization between these two femtosecond pulses.

  14. 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.

  15. Thermally induced twist in graphite-epoxy tubes

    NASA Technical Reports Server (NTRS)

    Hyer, M. W.; Rousseau, C. Q.; Tompkins, S. S.

    1988-01-01

    This paper discusses an analytical and experimental study to investigate the thermally induced twist in laminated angle-ply graphite-epoxy tubes. Attention is focused on balanced laminates which, contrary to intuition, exhibit twist when the temperature is changed. The twisting is due to the fact that a lamina with ( a + phi) orientation and a lamina with (a - phi) orientation must be at slightly different radial positions in the twist. The lamina with the greater radial position determines the sense of the twist. Classical lamination theory does not predict this phenomenon, and so as more sophisticated theory must be employed. This paper outlines such as theory, which is based on an generalized plane-deformation elasticity analysis, and presents experimental data to confirm the predictions of the theory. A brief description of the experimental apparatus and procedure used to measure twist is presented.

  16. Thermally induced recrystallization of textured hydrogenated nanocrystalline silicon

    NASA Astrophysics Data System (ADS)

    Fugallo, Giorgia; Mattoni, Alessandro

    2014-01-01

    By an analysis of the local crystallinity based on model potential molecular dynamics simulations we investigated the effect of dissolved hydrogen on the thermally induced recrystallization of nanocrystalline silicon. By using the Kolmogorov-Johnson-Mehl-Avrami theory to analyze the atomistic data, we find that the recrystallization rate decreases exponentially with the hydrogen contamination. At low concentration, the kinetics is moderately affected by the H atoms that tend to migrate to the boundaries increasing their effective interface. At higher H content, we find an increasing number of SimHn hydrides that affect the crystalline order of the material and severely impede recrystallization. The analysis based on crystallinity is supported by the atomic scale study of the recrystallization mechanism, here identified as an inverted bond-switching process, and by the ability of hydrates to pin the amorphous-crystalline boundaries.

  17. Thermally induced magnetization switching in Gd/Fe multilayers

    NASA Astrophysics Data System (ADS)

    Xu, C.; Ostler, T. A.; Chantrell, R. W.

    2016-02-01

    A theoretical model of Gd/Fe multilayers is constructed using the atomistic spin dynamics formalism. By varying the thicknesses and number of layers we have shown that a strong dependence of the energy required for thermally induced magnetization switching (TIMS) is present; with a larger number of interfaces, lower energy is required. The results of the layer resolved dynamics show that the reversal process of the multilayered structures, similar to that of a GdFeCo alloy, is driven by the antiferromagnetic interaction between the transition-metal and rare-earth components. Finally, while the presence of the interface drives the reversal process, we show here that the switching process does not initiate at the surface but from the layers furthest from it, a departure from the alloy behavior which expands the classes of material types exhibiting TIMS.

  18. Thermally induced stresses and deformations in layered composite tubes

    NASA Technical Reports Server (NTRS)

    Cooper, D. E.; Cohen, D.; Rousseau, C. Q.; Hyer, M. W.; Tompkins, S. S.

    1985-01-01

    The thermally induced stresses and deformations in layered, orthotropic tubes are studied. The motivation for studying tubes is their likely application for use in space structures. Tubes are a strong candidate for this application because of their high structural efficiency, as measured by stiffness per unit weight, and their relative ease of fabrication. Also, tubes have no free edges to deteriorate or delaminate. An anticipated thermal condition for tubes in space is a circumferential temperature gradient. This type of gradient will introduce dimensional changes into the structure and may cause stresses large enough to cause damage to the material. There are potentially large differences in temperatures at different circumferential locations on the tube. Because of this, the effects of temperature dependent material properties on the stresses and deformations may be important. The study is composed of three parts: experiments to determine the functional form of the circumferential gradient and to measure tube deflections; an elasticity solution to compute the stresses and deformations; and an approximate approach to determine the effects of temperature dependent material properties.

  19. A survey of methods for measuring thermally induced distortions of test articles undergoing solar thermal vacuum test

    NASA Technical Reports Server (NTRS)

    Rempt, R. D.

    1982-01-01

    Various methods of measuring the small thermally induced distortions experienced either by various points on the space vehicles or by deviations of surfaces from a known shape during solar thermal vacuum tests are examined. State-of-the-art application of both photographic and real time observation are discussed. The relative merits of each of the methods are compared and evaluated in their applications to different types of test articles and situations. Magnitudes of thermally induced distortions which may be expected to be routinely measurable by the various methods are presented and compared.

  20. Thermally-induced structural dynamic response of flexural configurations influenced by linear/non-linear thermal effects

    NASA Technical Reports Server (NTRS)

    Namburu, Raju R.; Tamma, Kumar K.

    1991-01-01

    The thermally-induced strucural dynamic response of flexural configurations influenced by linear/nonlinear thermal effects is presented in conjunction with 'unified' transient approaches for effectively tackling this class of interdisciplinary problems. For illustrative purposes, the flexural structural models are assumed to be of the Euler-Bernoulli type. The purpose of the present paper is to not only provide an understanding of the influence of general linear/nonlinear thermal effects on flexural configurations, but also to provide to the analyst effective computational tools which help preserve a unified technology for the interdisciplinary areas encompassing structural mechanics/dynamics and thermal sciences. Several numerical test models illustrate the representative thermally-induced structural dynamic response of flexural configurations subjected to general linear/nonlinear temperature effects.

  1. Thermal stability of DNA adducts induced by cyanomorpholinoadriamycin in vitro.

    PubMed Central

    Cullinane, C; Phillips, D R

    1993-01-01

    The Adriamycin derivative, cyanomorpholinoadriamycin (CMA) was reacted with DNA in vitro to form apparent interstrand crosslinks. The extent of interstrand crosslink formation was monitored by a gel electrophoresis assay and maximal crosslinking of DNA was observed within 1 hr with 5 microM of drug. The interstrand crosslinks were heat labile, with a midpoint melting temperature of 70 degrees C (10 min exposure to heat) in 45% formamide. When CMA-induced adducts were detected as blockages of lambda-exonuclease, 12 blockage sites were observed with 8 being prior to 5'-GG sequences, one prior to 5'-CC, one prior to 5'-GC and 2 at unresolved combinations of these sequences. These exonuclease-detected blockages reveal the same sites of CMA-induced crosslinking as detected by in vitro transcription footprinting and primer-extension blockages on single strand DNA, where the blockages at 5'-GG and 5'-CC were identified as sites of intrastrand crosslinking and the 5'-GC blockage as a probable site of interstrand crosslinking. The thermal stability of both types of crosslink (10 min exposure to heat) ranged from 63-70 degrees C at individual sites. High levels of adduct were detected with poly (dG-dC) but not with poly (dI-dC). These results suggest adduct formation involving an aminal linkage between the 3 position of the morpholino moiety and N2 of guanine. Images PMID:8493102

  2. The thermal stability of radiation-induced defects in illite

    NASA Astrophysics Data System (ADS)

    Riegler, T.; Allard, T.; Beaufort, D.; Cantin, J.-L.; von Bardeleben, H. J.

    2016-01-01

    High-purity illite specimens from the Mesoproterozoic unconformity-related uranium deposits of Kiggavik, Thelon basin, Nunavut (Canada), and Shea Creek (Athabasca basin, Saskatchewan, Canada) have been studied using electron paramagnetic resonance spectroscopy to determine the thermal stability of the main radiation-induced defects and question the potential of using illite as a natural dosimeter. The observed spectra are complex as they can show in the same region several contributions: (1) an unstable native defect, (2) the main stable defect named Ai by reference to a previous study (Morichon et al. in Phys Chem Minerals 35:339-346, 2008), (3) a signal at g = 2.063 assigned to a new defect, not yet fully characterized, named Ai2 center and (4) impurities such as vanadyl complex or divalent manganese. Isochronal heating shows that the new signal corresponds to a stable species. Isothermal heating experiments at 400 and 450 °C provide values of half-life extrapolated at room temperature and activation energy of 1.9-29,109 years and 1.3-1.4 eV, respectively, corresponding to the Ai center. These parameters allow the use of stable radiation-induced defects as a record of radioactivity down to the Paleoproterozoic period.

  3. Reversible Shape Memory Optical Gratings

    NASA Astrophysics Data System (ADS)

    Li, Qiaoxi; Tippets, Cary; Fu, Yulan; Donev, Eugene; Turner, Sara; Ashby, Valerie; Lopez, Rene; Sheiko, Sergei

    2015-03-01

    Recent advancements in the understanding of the mechanisms that control shape memory in semi-crystalline polymers, has led to the development of protocols that allow for reversibility in complex shape transformations. The shifting between two programmable shapes is reversible without applying any external force. This is made possible by thermodynamically driven relaxation of extended polymer chains on heating is then inverted by kinetically preferred pathways of polymer crystallization on cooling. Reversible shapeshifting was applied to modulation of photonic gratings to create hands-free reversibly tunable optical elements. We have fabricated a sub-micron ratio optical square grating that presents reversible magnitude changes of its diffraction intensity (up to about 38% modulation) when subject to changes in temperature. This result is attributed to programmable changes in the grating height due to reversible shape memory and is repeatable over multiple cycles. Besides, roughness-induced variations in scattering signal observed upon heating-cooling cycles may offer another way to monitor kinetics of polymer melting and crystallization. Grants: NSF DMR-1407645,

  4. Fiber Bragg grating cryogenic temperature sensors

    NASA Astrophysics Data System (ADS)

    Gupta, Sanjay; Mizunami, Toru; Yamao, Takashi; Shimomura, Teruo

    1996-09-01

    Temperature sensing to as low as 80 K was demonstrated with 1.55- mu m fiber Bragg gratings. The gratings were bonded on substrates to increase sensitivity, and a shift of the reflection wavelength was measured. The temperature sensitivity was 0.02 nm/K at 100 K when an aluminum substrate was used and 0.04 nm/K at 100 K when a poly(methyl methacrylate) substrate was used. These values are smaller than those at room temperature because of the nonlinearity of both the thermal expansion and the thermo-optic effect. Extension to the liquid helium temperature is also discussed.

  5. Microsecond switchable thermal antenna

    SciTech Connect

    Ben-Abdallah, Philippe Benisty, Henri; Besbes, Mondher

    2014-07-21

    We propose a thermal antenna that can be actively switched on and off at the microsecond scale by means of a phase transition of a metal-insulator material, the vanadium dioxide (VO{sub 2}). This thermal source is made of a periodically patterned tunable VO{sub 2} nanolayer, which support a surface phonon-polariton in the infrared range in their crystalline phase. Using electrodes properly registered with respect to the pattern, the VO{sub 2} phase transition can be locally triggered by ohmic heating so that the surface phonon-polariton can be diffracted by the induced grating, producing a highly directional thermal emission. Conversely, when heating less, the VO{sub 2} layers cool down below the transition temperature, the surface phonon-polariton cannot be diffracted anymore so that thermal emission is inhibited. This switchable antenna could find broad applications in the domain of active thermal coatings or in those of infrared spectroscopy and sensing.

  6. Spherical grating spectrometers

    NASA Astrophysics Data System (ADS)

    O'Donoghue, Darragh; Clemens, J. Christopher

    2014-07-01

    We describe designs for spectrometers employing convex dispersers. The Offner spectrometer was the first such instrument; it has almost exclusively been employed on satellite platforms, and has had little impact on ground-based instruments. We have learned how to fabricate curved Volume Phase Holographic (VPH) gratings and, in contrast to the planar gratings of traditional spectrometers, describe how such devices can be used in optical/infrared spectrometers designed specifically for curved diffraction gratings. Volume Phase Holographic gratings are highly efficient compared to conventional surface relief gratings; they have become the disperser of choice in optical / NIR spectrometers. The advantage of spectrometers with curved VPH dispersers is the very small number of optical elements used (the simplest comprising a grating and a spherical mirror), as well as illumination of mirrors off axis, resulting in greater efficiency and reduction in size. We describe a "Half Offner" spectrometer, an even simpler version of the Offner spectrometer. We present an entirely novel design, the Spherical Transmission Grating Spectrometer (STGS), and discuss exemplary applications, including a design for a double-beam spectrometer without any requirement for a dichroic. This paradigm change in spectrometer design offers an alternative to all-refractive astronomical spectrometer designs, using expensive, fragile lens elements fabricated from CaF2 or even more exotic materials. The unobscured mirror layout avoids a major drawback of the previous generation of catadioptric spectrometer designs. We describe laboratory measurements of the efficiency and image quality of a curved VPH grating in a STGS design, demonstrating, simultaneously, efficiency comparable to planar VPH gratings along with good image quality. The stage is now set for construction of a prototype instrument with impressive performance.

  7. Metal nanowire grating patterns.

    PubMed

    Kulkarni, G U; Radha, B

    2010-10-01

    Metal nanowire patterning in the form of grating structures has been carried out using a wide range of lithography techniques, and many hybrid methods derived from them. The challenge is to achieve sub-100 nm linewidths with controllable spacing and thickness over large areas of substrates with high throughput. In particular, the patterns with linewidth and spacing of a few tens of nm offer properties of great interest in optoelectronics and plasmonics. Crossbar grating structures--two gratings patterned perpendicular to each other--will play an important role as ultra-high density electrode grids in memristive devices for non-volatile memory. PMID:20945550

  8. Electrically-programmable diffraction grating

    DOEpatents

    Ricco, Antonio J.; Butler, Michael A.; Sinclair, Michael B.; Senturia, Stephen D.

    1998-01-01

    An electrically-programmable diffraction grating. The programmable grating includes a substrate having a plurality of electrodes formed thereon and a moveable grating element above each of the electrodes. The grating elements are electrostatically programmable to form a diffraction grating for diffracting an incident beam of light as it is reflected from the upper surfaces of the grating elements. The programmable diffraction grating, formed by a micromachining process, has applications for optical information processing (e.g. optical correlators and computers), for multiplexing and demultiplexing a plurality of light beams of different wavelengths (e.g. for optical fiber communications), and for forming spectrometers (e.g. correlation and scanning spectrometers).

  9. Prediction of thermal cycling induced cracking in polymer matrix composites

    NASA Technical Reports Server (NTRS)

    Mcmanus, Hugh L.

    1993-01-01

    This report summarizes the work done in the period February 1993 through July 1993 on the 'Prediction of Thermal Cycling Induced Cracking In Polymer Matrix Composites' program. An oral presentation of this work was given to Langley personnel in September of 1993. This document was prepared for archival purposes. Progress studies have been performed on the effects of spatial variations in material strength. Qualitative agreement was found with observed patterns of crack distribution. These results were presented to NASA Langley personnel in November 1992. The analytical methodology developed by Prof. McManus in the summer of 1992 (under an ASEE fellowship) has been generalized. A method for predicting matrix cracking due to decreasing temperatures and/or thermal cycling in all plies of an arbitrary laminate has been implemented as a computer code. The code also predicts changes in properties due to the cracking. Experimental progressive cracking studies on a variety of laminates were carried out at Langley Research Center. Results were correlated to predictions using the new methods. Results were initially mixed. This motivated an exploration of the configuration of cracks within laminates. A crack configuration study was carried out by cutting and/or sanding specimens in order to examine the distribution of cracks within the specimens. These investigations were supplemented by dye-penetrant enhanced X-ray photographs. The behavior of thin plies was found to be different from the behavior of thicker plies (or ply groups) on which existing theories are based. Significant edge effects were also noted, which caused the traditional metric of microcracking (count of cracks on a polished edge) to be very inaccurate in some cases. With edge and configuration taken into account, rough agreement with predictions was achieved. All results to date were reviewed with NASA Langley personnel in September 1993.

  10. Fabrication of a long-period grating in a fibre by second-harmonic radiation from a femtosecond Ti:sapphire laser

    SciTech Connect

    Zagorul'ko, K A; Kryukov, P G; Larionov, Yu V; Rybaltovsky, A A; Dianov, Evgenii M; Vorob'ev, Nikolai S; Smirnov, A V; Schelev, M Ya; Prokhorov, A M

    2001-11-30

    Long-period gratings are fabricated in an optical fibre for the first time by second-harmonic radiation from a femtosecond Ti:sapphire laser without the use of an amplifier. The photosensitivity of different fibres exposed to femtosecond pulses is studied. The estimates of the photosensitivity and the thermal properties of long-period gratings showed that the mechanism of the change in the refractive index induced by the 400-nm second-harmonic radiation differs from the corresponding mechanisms upon exposure to UV radiation from excimer lasers or irradiation by amplified 800-nm femtosecond pulses. (optical fibres)

  11. Detuning in apodized point-by-point fiber Bragg gratings: insights into the grating morphology.

    PubMed

    Williams, Robert J; Krämer, Ria G; Nolte, Stefan; Withford, Michael J; Steel, M J

    2013-11-01

    Point-by-point (PbP) inscription of fiber Bragg gratings using femtosecond laser pulses is a versatile technique that is currently experiencing significant research interest for fiber laser and sensing applications. The recent demonstration of apodized gratings using this technique provides a new avenue of investigation into the nature of the refractive index perturbation induced by the PbP modifications, as apodized gratings are sensitive to variation in the average background index along the grating. In this work we compare experimental results for Gaussian- and sinc-apodized PbP gratings to a coupled-mode theory model, demonstrating that the refractive index perturbation induced by the PbP modifications has a negative contribution to the average background index which is small, despite the presence of strong reflective coupling. By employing Fourier analysis to a simplified model of an individual modification, we show that the presence of a densified shell around a central void can produce strong reflective coupling with near-zero change in the average background index. This result has important implications for the experimental implementation of apodized PbP gratings, which are of interest for a range of fiber laser and fiber sensing technologies. PMID:24216907

  12. Color separation gratings

    NASA Technical Reports Server (NTRS)

    Farn, Michael W.; Knowlden, Robert E.

    1993-01-01

    In this paper, we describe the theory, fabrication and test of a binary optics 'echelon'. The echelon is a grating structure which separates electromagnetic radiation of different wavelengths, but it does so according to diffraction order rather than by dispersion within one diffraction order, as is the case with conventional gratings. A prototype echelon, designed for the visible spectrum, is fabricated using the binary optics process. Tests of the prototype show good agreement with theoretical predictions.

  13. Future Development for Laser-Induced Thermal Acoustics

    NASA Astrophysics Data System (ADS)

    Schlamp, Stefan

    2002-07-01

    The development of novel flow diagnostic techniques typically proceeds in certain stages from a proof of principle in a laboratory to a commercial product either for use in industry or as turn-key research tool. While the first usable versions are brought to market, further progress is made in the laboratory by improvements, refinements, and extensions of the technique. Consider Particle Image Velocimetry (PIV), which started by double-exposing a photographic film with the image of an illuminated particle-laden flow and where today turn-key, off-the-shelf CCD systems are available for purchase, which include the necessary data analysis software. At the same time, 3d PIV, dual-plane PIV, Doppler Global Velocimetry (DGV), etc. are being used in laboratories and will doubtless be available as integrated systems in the near future. In this paper, the origin, an overview over the current status and an outlook on the future potential of Laser-Induced Thermal Acoustics (LITA) will be given, where the focus will be on the possible technique extensions to other than the current applications. As such, it represents a collection of ideas and avenues for future research, which have not been applied as of yet, but are conceptually feasible.

  14. ATP-induced noncooperative thermal unfolding of hen lysozyme

    SciTech Connect

    Liu, Honglin; Yin, Peidong; He, Shengnan; Sun, Zhihu; Tao, Ye; Huang, Yan; Zhuang, Hao; Zhang, Guobin; Wei, Shiqiang

    2010-07-02

    To understand the role of ATP underlying the enhanced amyloidosis of hen egg white lysozyme (HEWL), the synchrotron radiation circular dichroism, combined with tryptophan fluorescence, dynamic light-scattering, and differential scanning calorimetry, is used to examine the alterations of the conformation and thermal unfolding pathway of the HEWL in the presence of ATP, Mg{sup 2+}-ATP, ADP, AMP, etc. It is revealed that the binding of ATP to HEWL through strong electrostatic interaction changes the secondary structures of HEWL and makes the exposed residue W62 move into hydrophobic environments. This alteration of W62 decreases the {beta}-domain stability of HEWL, induces a noncooperative unfolding of the secondary structures, and produces a partially unfolded intermediate. This intermediate containing relatively rich {alpha}-helix and less {beta}-sheet structures has a great tendency to aggregate. The results imply that the ease of aggregating of HEWL is related to the extent of denaturation of the amyloidogenic region, rather than the electrostatic neutralizing effect or monomeric {beta}-sheet enriched intermediate.

  15. Heterogeneous shock-induced thermal radiation in minerals

    NASA Technical Reports Server (NTRS)

    Kondo, K.-I.; Ahrens, T. J.

    1983-01-01

    A 500-channel optical imaging intensifying and spectral digital recording system is used for recording the shock-induced radiation emitted from 406 to 821 nm from transparent minerals during the time interval that a shock wave propagates through the sample. The initial results obtained for single crystals of gypsum, calcite and halite in the 30 to 40 GPa (300 to 400 kbar) pressure range reveal grey-body emission spectra corresponding to temperatures in the 3000 to 4000 K range and emissivities ranging from 0.003 to 0.02. With gypsum and calcite, distinctive line spectra are superimposed on the thermal radiation. The observed color temperatures are greater than the Hugoniot temperature by a factor of 2 to 10; this is calculable on the basis of continuum thermodynamics and equation of state models for the shock states achieved in the three minerals. These observed high temperatures are thought to be real. It is concluded that a large number of closed spaced high temperature shear-band regions are being detected immediately behind the shock front.

  16. Thermally-induced voltage alteration for integrated circuit analysis

    DOEpatents

    Cole, Jr., Edward I.

    2000-01-01

    A thermally-induced voltage alteration (TIVA) apparatus and method are disclosed for analyzing an integrated circuit (IC) either from a device side of the IC or through the IC substrate to locate any open-circuit or short-circuit defects therein. The TIVA apparatus uses constant-current biasing of the IC while scanning a focused laser beam over electrical conductors (i.e. a patterned metallization) in the IC to produce localized heating of the conductors. This localized heating produces a thermoelectric potential due to the Seebeck effect in any conductors with open-circuit defects and a resistance change in any conductors with short-circuit defects, both of which alter the power demand by the IC and thereby change the voltage of a source or power supply providing the constant-current biasing. By measuring the change in the supply voltage and the position of the focused and scanned laser beam over time, any open-circuit or short-circuit defects in the IC can be located and imaged. The TIVA apparatus can be formed in part from a scanning optical microscope, and has applications for qualification testing or failure analysis of ICs.

  17. Reactive Molecular Dynamics Studies of Thermal Induced Chemistry in TATB

    NASA Astrophysics Data System (ADS)

    Germann, Timothy; Quenneville, Jason

    2007-03-01

    Equilibrium molecular dynamics (MD) simulation of high explosives can provide important information on their thermal decomposition by helping to characterize processes with timescales that are much longer than those attainable with non-equilibrium MD shock studies. A reactive force field is used with MD to probe the chemisty induced by intense heating (`cook-off') of 1,3,5-triamino-2,4,6-trinitrobenzene (TATB). The force field (ReaxFF) was developed by van Duin, Goddard and coworkers [1] at CalTech and has already shown promise in predicting the chemistry in small samples of RDX under either shock compression or intense heat. Large-system simulations are desired for TATB because of the high degree of carbon clustering expected in this material. We will show results of 800-particle simulations at several temperatures, and detail current capabilities for large-scale (10^4 -- 10^5 atoms) systems carried out with the massively parallel GRASP MD software developed at Sandia National Lab. Finally, we will compare the reaction timescales with those of RDX and HMX. [1] A. C. T. Van Duin, et al, J. Phys. Chem. A, 1005, 9396 (2001).

  18. Molecular Dynamics Simulations of Thermal Induced Chemistry in TATB

    NASA Astrophysics Data System (ADS)

    Quenneville, Jason; Germann, Timothy

    2006-03-01

    Equilibrium molecular dynamics (MD) simulation of high explosives can provide important information on their thermal decomposition by helping to characterize processes with timescales that are much longer than those attainable with non-equilibrium MD shock studies. A reactive force field is used with MD to probe the chemisty induced by intense heating (`cook-off') of 1,3,5-triamino-2,4,6-trinitrobenzene (TATB). The force field (ReaxFF) was developed by van Duin, Goddard and coworkers^ at CalTech and has already shown promise in predicting the chemistry in small samples of RDX under either shock compression or intense heat. Large-system simulations are desired for TATB because of the high degree of carbon clustering expected in this material. We will show results of 100,000-particle simulations at several temperatures, carried out with the massively parallel GRASP MD software developed at Sandia National Lab. Finally, we will compare the reactions and reaction timescales with those of RDX and HMX. ^ A. C. T. Van Duin, et al, J. Phys. Chem. A, 1005, 9396 (2001).

  19. Seedless Laser Velocimetry Using Heterodyne Laser-Induced Thermal Acoustics

    NASA Technical Reports Server (NTRS)

    Hart, Roger C.; Balla, R. Jeffrey; Herring, G. C.; Jenkins, Luther N.; Bushnell, Dennis M. (Technical Monitor)

    2001-01-01

    A need exists for a seedless equivalent of laser Doppler velocimetry (LDV) for use in low-turbulence or supersonic flows or elsewhere where seeding is undesirable or impractical. A compact laser velocimeter using heterodyne non-resonant laser-induced thermal acoustics (LITA) to measure a single component of velocity is described. Neither molecular (e.g. NO2) nor particulate seed is added to the flow. In non-resonant LITA two beams split from a short-pulse pump laser are crossed; interference produces two counterpropagating sound waves by electrostriction. A CW probe laser incident on the sound waves at the proper angle is directed towards a detector. Measurement of the beating between the Doppler-shifted light and a highly attenuated portion of the probe beam allows determination of one component of flow velocity, speed of sound, and temperature. The sound waves essentially take the place of the particulate seed used in LDV. The velocimeter was used to study the flow behind a rearward-facing step in NASA Langley Research Center's Basic Aerodynamics Research Tunnel. Comparison is made with pitot-static probe data in the freestream over the range 0 m/s - 55 m/s. Comparison with LDV is made in the recirculation region behind the step and in a well-developed boundary layer in front of the step. Good agreement is found in all cases.

  20. Thermally-induced voltage alteration for analysis of microelectromechanical devices

    DOEpatents

    Walraven, Jeremy A.; Cole, Jr., Edward I.

    2002-01-01

    A thermally-induced voltage alteration (TIVA) apparatus and method are disclosed for analyzing a microelectromechanical (MEM) device with or without on-board integrated circuitry. One embodiment of the TIVA apparatus uses constant-current biasing of the MEM device while scanning a focused laser beam over electrically-active members therein to produce localized heating which alters the power demand of the MEM device and thereby changes the voltage of the constant-current source. This changing voltage of the constant-current source can be measured and used in combination with the position of the focused and scanned laser beam to generate an image of any short-circuit defects in the MEM device (e.g. due to stiction or fabrication defects). In another embodiment of the TIVA apparatus, an image can be generated directly from a thermoelectric potential produced by localized laser heating at the location of any short-circuit defects in the MEM device, without any need for supplying power to the MEM device. The TIVA apparatus can be formed, in part, from a scanning optical microscope, and has applications for qualification testing or failure analysis of MEM devices.

  1. Effects of thermal motion on electromagnetically induced absorption

    SciTech Connect

    Tilchin, E.; Wilson-Gordon, A. D.; Firstenberg, O.

    2011-05-15

    We describe the effect of thermal motion and buffer-gas collisions on a four-level closed N system interacting with strong pump(s) and a weak probe. This is the simplest system that experiences electromagnetically induced absorption (EIA) due to transfer of coherence via spontaneous emission from the excited state to the ground state. We investigate the influence of Doppler broadening, velocity-changing collisions (VCC), and phase-changing collisions (PCC) with a buffer gas on the EIA spectrum of optically active atoms. In addition to exact expressions, we present an approximate solution for the probe absorption spectrum, which provides physical insight into the behavior of the EIA peak due to VCC, PCC, and the wave-vector difference between the pump and probe beams. VCC are shown to produce a wide pedestal at the base of the EIA peak, which is scarcely affected by the pump-probe angular deviation, whereas the sharp central EIA peak becomes weaker and broader due to the residual Doppler-Dicke effect. Using diffusionlike equations for the atomic coherences and populations, we construct a spatial-frequency filter for a spatially structured probe beam and show that Ramsey narrowing of the EIA peak is obtained for beams of finite width.

  2. Thermally relativistic flows induced by gravitational-force-free particle motion in curved spacetime

    SciTech Connect

    Yano, Ryosuke; Suzuki, Kojiro; Kuroda, Hisayasu

    2009-12-15

    Thermally relativistic flows in the early Universe can be characterized by the emergence of flows induced by gravitational-force-free particle motion in curved spacetime as well as induced by the gravitational force. In this paper, thermally relativistic flows induced by gravitational-force-free particle motion in curved spacetime are discussed on the basis of the general relativistic Boltzmann equation. As an object of analysis, we consider the flow from the static state inside the Schwarzschild radius of a thermally relativistic stuffed black hole induced by such motion. Analytical results obtained using the collisionless, nongravitational general relativistic Boltzmann equation reveal that the initial cluster is induced by gravitational-force-free particle motion. Numerical results obtained using the nongravitational general relativistic Anderson-Witting model confirm the presence of an initial cluster inside the thermally relativistic stuffed black hole, which is induced by gravitational-force-free particle motion.

  3. Laser induced thermal-wave fields in bilayered spherical solids.

    PubMed

    Xie, Guangxi; Chen, Zhifeng; Wang, Chinhua; Mandelis, Andreas

    2009-03-01

    We present a theoretical model for evaluating solid bilayered spherical samples (surfaces) that are heated by a frequency modulated light beam generating thermal waves. The Green's function method is used as it provides a way of evaluating thermal-wave fields of bilayered spherical structures with arbitrary intensity distributions of incident laser beams. The specific thermal-wave Green's function corresponding to the composite structure has been derived. The characteristics of the thermal-wave field with respect to the thermal diffusivity of the material, the diameter of the sample, the size of the incident beam, and the polar angle at which the thermal-wave field is measured on the surface are presented. Experimental results obtained with laser infrared photothermal radiometry are fitted to the theory and the thermal diffusivities of steel spheres are deduced. PMID:19334944

  4. Velocimetry in laminar and turbulent flows using the photothermal deflection effect with a transient grating.

    PubMed

    Dasch, C J; Sell, J A

    1986-10-01

    An enhanced-precision, high-signal method for velocity measurements with photothermal deflection spectroscopy is presented. A transient refractive-index grating is formed by the interference of two pulsed, pump-laser beams in an absorbing gas. The motion of the grating is detected by the oscillatory deflection of a probe beam, which has a diameter smaller than the fringe spacing. This two-beam pump improves on single-beam pumps because there are more markers for the velocity determination, and the larger thermal gradients increase the probe deflection. The method is illustrated by velocity maps in a laminar ethylene/nitrogen jet using a CO(2) pump laser. Velocity distributions and noise levels were also measured with grid-induced turbulence above the jet. PMID:19738701

  5. Mirror and grating surface figure requirements for grazing incidence synchrotron radiation beamlines: Power loading effects

    SciTech Connect

    Hulbert, S.L.; Sharma, S.

    1987-10-21

    At present, grazing incidence mirrors are used almost exclusively as the first optical element in VUV and soft x-ray synchrotron radiation beam lines. The performance of these mirrors is determined by thermal and mechanical stress-induced figure errors as well as by figure errors remaining from the grinding and polishing process. With the advent of VUV and soft x-ray undulators and wigglers has come a new set of thermal stress problems related to both the magnitude and the spatial distribution of power from these devices. In many cases the power load on the entrance slits and gratings in these beamlines is no longer negligible. The dependence of thermally-induced front-end mirror figure errors on various storage ring and insertion device parameters (especially those at the NSLS) and the effects of these figure errors on a class of soft x-ray beam lines are presented. 17 refs., 5 figs., 2 tabs.

  6. Mirror and grating surface figure requirements for grazing incidence synchrotron radiation beamlines: Power loading effects

    SciTech Connect

    Hulbert, S.L.; Sharma, S.

    1987-01-01

    At present, grazing incidence mirrors are used almost exclusively as the first optical element in VUV and soft x-ray synchrotron radiation beamlines. The performance of these mirrors is determined by thermal and mechanical stress-induced figure errors as well as by figure errors remaining from the grinding and polishing process. With the advent of VUV and soft x-ray undulators and wigglers has come a new set of thermal stress problems related to both the magnitude and the spatial distribution of power from these devices. In many cases the power load on the entrance slits and gratings in these beamlines is no longer negligible. The dependence of thermally-induced front-end mirror figure errors on various storage ring and insertion device parameters (especially those at the National Synchrotron Light Source) and the effects of these figure errors on two classes of soft x-ray beamlines are presented.

  7. Thermally induced transformations of amorphous carbon nanostructures fabricated by electron beam induced deposition.

    PubMed

    Kulkarni, Dhaval D; Rykaczewski, Konrad; Singamaneni, Srikanth; Kim, Songkil; Fedorov, Andrei G; Tsukruk, Vladimir V

    2011-03-01

    We studied the thermally induced phase transformations of electron-beam-induced deposited (EBID) amorphous carbon nanostructures by correlating the changes in its morphology with internal microstructure by using combined atomic force microscopy (AFM) and high resolution confocal Raman microscopy. These carbon deposits can be used to create heterogeneous junctions in electronic devices commonly known as carbon-metal interconnects. We compared two basic shapes of EBID deposits: dots/pillars with widths from 50 to 600 nm and heights from 50 to 500 nm and lines with variable heights from 10 to 150 nm but having a constant length of 6 μm. We observed that during thermal annealing, the nanoscale amorphous deposits go through multistage transformation including dehydration and stress-relaxation around 150 °C, dehydrogenation within 150-300 °C, followed by graphitization (>350 °C) and formation of nanocrystalline, highly densified graphitic deposits around 450 °C. The later stage of transformation occurs well below commonly observed graphitization for bulk carbon (600-800 °C). It was observed that the shape of the deposits contribute significantly to the phase transformations. We suggested that this difference is controlled by different contributions from interfacial footprints area. Moreover, the rate of graphitization was different for deposits of different shapes with the lines showing a much stronger dependence of its structure on the density than the dots. PMID:21319745

  8. Thermally induced twin polymerization of 4H-1,3,2-benzodioxasilines.

    PubMed

    Kempe, Patrick; Löschner, Tina; Auer, Alexander A; Seifert, Andreas; Cox, Gerhard; Spange, Stefan

    2014-06-23

    The twin monomer 2,2'-spirobi[4H-1,3,2-benzodioxasiline] (1) can be polymerized to nanostructured SiO2/phenolic-resin composite material by thermally induced twin polymerization. Thermally induced twin polymerization represents a way to produce nanocomposites simply by thermal induction of twin monomers. Besides 1, the thermal reaction of several related salicylic (2-oxybenzylic) silicon molecules has been investigated. The thermal cleavage of the molecules is studied by using several trapping reagents (e.g., vinyl compounds). A significant occurrence of quinone methide adducts indicates that the thermal mechanism proceeds not only by a ring opening at the oxymethylene position, but also with the ortho-quinone methide as a central or alternative intermediate. This is supported by product analyses of thermally initialized reactions of 1 and its substituted analogues as well as by quantum chemical calculations. PMID:24849004

  9. Post-exposed fiber Bragg gratings

    NASA Astrophysics Data System (ADS)

    Miller, Gary A.

    This thesis explains the development and characterization of a novel technique to fabricate weak fiber Bragg gratings for highly specific multi-element sensor arrays. This method, termed the "rescan technique," involves re-exposing a local region of a grating to fringeless ultraviolet light to "trim" unwanted portions of the reflection spectrum. The spectral effects that result from a rescan can only be adequately described by inventing the concept of a three-dimensional index growth surface, where induced index is a function of both the writing intensity and the exposure time. Using this information, it is possible to predict the spectral response of a rescanned grating using a numerical model. For our model, we have modified the piecewise-uniform approach to include coefficients within the coupled-mode formulism that imitate the same scattering properties as the actual grating. By taking high accuracy measurements of the refractive index change in germanosilicate fiber, we have created the necessary 3D map of photoinduced index to accurately model gratings and their post-exposure spectra. We will also demonstrate that optical fiber exhibits what we call "exposure history"; the final index change in a region depends on the previous exposures conditions.

  10. Reannealed Fiber Bragg Gratings Demonstrated High Repeatability in Temperature Measurements

    NASA Technical Reports Server (NTRS)

    Adamovsky, Grigory; Juergens, Jeffrey R.

    2004-01-01

    Fiber Bragg gratings (FBGs) are formed by periodic variations of the refractive index of an optical fiber. These periodic variations allow an FBG to act as an embedded optical filter, passing the majority of light propagating through a fiber while reflecting back a narrow band of the incident light. The peak reflected wavelength of the FBG is known as the Bragg wavelength. Since the period and width of the refractive index variation in the fiber determines the wavelengths that are transmitted and reflected by the grating, any force acting on the fiber that alters the physical structure of the grating will change the wavelengths that are transmitted and reflected by it. Both thermal and mechanical forces acting on the grating will alter its physical characteristics, allowing the FBG sensor to detect both the temperature variations and the physical stresses and strains placed upon it. This ability to sense multiple physical forces makes the FBG a versatile sensor. To assess the feasibility of using Bragg gratings as temperature sensors for propulsion applications, researchers at the NASA Glenn Research Center evaluated the performance of Bragg gratings at elevated temperatures for up to 300 C. For these purposes, commercially available polyimide-coated high-temperature gratings were used that were annealed by the manufacturer to 300 C. To assure the most thermally stable gratings at the operating temperatures, we reannealed the gratings to 400 C at a very slow rate for 12 to 24 hr until their reflected optical powers were stabilized. The reannealed gratings were then subjected to periodic thermal cycling from room temperature to 300 C, and their peak reflected wavelengths were monitored. The setup shown is used for reannealing and thermal cycling the FBGs. Signals from the photodetectors and the spectrum analyzer were fed into a computer equipped with LabVIEW software. The software synchronously monitored the oven/furnace temperature and the optical spectrum analyzer

  11. High divergent 2D grating

    NASA Astrophysics Data System (ADS)

    Wang, Jin; Ma, Jianyong; Zhou, Changhe

    2014-11-01

    A 3×3 high divergent 2D-grating with period of 3.842μm at wavelength of 850nm under normal incidence is designed and fabricated in this paper. This high divergent 2D-grating is designed by the vector theory. The Rigorous Coupled Wave Analysis (RCWA) in association with the simulated annealing (SA) is adopted to calculate and optimize this 2D-grating.The properties of this grating are also investigated by the RCWA. The diffraction angles are more than 10 degrees in the whole wavelength band, which are bigger than the traditional 2D-grating. In addition, the small period of grating increases the difficulties of fabrication. So we fabricate the 2D-gratings by direct laser writing (DLW) instead of traditional manufacturing method. Then the method of ICP etching is used to obtain the high divergent 2D-grating.

  12. Thermal diffusivity in thin films measured by noncontact single-ended pulsed-laser-induced thermal radiometry. Technical report

    SciTech Connect

    Tam, A.C.; Leung, W.P.

    1983-11-22

    A pulsed nitrogen laser is used to induce a sharp thermal gradient in a thin film, and the thermal radiation (infrared) transient from the irradiated region is monitored from the same side as the excitation beam (ie.e, single-ended detection). We show that this pulsed photothermal radiometry lineshape can be analyzed to provide the thermal diffusivity or thickness of the sample, as well as information on subsurface modifications or the degree of thermal contact with a substrate. We present data for several important classes of films, including metal, polymer and paper (e.g., in currency) and show the important features of the present technique for thin-film characterization, namely nondestructive, fast and remote sensing.

  13. Thermal diffusivity in thin films measured by noncontact single-ended pulsed-laser-induced thermal radiometry

    SciTech Connect

    Leung, W.P.; Tam, A.C.

    1984-03-01

    A pulsed nitrogen laser is used to induce a sharp thermal gradient in a thin film, and the infrared thermal radiation from the irradiated region is monitored from the same side as the excitation beam (i.e., single-ended detection). We show that the profile of this pulsed photothermal radiometry signal can be analyzed to provide the thermal diffusivity or thickness of the sample as well as information on subsurface modifications or the degree of thermal contact with a substrate. We present data for several important classes of film, including metal, polymer, and paper (e.g., in currency) and show the important features of the present technique for thin-film characterization, namely, nondestructive, fast, and remote sensing.

