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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. Electromagnetically induced phase grating.

    PubMed

    de Araujo, Luís E E

    2010-04-01

    I propose an electromagnetically induced phase grating based on the giant Kerr nonlinearity of an atomic medium under electromagnetically induced transparency. The atomic phase grating behaves similarly to an ideal sinusoidal phase grating, and it is capable of producing a pi phase excursion across a weak probe beam along with high transmissivity. The grating is created with arbitrarily weak fields, and diffraction efficiencies as high as 30% are predicted.

  5. Thermal transport in suspended silicon membranes measured by laser-induced transient gratings

    NASA Astrophysics Data System (ADS)

    Vega-Flick, A.; Duncan, R. A.; Eliason, J. K.; Cuffe, J.; Johnson, J. A.; Peraud, J.-P. M.; Zeng, L.; Lu, Z.; Maznev, A. A.; Wang, E. N.; Alvarado-Gil, J. J.; Sledzinska, M.; Sotomayor Torres, C. M.; Chen, G.; Nelson, K. A.

    2016-12-01

    Studying thermal transport at the nanoscale poses formidable experimental challenges due both to the physics of the measurement process and to the issues of accuracy and reproducibility. The laser-induced transient thermal grating (TTG) technique permits non-contact measurements on nanostructured samples without a need for metal heaters or any other extraneous structures, offering the advantage of inherently high absolute accuracy. We present a review of recent studies of thermal transport in nanoscale silicon membranes using the TTG technique. An overview of the methodology, including an analysis of measurements errors, is followed by a discussion of new findings obtained from measurements on both "solid" and nanopatterned membranes. The most important results have been a direct observation of non-diffusive phonon-mediated transport at room temperature and measurements of thickness-dependent thermal conductivity of suspended membranes across a wide thickness range, showing good agreement with first-principles-based theory assuming diffuse scattering at the boundaries. Measurements on a membrane with a periodic pattern of nanosized holes (135nm) indicated fully diffusive transport and yielded thermal diffusivity values in agreement with Monte Carlo simulations. Based on the results obtained to-date, we conclude that room-temperature thermal transport in membrane-based silicon nanostructures is now reasonably well understood.

  6. Measurement of thermal conductivity of polycrystalline CVD diamond by laser-induced transient grating technique

    SciTech Connect

    Ivakin, E V; Sukhodolov, A V; Ralchenko, V G; Vlasov, A V; Khomich, A V

    2002-04-30

    The tangential thermal diffusivity D{sub ||} and thermal conductivity k{sub ||} of diamond plates grown from the gaseous phase by chemical vapour deposition (CVD diamond) are determined by the transient grating technique in the temperature range 25 - 200 {sup 0}C. Samples of insulating and boron-doped polycrystalline diamond of thickness about 0.3 mm and diameter 63 mm were synthesised in a microwave discharge in mixtures of methane and hydrogen. In view of the intense light scattering by the samples, a photosensitive grating recording technique was developed and used for measurements. It was found that the value k{sub ||} amounts to 18 - 20 W cm{sup -1} K{sup -1} at room temperature, approaching the thermal conductivity of the highest purity single crystals of diamond. A comparison of the value of k{sub ||} with the normal thermal conductivity k{sub perpendicular} determined by the flash method reveals a thermal conductivity anisotropy of about 10% - 20% associated with the texture of the diamond film, the normal component of thermal conductivity being larger than the tangential component. Boron-doped diamond displays a dependence of the transient grating kinetics on the excitation wavelength. The obtained results indicate that CVD diamond is a promising material for preparing efficient heat sinks, especially of large size, used in microelectronic devices and laser engineering. (laser applications and other topics in quantum electronics)

  7. The study of the thermal annealing of the Bragg gratings induced in the hydrogenated birefringent optical fiber with an elliptical stress cladding

    NASA Astrophysics Data System (ADS)

    Munko, A. S.; Varzhel', S. V.; Arkhipov, S. V.; Gribaev, A. I.; Konnov, K. A.; Belikin, M. N.

    2016-08-01

    In this work the comparative results on the dynamics of fiber Bragg gratings inscription in both the conventional and the subjected to hydrogenation birefringent optical fiber with elliptical stress cladding as well as in the same type of lightguide with the increased GeO2 concentration are presented. Also the research on the thermal impact on the fiber Bragg gratings written in the birefringent fiber with elliptical stress cladding has been carried out. The dependences of the fiber Bragg reflectance coefficient on the time of the thermal impact, obtained by annealing of the refractive index gratings, induced in the optical fibers with increased photorefractivity, are shown.

  8. 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

  9. 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

    2009-01-05

    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.

  10. Ultrafast laser-induced negative-index fiber Bragg gratings with enhanced thermal stability

    NASA Astrophysics Data System (ADS)

    He, Jun; Liao, Changrui; Yang, Kaiming; Wang, Yiping

    2017-04-01

    Negative-index fiber Bragg gratings (FBGs) were fabricated using 800 nm femtosecond laser overexposure and thermal regeneration. A positive-index type I-IR FBG was first inscribed in H2-free fiber with a uniform phase mask, and then a highly polarization dependent phase-shifted FBG (PSFBG) was created from the type I-IR FBG by overexposure. Subsequently, the PSFBG was annealed at 800 °C for 12 hours. A negative-index FBG was obtained with a reflectivity of 99.22%, an insertion loss of 0.08 dB, a blue-shift of 0.83 nm, and an operating temperature of up to 1000 °C.

  11. Thermometry in pressurized sooting flames using laser-induced gratings

    NASA Astrophysics Data System (ADS)

    Brown, Michael S.; Roberts, William L.

    1997-11-01

    We have performed non-intrusive thermometry in rich ethylene/air flames using a frequency measurement based on laser-induced gratings. Light from a cw probe beam is coherently scattered from a thermal or electrostrictive grating induced by the pulsed pump beams. The Doppler modulation of the signal beam is determined by the local speed of sound from which a temperature can be extracted. Soot particles, acting as blackbody absorbers do contribute to the signal.

  12. Fast thermal regeneration of fiber Bragg gratings.

    PubMed

    Bueno, Antonio; Kinet, Damien; Mégret, Patrice; Caucheteur, Christophe

    2013-10-15

    In this Letter we report a fast thermal regeneration of Type I fiber Bragg gratings inscribed with a UV laser in up to four different optical fibers: hydrogenated standard fiber, hydrogenated highly Ge-doped fiber, hydrogenated photosensitive fiber, and nonhydrogenated fiber. The thermal treatment consists in directly introducing the optical fiber into a preheated oven. The preheat temperature depends on the type of fiber used and is high enough to erase the grating and regenerate it afterward. The best results are obtained with hydrogenated photosensitive fiber and highly Ge-doped fiber, whereas no satisfactory results were obtained with hydrogenated standard fiber and nonhydrogenated photosensitive fiber. A regenerated grating with only 1.6 dB of loss was obtained in 10 min, reducing the time needed by a factor of 5.7. By adjusting the temperature of the oven, regenerated gratings of 13.7 dB of loss in 31 s and 5.8 dB of loss in 3 min were obtained. The factors of improvement in time are 110.3 and 19, respectively.

  13. 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.

  14. Effective diffraction gratings via acidic etching of thermally poled glass

    NASA Astrophysics Data System (ADS)

    Kamenskii, A. N.; Reduto, I. V.; Petrikov, V. D.; Lipovskii, A. A.

    2016-12-01

    Relief diffraction gratings are formed via acidic chemical etching of a periodically poled soda-lime glass. The thermal poling under 1000 V DC is performed at 325 °C using a thermally stable glassy-carbon anodic electrode with periodic grooves, the depth of the grooves being of ∼650 nm. Poling-induced modification of the glass results in deepening the glass anodic surface in the regions under the ribs of the anodic electrode due to volume relaxation and in increasing chemical durability of these regions in acidic media comparatively to the virgin glass. Chemical etching of the poled glass in NH4F:8H2O solution allows additional to the thermal poling shaping of the glass surface via faster dissolution of unpoled/less poled glass regions. The morphology of the glass surface before and after the etching is characterized with atomic force and scanning electron microscopy. About 30 min etching provides the formation of ∼0.9 μm in height relief diffraction gratings with the diffraction efficiency close to the theoretically achievable ∼30% for multi-order diffraction. In vivo measuring of the diffraction efficiency in the course of the etching allows precise fabrication of the gratings.

  15. Stress measurements in glass by use of double thermal gratings.

    PubMed

    Cannon, B D; Shepard, C; Khaleel, M

    2001-10-20

    We developed a nondestructive and noncontact method for measuring stress at the midplane of tempered glass plates that uses Bragg scattering from a pair of thermal gratings. These gratings are formed by 1064-nm beams from a seeded Nd:YAG laser, and we measure the polarization state of light from a 532-nm beam that scatters from both thermal gratings. The change in polarization of the doubly scattered light with separation between the two gratings allows measurement of the in-plane stress. A model of the Bragg scattering efficiency, experimental investigations of the scattered beams, and stress measurements are reported.

  16. Thermally tunable grating using thermo-responsive magnetic fluid

    NASA Astrophysics Data System (ADS)

    Zaibudeen, A. W.; Philip, John

    2017-04-01

    We report a thermally tunable grating prepared using poly(N-isopropylacrylamide) and super paramagnetic iron oxide nanoparticles. The array spacing is reversibly tuned by varying the temperature between 5 and 38 °C. Here, the ability of thermo-responsive polymer brushes to alter their conformation at an interface is exploited to control the grating spacing in nanoscale. The underlying mechanism for the temperature dependent conformational changes are studied by measuring the subtle intermolecular forces between the polymer covered interfaces. It is observed that the interparticle forces are repulsive and exponentially decaying with distance. The thermo-responsive grating is simple to use and offers a wide range of applications.

  17. Direct laser writing of thermally stabilized channel waveguides with Bragg gratings.

    PubMed

    Nishiyama, Hiroaki; Miyamoto, Isamu; Matsumoto, Shin-Ichi; Saito, Mitsunori; Kintaka, Kenji; Nishii, Junji

    2004-09-20

    Thermally stabilized photo-induced channel waveguides with Bragg gratings were fabricated in Ge-B-SiO2 thin glass films by exposure with KrF excimer laser and successive annealing at 600 degrees C. The annealing reversed the photo-induced refractive index pattern and also enhanced its thermal stability. The stabilized channel waveguide with a Bragg grating showed diffraction efficiency of 18.0 dB and 18.7 dB for TE- and TM-like modes, respectively. The diffraction efficiencies and wavelengths for both modes never changed after heat treatment at 500 degrees C, whereas the conventional photo-induced grating decayed even at 200 degrees C.

  18. Direct laser writing of thermally stabilized channel waveguides with Bragg gratings

    NASA Astrophysics Data System (ADS)

    Nishiyama, Hiroaki; Miyamoto, Isamu; Matsumoto, Shin-Ichi; Saito, Mitsunori; Kintaka, Kenji; Nishii, Junji

    2004-09-01

    Thermally stabilized photo-induced channel waveguides with Bragg gratings were fabricated in Ge-B-SiO2 thin glass films by exposure with KrF excimer laser and successive annealing at 600°C. The annealing reversed the photo-induced refractive index pattern and also enhanced its thermal stability. The stabilized channel waveguide with a Bragg grating showed diffraction efficiency of 18.0 dB and 18.7 dB for TE- and TM-like modes, respectively. The diffraction efficiencies and wavelengths for both modes never changed after heat treatment at 500°C, whereas the conventional photo-induced grating decayed even at 200°C.

  19. 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.

  20. Annealing dynamics of waveguide Bragg gratings: evidence of femtosecond laser induced colour centres.

    PubMed

    Dekker, P; Ams, M; Marshall, G D; Little, D J; Withford, M J

    2010-02-15

    There is still significant speculation regarding the nature of femtosecond laser induced index change in bulk glasses with colour centre formation and densification the main candidates. In the work presented here, we fabricated waveguide Bragg gratings in doped and undoped phosphate glasses and use these as a diagnostic for monitoring subtle changes in the induced refractive index during photo- and thermal annealing experiments. Reductions in grating strengths during such experiments were attributed to the annihilation of colour centres.

  1. Thermally Compensated Fiber Bragg Grating Mount

    DTIC Science & Technology

    2007-01-25

    more sensor channels at different wavelengths. Normally, the FBGls thermal sensitivity is dominated by the thermo-optic effect on the fibers index of...specifically designed to be sensitive to pressure, and the depth changes of a towed hydrophone array would also cause significant changes in the FBGs if wound...zirconium tungstate . The negative coefficient of thermal expansion is preferably about -9xi0-6OC-. An optic fiber including a FBG is wound onto the

  2. 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.

  3. UV induced permanent gratings in sol-gel germanosilicate thin films

    NASA Astrophysics Data System (ADS)

    Razafimahatratra, A. D.; Benatsou, M.; Bouazaoui, M.; Xie, W. X.; Mathieu, C.; Dacosta, A.; Douay, M.

    2000-01-01

    Germanosilicate thin films have been elaborated by the sol-gel process and the dip-coating technique. Pulsed or continuous wave UV laser (244 nm) was used to write permanent gratings in these films. In the case of exposure to cw laser, the grating diffraction efficiencies were measured using a focused beam from a He-Ne laser at 633 nm and photo-induced changes in refractive index as high as 4×10 -3 have been obtained. The thermal behaviour of these gratings has been investigated showing a good stability up to 400°C. Exposure to pulsed fringe pattern led to a glass photo-expansion modulated by a strong corrugation which can be due mainly to photo-ablation at the places of the bright fringes. The waveguide surface at the grating places was investigated through Atomic Force Microscopy (AFM) and microscopic profilometry techniques. Preliminary results on the kinetics of the grating growths are also reported.

  4. Analysis on volume grating induced by femtosecond laser pulses.

    PubMed

    Zhou, Keya; Guo, Zhongyi; Ding, Weiqiang; Liu, Shutian

    2010-06-21

    We report on a kind of self-assembled volume grating in silica glass induced by tightly focused femtosecond laser pulses. The formation of the volume grating is attributed to the multiple microexplosion in the transparent materials induced by the femtosecond pulses. The first order diffractive efficiency is in dependence on the energy of the pulses and the scanning velocity of the laser greatly, and reaches as high as 30%. The diffraction pattern of the fabricated grating is numerically simulated and analyzed by a two dimensional FDTD method and the Fresnel Diffraction Integral. The numerical results proved our prediction on the formation of the volume grating, which agrees well with our experiment results.

  5. Measurement of atomic diffraction phases induced by material gratings

    SciTech Connect

    Perreault, John D.; Cronin, Alexander D.

    2006-03-15

    Atom-surface interactions can significantly modify the intensity and phase of atom de Broglie waves diffracted by a silicon nitride grating. This affects the operation of a material grating as a coherent beam splitter. The phase shifts induced by diffraction are measured by comparing the relative phases of several interfering paths in a Mach-Zehnder Na atom interferometer formed by three material gratings. The values of the diffraction phases are consistent with a simple model which includes a van der Waals atom-surface interaction between the Na atoms and the silicon nitride grating bars.

  6. Thermal decay analysis of fiber Bragg gratings at different temperature annealing rates using demarcation energy approximation

    NASA Astrophysics Data System (ADS)

    Gunawardena, Dinusha Serandi; Lai, Man-Hong; Lim, Kok-Sing; Ahmad, Harith

    2017-03-01

    In this study the thermal degradation of gratings inscribed in three types of fiber namely, PS 1250/1500, SM 1500 and zero water peak single mode fiber is demonstrated. A comparative investigation is carried out on the aging characteristics of the gratings at three different temperature ramping rates of 3 °C/min, 6 °C/min and 9 °C/min. During the thermal annealing treatment, a significant enhancement in the grating reflectivity is observed for PS 1250/1500 fiber from ∼1.2 eV until 1.4 eV which indicates a thermal induced reversible effect. Higher temperature ramping rates lead to a higher regeneration temperature. In addition, the investigation also reflects that regardless of the temperature ramping rate the thermal decay behavior of a specific fiber can be successfully characterized when represented in a demarcation energy domain. Moreover, this technique can be accommodated when predicting the thermal decay characteristics of a specific fiber.

  7. Electromagnetically induced two-dimensional grating assisted by incoherent pump

    NASA Astrophysics Data System (ADS)

    Chen, Yu-Yuan; Liu, Zhuan-Zhuan; Wan, Ren-Gang

    2017-04-01

    We propose a scheme for realizing electromagnetically induced two-dimensional grating in a double-Λ system driven simultaneously by a coherent field and an incoherent pump field. In such an atomic configuration, the absorption is suppressed owing to the incoherent pumping process and the probe can be even amplified, while the refractivity is mainly attributed to the dynamically induced coherence. With the help of a standing-wave pattern coherent field, we obtain periodically modulated refractive index without or with gain, and therefore phase grating or gain-phase grating which diffracts a probe light into high-order direction efficiently can be formed in the medium via appropriate manipulation of the system parameters. The diffraction efficiency attainable by the present gratings can be controlled by tuning the coherent field intensity or the interaction length. Hence, the two-dimensional grating can be utilized as all-optical splitter or router in optical networking and communication.

  8. Fabrication of thermal-resistant gratings for high-temperature measurements using geometric phase analysis

    NASA Astrophysics Data System (ADS)

    Zhang, Q.; Liu, Z.; Xie, H.; Ma, K.; Wu, L.

    2016-12-01

    Grating fabrication techniques are crucial to the success of grating-based deformation measurement methods because the quality of the grating will directly affect the measurement results. Deformation measurements at high temperatures entail heating and, perhaps, oxidize the grating. The contrast of the grating lines may change during the heating process. Thus, the thermal-resistant capability of the grating becomes a point of great concern before taking measurements. This study proposes a method that combines a laser-engraving technique with the processes of particle spraying and sintering for fabricating thermal-resistant gratings. The grating fabrication technique is introduced and discussed in detail. A numerical simulation with a geometric phase analysis (GPA) is performed for a homogeneous deformation case. Then, the selection scheme of the grating pitch is suggested. The validity of the proposed technique is verified by fabricating a thermal-resistant grating on a ZrO2 specimen and measuring its thermal strain at high temperatures (up to 1300 °C). Images of the grating before and after deformation are used to obtain the thermal-strain field by GPA and to compare the results with well-established reference data. The experimental results indicate that this proposed technique is feasible and will offer good prospects for further applications.