  14. Differential regulation of peripheral IL-1β-induced mechanical allodynia and thermal hyperalgesia in rats.

    PubMed

    Kim, Min J; Lee, Sang Y; Yang, Kui Y; Nam, Soon H; Kim, Hyun J; Kim, Young J; Bae, Yong C; Ahn, Dong K

    2014-04-01

    This study examined the differential mechanisms of mechanical allodynia and thermal hyperalgesia after injection of interleukin (IL) 1β into the orofacial area of male Sprague-Dawley rats. The subcutaneous administration of IL-1β produced both mechanical allodynia and thermal hyperalgesia. Although a pretreatment with iodoresiniferatoxin (IRTX), a transient receptor potential vanilloid 1 (TRPV1) antagonist, did not affect IL-1β-induced mechanical allodynia, it significantly abolished IL-1β-induced thermal hyperalgesia. On the other hand, a pretreatment with D-AP5, an N-methyl-d-aspartate (NMDA) receptor antagonist, and NBQX, an α-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid (AMPA) receptor antagonist, blocked IL-1β-induced mechanical allodynia. Pretreatment with H89, a protein kinase A (PKA) inhibitor, blocked IL-1β-induced mechanical allodynia but not thermal hyperalgesia. In contrast, pretreatment with chelerythrine, a protein kinase C (PKC) inhibitor, inhibited IL-1β-induced thermal hyperalgesia. Subcutaneous injections of 2% lidocaine, a local anesthetic agent, blocked IL-1β-induced thermal hyperalgesia but not IL-1β-induced mechanical allodynia. In the resiniferatoxin (RTX)-pretreated rats, a subcutaneous injection of IL-1β did not produce thermal hyperalgesia due to the depletion of TRPV1 in the primary afferent fibers. Double immunofluorescence revealed the colocalization of PKA with neurofilament 200 (NF200) and of PKC with the calcitonin gene-related peptide (CGRP) in the trigeminal ganglion. Furthermore, NMDA receptor 1 (NR1) and TRPV1 predominantly colocalize with PKA and PKC, respectively, in the trigeminal ganglion. These results suggest that IL-1β-induced mechanical allodynia is mediated by sensitized peripheral NMDA/AMPA receptors through PKA-mediated signaling in the large-diameter primary afferent nerve fibers, whereas IL-1β-induced thermal hyperalgesia is mediated by sensitized peripheral TRPV1 receptors through PKC

  15. Charged particle accelerator grating

    DOEpatents

    Palmer, Robert B.

    1986-09-02

    A readily disposable and replaceable accelerator grating for a relativistic particle accelerator. The grating is formed for a plurality of liquid droplets that are directed in precisely positioned jet streams to periodically dispose rows of droplets along the borders of a predetermined particle beam path. A plurality of lasers are used to direct laser beams into the droplets, at predetermined angles, thereby to excite the droplets to support electromagnetic accelerating resonances on their surfaces. Those resonances operate to accelerate and focus particles moving along the beam path. As the droplets are distorted or destroyed by the incoming radiation, they are replaced at a predetermined frequency by other droplets supplied through the jet streams.

  16. Ion irradiation and thermally induced mixing of CoCrPt/Cr multilayered films

    SciTech Connect

    Georgieva, M. T.; Grundy, P. J.; Telling, N. D.

    2007-01-22

    A set of CoCrPt/Cr multilayered films with variable layer thicknesses has been used in an investigation of interlayer mixing and ''patterning'' of samples with relatively high coercivity and in-plane magnetization. The multilayers with the highest coercivities were irradiated with different doses of Ar{sup ++} ions in order to intermix the Cr and CoCrPt layers and push the CoCrPt stoichiometry into the nonmagnetic region of the phase diagram. Samples were also irradiated through a Ni-grating mask to obtain patterning by adjacent magnetic and nonmagnetic regions of the film. Thermal annealing experiments mirrored the change in magnetic properties of the irradiated samples.

  17. Enhancing the performance of multilayer-dielectric diffraction gratings through cleaning process modifications and defect mitigation

    NASA Astrophysics Data System (ADS)

    Liddell, Heather P. H.

    2014-05-01

    The laser-damage resistance of multilayer-dielectric (MLD) pulse compressor gratings currently limits the energy performance of the petawatt-class OMEGA EP laser system at University of Rochester's Laboratory for Laser Energetics. The cleanliness of these components is of paramount importance; contaminants can act as absorbers during laser irradiation, initiating intense local heating and catastrophic laser-induced damage. Unfortunately, some of the most effective cleaning methods for MLD gratings - usually involving high temperatures and strong acids or bases - can themselves induce chemical degradation and thermal stresses, leading to coating delamination and defects. This work explores ways to improve the laser-damage resistance of MLD gratings through modifications to the final cleaning phase of the manufacturing process. Processes of defect formation are investigated through a combination of chemical cleaning experiments, microscopy, and modeling. We use a fracture-mechanics approach to formulate a mechanism for the initiation of micrometer-scale delamination defects that are commonly observed after chemical cleaning. The stress responses of MLD coatings to elevated-temperature chemical cleaning are estimated using a thermomechanical model, enabling us to study the effects of substrate thickness, solution temperature, and heating rates on coating stresses (and thus the risk of stress-induced failure). Finally, a low-temperature chemical cleaning approach is developed to improve laser-damage resistance while avoiding defect formation and mitigating coating stresses. We find that grating coupons cleaned using the optimized method consistently meet OMEGA EP requirements on diffraction efficiency and 1054-nm laser-damage resistance at 10 ps.

  18. Thermally induced stresses and deformations in angle-ply composite tubes

    NASA Technical Reports Server (NTRS)

    Hyer, M. W.; Rousseau, Carl Q.

    1987-01-01

    Cure-induced uniform temperature change effects on the stresses, axial expansion, and thermally-induced twist of four specific angle-ply tube designs are discussed with a view to the tubes' use as major space structure components. The stresses and deformations in the tubes are studied as a function of the four designs, the off-axis angle, and the single-material and hybrid reinforcing-material construction used. It is found that tube design has a minor influence on the stresses, axial stiffness, and axial thermal expansion characteristics, which are more directly a function of off-axis angle and material selection; tube design is, however, the primary influence in the definition of thermally-induced twist and torsional stiffness characteristics. None of the designs is free of thermally induced twist.

  19. An evaluation of thermally-induced structural disturbances of spacecraft solar arrays

    SciTech Connect

    Johnston, J.D.; Thornton, E.A.

    1996-12-31

    Spacecraft have experienced attitude disturbances as a result of thermally-induced motions of flexible appendages for over 30 years. Thermally-induced deformations of appendages such as deployable booms and solar arrays may result in significant disturbance torques. These effects lead to a decrease in pointing accuracy, an increase in pointing jitter, and in extreme cases may affect the stability of the entire spacecraft. Examples of recent satellites whose performance has been degraded by thermally-induced structural disturbances are the Hubble Space Telescope (HST) and the Upper Atmosphere Research Satellite (UARS). This paper presents an evaluation of thermally-induced structural disturbances of solar arrays, including: (1) identification of disturbances sources and classifications, (2) assessment of the susceptibility of different types of solar array to the disturbances, and (3) discussion of potential methods for mitigating the effects of the disturbances.

  20. 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.

  1. Hybrid grating reflectors: Origin of ultrabroad stopband

    NASA Astrophysics Data System (ADS)

    Park, Gyeong Cheol; Taghizadeh, Alireza; Chung, Il-Sug

    2016-04-01

    Hybrid grating (HG) reflectors with a high-refractive-index cap layer added onto a high contrast grating (HCG) provide a high reflectance close to 100% over a broader wavelength range than HCGs. The combination of a cap layer and a grating layer brings a strong Fabry-Perot (FP) resonance as well as a weak guided mode (GM) resonance. Most of the reflected power results from the FP resonance, while the GM resonance plays a key role in achieving a reflectance close to 100% as well as broadening the stopband. An HG sample with 7 InGaAlAs quantum wells included in the cap layer has been fabricated by directly wafer-bonding a III-V cap layer onto a Si grating layer. Its reflection property has been characterized. This heterogeneously integrated HG reflector may allow for a hybrid III-V on Si laser to be thermally efficient, which has promising prospects for silicon photonics light sources and high-speed operation.

  2. Electrically-programmable diffraction grating

    DOEpatents

    Ricco, A.J.; Butler, M.A.; Sinclair, M.B.; Senturia, S.D.

    1998-05-26

    An electrically-programmable diffraction grating is disclosed. The programmable grating includes a substrate having a plurality of electrodes formed thereon and a moveable grating element above each of the electrodes. The grating elements are electrostatically programmable to form a diffraction grating for diffracting an incident beam of light as it is reflected from the upper surfaces of the grating elements. The programmable diffraction grating, formed by a micromachining process, has applications for optical information processing (e.g. optical correlators and computers), for multiplexing and demultiplexing a plurality of light beams of different wavelengths (e.g. for optical fiber communications), and for forming spectrometers (e.g. correlation and scanning spectrometers). 14 figs.

  3. Modeling Oxidation Induced Stresses in Thermal Barrier Coatings

    NASA Technical Reports Server (NTRS)

    Ferguson, B. L.; Freborg, A. M.; Petrus, G. J.; Brindley, William J.

    1998-01-01

    The use of thermal barrier coatings (TBC's) in gas turbines has increased dramatically in recent years, due mainly to the need for component protection from ever increasing service temperatures. Oxidation of the bond coat has been identified as an important contributing factor to spallation of the ceramic top coat during service. Additional variables found to influence TBC thermal cycle life include bond coat coefficient of thermal expansion, creep behavior of both the ceramic and bond coat layers, and modulus of elasticity. The purpose of this work was to characterize the effects of oxidation on the stress states within the TBC system, as well as to examine the interaction of oxidation with other factors affecting TBC life.

  4. Model and simulation of heat transfer, magnetite oxidation and NOx formation in a grate-kiln taconite pellet induration furnace

    SciTech Connect

    Davis, R.A.

    1996-12-31

    A numerical model was developed to simulate the combined effects of heat transfer, magnetite oxidation, and NO{sub x} formation in a grate-kiln furnace for taconite pellet induration. Heat transfer from the flame in the kiln was described by the net radiation method. The shrinking core model was used to account for magnetite oxidation on the grate. A novel approach to oxidation of tumbling pellets in a kiln was derived. The Zeldovich mechanism was used to predict thermal NO generation. Temperature fluctuations in the gas streams were estimated with a clipped Gaussian probability density function. The thermal energy balances and mass balances resulted in coupled systems of first-order differential equations, which were solved numerically. The model is capable of predicting NO production and magnetite oxidation in agreement with observation of plant performance. Although the design of the grate-kiln system is for efficient heat and mass transfer, it may not be the optimal design for minimizing the formation of NOx. When natural gas is used to fuel the kiln burner in the presence of excess air, the principal mechanism of NOx formation is the thermally induced combination of oxygen and nitrogen in the air in the post combustion zone after the burner.

  5. Thermally-induced bending-torsion coupling vibration of large scale space structures

    NASA Astrophysics Data System (ADS)

    Xue, Ming-De; Duan, Jin; Xiang, Zhi-Hai

    2007-09-01

    In this paper, a finite element scheme is developed to solve the problem of thermally-induced bending-torsion coupling vibration of large scale space structures, which are usually composed of thin-walled beams with open and closed cross-section. A two-noded finite element is proposed to analyze the transient temperature field over the longitudinal and circumferential direction of a beam. Since this temperature element can share the same mesh with the two-noded beam element of Euler-Bernoulli type, a unified finite element scheme is easily formulated to solve the thermal-structural coupling problem. This scheme is characterized with very strong nonlinear formulation, due to the consideration of the thermal radiation and the coupling effect between structural deformations and the incident normal heat flux. Moreover, because the warping is taken into account, not only the thermal axial force and thermal bending moments but also the thermal bi-moment are presented in the formulation. Consequently, the thermally-induced bending-torsion coupling vibration can be simulated. The performance of the proposed computational scheme is illustrated by the analysis of the well-known failure of Hubble space telescope solar arrays. The results reveal that the thermally-induced bending-torsion coupling vibration is obviously presented in that case and could be regarded as a cause of failure.

  6. Differences between thermal and laser-induced diffusion.

    PubMed

    Zaum, Ch; Meyer-Auf-der-Heide, K M; Mehlhorn, M; McDonough, S; Schneider, W F; Morgenstern, K

    2015-04-10

    A combination of femtosecond laser excitation with a low-temperature scanning tunneling microscope is used to study long-range interaction during diffusion of CO on Cu(111). Both thermal and laser-driven diffusion show an oscillatory energy dependence on the distance to neighboring molecules. Surprisingly, the phase is inverted; i.e., at distances at which thermal diffusion is most difficult, it is easiest for laser-driven diffusion and vice versa. We explain this unexpected behavior by a transient stabilization of the negative ion during diffusion as corroborated by ab initio calculations. PMID:25910140

  7. Curvature-induced and thermal strain in polyhedral gold nanocrystals

    SciTech Connect

    Kim, J. W.; Dietze, S. H.; Ulvestad, A.; Fohtung, E.; Shpyrko, O. G.; Manna, S.; Fullerton, E. E.; Harder, R.

    2014-10-27

    We use coherent x-ray diffractive imaging to map the local distribution of strain in gold (Au) polyhedral nanocrystals grown on a silicon (Si) substrate by a single-step thermal chemical vapor deposition process. The lattice strain at the surface of the octahedral nanocrystal agrees well with the predictions of the Young-Laplace equation quantitatively, but exhibits a discrepancy near the nanocrystal-substrate interface. We attribute this discrepancy to the dissimilar interfacial energies between Au/Air and Au/Si and to the difference in thermal expansion between the nanocrystal and the substrate during the cooling process.

  8. Onset of thermally induced gas convection in mine wastes

    USGS Publications Warehouse

    Lu, N.; Zhang, Y.

    1997-01-01

    A mine waste dump in which active oxidation of pyritic materials occurs can generate a large amount of heat to form convection cells. We analyze the onset of thermal convection in a two-dimensional, infinite horizontal layer of waste rock filled with moist gas, with the top surface of the waste dump open to the atmosphere and the bedrock beneath the waste dump forming a horizontal and impermeable boundary. Our analysis shows that the thermal regime of a waste rock system depends heavily on the atmospheric temperature, the strength of the heat source and the vapor pressure. ?? 1997 Elsevier Science Ltd. All rights reserved.

  9. Thermally induced osteocyte damage initiates pro-osteoclastogenic gene expression in vivo.

    PubMed

    Dolan, Eimear B; Tallon, David; Cheung, Wing-Yee; Schaffler, Mitchell B; Kennedy, Oran D; McNamara, Laoise M

    2016-06-01

    Bone is often subject to harsh temperatures during orthopaedic procedures resulting in thermally induced bone damage, which may affect the healing response. Postsurgical healing of bone is essential to the success of surgery, therefore, an understanding of the thermally induced responses of bone cells to clinically relevant temperatures in vivo is required. Osteocytes have been shown to be integrally involved in the bone remodelling cascade, via apoptosis, in micro-damage systems. However, it is unknown whether this relationship is similar following thermal damage. Sprague-Dawley rat tibia were exposed to clinically relevant temperatures (47°C or 60°C) to investigate the role of osteocytes in modulating remodelling related factors. Immunohistochemistry was used to quantify osteocyte thermal damage (activated caspase-3). Thermally induced pro-osteoclastogenic genes (Rankl, Opg and M-csf), in addition to genes known to mediate osteoblast and osteoclast differentiation via prostaglandin production (Cox2), vascularization (Vegf) and inflammatory (Il1a) responses, were investigated using gene expression analysis. The results demonstrate that heat-treatment induced significant bone tissue and cellular damage. Pro-osteoclastogenic genes were upregulated depending on the amount of temperature elevation compared with the control. Taken together, the results of this study demonstrate the in vivo effect of thermally induced osteocyte damage on the gene expression profile. PMID:27335224

  10. Spatio-temporal modeling and optimization of a deformable-grating compressor for short high-energy laser pulses.

    PubMed

    Qiao, J; Papa, J; Liu, X

    2015-10-01

    Monolithic large-scale diffraction gratings are desired to improve the performance of high-energy laser systems and scale them to higher energy, but the surface deformation of these diffraction gratings induce spatio-temporal coupling that is detrimental to the focusability and compressibility of the output pulse. A new deformable-grating-based pulse compressor architecture with optimized actuator positions has been designed to correct the spatial and temporal aberrations induced by grating wavefront errors. An integrated optical model has been built to analyze the effect of grating wavefront errors on the spatio-temporal performance of a compressor based on four deformable gratings. A 1.5-meter deformable grating has been optimized using an integrated finite-element-analysis and genetic-optimization model, leading to spatio-temporal performance similar to the baseline design with ideal gratings. PMID:26480107

  11. Simulation of thermal-transient-induced-pipe-flow stratification using COMMIX-2

    SciTech Connect

    Shah, V.L.; Domanus, H.M.; Miao, C.C.; Schmitt, R.C.; Sha, W.T.

    1982-01-01

    At low-flow (high Richardson number) in a piping system with thermal transient, thermal-buoyancy-induced secondary flows exist. Three-dimensional computer codes are, therefore, necessary to model correctly the non-axisymmetric, thermally stratified flow through a piping system. This paper presents the results of the numerical simulation of thermal-hydraulic behavior in a pipe during a thermal transient. The particular transient considered was the experimental test No. PIPE2, and carried out at the Mixing Components Test Facility (MCTF). The numerical simulation was performed using COMMIX-2. COMMIX-2 is a computer code for steady/unsteady, three-dimensional, two-phase thermal-hydraulic analysis of reactor components under normal and off-normal operating conditions. The results of simulation are compared with the experimental measurements and they are in reasonable agreement with experimental data.

  12. Charged particle accelerator grating

    DOEpatents

    Palmer, R.B.

    1985-09-09

    A readily disposable and replaceable accelerator grating for a relativistic particle accelerator is described. The grating is formed for a plurality of liquid droplets that are directed in precisely positioned jet streams to periodically dispose rows of droplets along the borders of a predetermined particle beam path. A plurality of lasers are used to direct laser beams onto the droplets, at predetermined angles, thereby to excite the droplets to support electromagnetic accelerating resonances on their surfaces. Those resonances operate to accelerate and focus particles moving along the beam path. As the droplets are distorted or destroyed by the incoming radiation, they are replaced at a predetermined frequency by other droplets supplied through the jet streams.

  13. Thermally induced micromechanical stresses in ceramic/ceramic composites

    SciTech Connect

    Li, Zhuang; Bradt, R.C.

    1992-11-01

    The internal micromechanical stresses which develop in ceramic-ceramic composites as a consequence of temperature changes and thermoelastic property differences between the reinforcing and matrix phases are addressed by the Eshelby method. Results for two whisker reinforced ceramic matrix composites and for quartz particles in porcelain are discussed. It is concluded that the stresses which develop in the second phase reinforcing inclusions are quite substantial (GPa-levels) and may be highly anisotropic in character. These stresses are additive to the macroscopic thermal stresses from temperature gradients which are encountered during heating and cooling, and also to externally apphed mechanical stresses (loads). These micromechanical stresses are expected to be highly significant for thermal cycling fatigue and other failure processes.

  14. Investigating the thermally induced acoustoelastic effect in isotropic media with Lamb waves

    PubMed Central

    Dodson, Jacob C.; Inman, Daniel J.

    2014-01-01

    Elastic wave velocities in metallic structures are affected by variations in environmental conditions such as changing temperature. This paper extends the theory of acoustoelasticity by allowing thermally induced strains in unconstrained isotropic media, and it experimentally examines the velocity variation of Lamb waves in aluminum plates (AL-6061) due to isothermal temperature deviations. This paper presents both thermally induced acoustoelastic constants and thermally varying effective Young's modulus and Poisson's ratio which include the third order elastic material constants. The experimental thermal sensitivity of the phase velocity (∂vP/∂θ) for both the symmetric and antisymmetric modes are bounded by two theories, the acoustoelastic Lamb wave theory with thermo-acoustoelastic tensors and the thermoelastic Lamb wave theory using an effective thermo-acoustoelastic moduli. This paper shows the theoretical thermally induced acoustoelastic Lamb wave thermal sensitivity (∂vP/∂θ) is an upper bound approximation of the experimental thermal changes, but the acoustoelastic Lamb wave theory is not valid for predicting the antisymmetric (A0) phase velocity at low frequency-thickness values, <1.55 MHz mm for various temperatures. PMID:25373955

  15. Investigating the thermally induced acoustoelastic effect in isotropic media with Lamb waves.

    PubMed

    Dodson, Jacob C; Inman, Daniel J

    2014-11-01

    Elastic wave velocities in metallic structures are affected by variations in environmental conditions such as changing temperature. This paper extends the theory of acoustoelasticity by allowing thermally induced strains in unconstrained isotropic media, and it experimentally examines the velocity variation of Lamb waves in aluminum plates (AL-6061) due to isothermal temperature deviations. This paper presents both thermally induced acoustoelastic constants and thermally varying effective Young's modulus and Poisson's ratio which include the third order elastic material constants. The experimental thermal sensitivity of the phase velocity (∂v(P)/∂θ) for both the symmetric and antisymmetric modes are bounded by two theories, the acoustoelastic Lamb wave theory with thermo-acoustoelastic tensors and the thermoelastic Lamb wave theory using an effective thermo-acoustoelastic moduli. This paper shows the theoretical thermally induced acoustoelastic Lamb wave thermal sensitivity (∂v(P)/∂θ) is an upper bound approximation of the experimental thermal changes, but the acoustoelastic Lamb wave theory is not valid for predicting the antisymmetric (A0) phase velocity at low frequency-thickness values, <1.55 MHz mm for various temperatures. PMID:25373955

  16. The Cryogenic Grating Spectrometer

    NASA Technical Reports Server (NTRS)

    Erickson, Edwin F.; Haas, Michael R.; Colgan, Sean W. J.; Simpson, Janet P.; Rubin, Robert H.

    1995-01-01

    The Cryogenic Grating Spectrometer (CGS) first flew on the KAO in 1982 December and has been open to guest investigators since 1984 October. In the past 12 years it has completed over 100 research flights supporting 13 different principal investigators studying a variety of objects. We briefly describe the instrument, its capabilities and accomplishments, and acknowledge the people who have contributed to its development and operation.

  17. Error compensation for thermally induced errors on a machine tool

    SciTech Connect

    Krulewich, D.A.

    1996-11-08

    Heat flow from internal and external sources and the environment create machine deformations, resulting in positioning errors between the tool and workpiece. There is no industrially accepted method for thermal error compensation. A simple model has been selected that linearly relates discrete temperature measurements to the deflection. The biggest problem is how to locate the temperature sensors and to determine the number of required temperature sensors. This research develops a method to determine the number and location of temperature measurements.

  18. Thermal Drawdown-Induced Flow Channeling in Fractured Geothermal Reservoirs

    NASA Astrophysics Data System (ADS)

    Fu, Pengcheng; Hao, Yue; Walsh, Stuart D. C.; Carrigan, Charles R.

    2016-03-01

    We investigate the flow-channeling phenomenon caused by thermal drawdown in fractured geothermal reservoirs. A discrete fracture network-based, fully coupled thermal-hydrological-mechanical simulator is used to study the interactions between fluid flow, temperature change, and the associated rock deformation. The responses of a number of randomly generated 2D fracture networks that represent a variety of reservoir characteristics are simulated with various injection-production well distances. We find that flow channeling, namely flow concentration in cooled zones, is the inevitable fate of all the scenarios evaluated. We also identify a secondary geomechanical mechanism caused by the anisotropy in thermal stress that counteracts the primary mechanism of flow channeling. This new mechanism tends, to some extent, to result in a more diffuse flow distribution, although it is generally not strong enough to completely reverse flow channeling. We find that fracture intensity substantially affects the overall hydraulic impedance of the reservoir but increasing fracture intensity generally does not improve heat production performance. Increasing the injection-production well separation appears to be an effective means to prolong the production life of a reservoir.

  19. Gaussian entanglement induced by an extended thermal environment

    NASA Astrophysics Data System (ADS)

    Valido, Antonio A.; Alonso, Daniel; Kohler, Sigmund

    2013-10-01

    We study stationary entanglement between three harmonic oscillators which are dipole coupled to a one-dimensional or a three-dimensional bosonic environment. The analysis of the open-system dynamics is performed with generalized quantum Langevin equations which we solve exactly in a Fourier representation. The focus lies on Gaussian bipartite and tripartite entanglement induced by the highly non-Markovian interaction mediated by the environment. This environment-induced interaction represents an effective many-party interaction with a spatial long-range feature: A main finding is that the presence of a passive oscillator is detrimental for stationary two-mode entanglement. Furthermore, our results indicate that the environment-induced entanglement mechanism corresponds to uncontrolled feedback which is predominantly coherent at low temperatures and for moderate oscillator-environment coupling as compared to the oscillator frequency.

  20. Ultrafast thermally induced magnetic switching in synthetic ferrimagnets

    SciTech Connect

    Evans, Richard F. L. Ostler, Thomas A.; Chantrell, Roy W.; Radu, Ilie; Rasing, Theo

    2014-02-24

    Synthetic ferrimagnets are composite magnetic structures formed from two or more anti-ferromagnetically coupled magnetic sublattices with different magnetic moments. Here, we report on atomistic spin simulations of the laser-induced magnetization dynamics on such synthetic ferrimagnets and demonstrate that the application of ultrashort laser pulses leads to sub-picosecond magnetization dynamics and all-optical switching in a similar manner as in ferrimagnetic alloys. Moreover, we present the essential material properties for successful laser-induced switching, demonstrating the feasibility of using a synthetic ferrimagnet as a high density magnetic storage element without the need of a write field.

  1. Influence of thermal agitation on the electric field induced precessional magnetization reversal with perpendicular easy axis

    SciTech Connect

    Cheng, Hongguang Deng, Ning

    2013-12-15

    We investigated the influence of thermal agitation on the electric field induced precessional magnetization switching probability with perpendicular easy axis by solving the Fokker-Planck equation numerically with finite difference method. The calculated results show that the thermal agitation during the reversal process crucially influences the switching probability. The switching probability can be achieved is only determined by the thermal stability factor Δ of the free layer, it is independent on the device dimension, which is important for the high density device application. Ultra-low error rate down to the order of 10{sup −9} can be achieved for the device of thermal stability factor Δ of 40. Low damping factor α material should be used for the free layer for high reliability device applications. These results exhibit potential of electric field induced precessional magnetization switching with perpendicular easy axis for ultra-low power, high speed and high density magnetic random access memory (MRAM) applications.

  2. Cell death induced by ozone and various non-thermal plasmas: therapeutic perspectives and limitations

    PubMed Central

    Lunov, Oleg; Zablotskii, Vitalii; Churpita, Olexander; Chánová, Eliška; Syková, Eva; Dejneka, Alexandr; Kubinová, Šárka

    2014-01-01

    Non-thermal plasma has been recognized as a promising tool across a vast variety of biomedical applications, with the potential to create novel therapeutic methods. However, the understanding of the molecular mechanisms behind non-thermal plasma cellular effects remains a significant challenge. In this study, we show how two types of different non-thermal plasmas induce cell death in mammalian cell cultures via the formation of multiple intracellular reactive oxygen/nitrogen species. Our results showed a discrepancy in the superoxide accumulation and lysosomal activity in response to air and helium plasma, suggesting that triggered signalling cascades might be grossly different between different plasmas. In addition, the effects of ozone, a considerable component of non-thermal plasma, have been simultaneously evaluated and have revealed much faster and higher cytotoxic effects. Our findings offer novel insight into plasma-induced cellular responses, and provide a basis for better controlled biomedical applications. PMID:25410636

  3. Cell death induced by ozone and various non-thermal plasmas: therapeutic perspectives and limitations

    NASA Astrophysics Data System (ADS)

    Lunov, Oleg; Zablotskii, Vitalii; Churpita, Olexander; Chánová, Eliška; Syková, Eva; Dejneka, Alexandr; Kubinová, Šárka

    2014-11-01

    Non-thermal plasma has been recognized as a promising tool across a vast variety of biomedical applications, with the potential to create novel therapeutic methods. However, the understanding of the molecular mechanisms behind non-thermal plasma cellular effects remains a significant challenge. In this study, we show how two types of different non-thermal plasmas induce cell death in mammalian cell cultures via the formation of multiple intracellular reactive oxygen/nitrogen species. Our results showed a discrepancy in the superoxide accumulation and lysosomal activity in response to air and helium plasma, suggesting that triggered signalling cascades might be grossly different between different plasmas. In addition, the effects of ozone, a considerable component of non-thermal plasma, have been simultaneously evaluated and have revealed much faster and higher cytotoxic effects. Our findings offer novel insight into plasma-induced cellular responses, and provide a basis for better controlled biomedical applications.

  4. Faraday isolator based on a TSAG single crystal with compensation of thermally induced depolarization inside magnetic field

    NASA Astrophysics Data System (ADS)

    Snetkov, Ilya; Palashov, Oleg

    2015-04-01

    A Faraday isolator based on a terbium scandium aluminum garnet (TSAG) single crystal with compensation of thermally induced depolarization inside magnetic field was demonstrated. An isolation ratio of 32 dB at 350 W cw laser radiation power was achieved. Thermally induced depolarization and thermal lens were studied and compared with similar thermal effects arising in the widely used terbium gallium garnet crystal (TGG) for the first time.

  5. Thermal emittance from ionization-induced trapping in plasma accelerators

    NASA Astrophysics Data System (ADS)

    Schroeder, C. B.; Vay, J.-L.; Esarey, E.; Bulanov, S. S.; Benedetti, C.; Yu, L.-L.; Chen, M.; Geddes, C. G. R.; Leemans, W. P.

    2014-10-01

    The minimum obtainable transverse emittance (thermal emittance) of electron beams generated and trapped in plasma-based accelerators using laser ionization injection is examined. The initial transverse phase space distribution following ionization and passage through the laser is derived, and expressions for the normalized transverse beam emittance, both along and orthogonal to the laser polarization, are presented. Results are compared to particle-in-cell simulations. Ultralow emittance beams can be generated using laser ionization injection into plasma accelerators, and examples are presented showing normalized emittances on the order of tens of nm.

  6. Thermally induced secondary atomization of droplet in an acoustic field

    NASA Astrophysics Data System (ADS)

    Basu, Saptarshi; Saha, Abhishek; Kumar, Ranganathan

    2012-01-01

    We study the thermal effects that lead to instability and break up in acoustically levitated vaporizing fuel droplets. For selective liquids, atomization occurs at the droplet equator under external heating. Short wavelength [Kelvin-Helmholtz (KH)] instability for diesel and bio-diesel droplets triggers this secondary atomization. Vapor pressure, latent heat, and specific heat govern the vaporization rate and temperature history, which affect the surface tension gradient and gas phase density, ultimately dictating the onset of KH instability. We develop a criterion based on Weber number to define a condition for the inception of secondary atomization.

  7. Extreme Thermal Noxious Stimuli Induce Pain Responses in Zebrafish Larvae

    PubMed Central

    Malafoglia, Valentina; Colasanti, Marco; Raffaeli, William; Balciunas, Darius; Giordano, Antonio; Bellipanni, Gianfranco

    2014-01-01

    Exposing tissues to extreme high or low temperature leads to burns. Burned animals sustain several types of damage, from the disruption of the tissue to degeneration of axons projecting through muscle and skin. Such damage causes pain due to both inflammation and axonal degeneration (neuropathic-like pain). Thus, the approach to cure and alleviate the symptoms of burns must be twofold: rebuilding the tissue that has been destroyed and alleviating the pain derived from the burns. While tissue regeneration techniques have been developed, less is known on the treatment of the induced pain. Thus, appropriate animal models are necessary for the development of the best treatment for pain induced in burned tissues. We have developed a methodology in the zebrafish aimed to produce a new animal model for the study of pain induced by burns. Here we show that two events linked to the onset of burn-induced inflammation and neuropathic-like pain in mammals, degeneration of axons innervating the affected tissues and over-expression of specific genes in sensory tissues, are conserved from zebrafish to mammals. PMID:23929528

  8. Extreme thermal noxious stimuli induce pain responses in zebrafish larvae.

    PubMed

    Malafoglia, Valentina; Colasanti, Marco; Raffaeli, William; Balciunas, Darius; Giordano, Antonio; Bellipanni, Gianfranco

    2014-03-01

    Exposing tissues to extreme high or low temperature leads to burns. Burned animals sustain several types of damage, from the disruption of the tissue to degeneration of axons projecting through muscle and skin. Such damage causes pain due to both inflammation and axonal degeneration (neuropathic-like pain). Thus, the approach to cure and alleviate the symptoms of burns must be twofold: rebuilding the tissue that has been destroyed and alleviating the pain derived from the burns. While tissue regeneration techniques have been developed, less is known on the treatment of the induced pain. Thus, appropriate animal models are necessary for the development of the best treatment for pain induced in burned tissues. We have developed a methodology in the zebrafish aimed to produce a new animal model for the study of pain induced by burns. Here, we show that two events linked to the onset of burn-induced inflammation and neuropathic-like pain in mammals, degeneration of axons innervating the affected tissues and over-expression of specific genes in sensory tissues, are conserved from zebrafish to mammals. PMID:23929528

  9. Laser-Induced Thermal Acoustics (LITA): Four-wave mixing measurement of sound speed, thermal diffusivity, and viscosity

    NASA Astrophysics Data System (ADS)

    Cummings, Eric B.

    1994-08-01

    Laser-induced thermal acoustics (LITA) is a promising optical four-wave mixing technique for gasdynamic measurement. The Chi(3) nonlinear process is a sequence of two opto-acoustic effects, electrostriction and absorption/ rapid-thermalization, and the acousto-optic effect. The evolution of the laser-induced acoustic structures temporally modulates Chi(3) and thereby the LITA signal. Time resolution of the signal provides the sound speed, thermal diffusivity, and acoustic damping rate, along with information about atomic or molecular energy transfer rates. LITA can also measure spectra of both the real and imaginary gas susceptibility. The physics of LITA is discussed and the derivation is sketched of a simple analytical expression that accurately describes both the magnitude and time history of the LITA signal. Early experimental results are presented. Sound speeds accurate to 0.5% and transport properties accurate to 30% have been measured in a single-shot without calibration. More realistic modeling should dramatically improve transport-property measurement. LITA spectra have been taken of weak spectral lines of NO2 in concentrations less than 50 ppb. Signal reflectivities as high as 0.0001 have been estimated. New applications of LITA, including velocimetry, are suggested.

  10. Noise-induced relaxation of a quantum oscillator interacting with a thermal bath

    NASA Astrophysics Data System (ADS)

    Efremov, G. F.; Mourokh, L. G.; Smirnov, A. Yu.

    1993-04-01

    The non-Markovian theory of quantum Brownian motion is used to analyse the relaxation of a harmonic oscillator nonlinearly coupled to a thermal bath and driven by external noise. It is shown that this nonlinearity leads to interference between additive noise and multiplicative noise and to the effect of additive noise-induced relaxation of a high frequency oscillator interacting with a low frequency thermal bath.

  11. Thermally induced all-optical inverter and dynamic hysteresis loops in graphene oxide dispersions.

    PubMed

    Melle, Sonia; Calderón, Oscar G; Egatz-Gómez, Ana; Cabrera-Granado, E; Carreño, F; Antón, M A

    2015-11-01

    We experimentally study the temporal dynamics of amplitude-modulated laser beams propagating through a water dispersion of graphene oxide sheets in a fiber-to-fiber U-bench. Nonlinear refraction induced in the sample by thermal effects leads to both phase reversing of the transmitted signals and dynamic hysteresis in the input-output power curves. A theoretical model including beam propagation and thermal lensing dynamics reproduces the experimental findings. PMID:26560566

  12. Direct observations of thermally induced structural changes in amorphous silicon carbide

    SciTech Connect

    Ishimaru, Manabu; Hirata, Akihiko; Naito, Muneyuki; Bae, In-Tae; Zhang, Yanwen; Weber, William J.

    2008-08-01

    Thermally induced structural relaxation in amorphous silicon carbide (SiC) has been examined by means of in situ transmission electron microscopy (TEM). The amorphous SiC was prepared by high-energy ion-beam-irradiation into a single crystalline 4H-SiC substrate. Cross-sectional TEM observations and electron energy-loss spectroscopy measurements revealed that thermal annealing induces a remarkable volume reduction, so-called densification, of amorphous SiC. From radial distribution function analyses using electron diffraction, notable changes associated with structural relaxation were observed in chemical short-range order. On the basis of the alteration of chemical short-range order, we discuss the origin of thermally induced densification in amorphous SiC.

  13. Characterization of pinhole transmission gratings.

    PubMed

    Eidmann, K; Kühne, M; Müller, P; Tsakiris, G D

    1990-01-01

    Gold pinhole transmission gratings fabricated by Heidenhain GmbH primarily for the purpose of studying the radiation of intense soft x-ray sources have been tested with the synchrotron radiation of BESSY. Typical results for the spectral dependence of the grating efficiency into the various diffraction orders are presented in a wavelength region ranging from 4 to 20 nm. Also the influence of grating irregularities has been studied. With appropriate grating parameters quite good agreement between the experimental results and theoretical Calculations is Obtained. PMID:21307429

  14. Visualization of thermal lensing induced image distortion using Zemax ray tracing and BTEC thermal modeling

    NASA Astrophysics Data System (ADS)

    Towle, Erica L.; Clark, Clifton D.; Aaron, Michelle T.; Dunn, Andrew K.; Welch, Ashley J.; Thomas, Robert J.

    2013-02-01

    In recent years, several studies have been investigating the impact of thermal lensing in ocular media on the visual function. These studies have shown that when near-infrared (NIR) laser energy (1319 nm) is introduced to a human eye, the heating of the eye can be sufficient to alter the index of refraction of the media leading to transient changes in the visible wavefront through an effect known as thermal lensing, while remaining at a safe level. One of the main limitations of experimentation with human subjects, however, is the reliance on a subject's description of the effect, which can vary greatly between individuals. Therefore, a computational model was needed that could accurately represent the changes of an image as a function of changes in the index of refraction. First, to model changes in the index of refraction throughout the eye, a computational thermal propagation model was used. These data were used to generate a comprehensive ray tracing model of the human eye using Zemax ( Radiant Zemax Inc, Redmond WA) via a gradient lens surface. Using this model, several different targets have been analyzed which made it possible to calculate real-world visual acuity so that the effect of changes in the index of refraction could be related back to changes in the image of a visual scene.

  15. Coherent frequency-modulated continuous wave reflectometry for measuring stationary Brillouin grating induced under uniform pumping by counterpropagating nonmodulated light waves.

    PubMed

    Takada, Kazumasa; Yasuno, Takahiro

    2016-05-20

    We describe theoretically and experimentally how valuable information on the distributed Brillouin spectra of an optical waveguide is derived from the stationary Brillouin grating measurement under uniform pumping over the waveguide by using the coherent frequency-modulated continuous wave reflectometry. We upconvert the frequencies of the probe and pumping light waves by the Brillouin frequency with one modulator and detect the Stokes light in the same way that we detect the Fresnel and Rayleigh backreflections in the fiber. The intrinsic coherent spike is reduced by using the lock-in detection and the least squares method to reveal the distributed Brillouin spectra of a short optical fiber consisting of two different fibers spliced together. PMID:27411124

  16. Design of a full-silica pulse-compression grating.

    PubMed

    Bonod, Nicolas; Neauport, Jérôme

    2008-03-01

    A diffraction grating engraved on a two-dimensional photonic crystal composed of square air holes in a silica matrix is numerically studied for the compression of ultrashort pulses. The silica is therefore the only solid material of the grating, and the reflection of the incident beam is based on the contrast of the air and silica refractive indices. This optical component enables the single use of silica as a solid material, presenting a high laser-induced damage threshold. In comparison to gratings engraved on a dielectric stack, multilayer dielectric, it offers the advantage of avoiding the presence of interfaces between two solid materials with different mechanical properties and sources of mechanical constraints that can distort the grating. PMID:18311291

  17. Rock properties and their effect on thermally-induced displacements and stresses

    SciTech Connect

    Chan, T.; Hood, M.; Board, M.

    1980-02-01

    A discussion is given of the importance of material properties in the finite-element calculations for thermally induced displacements and stresses resulting from a heating experiment in an in-situ granitic rock, at Stripa, Sweden. Comparisons are made between field measurements and finite element method calculations using (1) temperature independent, (2) temperature dependent thermal and thermomechanical properties and (3) in-situ and laboratory measurements for Young's modulus. The calculations of rock displacements are influenced predominantly by the temperature dependence of the thermal expansion coefficient, whereas the dominant factor affecting predictions for rock stresses is the in-situ modulus.

  18. Rock properties and their effect on thermally induced displacements and stresses

    SciTech Connect

    Chan, T.; Mood, M.

    1982-12-01

    A discussion is given of the importance of material properties in the finite-element calculations for thermally induced displacements and stresses resulting from a heating experiment in an in-situ granitic rock, at Stripa, Sweden. Comparisons are made between field measurements and finite element method calculations using (i) temperature independent, (ii) temperature dependent thermal and thermomechanical properties, and (iii) in-situ and laboratory measurements for Young's modulus. The calculations of rock displacements are influenced predominantly by the temperature dependence of the thermal expansion coefficient, whereas the dominant factor affecting predictions or rock stresses is the in-situ modulus.

  19. Thermal study of PN thermoelectric couple by laser induced Seebeck EMF measurement

    NASA Astrophysics Data System (ADS)

    Patiño-Lopez, Luis-David; Amine Salhi, M.; Dilhaire, Stefan; Grauby, Stéphane; Rampnoux, Jean-Michel; Jorez, Sébastien; Claeys, Wilfrid

    2004-03-01

    We propose in this paper an in-depth study of a method, both experimental and theoretical, for the determination of thermoelectric properties, in single, or multi-layered thermoelectric devices. We use a modulated laser beam as a heater in order to generate a thermally induced Seebeck EMF. The laser beam, line shaped, can be focused at any location along the sample surface, allowing spatially resolved measurements. Seebeck EMF measurements, associated with a versatile modeling method based on the thermal quadrupoles, allow determining sample Seebeck EMF profile. We contemplate to apply this technique to thermal and thermoelectric properties identification.

  20. Optical limiter with an organic solution sandwiched between a polymer slab and a polymer grating

    SciTech Connect

    Chen Ming; Li Chunfei; Zhang Yundong; Xu Mai; Ma Shaojie; Wang Weibiao; Xia Yuxue

    2005-08-10

    An optical limiter was designed and fabricated. The device consists of an organic solution sandwiched between a polymer slab and a transparent relief polymer grating with a triangular groove. At low power the device has a high transmittance because the refractive index of the solution is matched with those of the slab and the grating materials and because the grating does not diffract. However, high power makes the organic solution thermally vaporize and makes the indices of the solution, slab, and grating materials become mismatched, which causes the grating to appear. The incident light is strongly absorbed, scattered, and self-defocused by the organic solution, and the grating suppresses the zero-order diffraction. Thus the transmitted light energy becomes lower than the damage threshold of human eyes or optical sensors. The device is an effective protection for human eyes or optical sensors against broadband pulsed-laser damage.

  1. Electromagnetically induced classical and quantum Lau effect

    NASA Astrophysics Data System (ADS)

    Qiu, Tianhui; Yang, Guojian; Xiong, Jun; Xu, Deqin

    2016-07-01

    We present two schemes of Lau effect for an object, an electromagnetically induced grating generated based on the electromagnetically induced effect. The Lau interference pattern is detected either directly in the way of the traditional Lau effect measurement with a classical thermal light being the imaging light, or indirectly and nonlocally in the way of two-photon coincidence measurement with a pair of entangled photons being the imaging light.

  2. Fiber-matrix interface effects in the presence of thermally induced residual stresses

    SciTech Connect

    Nimmer, R.P. )

    1990-01-01

    The mechanics of transversely loaded high-temperature composites with a thermally induced residual stress field and a vanishingly weak fiber-matrix interface strength was investigated using two analytical models. In particular, the effects of several physical properties defining the performance of the constituent fiber, matrix, and interface are examined relative to their effect on composite's behavior. Both models demonstrate that, if there is a thermally induced residual stress field in the composite, the initial transverse modulus for the composite will be the same regardless of whether there is a well-bonded or an unbonded interface. 10 refs.

  3. Emergence of self-organized long-period fiber gratings in supercontinuum-generating optical fibers

    PubMed Central

    Tu, Haohua; Liang, Xing; Marks, Daniel L.; Boppart, Stephen A.

    2010-01-01

    A localized long-period fiber grating emerges in a silica optical fiber transmitting femtosecond pulse-induced supercontinuum. Simultaneously, a specific higher-order fiber cladding mode associated with the grating gains amplification at the expense of the fiber core mode. The grating has a period dependent on the dielectric structure of the fiber and is therefore classified as a self-organized structure. PMID:19252587

  4. Radiation Induced Degradation of White Thermal Control Paint

    NASA Technical Reports Server (NTRS)

    Edwards, D. L.; Zwiener, J. M.; Wertz, G. E.; Vaughn, Jason A.; Kamenetzky, Rachel R.; Finckenor, M. M.; Meshishnek, M. J.

    1999-01-01

    This paper details a comparison analysis of the zinc-oxide pigmented white thermal control paints Z-93 and Z-93P. Both paints were simultaneously exposed to combined space environmental effects and analyzed using an in-vacuo reflectance technique. The dose applied to the paints was approximately equivalent to 5 yr in a geosynchronous orbit. This comparison analysis showed that Z-93P is an acceptable substitute for Z-93. Irradiated samples of Z-93 and Z-93P were subjected to additional exposures of ultraviolet (UV) radiation and analyzed using the in-vacuo reflectance technique to investigate UV activated reflectance recovery. Both samples showed minimal UV activated reflectance recovery after an additional 190 equivalent Sun hour (ESH) exposure. Reflectance response utilizing nitrogen as a repressurizing gas instead of air was also investigated. This investigation found the rates of reflectance recovery when repressurized with nitrogen are slower than when repressurized with air.

  5. Thermally induced nonlinear optical absorption in metamaterial perfect absorbers

    NASA Astrophysics Data System (ADS)

    Guddala, Sriram; Kumar, Raghwendra; Ramakrishna, S. Anantha

    2015-03-01

    A metamaterial perfect absorber consisting of a tri-layer (Al/ZnS/Al) metal-dielectric-metal system with top aluminium nano-disks was fabricated by laser-interference lithography and lift-off processing. The metamaterial absorber had peak resonant absorbance at 1090 nm and showed nonlinear absorption for 600ps laser pulses at 1064 nm wavelength. A nonlinear saturation of reflectance was measured to be dependent on the average laser power incident and not the peak laser intensity. The nonlinear behaviour is shown to arise from the heating due to the absorbed radiation and photo-thermal changes in the dielectric properties of aluminium. The metamaterial absorber is seen to be damage resistant at large laser intensities of 25 MW/cm2.

  6. Thermally induced nonlinear optical absorption in metamaterial perfect absorbers

    SciTech Connect

    Guddala, Sriram Kumar, Raghwendra; Ramakrishna, S. Anantha

    2015-03-16

    A metamaterial perfect absorber consisting of a tri-layer (Al/ZnS/Al) metal-dielectric-metal system with top aluminium nano-disks was fabricated by laser-interference lithography and lift-off processing. The metamaterial absorber had peak resonant absorbance at 1090 nm and showed nonlinear absorption for 600ps laser pulses at 1064 nm wavelength. A nonlinear saturation of reflectance was measured to be dependent on the average laser power incident and not the peak laser intensity. The nonlinear behaviour is shown to arise from the heating due to the absorbed radiation and photo-thermal changes in the dielectric properties of aluminium. The metamaterial absorber is seen to be damage resistant at large laser intensities of 25 MW/cm{sup 2}.

  7. Radiation Induced Degradation of White Thermal Control Paint

    NASA Technical Reports Server (NTRS)

    Edwards, D. L.; Zwiener, J. M.; Wertz, G. E.; Vaughn, J. A.; Kamenetzky, R. R.; Finckenor, M. M.; Meshishnek, M. J.

    1998-01-01

    This paper details a comparison analysis of the Zinc Oxide pigmented white thermal control paints Z-93 and Z-93P. Both paints were simultaneously exposed to combined space environmental effects and analyzed using an in-vacuum reflectance technique. The dose applied to the paints was approximately equivalent to 5 years in a geosynchronous orbit. This comparison analysis showed that Z-93P is an acceptable substitute for Z-93. Irradiated samples of Z-93 and Z-93P were subjected to additional exposures of ultraviolet (UV) radiation and analyzed using the in-vacuum reflectance technique to investigate UV activated reflectance recovery. Both samples showed minimal UV activated reflectanc6 recovery after an additional 190 Equivalent Sun Hour (ESH) exposure. Reflectance response utilizing nitrogen as a repressurizing gas instead of air was also investigated. This investigation found the rates of reflectance recovery when repressurized with nitrogen are slower than when repressurized with air.

  8. Radiation Induced Degradation of White Thermal Control Paint

    NASA Technical Reports Server (NTRS)

    Edwards, D. L.; Zwiener, J. M.; Wertz, G. E.; Vaughn, Jason A.; Kamenetzky, Rachel R.; Finckenor, M. M.; Meshishnek, M. J.

    1998-01-01

    This paper details a comparison analysis of the zinc-oxide pigmented white thermal control paints Z-93 and Z-93P. Both paints were simultaneously exposed to combined space environmental effects and analyzed using an in-vacuo reflectance technique. The dose applied to the paints was approximately equivalent to 5 yr in a geosynchronous orbit. This comparison analysis showed that Z-93P is an acceptable substitute for Z-93. Irradiated samples of Z-93 and Z-93P were subjected to additional exposures of ultraviolet (UV) radiation and analyzed using the in-vacuo reflectance technique to investigate UV activated reflectance recovery. Both samples showed minimal UV activated reflectance recovery after an additional 190 equivalent Sun hour (ESH) exposure. Reflectance response utilizing nitrogen as a repressurizing gas instead of air was also investigated. This investigation found the rates of reflectance recovery when repressurized with nitrogen are slower than when repressurized with air.

  9. Thermally induced native defect transform in annealed GaSb

    NASA Astrophysics Data System (ADS)

    Jie, Su; Tong, Liu; Jing-Ming, Liu; Jun, Yang; Yong-Biao, Bai; Gui-Ying, Shen; Zhi-Yuan, Dong; Fang-Fang, Wang; You-Wen, Zhao

    2016-07-01

    Undoped p-type GaSb single crystals were annealed at 550–600 °C for 100 h in ambient antimony. The annealed GaSb samples were investigated by Hall effect measurement, glow discharge mass spectroscopy (GDMS), infrared (IR) optical transmission and photoluminescence (PL) spectroscopy. Compared with the as-grown GaSb single crystal, the annealed GaSb samples have lower hole concentrations and weak native acceptor related PL peaks, indicating the reduction of the concentration of gallium antisite related native acceptor defects. Consequently, the below gap infrared transmission of the GaSb samples is enhanced after the thermal treatment. The mechanism about the reduction of the native defect concentration and its influence on the material property were discussed. Project supported by the National Natural Science Foundation of China (Grant Nos. 61474104 and 61504131).

  10. Thermal annealing-induced electric dipole relaxation in natural alexandrite

    NASA Astrophysics Data System (ADS)

    Scalvi, Rosa M. Fernandes; Li, Maximo Siu; Scalvi, Luis V. A.

    2005-02-01

    Electrical properties of natural alexandrite (BeAl2O4:Cr3+) are investigated by the thermally stimulated depolarization current (TSDC) technique. Samples are submitted to consecutive annealing processes and TSDC is carried out after each annealing, yielding bands with different parameters. These bands are fitted by a continuous distribution of relaxation parameters: activation energy and pre-exponential factor of the Arrhenius equation. It has been observed that annealing influences the dipole relaxation behavior, since it promotes a modification of Fe3+ and Cr3+ impurity distributions on sites of distinct symmetry: Al1 and Al2. In order to have a reference for comparison, TSDC is also carried out on a synthetic alexandrite sample, where the only impurity present is Cr3+ ion.

  11. Analysis of thermally induced permeability enhancement in geothermal injection wells

    SciTech Connect

    Benson, S.M.; Daggett, J.S.; Iglesias, E.; Arellano, V.; Ortiz-Ramirez, J.

    1987-02-01

    Reinjection of spent geothermal brine is a common means of disposing of geothermal effluents and maintaining reservoir pressures. Contrary to the predictions of two-fluid models (two-viscosity) of nonisothermal injection, an increase of injectivity, with continued injection, is often observed. Injectivity enhancement and thermally-affected pressure transients are particularly apparent in short-term injection tests at the Los Azufres Geothermal Field, Mexico. During an injection test, it is not uncommon to observe that after an initial pressure increase, the pressure decreases with time. As this typically occurs far below the pressure at which hydraulic fracturing is expected, some other mechanism for increasing the near-bore permeability must explain the observed behavior. This paper focuses on calculating the magnitude of the nearbore permeability changes observed in several nonisothermal injection tests conducted at the Los Azufres Geothermal Field.

  12. Humidity and temperature response of photopolymer-based holographic gratings

    NASA Astrophysics Data System (ADS)

    Mikulchyk, Tatsiana; Walshe, James; Cody, Dervil; Martin, Suzanne; Naydenova, Izabela

    2015-05-01

    Holographic sensors have significant potential in various applications ranging from in vitro diagnostics to optical security. They are capable of providing fast, real-time, reversible or irreversible, visual colorimetric or optical readouts. The main challenge in the development of holographic sensors is to improve their selectivity by functionalizing the holographic recording material and achieve a response to a specific analyte. This material should be permeable to the analyte and its properties should change under exposure to the analyte. This work explores the humidity and temperature response of volume phase gratings recorded in photopolymers containing acrylamide and diacetone acrylamide as monomers, and triethanolamine and N-phenylglycine as photoinitiators. Characterization of the humidity response of photopolymer-based gratings in the relative humidity (RH) range of 20-90 % was carried out by measuring the diffraction efficiency of slanted transmission gratings and the position of the maximum intensity in the spectral response of reflection gratings. A strong humidity dependence of the diffraction efficiency of diacetone acrylamide-based transmission gratings was observed at RH=20-90%. The humidity dependence of the spectral response of the reflection gratings showed that photopolymers containing triethanolamine are more hydrophilic than photopolymers containing N-phenylglycine. The temperature response of slanted transmission gratings was investigated in the temperature (T) range of 20-60 °C. Exposure of the photopolymer layers containing triethanolamine to elevated temperature showed that the observed Bragg angle shift was caused by layer shrinkage due to water evaporation. The application of a sealing technique allowed for the observation of the photopolymer layer swelling due to the layer's thermal expansion. The results demonstrate an effective approach to obtaining photopolymer-based gratings with tuneable temperature and humidity sensitivity.

  13. ATLAST ULE mirror segment performance analytical predictions based on thermally induced distortions

    NASA Astrophysics Data System (ADS)

    Eisenhower, Michael J.; Cohen, Lester M.; Feinberg, Lee D.; Matthews, Gary W.; Nissen, Joel A.; Park, Sang C.; Peabody, Hume L.

    2015-09-01

    The Advanced Technology Large-Aperture Space Telescope (ATLAST) is a concept for a 9.2 m aperture space-borne observatory operating across the UV/Optical/NIR spectra. The primary mirror for ATLAST is a segmented architecture with pico-meter class wavefront stability. Due to its extraordinarily low coefficient of thermal expansion, a leading candidate for the primary mirror substrate is Corning's ULE® titania-silicate glass. The ATLAST ULE® mirror substrates will be maintained at `room temperature' during on orbit flight operations minimizing the need for compensation of mirror deformation between the manufacturing temperature and the operational temperatures. This approach requires active thermal management to maintain operational temperature while on orbit. Furthermore, the active thermal control must be sufficiently stable to prevent time-varying thermally induced distortions in the mirror substrates. This paper describes a conceptual thermal management system for the ATLAST 9.2 m segmented mirror architecture that maintains the wavefront stability to less than 10 pico-meters/10 minutes RMS. Thermal and finite element models, analytical techniques, accuracies involved in solving the mirror figure errors, and early findings from the thermal and thermal-distortion analyses are presented.

  14. Thermally induced changes in dynamic mechanical properties of native silks.

    PubMed

    Guan, Juan; Porter, David; Vollrath, Fritz

    2013-03-11

    Dynamic mechanical thermal analysis (DMTA) on individual native silk fibers demonstrates changes in the dynamic mechanical properties of storage modulus and loss tangent as a function of temperature and temperature history ranging from -100 to 250 °C. These property changes are linked quantitatively to two main types of change in the silk structure. First, the evaporation of water with increasing temperature up to 100 °C increases the storage modulus and removes two characteristic loss tangent peaks at -60 and +60 °C. Second, various discrete loss tangent peaks in the range 150-220 °C are associated with specific disordered silk structures that are removed or converted to a limiting high-temperature relaxed structure by the combination of increasing temperature and static load in the DMTA tests. The results identify important origins of silk filament quality based on the analysis of measurements that can be traced back to differences in production and processing history. PMID:23405856

  15. Fibre gratings and their applications

    SciTech Connect

    Vasil'ev, Sergei A; Medvedkov, O I; Korolev, I G; Bozhkov, A S; Kurkov, Andrei S; Dianov, Evgenii M

    2005-12-31

    A brief review is given of the state of the art in the research on the photosensitivity of fibres and photoinduced fibre gratings. The most important properties of fibre gratings are considered and the main methods of their production and their applications are discussed. The photosensitive compositions of silica glasses are presented and methods for increasing their photosensitivity are indicated. (review)

  16. Recurrent acute thermal lesion induces esophageal hyperproliferative premalignant lesions in mice esophagus.

    PubMed

    Rapozo, D C M; Blanco, T C M; Reis, B B; Gonzaga, I M; Valverde, P; Canetti, C; Barja-Fidalgo, C; Simao, T A; Albano, R M; Kruel, C D P; Ribeiro Pinto, L F

    2016-04-01

    Hot beverage consumption is a risk factor for esophageal squamous cell carcinoma, but the underlying mechanisms are still unknown. We developed an experimental mouse model to understand the mechanism of thermal lesion to esophageal carcinogenesis. Female BALB/c mice were treated by gavage with water at different temperatures three times a week and nitrosamines in the drinking water. Water at 70°C, but not at lower temperatures, initially induced an esophageal necrosis that healed and became resistant to necrosis after further administrations. However, when 70°C water was associated with N-nitrosodiethylamine at doses above 1ppm, there was interference in epithelial regeneration, allowing recurrent thermal injury and inflammation. Recurrent thermal injury resulted in hyper proliferative premalignant lesions being induced earlier (at 4weeks) and at a higher frequency (4-fold increase at 16weeks) when compared to mice treated with NDEA only. Ki-67 immunostaining revealed that recurrent thermal injury induced basal cell proliferation resulting in the expansion of epithelial basal cells, confirmed by the increase in cytokeratin 14 positive cells with concomitant reduction of differentiated cytokeratin 5 positive cells. We conclude that recurrent thermal lesion may act as a tumor promoter though a strong proliferation stimulus of esophageal epithelial basal cells. PMID:26899552

  17. Molecular Dynamics Studies of Thermal Induced Chemistry in Tatb

    NASA Astrophysics Data System (ADS)

    Quenneville, J.; Germann, T. C.; Thompson, A. P.; Kober, E. M.

    2007-12-01

    A reactive force field (ReaxFF) is used with molecular dynamics to probe the chemistry induced by intense heating (`accelerated cook-off') of 1,3,5-triamino-2,4,6-trinitrobenzene (TATB). Large-system simulations are desired for TATB because of the high degree of carbon clustering expected in this material. Using small, 32-molecule simulations, we calculate the reaction rate as a function of temperature and compare the Arrhenius-predicted activation energy with experiment. Decomposition product evolution (mainly N2, H2O, CO2 and graphitic carbon clusters) is followed using a 576-molecule larger simulation, which also illustrates the effect of system size on both carbon clustering and reaction rate.

  18. Phononic crystal diffraction gratings

    NASA Astrophysics Data System (ADS)

    Moiseyenko, Rayisa P.; Herbison, Sarah; Declercq, Nico F.; Laude, Vincent

    2012-02-01

    When a phononic crystal is interrogated by an external source of acoustic waves, there is necessarily a phenomenon of diffraction occurring on the external enclosing surfaces. Indeed, these external surfaces are periodic and the resulting acoustic diffraction grating has a periodicity that depends on the orientation of the phononic crystal. This work presents a combined experimental and theoretical study on the diffraction of bulk ultrasonic waves on the external surfaces of a 2D phononic crystal that consists of a triangular lattice of steel rods in a water matrix. The results of transmission experiments are compared with theoretical band structures obtained with the finite-element method. Angular spectrograms (showing frequency as a function of angle) determined from diffraction experiments are then compared with finite-element simulations of diffraction occurring on the surfaces of the crystal. The experimental results show that the diffraction that occurs on its external surfaces is highly frequency-dependent and has a definite relation with the Bloch modes of the phononic crystal. In particular, a strong influence of the presence of bandgaps and deaf bands on the diffraction efficiency is found. This observation opens perspectives for the design of efficient phononic crystal diffraction gratings.

  19. Radiation combined with thermal injury induces immature myeloid cells.

    PubMed

    Mendoza, April Elizabeth; Neely, Crystal Judith; Charles, Anthony G; Kartchner, Laurel Briane; Brickey, Willie June; Khoury, Amal Lina; Sempowski, Gregory D; Ting, Jenny P Y; Cairns, Bruce A; Maile, Robert

    2012-11-01

    The continued development of nuclear weapons and the potential for thermonuclear injury necessitates the further understanding of the immune consequences after radiation combined with injury (RCI). We hypothesized that sublethal ionization radiation exposure combined with a full-thickness thermal injury would result in the production of immature myeloid cells. Mice underwent either a full-thickness contact burn of 20% total body surface area or sham procedure followed by a single whole-body dose of 5-Gy radiation. Serum, spleen, and peripheral lymph nodes were harvested at 3 and 14 days after injury. Flow cytometry was performed to identify and characterize adaptive and innate cell compartments. Elevated proinflammatory and anti-inflammatory serum cytokines and profound leukopenia were observed after RCI. A population of cells with dual expression of the cell surface markers Gr-1 and CD11b were identified in all experimental groups, but were significantly elevated after burn alone and RCI at 14 days after injury. In contrast to the T-cell-suppressive nature of myeloid-derived suppressor cells found after trauma and sepsis, myeloid cells after RCI augmented T-cell proliferation and were associated with a weak but significant increase in interferon γ and a decrease in interleukin 10. This is consistent with previous work in burn injury indicating that a myeloid-derived suppressor cell-like population increases innate immunity. Radiation combined injury results in the increase in distinct populations of Gr-1CD11b cells within the secondary lymphoid organs, and we propose these immature inflammatory myeloid cells provide innate immunity to the severely injured and immunocompromised host. PMID:23042190

  20. Radiation Combined with Thermal Injury Induces Immature Myeloid Cells

    PubMed Central

    Mendoza, April Elizabeth; Neely, Crystal Judith; Charles, Anthony G.; Kartchner, Laurel Briane; Brickey, Willie June; Khoury, Amal Lina; Sempowski, Gregory D.; Ting, Jenny P.Y.; Cairns, Bruce A.; Maile, Robert

    2012-01-01

    The continued development of nuclear weapons and the potential for thermonuclear injury necessitates the further understanding of the immune consequences after radiation combined with injury (RCI). We hypothesized that sub-lethal ionization radiation exposure combined with a full thickness thermal injury would result in the production of immature myeloid cells. Mice underwent either a 20% total body surface area (TBSA) full-thickness contact burn or sham procedure followed by a single whole body dose of 5-Gy radiation. Serum, spleen and peripheral lymph nodes were harvested at 3 and 14 days post-injury. Flow cytometry was performed to identify and characterize adaptive and innate cell compartments. Elevated pro- and anti-inflammatory serum cytokines and profound leukopenia were observed after RCI. A population of cells with dual expression of the cell surface markers Gr-1 and CD11b were identified in all experimental groups, but was significantly elevated after burn alone and RCI at 14 days post-injury. In contrast to the T-cell suppressive nature of myeloid-derived suppressor cells (MDSC) found after trauma and sepsis, myeloid cells after RCI augmented T-cell proliferation and were associated with a weak but significant increase in IFN-γ and a decrease in IL-10. This is consistent with previous work in burn injury indicating that a MDSC-like population increases innate immunity. RCI results in the increase of distinct populations of Gr-1+ CD11b+cells within the secondary lymphoid organs, and we propose these immature inflammatory myeloid cells provide innate immunity to the severely injured and immunocompromised host. PMID:23042190

  1. Long period gratings coated with hafnium oxide by plasma-enhanced atomic layer deposition for refractive index measurements.

    PubMed

    Melo, Luis; Burton, Geoff; Kubik, Philip; Wild, Peter

    2016-04-01

    Long period gratings (LPGs) are coated with hafnium oxide using plasma-enhanced atomic layer deposition (PEALD) to increase the sensitivity of these devices to the refractive index of the surrounding medium. PEALD allows deposition at low temperatures which reduces thermal degradation of UV-written LPGs. Depositions targeting three different coating thicknesses are investigated: 30 nm, 50 nm and 70 nm. Coating thickness measurements taken by scanning electron microscopy of the optical fibers confirm deposition of uniform coatings. The performance of the coated LPGs shows that deposition of hafnium oxide on LPGs induces two-step transition behavior of the cladding modes. PMID:27137052

  2. 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.

  3. Thermal effusivity: a promising imaging biomarker to predict radiation-induced skin injuries.

    SciTech Connect

    Chu, J. C. H.; Templeton, A.; Yao, R.; Griem, K. L.; Sun, J. G.

    2012-01-01

    An effective screening technology is needed to triage individuals at the time of radiation incidents involving a large population. Three-dimensional thermal tomography is a relatively new development in active thermal imaging technology that produces cross-sectional images based on the subject's ability to transfer heat thermal effusivity at the voxel level. This noninvasive imaging modality has been used successfully in nondestructive examination of complex materials; also it has been shown to predict the severity of radiation-induced skin injuries several days before the manifestation of severe moist desquamations or blister formation symptoms in mice at 40 Gy. If these results are confirmed at lower dose levels in human subjects, a thermal tomography imaging device may be an ideal screening tool in radiation emergencies. This imaging method is non-invasive, relatively simple, easily adaptable for field use, and when properly deployed, it will enhance public emergency preparedness for incidents involving unexpected radiation exposure.

  4. Thermally induced phase transitions and morphological changes in organoclays.

    PubMed

    Gelfer, M; Burger, C; Fadeev, A; Sics, I; Chu, B; Hsiao, B S; Heintz, A; Kojo, K; Hsu, S L; Si, M; Rafailovich, M

    2004-04-27

    Thermal transitions and morphological changes in Cloisite organoclays were investigated by differential scanning calorimetry (DSC), thermogravimetric analysis (TGA), Fourier transform infrared (FTIR) spectroscopy, and in situ simultaneous small-angle X-ray scattering (SAXS) and wide-angle X-ray diffraction (WAXD) over the temperature range of 30-260 degrees C. On the basis of DSC and FTIR results, the surfactant component in organoclays was found to undergo a melting-like order-disorder transition between 35 and 50 degrees C. The transition temperatures of the DSC peaks (Ttr) in the organoclays varied slightly with the surfactant content; however, they were significantly lower than the melting temperature of the free surfactant (dimethyldihydrotallowammonium chloride; Tm = 70 degrees C). FTIR results indicated that within the vicinity of Ttr, the gauche content increased significantly in the conformation of surfactant molecules, while WAXD results did not show any change in three-dimensional ordering. Multiple scattering peaks were observed in SAXS profiles. In the SAXS data acquired below Ttr, the second scattering peak was found to occur at an angle lower than twice that of the first peak position (i.e., nonequidistant scattering maxima). In the data acquired above Ttr, the second peak was found to shift toward the equidistant position (the most drastic shift was seen in the system with the highest surfactant content). Using a novel SAXS modeling technique, we suggest that the appearance of nonequidistant SAXS maxima could result from a bimodal layer thickness distribution of the organic layers in organoclays. The occurrence of the equidistant scattering profile above Ttr could be explained by the conversion of the bimodal distribution to the unimodal distribution, indicating a redistribution of the surfactant that is nonbounded to the clay surface. At temperatures above 190 degrees C, the scattering maxima gradually broadened and became nonequidistant again but

  5. Correction: Decrease in thermal conductivity in polymeric P3HT nanowires by size-reduction induced by crystal orientation: new approaches towards thermal transport engineering of organic materials.

    PubMed

    Muñoz Rojo, Miguel; Martín, Jaime; Grauby, Stéphane; Borca-Tasciuc, Theodorian; Dilhaire, Stefan; Martin-Gonzalez, Marisol

    2015-03-01

    Correction for 'Decrease in thermal conductivity in polymeric P3HT nanowires by size-reduction induced by crystal orientation: new approaches towards thermal transport engineering of organic materials' by Miguel Muñoz Rojo et al., Nanoscale, 2014, 6, 7858-7865. PMID:25668105

  6. Bandwidth-Tunable Fiber Bragg Gratings Based on UV Glue Technique

    NASA Astrophysics Data System (ADS)

    Fu, Ming-Yue; Liu, Wen-Feng; Chen, Hsin-Tsang; Chuang, Chia-Wei; Bor, Sheau-Shong; Tien, Chuen-Lin

    2007-07-01

    In this study, we have demonstrated that a uniform fiber Bragg grating (FBG) can be transformed into a chirped fiber grating by a simple UV glue adhesive technique without shifting the reflection band with respect to the center wavelength of the FBG. The technique is based on the induced strain of an FBG due to the UV glue adhesive force on the fiber surface that causes a grating period variation and an effective index change. This technique can provide a fast and simple method of obtaining the required chirp value of a grating for applications in the dispersion compensators, gain flattening in erbium-doped fiber amplifiers (EDFAs) or optical filters.

  7. Distributed feedback sol-gel zirconia waveguide lasers based on surface relief gratings

    NASA Astrophysics Data System (ADS)

    Ye, Chao; Wong, K. Y.; He, Yaning; Wang, Xiaogang

    2007-02-01

    Distributed feedback waveguide lasers based on dye-doped sol-gel zirconia films with permanent grating structures were demonstrated. The permanent grating was realized by employing a novel epoxy-based azo-polymer that generates a surface relief grating by a photo-isomerization process induced by two interfering writing beams. When employing the rhodamine 6G dye, tuning of the output wavelength of the distributed feedback waveguide laser from around 575 nm to 610 nm can be achieved by adjusting the tilting angle between the orientation of the grating and the pump beam.

  8. Type IIa Bragg grating based ultra-short DBR fiber laser with high temperature resistance.

    PubMed

    Ran, Yang; Feng, Fu-Rong; Liang, Yi-Zhi; Jin, Long; Guan, Bai-Ou

    2015-12-15

    We report on the fabrication of a thermally resistant ultra-short distributed Bragg reflector (DBR) fiber laser based on the photo inscription of two wavelength-matched type IIa gratings in a thin-core Er-doped fiber. With continuous UV exposure, each Bragg reflector initially grows as a type I grating, followed by decay in strength, and then re-grows as a type IIa grating with enhanced thermal resistance. The DBR laser, with an entire length of 13 mm, can stably operate at 600°C with single longitude mode, which provides potential applications in high temperature environments. PMID:26670491

  9. Pressure-induced reversal between thermal contraction and expansion in ferroelectric PbTiO3

    NASA Astrophysics Data System (ADS)

    Zhu, Jinlong; Zhang, Jianzhong; Xu, Hongwu; Vogel, Sven C.; Jin, Changqing; Frantti, Johannes; Zhao, Yusheng

    2014-01-01

    Materials with zero/near zero thermal expansion coefficients are technologically important for applications in thermal management and engineering. To date, this class of materials can only be produced by chemical routes, either by changing chemical compositions or by composting materials with positive and negative thermal expansion. Here, we report for the first time a physical route to achieve near zero thermal expansion through application of pressure. In the stability field of tetragonal PbTiO3 we observed pressure-induced reversals between thermal contraction and expansion between ambient pressure and 0.9 GPa. This hybrid behavior leads to a mathematically infinite number of crossover points in the pressure-volume-temperature space and near-zero thermal expansion coefficients comparable to or even smaller than those attained by chemical routes. The observed pressures for this unusual phenomenon are within a small range of 0.1-0.9 GPa, potentially feasible for designing stress-engineered materials, such as thin films and nano-crystals, for thermal management applications.

  10. Pressure-induced reversal between thermal contraction and expansion in ferroelectric PbTiO3.

    PubMed

    Zhu, Jinlong; Zhang, Jianzhong; Xu, Hongwu; Vogel, Sven C; Jin, Changqing; Frantti, Johannes; Zhao, Yusheng

    2014-01-01

    Materials with zero/near zero thermal expansion coefficients are technologically important for applications in thermal management and engineering. To date, this class of materials can only be produced by chemical routes, either by changing chemical compositions or by composting materials with positive and negative thermal expansion. Here, we report for the first time a physical route to achieve near zero thermal expansion through application of pressure. In the stability field of tetragonal PbTiO3 we observed pressure-induced reversals between thermal contraction and expansion between ambient pressure and 0.9 GPa. This hybrid behavior leads to a mathematically infinite number of crossover points in the pressure-volume-temperature space and near-zero thermal expansion coefficients comparable to or even smaller than those attained by chemical routes. The observed pressures for this unusual phenomenon are within a small range of 0.1-0.9 GPa, potentially feasible for designing stress-engineered materials, such as thin films and nano-crystals, for thermal management applications. PMID:24424396

  11. Diffractive coherence in multilayer dielectric gratings

    SciTech Connect

    Shore, B.W.; Feit, M.D.; Perry, M.D.; Boyd, R.D.; Britten, J.A.; Li, Lifeng

    1995-05-26

    Successful operation of large-scale high-power lasers, such as those in use and planned at LLNL and elsewhere, require optical elements that can withstand extremely high fluences without suffering damage. Of particular concern are dielectric diffraction gratings used for beam sampling and pulse compression. Laser induced damage to bulk dielectric material originates with coupling of the electric field of the radiation to bound electrons, proceeding through a succession of mechanisms that couple the electron kinetic energy to lattice energy and ultimately to macroscopic structural changes (e.g. melting). The constructive interference that is responsible for the diffractive behavior of a grating or the reflective properties of a multilayer dielectric stack can enhance the electric field above values that would occur in unstructured homogeneous material. Much work has been done to model damage to bulk matter. The presence of nonuniform electric fields, resulting from diffractive coherence, has the potential to affect damage thresholds and requires more elaborate theory. We shall discuss aspects of work directed towards understanding the influence of dielectric structures upon damage, with particular emphasis on computations and interpretation of electric fields within dielectric gratings and multilayer dielectric stacks, noting particularly the interference effects that occur in these structures.

  12. Thermally-induced microstructural changes in a three-way automotive catalyst

    SciTech Connect

    More, K.L.; Kenik, E.A.; Coffey, D.W.; Geer, T.S.; Theis, J.; LaBarge, W.; Beckmeyer, R.

    1997-12-01

    The use of advanced electron microscopy techniques to characterize both the bulk and near-atomic level microstructural evolution of catalyst materials during different dynamometer/vehicle aging cycles is an integral part of understanding catalyst deactivation. The study described here was undertaken to evaluate thermally-induced microstructural changes which caused the progressive loss of catalyst performance in a three-way automotive catalyst. Several different catalyst processing variables, for example changing the washcoat ceria content, were also evaluated as a function of aging cycle and thermal history. A number of thermally-induced microstructural changes were identified using high resolution electron microscopy techniques that contributed to the deactivation of the catalyst, including sintering of all washcoat constituents, {gamma}-alumina transforming to {alpha}-, {beta}-, and {delta}-alumina, precious metal redistribution, and constituent encapsulation. The data accumulated in this study have been used to correlate microstructural evolution with thermal history and catalyst performance during various aging cycles and to subsequently evaluate different washcoat formulations for increased thermal stability.

  13. Molecular alignment in molecular fluids induced by coupling between density and thermal gradients.

    PubMed

    Daub, Christopher D; Tafjord, Joakim; Kjelstrup, Signe; Bedeaux, Dick; Bresme, Fernando

    2016-04-28

    We investigate, using non-equilibrium molecular dynamics simulations and theory, the response of molecular fluids confined in slit pores under the influence of a thermal gradient and/or an applied force. The applied force which has the same functional form as a gravitational force induces an inhomogeneous density in the confined fluid, which results in a net orientation of the molecules with respect to the direction of the force. The orientation is qualitatively similar to that induced by a thermal gradient. We find that the average degree of orientation is proportional to the density gradient of the fluid in the confined region and that the orientation increases with the magnitude of the force. The concurrent application of the external force and the thermal gradient allows us to disentangle the different mechanisms leading to the thermal orientation of molecular fluids. One mechanism is connected to the density variation of the fluid, while the second mechanism can be readily observed in molecular fluids consisting of molecules with mass or size asymmetry, even in the absence of a density gradient, hence it is connected to the application of the thermal gradient only. PMID:27079162

  14. Birefringence compensation of two tandem-set Nd:YAG rods with different thermally induced features

    NASA Astrophysics Data System (ADS)

    Wang, You; Inoue, Koichi; Kan, Hirofumi; Ogawa, Takayo; Wada, Satoshi

    2009-12-01

    How to reduce the thermally induced effects in a solid-state rod is a critical assignment for the applications of high-powered diode-pumped solid-state lasers (DPSSLs). In this paper, we study the birefringence compensation in a solid-state laser system containing two tandem-set Nd:YAG rods with different thermally induced characteristics. By reason of the uneven emission wavelengths of the pump LDs, the thermal focal length of one Nd:YAG rod is about 1.3 times as much as that of the other in our study. Using a 90° quartz rotator and a pair of coupling lenses, we investigated the depolarization dependence on different laser structures. It has been found that the birefringence in two laser rods with such different thermally induced features can be excellently reduced by adopting an optimized lens configuration which is not a traditional telescope image system as usually adopted by many researchers. Both the theoretical analyses and the experimental results have demonstrated the performance of our approach. The conclusions have been thought to be useful for constructing a high-average-power laser oscillator with a near- TEM00 mode.

  15. Feasibility of using Nakagami distribution in evaluating the formation of ultrasound-induced thermal lesions.

    PubMed

    Zhang, Siyuan; Zhou, Fanyu; Wan, Mingxi; Wei, Min; Fu, Quanyou; Wang, Xing; Wang, Supin

    2012-06-01

    The acoustic posterior shadowing effects of bubbles influence the accuracy for defining the location and range of ablated thermal lesions during focused ultrasound surgery when using ultrasonic monitoring imaging. This paper explored the feasibility of using Nakagami distribution to evaluate the ablated region induced by focused ultrasound exposures at different acoustic power levels in transparent tissue-mimicking phantoms. The mean value of the Nakagami parameter m was about 0.5 in the cavitation region and increased to around 1 in the ablated region. Nakagami images were not subject to significant shadowing effects of bubbles. Ultrasound-induced thermal lesions observed in the photos and Nakagami images were overshadowed by bubbles in the B-mode images. The lesion size predicted in the Nakagami images was smaller than that predicted in the photos due to the sub resolvable effect of Nakagami imaging at the interface. This preliminary study on tissue-mimicking phantom suggested that the Nakagami parameter m may have the potential use in evaluating the formation of ultrasound-induced thermal lesion when the shadowing effect of bubbles is strong while the thermal lesion was small. Further studies in vivo and in vitro will be needed to evaluate the potential application. PMID:22712954

  16. Thermal damages on the surface of a silicon wafer induced by a near-infrared laser

    NASA Astrophysics Data System (ADS)

    Choi, Sungho; Jhang, Kyung-Young

    2014-01-01

    Laser-induced thermal damages of a silicon wafer surface subjected to continuous near-infrared laser irradiation were investigated. Silicon wafer specimens were illuminated by a continuous-wave fiber laser beam (1070-nm wavelength) with irradiances from 93 to 186 W/cm2, and the surface morphology of each specimen was analyzed using optical microscopy. With increasing irradiance, straight cracks in the <110> direction appeared first, and partial melting and complete melting were subsequently observed. The mechanism of these laser-induced thermal damages in the silicon wafer surface was discussed with numerical analysis based on the heat transfer and thermoelasticity model. The irradiances initiating the cracking and melting were predicted by determining the irradiances in which the calculated thermal stress and temperature exceeded the corresponding limits of the fracture strength and melting point, respectively. These predictions agreed well with the experimental findings. Laser-induced thermal damages of the silicon wafer surface subjected to a continuous near-infrared laser irradiation were identified based on these investigations.

  17. Thermal conductivity of graphene with defects induced by electron beam irradiation

    NASA Astrophysics Data System (ADS)

    Malekpour, Hoda; Ramnani, Pankaj; Srinivasan, Srilok; Balasubramanian, Ganesh; Nika, Denis L.; Mulchandani, Ashok; Lake, Roger K.; Balandin, Alexander A.