  9. Fabrication of thermal-resistant gratings for high-temperature measurements using geometric phase analysis.

    PubMed

    Zhang, Q; Liu, Z; Xie, H; Ma, K; Wu, L

    2016-12-01

    Grating fabrication techniques are crucial to the success of grating-based deformation measurement methods because the quality of the grating will directly affect the measurement results. Deformation measurements at high temperatures entail heating and, perhaps, oxidize the grating. The contrast of the grating lines may change during the heating process. Thus, the thermal-resistant capability of the grating becomes a point of great concern before taking measurements. This study proposes a method that combines a laser-engraving technique with the processes of particle spraying and sintering for fabricating thermal-resistant gratings. The grating fabrication technique is introduced and discussed in detail. A numerical simulation with a geometric phase analysis (GPA) is performed for a homogeneous deformation case. Then, the selection scheme of the grating pitch is suggested. The validity of the proposed technique is verified by fabricating a thermal-resistant grating on a ZrO2 specimen and measuring its thermal strain at high temperatures (up to 1300 °C). Images of the grating before and after deformation are used to obtain the thermal-strain field by GPA and to compare the results with well-established reference data. The experimental results indicate that this proposed technique is feasible and will offer good prospects for further applications.

  10. Electromagnetically Induced Grating Without Absorption Using Incoherent Pump

    NASA Astrophysics Data System (ADS)

    Chen, Yu-Yuan; Liu, Zhuan-Zhuan; Wan, Ren-Gang

    2017-10-01

    We propose a scheme for creating electromagnetically induced grating in a four-level double- Λ atomic system driven by a coupling field and an incoherent pump field. Owing to the incoherent pumping process, large refractivity accompanied with vanishing absorption or even gain across the probe field can be built up in the atoms, thus phase grating or gain-phase grating, which diffracts a probe light into different directions, can be formed with the help of a standing-wave coupling field. The diffraction efficiency of the gratings can be tuned by the coupling field intensity and the incoherent pump rate, hence the proposed gratings should be suitable for beam splitter and optical switching in optical communication and networking.

  11. Electromagnetically Induced Grating Without Absorption Using Incoherent Pump

    NASA Astrophysics Data System (ADS)

    Chen, Yu-Yuan; Liu, Zhuan-Zhuan; Wan, Ren-Gang

    2017-07-01

    We propose a scheme for creating electromagnetically induced grating in a four-level double- Λ atomic system driven by a coupling field and an incoherent pump field. Owing to the incoherent pumping process, large refractivity accompanied with vanishing absorption or even gain across the probe field can be built up in the atoms, thus phase grating or gain-phase grating, which diffracts a probe light into different directions, can be formed with the help of a standing-wave coupling field. The diffraction efficiency of the gratings can be tuned by the coupling field intensity and the incoherent pump rate, hence the proposed gratings should be suitable for beam splitter and optical switching in optical communication and networking.

  12. Fibre Bragg Gratings, towards a Better Thermal Stability at High Temperatures

    NASA Astrophysics Data System (ADS)

    de Oliveira, Valmir; Abe, Ilda; Alberto, Nelia Jordão; Kalinowski, Hypolito José

    Regenerated fibre Bragg gratings (RFBG) are obtained by heating an original seed grating until its reflection practically vanishes, which is followed by the growth of a new reflection band. Advantages of RFBG for sensing purposes are the longer lifetime and higher thermal stability at higher temperatures, as they have been observed to survive temperatures in the range 1300-1500 °C. The thermal stability of the RFBG permits several applications not attained by standard Bragg gratings.

  13. Laser beam steering via wave mixing in volumetric thermal gratings

    NASA Astrophysics Data System (ADS)

    Tyler, David W.

    1992-06-01

    A volumetric thermal grating (VTG) is a spatially periodic refractive index variation in a volume of gas or liquid, generated by imaging interference fringes into the medium. The fringes can be created and varied by steering laser write beams electronically with acousto- optic (A-O) cells. While the wavelength of the write beams is chosen to be absorbed by a dopant in the VTG medium, a read beam at an off-resonance wavelength can be manipulated by diffraction from the resulting index grating. Potential applications include resonator and amplifier optical isolation prepulse suppression in high-gain amplifiers, noninertial steering of large-diameter laser beams, transfer of phase information between beams to facilitate adaptive optics, Q-switching of chemical lasers, and line selection in broadband lasers. In this paper, we present a preliminary assessment of VTG utility for these optical systems applications by quantitative analysis of the medium density dynamics. In Section 2, we derive a relation between A-O acoustic frequency uncertainty and VTG pointing/steering uncertainty, which also scales desired steering range to required A-O frequency modulation bandwidth. In Section 3, we discuss the temporal response of a doped rare-gas VTG medium. Section 4 is an assessment of VTG beam-steering performance potential using available technology.

  14. UV-induced photodarkening and photobleaching in UV-femtosecond-pulse-written fibre Bragg gratings

    NASA Astrophysics Data System (ADS)

    Fiebrandt, Julia; Jetschke, Sylvia; Leich, Martin; Rothhardt, Manfred; Bartelt, Hartmut

    2013-08-01

    Photodarkening and photobleaching effects in the case of UV femtosecond-pulse exposure of optical fibres are investigated. We evaluate the existence of loss equilibrium states in Yb-doped and Yb-free fibres. Supposing that parasitic VIS to NIR losses induced by fibre Bragg grating (FBG) inscription can also be addressed by a photobleaching treatment, we find grating absorption remarkably reduced by a post-exposure treatment. We also present photobleaching applied directly after FBG inscription with UV femtosecond pulses to improve the wavelength and power stability of a monolithic FBG-based fibre laser as a noteworthy alternative to subsequent thermal treatment.

  15. 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

  16. 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.

  17. Femtosecond laser induced damage of pulse compression gratings

    NASA Astrophysics Data System (ADS)

    Kong, Fanyu; Huang, Haopeng; Wang, Leilei; Shao, Jianda; Jin, Yunxia; Xia, Zhilin; Chen, Junming; Li, Linxin

    2017-12-01

    Laser induced damage of Au-coated gratings (ACG) and metal multilayer dielectric gratings (MMDG) for pulse compression were measured using 800 ± 35 nm femto-laser with pulse width of 30.2 fs. The -1st order diffraction efficiency of the ACG is over 90% in wavelength range from 700 to 1000 nm. The MMDG has a 148 nm bandwidth (750-897 nm) with -1st order diffraction efficiency greater than 90%. The laser damage experiment on grating samples was performed in air for single-shot damage. The single-shot damage threshold of the ACG and MMDG was determined to be 0.32 ± 0.02 J/cm2 and 0.31 ± 0.02 J/cm2, respectively. The damage morphologies of the ACG revealed that the damage was attributed to the pinholes at the base of the grating pillars and the weak adhesion between metal layer and photoresist gratings layer. The damage feature combined with near field distribution of MMDG indicated that the damage was due to the nonlinear ionization process of the valence electrons in HfO2 film. According to analysis results, the laser damage resistance of the ACG can be enhanced through avoiding the appearance of pinholes and increasing adhesion between metal layer and photoresist layer. And for the MMDG, good performance of HfO2 film, low near field enhancement and single HfO2 grating structures may increase its laser damage resistance.

  18. 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.

  19. 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.

  20. Varied laser induced damage phenomena of gold coated gratings for pulse compression

    NASA Astrophysics Data System (ADS)

    Xia, Zhilin; Huang, Haopeng; Kong, Fanyu; Wang, Leilei; Jin, Yunxia

    2017-08-01

    In this paper, gold-coated gratings for pulse compression have been prepared and their laser damage experiments have been performed. Varied laser damage morphologies have been observed: when a 60 fs-pulsed laser with energy density slightly higher than the damage threshold was used, damage morphology with a characteristic of discrete distribution of small pits was appeared. These damage pits are linearly distributed at the junction of ridges and grooves. If the laser energy density is much higher than the damage threshold, the gold films was overall ablated and the grating structure disappeared. Besides, if the gold film has poor adhesion, it was peeled off. When a 450 ps-pulsed laser with energy density slightly higher than the damage threshold was used, part of grating ridges will be ablated and an obvious line exists between the ablated area and the unchanged area. In theory, the laser induced temperature field and stress field in gold-coated gratings were calculated based on the electromagnetic field using the finite element method. It is demonstrated that the temperature and thermal stress distribution characteristics are affected by the laser heating rate and the heat diffusion time (the calculated diffusion time ranges from 6 fs to 450 ps), which determines the laser damage characteristics. The possible damage drivers have electron hydrodynamic pressure, thermal ablation and thermal stress.

  1. Polarization-independent mechanically induced long-period fiber gratings

    NASA Astrophysics Data System (ADS)

    Block, Ueyn L.; Ozcan, Aydogan; Digonnet, Michel J. F.; Fejer, Martin M.

    2002-05-01

    We have developed long-period fiber gratings (LPFGs) utilizing the photoelastic effect and have demonstrated polarization-independent operation. The LPFG is made by pressing a standard, jacketed single-mode fiber between a flat plate and a plate with grooves mechanically machined with a suitable period. The grating's transmission spectrum is easily tuned by adjusting pressure, grating tilt, and length. Furthermore, the grating can be completely erased by removing the pressure from the fiber. Grating attenuation greater than 25 dB has been demonstrated with a notch-location polarization dependence of +-4 nm. In this paper we report drastic reduction in this polarization dependence by two different approaches. Passing through the grating a second time after reflecting off a Faraday rotator mirror was successful; this method may be used with other types of LPFGs. The second approach utilizes our mechanical grating's ability to be double-passed with two fibers side-by-side. Between passes, a fiber-loop half-wave plate aligned at 45 degrees to the plane of the grooved plate swaps power between x- and y-polarization states. The resulting output's measured polarization dependence was smaller than +/- 0.2 nm. Further improvement is expected through careful tuning of the wave plate. We also report a computer model of the filter spectrum and its polarization dependence, which takes into account non-uniform index perturbation, lossy cladding modes, cladding index perturbation, as well as the polarization dependence of the photoelastic effect, characteristics not usually present in UV-induced LPFGs. The model generates transmission spectra that agree quite well with experimental results.

  2. Replica grating study. [response to aerospace environment, thermal vacuum, and electron irradiation

    NASA Technical Reports Server (NTRS)

    Gunter, R. C., Jr.

    1975-01-01

    Methods are outlined which were used to test the response of replica diffraction gratings to a space environment, specifically the response of the replica gratings to thermal-vacuum and electron irradiation stress. It is concluded that there probably is some degradation to thermal stress, but that there is probably no significant degradation due to a vacuum environment. It is further concluded that the degradation of performance of replica gratings because of electron irradiation is due to the interaction of the electrons and the replica grating substrate and not to the replication material itself. Replica and original gratings on the same substrate material should thus respond to particle irradiation in the same manner. A study is presented on the variation of refraction index of a space-related material, Nd:CaF2, with wavelength, percent neodymium doping, and temperature.

  3. Manipulating feature sizes in Si-based grating structures by thermal oxidation

    NASA Astrophysics Data System (ADS)

    Chen, Xin; Ji, Ran; Dai, Ning; Scholz, Roland; Steinhart, Martin; Nielsch, Kornelius; Gösele, Ulrich

    2008-08-01

    We report a method for manipulating feature sizes in Si-based grating structures by thermal oxidation, which allows the realization of fin width/period ratios not directly accessible by laser interference lithography. Taking advantage of the expansion in volume associated with the thermal oxidation of Si, grating structures with very high fin width/period ratios of the order of 0.96 were obtained, whereas subsequent chemical etching of the oxide yields grating structures with fin width/period ratios as small as ~0.06.

  4. Misalignment Effects in Laser-Induced Grating Experiments.

    PubMed

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

    2016-12-01

    Laser-induced grating spectroscopy (LIGS) is an experimental method in which two pulsed laser beams and a continuous-wave laser beam have to be superimposed under well-defined angles to generate a coherent signal beam. In this Note, the possible effects of different forms of misalignment are examined. This includes the overlap of the pump lasers as well as the influence of the probe laser alignment on the temporal profile of the signal.

  5. 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.

  6. Embedded fiber Bragg grating pressure measurement during thermal ignition of a high explosive

    SciTech Connect

    Rodriguez, George; Smilowitz, Laura Beth; Henson, Bryan Fayne

    2016-10-17

    A high-speed fiber Bragg grating based pressure-only measurement is reported for the high explosive PBXN-9 under thermal initiation conditions. During exothermic thermal runaway, an explosion rise time of 500 μs reaching a peak pressure of 660 MPa is measured. Lastly, the approach offers a direct measure pressure diagnostic useful for quantifying reaction violence for high explosive chemistry.

  7. Embedded fiber Bragg grating pressure measurement during thermal ignition of a high explosive

    NASA Astrophysics Data System (ADS)

    Rodriguez, G.; Smilowitz, L.; Henson, B. F.

    2016-10-01

    A high-speed fiber Bragg grating based pressure-only measurement is reported for the high explosive PBXN-9 under thermal initiation conditions. During exothermic thermal runaway, an explosion rise time of 500 μs reaching a peak pressure of 660 MPa is measured. The approach offers a direct measure pressure diagnostic useful for quantifying reaction violence for high explosive chemistry.

  8. Thermal tuning of volume Bragg gratings for spectral beam combining of high-power fiber lasers.

    PubMed

    Drachenberg, Derrek R; Andrusyak, Oleksiy; Venus, George; Smirnov, Vadim; Glebov, Leonid B

    2014-02-20

    High-radiance lasers are desired for many applications in defense and manufacturing. Spectral beam combining (SBC) by volume Bragg gratings (VBGs) is a very promising method for high-radiance lasers that need to achieve 100 kW level power. Laser-induced heating of VBGs under high-power radiation presents a challenge for maintaining Bragg resonance at various power levels without mechanical realignment. A novel thermal tuning technique and apparatus is presented that enables maintaining peak efficiency operation of the SBC system at various power levels without any mechanical adjustment. The method is demonstrated by combining two high-power ytterbium fiber lasers with high efficiency from low power to full combined power of 300 W (1.5 kW effective power), while maintaining peak combining efficiency within 0.5%.

  9. Investigation on the thermal properties of volume Bragg grating in laser diodes with external cavities

    NASA Astrophysics Data System (ADS)

    Li, Zhiyong; Tan, Rongqing; Huang, Wei; Ye, Qing; Han, Gaoce; Li, Hui; Zheng, Yijun

    2016-08-01

    Thermal control of the volume Bragg grating (VBG) in the laser diode (LD) with the external cavity is critical for the tuning of the wavelength and the narrowing of the bandwidth. Based on finite element theories, thermal properties of the VBG were researched under different conditions of the LD illuminated area, laser power, gratings' working temperature, and heat convection. Both the VBGs in the external cavity of the LD bar and stack were considered in the experiments. The results show that higher working temperature of the VBG and adopting better heat convection cooling methods are beneficial to realize the uniformity of the VBG temperature distribution.

  10. Investigation on the thermal properties of volume Bragg grating in laser diodes with external cavities

    NASA Astrophysics Data System (ADS)

    Li, Zhiyong; Tan, Rongqing; Huang, Wei; Ye, Qing; Han, Gaoce; Li, Hui; Zheng, Yijun

    2016-10-01

    Thermal control of the volume Bragg grating (VBG) in the LD with the external cavity is critical for the tuning of the wavelength and the narrowing of the bandwidth. Based on finite element theories, thermal properties of the VBG were researched under different conditions of LD illumining area, laser power, gratings' working temperature and heat convection. Both the VBGs in the external cavity of LD bar and LD stack were considered in the experiments. The results show that higher working temperature of the VBG and adopting better heating convection cooling methods is beneficial to realize the uniformity of the VBG temperature distribution.

  11. 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.

  12. 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.

  13. 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).

  14. Influence of thermal deformation of a multilayer dielectric grating on a spectrally combined beam.

    PubMed

    Yang, Lei; Wu, Zhen; Zhang, Bin

    2016-11-10

    In spectral beam combining (SBC) systems, temperature rise inevitably happens to the multilayer dielectric grating (MDG) due to irradiation of the high-power continuous-wave (CW) laser, resulting in thermal deformation of the MDG and degradation of the characteristics of the combined beam due to thermal deformation of the grating. The calculation model of thermal deformation of the MDG has been proposed, and the distributions of temperature field and thermal deformation of the grating have been analyzed. On this basis, a propagation model of a SBC system has further been built up. By utilizing the diffraction integral method and the principle of incoherent superposition, the intensity distribution and the beam quality of the combined beam with different power densities based on the MDG have been numerically calculated and analyzed in detail. The results show that both the maximum temperature rise and the thermal deformation of the MDG increase dramatically with the increasing power density of the incident laser beam. Side lobes appear in the intensity distribution of the combined beam due to thermal deformation of the MDG. Furthermore, the side lobes of the combined beam become increasingly obvious with increasing power density. Additionally, the beam quality of the combined beam degrades significantly with increasing power density of the incident laser beam.

  15. 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.

  16. Thermal and chemical treatment of polymer optical fiber Bragg grating sensors for enhanced mechanical sensitivity

    NASA Astrophysics Data System (ADS)

    Pospori, A.; Marques, C. A. F.; Sáez-Rodríguez, D.; Nielsen, K.; Bang, O.; Webb, D. J.

    2017-07-01

    An investigation of the thermal annealing effects on the strain, stress, and force sensitivities of polymer optical fiber Bragg grating sensors is performed. We demonstrate for the first time that the fiber annealing can enhance both stress and force sensitivities of Bragg grating sensors, with the possible cause being the molecular relaxation of the polymer when fiber is raised above the β -transition temperature. A simple, cost-effective, but well controlled method for fiber annealing is also presented in this work. In addition, the effects of chemical etching on the strain, stress, and force sensitivities have been investigated. Results show that fiber etching too can increase the force sensitivity, and it can also affect the strain and stress sensitivities of the Bragg grating sensors.

  17. 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

  18. Thermal characterization of Bragg gratings in polarization-maintaining optical fibres: analysis of birefringence and regeneration

    NASA Astrophysics Data System (ADS)

    Abe, I.; de Oliveira, V.; Fiorin, R.; Kalinowski, H. J.

    2017-04-01

    This paper presents an analysis of birefringence and regeneration of fibre Bragg gratings (FBGs) in two types of polarization-maintaining (PM) optical fibres, bow tie and internal elliptical cladding (IEC), with different diameters. The thermal regeneration of FBGs in PM fibres with different degrees of saturation (weakly, slightly, and strongly saturated) is presented and the influence of the gratings’ saturation degree on the birefringence of PM fibres is shown. The birefringence values obtained for IEC fibres with 80 µm of diameter were for a strongly saturated seed grating of 5.3  ×  10-4 and 6.2  ×  10-4 refractive index units after the regeneration. The evolution of the fibre birefringence as a function of the temperature is presented and the results show hysteresis and nonlinear dependence of the birefringence on temperature. The thermal stability of regenerated gratings in PM fibres is demonstrated, and a sensitivity coefficient value of 0.0035 dBm min-1 at 900 °C was obtained. The results obtained show the feasibility of optimization of fibre birefringence; this could allow such fibers to be used as temperature sensors and even improve the birefringence after the grating regeneration.