    2016-07-01

    We investigate the thermal conductivity of suspended graphene as a function of the density of defects, ND, introduced in a controllable way. High-quality graphene layers are synthesized using chemical vapor deposition, transferred onto a transmission electron microscopy grid, and suspended over ~7.5 μm size square holes. Defects are induced by irradiation of graphene with the low-energy electron beam (20 keV) and quantified by the Raman D-to-G peak intensity ratio. As the defect density changes from 2.0 × 1010 cm-2 to 1.8 × 1011 cm-2 the thermal conductivity decreases from ~(1.8 +/- 0.2) × 103 W mK-1 to ~(4.0 +/- 0.2) × 102 W mK-1 near room temperature. At higher defect densities, the thermal conductivity reveals an intriguing saturation-type behavior at a relatively high value of ~400 W mK-1. The thermal conductivity dependence on the defect density is analyzed using the Boltzmann transport equation and molecular dynamics simulations. The results are important for understanding phonon - point defect scattering in two-dimensional systems and for practical applications of graphene in thermal management.We investigate the thermal conductivity of suspended graphene as a function of the density of defects, ND, introduced in a controllable way. High-quality graphene layers are synthesized using chemical vapor deposition, transferred onto a transmission electron microscopy grid, and suspended over ~7.5 μm size square holes. Defects are induced by irradiation of graphene with the low-energy electron beam (20 keV) and quantified by the Raman D-to-G peak intensity ratio. As the defect density changes from 2.0 × 1010 cm-2 to 1.8 × 1011 cm-2 the thermal conductivity decreases from ~(1.8 +/- 0.2) × 103 W mK-1 to ~(4.0 +/- 0.2) × 102 W mK-1 near room temperature. At higher defect densities, the thermal conductivity reveals an intriguing saturation-type behavior at a relatively high value of ~400 W mK-1. The thermal conductivity dependence on the defect density is

  18. Materials for damping the PTC-induced thermal fluctuations of the cold-head

    NASA Astrophysics Data System (ADS)

    Catarino, I.; Martins, D.; Sudiwala, R.

    2015-12-01

    The cold head on mechanical Pulse Tube Cryocoolers (PTCs) is subject to substantially less mechanical vibration and electromagnetic interference compared to that typically found in Gifford MacMahon coolers. However, thermal fluctuations at the PTC frequency are still present at the cold-head, typically at a level of 200 mK peak-to-peak at 1.4 Hz for a Cryomech Model PT405 cooler running at 4 K. It is highly desirable to damp out these fluctuations if PTCs are to be used successfully for running systems sensitive to such thermal fluctuations, for example, bolometeric detectors. We report here the characterization over the temperature range 2.5 K to 6 K of two materials, GOS (Gd2O2S) and GAP (GdAlO3), for use as low-pass thermal filters. These materials have antiferromagnetic transitions at around 4 K giving rise to an enhanced heat capacity and have a high thermal conductance. These are two highly desirable properties for thermal dampers in this application. Those materials were fired as ceramic discs to be tested as thermal dumpers. Thermal filter assemblies with discs of diameter 75 mm and thickness 2.5 mm and 1.6 mm (GOS and GAP, respectively) mounted in a PTC show thermal attenuation levels of x0.12 (GOS) and x0.11 (GAP) at 0.01Hz with a clean-side temperature of 4 K; the PTC induced fluctuations at 1.48 Hz are damped completely to within the noise limits (0.2 mK) of the thermometers. Experimentally determined thermal conductance and heat capacity data are reported. For this system, with a PTC cold-head (dirty-side) temperature of 3.3 K, a clean-side power dissipation of up to 30 mW is realized before its temperature rises above 4.2 K.

  19. Flexible gratings fabricated in polymeric plate using femtosecond laser irradiation

    NASA Astrophysics Data System (ADS)

    Park, Jung-Kyu; Cho, Sung-Hak

    2011-05-01

    Flexible gratings embedded in poly-dimethlysiloxane (PDMS) were fabricated using femtosecond laser pulses. Photo-induced gratings in a flexible PDMS plate were directly written by a high-intensity femtosecond (130 fs) Ti: Sapphire laser ( λp=800 nm). Refractive index modifications with 4 μm diameters were photo-induced after irradiation of the femtosecond pulses with peak intensities of more than 1×10 11 W/cm 2. The graded refractive index profile was fabricated to be symmetric around the center of the focal point. The diffraction efficiency of the grating samples is measured by an He-Ne laser. The maximum value of refractive index change (Δ n) in the laser-modified regions was estimated to be approximately 3.17×10 -3.

  20. Changes in laser-induced fluorescence responses of 3T3 fibroblasts to repetitive thermal stress

    NASA Astrophysics Data System (ADS)

    Beuthan, J.; Dressler, C.; Zabarylo, U.; Minet, O.

    2009-04-01

    The combined experimental use of laser-induced autofluorescence of cellular metabolites and methodological fundamentals of systems biology will provide access to biological thermal stress analysis on a sub cellular level. A test setup incorporating a pulsed nitrogen laser was realized with which autofluorescence of the coenzyme NADH could be measured in living 3T3 cells. The cells were subjected to different temperature stress at repetitive time intervals. When subjected to a simple mathematical analysis, the NADH concentration change measured through autofluorescence in biological cells exhibited approximate concentration-equivalent balance curves. These results add up to the fundamental know-how about the dosimetry of thermally therapeutic methods.

  1. Spin-pump-induced spin transport in a thermally evaporated pentacene film

    NASA Astrophysics Data System (ADS)

    Tani, Yasuo; Teki, Yoshio; Shikoh, Eiji

    2015-12-01

    We report the spin-pump-induced spin transport properties of a pentacene film prepared by thermal evaporation. In a palladium(Pd)/pentacene/Ni80Fe20 tri-layer sample, a pure spin-current is generated in the pentacene layer by the spin-pumping of Ni80Fe20, which is independent of the conductance mismatch problem in spin injection. The spin current is absorbed into the Pd layer, converted into a charge current with the inverse spin-Hall effect in Pd, and detected as an electromotive force. This is clear evidence for the pure spin current at room temperature in pentacene films prepared by thermal evaporation.

  2. Thermally-induced stresses in graphite-epoxy tubes coated with aluminum foil

    NASA Technical Reports Server (NTRS)

    Knott, Tamara W.; Hyer, M. W.

    1989-01-01

    Thermally-induced stresses in the foil, adhesive, and graphite-epoxy layers of composite tubes with aluminum foil bonded to the inner and outer surface are computed. The thermal effects are due to a temperature decrease from the processing temperature of the material to a temperature felt to represent the space environment, the intended operating environment of the tubes. Tubes fabricated from T300/934 and P75s/934 material systems are considered. The results indicate that the presence of the foil and adhesive have no detrimental effect on the stresses in the tube.

  3. Elastoplastic analysis of process induced residual stresses in thermally sprayed coatings

    SciTech Connect

    Chen Yongxiong; Liang Xiubing; Liu Yan; Xu Binshi

    2010-07-15

    The residual stresses induced from thermal spraying process have been extensively investigated in previous studies. However, most of such works were focused on the elastic deformation range. In this paper, an elastoplastic model for predicting the residual stresses in thermally sprayed coatings was developed, in which two main contributions were considered, namely the deposition induced stress and that due to differential thermal contraction between the substrate and coating during cooling. The deposition induced stress was analyzed based on the assumption that the coating is formed layer-by-layer, and then a misfit strain is accommodated within the multilayer structure after the addition of each layer (plastic deformation is induced consequently). From a knowledge of specimen dimensions, processing temperatures, and material properties, residual stress distributions within the structure can be determined by implementing the model with a simple computer program. A case study for the plasma sprayed NiCoCrAlY on Inconel 718 system was performed finally. Besides some similar phenomena observed from the present study as compared with previous elastic model reported in literature, the elastoplastic model also provides some interesting features for prediction of the residual stresses.

  4. Nakagami imaging for detecting thermal lesions induced by high-intensity focused ultrasound in tissue.

    PubMed

    Rangraz, Parisa; Behnam, Hamid; Tavakkoli, Jahan

    2014-01-01

    High-intensity focused ultrasound induces focalized tissue coagulation by increasing the tissue temperature in a tight focal region. Several methods have been proposed to monitor high-intensity focused ultrasound-induced thermal lesions. Currently, ultrasound imaging techniques that are clinically used for monitoring high-intensity focused ultrasound treatment are standard pulse-echo B-mode ultrasound imaging, ultrasound temperature estimation, and elastography-based methods. On the contrary, the efficacy of two-dimensional Nakagami parametric imaging based on the distribution of the ultrasound backscattered signals to quantify properties of soft tissue has recently been evaluated. In this study, ultrasound radio frequency echo signals from ex vivo tissue samples were acquired before and after high-intensity focused ultrasound exposures and then their Nakagami parameter and scaling parameter of Nakagami distribution were estimated. These parameters were used to detect high-intensity focused ultrasound-induced thermal lesions. Also, the effects of changing the acoustic power of the high-intensity focused ultrasound transducer on the Nakagami parameters were studied. The results obtained suggest that the Nakagami distribution's scaling and Nakagami parameters can effectively be used to detect high-intensity focused ultrasound-induced thermal lesions in tissue ex vivo. These parameters can also be used to understand the degree of change in tissue caused by high-intensity focused ultrasound exposures, which could be interpreted as a measure of degree of variability in scatterer concentration in various parts of the high-intensity focused ultrasound lesion. PMID:24264647

  5. Performance Evaluation of Fiber Bragg Gratings at Elevated Temperatures

    NASA Technical Reports Server (NTRS)

    Juergens, Jeffrey; Adamovsky, Grigory; Floyd, Bertram

    2004-01-01

    The development of integrated fiber optic sensors for smart propulsion systems demands that the sensors be able to perform in extreme environments. In order to use fiber optic sensors effectively in an extreme environment one must have a thorough understanding of the sensor s limits and how it responds under various environmental conditions. The sensor evaluation currently involves examining the performance of fiber Bragg gratings at elevated temperatures. Fiber Bragg gratings (FBG) are periodic variations of the refractive index of an optical fiber. These periodic variations allow the FBG to act as an embedded optical filter passing the majority of light propagating through a fiber while reflecting back a narrow band of the incident light. The peak reflected wavelength of the FBG is known as the Bragg wavelength. Since the period and width of the refractive index variation in the fiber determines the wavelengths that are transmitted and reflected by the grating, any force acting on the fiber that alters the physical structure of the grating will change what wavelengths are transmitted and what wavelengths are reflected by the grating. Both thermal and mechanical forces acting on the grating will alter its physical characteristics allowing the FBG sensor to detect both temperature variations and physical stresses, strain, placed upon it. This ability to sense multiple physical forces makes the FBG a versatile sensor. This paper reports on test results of the performance of FBGs at elevated temperatures. The gratings looked at thus far have been either embedded in polymer matrix materials or freestanding with the primary focus of this paper being on the freestanding FBGs. Throughout the evaluation process, various parameters of the FBGs performance were monitored and recorded. These parameters include the peak Bragg wavelength, the power of the Bragg wavelength, and total power returned by the FBG. Several test samples were subjected to identical test conditions to

  6. 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.

  7. Energy resolved X-ray grating interferometry

    SciTech Connect

    Thuering, T.; Stampanoni, M.; Barber, W. C.; Iwanczyk, J. S.; Seo, Y.; Alhassen, F.

    2013-05-13

    Although compatible with polychromatic radiation, the sensitivity in X-ray phase contrast imaging with a grating interferometer is strongly dependent on the X-ray spectrum. We used an energy resolving detector to quantitatively investigate the dependency of the noise from the spectral bandwidth and to consequently optimize the system-by selecting the best energy band matching the experimental conditions-with respect to sensitivity maximization and, eventually, dose. Further, since theoretical calculations of the spectrum are usually limited due to non-ideal conditions, an energy resolving detector accurately quantifies the spectral changes induced by the interferometer including flux reduction and beam hardening.

  8. Thin-foil reflection gratings for Constellation-X

    NASA Astrophysics Data System (ADS)

    Heilmann, Ralf K.; Akilian, Mireille; Chang, Chih-Hao; Forest, Craig R.; Joo, Chulmin; Lapsa, Andrew; Montoya, Juan C.; Schattenburg, Mark L.

    2004-10-01

    The Reflection Grating Spectrometer (RGS) on Constellation-X is designed to supply astronomers with high spectral resolution in the soft x-ray band from 0.25 to 2 keV. High resolution, large collecting area and low mass at grazing incidence require very flat and thin grating substrates, or thin-foil optics. Thin foils typically have a diameter-to-thickness ratio of 200 or higher and as a result very low stiffness. This poses a number of technological challenges in the areas of shaping, handling, positioning, and mounting of such optics. The most minute forces (gravity sag, friction, thermal mismatch with optic mount, etc.) can lead to intolerable deformations and limit figure metrology repeatability. We present results of our efforts in the manipulation and metrology of suitable grating substrates, utilizing a novel low-stress foil holder with friction-reducing flexures. A large number of reflection gratings is needed to achieve the required collecting area. We have employed nanoimprint lithography (NIL) - which uses imprint films as thin as 100 nm or less - for the high-fidelity and low-stress replication from 100 mm diameter saw-tooth grating masters.

  9. Fiber Bragg gratings for low-temperature measurement.

    PubMed

    Filho, Elton Soares de Lima; Baiad, Mohamad Diaa; Gagné, Mathieu; Kashyap, Raman

    2014-11-01

    We demonstrate the use of fiber Bragg gratings (FBGs) as a monolithic temperature sensor from ambient to liquid nitrogen temperatures, without the use of any auxiliary embedding structure. The Bragg gratings, fabricated in three different types of fibers and characterized with a high density of points, confirm a nonlinear thermal sensitivity of the fibers. With a conventional interrogation scheme it is possible to have a resolution of 0.5 K for weak pure-silica-core FBGs and 0.25 K using both boron-doped and germanium-doped standard fibers at 77 K. We quantitatively show for the first time that the nonlinear thermal sensitivity of the FBG arises from the nonlinearity of both thermo-optic and thermal expansion coefficients, allowing consistent modeling of FBGs at low temperatures. PMID:25401912

  10. Gravitational effects of process-induced dislocations in silicon. [during thermal cycling

    NASA Technical Reports Server (NTRS)

    Porter, W. A.; Parker, D. L.

    1974-01-01

    Matters pertaining to semiconductor device fabrication were studied in terms of the influence of gravity on the production of dislocations in silicon wafers during thermal cycling in a controlled ambient where no impurities are present and oxidation is minimal. Both n-type and p-type silicon wafers having a diameter of 1.25 in to 1.5 in, with fixed orientation and resistivity values, were used. The surface dislocation densities were measured quantitatively by the Sirtl etch technique. The results show two significant features of the plastic flow phenomenon as it is related to gravitational stress: (1) the density of dislocations generated during a given thermal cycle is directly related to the duration of the cycle; and (2) the duration of the thermal cycle required to produce a given dislocation density is inversely related to the equilibrium temperature. Analysis of the results indicates that gravitational stress is instrumental in process-induced defect generation.

  11. Characteristics of thermally-induced transverse cracks in graphite epoxy composite laminates

    NASA Technical Reports Server (NTRS)

    Adams, D. S.; Bowles, D. E.; Herakovich, C. T.

    1983-01-01

    The characteristics of thermally induced transverse cracks in T300/5208 graphite-epoxy cross-ply and quasi-isotropic laminates were investigated both experimentally and analytically. The formation of transverse cracks and the subsequent crack spacing present during cool down to -250 F (116K) and thermal cycling between 250 and -250 F (116 and 394K) was investigated. The state of stress in the vicinity of a transverse crack and the influence of transverse cracking on the laminate coefficient of thermal expansion (CTE) was predicted using a generalized plane strain finite element analysis and a modified shear lag analysis. A majority of the cross-ply laminates experienced transverse cracking during the initial cool down to -250 F whereas the quasi-isotropic laminates remained uncracked. The in situ transverse strength of the 90 degree layers was more than 1.9 times greater than the transverse strength of the unidirectional 90 degree material for all laminates investigated.

  12. Thermally-induced interlaminar crack-tip singularities in laminated anisotropic composites

    NASA Astrophysics Data System (ADS)

    Choi, Hyung J.; Thangjitham, S.

    1993-04-01

    Thermally-induced stress singularities of an interlaminar crack in a fiber-reinforced composite laminate under a state of generalized plane deformation are examined within the framework of steady-state anisotropic thermoelasticity. The crack is assumed to be embedded within a matrix-rich interlaminar region of the composite. The Fourier integral transform technique and the flexibility/stiffness matrix method are introduced to formulate the current mixed boundary value problem. As a result, two sets of simultaneous Cauchy-type singular integral equations of the first kind are derived for the heat conduction and thermoelasticity. Within the context of linear elastic fracture mechanics, the mixed-mode thermal stress intensity factors are defined in terms of the solutions of the corresponding integral equations. Numerical results are presented, addressing the effects of laminate stacking sequence, crack 1ocation, and crack surface partial insulation on the values of thermal stress intensity factors.

  13. Exploring thermally induced states in square artificial spin-ice arrays

    NASA Astrophysics Data System (ADS)

    Porro, J. M.; Bedoya-Pinto, A.; Berger, A.; Vavassori, P.

    2013-05-01

    We present a methodology to explore experimentally the formation of thermally induced long-range ground-state ordering in artificial spin-ice systems. Our novel approach is based on the thermalization from a square artificial spin-ice array of elongated ferromagnetic nanoislands made of a FeNi alloy characterized by a Curie temperature about 100 K lower than that of Permalloy (Ni81Fe19), which is commonly used for this kind of investigation. The decrease in M(T) when the sample is heated close to its Curie temperature reduces the shape anisotropy barrier of each island and allows us to bring the artificial spin-ice pattern above the blocking temperature of the islands, thus ‘melting’ the spin-ice system, without damaging the sample. The magnetization configuration resulting from the thermal excitation of the islands and the frustrated dipolar interactions among them can be then imaged by magnetic force microscopy or any other kind of magnetic microscopy imaging after cooling down the sample back to room temperature. This thermally induced melting-freezing protocol can be repeated as many times as desired on the same sample and the heating and cooling parameters (max T, heating and cooling rates, number of cycles, application of external fields) varied at will. Thereby, the approach proposed here opens up a pathway to the systematic experimental study of thermally induced frozen states in artificial spin-ice systems, which have been the subject of many recent theoretical studies due to their interesting physical properties but, because of the difficulties in obtaining them in real samples and in a controlled manner, remain experimentally an almost completely unexplored terrain.

  14. Forward model of thermally-induced acoustic signal specific to intralumenal detection geometry

    NASA Astrophysics Data System (ADS)

    Mukherjee, Sovanlal; Bunting, Charles F.; Piao, Daqing

    2011-03-01

    This work investigates a forward model associated with intra-lumenal detection of acoustic signal originated from transient thermal-expansion of the tissue. The work is specific to intra-lumenal thermo-acoustic tomography (TAT) which detects the contrast of tissue dielectric properties with ultrasonic resolution, but it is also extendable to intralumenal photo-acoustic tomography (PAT) which detects the contrast of light absorption properties of tissue with ultrasound resolution. Exact closed-form frequency-domain or time-domain forward model of thermally-induced acoustic signal have been studied rigorously for planar geometry and two other geometries, including cylindrical and spherical geometries both of which is specific to external-imaging, i.e. breast or brain imaging using an externally-deployed applicator. This work extends the existing studies to the specific geometry of internal or intra-lumenal imaging, i.e., prostate imaging by an endo-rectally deployed applicator. In this intra-lumenal imaging geometry, both the source that excites the transient thermal-expansion of the tissue and the acoustic transducer that acquires the thermally-induced acoustic signal are assumed enclosed by the tissue and on the surface of a long cylindrical applicator. The Green's function of the frequency-domain thermo-acoustic equation in spherical coordinates is expanded to cylindrical coordinates associated with intra-lumenal geometry. Inverse Fourier transform is then applied to obtain a time-domain solution of the thermo-acoustic pressure wave for intra-lumenal geometry. Further employment of the boundary condition to the "convex" applicator-tissue interface would render an exact forward solution toward accurate reconstruction for intra-lumenal thermally-induced acoustic imaging.

  15. Selective thermal desorption of ultrathin aluminum oxide layers induced by electron beams

    SciTech Connect

    Kundu, Manisha; Miyata, Noriyuki; Ichikawa, Masakazu

    2001-08-06

    The mechanism of electron-beam-induced selective thermal desorption of ultrathin aluminum-oxide layer ({approx}0.4 nm) on Si(001) surface was investigated by using scanning reflection electron microscopy, reflection high-energy electron diffraction, and Auger electron spectroscopy. We found that the change in the aluminum-oxide layer composition induced by electron-stimulated oxygen desorption accounted for the selective thermal desorption of the oxide layer. A systematic increase in the vacuum-annealing temperature to 500{sup o}C, 600{sup o}C and 720{sup o}C resulted in the formation of three-dimensional metal aluminum clusters, desorption of these clusters, and creation of a nanometer-scale clean Si(001)-2 x 1 open window in the selected electron-beam-irradiated area. {copyright} 2001 American Institute of Physics.

  16. Measurement of delayed-neutron yield from 237Np fission induced by thermal neutrons

    NASA Astrophysics Data System (ADS)

    Gundorin, N. A.; Zhdanova, K. V.; Zhuchko, V. E.; Pikelner, L. B.; Rebrova, N. V.; Salamatin, I. M.; Smirnov, V. I.; Furman, V. I.

    2007-06-01

    The delayed-neutron yield from thermal-neutron-induced fission of the 237Np nucleus was measured using a sample periodically exposed to a pulsed neutron beam with subsequent detection of neutrons during the time intervals between pulses. The experiment was realized on an Isomer-M setup mounted in the IBR-2 pulsed reactor channel equipped with a mirror neutron guide. The setup and the experimental procedure are described, the background sources are thoroughly analyzed, and the experimental data are presented. The total delayed-neutron yield from 237Np fission induced by thermal neutrons is ν d = 0.0110 ± 0.0009. This study was performed at the Frank Laboratory of Neutron Physics (JINR, Dubna).

  17. Defects-induced thermal instability in YBCO films in microwave field

    NASA Astrophysics Data System (ADS)

    Pan, Vladimir M.; Tretiatchenko, Constantin G.; Flis, Victor S.; Komashko, Valentin A.; Pashitskii, Ernst A.; Ivanyuta, Alexander N.; Melkov, Gennadiy A.; Zandbergen, Henny; Svetchnikov, Vassily L.

    2003-05-01

    The heat instability induced by linear defects is assumed to enhance the remarkable difference between microwave properties of YBCO single crystals and thin films due to extended strain fields near out-of-plane edge dislocations. We have shown theoretically and confirmed experimentally that a single dislocation cannot have a strong effect on the surface resistance Rs, but dislocation arrays, which were observed experimentally, can induce the thermal instability, if edge dislocations in the arrays are spaced closer than the heat relaxation length. Ordered dislocation structures provide much higher local temperature perturbation than randomly distributed dislocations.

  18. Muramyl dipeptide enhances thermal injury-induced inflammatory cytokine production and organ function injury in rats.

    PubMed

    Liang, Hui; Song, Xue-Min; Wu, Xiao-Jing; Li, Jian-Guo; Han, Yi; Wang, Yan-Lin; Li, Hui; Zhang, Zong-Ze; Le, Lin-Li; Xu, Yang

    2014-08-01

    The bacterial infection following thermal injury is a very important factor of excessive inflammatory response and multiple organ damage. Muramyl dipeptide (MDP) is the key structure of gram-positive bacteria and gram-negative bacteria triggering the innate immune system. The aim of the present study was to determine the effect of MDP on thermal injury-induced inflammatory responses, organ function injury, and mortality in rats. Fifty male Sprague-Dawlay rats were randomly divided into three groups: normal control group, scald group, and MDP group. Scald group only suffered 20% total body surface area third-degree thermal injury. Muramyl dipeptide 5 mg·kg was administered through the femoral vein at 24 h after thermal injury in the MDP group. Plasma inflammatory cytokine levels were measured by enzyme-linked immunosorbent assay. An additional 90 male Sprague-Dawley rats were randomly divided into three groups to observe the survival rate in 72 h. Plasma levels of interleukin-6, interleukin-10, interferon-γ, and high-mobility group box 1; the white blood cell counts; the serum concentrations of alanine aminotransferase, aspartate aminotransferase, total bilirubin, creatine kinase isoenzyme-MB, blood urea nitrogen, and creatinine; and the activity of lung tissue myeloperoxidase significantly increased after thermal injury alone. Compared with the scald group, MDP led to more serious inflammatory responses and organ function damage and higher mortality (P < 0.05, respectively). These data indicate that MDP exacerbates thermal injury-induced inflammatory cytokine production, accompanied by multiple organ dysfunction syndrome and high mortality in rats. PMID:24667616

  19. ACTIVE MEDIA: Nonlinear thermally induced distortions of a laser beam in a cryogenic disk amplifier

    NASA Astrophysics Data System (ADS)

    Vyatkin, A. G.; Khazanov, Efim A.

    2009-09-01

    Taking into account the temperature dependences of the heat conductivity, the refractive index, and the thermal expansion coefficient, we calculated the temperature, elastic stresses, a thermally induced lens and depolarisation of a beam in a cryogenic disk amplifier (an Yb:YAG disk placed between a copper cylinder and a sapphire disk cooled by liquid nitrogen). When the active element (the thickness is 0.6 mm, the orientation is [001], the atomic concentration of Yb is 10%) is pumped by radiation from a diode laser (the beam diameter is 6 mm), the temperature does not exceed 140 K for the heat release power of 100 W. In this case, elastic stresses in the active element are six times lower than the maximum permissible value. The focal distance of the thermally induced lens is 5.5 m and the depolarisation rate is 0.038% per two passes through the active element. Although the heat conductivity of the active element rapidly decreases with temperature, the thermal load can be increased by 1.5-2 times when the dimensions of the active element remain constant.

  20. Precipitation of energetic neutral atoms and induced non-thermal escape fluxes from the Martian atmosphere

    SciTech Connect

    Lewkow, N. R.; Kharchenko, V.

    2014-08-01

    The precipitation of energetic neutral atoms, produced through charge exchange collisions between solar wind ions and thermal atmospheric gases, is investigated for the Martian atmosphere. Connections between parameters of precipitating fast ions and resulting escape fluxes, altitude-dependent energy distributions of fast atoms and their coefficients of reflection from the Mars atmosphere, are established using accurate cross sections in Monte Carlo (MC) simulations. Distributions of secondary hot (SH) atoms and molecules, induced by precipitating particles, have been obtained and applied for computations of the non-thermal escape fluxes. A new collisional database on accurate energy-angular-dependent cross sections, required for description of the energy-momentum transfer in collisions of precipitating particles and production of non-thermal atmospheric atoms and molecules, is reported with analytic fitting equations. Three-dimensional MC simulations with accurate energy-angular-dependent cross sections have been carried out to track large ensembles of energetic atoms in a time-dependent manner as they propagate into the Martian atmosphere and transfer their energy to the ambient atoms and molecules. Results of the MC simulations on the energy-deposition altitude profiles, reflection coefficients, and time-dependent atmospheric heating, obtained for the isotropic hard sphere and anisotropic quantum cross sections, are compared. Atmospheric heating rates, thermalization depths, altitude profiles of production rates, energy distributions of SH atoms and molecules, and induced escape fluxes have been determined.

  1. Nonlinear thermally induced distortions of a laser beam in a cryogenic disk amplifier

    SciTech Connect

    Vyatkin, A G; Khazanov, Efim A

    2009-09-30

    Taking into account the temperature dependences of the heat conductivity, the refractive index, and the thermal expansion coefficient, we calculated the temperature, elastic stresses, a thermally induced lens and depolarisation of a beam in a cryogenic disk amplifier (an Yb:YAG disk placed between a copper cylinder and a sapphire disk cooled by liquid nitrogen). When the active element (the thickness is 0.6 mm, the orientation is [001], the atomic concentration of Yb is 10%) is pumped by radiation from a diode laser (the beam diameter is 6 mm), the temperature does not exceed 140 K for the heat release power of 100 W. In this case, elastic stresses in the active element are six times lower than the maximum permissible value. The focal distance of the thermally induced lens is 5.5 m and the depolarisation rate is 0.038% per two passes through the active element. Although the heat conductivity of the active element rapidly decreases with temperature, the thermal load can be increased by 1.5-2 times when the dimensions of the active element remain constant. (active media)

  2. Rapid thermal process-induced recombination centers in ion implanted silicon

    NASA Astrophysics Data System (ADS)

    Eichhammer, W.; Hage-Ali, M.; Stuck, R.; Siffert, P.

    1990-04-01

    This work presents direct evidence for a correlation between rapid thermal process-induced recombination centers and co-implanted metallic impurities in ion implanted silicon. Experimental evidence includes the dose dependence of the minority carrier diffusion length measured by the SPV technique, SIMS and RBS analysis of high-dose implantations which show the presence of heavy metals, the dependence of the final diffusion lengths on the mass of the implanted ions, as well as the successful modification of an implantation equipment.

  3. Temperature influence on the cladding mode distribution in highly localized point-by-point fibre Bragg gratings

    NASA Astrophysics Data System (ADS)

    Caucheteur, C.; Gonzalez-Vila, A.; Chikh-Bled, H.; Lasri, B.; Kinet, D.; Chah, K.

    2016-05-01

    An infrared femtosecond pulses laser is used to manufacture point-by-point gratings in telecommunication-grade optical fibres. The refractive index modulations are localized close to the core-cladding interface, yielding a strong coupling to cladding mode resonances together with an important photo-induced birefringence. Such gratings have been recently used for refractrometric measurements. In this work, their transmitted amplitude spectrum is measured with polarized light while they are exposed to temperature changes up to 900 °C. Despite an overall good thermal stability of the gratings that confirms their robustness for high-temperature refractometry, we report an interesting polarization effect depending on both the cladding mode resonance family (radially- and azimuthally-polarized modes) and mode order. While the birefringence of the core mode resonance decreases with the temperature, certain cladding mode resonances show an increase of the wavelength splitting between their orthogonally-polarized components. This differential behaviour can be of high interest to develop high-resolution multiparametric sensing platforms.

  4. The anti-nociceptive potential of tilmicosin against chemical-induced but not thermal-induced pain in mice.

    PubMed

    El-Mahmoudy, A; Gheith, I

    2016-03-01

    The aim of the present study was to assess the analgesic activity of the macrolide antibiotic tilmicosin at dose levels of 20 and 40 mg/kg of body weight, subcutaneously, against chemical- and thermal-induced acute pains, using acetic acid-induced writhing, formalin-induced pain, hot-plate, and tail-flick models in mice. Tilmicosin showed a dose-dependent significant decrease in the number of writhes in the acetic acid-induced writhing test and significant decrease in hind paw-licking time in the late phase of the formalin test. However, it did not cause any significant changes in the reaction times to heat stimuli in the hot-plate and tail-flick models. In chemically-induced pains, both dose levels of tilmicosin showed significant effects compared to those of the corresponding standard peripheral analgesic, acetylsalicylic acid (200 mg/kg of body weight, subcutaneously) being 26.37±2.88 and 43.64±3.85% vs. 73.35±1.44% in acetic acid test; and 19.23±3.85 and 44.90±1.80% vs. 73.63±2.39% in the late phase of formalin test, respectively. These results may indicate that tilmicosin possesses a significant peripheral but not central analgesic potential that may be beneficial in symptomatic relief of pain when it is used in therapy, in addition to its well-established antibacterial effect. PMID:26519523

  5. Tip-induced nano-writing/machining of Si and DLC surfaces ``anodic'' versus thermal oxidation?

    NASA Astrophysics Data System (ADS)

    Myhra, S.; Watson, G. S.

    2005-08-01

    Tip-induced oxidative manipulation of conducting surfaces, e.g., Si and some metals, has conventionally been described by a field-induced anodic mechanism. Likewise, in the case of electrically conducting graphitic and diamond-like carbon (DLC) films, tip-induced conversion of carbon to CO2 was initially thought to be due to an ionisation process. There is now mounting evidence for thermal activation playing an important role. The state of the tip is a critical, but largely disregarded, factor in such experiments. The present project has been prepared and characterized by I V analysis, tips with different initial characteristics (e.g., H-termination , Au-coating, native oxide). Likewise, several surfaces have been prepared (e.g., Si plus termination by either native or thermal oxide, or plus H-termination, DLC and Au), and also subjected to I V analysis. The resultant point-contact characteristics were found to range from ohmic to non-ohmic (the latter due to either direct or Fowler Nordheim tunnelling). The various combinations were tested with respect to oxidative yield and tip durability. It was found that the presence of a tunnelling barrier at the point of contact is essential for enhancing yield. Tip durability, on the other hand, is promoted by the barrier being located in the surface thus localizing thermal deposition in the surface rather than in the tip.

  6. Thermally-induced ventilation applications in atria: a state-of-the-art report

    SciTech Connect

    Not Available

    1981-06-01

    Atria dating back as far as the Roman Empire from fourteen countries were reviewed. Several tentative conclusions have emerged regarding optimal atria aspect ratios and mechanisms to control the atria microclimate. Three areas were considered in the review of atrium technical considerations: cooling design concepts, thermal functions and atrium operating principles. The cooling design concepts discussed include radiative cooling, shading, convective cooling (wind-driven and thermally-induced), and thermal mass. Assumed atrium thermal functions consist of the control of incoming solar radiation, ventilation, cooling and day-lighting. Primary atrium operating mechanisms are convective, conductive and radiative heat transfer. The partitioning of these energy flows are highly dependent upon specific atrium system parameters. Existing natural convection heat transfer and ventilation algorithms as they pertain to atria are presented. The limitations and major assumptions used in developing these algorithms are discussed. The computer programs reviewed include: (1) BLAST, (2) CALPAS3, (3) DEROB, (4) DOE-2A, (5) FREHEAT, (6) PASOLE, (7) PEGFIX, (8) NBSLD, (9) TWOZONE, and (10) UWENSOL. Out of the many atria surveyed, forty-one from thirty-seven locations in the US have been identified and documented. Most of the sites identified are commercial buildings. Sites are categorized into those already constructed and those still in the planning or building stages. Annotated bibliographies for information about atria are presented. These are grouped into the following subject areas: (1) general passive cooling, (2) climate and human comfort, (3) thermal and ventilation equations, (4) atria, (5) courtyards, and (6) measurement techniques.

  7. Thermal conductivity of graphene with defects induced by electron beam irradiation.

    PubMed

    Malekpour, Hoda; Ramnani, Pankaj; Srinivasan, Srilok; Balasubramanian, Ganesh; Nika, Denis L; Mulchandani, Ashok; Lake, Roger K; Balandin, Alexander A

    2016-08-14

    We investigate the thermal conductivity of suspended graphene as a function of the density of defects, ND, introduced in a controllable way. High-quality graphene layers are synthesized using chemical vapor deposition, transferred onto a transmission electron microscopy grid, and suspended over ∼7.5 μm size square holes. Defects are induced by irradiation of graphene with the low-energy electron beam (20 keV) and quantified by the Raman D-to-G peak intensity ratio. As the defect density changes from 2.0 × 10(10) cm(-2) to 1.8 × 10(11) cm(-2) the thermal conductivity decreases from ∼(1.8 ± 0.2) × 10(3) W mK(-1) to ∼(4.0 ± 0.2) × 10(2) W mK(-1) near room temperature. At higher defect densities, the thermal conductivity reveals an intriguing saturation-type behavior at a relatively high value of ∼400 W mK(-1). The thermal conductivity dependence on the defect density is analyzed using the Boltzmann transport equation and molecular dynamics simulations. The results are important for understanding phonon - point defect scattering in two-dimensional systems and for practical applications of graphene in thermal management. PMID:27432290

  8. Performance of silicon immersed gratings: measurement, analysis, and modeling

    NASA Astrophysics Data System (ADS)

    Rodenhuis, Michiel; Tol, Paul J. J.; Coppens, Tonny H. M.; Laubert, Phillip P.; van Amerongen, Aaldert H.

    2015-09-01

    The use of Immersed Gratings offers advantages for both space- and ground-based spectrographs. As diffraction takes place inside the high-index medium, the optical path difference and angular dispersion are boosted proportionally, thereby allowing a smaller grating area and a smaller spectrometer size. Short-wave infrared (SWIR) spectroscopy is used in space-based monitoring of greenhouse and pollution gases in the Earth atmosphere. On the extremely large telescopes currently under development, mid-infrared high-resolution spectrographs will, among other things, be used to characterize exo-planet atmospheres. At infrared wavelengths, Silicon is transparent. This means that production methods used in the semiconductor industry can be applied to the fabrication of immersed gratings. Using such methods, we have designed and built immersed gratings for both space- and ground-based instruments, examples being the TROPOMI instrument for the European Space Agency Sentinel-5 precursor mission, Sentinel-5 (ESA) and the METIS (Mid-infrared E-ELT Imager and Spectrograph) instrument for the European Extremely Large Telescope. Three key parameters govern the performance of such gratings: The efficiency, the level of scattered light and the wavefront error induced. In this paper we describe how we can optimize these parameters during the design and manufacturing phase. We focus on the tools and methods used to measure the actual performance realized and present the results. In this paper, the bread-board model (BBM) immersed grating developed for the SWIR-1 channel of Sentinel-5 is used to illustrate this process. Stringent requirements were specified for this grating for the three performance criteria. We will show that -with some margin- the performance requirements have all been met.

  9. Non-thermal Plasma Induces Apoptosis in Melanoma Cells via Production of Intracellular Reactive Oxygen Species

    PubMed Central

    Sensenig, Rachel; Kalghatgi, Sameer; Cerchar, Ekaterina; Fridman, Gregory; Shereshevsky, Alexey; Torabi, Behzad; Arjunan, Krishna Priya; Podolsky, Erica; Fridman, Alexander; Friedman, Gary; Azizkhan-Clifford, Jane; Brooks, Ari D.

    2012-01-01

    Non-thermal atmospheric pressure dielectric barrier discharge (DBD) plasma may provide a novel approach to treat malignancies via induction of apoptosis. The purpose of this study was to evaluate the potential of DBD plasma to induce apoptosis in melanoma cells. Melanoma cells were exposed to plasma at doses that did not induce necrosis, and cell viability and apoptotic activity were evaluated by Trypan blue exclusion test, Annexin-V/PI staining, caspase-3 cleavage, and TUNEL® analysis. Trypan blue staining revealed that non-thermal plasma treatment significantly decreased the viability of cells in a dose-dependent manner 3 and 24 h after plasma treatment. Annexin-V/PI staining revealed a significant increase in apoptosis in plasma-treated cells at 24, 48, and 72 h post-treatment (p<0.001). Caspase-3 cleavage was observed 48 h post-plasma treatment at a dose of 15 J/cm2. TUNEL® analysis of plasma-treated cells demonstrated an increase in apoptosis at 48 and 72 h post-treatment (p<0.001) at a dose of 15 J/cm2. Pre-treatment with N-acetyl-L-cysteine (NAC), an intracellular reactive oxygen species (ROS) scavenger, significantly decreased apoptosis in plasma-treated cells at 5 and 15 J/cm2. Plasma treatment induces apoptosis in melanoma cells through a pathway that appears to be dependent on production of intracellular ROS. DBD plasma production of intracellular ROS leads to dose-dependent DNA damage in melanoma cells, detected by γ-H2AX, which was completely abrogated by pre-treating cells with ROS scavenger, NAC. Plasma-induced DNA damage in turn may lead to the observed plasma-induced apoptosis. Since plasma is non-thermal, it may be used to selectively treat malignancies. PMID:21046465

  10. Theoretical analysis of novel fiber grating pair

    NASA Astrophysics Data System (ADS)

    Wang, Liao; Jia, Hongzhi; Fang, Liang; You, Bei

    2016-06-01

    A novel fiber grating pair that consists of a conventional long-period fiber grating and a fiber Bragg cladding grating (FBCG) is proposed. The FBCG is a new type of fiber grating in which refractive index modulation is formed in the cladding. Through the coupled-mode theory, we accurately calculate the coupling coefficients between modes supported in the fibers. And some other mode coupling features in the fiber cladding gratings are analyzed in detail. The calculation of the modes involved in this paper is based on a model of three-layer step-index fiber geometry. Then, we have investigated the sensitivity characteristics for variation of the modulation strengths of the fiber Bragg cladding gratings' resonance peaks and the long-period cladding gratings' (LPCGs) dual resonant peaks. Finally, the modulation strength sensitivity of the grating pair's three resonant peaks is demonstrated, and the results indicate that these grating pairs may find potential applications in optical fiber sensing.