  19. Electromagnetically Induced Grating via Coherently Driven Four-Level Atoms in a N-Type Configuration

    NASA Astrophysics Data System (ADS)

    Guo, Yu; Li, Jia-Yu; Liu, Ming

    2015-03-01

    We propose a scheme to generate an electromagnetically induced grating via coherently driven four-level atoms in a N-type configuration in the presence of a standing signal field, a coupling field and a probe field. We show that a nearly ideal phase grating can be realized by adjusting the frequency detuning of signal field, the interaction length of atomic medium, and the ratio of the intensity between the signal field and the coupling field. The first-order diffraction efficiency of the grating is about 29.9 %, which is close to that of an ideal sinusoidal phase grating.

  20. 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.

  1. Comparison of a transmission grating spectrometer to a reflective grating spectrometer for standoff laser-induced breakdown spectroscopy measurements

    SciTech Connect

    Weisberg, Arel; Craparo, Joseph; De Saro, Robert; Pawluczyk, Romuald

    2010-05-01

    We evaluate a new transmission grating spectrometer for standoff laser-induced breakdown spectroscopy (LIBS) measurements. LIBS spectra collected from standoff distances are often weak, with smaller peaks blending into the background and noise. Scattered light inside the spectrometer can also contribute to poor signal-to-background and signal-to-noise ratios for smaller emission peaks. Further, collecting standoff spectra can be difficult because most spectrometers are designed for laboratory environments and not for measurements in the field. To address these issues, a custom-designed small, lightweight transmission grating spectrometer with no moving parts was built that is well suited for standoff LIBS field measurements. The performance of the spectrometer was quantified through 10 m standoff LIBS measurements collected from aluminum alloy samples and measurements from spectra of a Hg-Ar lamp. The measurements were compared to those collected using a Czerny-Turner reflective grating spectrometer that covered a similar spectral range and used the same ICCD camera. Measurements using the transmission grating spectrometer had a 363% improved signal-to-noise ratio when measured using the 669 nm aluminum emission peak.

  2. Thermal effects of the functionalities of chain transfer agent on photopolymer holographic volume gratings

    NASA Astrophysics Data System (ADS)

    Guo, Jinxin; Tomita, Yasuo; Zhang, Xinping

    2017-05-01

    The photopolymerizable nanoparticle-polymer composites (NPCs) have thus far shown their excellent performance in practical applications, such as holographic data storage, nonlinear optics and neutron optics. We have demonstrated twofold enhancement of the saturated refractive index modulation (Δnsat) of ZrO2 NPC volume gratings recorded at high spatial frequencies by doping with a single functional thiol as a chain transfer agent (CTA). This result suggested that the incorporation of a CTA in an NPC is very useful for holographic applications of volume gratings in light and neutron optics. Such chemical modification of NPC volume gratings may be more effective by doping with multifunctional thiols. This is so because polymer features such as the molecular weight and the crosslinking network density can be tailored more diversely by introducing multifunctional thiols in photopolymers. The influences of varying functionalities of thiols as chain transfer agents on the thermal stability of a volume grating recorded in a photopolymerizable ZrO2 nanoparticle-polymer composite film have been investigated.

  3. Imaging of flames and cold flows in air by diffraction from a laser-induced grating

    NASA Astrophysics Data System (ADS)

    Hemmerling, B.; Stampanoni-Panariello, A.

    1993-10-01

    Nonresonant laser-induced gratings are created in gases employing the second-harmonic output of a Nd: YAG laser in a degenerate four-wave mixing beam geometry. The diffraction efficiency of the gratings has been investigated as a function of laser intensity and gas pressure. Single-shot images of a helium flow in ambient air illustrate that diffraction of light from a laser-induced grating has the potential for remote, two-dimensional diagnostics of gas mixing processes. In addition, this coherent technique is used to image a sooty flame.

  4. Multipoint temperature measurements in gas flows using 1-D laser-induced grating scattering

    NASA Astrophysics Data System (ADS)

    Willman, Christopher; Ewart, Paul

    2016-12-01

    A technique is reported for simultaneous, time- and space-resolved measurements of temperature using laser-induced thermal grating scattering, LITGS, from four points on a 1-D line. Signals from four separate points on the line, separated by 1 mm, in toluene-seeded nitrogen flows, were imaged onto a fibre-optic array and delivered to separate photodiode detectors to record their temporal evolution from which the temperatures at each point were derived with a spatial resolution of 1 mm and a precision of 0.7% at atmospheric pressure. Effects of variation of composition on the accuracy of the measurements were compensated by a calibration method providing good agreement with values inferred from thermocouple measurements. Temperature gradients at the boundary between parallel gas flows and at the surface of hot and cold surfaces were measured with a resolution of 5 K mm-1. Extension of the technique to more measurement points and improvements in spatial resolution are briefly discussed.

  5. Spatial splitting of femtosecond laser pulse induced by infrared plasma grating

    NASA Astrophysics Data System (ADS)

    Liu, Zuoye; Hu, Bitao

    2014-04-01

    Spatial splitting of a probe femtosecond filament induced by plasma grating is observed in air. The refractive index is redistributed by the leading part of the probe pulse, inducing the defocusing of the trailing part with slight modification of its propagation direction. After undergoing a few cycles of total reflection between two plasma walls, the trailing part is refocused at the trailing part of the plasma grating and escapes.

  6. Observations from direct UV-written, non-hydrogen-loaded, thermally regenerated Bragg gratings in double-clad photosensitive fiber.

    PubMed

    Jantzen, Alexander; Bannerman, Rex H S; Berry, Sam A; Gates, James C; Gow, Paul C; Boyd, Lewis J; Smith, Peter G R; Holmes, Christopher

    2017-10-01

    In this Letter, experimental evidence is provided for an enhanced thermal sensitivity for a double thermal regeneration feature in fiber Bragg gratings fabricated by direct ultraviolet (UV) writing. Here 47 gratings of varying fluence and wavelength were written along a double-clad, germanium-doped core fiber. Subsequently thermal processing without hydrogen loading the fiber was performed and thermal treatment was carried out in a pure oxygen environment. Thermal sensitivity for the double regeneration increased from 13.6±0.3  pm/°C to 21.3±0.2  pm/°C. Furthermore, one of the highest nominal fluence gratings, #45, exhibited a regeneration factor of 1.73.

  7. An Intensity-Based Demodulation Approach for the Measurement of Strains Induced by Structural Vibrations using Bragg Gratings

    DTIC Science & Technology

    2011-02-01

    gratings for response measurement. DSTO’s involvement in this program is to develop the distributed Bragg grating in- terrogation system and conduct... Calibration 29 E System Operation Documentation 30 E.1 Configuration Screen . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 30 E.2 Scan Screen...challenges associated with this type of distributed response measurement using Bragg gratings is that the strains induced by structural vibrations tend

  8. Laser Induced Thermal Keratoplasty

    NASA Astrophysics Data System (ADS)

    Householder, John; Horwitz, Larry S.; Lowe, Kenneth W.; Murrillo, Adolfo

    1989-09-01

    A technique of corneal surgery that is thermally induced and relatively nonenvasive has been studied by the authors, and the preliminary results of the thermal keratoplasty performed on live rabbits are reported here. A carbon dioxide laser was used with simple optical and pointing systems to thermally induce several arbitrary patterns of corneal reformation. Endothelial photographs were taken before the procedure and then again ten days after. They indicated no damage in the Descemet's membrane nor was there damage observed to the endothelium. As much, as 14 "diopters" of change occurred in the corneal keratometry with both positive and negative directions signs. The magnitude and direction of the change were recorded as functions of the pattern of the therapy produced and the laser energy deposited in the stroma. Any corneal reformation was tracked as a function of time subsequent to the procedure. A-minor decay was observed within the first three days of the procedure and the majority of the reformations have maintained at the time of this writing. Since radiation at this wavelength is highly attenuated and absorbed in cornea, no change was observed beyond mid-stroma and the lens and retina appeared uneffective. The authors believe that this technology will be a significant contributor to corneal refractive procedures in the near future. Unlike any refractive surgery currently practiced, this technology may lead to a procedure that: 1) is reversible, 2) is re.eatable, 3) stren thens rather then weakens the cornea, 4) is a..arentl more stable, 5) is more flexible in the types of corneal curvature changes it can produce, 6) results in very clean mires, 7) is painless, and 8) results in total corneal clarity.

  9. 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.

  10. Temperature-induced spectrum response of a volume grating as an effective strategy for holographic sensing in an acrylamide polymer part II: physical mechanism.

    PubMed

    Liu, Hongpeng; Yu, Dan; Zhou, Ke; Mao, Dongyao; Liu, Langbo; Wang, Hui; Wang, Weibo; Song, Qinggong

    2016-12-10

    The temperature response mechanism of a diffraction spectrum in a holographic grating is characterized. Two possible major factors, changes in the refractive index and thermal expansion, are measured and analyzed to identify the sensing physical mechanism. Average refractive indices at various temperatures and relative humidity values are independently measured. Thermal optical coefficients of polymers are estimated quantitatively to evaluate the temperature response capability of the refractive index. Angle selectivity of multiplexing gratings is scanned at various temperatures to obtain magnitudes of Bragg angle detuning. The linear thermal expansion coefficients are extracted by the nonlinear fitting reading angle dependence of angle detuning. The significance of the thermal optical coefficient and the thermal expansion coefficient for holographic sensing is discussed. Finally, the primary factor for temperature-induced wavelength blueshift is analyzed theoretically.

  11. Grating-coupled surface plasmon resonance enhanced organic photovoltaic devices induced by Blu-ray disc recordable and Blu-ray disc grating structures.

    PubMed

    Nootchanat, Supeera; Pangdam, Apichat; Ishikawa, Ryousuke; Wongravee, Kanet; Shinbo, Kazunari; Kato, Keizo; Kaneko, Futao; Ekgasit, Sanong; Baba, Akira

    2017-04-13

    In this work, we studied the performance enhancement of organic thin-film solar cells (OSCs) originating from the presence of diffraction gratings on the surface of the active layer. Two types of diffraction gratings, periodic gratings (Blu-ray disc recordable: BD-R) and quasi-random gratings (Blu-ray disc: BD), were employed as master templates for grating structures. The grating structures were introduced to the surfaces of poly(3-hexylthiophene) (P3HT):phenyl-C61-butyric acid methyl ester (PCBM) films, which were the active layers of the solar cells. The addition of the grating structures led to an increase of light absorption in the absorption region of P3HT:PCBM induced by light scattering. Furthermore, the grating-coupled surface plasmon resonance generated additional light absorption peaks. With illumination of non-polarized light at a normal incident angle, the short-circuit current densities of the BD-R and BD solar cells improved by 11.05% and 10.6%, respectively. Efficiency improvements of 19.28% and 3.21% were also observed for the BD-R and BD devices, respectively. Finally, the finite-difference time-domain simulation results revealed an enhanced electric field in the P3HT:PCBM layer, especially in the BD-R OSC devices.

  12. Non-diffusive relaxation of a transient thermal grating analyzed with the Boltzmann transport equation

    NASA Astrophysics Data System (ADS)

    Collins, Kimberlee C.; Maznev, Alexei A.; Tian, Zhiting; Esfarjani, Keivan; Nelson, Keith A.; Chen, Gang

    2013-09-01

    The relaxation of an one-dimensional transient thermal grating (TTG) in a medium with phonon-mediated thermal transport is analyzed within the framework of the Boltzmann transport equation (BTE), with the goal of extracting phonon mean free path (MFP) information from TTG measurements of non-diffusive phonon transport. Both gray-medium (constant MFP) and spectrally dependent MFP models are considered. In the gray-medium approximation, an analytical solution is derived. For large TTG periods compared to the MFP, the model yields an exponential decay of grating amplitude with time in agreement with Fourier's heat diffusion equation, and at shorter periods, phonon transport transitions to the ballistic regime, with the decay becoming strongly non-exponential. Spectral solutions are obtained for Si and PbSe at 300 K using phonon dispersion and lifetime data from density functional theory calculations. The spectral decay behaviors are compared to several approximate models: a single MFP solution, a frequency-integrated gray-medium model, and a "two-fluid" BTE solution. We investigate the utility of using the approximate models for the reconstruction of phonon MFP distributions from non-diffusive TTG measurements.

  13. Electromagnetically induced 2D grating via refractive index enhancement in a far-off resonant system

    NASA Astrophysics Data System (ADS)

    Chen, Yu-Yuan; Liu, Zhuan-Zhuan; Wan, Ren-Gang

    2017-07-01

    We propose a scheme for electromagnetically induced 2D grating in a mixture of two three-level Λ systems driven by two pairs of far-detuned coherent standing-wave fields. The key idea, which has been used to achieve the refractive index enhancement with vanishing absorption, is to induce two Raman resonances for the probe field, and their strength can be tuned via the two-photon detunings and the intensity of coupling field. By manipulating the absorption and gain properties of these two Raman resonances, absorption-phase grating, phase grating and gain-phase grating which effectively diffract a probe field into high-order directions can be formed in the atoms with the help of standing-wave pattern coherent fields. The diffracting power of the presented gratings strongly depends on the two-photon resonance condition and amplitude of coherent fields, hence the gratings can be used as all-optical multi-channel splitters or all-optical router in optical networking and communication.

  14. 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.

  15. High frequency resonant waveguide grating imager for assessing drug-induced cardiotoxicity

    NASA Astrophysics Data System (ADS)

    Ferrie, Ann M.; Wu, Qi; Deichmann, Oberon D.; Fang, Ye

    2014-05-01

    We report a high-frequency resonant waveguide grating imager for assessing compound-induced cardiotoxicity. The imager sweeps the wavelength range from 823 nm to 838 nm every 3 s to identify and monitor compound-induced shifts in resonance wavelength and then switch to the intensity-imaging mode to detect the beating rhythm and proarrhythmic effects of compounds on induced pluripotent stem cell-derived cardiomyocytes. This opens possibility to study cardiovascular biology and compound-induced cardiotoxicity.

  16. 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.

  17. 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.

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

    SciTech Connect

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

    2016-02-28

    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. (laser crystals and braggg ratings)

  19. Thermo-driven light controller by using thermal modulation of diffraction wavelength in holographic polymer dispersed liquid crystal grating

    NASA Astrophysics Data System (ADS)

    Ogiwara, Akifumi; Kakiuchida, Hiroshi

    2014-02-01

    A microperiodic structure composed of polymer and liquid crystal (LC) phases, called holographic polymer dispersed liquid crystal (HPDLC), was fabricated based on a photo-induced phase separation technique by laser interferometric exposure. The diffraction wavelength of HPDLC gratings formed by different LC composites and grating structures was experimentally investigated by spectroscopic measurements as a function of temperature at around 30 °C. The HPDLC gratings composed of nematic LC having low nematic to isotropic temperature (TNI) and film thickness of 25 μm showed the switch of diffraction wavelength between visible and infrared lights by the change of temperature. The optical characteristics achieved in HPDLC gratings are expected to be applicable for the basis of diffractive type of thermodriven light controller which can supply visibility constantly for solar-ray control windows.

  20. Investigation of dual electromagnetically induced grating based on spatial modulation in quantum well nanostructures via biexciton coherence

    NASA Astrophysics Data System (ADS)

    Naseri, Tayebeh

    2017-04-01

    A new scheme for obtaining an electromagnetically induced grating (EIG) via biexciton coherence in quantum well nanostructures is developed. It is theoretically shown that exciton spin relaxation and biexciton binding energy have important roles in producing efficient dual electromagnetically induced phase grating. In this structure, due to biexciton coherence, the higher order diffraction intensities of the grating can be observed. Furthermore, it is shown that the efficiency of different orders in the grating patterns could be controlled by biexciton energy renormalization (ESR) and relative phase between the applied laser fields.

  1. Optical Sensor of Thermal Gas Flow Based on Fiber Bragg Grating

    PubMed Central

    Jiang, Xu; Wang, Keda; Li, Junqing; Zhan, Hui; Song, Zhenan; Che, Guohang; Lyu, Guohui

    2017-01-01

    This paper aims at solving the problem of explosion proof in measurement of thermal gas flow using electronic sensor by presenting a new type of flow sensor by optical fiber heating. A measuring unit based on fiber Bragg grating (FBG) for fluid temperature and a unit for heat dissipation are designed to replace the traditional electronic sensors. The light in C band from the amplified spontaneous emission (ASE) light source is split, with one part used to heat the absorbing coating and the other part used in the signal processing unit. In the heating unit, an absorbing coating is introduced to replace the traditional resistance heating module to minimize the risk of explosion. The measurement results demonstrate a fine consistency between the flow and temperature difference in simulation. The method to enhance the measurement resolution of flow is also discussed. PMID:28212268

  2. 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.

  3. Interface Selective Transient Grating Spectroscopy: Theory and Applications to Thermal Flow and Acoustic Propagation in Thin Films.

    NASA Astrophysics Data System (ADS)

    Marshall, Christopher David

    A general theoretical and experimental treatment of transient grating diffraction is developed for interfacial holographic gratings in thin film structures. The gratings are assumed to have nonuniform spatial amplitude throughout the sample. Both reflection and transmission diffraction geometries are examined where the probe beam is incident on either side of the film-substrate interface with the grating wave-vector parallel to the interface. For samples in which the grating amplitude perpendicular to the sample interface varies slowly relative to the optical wavelength, the majority of the reflection geometry signal amplified is shown to arise from the surface or interfacial region. In contrast, the transmission geometry signal amplitude is dominated by contributions from the bulk of the sample. Three different material systems are examined. The first is a thin (<1 mm) molecular anthracene crystal on a glass substrate in which electronic (exciton) and wave-guided acoustic gratings are generated and probed. Four different transient grating geometries are shown to yield unique time dependent responses illustrating the sensitivity of the transient grating geometry to the spatial origin of the signal. A theoretical model is developed to demonstrate the spatial selectivity of the technique. The second and third systems are thin (50-350 nm thick) films of the high temperature superconductor YBa_2Cu _3O_{rm 7-x} (YBCO) on either MgO or SrTiO _3 substrates. Anisotropic thermal diffusion constants in the YBCO films are measured over a 17 to 300 K temperature range. A detailed understanding is obtained of the time dependent heat flow in the regions adjacent to the film-substrate interface, the free film surface, and the bulk of the film. A temperature dependent thermal barrier that significantly restricts heat transfer from the film into the MgO substrate is observed and quantified. The rate of flow thru the YBCO/MgO interface is measured to be 10 to 100 times less than the

  4. Realization of electromagnetically induced phase grating and Kerr nonlinearity in a graphene ensemble under Raman excitation

    NASA Astrophysics Data System (ADS)

    Naseri, Tayebeh; Moradi, Ronak

    2017-01-01

    Some optical properties including the linear and nonlinear susceptibility and electromagnetically induced phase grating (EIG) in graphene under Raman excitation is studied. A single-layer graphene nanostructure driven by coherent and incoherent fields is investigated theoretically. It is revealed that by adjusting the amplitude of control and incoherent fields, the linear and nonlinear absorption as well as Kerr nonlinearity of the medium can be optimized. It is realized that the enhanced Kerr nonlinearity can occur with zero linear absorption and nonlinear amplification. Furthermore, it should be noted that EIG in graphene is studied for the first time. The results indicate that the diffraction efficiency of the phase grating is dramatically enhanced by controlling the amplitude of coherent and incoherent fields, and an efficient electromagnetically induced phase grating can be obtained. A novel result shows a considerable improvement of the intensity of higher-order diffractions and switching between different orders of grating via incoherent pumping field. Therefore, this model can be used in real experiments for the development of new types of nanoelectronic devices used for the realization of all-optical switching processes.