  11. Deformation monitoring of painted wood panels by fiber Bragg gratings

    NASA Astrophysics Data System (ADS)

    Falciai, Riccardo; Trono, Cosimo; Lanterna, Giancarlo; Castelli, Ciro

    2003-11-01

    The conservation of painted panel supports is a fundamental aim of the whole restoration process. The measurement method up to now utilized by Opificio is based on the application on the panel of reference points, through which a centesimal gauge measures positive and negative movements. We propose a measurement method based on fiber Bragg grating (FBG) sensors. An array of Bragg gratings was glued on several crucial points of the wood structure, and the data were continuously collected. A set of measurements were performed in order to study the deformations of a painted wood panel, induced by relative humidity changes.

  12. Modeling of spectral changes in bent fiber Bragg gratings.

    PubMed

    Zhang, Wei; Lei, Xiaohua; Chen, Weimin; Xu, Hengyi; Wang, Anbo

    2015-07-15

    To better apply fiber Bragg gratings (FBGs) to various bending required situations, good understanding of their bending characteristics is crucial. In this Letter, a theoretical model to describe the changes of spectral properties of an FBG against the bending radius is proposed. This model shows that all the bend-induced spectral changes, the shift of center wavelength, decrease of reflectivity, and reduction of bandwidth, may be explained by the decrease of the effective "dc" refractive index change spatially averaged over one grating period. Experimental results are in agreement with theoretical predictions and confirm the effectiveness of the proposed model. PMID:26176444

  13. Application of laser-induced thermal acoustics in air to measurement of shock-induced temperature changes

    NASA Astrophysics Data System (ADS)

    Mizukaki, Toshiharu; Matsuzawa, Toyoki

    2009-10-01

    The laser-induced thermal acoustics (LITA) method was used to measure the temperature profiles induced behind spherical shock waves, generated by high-voltage discharge in air with an energy of 6 J. A Nd:YAG laser (wavelength 532 nm, energy 300 mJ, pulse duration 10 ns, line width 0.005 cm-1) and an Ar-ion laser (wavelength 488 nm, power 4 W) served as the pump and probe lasers, respectively for the LITA measurements. The peak temperatures were in good agreement with results calculated with the Euler equations. The temperature profiles behind the shock, however, differed in decay rates. The peak temperatures behind the shock wave were determined by reflected overpressure and agreed with those from the LITA measurements within a maximum error of 5%.

  14. Enhancement of thermal diagnostics on tumors underneath the skin by induced evaporation.

    PubMed

    Deng, Zhong-Shan; Liu, Jing

    2005-01-01

    Infrared imaging has frequently been used in clinics to detect changes in skin surface temperature associated with some superficial tumors. In order to accurately detect and diagnose tumors (especially in their early stages) using infrared thermography, enhancement of thermal expression on the skin over the tumor is desired. This study proposed a novel approach to effectively enhance the skin thermal expression of tumor by induced evaporation on skin surface. To illustrate its feasibility, numerical calculation was first applied to simulate the corresponding heat transfer process, from which the three-dimensional transient temperatures of the biological bodies subjected to induced evaporation were theoretically predicted. Further, preliminary infrared imaging experiments on human forearm were also performed, in which water and 75% (V/V) medical ethanol were particularly chosen to be respectively sprayed on the skin surface. Both the numerical and experimental results indicate that the induced evaporation can significantly enhance the sensitivity of temperature mapping on skin surface over the tumor. The results also suggest that the induced evaporation method can be used to improve the diagnostic accuracy of infrared thermography, especially for tumors at early stages and/or deeply embedded. PMID:17282022

  15. Holographic Gratings for Optical Processing

    NASA Technical Reports Server (NTRS)

    Kukhtarev, Nickolai

    2002-01-01

    Investigation of astronomical objects and tracking of man-made space objects lead to generation of huge amount of information for optical processing. Traditional big-size optical elements (such as optical telescopes) have a tendency for increasing aperture size in order to improve sensitivity. This tendency leads to increasing of weight and costs of optical systems and stimulate search for the new, more adequate technologies. One approach to meet these demands is based on developing of holographic optical elements using new polymeric materials. We have investigated possibility to use new material PQ-PMMA (phenantrenequinone-doped PMMA (Polymethyl Methacrylate)) for fabrication of highly selective optical filters and fast spatial-temporal light modulators. This material was originally developed in Russia and later was tested in CalTech as a candidate material for optical storage. Our theoretical investigation predicts the possibility of realization of fast spatial and temporal light modulation, using volume reflection-type spectral filter. We have developed also model of holographic-grating recording in PQ-PMMA material, based on diffusional amplification. This mechanism of recording allow to receive high diffraction efficiency during recording of reflection-type volume holographic grating (holographic mirror). We also investigated recording of dynamic gratings in the photorefractive crystals LiNbO3 (LN) for space-based spectroscopy and for adaptive correction of aberrations in the telescope's mirrors. We have shown, that specific 'photogalvanic' mechanism of holographic grating recording in LN allow to realize recording of blazed gratings for volume and surface gratings. Possible applications of dynamic gratings in LN for amplification of images, transmitted through an imaging fiber guide was also demonstrated.

  16. Rockslides in Masada: thermally induced "ratchet" mechanism vs. response to seismic loading

    NASA Astrophysics Data System (ADS)

    Bakun-Mazor, D.; Hatzor, Y. H.

    2012-04-01

    Annual temperature fluctuations are responsible for generating irreversible displacements of removable rock blocks that are separated from the rock mass by the intersections of pre-existing discontinuities in the rock mass. A new mechanism, referred to as "ratchet" model, is proposed to explain how cyclic thermal oscillations induce intermittent expansion and contraction of the tension crack, thus causing seasonal translations of rock blocks. New evidence for thermally induced block displacements is presented using both climate and displacement data from a carefully monitored rock block in the West face of the Masada Mountain, a UNESCO World Heritage site, along with re-visited and re-analyzed monitoring data from the East face of mountain. The monitored deformation is explained here in terms of a weather-induced wedging failure that essentially operates as a "ratchet" mechanism involving the rock mass, tension crack, sliding block, and sliding surface. In order to validate the proposed mechanism the discrete element, numerical Discontinuous Deformation Analysis (DDA) method is employed to analyze the proposed "ratchet" model and to simulate the monitored block displacements in the field. The numerical analysis results provide a comparison between the thermal and the seismic driving mechanisms for a mapped block in the East slope of Masada, which climatically is situated in the Eastern part of the arid Judean Desert, and seismically is located on the western margins of the Dead Sea rift (DSR) valley. Based on the long-term climatic conditions and the seismic hazard assessment for the region, including topographical site effect on the mountain top, it is found that the thermal effect is the more dominant mechanism that drives the displacement of the analyzed block over time. Therefore, understanding the mechanism of the "ratchet" model, and identifying its potential in the field, can help mitigate rock slope stability risks in rock masses that are prone to such a

  17. Three-dimensional grating nanowires for enhanced light trapping.

    PubMed

    Lee, Hoo-Cheol; Na, Jin-Young; Moon, Yoon-Jong; Park, Jin-Sung; Ee, Ho-Seok; Park, Hong-Gyu; Kim, Sun-Kyung

    2016-04-01

    We propose rationally designed 3D grating nanowires for boosting light-matter interactions. Full-vectorial simulations show that grating nanowires sustain high-amplitude waveguide modes and induce a strong optical antenna effect, which leads to an enhancement in nanowire absorption at specific or broadband wavelengths. Analyses of mode profiles and scattering spectra verify that periodic shells convert a normal plane wave into trapped waveguide modes, thus giving rise to scattering dips. A 200 nm diameter crystalline Si nanowire with designed periodic shells yields an enormously large current density of ∼28  mA/cm2 together with an absorption efficiency exceeding unity at infrared wavelengths. The grating nanowires studied herein will provide an extremely efficient absorption platform for photovoltaic devices and color-sensitive photodetectors. PMID:27192291

  18. Increase of the grating coupler bandwidth with a graphene overlay

    SciTech Connect

    Cheng, Zhenzhou; Li, Zhen; Xu, Ke; Tsang, Hon Ki

    2014-03-17

    We present theoretical and experimental results that demonstrate an increase in the grating bandwidth by placing a graphene on the chip. A focusing subwavelength grating with coupling efficiency of −4.3 dB and 1 dB bandwidth of ∼60 nm was demonstrated. After a graphene sheet was transferred onto the chip, the maximum 1 dB bandwidth was increased to ∼72 nm. Experimental results are consistent with the calculated graphene induced waveguide refractive index and dispersion changes, and the bandwidth improvement may be attributed to the reduction of grating dispersion. This study may be of interest for graphene-on-silicon photonic integrated circuit applications.

  19. Near-perfect diffraction grating rhomb

    DOEpatents

    Wantuck, Paul J.

    1990-01-01

    A near-perfect grating rhomb enables an output beam to be diffracted to an angle offset from the input beam. The correcting grating is tipped relative to the dispersing grating to provide the offset angle. The correcting grating is further provided with a groove spacing which differs from the dispersing grating groove space by an amount effective to substantially remove angular dispersion in the output beam. A near-perfect grating rhomb has the capability for selective placement in a FEL to suppress sideband instabilities arising from the FEL.

  20. Diffraction by dual-period gratings.

    PubMed

    Skigin, Diana C; Depine, Ricardo A

    2007-03-20

    The dynamical characteristics of dual-period perfectly conducting gratings are explored. Gratings with several grooves (reflection) or slits (transmission) within each period are considered. A scalar approach is proposed to derive the general characteristics of the diffracted response. It was found that compound gratings can be designed to cancel as well as to intensify a given diffraction order. These preliminary estimations for finite gratings are validated by numerical examples for infinitely periodic reflection and transmission gratings with finite thickness, performed using an extension of the rigorous modal method to compound gratings, for both polarization cases. PMID:17334426

  1. Thermosensitivity of muscle: high-intensity thermal stimulation of muscle tissue induces muscle pain in humans.

    PubMed

    Graven-Nielsen, T; Arendt-Nielsen, L; Mense, S

    2002-04-15

    Small-calibre afferent units responding to thermal stimuli have previously been reported to exist in muscle. The question as to whether these receptors in humans mediate subjective thermal sensations from muscle remains unresolved. The aims of the present study were to determine in humans whether intramuscular injection of warm and cold isotonic saline elicits temperature sensations, muscle pain or any other sensations. In 15 subjects, no thermal sensations assessed on a temperature visual analogue scale (VAS) could be detected with intramuscular injections of isotonic saline (1.5 ml) into the anterior tibial muscle at temperatures ranging from 8 to 48 degrees C. The same subjects recorded strongly increasing scores on a temperature VAS when thermal stimuli in the same intensity range were applied to the skin overlying the muscle by a contact thermode. However, I.M. isotonic saline of 48 degrees C induced muscle pain with peak scores of 3.2 +/- 0.8 cm on a VAS scale ranging from 0 to 10 cm. Using the the McGill pain questionnaire a subgroup, of subjects qualitatively described the pain using the 'thermal hot' and 'dullness' word groups. Temperature measurements within the muscle during the stimulating injections showed that the time course of the pain sensation elicited by saline at 48 degrees C paralleled that of the intramuscular temperature and far outlasted the injection time. The present data show that high-intensity thermal stimulation of muscle is associated with muscle pain. High-threshold warm-sensitive receptors may mediate the pain following activation by temperatures of 48 degrees C or more. Taken together, the data indicate that thermosensation from a given volume of muscle is less potent than nociception. PMID:11956350

  2. Magnetic Resonance-Guided Focal Laser-Induced Interstitial Thermal Therapy in a Canine Prostate Model

    PubMed Central

    Stafford, R. Jason; Shetty, Anil; Elliott, Andrew M.; Klumpp, Sherry A.; McNichols, Roger J.; Gowda, Ashok; Hazle, John D.; Ward, John F.

    2014-01-01

    Purpose To evaluate a newly FDA-cleared closed-loop, magnetic resonance (MR)-guided laser-induced interstitial thermal therapy (LITT) system for targeted ablation of prostate tissue in order to assess targeting ability, lesion generation and feasibility. Materials and Methods Mongrel dogs with (n = 2) and without (n = 5) canine transmissible venereal tumors in the prostate were imaged with a 1.5-T MR imaging scanner. Real-time 3D MR imaging was used to accurately position water-cooled 980-nm laser applicators to pre-determined targets within the canine prostates. Destruction of targeted tissue was guided with MR temperature imaging in real time for precise control of thermal ablation. MR predictions of thermal damage were correlated with findings from post-treatment images and compared to histopathology. Results Template-based targeting using MR guidance allowed the laser applicator to be placed within a mean of 1.1 mm (SD = 0.7 mm) of the target location. The mean width and length of the ablation zone by MR were 13.7 mm (SD = 1.3 mm) and 19.0 mm (SD = 4.2 mm) using single and compound exposures. The thermal damage predicted by MR correlated with the thermal damage determined by post-treatment imaging with a slope near unity and excellent correlation (R2 = 0.94). Conclusions This LITT system provided rapid and localized heating of tissue with minimal collateral thermal spread or injury. Combined with real-time monitoring and template-based planning, MR-guided LITT is an attractive modality for prostate cancer focal therapy. PMID:20727549

  3. Thermal Stress-Induced Depolarization Loss in Conventional and Panda-Shaped Photonic Crystal Fiber Lasers

    NASA Astrophysics Data System (ADS)

    Mousavi, Seyedeh Laleh; Sabaeian, Mohammad

    2016-07-01

    We report on the modeling of the depolarization loss in the conventional and panda-shaped photonic crystal fiber lasers (PCFLs) due to the self-heating of the fiber, which we call it thermal stress-induced depolarization loss (TSIDL). We first calculated the temperature distribution over the fiber cross sections and then calculated the thermal stresses/strains as a function of heat load per meter. Thermal stress-induced birefringence (TSIB), which is defined as |n x - n y |, in the core and cladding regions was calculated. Finally, TSIDL was calculated for the conventional and panda-shaped PCFLs as a function of fiber length and, respectively, saturated values of 22 and 25 % were obtained which were independent of heat load per meter. For panda-shaped PCFLs, prior to being saturated, an oscillating and damping behavior against the fiber length was seen where in some lengths reached 35 %. The results are close to an experimental value of 30 % reported for a pulsed PCFL (Limpert et al., Opt Express 12:1313-1319, 2004) where the authors reported a degree of polarization of 70 % (i.e., a depolarization of 30 %). The most important result of this work is a saturation behavior of TSIDL at long-enough lengths of the fiber laser which is independent of heat load per meter. To our knowledge, this the first report of TSIBL for PCFLs.

  4. Pressure induced by thermal fluctuation of an elastic filament confined within a narrow channel

    NASA Astrophysics Data System (ADS)

    Freund, L. B.

    2016-08-01

    Consider a flexible macro-molecule that is immersed in water at or above room temperature. As a result of thermal motion within the water, the filament is driven to undergo random fluctuations in shape. These fluctuations are a consequence of uncoordinated motion of water molecules. If the range of filament motion is restricted by nearby surfaces, the phenomenon becomes more complex. In this study, it is presumed that the filament is restricted to lie within a plane so that the motion is two dimensional. Furthermore, the range of the planar motion of the filament is confined to the region between inflexible straight boundaries lying in the plane of motion. A result of thermal fluctuation of the filament is that, when in close proximity to a boundary, a normal pressure is induced between the filament and that confining boundary. In the present development, frictional interaction of the filament with either confining boundary is presumed to be negligible. The goal is to determine the dependence of the induced pressure on the separation distance between the confining boundaries in terms of prevailing thermal conditions and physical characteristics of the system.

  5. Swim therapy reduces mechanical allodynia and thermal hyperalgesia induced by chronic constriction nerve injury in rats

    PubMed Central

    Shen, Jun; Fox, Lyle E.; Cheng, Jianguo

    2013-01-01

    Objective Neuropathic pain is common and often difficult to treat because it generally does not respond well to the currently available pain medications or nerve blocks. Recent studies in both humans and animals have suggested that exercise may induce a transient analgesia and reduce acute pain in normal healthy individuals. We examined whether swim therapy could alleviate neuropathic pain in rats. Design Rats were trained to swim over a two week period in warm water. After the rats were trained, neuropathic pain was induced by constricting the right sciatic nerve and regular swimming was resumed. The sensitivity of each hind paw was monitored using the Hargreaves test and von Frey test to evaluate the withdrawal response thresholds to heat and touch. Results The paw ipsilateral to the nerve ligation expressed pain-like behaviors including thermal hyperalgesia and mechanical allodynia. Regular swim therapy sessions significantly reduced the mechanical allodynia and thermal hyperalgesia. Swim therapy had little effect on the withdrawal thresholds for the contralateral paw. In addition, swim therapy alone did not alter the thermal or mechanical thresholds of normal rats. Conclusions The results suggest that regular exercise, including swim therapy, may be an effective treatment for neuropathic pain caused by nerve injuries. This study, showing that swim therapy reduces neuropathic pain behavior in rats, provides a scientific rationale for clinicians to test the efficacy of exercise in the management of neuropathic pain. It may prove to be a safe and cost-effective therapy in a variety of neuropathic pain states. PMID:23438327

  6. Model-based planning and real-time predictive control for laser-induced thermal therapy

    PubMed Central

    Feng, Yusheng; Fuentes, David

    2014-01-01

    In this article, the major idea and mathematical aspects of model-based planning and real-time predictive control for laser-induced thermal therapy (LITT) are presented. In particular, a computational framework and its major components developed by authors in recent years are reviewed. The framework provides the backbone for not only treatment planning but also real-time surgical monitoring and control with a focus on MR thermometry enabled predictive control and applications to image-guided LITT, or MRgLITT. Although this computational framework is designed for LITT in treating prostate cancer, it is further applicable to other thermal therapies in focal lesions induced by radio-frequency (RF), microwave and high-intensity-focused ultrasound (HIFU). Moreover, the model-based dynamic closed-loop predictive control algorithms in the framework, facilitated by the coupling of mathematical modelling and computer simulation with real-time imaging feedback, has great potential to enable a novel methodology in thermal medicine. Such technology could dramatically increase treatment efficacy and reduce morbidity. PMID:22098360

  7. Multifrequency microwave-induced thermal acoustic imaging for breast cancer detection.

    PubMed

    Guo, Bin; Li, Jian; Zmuda, Henry; Sheplak, Mark

    2007-11-01

    Microwave-induced thermal acoustic imaging (TAI) is a promising early breast cancer detection technique, which combines the advantages of microwave stimulation and ultrasound imaging and offers a high imaging contrast, as well as high spatial resolution at the same time. A new multifrequency microwave-induced thermal acoustic imaging scheme for early breast cancer detection is proposed in this paper. Significantly more information about the human breast can be gathered using multiple frequency microwave stimulation. A multifrequency adaptive and robust technique (MART) is presented for image formation. Due to its data-adaptive nature, MART can achieve better resolution and better interference rejection capability than its data-independent counterparts, such as the delay-and-sum method. The effectiveness of this procedure is shown by several numerical examples based on 2-D breast models. The finite-difference time-domain method is used to simulate the electromagnetic field distribution, the absorbed microwave energy density, and the thermal acoustic field in the breast model. PMID:18018695

  8. A model evaluation study for treatment planning of laser-induced thermal therapy.

    PubMed

    Fahrenholtz, Samuel J; Moon, Tim Y; Franco, Michael; Medina, David; Danish, Shabbar; Gowda, Ashok; Shetty, Anil; Maier, Florian; Hazle, John D; Stafford, Roger J; Warburton, Tim; Fuentes, David

    2015-01-01

    A cross-validation analysis evaluating computer model prediction accuracy for a priori planning magnetic resonance-guided laser-induced thermal therapy (MRgLITT) procedures in treating focal diseased brain tissue is presented. Two mathematical models are considered. (1) A spectral element discretisation of the transient Pennes bioheat transfer equation is implemented to predict the laser-induced heating in perfused tissue. (2) A closed-form algorithm for predicting the steady-state heat transfer from a linear superposition of analytic point source heating functions is also considered. Prediction accuracy is retrospectively evaluated via leave-one-out cross-validation (LOOCV). Modelling predictions are quantitatively evaluated in terms of a Dice similarity coefficient (DSC) between the simulated thermal dose and thermal dose information contained within N = 22 MR thermometry datasets. During LOOCV analysis, the transient model's DSC mean and median are 0.7323 and 0.8001 respectively, with 15 of 22 DSC values exceeding the success criterion of DSC ≥ 0.7. The steady-state model's DSC mean and median are 0.6431 and 0.6770 respectively, with 10 of 22 passing. A one-sample, one-sided Wilcoxon signed-rank test indicates that the transient finite element method model achieves the prediction success criteria, DSC ≥ 0.7, at a statistically significant level. PMID:26368014

  9. Thermal gradient-induced forces on geodesic reference masses for LISA

    SciTech Connect

    Carbone, L.; Ciani, G.; Dolesi, R.; Hueller, M.; Tombolato, D.; Vitale, S.; Weber, W. J.; Cavalleri, A.

    2007-11-15

    The low frequency sensitivity of space-borne gravitational wave observatories will depend critically on the geodesic purity of the trajectories of orbiting test masses. Fluctuations in the temperature difference across the enclosure surrounding the free-falling test mass can produce noisy forces through several processes, including the radiometric effect, radiation pressure, and outgassing. We present here a detailed experimental investigation of thermal gradient-induced forces for the Laser Interferometer Space Antenna (LISA) gravitational wave mission and the LISA Pathfinder, employing high resolution torsion pendulum measurements of the torque on a LISA-like test mass suspended inside a prototype of the LISA gravitational reference sensor that will surround the test mass in orbit. The measurement campaign, accompanied by numerical simulations of the radiometric and radiation pressure effects, allows a more accurate and representative characterization of thermal-gradient forces in the specific geometry and environment relevant to LISA free-fall. The pressure dependence of the measured torques allows clear identification of the radiometric effect, in quantitative agreement with the model developed. In the limit of zero gas pressure, the measurements are most likely dominated by outgassing, but at a low level that does not threaten the current LISA noise estimate, which assumes a maximum net force per degree of temperature difference of 100(pN/K) for the overall thermal gradient-induced effects.

  10. Acoustic estimation of thermal distribution in the vicinity of femtosecond laser-induced optical breakdown.

    PubMed

    Zohdy, Marwa J; Tse, Christine; Ye, Jing Yong; O'Donnell, Matthew

    2006-11-01

    Laser-induced optical breakdown (LIOB), or photo-disruption, can generate individual microbubbles in tissues for biomedical applications. We have previously developed a co-localized high-frequency ultrasound system to detect and characterize these laser-induced microbubbles. Because ultrasound speed varies with temperature, this system can also be used to directly estimate thermal effects in the vicinity of photodisruption. In this study, individual bubbles (sizes 60-100 microm) were created at the bottom of a water tank using a 793-nm, 100-fs Ti:Sapphire laser pulsed at 250 kHz. During and after breakdown, pulse-echoes from the tank bottom in the region surrounding a bubble were recorded with a single-element 85-MHz ultrasonic transducer, and temperature-dependent pulse-echo displacements were calculated using phase-sensitive correlation tracking. These displacements were then fit to a finite-element heat transfer model to estimate the effective thermal distribution. Estimates were calculated for laser exposure times ranging from 6.25 to 312.5 ms (1600 to 78 000 laser pulses), at 1.5 and 4 J/cm2 fluences. Results suggest a minimal temperature increase (<1 degrees C) within 100 microm of a bubble created with <1600 laser pulses at 1.5 J/cm2 fluence. This implies that LIOB can be controlled to be thermally noninvasive in the bubble vicinity. PMID:17073341

  11. Calculation of Thermally-Induced Displacements in Spherically Domed Ion Engine Grids

    NASA Technical Reports Server (NTRS)

    Soulas, George C.

    2006-01-01

    An analytical method for predicting the thermally-induced normal and tangential displacements of spherically domed ion optics grids under an axisymmetric thermal loading is presented. A fixed edge support that could be thermally expanded is used for this analysis. Equations for the displacements both normal and tangential to the surface of the spherical shell are derived. A simplified equation for the displacement at the center of the spherical dome is also derived. The effects of plate perforation on displacements and stresses are determined by modeling the perforated plate as an equivalent solid plate with modified, or effective, material properties. Analytical model results are compared to the results from a finite element model. For the solid shell, comparisons showed that the analytical model produces results that closely match the finite element model results. The simplified equation for the normal displacement of the spherical dome center is also found to accurately predict this displacement. For the perforated shells, the analytical solution and simplified equation produce accurate results for materials with low thermal expansion coefficients.

  12. Assessment of Laser-Induced Thermal Load on Silicon Nanostructures Based on Ion Desorption Yields

    SciTech Connect

    Walker, Bennett N; Stolee, Jessica A; Pickel, Deanna L; Retterer, Scott T; Vertes, Akos

    2010-01-01

    Laser heating of macroscopic objects follows the Fourier law of diffusive heat conduction. However, when the dimensions of a structure approach the mean free path of the phonons, heat transport is properly described by the equations of ballistic-diffusive or ballistic transport. Due to the coexistence of these different mechanisms in most nanostructures, the description of their rapid laser heating becomes complex. Experimental assessment of the thermal load on these structures through IR imaging is currently too slow and lacks the spatial resolution to be useful. In this paper, we introduce a method based on measuring the laser-induced yields of quasimolecular ions that enables the comparison of the thermal loads on different structures. Due to the difference in the activation energies of the desorption processes, sodiated and potassiated peptide ion intensities become equal at a certain surface temperature. The laser fluences at which these ion yields are equal for two different structures correspond to equivalent thermal loads. As an example, we compare the nanosecond laser heating of silicon nanopost arrays (NAPA) with diverse post diameters and periodicities. Assessment of the thermal load through ion yield measurements can also be used to verify model assumptions for heat transport regimes of nanostructures.

  13. Microstructural modifications induced by rapid thermal annealing in plasma deposited SiOxNyHz films

    NASA Astrophysics Data System (ADS)

    del Prado, A.; San Andrés, E.; Mártil, I.; González-Díaz, G.; Bravo, D.; López, F. J.; Fernández, M.; Martínez, F. L.

    2003-07-01

    The effect of rapid thermal annealing (RTA) processes on the structural properties of SiOxNyHz films was investigated. The samples were deposited by the electron cyclotron resonance plasma method, using SiH4, O2 and N2 as precursor gases. For SiOxNyHz films with composition close to that of SiO2, which have a very low H content, RTA induces thermal relaxation of the lattice and improvement of the structural order. For films of intermediate composition and of compositions close to SiNyHz, the main effect of RTA is the release of H at high temperatures (T>700 °C). This H release is more significant in films containing both Si-H and N-H bonds, due to cooperative reactions between both kinds of bonds. In these films the degradation of structural order associated to H release prevails over thermal relaxation, while in those films with only N-H bonds, thermal relaxation predominates. For annealing temperatures in the 500-700 °C range, the passivation of dangling bonds by the nonbonded H in the films and the transition from the paramagnetic state to the diamagnetic state of the K center result in a decrease of the density of paramagnetic defects. The H release observed at high annealing temperatures is accompanied by an increase of density of paramagnetic defects.

  14. Genetics of Intraspecies Variation in Avoidance Behavior Induced by a Thermal Stimulus in Caenorhabditis elegans.

    PubMed

    Ghosh, Rajarshi; Bloom, Joshua S; Mohammadi, Aylia; Schumer, Molly E; Andolfatto, Peter; Ryu, William; Kruglyak, Leonid

    2015-08-01

    Individuals within a species vary in their responses to a wide range of stimuli, partly as a result of differences in their genetic makeup. Relatively little is known about the genetic and neuronal mechanisms contributing to diversity of behavior in natural populations. By studying intraspecies variation in innate avoidance behavior to thermal stimuli in the nematode Caenorhabditis elegans, we uncovered genetic principles of how different components of a behavioral response can be altered in nature to generate behavioral diversity. Using a thermal pulse assay, we uncovered heritable variation in responses to a transient temperature increase. Quantitative trait locus mapping revealed that separate components of this response were controlled by distinct genomic loci. The loci we identified contributed to variation in components of thermal pulse avoidance behavior in an additive fashion. Our results show that the escape behavior induced by thermal stimuli is composed of simpler behavioral components that are influenced by at least six distinct genetic loci. The loci that decouple components of the escape behavior reveal a genetic system that allows independent modification of behavioral parameters. Our work sets the foundation for future studies of evolution of innate behaviors at the molecular and neuronal level. PMID:26092720

  15. Holographic polymer-dispersed liquid crystal Bragg grating integrated inside a solid core photonic crystal fiber.

    PubMed

    Zito, Gianluigi; Pissadakis, Stavros

    2013-09-01

    A polymer/liquid crystal-based fiber Bragg grating (PLC-FBG) is fabricated with visible two-beam holography by photo-induced modulation of a prepolymer/liquid crystal solution infiltrated into the hollow channels of a solid core photonic crystal fiber (PCF). The fabrication process and effects related to the photonic bandgap guidance into the infiltrated PCF, and characterization of the PLC-FBG, are discussed. Experimental data presented here demonstrate that the liquid crystal inclusions of the PLC-FBG lead to high thermal and bending sensitivities. The microscopic behavior of the polymer/liquid crystal phase separation inside the PCF capillaries is examined using scanning electron microscopy, and is discussed further. PMID:23988927

  16. Exploiting a Transmission Grating Spectrometer

    SciTech Connect

    Ronald E. Bell

    2004-12-08

    The availability of compact transmission grating spectrometers now allows an attractive and economical alternative to the more familiar Czerny-Turner configuration for many high-temperature plasma applications. Higher throughput is obtained with short focal length refractive optics and stigmatic imaging. Many more spectra can be obtained with a single spectrometer since smaller, more densely packed optical input fibers can be used. Multiple input slits, along with a bandpass filter, can be used to maximize the number of spectra per detector, providing further economy. Curved slits can correct for the strong image curvature of the short focal length optics. Presented here are the governing grating equations for both standard and high-dispersion transmission gratings, defining dispersion, image curvature, and desired slit curvature, that can be used in the design of improved plasma diagnostics.

  17. Diffraction by random Ronchi gratings.

    PubMed

    Torcal-Milla, Francisco Jose; Sanchez-Brea, Luis Miguel

    2016-08-01

    In this work, we obtain analytical expressions for the near-and far-field diffraction of random Ronchi diffraction gratings where the slits of the grating are randomly displaced around their periodical positions. We theoretically show that the effect of randomness in the position of the slits of the grating produces a decrease of the contrast and even disappearance of the self-images for high randomness level at the near field. On the other hand, it cancels high-order harmonics in far field, resulting in only a few central diffraction orders. Numerical simulations by means of the Rayleigh-Sommerfeld diffraction formula are performed in order to corroborate the analytical results. These results are of interest for industrial and technological applications where manufacture errors need to be considered. PMID:27505363

  18. Demonstration of Electrostatic to Electromagnetic Conversion through Induced Nonlinear Scattering by Thermal Plasma

    NASA Astrophysics Data System (ADS)

    Tejero, Erik

    2015-11-01

    The nonlinear conversion of electrostatic (ES) to electromagnetic (EM) waves in the whistler branch through induced scattering by thermal electrons is an important contribution to the evolution of plasmas in weak turbulence when the wave amplitude is large enough for linear/quasi-linear approaches to break down. It has been theoretically shown that in isothermal low beta turbulent plasmas the rate of induced scattering by particles is much larger than three-wave coalescence and decay processes. It is particularly important to near-Earth space plasma evolution during disturbed times when wave amplitudes cross the threshold for nonlinear scattering. The change in k vector and group velocity of the waves resulting from the conversion from ES to EM enhances the efficiency of pitch-angle scattering, which plays a dramatic role in regulating the trapped energetic electron fluxes inthe Earth's radiation belts. This nonlinear process is being studied in the NRL Space Physics Simulation Chamber, demonstrating the induced nonlinear scattering of quasi-electrostatic pump waves by thermal electrons. The experimental results support theoretical predictions of the nonlinear interaction. Work supported by the Naval Reseach Laboratory Base Program.

  19. Thermally induced gel from cellulose/NaOH/PEG solution: preparation, characterization and mechanical properties

    NASA Astrophysics Data System (ADS)

    Wan, Caichao; Lu, Yun; Jin, Chunde; Sun, Qingfeng; Li, Jian

    2015-04-01

    In this paper, we reported a thermally induced gel with strong mechanical properties prepared from cellulose/NaOH/PEG aqueous solution following the procedures of dissolution, heating and freeze-drying. The as-prepared gel showed undeveloped networks composed of cross-linked fiber aggregations tightly coated with plenty of NaOH·H2O and PEG-aggregated fine particles, which led to the significant enhancement of thermal stability and the disappearance of the original cellulose crystalline structures. Furthermore, the elastic modulus, yield stress and toughness of the mechanically strong gel were measured to be up to 3,210, 325 kPa and 389 kJ m-3, respectively, comparable to those of cross-linked polymer gel materials with strong mechanical strength such as the microfibrillated cellulose aerogels and the three-dimensional architectures of graphene hydrogels.

  20. Spin-pump-induced spin transport in a thermally evaporated pentacene film

    SciTech Connect

    Tani, Yasuo; Shikoh, Eiji; Teki, Yoshio

    2015-12-14

    We report the spin-pump-induced spin transport properties of a pentacene film prepared by thermal evaporation. In a palladium(Pd)/pentacene/Ni{sub 80}Fe{sub 20} tri-layer sample, a pure spin-current is generated in the pentacene layer by the spin-pumping of Ni{sub 80}Fe{sub 20}, which is independent of the conductance mismatch problem in spin injection. The spin current is absorbed into the Pd layer, converted into a charge current with the inverse spin-Hall effect in Pd, and detected as an electromotive force. This is clear evidence for the pure spin current at room temperature in pentacene films prepared by thermal evaporation.

  1. Determination of the 243,246,248Cm thermal neutron induced fission cross sections

    NASA Astrophysics Data System (ADS)

    Serot, O.; Wagemans, C.; Vermote, S.; Heyse, J.; Soldner, T.; Geltenbort, P.

    2005-11-01

    The minor actinide waste produced in nuclear power plants contains various Cm-isotopes, and transmutation scenarios require improved fission cross section data. The available thermal neutron induced fission cross section data for 243Cm, 246Cm and 248Cm are not very accurate, so new cross section measurements have been performed at the high flux reactor of the ILL in Grenoble (France) under better experimental conditions (highly enriched samples, very intense and clean neutron beam). The measurements were performed at a neutron energy of 5.38 meV, yielding fission cross section values of (1240±28)b for 243Cm, (25±47)mb for 246Cm and (685±84)mb for 248Cm. From these results, thermal fission cross section values of (572±14)b; (12±25)mb and (316±43)mb have been deduced for 243Cm, 246Cm and 248Cm, respectively.

  2. Attosecond electron thermalization in laser-induced nonsequential multiple ionization: hard versus glancing collisions

    NASA Astrophysics Data System (ADS)

    Liu, X.; Figueira de Morisson Faria, C.; Becker, W.

    2008-02-01

    A recollision-based largely classical statistical model of laser-induced nonsequential multiple (N-fold) ionization of atoms is further explored. Upon its return to the ionic core, the first-ionized electron interacts with the other N- 1 bound electrons either through a contact or a Coulomb interaction. The returning electron may leave either immediately after this interaction or join the other electrons to form a thermalized complex which leaves the ion after the delay Δt, which is the sum of a thermalization time and a possible additional dwell time. Good agreement with the available triple and quadruple ionization data in neon and argon is obtained with the contact scenario and delays of Δt=0.17 T and 0.265 T, respectively, with T the laser period.

  3. Factors influencing the thermally-induced strength degradation of B/Al composites

    NASA Technical Reports Server (NTRS)

    Dicarlo, J. A.

    1982-01-01

    Literature data related to the thermally-induced strength degradation of B/Al composites were examined in the light of fracture theories based on reaction-controlled fiber weakening. Under the assumption of a parabolic time-dependent growth for the interfacial reaction product, a Griffith-type fracture model was found to yield simple equations whose predictions were in good agreement with data for boron fiber average strength and for B/Al axial fracture strain. The only variables in these equations were the time and temperature of the thermal exposure and an empirical factor related to fiber surface smoothness prior to composite consolidation. Such variables as fiber diameter and aluminum alloy composition were found to have little influence. The basic and practical implications of the fracture model equations are discussed.

  4. HF-induced airglow at magnetic zenith: Thermal and parametric instabilities near electron gyroharmonics

    NASA Astrophysics Data System (ADS)

    Mishin, E. V.; Kosch, M. J.; Pedersen, T. R.; Burke, W. J.

    2005-12-01

    We analyze airglow induced by intense radio waves at the High-frequency Active Auroral Research Program (HAARP) facility for pump frequencies f0 near the second and third electron gyroharmonic (fc). While passing through the double resonance in the weakening ionosphere during heating at f0 ~ 2fc, airglow intensities rose abruptly and remained elevated during four consecutive pulses. During this period both the thermal and parametric instabilities coexisted. Subsequently, the thermal parametric instability was hampered. The effectiveness of heating near the second gyroharmonic is ascribed to specific dispersion characteristics near the double resonance. The observations suggest that Langmuir waves participate in cyclotron acceleration when the local plasma and second gyroharmonic frequencies match. With f0 ~ 3fc the airglow terminated due to the suppression of cyclotron acceleration and parametric decay instability.

  5. Thermal-induced conversion of maleic and fumaric acid anion radicals in poly(methyl methacrylate)

    SciTech Connect

    Torikai, A.; Fukumoto, M.

    1980-04-01

    Thermal-induced conversion of maleic and fumaric acid anion radicals produced by ..gamma.. irradiation at 77/sup 0/K in poly(methyl methacrylate) (PMMA) was studied by electron spin resonance (ESR) and optical absorption spectroscopic measurements. The ESR spectra of these acid anion radicals change into two-line spectra with a line separation of ca. 10 G by thermal annealing. This spectrum is assigned to a protonated radical of each acid anion radical. Anion radicals of the solutes are relatively stable below the ..gamma.. transition point of PMMA and the conversion reaction takes place near this point. This means that the molecular motion of matrix molecule affects the radical conversion reaction.

  6. Very low thermally induced tip expansion by vacuum ultraviolet irradiation in a scanning tunneling microscope junction

    NASA Astrophysics Data System (ADS)

    Riedel, D.; Delacour, C.; Mayne, A. J.; Dujardin, G.

    2009-10-01

    The thermal and photoelectronic processes induced when a vacuum ultraviolet (VUV) laser irradiates the junction of a scanning tunneling microscope (STM) are studied. This is performed by synchronizing the VUV laser shots with the STM scan signal. Compared to other wavelengths, the photoinduced thermal STM-tip expansion is not observed when the VUV radiation is freed from spurious emissions. Furthermore, we demonstrate that the purified VUV photoinduced transient signal detected in the tunnel current is entirely due to photoelectronic emission and not combined with thermionic processes. The ensuing photoelectron emission is shown to be independent of the tip-surface distance while varying linearly with the pure VUV laser intensity. These results illustrate a strong decoupling between phonons and photoelectrons which allows a very weak STM-tip expansion.

  7. Cracks in Martian boulders exhibit preferred orientations that point to solar-induced thermal stress.

    PubMed

    Eppes, Martha-Cary; Willis, Andrew; Molaro, Jamie; Abernathy, Stephen; Zhou, Beibei

    2015-01-01

    The origins of fractures in Martian boulders are unknown. Here, using Mars Exploration Rover 3D data products, we obtain orientation measurements for 1,857 cracks visible in 1,573 rocks along the Spirit traverse and find that Mars rock cracks are oriented in statistically preferred directions similar to those compiled herein for Earth rock cracks found in mid-latitude deserts. We suggest that Martian directional cracking occurs due to the preferential propagation of microfractures favourably oriented with respect to repeating geometries of diurnal peaks in sun-induced thermal stresses. A numerical model modified here with Mars parameters supports this hypothesis both with respect to the overall magnitude of stresses as well as to the times of day at which the stresses peak. These data provide the first direct field and numerical evidence that insolation-related thermal stress potentially plays a principle role in cracking rocks on portions of the Martian surface. PMID:25813699

  8. Towards thermally induced spin accumulation in Fe/GaAs structures

    NASA Astrophysics Data System (ADS)

    Wagner, Thomas; Olejnik, Kamil; Haigh, James; Irvine, Andrew; Martin, Sylvain; Campion, Richard; Wunderlich, Joerg

    We study non-local spin valves of semiconductor-ferromagnetic metal hybrid systems. The epitaxially grown samples consist of a low doped GaAs transport channel with ultrathin Fe top contacts. Magnetic fields applied along the easy and hard axis show spin-valve and Hanle-type curves, respectively. The latter can be used to determine the spin-dephasing time in our samples. We further investigate the potential of non-local spin valves for electrical detection of thermally induced spin accumulation in semiconductors. Thermal spin injection is driven by temperature gradients across interfaces between ferromagnetic and non-magnetic materials. Common ways to establish the required temperature gradients are Joule heating and absorption of focused laser light. We present finite-element simulations of the temperature profile expected in our microdevices. This is of interest in the emerging field of spin caloritronics. We acknowledge funding by the European Union under Grant agreement 316657 (SpinIcur).