  5. Laser-induced effects in carbon suspensions and diffraction by volume gratings in liquids

    NASA Astrophysics Data System (ADS)

    Chen, Huxiong

    1997-12-01

    Two projects are covered in this thesis. The first project is an investigation of acoustic and chemical effects generated by high power laser pulses in carbon suspensions. Carbon particles absorb energy from the laser pulses and are heated to a few thousand degrees C. The high temperatures initiate reactions between carbon and the surrounding water generating permanent gases. Hydrogen, carbon monoxide, carbon dioxide, and several hydrocarbons have been identified as product gases. With respect to sound wave generation the change in volume of the material owing to thermal and chemical expansion is discussed. A thermodynamic theory governing the generation of the photoacoustic waves from these two mechanism is developed. A comparison between photoacoustic effects caused mainly by the chemical mechanism and those generated by the thermal mechanism is given. The chemical mechanism gives an acoustic signal 2,000 times greater in magnitude than would be generated by purely thermal mechanism (normalized to absorption coefficient). Structural changes of the carbon particle are reported. The originally solid particles first become large hollow particles and then disappear according to electron microscopy. The second project deals with diffraction by volume gratings. A rigorous theory governing non-attentuated planar volume gratings developed by Gaylord and Moharam is utilized. A generalized theory incorporating attentuation along the depth for planar volume gratings with TE incident probe beams is developed. Experiments have been carried out to investigate the diffraction of volume gratings generated by two coherent nanosecond laser pulses in methanol. The magnitude of the change in index of refraction is extracted. Criteria for delineation of different diffraction regimes are discussed. Approximate solutions to the first order coupled-wave equations are given substantiating the criteria.

  6. 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.

  7. Squeezing induced high-efficiency diffraction grating in two-level system.

    PubMed

    Cheng, Guang-Ling; Chen, Ai-Xi

    2017-02-20

    We show the effect of squeezed vacuum on laser-induced grating in a weak standing-wave-driving two-level atomic system. Using the optical Bloch equation and the Floquet harmonic expansion, we obtain the linear response of the medium with respect to the probe field, which determines the transmission spectrum and diffraction intensity. At the presence of the squeezing, the grating with large intensity both in the first- and higher-order directions can be obtainable even though the driving is relatively weak. The responsible mechanism is due to squeezing-induced gain accompanied by the large dispersion. Based on the spatial gain and phase modulations, the first- and high-order diffraction intensities simultaneously could have the large values. Such a scheme we present could have potential applications in implementing lensless imaging and developing the photon devices in quantum information processing.

  8. Post-treatment techniques for enhancing mode-coupling in long period fiber gratings induced by CO2 laser

    NASA Astrophysics Data System (ADS)

    Xu, Xizhen; Tang, Jian; Zhao, Jing; Yang, Kaiming; Fu, Cailing; Wang, Qiao; Liu, Shen; Liao, Changrui; Lian, Jiarong; Wang, Yiping

    2015-12-01

    Two promising post-treatment techniques, i.e. applying tensile strain and rising temperature, are demonstrated to enhance the mode-coupling efficiency of the CO2-laser-induced long period fiber gratings (LPFGs) with periodic grooves. Such two post-treatment techniques can be used to enhance the resonant attenuation of the grating to achieve a LPFG-based filter with an extremely large attenuation and to tailor the transmission spectrum of the CO2-laser-induced LPFG after grating fabrication.

  9. A tunable wavelength erbium doped fiber ring laser based on mechanically induced long-period fiber gratings

    NASA Astrophysics Data System (ADS)

    Pérez Maciel, M.; López Dieguez, Y.; Montenegro Orenday, J. A.; Jáuregui Vázquez, D.; Sierra Hernández, J. M.; Huerta Masscote, E. H.; Rojas Laguna, R.; Estudillo Ayala, J. M.

    2015-08-01

    A tunable wavelength erbium doped fiber ring laser, based on mechanically induced long-period fiber gratings (MLPFG) is presented. The laser was tuned applying pressure over the MLPFG, in order to control this, pressure is applied over a plate with periodic grooves that has a short length, this pressure is applied by a digital torque tester, as a result tunable effect is observed. The grooves have a period of 630μm and the maximal pressure without breakpoint fiber is around 0.80lb-in2. Furthermore, the MLPFG used can be erased, reconfigured and exhibit a transmission spectra with thermal stability, similar to high cost photoinduced long period gratings. In this work, by pressure increment distributed over the MLPFG from 0.20 lb-in2 to 0.50 lb-inμ, tuned operation range of 10nm was observed and single line emission was tuned between C and L telecommunications bands. According to the stability analysis the signal to noise ratio and linewidth observed were 35dB and 0.2nm respectively.

  10. Elastic and thermal properties of free-standing molybdenum disulfide membranes measured using ultrafast transient grating spectroscopy

    NASA Astrophysics Data System (ADS)

    Kim, Taeyong; Ding, Ding; Yim, Jong-Hyuk; Jho, Young-Dahl; Minnich, Austin J.

    2017-08-01

    Molybdenum disulfide (MoS2), a member of transition-metal dichalcogenide family, is of intense interest due to its unique electronic and thermoelectric properties. However, reports of its in-plane thermal conductivity vary due to the difficulty of in-plane thermal conductivity measurements on thin films, and an experimental measurement of the in-plane sound velocity has not been reported. Here, we use time-resolved transient grating spectroscopy to simultaneously measure the in-plane elastic and thermal properties of free-standing MoS2 membranes at room temperature. We obtain a longitudinal acoustic phonon velocity of 7000 ± 40 m s-1 and an in-plane thermal conductivity of 74 ± 21 W m-1K-1. Our measurements provide useful insights into the elastic and thermal properties of MoS2 and demonstrate the capability of transient grating spectroscopy to investigate the in-plane vibrational properties of van der Waals materials that are challenging to characterize with conventional methods.

  11. Coupled wave analysis of holographically induced transparency (HIT) generated by two multiplexed volume gratings.

    PubMed

    Carretero, Luis; Blaya, Salvador; Acebal, Pablo; Fimia, Antonio; Madrigal, Roque; Murciano, Angel

    2011-04-11

    We present a holographic system that can be used to manipulate the group velocity of light pulses. The proposed structure is based on the multiplexing of two sequential holographic volume gratings, one in transmission and the other in reflection geometry, where one of the recording beams must be the same for both structures. As in other systems such as grating induced transparency (GIT) or coupled-resonator-induced transparency (CRIT), by using the coupled wave theory it is shown that this holographic structure represents a classical analogue of the electromagnetically induced transparency (EIT). Analytical expressions were obtained for the transmittance induced at the forbidden band (spectral hole) and conditions where the group velocity was slowed down were analyzed. Moreover, the propagation of Gaussian pulses is analyzed for this system by obtaining, after further approximations, analytical expressions for the distortion of the transmitted field. As a result, we demonstrate the conditions where the transmitted pulse is slowed down and its shape is only slightly distorted. Finally, by comparing with the exact solutions obtained, the range of validity of all the analytical formulae was verified, demonstrating that the error is very low.

  12. 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.

  13. Generation of femtosecond optical vortex pulse in fiber based on an acoustically induced fiber grating.

    PubMed

    Zhang, Wending; Wei, Keyan; Mao, Dong; Wang, Heng; Gao, Feng; Huang, Ligang; Mei, Ting; Zhao, Jianlin

    2017-02-01

    We proposed a method for generation of a femtosecond optical vortex pulse in a two-mode fiber based on an acoustically induced fiber grating (AIFG) driven by a radio frequency source. Theoretical analysis and experimental results demonstrated that the left- and right-handed circular polarization fundamental modes of the femtosecond optical pulse could be converted to the linearly polarized ±1-order optical vortex modes through the AIFG with the mode conversion efficiency of ∼95%. The off-axial interference experiment and the polarization angle-dependent intensity examination were performed to verify the topological charge and the polarization state of the femtosecond optical vortex, respectively.

  14. Acoustic-induced switching of the reflection wavelength in a fiber Bragg grating.

    PubMed

    Liu, W F; Liu, I M; Chung, L W; Huang, D W; Yang, C C

    2000-09-15

    Coupling between copropagating core and cladding modes was implemented by acoustic generation of lateral vibration of an etched fiber. When these coupling processes were combined with counterpropagating coupling of a core mode and a cladding mode and the Bragg reflection of a fiber grating, switching of reflection wavelength between the Bragg wavelength and cladding-mode coupling wavelengths was achieved. We report the implementation of such acoustically induced switching behaviors and explain their operation principles. The implemented results can be used for wavelength-division multiplexed add-drop filtering.