  9. Thermally induced release from polymeric microparticles with liquid core: the mechanism.

    PubMed

    Latnikova, Alexandra; Yildirim, Arda

    2015-03-14

    Herein we demonstrate how the volatility of a liquid can be manipulated by enclosing microdroplets of the liquid into thin polymeric shells. In this way, composite core-shell microparticles consisting of 80 wt% of a liquid core material and 20 wt% of a polymer can be made 150 °C more stable than the individual core component. The thermal stability of the composite microparticles is found to be determined by the boiling point of the core material and the average particle size, while the role of the particle shell thickness is much less relevant. Two mechanisms responsible for the release of the core material from the microparticles at elevated temperatures were resolved: (1) thermally induced degradation of the shell and (2) diffusion of the core material through the polymeric shell boosted by the increased inner pressure. PMID:25627164

  10. Recent progress in polymer optical fibre gratings

    NASA Astrophysics Data System (ADS)

    Zhang, C.; Carroll, K.; Webb, D. J.; Bennion, I.; Kalli, K.; Emiliyanov, G.; Bang, O.; Kjær, E.; Peng, G. D.

    2008-04-01

    We describe our recent progress in polymer fibre Bragg grating technology, including the writing of the first FBGs in TOPAS cyclic olefin copolymer, enhancements to photosensitivity brought about by dopants and studies on grating annealing.

  11. Sensitivity of a laser-driven-grating linac to grating errors

    SciTech Connect

    Kroll, N.M.

    1982-04-01

    The effect of grating errors on transverse beam stability is analyzed. We characterize grating errors by random groove displacements and find that transverse displacements due to such errors approach limiting values of the same order as the grating displacements themselves. It therefore appears that transverse stability requirements will not impose unusually stringent precision requirements on the grating structure.

  12. Technical textiles with embedded fibre Bragg grating sensors

    NASA Astrophysics Data System (ADS)

    Bilro, L.; Cunha, H.; Pinto, J. L.; Nogueira, R. N.

    2009-10-01

    The characterization of fiber Bragg grating (FBG) sensors integrated on 2D and 3D mesh structures is presented. Several materials and configurations were tested, namely cork, foams, PVC, hexagonal 3D. Sensors were embedded between two substrates using textile lamination technique. Every sample was subjected to temperature variations and mechanical deformations. Through Bragg wavelength monitoring, thermal, deformation and pressure performance were evaluated. These results provide significant information to the conception of smart textiles.

  13. Gratings for High-Energy Petawatt Lasers

    SciTech Connect

    Nguyen, H T; Britten, J A; Carlson, T C; Nissen, J D; Summers, L J; Hoaglan, C R; Aasen, M D; Peterson, J E; Jovanovic, I

    2005-11-08

    To enable high-energy petawatt laser operation we have developed the processing methods and tooling that produced both the world's largest multilayer dielectric reflection grating and the world's highest laser damage resistant gratings. We have successfully delivered the first ever 80 cm aperture multilayer dielectric grating to LLNL's Titan Intense Short Pulse Laser Facility. We report on the design, fabrication and characterization of multilayer dielectric diffraction gratings.

  14. Thermal cycling induced load on copper-ribbons in crystalline photovoltaic modules

    NASA Astrophysics Data System (ADS)

    Meier, R.; Kraemer, F.; Wiese, S.; Wolter, K.-J.; Bagdahn, J.

    2010-08-01

    Solar module lifetime is limited by the fatigue behavior of its cell interconnectors: the copper-ribbons. Every change in temperature induces thermo-mechanical stresses in the module components due to their thermo-mechanical mismatch. The purpose of this work is to quantify this load on the copper-ribbons between the individual cells of a cell string during a thermal cycling test by measuring cell displacement using digital image correlation and to compare the results to finite element analysis (FEM). Furthermore with help of FEM the influences of different materials were investigated, allowing material and layout optimizations with respect to copper-ribbon loading.

  15. Moisture-Induced Delamination Video of an Oxidized Thermal Barrier Coating

    NASA Technical Reports Server (NTRS)

    Smialek, James L.; Zhu, Dongming; Cuy, Michael D.

    2008-01-01

    PVD TBC coatings were thermally cycled to near-failure at 1150 C. Normal failure occurred after 200-300 1-hr cycles with only moderate weight gains (0.5 mg/cm2). Delamination and buckling was often delayed until well after cooldown (desktop spallation), but could be instantly induced by the application of water drops, as shown in an accompanying video-recording. Moisture therefore plays a primary role in delayed desktop TBC failure. Hydrogen embrittlement is proposed as the underlying mechanism.

  16. Direct laser writing of polymeric nanostructures via optically induced local thermal effect

    NASA Astrophysics Data System (ADS)

    Tong, Quang Cong; Nguyen, Dam Thuy Trang; Do, Minh Thanh; Luong, Mai Hoang; Journet, Bernard; Ledoux-Rak, Isabelle; Lai, Ngoc Diep

    2016-05-01

    We demonstrate the fabrication of desired structures with feature size below the diffraction limit by use of a positive photoresist. The direct laser writing technique employing a continuous-wave laser was used to optically induce a local thermal effect in a positive photoresist, which then allowed the formation of solid nanostructures. This technique enabled us to realize multi-dimensional sub-microstructures by use of a positive photoresist, with a feature size down to 57 nm. This mechanism acting on positive photoresists opens a simple and low-cost way for nanofabrication.

  17. Thermocapillary Migration of Liquid Droplets Induced by a Unidirectional Thermal Gradient.

    PubMed

    Dai, Qingwen; Khonsari, M M; Shen, Cong; Huang, Wei; Wang, Xiaolei

    2016-08-01

    A liquid droplet placed on a nonuniformly heated solid surface will migrate from a high-temperature region to a low-temperature region. This study reports the development of a theoretical model and experimental investigation on the migration behavior of paraffin oil droplets induced by the unidirectional thermal gradient. Thin-film lubrication theory is employed to determine the migration velocity of droplets, and temperature dependence of viscosity is taken into account. Comparisons between experimental and numerical results are presented. An effective approach for estimating the thermocapillary migration velocity of droplets on lubrication is proposed. PMID:27400229

  18. Sub-Microsecond Temperature Measurement in Liquid Water Using Laser Induced Thermal Acoustics

    NASA Technical Reports Server (NTRS)

    Alderfer, David W.; Herring, G. C.; Danehy, Paul M.; Mizukaki, Toshiharu; Takayama, Kazuyoshi

    2005-01-01

    Using laser-induced thermal acoustics, we demonstrate non-intrusive and remote sound speed and temperature measurements over the range 10 - 45 C in liquid water. Averaged accuracy of sound speed and temperature measurements (10 s) are 0.64 m/s and 0.45 C respectively. Single-shot precisions based on one standard deviation of 100 or greater samples range from 1 m/s to 16.5 m/s and 0.3 C to 9.5 C for sound speed and temperature measurements respectively. The time resolution of each single-shot measurement was 300 nsec.

  19. Spectroscopic Evidence for Exceptional Thermal Contribution to Electron-Beam Induced Fragmentation

    SciTech Connect

    Caldwell, Marissa A.; Haynor, Ben; Aloni, Shaul; Ogletree, D. Frank; Wong, H.-S. Philip; Urban, Jeffrey J.; Milliron, Delia J.

    2010-11-16

    While electron beam induced fragmentation (EBIF) has been reported to result in the formation of nanocrystals of various compositions, the physical forces driving this phenomenon are still poorly understood. We report EBIF to be a much more general phenomenon than previously appreciated, operative across a wide variety of metals, semiconductors and insulators. In addition, we leverage the temperature dependent bandgap of several semiconductors to quantify -- using in situ cathodoluminescence spectroscopy -- the thermal contribution to EBIF, and find extreme temperature rises upwards of 1000K.

  20. Thermally induced vibrations in a generalized thermoelastic solid with a cavity

    SciTech Connect

    Erbay, H.A.; Erbay, S.; Dost, S. )

    1991-06-01

    The present work deals with thermally induced vibrations in an infinite solid with a cavity. The medium is assumed to be linear, isotropic, temperature-rate-dependent thermoelastic. The problem is solved for the cases of cylindrical and spherical cavities. The surface of the cavity is assumed to be subjected to a temperature varying harmonically with time, and free of stress. For the cases considered, the coupled field equations admit exact solutions in terms of Hankel and the spherical Hankel functions, respectively. Numerical results are compared with those of classical thermoelasticity. The contribution of the second sound parameters in these problems becomes more significant as the frequency of applied temperature increases. 8 refs.

  1. Non-Intrusive and Quick Response Thermometry Using Laser-Induced Thermal Acoustics (LITA)

    NASA Astrophysics Data System (ADS)

    Mizukaki, Toshiharu

    By using laser-induced thermal acoustics, we demonstrate a non-invasive and remote method to measure the speed of sound and temperature ranging from 278 K to 341 K in distilled water at atmospheric pressure. The accuracies of the measured speed of sound and temperature were found to be 3% and 4%, respectively. Single-shot precisions based on three standard deviations of 20 samples were within 4% for the speed of sound and the temperature. The time resolution for each measurement was 300 ns.

  2. Pressure measurement in supersonic air flow by differential absorptive laser-induced thermal acoustics

    NASA Astrophysics Data System (ADS)

    Hart, Roger C.; Herring, G. C.; Balla, R. Jeffrey

    2007-06-01

    Nonintrusive, off-body flow barometry in Mach 2 airflow has been demonstrated in a large-scale supersonic wind tunnel using seedless laser-induced thermal acoustics (LITA). The static pressure of the gas flow is determined with a novel differential absorption measurement of the ultrasonic sound produced by the LITA pump process. Simultaneously, the streamwise velocity and static gas temperature of the same spatially resolved sample volume were measured with this nonresonant time-averaged LITA technique. Mach number, temperature, and pressure have 0.2%, 0.4%, and 4% rms agreement, respectively, in comparison with known free-stream conditions.

  3. Numerical simulation of thermally induced near-surface flows over Martian terrain

    NASA Technical Reports Server (NTRS)

    Parish, T. R.; Howard, A. D.

    1993-01-01

    Numerical simulations of the Martian near-surface wind regime using a mesoscale atmospheric model have shown that the thermally induced near-surface winds are analogous to terrestrial circulations. In particular, katabatic wind displays a striking similarity to flow observed over Antarctica. Introduction of solar radiation strongly perturbs the slope flows; anabatic conditions develop in middle to high latitudes during the daytime hours due to the solar heating of the sloping terrain. There appears to be a rapid transition from the katabatic to the anabatic flow regimes, emphasizing the primary importance of radiative exchanges at the surface in specifying the horizontal pressure gradient force.

  4. Pressure Measurement in Supersonic Air Flow by Differential Absorptive Laser-Induced Thermal Acoustics

    NASA Technical Reports Server (NTRS)

    Hart, Roger C.; Herring, Gregory C.; Balla, Robert J.

    2007-01-01

    Nonintrusive, off-body flow barometry in Mach-2 airflow has been demonstrated in a large-scale supersonic wind tunnel using seedless laser-induced thermal acoustics (LITA). The static pressure of the gas flow is determined with a novel differential absorption measurement of the ultrasonic sound produced by the LITA pump process. Simultaneously, stream-wise velocity and static gas temperature of the same spatially-resolved sample volume were measured with this nonresonant time-averaged LITA technique. Mach number, temperature and pressure have 0.2%, 0.4%, and 4% rms agreement, respectively, in comparison with known free-stream conditions.

  5. Common-Path Heterodyne Laser-Induced Thermal Acoustics for Seedless Laser Velocimetry

    NASA Technical Reports Server (NTRS)

    Hart, Roger C.; Herring, G. C.; Balla, R. Jeffrey; Bushnell, Dennis M. (Technical Monitor)

    2001-01-01

    We demonstrate the use of a novel technique for the detection of heterodyne laser-induced thermal acoustics signals, which allows the construction of a highly stable seedless laser velocimeter. A common-path configuration is combined with quadrature detection to provide flow direction, greatly improve robustness to misalignment and vibration, and give reliable velocity measurement at low flow velocities. Comparison with Pitot tube measurements in the freestream of a wind tunnel shows root-mean-square errors of 0.67 m/s over the velocity range 0.55 m/s.

  6. Long-lived anomalous thermal diffusion induced by elastic cell membranes on nearby particles

    NASA Astrophysics Data System (ADS)

    Daddi-Moussa-Ider, Abdallah; Guckenberger, Achim; Gekle, Stephan

    2016-01-01

    The physical approach of a small particle (virus, medical drug) to the cell membrane represents the crucial first step before active internalization and is governed by thermal diffusion. Using a fully analytical theory we show that the stretching and bending of the elastic membrane by the approaching particle induces a memory in the system, which leads to anomalous diffusion, even though the particle is immersed in a purely Newtonian liquid. For typical cell membranes the transient subdiffusive regime extends beyond 10 ms and can enhance residence times and possibly binding rates up to 50%. Our analytical predictions are validated by numerical simulations.

  7. Moisture-Induced Delamination Video of an Oxidized Thermal Barrier Coating

    NASA Technical Reports Server (NTRS)

    Smialek, James L.; Zhu, Dongming; Cuy, Michael D.

    2008-01-01

    PVD TBC coatings were thermally cycled to near-failure at 1150 C. Normal failure occurred after 200 to 300 1-hr cycles with only moderate weight gains (0.5 mg/sq cm). Delamination and buckling was often delayed until well after cooldown (desktop spallation), but could be instantly induced by the application of water drops, as shown in a video clip which can be viewed by clicking on figure 2 of this report. Moisture therefore plays a primary role in delayed desktop TBC failure. Hydrogen embrittlement is proposed as the underlying mechanism.

  8. Fabrication of triple layered vascular scaffolds by combining electrospinning, braiding, and thermally induced phase separation

    NASA Astrophysics Data System (ADS)

    Mi, Hao-Yang; Jing, Xin; Yu, Emily; McNulty, Jason; Turng, Lih-Sheng

    2015-12-01

    Triple layered small diameter vascular scaffolds, which consisted of thermoplastic polyurethane (TPU) and silk, were fabricated in this study for the first time by combining electrospinning, braiding, and thermally induced phase separation methods. These novel vascular scaffolds, which possess three layers of different structures (nanofibrous inner layer, woven silk filament middle layer, and porous outer layer) have a desired toe region in the tensile test and sufficient suture retention and burst pressure for vascular graft applications. The endothelia cell culture tests showed that a cell layer could form on the inner surface of a scaffold with high cell viability. Furthermore, the cells showed favorable morphology on the scaffold.

  9. Influence of cubic nonlinearity on compensation of thermally induced polarisation distortions in Faraday isolators

    SciTech Connect

    Kuzmina, M S; Khazanov, E A

    2013-10-31

    The problem on laser radiation propagation in a birefringent medium is solved with the allowance made for thermally induced linear birefringence under the conditions of cubic nonlinearity. It is shown that at high average and peak radiation powers the degree of isolation in a Faraday isolator noticeably reduces due to the cubic nonlinearity: by more than an order of magnitude when the B-integral is equal to unity. This effect is substantial for pulses with the energy of 0.2 – 3 J, duration of 10 ps to 4 ns and pulse repetition rate of 0.2 – 40 kHz. (components of laser devices)

  10. Thermal Injury Lowers the Threshold for Radiation-Induced Neuroinflammation and Cognitive Dysfunction

    PubMed Central

    Cherry, Jonathan D.; Williams, Jacqueline P.; O’Banion, M. Kerry; Olschowka, John A.

    2013-01-01

    The consequences of radiation exposure alone are relatively well understood, but in the wake of events such as the World War II nuclear detonations and accidents such as Chernobyl, other critical factors have emerged that can substantially affect patient outcome. For example, ~70% of radiation victims from Hiroshima and Nagasaki received some sort of additional traumatic injury, the most common being thermal burn. Animal data has shown that the addition of thermal insult to radiation results in increased morbidity and mortality. To explore possible synergism between thermal injury and radiation on brain, C57BL/6J female mice were exposed to either 0 or 5 Gy whole-body gamma irradiation. Irradiation was immediately followed by a 10% total-body surface area full thickness thermal burn. Mice were sacrificed 6 h, 1 week or 6 month post-injury and brains and plasma were harvested for histology, mRNA analysis and cytokine ELISA. Plasma analysis revealed that combined injury synergistically upregulates IL-6 at acute time points. Additionally, at 6 h, combined injury resulted in a greater upregulation of the vascular marker, ICAM-1 and TNF-α mRNA. Enhanced activation of glial cells was also observed by CD68 and Iba1 immunohistochemistry at all time points. Additionally, doublecortin staining at 6 months showed reduced neurogenesis in all injury conditions. Finally, using a novel object recognition test, we observed that only mice with combined injury had significant learning and memory deficits. These results demonstrate that thermal injury lowers the threshold for radiation-induced neuroinflammation and long-term cognitive dysfunction. PMID:24059681

  11. Advanced Fibre Bragg Grating and Microfibre Bragg Grating Fabrication Techniques

    NASA Astrophysics Data System (ADS)

    Chung, Kit Man

    Fibre Bragg gratings (FBGs) have become a very important technology for communication systems and fibre optic sensing. Typically, FBGs are less than 10-mm long and are fabricated using fused silica uniform phase masks which become more expensive for longer length or non-uniform pitch. Generally, interference UV laser beams are employed to make long or complex FBGs, and this technique introduces critical precision and control issues. In this work, we demonstrate an advanced FBG fabrication system that enables the writing of long and complex gratings in optical fibres with virtually any apodisation profile, local phase and Bragg wavelength using a novel optical design in which the incident angles of two UV beams onto an optical fibre can be adjusted simultaneously by moving just one optical component, instead of two optics employed in earlier configurations, to vary the grating pitch. The key advantage of the grating fabrication system is that complex gratings can be fabricated by controlling the linear movements of two translation stages. In addition to the study of advanced grating fabrication technique, we also focus on the inscription of FBGs written in optical fibres with a cladding diameter of several ten's of microns. Fabrication of microfibres was investigated using a sophisticated tapering method. We also proposed a simple but practical technique to filter out the higher order modes reflected from the FBG written in microfibres via a linear taper region while the fundamental mode re-couples to the core. By using this technique, reflection from the microfibre Bragg grating (MFBG) can be effectively single mode, simplifying the demultiplexing and demodulation processes. MFBG exhibits high sensitivity to contact force and an MFBG-based force sensor was also constructed and tested to investigate their suitability for use as an invasive surgery device. Performance of the contact force sensor packaged in a conforming elastomer material compares favourably to one

  12. Diffraction gratings used as identifying markers

    DOEpatents

    Deason, Vance A.; Ward, Michael B.

    1991-01-01

    A finely detailed defraction grating is applied to an object as an identifier or tag which is unambiguous, difficult to duplicate, or remove and transfer to another item, and can be read and compared with prior readings with relative ease. The exact pattern of the defraction grating is mapped by diffraction moire techniques and recorded for comparison with future readings of the same grating.

  13. Embedded high-contrast distributed grating structures

    DOEpatents

    Zubrzycki, Walter J.; Vawter, Gregory A.; Allerman, Andrew A.

    2002-01-01

    A new class of fabrication methods for embedded distributed grating structures is claimed, together with optical devices which include such structures. These new methods are the only known approach to making defect-free high-dielectric contrast grating structures, which are smaller and more efficient than are conventional grating structures.

  14. Investigations on birefringence effects in polymer optical fiber Bragg gratings

    NASA Astrophysics Data System (ADS)

    Hu, X.; Sáez-Rodríguez, D.; Bang, O.; Webb, D. J.; Caucheteur, C.

    2014-05-01

    Step-index polymer optical fiber Bragg gratings (POFBGs) and microstructured polymer optical fiber Bragg gratings (mPOFBGs) present several attractive features, especially for sensing purposes. In comparison to FBGs written in silica fibers, they are more sensitive to temperature and pressure because of the larger thermo-optic coefficient and smaller Young's modulus of polymer materials. (M)POFBGs are most often photowritten in poly(methylmethacrylate) (PMMA) materials using a continuous-wave 325 nm HeCd laser. For the first time to the best of our knowledge, we study photoinduced birefringence effects in (m)POFBGs. To achieve this, highly reflective gratings were inscribed with the phase mask technique. They were then monitored in transmission with polarized light. For this, (m)POF sections a few cm in length containing the gratings were glued to angled silica fibers. Polarization dependent loss (PDL) and differential group delay (DGD) were computed from the Jones matrix eigenanalysis using an optical vector analyser. Maximum values exceeding several dB and a few picoseconds were obtained for the PDL and DGD, respectively. The response to lateral force was finally investigated. As it induces birefringence in addition to the photo-induced one, an increase of the PDL and DGD values were noticed.

  15. Synthesis of semicrystalline nanocapsular structures obtained by Thermally Induced Phase Separation in nanoconfinement

    PubMed Central

    Torino, Enza; Aruta, Rosaria; Sibillano, Teresa; Giannini, Cinzia; Netti, Paolo A.

    2016-01-01

    Phase separation of a polymer solution exhibits a peculiar behavior when induced in a nanoconfinement. The energetic constraints introduce additional interactions between the polymer segments that reduce the number of available configurations. In our work, this effect is exploited in a one-step strategy called nanoconfined-Thermally Induced Phase Separation (nc-TIPS) to promote the crystallization of polymer chains into nanocapsular structures of controlled size and shell thickness. This is accomplished by performing a quench step of a low-concentrated PLLA-dioxane-water solution included in emulsions of mean droplet size <500 nm acting as nanodomains. The control of nanoconfinement conditions enables not only the production of nanocapsules with a minimum mean particle diameter of 70 nm but also the tunability of shell thickness and its crystallinity degree. The specific properties of the developed nanocapsular architectures have important implications on release mechanism and loading capability of hydrophilic and lipophilic payload compounds. PMID:27604818

  16. Synthesis of semicrystalline nanocapsular structures obtained by Thermally Induced Phase Separation in nanoconfinement.

    PubMed

    Torino, Enza; Aruta, Rosaria; Sibillano, Teresa; Giannini, Cinzia; Netti, Paolo A

    2016-01-01

    Phase separation of a polymer solution exhibits a peculiar behavior when induced in a nanoconfinement. The energetic constraints introduce additional interactions between the polymer segments that reduce the number of available configurations. In our work, this effect is exploited in a one-step strategy called nanoconfined-Thermally Induced Phase Separation (nc-TIPS) to promote the crystallization of polymer chains into nanocapsular structures of controlled size and shell thickness. This is accomplished by performing a quench step of a low-concentrated PLLA-dioxane-water solution included in emulsions of mean droplet size <500 nm acting as nanodomains. The control of nanoconfinement conditions enables not only the production of nanocapsules with a minimum mean particle diameter of 70 nm but also the tunability of shell thickness and its crystallinity degree. The specific properties of the developed nanocapsular architectures have important implications on release mechanism and loading capability of hydrophilic and lipophilic payload compounds. PMID:27604818

  17. Thermally induced phase changes, lateral heterogeneity of the mantle, continental roots, and deep slab anomalies

    NASA Technical Reports Server (NTRS)

    Anderson, Don L.

    1987-01-01

    Factors which influence the lateral heterogeneity in density and seismic velocity with depth in the upper earth mantle are discussed. It is emphasized that most of the increases in density and seismic velocity with depth are caused by pressure-induced solid-solid phase changes in the high-density high-velocity phases of mineral assemblage, due to variations in temperature. In particular, the ilmenite form of MgSiO3 and the gamma-spinel form of Mg2SiO4 have broad stability fields in cold mantle and are not stable in hotter mantle. It is emphasized that the density and velocity anomalies associated with temperature-induced phase changes in mineral assemblage must be taken into account in the thermal models of the slabs; when these effects are accounted for, the geoid and seismic anomalies associated with subducted slabs are consistent with slab confinement to the upper mantle and with layered models of mantle convection.

  18. Modulation polarimetry of thermoelasticity induced by thermal radiation in a glass

    NASA Astrophysics Data System (ADS)

    Matyash, I. E.; Minailova, I. A.; Mishchuk, O. N.; Serdega, B. K.

    2014-07-01

    The phenomenon of thermoelasticity induced by an external thermal radiation in a model glass sample was investigated experimentally. The thermoelasticity was detected by the optical polarization method used in studies of the photoelastic effect and modified by the probe radiation polarization modulation technique. This technique made it possible to increase the sensitivity of the measurement system to the strain state of a solid so that it became possible to detect thermoelasticity under conditions where the temperature gradient across the sample reaches a few fractions of a degree. The spatial and temporal changes of the mechanical stresses induced in the sample by a nonuniform radiation heating and, consequently, by a heat flux were measured. The coordinate functions of temperature as solutions of the inverse problem of thermoelasticity were obtained using the graphical integration of the experimental characteristics. The characteristic parameters of some of the heat transfer mechanisms were determined by analyzing the experimental characteristics of the kinetics and dynamics of mechanical stresses.

  19. Development of a complete plasmonic grating-based sensor and its application for self-assembled monolayer detection.

    PubMed

    Perino, M; Pasqualotto, E; De Toni, A; Garoli, D; Scaramuzza, M; Zilio, P; Ongarello, T; Paccagnella, A; Romanato, F

    2014-09-10

    This work presents an integrated plasmonic biosensing device consisting of a one-dimensional metallic lamellar grating designed to exploit extraordinary transmission of light toward an underlying silicon photodetector. By means of finite element simulations, the grating parameters have been optimized to maximize the light transmission variation induced by the functionalization of the gold nanostructures. An optimized grating was fabricated using an electron beam process and an optoelectronic test bench suitable for sample tests was developed. A clear difference in the grating transmitted light due to surface functionalization was observed in presence of TM polarized illumination. PMID:25321677

  20. Cooled grating infrared spectrometer for astronomical observations

    NASA Astrophysics Data System (ADS)

    Houck, J. R.; Gull, G. E.

    A liquid helium-cooled infrared spectrometer for the 16 to 50 micron range is described. The instrument has six detectors, three each of Si:Sb and Ge:Ga and two diffraction gratings mounted back-to-back. Cold preoptics are used to match the spectrometer to the telescope. In its nominal configuration the system resolution is 0.03 micron from 16 to 30 microns and 0.07 micron from 28 to 50 microns. A cooled filter wheel is used to change order sorting filters. The gratings are driven by a steel band and gear train operating at 4 K. The detector outputs are amplified by a TIA, employing a matched pair of JFETs operating at 70 K inside the dewar. The external warm electronics include a gain stage for the TIA and dc-coupled gating circuit to remove charged-particle (cosmic-ray secondary)-induced noise spikes. The gating circuit reduces the overall system noise by a factor of two when the spectrometer is used on NASA's Kuiper Airborne Observatory. Sample spectra are presented and the deglitcher performance is illustrated.

  1. Radiative heat transfer between two dielectric-filled metal gratings

    NASA Astrophysics Data System (ADS)

    Dai, J.; Dyakov, S. A.; Yan, M.

    2016-04-01

    Nanoscale surface corrugation is known to be able to drastically enhance radiative heat transfer between two metal plates. Here we numerically calculate the radiative heat transfer between two dielectric-filled metal gratings at dissimilar temperatures based on a scattering approach. It is demonstrated that, compared to unfilled metal gratings, the heat flux for a fixed geometry can be further enhanced, by up to 650% for the geometry separated by a vacuum gap of g =1 μ m and temperature values concerned in our study. The enhancement in radiative heat transfer is found to depend on refractive index of the filling dielectric, the specific grating temperatures, and naturally the gap size between the two gratings. The enhancement can be understood through examining the transmission factor spectra, especially the spectral locations of the spoof surface plasmon polariton modes. Of more practical importance, it's shown that the radiative heat flux can exceed that between two planar SiC plates with same thickness, separation, and temperature settings over a wide temperature range. This reaffirms that one can harness rich electromagnetic modal properties in nanostructured materials for efficient thermal management at nanoscale.

  2. Simultaneous, inherently temperature and strain insensitive bio-sensors based on dual-resonance long-period gratings

    NASA Astrophysics Data System (ADS)

    Mani Tripathi, Saurabh; Verma, Deep Shikha; Bock, Wojtek J.; Mikulic, Predrag

    2016-05-01

    Addressing temperature and strain induced cross-talks simultaneously, we propose an inherently strain and temperature insensitive fiber-optic bio-sensor. The insensitivity has been achieved by properly adjusting the dopants and their concentrations, and by optimizing the grating period and the strength of concatenated dual-resonance long-period-gratings.

  3. Thermal analysis of induced damage to the healthy cell during RFA of breast tumor.

    PubMed

    Singh, Sundeep; Bhowmik, Arka; Repaka, Ramjee

    2016-05-01

    Effective pre-clinical computational modeling strategies have been demonstrated in this article to enable risk free clinical application of radiofrequency ablation (RFA) of breast tumor. The present study (a) determines various optimal regulating parameters required for RFA of tumor and (b) introduces an essential clinical monitoring scheme to minimize the extent of damage to the healthy cell during RFA of tumor. The therapeutic capabilities offered by RFA of breast tumor, viz., the rise in local temperature and induced thermal damage have been predicted by integrating the bioheat transfer model, the electric field distribution model and the thermal damage model. The mathematical model has been validated with the experimental results available in the literature. The results revealed that, the effective damage of tumor volume sparing healthy tissue essentially depends on the voltage, the exposure time, the local heat distribution, the tumor stage and the electrode geometric configuration. It has been confirmed that, the assessment of damage front can accurately determine the extent of damage as compared to the thermal front. The study further evaluates the damaged healthy and tumor volumes due to RFA of different stages of breast cancer. The assessment of cell survival and damage fractions discloses the propensity of reappearance/healing of tumor cells after treatment. PMID:27157337

  4. Thermalization of electrons in decaying extreme ultraviolet photons induced low pressure argon plasma

    NASA Astrophysics Data System (ADS)

    Beckers, J.; van der Horst, R. M.; Osorio, E. A.; Kroesen, G. M. W.; Banine, V. Y.

    2016-06-01

    We monitored—in the pressure range: 0.5–15 Pa—the electron temperature in decaying plasmas induced in argon gas by pulsed irradiation with extreme ultraviolet (EUV) photons with wavelengths closely around 13.5 nm. For this purpose, temporal measurements of the space-averaged and electric field weighted electron density after pulsed EUV irradiation are combined with an ambipolar diffusion model of the plasma. Results demonstrate that electrons are thermalized to room temperature before the plasma has fully expanded to the chamber walls for pressures of 3 Pa and higher. At pressures below 3 Pa, the electron temperature was found to be up to 0.1 eV above room temperature which is explained by the fact that plasma expansion is too quick for the electrons to fully thermalize. The comparison between plasma expansion duration towards a surface, plasma decay at a surface and time needed for thermalization and cooling of electrons is essential for designers of EUV lithography tools and EUV sources since the temperature of electrons dictates many fundamental physical processes.

  5. Measurement-induced disturbance and thermal negativity in 1D optical lattice chain

    SciTech Connect

    Guo, Jin-Liang; Lin-Wang; Long, Gui-Lu

    2013-03-15

    We study the measurement-induced disturbance (MID) in a 1D optical lattice chain with nonlinear coupling. Special attention is paid to the difference between the thermal entanglement and MID when considering the influences of the linear coupling constant, nonlinear coupling constant and external magnetic field. It is shown that MID is more robust than thermal entanglement against temperature T and external magnetic field B, and MID may reveal more properties about quantum correlations of the system, which can be seen from the point of view that MID can be nonzero when there is no thermal entanglement and MID can detect the critical point of quantum phase transition at finite temperature. - Highlights: Black-Right-Pointing-Pointer The nonlinear coupling constant can strengthen the quantum correlation. Black-Right-Pointing-Pointer MID is more robust than entanglement against temperature and magnetic field. Black-Right-Pointing-Pointer MID exhibits more information about quantum correlation than entanglement. Black-Right-Pointing-Pointer MID can detect the critical point of quantum phase transition at finite temperature.

  6. Dynamic thermal field-induced gradient soft-shear for highly oriented block copolymer thin films.

    PubMed

    Singh, Gurpreet; Yager, Kevin G; Berry, Brian; Kim, Ho-Cheol; Karim, Alamgir

    2012-11-27

    As demand for smaller, more powerful, and energy-efficient devices continues, conventional patterning technologies are pushing up against fundamental limits. Block copolymers (BCPs) are considered prime candidates for a potential solution via directed self-assembly of nanostructures. We introduce here a facile directed self-assembly method to rapidly fabricate unidirectionally aligned BCP nanopatterns at large scale, on rigid or flexible template-free substrates via a thermally induced dynamic gradient soft-shear field. A localized differential thermal expansion at the interface between a BCP film and a confining polydimethylsiloxane (PDMS) layer due to a dynamic thermal field imposes the gradient soft-shear field. PDMS undergoes directional expansion (along the annealing direction) in the heating zone and contracts back in the cooling zone, thus setting up a single cycle of oscillatory shear (maximum lateral shear stress ∼12 × 10(4) Pa) in the system. We successfully apply this process to create unidirectional alignment of BCP thin films over a wide range of thicknesses (nm to μm) and processing speeds (μm/s to mm/s) using both a flat and patterned PDMS layer. Grazing incidence small-angle X-ray scattering measurements show absolutely no sign of isotropic population and reveal ≥99% aligned orientational order with an angular spread Δθ(fwhm) ≤ 5° (full width at half-maximum). This method may pave the way to practical industrial use of hierarchically patterned BCP nanostructures. PMID:23106286

  7. Mechanisms of thermally induced threshold voltage instability in GaN-based heterojunction transistors

    SciTech Connect

    Yang, Shu; Liu, Shenghou; Liu, Cheng; Lu, Yunyou; Chen, Kevin J.

    2014-12-01

    In this work, we attempt to reveal the underlying mechanisms of divergent V{sub TH}-thermal-stabilities in III-nitride metal-insulator-semiconductor high-electron-mobility transistor (MIS-HEMT) and MOS-Channel-HEMT (MOSC-HEMT). In marked contrast to MOSC-HEMT featuring temperature-independent V{sub TH}, MIS-HEMT with the same high-quality gate-dielectric/III-nitride interface and similar interface trap distribution exhibits manifest thermally induced V{sub TH} shift. The temperature-dependent V{sub TH} of MIS-HEMT is attributed to the polarized III-nitride barrier layer, which spatially separates the critical gate-dielectric/III-nitride interface from the channel and allows “deeper” interface trap levels emerging above the Fermi level at pinch-off. This model is further experimentally validated by distinct V{sub G}-driven Fermi level movements at the critical interfaces in MIS-HEMT and MOSC-HEMT. The mechanisms of polarized III-nitride barrier layer in influencing V{sub TH}-thermal-stability provide guidelines for the optimization of insulated-gate III-nitride power switching devices.

  8. Thermal- and electromigration-induced stresses in passivated Al- and AlSiCu-interconnects

    SciTech Connect

    Beckers, D.; Schroeder, H.; Schilling, W.; Eppler, I.

    1997-05-01

    Mechanical stresses in microelectronic devices are of special interest because of degradation effects in microelectronic circuits such as stress induced voiding or electromigration. Al and al-alloys are commonly used as interconnect materials in integrated electronic devices. Stress induced voiding and degradation of metal lines by electromigration are closely related to the stresses in the lines. The authors have studied the strain and stress evolution during thermal cycling, isothermal relaxation and due to electromigration in passivated Al and AlSi(1%)Cu(0.5%) lines by X-Ray diffraction with variation of experimental parameters such as the aspect ratio and the electrical current density. Furthermore the extent of voiding and plastic shear deformation has been determined from the experimental metal strains with the help of finite element calculations. Main results are: (1) During thermal cycling the voiding is less than 2 {center_dot} 10{sup {minus}3}. The extent of plastic shear deformation increases with increasing line width and with decreasing flowstress. (2) During isothermal relaxation void growth occurs but no significant change in the plastic shear deformation. (3) An electric current in the lines causes no measurable additional change of the volume averaged stresses up to line failure.

  9. Dynamics of ultrashort pulsed laser radiation induced non-thermal ablation of graphite

    NASA Astrophysics Data System (ADS)

    Reininghaus, M.; Kalupka, C.; Faley, O.; Holtum, T.; Finger, J.; Stampfer, C.

    2014-12-01

    We report on the dependence of a laser radiation induced ablation process of graphite on the applied pulse duration of ultrashort pulsed laser radiation smaller than 4 ps. The emerging so-called non-thermal ablation process of graphite has been confirmed to be capable to physically separate ultrathin graphitic layers from the surface of pristine graphite bulk crystal. This allows the deposition of ablated graphitic flakes on a substrate in the vicinity of the target. The observed ablation threshold determined at different pulse durations shows a modulation, which we ascribe to lattice motions along the c axis that are theoretically predicted to induce the non-thermal ablation process. In a simple approach, the ablation threshold can be described as a function of the energy penetration depth and the absorption of the applied ultrashort pulsed laser radiation. Based on the analysis of the pulse duration dependence of those two determining factors and the assumption of an invariant ablation process, we are able to reproduce the pulse duration dependence of the ablation threshold. Furthermore, the observed pulse duration dependences confirm the assumption of a fast material specific response of graphite target subsequent to optical excitation within the first 2 ps.

  10. Thermally induced single crystal to single crystal transformation leading to polymorphism

    NASA Astrophysics Data System (ADS)

    Saha, Rajat; Biswas, Susobhan; Dey, Sanjoy Kumar; Sen, Arijit; Roy, Madhusudan; Steele, Ian M.; Dey, Kamalendu; Ghosh, Ashutosh; Kumar, Sanjay

    2014-09-01

    The robust complex [La(1,10-phen)2(NO3)3] (1,10-phen = 1,10-phenanthroline) exhibits thermally induced single crystal to single crystal transformation from one polymorphic phase to another. The complex crystallizes in monoclinic C2/c space group with C2 molecular symmetry at 293 K while at 100 K it shows P21/c space group with C1 molecular symmetry. Supramolecular investigation shows that at 100 K the complex forms 2D achiral sheets whereas at 293 K forms two different homochiral 2D sheets. Low temperature DSC analysis indicates that this structural transformation occurs at 246 K and also this transformation is reversible in nature. We have shown that thermally induced coherent movement of ligands changes the molecular symmetry of the complex and leads to polymorphism. Photoluminescence property of complex has been studied in both solid state and in methanolic solution at room temperature. The effect of the presence low-lying LUMO orbital of π-character in the complex is elucidated by theoretical calculation using DFT method.

  11. Cancelation of thermally induced frequency shifts in bimaterial cantilevers by nonlinear optomechanical interactions

    NASA Astrophysics Data System (ADS)

    Vy, Nguyen Duy; Tri Dat, Le; Iida, Takuya

    2016-08-01

    Bimaterial cantilevers have recently been used in, for example, the calorimetric analysis with picowatt resolution in microscopic space based on state-of-the-art atomic force microscopes. However, thermally induced effects usually change physical properties of the cantilevers, such as the resonance frequency, which reduce the accuracy of the measurements. Here, we propose an approach to circumvent this problem that uses an optical microcavity formed between a metallic layer coated on the back of the cantilever and one coated at the end of an optical fiber irradiating the cantilever. In addition to increasing the sensitivity, the optical rigidity of this system diminishes the thermally induced frequency shift. For a coating thickness of several tens of nanometers, the input power is 5-10 μW. These values can be evaluated from parameters derived by directly irradiating the cantilever in the absence of the microcavity. The system has the potential of using the cantilever both as a thermometer without frequency shifting and as a sensor with nanometer-controlled accuracy.

  12. Coda wave interferometry for the measurement of thermally induced ultrasonic velocity variations in CFRP laminates

    NASA Astrophysics Data System (ADS)

    Livings, Richard; Dayal, Vinay; Barnard, Dan

    2016-02-01

    Ultrasonic velocity measurement is a well-established method to measure properties and estimate strength as well as detect and locate damage. Determination of accurate and repeatable ultrasonic wave velocities can be difficult due to the influence of environmental and experimental factors. Diffuse fields created by a multiple scattering environment have been shown to be sensitive to homogeneous strain fields such as those caused by temperature variations, and Coda Wave Interferometry has been used to measure the thermally induced ultrasonic velocity variation in concrete, aluminum, and the Earth's crust. In this work, we analyzed the influence of several parameters of the experimental configuration on the measurement of thermally induced ultrasonic velocity variations in a carbon-fiber reinforced polymer plate. Coda Wave Interferometry was used to determine the relative velocity change between a baseline signal taken at room temperature and the signal taken at various temperatures. The influence of several parameters of the experimental configuration, such as the material type, the receiver aperture size, and fiber orientation on the results of the processing algorithm was evaluated in order to determine the optimal experimental configuration.---This work is supported by the NSF Industry/University Cooperative Research Program of the Center for Nondestructive Evaluation at Iowa State University.

  13. Compact Imaging Spectrometer Utilizing Immersed Gratings

    DOEpatents

    Chrisp, Michael P.; Lerner, Scott A.; Kuzmenko, Paul J.; Bennett, Charles L.

    2006-03-21

    A compact imaging spectrometer with an immersive diffraction grating that compensates optical distortions. The imaging spectrometer comprises an entrance slit for transmitting light, a system for receiving the light and directing the light, an immersion grating, and a detector array. The entrance slit, the system for receiving the light, the immersion grating, and the detector array are positioned wherein the entrance slit transmits light to the system for receiving the light and the system for receiving the light directs the light to the immersion grating and the immersion grating receives the light and directs the light through an optical element to the detector array.

  14. Distributed etched diffraction grating demultiplexer

    NASA Astrophysics Data System (ADS)

    Jafari, Amir

    This doctoral thesis studies the concept of a distributed etched diffraction grating (DEDG) and presents a methodology to engineer the spectral response of the device. The design which incorporates a distributed Bragg reflector (DBR) at the facets of a conventional etched diffraction grating demultiplexer promises for a superior performance in multiple aspects. Where in a conventional etched diffraction grating, smooth vertical deep etched walls are required in order to realize a low insertion loss device; in the DEDG such requirement is significantly mitigated. Deep etched walls are replaced with shallowly etched diffraction grating facets followed by a DBR structure and as a result devices with significantly lower insertion loss are achievable. The feasibility of the application of DEDG as a wavelength demultiplexer was demonstrated through fabrication and characterization of a prototype device. The proof of concept device was fabricated using the state of the art deep UV optical lithography and reactive ion etching in a nano-photonic silicon-on-insulator (SOI) material platform. The fabricated device was then characterized in the lab. Furthermore, incorporation of the DBR structure at the facets of the conventional etched diffraction grating decouples the reflection and diffraction functionalities, rendering the DEDG suitable for spectral response engineering. According to the application, the output spectral response of the device can be tailored through careful design and optimization of the incorporated DBR. In this thesis, through numerical simulations we have shown that functionalities such as polarization independent performance and at top insertion loss envelop are viable. A methodology to engineer the spectral response of the DEDG is discussed in details.

  15. Non-thermal atmospheric plasma brush induces HEMA grafting onto dentin collagen

    PubMed Central

    Chen, Mingsheng; Zhang, Ying; Dusevich, Vladimir; Liu, Yi; Yu, Qingsong; Wang, Yong

    2014-01-01

    Objective Non-thermal atmospheric plasma (NTAP) brush has been regarded as a promising technique to enhance dental interfacial bonding. However, the principal enhancement mechanisms have not been well identified. In this study, the effect of non-thermal plasmas on grafting of HEMA, a typical dental monomer, onto dentin collagen thin films was investigated. Methods Human dentin was sectioned into 10-um-thick films. After total demineralization in 0.5 M EDTA solution for 30 min, the dentin collagen films were water-rinsed, air-dried, treated with 35 wt% HEMA aqueous solution. The films were then subject to plasma-exposure under a NTAP brush with different time (1–8 min) / input power (5–15 w). For comparison, the dentin collagen films were also treated with the above HEMA solution containing photo-initiators, then subject to light-curing. After plasma-exposure or light-curing, the HEMA-collagen films were rinsed in deionized water, and then examined by FTIR spectroscopy and TEM. Results The FITR results indicated that plasma-exposure could induce significant HEMA grafting onto dentin collagen thin films. In contrast, light-curing led to no detectable interaction of HEMA with dentin collagen. Quantitative IR spectral analysis (i.e., 1720/3075 or 749/3075, HEMA/collagen ratios) further suggested that the grafting efficacy of HEMA onto the plasma-exposed collagen thin films strongly depended on the treatment time and input power of plasmas. TEM results indicated that plasma treatment did not alter collagen’s banding structure. Significance The current study provides deeper insight into the mechanism of dental adhesion enhancement induced by non-thermal plasmas treatment. The NTAP brush could be a promising method to create chemical bond between resin monomers and dentin collagen. PMID:25458523

  16. Thermally induced irreversible conformational changes in collagen probed by optical second harmonic generation and laser-induced fluorescence.

    PubMed

    Theodossiou, T; Rapti, G S; Hovhannisyan, V; Georgiou, E; Politopoulos, K; Yova, D

    2002-01-01

    Irreversible thermal conformational changes induced to collagen have been studied by optical methods. More specifically, second harmonic generation (SHG) from incident nanosecond Ng:YAG 1064 nm radiation and laser-induced fluorescence by 337 nm, pulsed nanosecond nitrogen laser excitation, at 405, 410 and 415 nm emission wavelengths were registered at eight temperatures (40 degrees, 50 degrees, 55 degrees, 60 degrees, 65 degrees, 70 degrees, 75 degrees and 80 degrees C) and normalised with respect to the corresponding values at the ambient temperature of 30 degrees C. The heating protocol used in this work, was selected to monitor only permanent changes reflecting in the optical properties of the samples under investigation. In this context, the SHG, directly related to the collagen fibril population in triple helix conformation, indicated on irreversible phase transition around 64 degrees C. On the other hand fluorescence related to the destruction of cross-linked chromophores in collagen, some of which are related to the triple helix tertiary structure, also indicated a permanent phase transition around 63 degrees C. These results are in agreement with previous results from studies with differential scanning calorimetry. However SHG and fluorescence, being non-invasive optical methods are expected to have a significant impact in the fields of laser ablative surgery and laser tissue welding. PMID:11845366

  17. Curved VPH gratings for novel spectrographs

    NASA Astrophysics Data System (ADS)

    Clemens, J. Christopher; O'Donoghue, Darragh; Dunlap, Bart H.

    2014-07-01

    The introduction of volume phase holographic (VPH) gratings into astronomy over a decade ago opened new possibilities for instrument designers. In this paper we describe an extension of VPH grating technology that will have applications in astronomy and beyond: curved VPH gratings. These devices can disperse light while simultaneously correcting aberrations. We have designed and manufactured two different kinds of convex VPH grating prototypes for use in off-axis reflecting spectrographs. One type functions in transmission and the other in reflection, enabling Offnerstyle spectrographs with the high-efficiency and low-cost advantages of VPH gratings. We will discuss the design process and the tools required for modelling these gratings along with the recording layout and process steps required to fabricate them. We will present performance data for the first convex VPH grating produced for an astronomical spectrograph.

  18. Thermal stress induced voids in nanoscale copper interconnects by in-situ TEM heating

    NASA Astrophysics Data System (ADS)

    An, Jin Ho

    Stress induced void formation in Cu interconnects, due to thermal stresses generated during the processing of semiconductors, is an increasing reliability issue in the semiconductor industry as Cu interconnects are being downscaled to follow the demand for faster chip speed. In this work, 1.8 micron and 180 nm wide Cu interconnects, fabricated by Freescale Semiconductors, were subjected to thermal cycles, in-situ in the TEM, to investigate the stress relaxation mechanisms as a function of interconnect linewidth. The experiments show that the 1.8 micron Cu interconnect lines relax the thermal stresses through dislocation nucleation and motion while the Cu interconnect 180 nm lines exhibit void formation. Void formation in 180 nm lines occurs predominantly at triple junctions where the Ta diffusion barrier meets a Cu grain boundary. In order to understand void formation in 180 nm lines, the grain orientation and local stresses are determined. In particular, Nanobeam Diffraction (NBD) in the TEM is used to obtain the diffraction pattern of each grain, from which the crystal orientation is evaluated by the ACT (Automated Crystallography for TEM) software. In addition, 2D Finite Element Method (FEM) simulations are performed using the Object Oriented Finite Modeling (OOF2) software to correlate grain orientation with local stresses, and consequently void formation. According to the experimental and simulation results obtained, void formation in 180nm Cu interconnects does not seem to be solely dependent on local stresses, but a combination of diffusion paths available, stress gradients and possibly the presence of defects. In addition, based on the in-situ TEM observations, void growth seems to occur through grain boundary and/or interfacial diffusion. However, in-situ STEM observations of fully opened voids post-failure show pileup of material at the Cu grain surfaces. This means that surface or interface diffusion is also very active during void growth in the presence

  19. High contrast gratings for high-precision metrology

    NASA Astrophysics Data System (ADS)

    Kroker, Stefanie; Steiner, Stefan; Käsebier, Thomas; Kley, Ernst-Bernhard; Tünnermann, Andreas

    2013-03-01

    Experiments in the field of high-precision optical metrology are crucially limited by thermal noise of the optical components such as mirrors or beam splitters. Amorphous coatings stacks are found to be a main source for these thermal fluctuations. In this contribution we present approaches to realize coating free optical components based on resonant high contrast gratings (HCGs) made of crystalline silicon. It is shown that beside classical cavity mirrors the concept of HCGs can also be used for reflective cavity couplers. We compare the advantages and challenges of these HCG reflectors with distributed Bragg reflectors made of crystalline coatings for applications in optical metrology.

  20. Factors influencing the temperature sensitivity of PMMA based optical fiber Bragg gratings

    NASA Astrophysics Data System (ADS)

    Zhang, Wei; Webb, David J.

    2014-05-01

    The Bragg wavelength of a PMMA based fiber grating is determined by the effective core index and the grating pitch, which, in temperature sensing, depend on the thermo-optic and thermal expansion coefficients of PMMA. These two coefficients are a function of surrounding temperature and humidity. Amorphous polymers including PMMA exhibit a certain degree of anisotropic thermal expansion. The anisotropic nature of expansion mainly depends on the polymer processing history. The expansion coefficient is believed to be lower in the direction of the molecular orientation than in the direction perpendicular to the draw direction. Such anisotropic behavior of polymers can be expected in drawn PMMA based optical fiber, and will lead to a reduced thermal expansion coefficient and larger temperature sensitivity than would be the case were the fiber to be isotropic. Extensive work has been carried out to identify these factors. The temperature responses of gratings have been measured at different relative humidity. Gratings fabricated on annealed and non-annealed PMMA optical fibers are used to compare the sensitivity performance as annealing is considered to be able to mitigate the anisotropic effect in PMMA optical fiber. Furthermore an experiment has been designed to eliminate the thermal expansion contribution to the grating wavelength change, leading to increased temperature sensitivity and improved response linearity.

  1. All-Optical Micro Motors Based on Moving Gratings in Photosensitive Media

    NASA Technical Reports Server (NTRS)

    Curley, M.; Sarkisov, S. S.; Fields, A.; Smith, C.; Kukhtarev, N.; Kulishov, M. B.; Adamovsky, G. (Technical Monitor)

    2000-01-01

    An all-optical micro motor with a rotor driven by a traveling wave of surface deformation of a stator being in contact with the rotor is being studied. Instead of an ultrasonic wave produced by an electrically driven piezoelectric actuator as in ultrasonic motors, the wave is a result of a photo induced surface deformation of a photosensitive material produced by a traveling holographic grating. Two phase modulated coherent optical beams generate the grating. Several types of photosensitive materials are studied such as photorefractive crystals, photosensitive piezoelectric ceramics, and side-chain liquid crystalline polyesters. In order to be considered as a possible candidate for micro motors, the material should exhibit surface deformation produced by moving grating of the order of 10 micron. Deformations produced by static holographic gratings are studied in photorefractive crystals of LiNbO3 using high vertical resolution surface profilometer Dektak 3 and surface interferometer WYKO. An experimental set-up with moving grating has been developed. The set-up uses a two-beam interferometry configuration with one beam being reflected by a thin mirror mounted on a loud speaker. A ramp voltage signal generator drives the speaker. Changing voltage, polarity, and frequency of the signal can easily generate vibrating gratings or moving gratings in both directions. A vibrating grating has been applied to a photorefractive crystal of BSO controlled by an external electric field of the order of 104 V/cm. We have additionally studied effects of moving grating interaction with light absorbing fluids such as solutions of 2,9,16,23-Tetrakis(phenylthio)-29H, 31 Hphthalocyanine in chlorobenzene in capillary tubes. The purpose of using a liquid is to show that the moving gratings can force a liquid to shift. The interaction of a single low power focused laser beam at 633 nm with such fluid produced an intensive circular motion, which also might be applied to all-optical micro

  2. Slow slip generated by dehydration reaction coupled with slip-induced dilatancy and thermal pressurization

    NASA Astrophysics Data System (ADS)

    Yamashita, Teruo; Schubnel, Alexandre

    2016-05-01

    Sustained slow slip, which is a distinctive feature of slow slip events (SSEs), is investigated theoretically, assuming a fault embedded within a fluid-saturated 1D thermo-poro-elastic medium. The object of study is specifically SSEs occurring at the down-dip edge of seismogenic zone in hot subduction zones, where mineral dehydrations (antigorite, lawsonite, chlorite, and glaucophane) are expected to occur near locations where deep slow slip events are observed. In the modeling, we introduce dehydration reactions, coupled with slip-induced dilatancy and thermal pressurization, and slip evolution is assumed to interact with fluid pressure change through Coulomb's frictional stress. Our calculations show that sustained slow slip events occur when the dehydration reaction is coupled with slip-induced dilatancy. Specifically, slow slip is favored by a low initial stress drop, an initial temperature of the medium close to that of the dehydration reaction equilibrium temperature, a low permeability, and overall negative volume change associated with the reaction (i.e., void space created by the reaction larger than the space occupied by the fluid released). Importantly, if we do not assume slip-induced dilatancy, slip is accelerated with time soon after the slip onset even if the dehydration reaction is assumed. This suggests that slow slip is sustained for a long time at hot subduction zones because dehydration reaction is coupled with slip-induced dilatancy. Such slip-induced dilatancy may occur at the down-dip edge of seismogenic zone at hot subduction zones because of repetitive occurrence of dehydration reaction there.

  3. Refractive index and temperature sensitivity characteristics of a micro-slot fiber Bragg grating.

    PubMed

    Saffari, Pouneh; Yan, Zhijun; Zhou, Kaiming; Zhang, Lin

    2012-07-10

    Fabrication and characterization of a UV inscribed fiber Bragg grating (FBG) with a micro-slot liquid core is presented. Femtosecond (fs) laser patterning/chemical etching technique was employed to engrave a micro-slot with dimensions of 5.74 μm(h)×125 μm(w)×1388.72 μm(l) across the whole grating. The device has been evaluated for refractive index (RI) and temperature sensitivities and exhibited distinctive thermal response and RI sensitivity beyond the detection limit of reported fiber gratings. This structure has not just been RI sensitive, but also maintained the robustness comparing with the bare core FBGs and long-period gratings with the partial cladding etched off. PMID:22781247

  4. Recent developments of Bragg gratings in PMMA and TOPAS polymer optical fibers

    NASA Astrophysics Data System (ADS)

    Webb, David J.; Kalli, Kyriacos; Carroll, Karen; Zhang, Chi; Komodromos, Michalis; Argyros, Alex; Large, Maryanne; Emiliyanov, Grigoriy; Bang, Ole; Kjaer, Eric

    2007-11-01

    We report on the temperature response of FBGs recorded in pure PMMA and TOPAS holey fibers. The gratings are fabricated for operational use at near IR wavelengths, using a phase mask and a cw He-Cd laser operating at 325nm. The room temperature grating response is non-linear and characterized by quadratic behavior for temperatures from room temperature to the glass transition temperature, and this permanent change is affected by the thermal history of the gratings. We also report the first FBG inscription in microstructured polymer optical fibers fabricated from TOPAS. This material is fully polymerized and has very low moisture absorption, leading to very good fiber drawing properties. Furthermore, although TOPAS is chemically inert and bio-molecules do not readily bind to its surface, treatment with Antraquinon and subsequent UV activation allows sensing molecules to be deposited in well defined spatial locations. When combined with grating technology this provides considerable potential for label-free bio-sensing.

  5. Temperature sensitivity of Bragg gratings in PMMA and TOPAS microstructured polymer optical fibres

    NASA Astrophysics Data System (ADS)

    Webb, David J.; Kalli, Kyriacos; Zhang, Chi; Komodromos, Michael; Argyros, Alexander; Large, Maryanne; Emiliyanov, Grigoriy; Bang, Ole; Kjaer, Erik

    2008-04-01

    We report on the temperature response of FBGs recorded in pure PMMA and TOPAS holey fibres. The gratings are fabricated for operational use at near IR wavelengths, using a phase mask and a CW He-Cd laser operating at 325nm. The room temperature grating response is non-linear and characterized by quadratic behaviour for temperatures from room temperature to the glass transition temperature, and this permanent change is affected by the thermal history of the gratings. We also report the first FBG inscription in microstructured polymer optical fibres fabricated from TOPAS. This material is fully polymerized and has very low moisture absorption, leading to very good fibre drawing properties. Furthermore, although TOPAS is chemically inert and bio-molecules do not readily bind to its surface, treatment with Antraquinon and subsequent UV activation allows sensing molecules to be deposited in well defined spatial locations. When combined with grating technology this provides considerable potential for label-free bio-sensing.

  6. Visco-elastic and thermal-induced damaging in time-dependent reshaping of human cornea after conductive keratoplasty

    NASA Astrophysics Data System (ADS)

    Fraldi, M.; Cutolo, A.; Esposito, L.; D'Amore, A.

    2016-06-01

    With the aim of investigating the role played by both the radiofrequency-induced thermal damaging and the viscoelasticity of the tissue in human cornea surface reshaping—time dependent key factors for the success of the surgical outcome in the short-term post-intervention period—the Conductive Keratoplasty (CK, a surgical technique used for the correction of farsightedness) has been simulated with reference to the protocol adopted for moderate hyperopia. By means of a transient thermal analysis, the amount of the local thermal-induced tissue damaging has been computed in order to remap the constitutive properties of the corneal tissue. Successively, a mechanical non-linear analysis has been performed for predicting the corneal curvature around the optical zone during the post-surgery period. The study aims to contribute some firm thermo-mechanical roots to better understand the corneal tissue response to thermal insults and its reshaping predictability in a long period.

  7. Ageing and thermal recovery of paramagnetic centers induced by electron irradiation in yttria-stabilized zirconia

    NASA Astrophysics Data System (ADS)

    Costantini, J. M.; Beuneu, F.

    We have used electron spin resonance spectroscopy to study the defects induced in yttria-stabilized zirconia (YSZ) single crystals by 2.5-MeV electron irradiations. Two paramagnetic centers are produced: the first one with an axial <111> symmetry is similar to the trigonal Zr3+ electron center (T center) found after X-ray irradiation or thermo-chemical reduction, whereas the second one is a new oxygen hole center with an axial <100> symmetry different from the orthorhombic O- center induced by X-ray irradiation. At a fluence around 10(18) e/cm(2) , both centers are bleached out near 600 K, like the corresponding X-ray induced defects. At a fluence around 10(19) e/cm(2) , defects are much more stable, since complete thermal bleaching occurs near 1000 K. Accordingly, ageing of as-irradiated samples shows that high-dose defects at more stable than the low-dose ones.

  8. An ultrafast nanotip electron gun triggered by grating-coupled surface plasmons

    NASA Astrophysics Data System (ADS)

    Schröder, Benjamin; Sivis, Murat; Bormann, Reiner; Schäfer, Sascha; Ropers, Claus

    2015-12-01

    We demonstrate multiphoton photoelectron emission from gold nanotips induced by nanofocusing surface plasmons, resonantly excited on the tip shaft by a grating coupler. The tip is integrated into an electron gun assembly, which facilitates control over the spatial emission sites and allows us to disentangle direct grating emission from plasmon-triggered apex emission. The nanoscale source size of this electron gun concept enables highly coherent electron pulses with applications in ultrafast electron imaging and diffraction.

  9. An ultrafast nanotip electron gun triggered by grating-coupled surface plasmons

    SciTech Connect

    Schröder, Benjamin; Sivis, Murat; Bormann, Reiner; Schäfer, Sascha; Ropers, Claus

    2015-12-07

    We demonstrate multiphoton photoelectron emission from gold nanotips induced by nanofocusing surface plasmons, resonantly excited on the tip shaft by a grating coupler. The tip is integrated into an electron gun assembly, which facilitates control over the spatial emission sites and allows us to disentangle direct grating emission from plasmon-triggered apex emission. The nanoscale source size of this electron gun concept enables highly coherent electron pulses with applications in ultrafast electron imaging and diffraction.

  10. Fiber Bragg gratings in the radiation environment: Change under the influence of radiolytic hydrogen

    SciTech Connect

    Butov, Oleg V. Golant, Konstantin M.; Shevtsov, Igor' A.; Fedorov, Artem N.

    2015-08-21

    The change of the transmission spectra of fiber Bragg gratings written in the optical fibers, whose silica cores are doped with either germanium or nitrogen, is studied experimentally under the influence of gamma-radiation. The transmission spectra in the neighborhood of the resonance (Bragg) wavelengths were regularly recorded “in-situ” in the course of irradiation during 24 days. For this purpose, uncoated gratings were placed in a pool near the spent fuel rods of a nuclear reactor. The fibers with the gratings written in them were in immediate contact with water. The estimated total absorbed radiation dose of the fibers is approximately 5 MGy. Molecular hydrogen, which is produced by radiolysis of water and penetrates into the core of silica fiber, is found to interact with the defects of Ge-doped silica induced by gamma-radiation, thereby causing a strong impact on the parameters of the spectrum of the Bragg gratings. On the contrary, in the case of gratings inscribed in N-doped silica fibers, the hydrogen molecules interact with defects induced in the course of laser UV exposure during the grating writing only. The possible subsequent formation of additional defects in N-doped silica under the influence of gamma-radiation has no substantial impact on the transmission spectra of Bragg gratings, which remained stable. The obtained results suggest that a small amount of molecular hydrogen resided in the fiber core is the main source of radiation instability of Ge-doped fiber Bragg grating sensors in radiation environments. These hydrogen molecules can remain in the Bragg gratings, in particular, after the inscription process in the hydrogen-loaded fibers.

  11. Fiber Bragg gratings in the radiation environment: Change under the influence of radiolytic hydrogen

    NASA Astrophysics Data System (ADS)

    Butov, Oleg V.; Golant, Konstantin M.; Shevtsov, Igor'A.; Fedorov, Artem N.

    2015-08-01

    The change of the transmission spectra of fiber Bragg gratings written in the optical fibers, whose silica cores are doped with either germanium or nitrogen, is studied experimentally under the influence of gamma-radiation. The transmission spectra in the neighborhood of the resonance (Bragg) wavelengths were regularly recorded "in-situ" in the course of irradiation during 24 days. For this purpose, uncoated gratings were placed in a pool near the spent fuel rods of a nuclear reactor. The fibers with the gratings written in them were in immediate contact with water. The estimated total absorbed radiation dose of the fibers is approximately 5 MGy. Molecular hydrogen, which is produced by radiolysis of water and penetrates into the core of silica fiber, is found to interact with the defects of Ge-doped silica induced by gamma-radiation, thereby causing a strong impact on the parameters of the spectrum of the Bragg gratings. On the contrary, in the case of gratings inscribed in N-doped silica fibers, the hydrogen molecules interact with defects induced in the course of laser UV exposure during the grating writing only. The possible subsequent formation of additional defects in N-doped silica under the influence of gamma-radiation has no substantial impact on the transmission spectra of Bragg gratings, which remained stable. The obtained results suggest that a small amount of molecular hydrogen resided in the fiber core is the main source of radiation instability of Ge-doped fiber Bragg grating sensors in radiation environments. These hydrogen molecules can remain in the Bragg gratings, in particular, after the inscription process in the hydrogen-loaded fibers.

  12. Femtosecond laser embedded grating micromachining of flexible PDMS plates

    NASA Astrophysics Data System (ADS)

    Cho, Sung-Hak; Chang, Won-Seok; Kim, Kwang-Ryul; Hong, Jong Wook

    2009-04-01

    We report on the femtosecond laser micromachining of photo-induced embedded diffraction grating in flexible Poly (Dimethly Siloxane) (PDMS) plates using a high-intensity femtosecond (130 fs) Ti: sapphire laser ( λp = 800 nm). The refractive index modifications with diameters ranging from 2 μm to 5 μm were photo-induced after the irradiation with peak intensities of more than 1 × 10 11 W/cm 2. The graded refractive index profile was fabricated to be a symmetric around from the center of the point at which femtosecond laser was focused. The maximum refractive index change (Δ n) was estimated to be 2 × 10 -3. By the X- Y- Z scanning of sample, the embedded diffraction grating in PDMS plate was fabricated successfully using a femtosecond laser.

  13. Thermal gradient induced flexoelectric effects in bulk Ba0.67Sr0.33TiO3

    NASA Astrophysics Data System (ADS)

    Kim, Taeyang; Huang, Wenbin; Huang, Shujin; Jiang, Xiaoning

    2016-05-01

    Flexoelectric effect, denoting electric field gradient induced mechanical strain or mechanical strain gradient induced electric polarization, is a universal phenomenon in all dielectrics. Although research on the topic of flexoelectricity under stress fields and electric fields has advanced significantly, information regarding the phenomenon under thermal fields is rather limited. In this letter, the flexoelectricity field of Ba0.67Sr0.33TiO3 (BST) was investigated by generating temperature gradients along the lengths of samples with symmetric geometry. An electric field gradient induced by a thermal gradient was analyzed based on the temperature-dependent dielectric property of BST. The strain was then experimentally verified due to the electric field gradient. Experimental results suggest converse flexoelectric effect of BST samples with symmetric geometry in a thermal field. This result was not only consistent with the theoretical prediction, but it also followed the scaling effect of flexoelectricity.

  14. Relation of thermal conductivity with process induced anisotropic void system in EB-PVD PYSZ thermal barrier coatings.

    SciTech Connect

    Renteria, A. F.; Saruhan, B.; Ilavsky, J.; German Aerospace Center

    2007-01-01

    Thermal barrier coatings (TBCs) deposited by Electron-beam physical deposition (EB-PVD) protect the turbine blades situated at the high pressure sector of the aircraft and stationary turbines. It is an important task to uphold low thermal conductivity in TBCs during long-term service at elevated temperatures. One of the most promising methods to fulfil this task is to optimize the properties of PYSZ-based ,TBC by tailoring its microstructure. Thermal conductivity of the EB-PVD produced PYSZ TBCs is influenced mainly by the size, shape, orientation and volume of the various types of porosity present in the coatings. These pores can be classified as open (inter-columnar and between feather arms gaps) and closed (intra-columnar pores). Since such pores are located within the three-dimensionally deposited columns and enclose large differences in their sizes, shapes, distribution and anisotropy, the accessibility for their characterization is very complex and requires the use of sophisticated methods. In this work, three different EB-PVD TBC microstructures were manufactured by varying the process parameters, yielding various characteristics of their pores. The corresponding thermal conductivities in as-coated state and after ageing at 1100C/1h and 100h were measured via Laser Flash Analysis Method (LFA). The pore characteristics and their individual effect on the thermal conductivity are analysed by USAXS which is supported by subsequent modelling and LFA methods, respectively. Evident differences in the thermal conductivity values of each microstructure were found in as-coated and aged conditions. In summary, broader columns introduce higher values in thermal conductivity. In general, thermal conductivity increases after ageing for all three investigated microstructures, although those with initial smaller pore surface area show smaller changes.

  15. Relation of Thermal Conductivity with Process Induced Anisotropic Void Systems in EB-PVD PYSZ Thermal Barrier Coatings

    SciTech Connect

    Renteria, A. Flores; Saruhan-Brings, B.; Ilavsky, J.

    2008-03-03

    Thermal barrier coatings (TBCs) deposited by Electron-beam physical deposition (EB-PVD) protect the turbine blades situated at the high pressure sector of the aircraft and stationary turbines. It is an important task to uphold low thermal conductivity in TBCs during long-term service at elevated temperatures. One of the most promising methods to fulfil this task is to optimize the properties of PYSZ-based TBC by tailoring its microstructure. Thermal conductivity of the EB-PVD produced PYSZ TBCs is influenced mainly by the size, shape, orientation and volume of the various types of porosity present in the coatings. These pores can be classified as open (inter-columnar and between feather arms gaps) and closed (intra-columnar pores). Since such pores are located within the three-dimensionally deposited columns and enclose large differences in their sizes, shapes, distribution and anisotropy, the accessibility for their characterization is very complex and requires the use of sophisticated methods. In this work, three different EB-PVD TBC microstructures were manufactured by varying the process parameters, yielding various characteristics of their pores. The corresponding thermal conductivities in as-coated state and after ageing at 11000C/1h and 100h were measured via Laser Flash Analysis Method (LFA). The pore characteristics and their individual effect on the thermal conductivity are analysed by USAXS which is supported by subsequent modelling and LFA methods, respectively. Evident differences in the thermal conductivity values of each microstructure were found in as-coated and aged conditions. In summary, broader columns introduce higher values in thermal conductivity. In general, thermal conductivity increases after ageing for all three investigated microstructures, although those with initial smaller pore surface area show smaller changes.

  16. Global representation of tropical cyclone-induced short-term ocean thermal changes using Argo data

    NASA Astrophysics Data System (ADS)

    Cheng, L.; Zhu, J.; Sriver, R. L.

    2015-09-01

    Argo floats are used to examine tropical cyclone (TC) induced ocean thermal changes on the global scale by comparing temperature profiles before and after TC passage. We present a footprint method that analyzes cross-track thermal responses along all storm tracks during the period 2004-2012. We combine the results into composite representations of the vertical structure of the average thermal response for two different categories: tropical storms/tropical depressions (TS/TD) and hurricanes. The two footprint composites are functions of three variables: cross-track distance, water depth and time relative to TC passage. We find that this footprint strategy captures the major features of the upper-ocean thermal response to TCs on timescales up to 20 days when compared against previous case study results using in situ measurements. On the global scale, TCs are responsible for 1.87 PW (11.05 W m-2) of heat transfer annually from the global ocean to the atmosphere during storm passage (0-3 days). Of this total, 1.05 ± 0.20 PW (4.80 ± 0.85 W m-2) is caused by TS/TD and 0.82 ± 0.21 PW (6.25 ± 1.5 W m-2) is caused by hurricanes. Our findings indicate that ocean heat loss by TCs may be a substantial missing piece of the global ocean heat budget. Changes in ocean heat content (OHC) after storm passage are estimated by analyzing the temperature anomalies during wake recovery following storm events (4-20 days after storm passage) relative to pre-storm conditions. Results indicate the global ocean experiences a 0.75 ± 0.25 PW (5.98 ± 2.1 W m-2) heat gain annually for hurricanes. In contrast, under TS/TD conditions, the ocean experiences 0.41 ± 0.21 PW (1.90 ± 0.96 W m-2) ocean heat loss, suggesting the overall oceanic thermal response is particularly sensitive to the intensity of the event. The ocean heat uptake caused by all storms during the restorative stage is 0.34 PW.

  17. 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.

  18. Temperature-compensated fibre Bragg grating -based sensor with variable sensitivity

    NASA Astrophysics Data System (ADS)

    Di Sante, Raffaella; Bastianini, Filippo

    2015-12-01

    In this paper a Fibre Bragg Grating (FBG)-based sensor device for strain measurement with adjustable full-scale sensitivity is proposed. Installation flanges of the sensor can be moved with respect to the internal fixed FBG sensing length in order to adjust the overall strain sensitivity and the full scale measurement range of the device. Thermal drift is compensated using a technique based on the thermal expansion of a solid block connected to the fibre, in the pre-stressed region outside the grating. Typical calibration curves are reported to illustrate the sensor sensitivity variation with the layout and temperature.

  19. Assessment of thermal sensitivity in rats using the thermal place preference test: description and application in the study of oxaliplatin-induced acute thermal hypersensitivity and inflammatory pain models.

    PubMed

    Balayssac, David; Ling, Bing; Ferrier, Jérémy; Pereira, Bruno; Eschalier, Alain; Authier, Nicolas

    2014-04-01

    Thermal sensitivity is an essential characteristic of some painful states, including oxaliplatin-induced neuropathy. The thermal place preference test (TPPT) was designed to finely assess thermal sensitivity in rodents. The TPPT monitors the time spent by unrestrained rodents on a test plate at fixed temperatures (5-50°C) compared with an adjacent reference plate at a neutral temperature (25°C). Here, we report the results of a study designed (i) to validate the optimal methodological parameters for measuring thermal sensitivity in rats, (ii) to assess the thermal sensitivity of healthy rats and animal models of pain and (iii) to explore the pharmacological effects of analgesic drugs. The most reproducible conditions occurred when the TPPT was performed in the morning and in the dark for 3 min with the reference plate set to 25°C. The temperature preferences of healthy rats were more than 17°C and less than 40°C. When compared with control animals, oxaliplatin-treated rats showed thermal hypersensitivity at 12, 20 and 35°C, and carrageenan-treated rats showed thermal hypersensitivity at 15 and 45°C. Duloxetine (2.5 mg/kg, intraperitoneal) reversed oxaliplatin-induced cold hypersensitivity (20°C) and morphine (1 mg/kg, intravenous) reversed carrageenan-induced heat hypersensitivity (45°C). We conclude that the TPPT enables a fine-grained assessment of thermal sensitivity that is relevant to the pathophysiological exploration of animal pain models and to the pharmacological assessment of analgesic drugs. PMID:24525711

  20. High Efficiency Germanium Immersion Gratings

    SciTech Connect

    Kuzmenko, P J; Davis, P J; Little, S L; Little, L M; Bixler, J V

    2006-05-01

    We have fabricated several germanium immersion gratings by single crystal, single point diamond flycutting on an ultra-precision lathe. Use of a dead sharp tool produces groove corners less than 0.1 micron in radius and consequently high diffraction efficiency. We measured first order efficiencies in immersion of over 80% at 10.6 micron wavelength. Wavefront error was low averaging 0.06 wave rms (at 633 nm) across the full aperture. The grating spectral response was free of ghosts down to our detection limit of 1 part in 10{sup 4}. Scatter should be low based upon the surface roughness. Measurement of the spectral line profile of a CO{sub 2} laser sets an upper bound on total integrated scatter of 0.5%.

  1. High efficiency germanium immersion gratings

    NASA Astrophysics Data System (ADS)

    Kuzmenko, Paul J.; Davis, Pete J.; Little, Steve L.; Little, Liesl M.; Bixler, Jay V.

    2006-06-01

    We have fabricated several germanium immersion gratings by single crystal, single point diamond flycutting on an ultra-precision lathe. Use of a dead sharp tool produces groove corners less than 0.1 micron in radius and consequently high diffraction efficiency. We measured first order efficiencies in immersion of over 80% at 10.6 micron wavelength. Wavefront error was low averaging 0.06 wave rms (at 633 nm) across the full aperture. The grating spectral response was free of ghosts down to our detection limit of 1 part in 104. Scatter should be low based upon the surface roughness. Measurement of the spectral line profile of a CO II laser sets an upper bound on total integrated scatter of 0.5%.

  2. Time-resolved investigations of the non-thermal ablation process of graphite induced by femtosecond laser pulses

    NASA Astrophysics Data System (ADS)

    Kalupka, C.; Finger, J.; Reininghaus, M.

    2016-04-01

    We report on the in-situ analysis of the ablation dynamics of the, so-called, laser induced non-thermal ablation process of graphite. A highly oriented pyrolytic graphite is excited by femtosecond laser pulses with fluences below the classic thermal ablation threshold. The ablation dynamics are investigated by axial pump-probe reflection measurements, transversal pump-probe shadowgraphy, and time-resolved transversal emission photography. The combination of the applied analysis methods allows for a continuous and detailed time-resolved observation of the non-thermal ablation dynamics from several picoseconds up to 180 ns. Formation of large, μm-sized particles takes place within the first 3.5 ns after irradiation. The following propagation of ablation products and the shock wave front are tracked by transversal shadowgraphy up to 16 ns. The comparison of ablation dynamics of different fluences by emission photography reveals thermal ablation products even for non-thermal fluences.

  3. Thermal-light-induced dynamics: Coherence and revivals in V -type and molecular Jaynes-Cummings systems

    NASA Astrophysics Data System (ADS)

    Avisar, David; Wilson-Gordon, A. D.

    2016-03-01

    We examine the interaction of thermal light with matter with emphasis on two aspects that have not been considered before. By employing a fully quantized Jaynes-Cummings-type interaction model on a V -type three-level system, we show that multimode thermal light induces coherence in the excited material states. This is in contrast to previous studies that suggest thermal light cannot induce coherence in material systems. We also show that the ratio between the field detuning and the interaction constant has a significant influence on the characteristic time-dependent dynamics. In particular, for some ratio regimes, the thermal light induces dynamics with a "coherentlike" collapse and revivals pattern rather than the familiar pattern. We then extend the Jaynes-Cummings model to a two-state Born-Oppenheimer potential energy surface molecular system where the internal vibrational degrees of freedom are fully taken into account. The matter-field bipartite system is represented, and propagated, in the full electronic bond-coordinate Fock product space. We show that single-mode thermal light induces extensive excited-state vibrational coherence in the molecule that, when observed in coordinate space, exhibits wave-packet-like dynamics. The molecular Jaynes-Cummings model we propose is useful for cavity molecular dynamics simulations.

  4. Diffraction gratings for lighting applications

    NASA Astrophysics Data System (ADS)

    Cornelissen, Hugo J.; de Boer, Dick K. G.; Tukker, Teus

    2013-09-01

    Sub-micron diffraction gratings have been used for two LED illumination applications. One is to create a transparent see through luminaire which can be used to illuminate and read a paper document or e-book. A second is a light sensor that can be used in a feedback loop to control a multicolor LED lamp. Optical design and experimental proof-of-principle are presented.

  5. Two-magnon bound state causes ultrafast thermally induced magnetisation switching

    PubMed Central

    Barker, J.; Atxitia, U.; Ostler, T. A.; Hovorka, O.; Chubykalo-Fesenko, O.; Chantrell, R. W.

    2013-01-01

    There has been much interest recently in the discovery of thermally induced magnetisation switching using femtosecond laser excitation, where a ferrimagnetic system can be switched deterministically without an applied magnetic field. Experimental results suggest that the reversal occurs due to intrinsic material properties, but so far the microscopic mechanism responsible for reversal has not been identified. Using computational and analytic methods we show that the switching is caused by the excitation of two-magnon bound states, the properties of which are dependent on material factors. This discovery allows us to accurately predict the onset of switching and the identification of this mechanism will allow new classes of materials to be identified or designed for memory devices in the THz regime. PMID:24253110

  6. Quantifying the Rates of Sn Whisker Growth and Plastic Strain Relaxation Using Thermally-Induced Stress

    NASA Astrophysics Data System (ADS)

    Pei, Fei; Bower, Allan F.; Chason, Eric

    2016-01-01

    Whiskers and hillocks that grow out of Sn-based coatings are a critical reliability issue in Pb-free electronics. Although their growth is widely regarded as a stress-relaxation mechanism, quantitative understanding of the relationship between the stress, growth kinetics, and strain relaxation is still lacking. In this work, the well-controlled strain induced by thermal-expansion mismatch was used to study the whiskering behavior of electroplated Sn films. Stress was quantified by monitoring wafer-curvature and the density of whiskers and hillocks was measured simultaneously by use of optical microscopy. Evolution of the volume of individual features was also measured by scanning electron microscopy after different periods of heating. The measurements were used to develop a model for temperature-dependent and stress-dependent growth kinetics of whiskers and hillocks and to determine the amount of strain relaxation which occurs as a result of their formation.

  7. Thermally Induced Leakage from Vibrio marinus, an Obligately Psychrophilic Marine Bacterium1

    PubMed Central

    Haight, Roger D.; Morita, Richard Y.

    1966-01-01

    Haight, Rodger D. (Oregon State University, Corvallis), and Richard Y. Morita. Thermally induced leakage from Vibrio marinus, an obligately psychrophilic bacterium. J. Bacteriol. 92:1388–1393. 1966.—Leakage of various cellular components into the surrounding menstruum occurred when Vibrio marinus was subjected to temperatures above 20 C (organism's maximal growth temperature). These materials, listed in decreasing rates of leakage, were identified as protein, deoxyribonucleic acid, ribonucleic acid, and amino acids. The amount of polar amino acids increased as the time and temperature of heat treatment were increased, whereas the nonpolar amino acids decreased. The ribonucleic acid in the supernatant fluid resulting from heat treatment was both polymeric and nonpolymeric. Leakage of cellular components may be one of the reasons that V. marinus MP-1 loses viability when exposed to temperatures above its maximal temperature for growth. PMID:5924270

  8. Dynamic model of thermal reaction of biological tissues to laser-induced fluorescence and photodynamic therapy.

    PubMed

    Seteikin, Alexey Yu; Krasnikov, Ilya V; Drakaki, Eleni; Makropoulou, Mersini

    2013-07-01

    The aim of this work was to evaluate the temperature fields and the dynamics of heat conduction into the skin tissue under several laser irradiation conditions with both a pulsed ultraviolet (UV) laser (λ=337  nm) and a continuous-wave (cw) visible laser beam (λ=632.8  nm) using Monte Carlo modeling. Finite-element methodology was used for heat transfer simulation. The analysis of the results showed that heat is not localized on the surface, but is collected inside the tissue in lower skin layers. The simulation was made with the pulsed UV laser beam (used as excitation source in laser-induced fluorescence) and the cw visible laser (used in photodynamic therapy treatments), in order to study the possible thermal effects. PMID:23839531

  9. Effect of local stress induced by thermal expansion of underfill in three-dimensional stacked IC

    NASA Astrophysics Data System (ADS)

    Kino, Hisashi; Hashiguchi, Hideto; Tanikawa, Seiya; Sugawara, Youhei; Ikegaya, Shunsuke; Fukushima, Takafumi; Koyanagi, Mitsumasa; Tanaka, Tetsu

    2016-04-01

    A three-dimensional stacked IC (3D IC) is a one of the promising structures for enhancing IC performances. A 3D IC consists of several materials such as a Si substrate, metal for through Si via (TSV) and microbump, organic adhesive called the underfill, and so on. These materials generate a coefficient of thermal expansion (CTE) mismatch. On the other hand, heat is generated in the Si substrate during circuit operation and in the environment outside 3D IC, for example. Both the CTE mismatch and heat generation induce local stress caused by expansion of the underfill injected around metal microbumps. In this paper, we report our investigation results of the effects of adhesive expansion on transistor performances by finite element method (FEM) simulation and measurement of transistor characteristics.

  10. Metal Chloride Induced Formation of Porous Polyhydroxybutyrate (PHB) Films: Morphology, Thermal Properties and Crystallinity

    NASA Astrophysics Data System (ADS)

    Tan, W. L.; Yaakob, N. N.; Zainal Abidin, A.; Abu Bakar, M.; Abu Bakar, N. H. H.

    2016-06-01

    Polyhydroxybutyrate (PHB) films with highly porous structures were synthesized using a one phase system comprising of metal chloride/methanol/PHB/chloroform (MCl2/CH3OH/PHB/CHCl3). SEM analyses confirmed that the MCl2 (where M = Cu2+ or Ni2+) induced porous structures with pore sizes ranging from 0.3 - 2.0 μm. The average pore size increased with the increasing MCl2 content. There existed weak physical interactions between the PHB chains and MCl2 as revealed by FTIR and NMR spectroscopies. The residue of MCl2 in the porous PHB film does not exert significant influence on the thermal stability of PHB. Nevertheless, the crystallinity of the prepared film is enhanced, as MCl2 acts as the nucleation sites to promote the growth of spherullites.

  11. Optically and thermally controlled terahertz metamaterial via transition between direct and indirect electromagnetically induced transparency

    SciTech Connect

    Sui, Jiawei Feng, Ls

    2014-12-15

    This passage presents a design of tunable terahertz metamaterials via transition between indirect and direct electromagnetically induced transparency (EIT) effects by changing semiconductor InSb’s properties to terahertz wave under optical and thermal stimuli. Mechanical model and its electrical circuit model are utilized in analytically calculating maximum transmission of transparency window. Simulated results show consistency with the analytical expressions. The results show that the metamaterials hold 98.4% modulation depth at 189 GHz between 300 K, σ{sub InSb} =256000 S/m, and 80 K, σ{sub InSb} =0.0162 S/m conditions , 1360 ps recovery time of the excited electrons in InSb under optical stimulus at 300 K mainly considering the direct EIT effect, and minimum bandwidth 1 GHz.

  12. Optimal electron, phonon, and magnetic characteristics for low energy thermally induced magnetization switching

    SciTech Connect

    Atxitia, U.; Ostler, T. A.; Chantrell, R. W.; Chubykalo-Fesenko, O.

    2015-11-09

    Using large-scale computer simulations, we thoroughly study the minimum energy required to thermally induced magnetization switching (TIMS) after the application of a femtosecond heat pulse in transition metal-rare earth ferrimagnetic alloys. We find that for an energy efficient TIMS, a low ferrimagnetic net magnetization with a strong temperature dependence is the relevant factor for the magnetic system. For the lattice and electron systems, the key physics for efficient TIMS is a large electron-phonon relaxation time. Importantly, we show that as the cooling time of the heated electrons is increased, the minimum power required to produce TIMS can be reduced by an order of magnitude. Our results show the way to low power TIMS by appropriate engineering of magnetic heterostructures.

  13. Supplementary Microstructural Features Induced During Laser Surface Melting of Thermally Sprayed Inconel 625 Coatings

    NASA Astrophysics Data System (ADS)

    Ahmed, Nauman; Voisey, K. T.; McCartney, D. G.

    2014-02-01

    Laser surface melting of thermally sprayed coatings has the potential to enhance their corrosion properties by incorporating favorable microstructural changes. Besides homogenizing the as-sprayed structure, laser melting may induce certain microstructural modifications (i.e., supplementary features) in addition to those that directly improve the corrosion performance. Such features, being a direct result of the laser treatment process, are described in this paper which is part of a broader study in which high velocity oxy-fuel sprayed Inconel 625 coatings on mild-steel substrates were treated with a diode laser and the modified microstructure characterized using optical and scanning electron microscopy and x-ray diffraction. The laser treated coating features several different zones, including a region with a microstructure in which there is a continuous columnar dendritic structure through a network of retained oxide stringers.

  14. Generation of Radiation Pressure in Thermally Induced Ultrasonic Emitter Based on Nanocrystalline Silicon

    NASA Astrophysics Data System (ADS)

    Hirota, Jun; Shinoda, Hiroyuki; Koshida, Nobuyoshi

    2004-04-01

    To confirm the applicability of thermally induced ultrasonic emission from nanocrystalline silicon (nc-Si) devices as radiation pressure generators, the dynamic response has been investigated under a pulse operation mode. The nc-Si emitter is fabricated on a p-type Si wafer by conventional electrochemical anodization with subsequent formation of the surface electrode. Due to the flat nature of the frequency response of this emitter, the device emits an acoustic wave with little distortion under the pulse-drive condition. It is shown that a significant radiation pressure of 34.5 Pa is generated by a concentrated burst-like electrical input, and that a beam located at a distance can be levitated as a result of the mechanical loading effect. This silicon-based emitter is attractive for applications to integrated nano- or micro-electromechanical systems.

  15. Thermal noise induced stochastic resonance in self organizing Fe nanoparticle system

    NASA Astrophysics Data System (ADS)

    Pal, Satyendra Prakash; Sen, P.

    2014-12-01

    The natural world is replete with examples of multistable systems, known to respond to periodic modulations and produce a signal that exhibits resonance with noise amplitude. This is a concept not demonstrated in pure materials, which involve a measured physical property. In a thermoremanent magnetization experiment with a common magnetic material, Fe, in the nanoparticulate form, we establish how magnetization in a system of dilute spins during dissipation of stored magnetic energy breaks up into spontaneous oscillatory behavior. Starting at 175 K and aided by temperature (stochastic noise) the oscillation amplitude goes through a maximum reminiscent of stochastic resonance. Our observation of thermal noise induced coherent resonance is due to intrinsic self-organizing magnetic dynamics of the Fe nanoparticle system without applying any external periodic force. These results yield new possibilities in the design of magnetic materials and a platform to understand stochastic interference and phase synchronization in neural activity, as models for neural communication.

  16. Beam misalignments and fluid velocities in laser-induced thermal acoustics

    SciTech Connect

    Schlamp, S.; Hornung, H.G.; Cummings, E.B.

    1999-09-01

    Beam misalignments and bulk fluid velocities can influence the time history and intensity of laser-induced thermal acoustics (LITA) signals. A closed-form analytic expression for LITA signals incorporating these effects is derived, allowing the magnitude of beam misalignment and velocity to be inferred from the signal shape. It is demonstrated how instantaneous, nonintrusive, and remote measurement of sound speed and velocity (Mach number) can be inferred simultaneously from homodyne-detected LITA signals. The effects of different forms of beam misalignment are explored experimentally and compared with theory, with good agreement, allowing the amount of misalignment to be measured from the LITA signal. This capability could be used to correct experimental misalignments and account for the effects of misalignment in other LITA measurements. It is shown that small beam misalignments have no influence on the accuracy or repeatability of sound speed measurements with LITA. {copyright} 1999 Optical Society of America

  17. Beam Misalignments and Fluid Velocities in Laser-Induced Thermal Acoustics

    NASA Astrophysics Data System (ADS)

    Schlamp, Stefan; Cummings, Eric B.; Hornung, Hans G.

    1999-09-01

    Beam misalignments and bulk fluid velocities can influence the time history and intensity of laser-induced thermal acoustics (LITA) signals. A closed-form analytic expression for LITA signals incorporating these effects is derived, allowing the magnitude of beam misalignment and velocity to be inferred from the signal shape. It is demonstrated how instantaneous, nonintrusive, and remote measurement of sound speed and velocity (Mach number) can be inferred simultaneously from homodyne-detected LITA signals. The effects of different forms of beam misalignment are explored experimentally and compared with theory, with good agreement, allowing the amount of misalignment to be measured from the LITA signal. This capability could be used to correct experimental misalignments and account for the effects of misalignment in other LITA measurements. It is shown that small beam misalignments have no influence on the accuracy or repeatability of sound speed measurements with LITA.

  18. Optimal electron, phonon, and magnetic characteristics for low energy thermally induced magnetization switching

    NASA Astrophysics Data System (ADS)

    Atxitia, U.; Ostler, T. A.; Chantrell, R. W.; Chubykalo-Fesenko, O.

    2015-11-01

    Using large-scale computer simulations, we thoroughly study the minimum energy required to thermally induced magnetization switching (TIMS) after the application of a femtosecond heat pulse in transition metal-rare earth ferrimagnetic alloys. We find that for an energy efficient TIMS, a low ferrimagnetic net magnetization with a strong temperature dependence is the relevant factor for the magnetic system. For the lattice and electron systems, the key physics for efficient TIMS is a large electron-phonon relaxation time. Importantly, we show that as the cooling time of the heated electrons is increased, the minimum power required to produce TIMS can be reduced by an order of magnitude. Our results show the way to low power TIMS by appropriate engineering of magnetic heterostructures.

  19. Polymeric scaffolds prepared via Thermally Induced Phase Separation (TIPS): tuning of structure and morphology

    NASA Astrophysics Data System (ADS)

    Pavia, F. Carfı; La Carrubba, V.; Brucato, V.; Piccarolo, S.

    2007-04-01

    Scaffolds suitable for tissue engineering applications were prepared by Thermally Induced Phase Separation (TIPS) starting from a ternary solution PLLA/dioxane/water. The experimental protocol consisted of three consecutive steps, a first quench from the homogeneous solution to an appropriate demixing temperature (within the metastable region), a holding stage for a given residence time and a final quench from the demixing temperature to a low temperature (within the unstable region). A large variety of morphologies, in terms of average pore size and interconnection, were obtained upon modifying the demixing time and temperature, owing to the interplay of nucleation and growth processes during the residence in the metastable state. An interesting combination of micro and macro-porosity was observed for long residence times in the metastable state (above 30 min at 35°C).

  20. Nonlinear Generation of Electromagnetic Waves through Induced Scattering by Thermal Plasma.

    PubMed

    Tejero, E M; Crabtree, C; Blackwell, D D; Amatucci, W E; Mithaiwala, M; Ganguli, G; Rudakov, L

    2015-01-01

    We demonstrate the conversion of electrostatic pump waves into electromagnetic waves through nonlinear induced scattering by thermal particles in a laboratory plasma. Electrostatic waves in the whistler branch are launched that propagate near the resonance cone. When the amplitude exceeds a threshold ~5 × 10(-6) times the background magnetic field, wave power is scattered below the pump frequency with wave normal angles (~59°), where the scattered wavelength reaches the limits of the plasma column. The scattered wave has a perpendicular wavelength that is an order of magnitude larger than the pump wave and longer than the electron skin depth. The amplitude threshold, scattered frequency spectrum, and scattered wave normal angles are in good agreement with theory. The results may affect the analysis and interpretation of space observations and lead to a comprehensive understanding of the nature of the Earth's plasma environment. PMID:26647962

  1. Electrical parameter changes in silicon solar cells induced by thermal donor formation

    NASA Astrophysics Data System (ADS)

    Ruiz, J. M.; Cid, M.

    Statistical results of 450 C annealing experiments of variable duration, performed on n(+)pp(+), 10-ohm-cm Czochralski silicon (Cz silicon), bifacial solar cells are presented. The specific temperature used is known to favor the nucleation of interstitial oxygen, creating the thermal donors, with important effects on the electrical properties of Cz silicon. Two distinct behaviors are observed with solar cells. The annealing during moderate time (below 4-5 h) leads, on the average, to an improvement of the photovoltaic performances. Longer heat treatments (mainly above 8 h) induce an effective inversion of the base polarity (from p type to n type), with the net result of partially losing the precedent benefits. Both phenomena have been found to be permanent, provided further processes at higher temperatures are avoided.

  2. Nonlinear Generation of Electromagnetic Waves through Induced Scattering by Thermal Plasma

    PubMed Central

    Tejero, E. M.; Crabtree, C.; Blackwell, D. D.; Amatucci, W. E.; Mithaiwala, M.; Ganguli, G.; Rudakov, L.

    2015-01-01

    We demonstrate the conversion of electrostatic pump waves into electromagnetic waves through nonlinear induced scattering by thermal particles in a laboratory plasma. Electrostatic waves in the whistler branch are launched that propagate near the resonance cone. When the amplitude exceeds a threshold ~5 × 10−6 times the background magnetic field, wave power is scattered below the pump frequency with wave normal angles (~59°), where the scattered wavelength reaches the limits of the plasma column. The scattered wave has a perpendicular wavelength that is an order of magnitude larger than the pump wave and longer than the electron skin depth. The amplitude threshold, scattered frequency spectrum, and scattered wave normal angles are in good agreement with theory. The results may affect the analysis and interpretation of space observations and lead to a comprehensive understanding of the nature of the Earth’s plasma environment. PMID:26647962

  3. Yield of delayed neutrons in the thermal-neutron-induced reaction 245Cm( n, f)

    NASA Astrophysics Data System (ADS)

    Andrianov, V. R.; Vyachin, V. N.; Gundorin, N. A.; Druzhinin, A. A.; Zhdanova, K. V.; Lihachev, A. N.; Pikelner, L. B.; Rebrova, N. V.; Salamatin, I. M.; Furman, V. I.

    2008-10-01

    The yield of delayed neutrons, v d , from thermal-neutron-induced fission of 245Cm is measured. Experiments aimed at studying the properties of delayed neutrons from the fission of some reactor isotopes and initiated in 1997 were continued at the upgraded Isomer-M facility by a method according to which a periodic irradiation of a sample with a pulsed neutron beam from the IBR-2 reactor was accompanied by recording emitted neutrons in the intervals between the pulses. The accuracy of the resulting total delayed-neutron yield v d = (0.64 ± 0.02)% is two times higher than that in previous measurements. This work was performed at the Frank Laboratory of Neutron Physics at the Joint Institute for Nuclear Research (JINR, Dubna).

  4. Effect of thermally induced porosity on an as-HIP powder metallurgy superalloy

    NASA Technical Reports Server (NTRS)

    Dreshfield, R. L.; Miner, R. V., Jr.

    1979-01-01

    The impact of thermally induced porosity on the mechanical properties of an as-hot-isostatically-pressed and heat treated pressing made from low carbon Astroloy was determined. Porosity in the disk-shape pressing studied ranged from 2.6 percent at the bore to 1.4 percent at the rim. Tensile, yield strength, ductility, and rupture life of the rim of the porous pressing was only slightly inferior to the rim of sound pressings. The strength, ductility, and rupture life of the bore of the porous pressing was severely degraded compared to sound pressings. At strain ranges typical of commercial jet engine designs, the rim of the porous pressing had slightly inferior fatigue life to sound pressings.

  5. Nonlinear Generation of Electromagnetic Waves through Induced Scattering by Thermal Plasma

    NASA Astrophysics Data System (ADS)

    Tejero, E. M.; Crabtree, C.; Blackwell, D. D.; Amatucci, W. E.; Mithaiwala, M.; Ganguli, G.; Rudakov, L.

    2015-12-01

    We demonstrate the conversion of electrostatic pump waves into electromagnetic waves through nonlinear induced scattering by thermal particles in a laboratory plasma. Electrostatic waves in the whistler branch are launched that propagate near the resonance cone. When the amplitude exceeds a threshold ~5 × 10-6 times the background magnetic field, wave power is scattered below the pump frequency with wave normal angles (~59°), where the scattered wavelength reaches the limits of the plasma column. The scattered wave has a perpendicular wavelength that is an order of magnitude larger than the pump wave and longer than the electron skin depth. The amplitude threshold, scattered frequency spectrum, and scattered wave normal angles are in good agreement with theory. The results may affect the analysis and interpretation of space observations and lead to a comprehensive understanding of the nature of the Earth’s plasma environment.

  6. Thermally induced depolarization in terbium gallium garnet ceramics rod with natural convection cooling

    NASA Astrophysics Data System (ADS)

    Slezak, Ondrej; Yasuhara, Ryo; Lucianetti, Antonio; Vojna, David; Mocek, Tomas

    2015-06-01

    Thermal birefringence-induced depolarization in terbium gallium garnet (TGG) ceramic rods has been numerically evaluated for the geometry and heating conditions in a previous experiment. In this model, the spatially resolved heat transfer coefficient corresponding to natural convection cooling and the offset of the beam from the rotational axis of the rod have been incorporated and the realistic beam profile used in the experiment has been considered. A resulting beam depolarization ratio of 4.3 × 10-4 has been calculated for an input power of 117 W. The results were found to be in good agreement with the measured values. Furthermore, a parametric study of the depolarization ratio for higher input powers has been performed leading to a depolarization ratio of 3.3 × 10-2 for 1 kW input power.

  7. Detecting hepatic steatosis using ultrasound-induced thermal strain imaging: an ex vivo animal study

    NASA Astrophysics Data System (ADS)

    Mahmoud, Ahmed M.; Ding, Xuan; Dutta, Debaditya; Singh, Vijay P.; Kim, Kang

    2014-02-01

    Hepatic steatosis or fatty liver disease occurs when lipids accumulate within the liver and can lead to steatohepatitis, cirrhosis, liver cancer and eventual liver failure requiring liver transplant. Conventional brightness mode (B-mode) ultrasound (US) is the most common noninvasive diagnostic imaging modality used to diagnose hepatic steatosis in clinics. However, it is mostly subjective or requires a reference organ such as the kidney or spleen with which to compare. This comparison can be problematic when the reference organ is diseased or absent. The current work presents an alternative approach to noninvasively detecting liver fat content using US-induced thermal strain imaging (US-TSI). This technique is based on the difference in the change in the speed of sound as a function of temperature between water- and lipid-based tissues. US-TSI was conducted using two system configurations including a mid-frequency scanner with a single linear array transducer (5-14 MHz) for both imaging and heating and a high-frequency (13-24 MHz) small animal imaging system combined with a separate custom-designed US heating transducer array. Fatty livers (n = 10) with high fat content (45.6 ± 11.7%) from an obese mouse model and control livers (n = 10) with low fat content (4.8 ± 2.9%) from wild-type mice were embedded in gelatin. Then, US imaging was performed before and after US induced heating. Heating time periods of ˜3 s and ˜9.2 s were used for the mid-frequency imaging and high-frequency imaging systems, respectively, to induce temperature changes of approximately 1.5 °C. The apparent echo shifts that were induced as a result of sound speed change were estimated using 2D phase-sensitive speckle tracking. Following US-TSI, histology was performed to stain lipids and measure percentage fat in the mouse livers. Thermal strain measurements in fatty livers (-0.065 ± 0.079%) were significantly (p < 0.05) higher than those measured in control livers (-0.124 ± 0

  8. Axisymmetric deformations and stresses of unsymmetrically laminated composite cylinders in axial compression with thermally-induced preloading effects

    NASA Technical Reports Server (NTRS)

    Paraska, Peter J.

    1993-01-01

    This report documents an analytical study of the response of unsymmetrically laminated cylinders subjected to thermally-induced preloading effects and compressive axial load. Closed-form solutions are obtained for the displacements and intralaminar stresses and recursive relations for the interlaminar shear stress were obtained using the closed-form intralaminar stress solutions. For the cylinder geometries and stacking sequence examples analyzed, several important and as yet undocumented effects of including thermally-induced preloading in the analysis are observed. It should be noted that this work is easily extended to include uniform internal and/or external pressure loadings and the application of strain and stress failure theories.

  9. Abolished thermal and mechanical antinociception but retained visceral chemical antinociception induced by butorphanol in mu-opioid receptor knockout mice.

    PubMed

    Ide, Soichiro; Minami, Masabumi; Ishihara, Kumatoshi; Uhl, George R; Satoh, Masamichi; Sora, Ichiro; Ikeda, Kazutaka

    2008-06-01

    Butorphanol is hypothesized to induce analgesia via opioid pathways, although the precise mechanisms for its effects remain unknown. In this study, we investigated the role of the mu-opioid receptor (MOP) in thermal, mechanical, and visceral chemical antinociception induced by butorphanol using MOP knockout (KO) mice. Butorphanol-induced thermal antinociception, assessed by the hot-plate and tail-flick tests, was significantly reduced in heterozygous and abolished in homozygous MOP-KO mice compared with wildtype mice. The results obtained from our butorphanol-induced mechanical antinociception experiments, assessed by the Randall-Selitto test, were similar to the results obtained from the thermal antinociception experiments in these mice. Interestingly, however, butorphanol retained its ability to induce significant visceral chemical antinociception, assessed by the writhing test, in homozygous MOP-KO mice. The butorphanol-induced visceral chemical antinociception that was retained in homozygous MOP-KO mice was completely blocked by pretreatment with nor-binaltorphimine, a kappa-opioid receptor (KOP) antagonist. In vitro binding and cyclic adenosine monophosphate assays also showed that butorphanol possessed higher affinity for KOPs and MOPs than for delta-opioid receptors. These results molecular pharmacologically confirmed previous studies implicating MOPs, and partially KOPs, in mediating butorphanol-induced analgesia. PMID:18417173

  10. Bragg gratings inscription in step-index PMMA optical fiber by femtosecond laser pulses at 400 nm

    NASA Astrophysics Data System (ADS)

    Hu, X.; Kinet, D.; Chah, K.; Mégret, P.; Caucheteur, C.

    2016-05-01

    In this paper, we report photo-inscription of uniform Bragg gratings in trans-4-stilbenemethanol-doped photosensitive step-index polymer optical fiber. Gratings were produced at ~1575 nm by the phase mask technique with a femtosecond laser emitting at 400 nm with different average optical powers (8 mW, 13 mW and 20 mW). The grating growth dynamics in transmission were monitored during the manufacturing process, showing that the grating grows faster with higher power. Using 20 mW laser beam power, the reflectivity reaches 94 % (8 dB transmission loss) in 70 seconds. Finally, the gratings were characterized in temperature in the range 20 - 45 °C. The thermal sensitivity has been computed equal to - 86.6 pm/°C.

  11. Non-thermal dielectric barrier discharge plasma induces angiogenesis through reactive oxygen species

    PubMed Central

    Arjunan, Krishna Priya; Friedman, Gary; Fridman, Alexander; Clyne, Alisa Morss

    2012-01-01

    Vascularization plays a key role in processes such as wound healing and tissue engineering. Non-thermal plasma, which primarily produces reactive oxygen species (ROS), has recently emerged as an efficient tool in medical applications including blood coagulation, sterilization and malignant cell apoptosis. Liquids and porcine aortic endothelial cells were treated with a non-thermal dielectric barrier discharge plasma in vitro. Plasma treatment of phosphate-buffered saline (PBS) and serum-free medium increased ROS concentration in a dose-dependent manner, with a higher concentration observed in serum-free medium compared with PBS. Species concentration inside cells peaked 1 h after treatment, followed by a decrease 3 h post treatment. Endothelial cells treated with a plasma dose of 4.2 J cm–2 had 1.7 times more cells than untreated samples 5 days after plasma treatment. The 4.2 J cm–2 plasma dose increased two-dimensional migration distance by 40 per cent compared with untreated control, while the number of cells that migrated through a three-dimensional collagen gel increased by 15 per cent. Tube formation was also enhanced by plasma treatment, with tube lengths in plasma-treated samples measuring 2.6 times longer than control samples. A fibroblast growth factor-2 (FGF-2) neutralizing antibody and ROS scavengers abrogated these angiogenic effects. These data indicate that plasma enhanced proliferation, migration and tube formation is due to FGF-2 release induced by plasma-produced ROS. Non-thermal plasma may be used as a potential tool for applying ROS in precise doses to enhance vascularization. PMID:21653568

  12. Shock Compression Induced Hot Spots in Energetic Material Detected by Thermal Imaging Microscopy

    NASA Astrophysics Data System (ADS)

    Chen, Ming-Wei; Dlott, Dana

    2014-06-01

    The chemical reaction of powder energetic material is of great interest in energy and pyrotechnic applications since the high reaction temperature. Under the shock compression, the chemical reaction appears in the sub-microsecond to microsecond time scale, and releases a large amount of energy. Experimental and theoretical research progresses have been made in the past decade, in order to characterize the process under the shock compression. However, the knowledge of energy release and temperature change of this procedure is still limited, due to the difficulties of detecting technologies. We have constructed a thermal imaging microscopy apparatus, and studied the temperature change in energetic materials under the long-wavelength infrared (LWIR) and ultrasound exposure. Additionally, the real-time detection of the localized heating and energy concentration in composite material is capable with our thermal imaging microscopy apparatus. Recently, this apparatus is combined with our laser driven flyer plate system to provide a lab-scale source of shock compression to energetic material. A fast temperature increase of thermite particulars induced by the shock compression is directly observed by thermal imaging with 15-20 μm spatial resolution. Temperature change during the shock loading is evaluated to be at the order of 10^9K/s, through the direct measurement of mid-wavelength infrared (MWIR) emission intensity change. We observe preliminary results to confirm the hot spots appear with shock compression on energetic crystals, and will discuss the data and analysis in further detail. M.-W. Chen, S. You, K. S. Suslick, and D. D. Dlott, {Rev. Sci. Instr., 85, 023705 (2014) M.-W. Chen, S. You, K. S. Suslick, and D. D. Dlott, {Appl. Phys. Lett., 104, 061907 (2014)} K. E. Brown, W. L. Shaw, X. Zheng, and D. D. Dlott, {Rev. Sci. Instr., 83, 103901 (2012)}

  13. Thermal-induced surface plasmon band shift of gold nanoparticle monolayer: morphology and refractive index sensitivity.

    PubMed

    Zhang, Xuemin; Zhang, Junhu; Wang, Huan; Hao, Yudong; Zhang, Xun; Wang, Tieqiang; Wang, Yunan; Zhao, Ran; Zhang, Hao; Yang, Bai

    2010-11-19

    In this paper, thermal-induced behaviors of a gold nanoparticle monolayer on glass slides are investigated. First, through horizontal lifting, gold nanoparticle monolayers are transferred from a water/hexane interface to glass slides. Then thermal treatment is carried out in air, after which an apparent color change of the obtained samples is noticed, depending on the annealing temperature, reflecting a shift of the surface plasmon band (SPB). Depending on the trend of SPB shift, the overall thermal process is divided into three stages. In the first stage, SPB shows a redshift trend with concomitant band broadening. Further increase of the annealing temperature in the second stage results in an increase of interparticle distance. Thus an apparent decrease in absorbance takes place with SPB shift to shorter wavelengths. In the third stage, the SPB redshifts again. Bulk refractive index sensitivity (RIS) measurements are taken by immersing the obtained samples in solutions of various refractive indices and a linear dependence of RIS(λ) and RIS(ext) on refractive index is concluded. In particular, the influences of parameters such as particle sizes, location of SPB, substrate effect and morphology effect on RIS are discussed in detail. The corresponding performance of each sample as a localized surface plasmon resonance-based sensor is evaluated by a figure of merit (FOM) represented as FOM(λ) and FOM(ext). It is found that the optimum annealing temperature is 500 °C. In terms of nanoparticle sizes, samples with a 35 nm gold nanoparticle monolayer perform better than those with 15 nm. The current strategy is simple and facile to achieve fine control of the SPB, in which large-size precision instruments or complex chemosynthesis are unnecessary. Therefore, this method has not only significance for theory but also usefulness in practical applications. PMID:20972320

  14. Thermal-induced surface plasmon band shift of gold nanoparticle monolayer: morphology and refractive index sensitivity

    NASA Astrophysics Data System (ADS)

    Zhang, Xuemin; Zhang, Junhu; Wang, Huan; Hao, Yudong; Zhang, Xun; Wang, Tieqiang; Wang, Yunan; Zhao, Ran; Zhang, Hao; Yang, Bai

    2010-11-01

    In this paper, thermal-induced behaviors of a gold nanoparticle monolayer on glass slides are investigated. First, through horizontal lifting, gold nanoparticle monolayers are transferred from a water/hexane interface to glass slides. Then thermal treatment is carried out in air, after which an apparent color change of the obtained samples is noticed, depending on the annealing temperature, reflecting a shift of the surface plasmon band (SPB). Depending on the trend of SPB shift, the overall thermal process is divided into three stages. In the first stage, SPB shows a redshift trend with concomitant band broadening. Further increase of the annealing temperature in the second stage results in an increase of interparticle distance. Thus an apparent decrease in absorbance takes place with SPB shift to shorter wavelengths. In the third stage, the SPB redshifts again. Bulk refractive index sensitivity (RIS) measurements are taken by immersing the obtained samples in solutions of various refractive indices and a linear dependence of RISλ and RISext on refractive index is concluded. In particular, the influences of parameters such as particle sizes, location of SPB, substrate effect and morphology effect on RIS are discussed in detail. The corresponding performance of each sample as a localized surface plasmon resonance-based sensor is evaluated by a figure of merit (FOM) represented as FOMλ and FOMext. It is found that the optimum annealing temperature is 500 °C. In terms of nanoparticle sizes, samples with a 35 nm gold nanoparticle monolayer perform better than those with 15 nm. The current strategy is simple and facile to achieve fine control of the SPB, in which large-size precision instruments or complex chemosynthesis are unnecessary. Therefore, this method has not only significance for theory but also usefulness in practical applications.

  15. Effect of implanted species on thermal evolution of ion-induced defects in ZnO

    SciTech Connect

    Azarov, A. Yu.; Rauwel, P.; Kuznetsov, A. Yu.; Svensson, B. G.; Hallén, A.; Du, X. L.

    2014-02-21

    Implanted atoms can affect the evolution of ion-induced defects in radiation hard materials exhibiting a high dynamic annealing and these processes are poorly understood. Here, we study the thermal evolution of structural defects in wurtzite ZnO samples implanted at room temperature with a wide range of ion species (from {sup 11}B to {sup 209}Bi) to ion doses up to 2 × 10{sup 16} cm{sup −2}. The structural disorder was characterized by a combination of Rutherford backscattering spectrometry, nuclear reaction analysis, and transmission electron microscopy, while secondary ion mass spectrometry was used to monitor the behavior of both the implanted elements and residual impurities, such as Li. The results show that the damage formation and its thermal evolution strongly depend on the ion species. In particular, for F implanted samples, a strong out-diffusion of the implanted ions results in an efficient crystal recovery already at 600 °C, while co-implantation with B (via BF{sub 2}) ions suppresses both the F out-diffusion and the lattice recovery at such low temperatures. The damage produced by heavy ions (such as Cd, Au, and Bi) exhibits a two-stage annealing behavior where efficient removal of point defects and small defect clusters occurs at temperatures ∼500 °C, while the second stage is characterized by a gradual and partial annealing of extended defects. These defects can persist even after treatment at 900 °C. In contrast, the defects produced by light and medium mass ions (O, B, and Zn) exhibit a more gradual annealing with increasing temperature without distinct stages. In addition, effects of the implanted species may lead to a nontrivial defect evolution during the annealing, with N, Ag, and Er as prime examples. In general, the obtained results are interpreted in terms of formation of different dopant-defect complexes and their thermal stability.

  16. Thermal runaway during the evolution of ONeMg cores towards accretion-induced collapse

    NASA Astrophysics Data System (ADS)

    Schwab, Josiah; Quataert, Eliot; Bildsten, Lars

    2015-10-01

    We study the evolution of degenerate electron cores primarily composed of the carbon burning products 16O, 20Ne, and 24Mg (hereafter ONeMg cores) that are undergoing compression. Electron capture reactions on A = 20 and 24 isotopes reduce the electron fraction and heat the core. We develop and use a new capability of the Modules for Experiments in Stellar Astrophysics (MESA) stellar evolution code that provides a highly accurate implementation of these key reactions. These new accurate rates and the ability of MESA to perform extremely small spatial zoning demonstrates a thermal runaway in the core triggered by the temperature and density sensitivity of the 20Ne electron capture reactions. Both analytics and numerics show that this thermal runaway does not trigger core convection, but rather leads to a centrally concentrated (r < km) thermal runaway that will subsequently launch an oxygen deflagration wave from the centre of the star. We use MESA to perform a parameter study that quantifies the influence of the 24Mg mass fraction, the central temperature, the compression rate, and uncertainties in the electron capture reaction rates on the ONeMg core evolution. This allows us to establish a lower limit on the central density at which the oxygen deflagration wave initiates of ρc ≳ 8.5 × 109 g cm- 3. Based on previous work and order-of-magnitude calculations, we expect objects which ignite oxygen at or above these densities to collapse and form a neutron star. Calculations such as these are an important step in producing more realistic progenitor models for studies of the signature of accretion-induced collapse.

  17. Thermally induced cation redistribution in Fe-bearing oxy-dravite and potential geothermometric implications

    NASA Astrophysics Data System (ADS)

    Bosi, Ferdinando; Skogby, Henrik; Hålenius, Ulf

    2016-05-01

    Iron-bearing oxy-dravite was thermally treated in air and hydrogen atmosphere at 800 °C to study potential changes in Fe, Mg and Al ordering over the octahedrally coordinated Y and Z sites and to explore possible applications to intersite geothermometry based on tourmaline. Overall, the experimental data (structural refinement, Mössbauer, infrared and optical absorption spectroscopy) show that heating Fe-bearing tourmalines results in disordering of Fe over Y and Z balanced by ordering of Mg at Y, whereas Al does not change appreciably. The Fe disorder depends on temperature, but less on redox conditions. The degree of Fe3+-Fe2+ reduction is limited despite strongly reducing conditions, indicating that the f O2 conditions do not exclusively control the Fe oxidation state at the present experimental conditions. Untreated and treated samples have similar short- and long-range crystal structures, which are explained by stable Al-extended clusters around the O1 and O3 sites. In contrast to the stable Al clusters that preclude any temperature-dependent Mg-Al order-disorder, there occurs Mg diffusion linked to temperature-dependent exchange with Fe. Ferric iron mainly resides around O2- at O1 rather than (OH)-, but its intersite disorder induced by thermal treatment indicates that Fe redistribution is the driving force for Mg-Fe exchange and that its diffusion rates are significant at these temperatures. With increasing temperature, Fe progressively disorders over Y and Z, whereas Mg orders at Y according to the order-disorder reaction: YFe + ZMg → ZFe + YMg. The presented findings are important for interpretation of the post-crystallization history of both tourmaline and tourmaline host rocks and imply that successful tourmaline geothermometers may be developed by thermal calibration of the Mg-Fe order-disorder reaction, whereas any thermometers based on Mg-Al disorder will be insensitive and involve large uncertainties.

  18. Effect of implanted species on thermal evolution of ion-induced defects in ZnO

    NASA Astrophysics Data System (ADS)

    Azarov, A. Yu.; Hallén, A.; Du, X. L.; Rauwel, P.; Kuznetsov, A. Yu.; Svensson, B. G.

    2014-02-01

    Implanted atoms can affect the evolution of ion-induced defects in radiation hard materials exhibiting a high dynamic annealing and these processes are poorly understood. Here, we study the thermal evolution of structural defects in wurtzite ZnO samples implanted at room temperature with a wide range of ion species (from 11B to 209Bi) to ion doses up to 2 × 1016 cm-2. The structural disorder was characterized by a combination of Rutherford backscattering spectrometry, nuclear reaction analysis, and transmission electron microscopy, while secondary ion mass spectrometry was used to monitor the behavior of both the implanted elements and residual impurities, such as Li. The results show that the damage formation and its thermal evolution strongly depend on the ion species. In particular, for F implanted samples, a strong out-diffusion of the implanted ions results in an efficient crystal recovery already at 600 °C, while co-implantation with B (via BF2) ions suppresses both the F out-diffusion and the lattice recovery at such low temperatures. The damage produced by heavy ions (such as Cd, Au, and Bi) exhibits a two-stage annealing behavior where efficient removal of point defects and small defect clusters occurs at temperatures ˜500 °C, while the second stage is characterized by a gradual and partial annealing of extended defects. These defects can persist even after treatment at 900 °C. In contrast, the defects produced by light and medium mass ions (O, B, and Zn) exhibit a more gradual annealing with increasing temperature without distinct stages. In addition, effects of the implanted species may lead to a nontrivial defect evolution during the annealing, with N, Ag, and Er as prime examples. In general, the obtained results are interpreted in terms of formation of different dopant-defect complexes and their thermal stability.

  19. Optically tunable Fano resonance in a grating-based Fabry-Perot cavity-coupled microring resonator on a silicon chip.

    PubMed

    Zhang, Weifeng; Li, Wangzhe; Yao, Jianping

    2016-06-01

    A grating-based Fabry-Perot (FP) cavity-coupled microring resonator on a silicon chip is reported to demonstrate an all-optically tunable Fano resonance. In the device, an add-drop microring resonator (MRR) is employed, and one of the two bus waveguides is replaced by an FP cavity consisting of two sidewall Bragg gratings. By choosing the parameters of the gratings, the resonant mode of the FP cavity is coupled to one of the resonant modes of the MRR. Due to the coupling between the resonant modes, a Fano resonance with an asymmetric line shape resulted. Measurement results show a Fano resonance with an extinction ratio of 22.54 dB, and a slope rate of 250.4 dB/nm is achieved. A further study of the effect of the coupling on the Fano resonance is performed numerically and experimentally. Thanks to the strong light-confinement capacity of the MRR and the FP cavity, a strong two-photon absorption induced nonlinear thermal-optic effect resulted, which is used to tune the Fano resonance optically. PMID:27244392

  20. Reduction of spinal PGE2 concentrations prevents swim stress-induced thermal hyperalgesia.

    PubMed

    Guevara, Coram; Fernandez, Ana Cristina; Cardenas, Ricardo; Suarez-Roca, Heberto

    2015-03-30

    We evaluated the association between spinal PGE2 and thermal hyperalgesia following repeated stress. Thermal nociception was determined in male Sprague-Dawley rats using the hot-plate test, before and after forced-swimming; non-conditioned rats served as controls. Animals were pretreated with ketoprofen or meloxicam, preferential COX-1 and COX-2 inhibitors, respectively. After the second hot-plate test, we measured serum corticosterone (stress marker), and lumbar spinal PGE2 (neuroinflammation marker) under peripheral inflammation (1% formalin plantar injection). Stressed rats displayed response latencies 40% shorter and inflammatory spinal PGE2 levels 95% higher than controls. Pretreatment with ketoprofen or meloxicam prevented hyperalgesia and elevation of spinal PGE2, increasing the escape behavior time during forced swimming 95% respect to saline-treated rats. Corticosterone levels in stressed rats were 97% higher than controls; COX inhibitors reduced them by 84%. PGE2 could participate in stress-induced hyperalgesia, learned helplessness, and corticosterone production, supporting the use of non-steroidal anti-inflammatory drugs (NSAIDs) for persistent pain associated with chronic stress and depression. PMID:25703222