  15. Magnetic induction-induced resistive heating of optical fibers and gratings.

    PubMed

    Canning, John; Naqshbandi, Masood; Cook, Kevin; Huyang, George

    2013-03-15

    Magnetic induction heating of optical fibers packaged with a steel plate is studied using a fiber Bragg grating. The dependence on the induced wavelength shift with magnetic field is obtained for a commercially available induction heater. More than a 300°C temperature rise is observed within seconds. The potential of magnetic induction as an efficient and rapid means of modulating devices and as a novel approach to potential optical based magnetic field and current sensing is proposed and discussed. The extension of the ideas into micro and nanophotonics is described.

  16. Fast Bragg Grating Inscription in PMMA Polymer Optical Fibres: Impact of Thermal Pre-Treatment of Preforms.

    PubMed

    Marques, Carlos A F; Pospori, Andreas; Demirci, Gökhan; Çetinkaya, Onur; Gawdzik, Barbara; Antunes, Paulo; Bang, Ole; Mergo, Pawel; André, Paulo; Webb, David J

    2017-04-18

    In this work, fibre Bragg gratings (FBGs) were inscribed in two different undoped poly- (methyl methacrylate) (PMMA) polymer optical fibres (POFs) using different types of UV lasers and their inscription times, temperature and strain sensitivities are investigated. The POF Bragg gratings (POFBGs) were inscribed using two UV lasers: a continuous UV HeCd @325 nm laser and a pulsed UV KrF @248 nm laser. Two PMMA POFs are used in which the primary and secondary preforms (during the two-step drawing process) have a different thermal treatment. The PMMA POFs drawn in which the primary or secondary preform is not specifically pre-treated need longer inscription time than the fibres drawn where both preforms have been pre-annealed at 80 °C for 2 weeks. Using both UV lasers, for the latter fibre much less inscription time is needed compared to another homemade POF. The properties of a POF fabricated with both preforms thermally well annealed are different from those in which just one preform step process is thermally treated, with the first POFs being much less sensitive to thermal treatment. The influence of annealing on the strain and temperature sensitivities of the fibres prior to FBG inscription is also discussed, where it is observed that the fibre produced from a two-step drawing process with well-defined pre-annealing of both preforms did not produce any significant difference in sensitivity. The results indicate the impact of preform thermal pre-treatment before the PMMA POFs drawing, which can be an essential characteristic in the view of developing POF sensors technology.

  17. Influence of surrounding media refractive index on the thermal and strain sensitivities of long-period gratings

    NASA Astrophysics Data System (ADS)

    Canute Kamikawachi, Ricardo; Rafael Collere Possetti, Gustavo; Falate, Rosane; Muller, Marcia; Luís Fabris, José

    2007-05-01

    A detailed study of the thermal and strain sensitivities of a long-period grating when the device is immersed in different external media is presented. The range of refractive indices analyzed are within 1.000 to 1.447, corresponding to samples of air, water, ethanol, naphtha, thinner, turpentine, and kerosene. Within the same range of refractive indices, the strain sensitivity is between (-0.24 ± 0.03) and (-0.94 ± 0.11) pm/μɛ. For the grating immersed in these fluids, the refractive index sensitivity ranges from -3 to -1035.6 nm per refractive index units. The coupling thermo-optic coefficients and the strain-optic coefficients are also measured, resulting in the range from (2.45 ± 0.04)×10-5 to (15.89 ± 0.82)×10-5 deg C-1 and (-1.15 ± 0.04) to (-1.61 ± 0.04) μɛ-1, respectively. A noticeable nonlinear behavior of the thermal sensitivity is found for external media with refractive indices higher than 1.430.

  18. 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.

  19. 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.

  20. 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.

  1. Isolation of Thermal and Strain Responses in Composites Using Embedded Fiber Bragg Grating Temperature Sensors

    DTIC Science & Technology

    2013-05-10

    epoxy resin to the optical fibers; the curing process described below ensured that they bonded well to the carbon fiber fabric. The middle layer...13. SUPPLEMENTARY NOTES 14. ABSTRACT In this research, fiber Bragg grating (FBG) optical temperature sensors are used for structural health...surface of a composite structure. FBG sensors also respond to axial strain in the optical fiber, thus any structural strain experienced by the composite

  2. Competition between atomic coherence and electromagnetically induced population grating in multi-wave mixing

    NASA Astrophysics Data System (ADS)

    Lou, Lin; Sun, Jia; Feng, Weikang; Wu, Zhenkun; Zhang, Yiqi; Zhang, Yanpeng

    2014-12-01

    We study the competition and transfer between atomic coherence and electromagnetically induced population grating of multi-wave mixing (MWM) in four- and five-level atomic systems. The MWM signal falls into a new type electromagnetically induced transparency (EIT) window that depends on propagating directions of the related fields rather than atomic system configuration. By blocking different coupling laser beams, we experimentally distinguish different wave mixing processes. In addition, by changing the detuning of pump beams, we can observe double peaks for both EIT and MWM signals. The results may have potential applications in correlated photon-pair generations in four-wave mixing as well as six-wave mixing and quantum information processing.

  3. 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.

  4. 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.

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

    PubMed

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

    2016-01-27

    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 (K D ) 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.

  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. Nano-indentation and laser-induced damage testing in optical multilayer-dielectric gratings [Nanomechanics and laser-induced damage in optical multilayer dielectric gratings

    DOE PAGES

    Mehrotra, K.; Corning Research & Development Corp., Coming, NY; Taylor, B. N.; ...

    2017-03-16

    Here, we demonstrate how a nanomechanical test can be used to generate metrics to complement laser-induced–damage testing (LIDT) measurements and show that differences in optical performance of the gratings (arising from changes in cleaning process and/or fabrication methods) can be related to their mechanical reliability. Data are presented on LIDT measurements in diffractive gratings of silica deposited on optical multilayers. The nano-indentation response of the diffraction gratings is measured in a new mode that allows for the extraction of a measurable metric characterizing the brittleness of the gratings, as well as their ductility. We show that lower LIDT’s are positivelymore » correlated with an increased grating brittleness, and therefore identify a nanomechanical approach to describe LIDT’s. We present extensive numerical simulations of nano-indentation tests and identify different deformation modes including stretching, shear concentration, and bending as precursors to mechanical failure in the nano-indentation test. The effects of geometrical inhomogeneities on enhanced stress generation in these gratings are specifically examined and addressed.« less

  8. Laser induced optically and thermally reversible birefringence in azopolymers

    NASA Astrophysics Data System (ADS)

    Nazarova, D.; Nedelchev, L.; Ivanov, D.; Blagoeva, B.; Berberova, N.; Stoykova, E.; Mateev, G.; Kostadinova, D.

    2016-01-01

    Azopolymers are well known organic materials for polarization holographic recording due to the induced anisotropy under illumination with polarized light. They possess all the desirable characteristics of the known polarization-sensitive materials, as high sensitivity and reversibility, but excel them substantially in the magnitude of the photoinduced birefringence. This makes possible to record reversible polarization gratings with high diffraction efficiency. In this paper results of experimental investigations on the reversibility properties of birefringence photoinduced in azopolymers are reported, depending on the conditions of subsequent optical and thermal treatment. Thin films of different polymers were prepared in order to examine the kinetics of multiple recording and erasure of birefringence in different types of azopolymers. The reversibility of the polarization recording has been studied using two different method of erasure - by increased temperature and on illumination with circularly polarized light.

  9. Real-time temperature monitoring with fiber Bragg grating sensor during diffuser-assisted laser-induced interstitial thermotherapy

    NASA Astrophysics Data System (ADS)

    Pham, Ngot Thi; Lee, Seul Lee; Park, Suhyun; Lee, Yong Wook; Kang, Hyun Wook

    2017-04-01

    High-sensitivity temperature sensors have been used to validate real-time thermal responses in tissue during photothermal treatment. The objective of the current study was to evaluate the feasible application of a fiber Bragg grating (FBG) sensor for diffuser-assisted laser-induced interstitial thermotherapy (LITT) particularly to treat tubular tissue disease. A 600-μm core-diameter diffuser was employed to deliver 980-nm laser light for coagulation treatment. Both a thermocouple and a FBG were comparatively tested to evaluate temperature measurements in ex vivo liver tissue. The degree of tissue denaturation was estimated as a function of irradiation times and quantitatively compared with light distribution as well as temperature development. At the closer distance to a heat source, the thermocouple measured up to 41% higher maximum temperature than the FBG sensor did after 120-s irradiation (i.e., 98.7°C±6.1°C for FBG versus 131.0°C±5.1°C for thermocouple; p<0.001). Ex vivo porcine urethra tests confirmed the real-time temperature measurements of the FBG sensor as well as consistently circumferential tissue denaturation after 72-s irradiation (coagulation thickness=2.2±0.3 mm). The implementation of FBG can be a feasible sensing technique to instantaneously monitor the temperature developments during diffuser-assisted LITT for treatment of tubular tissue structure.

  10. Graphene based silicon-air grating structure to realize electromagnetically-induced-transparency and slow light effect

    NASA Astrophysics Data System (ADS)

    Wei, Buzheng; Liu, Huaiqing; Ren, Guobin; Yang, Yuguang; Ye, Shen; Pei, Li; Jian, Shuisheng

    2017-01-01

    A broad band tunable graphene based silicon-air grating structure is proposed. Electromagnetically-induced-transparency (EIT) window can be successfully tuned by virtually setting the desired Fermi energy levels on graphene sheets. Carrier mobility plays an important role in modulating the resonant depth. Furthermore, by changing the grating periods, light can be trapped at corresponding resonant positions where slow down factor is relatively larger than in the previous works. This structure can be used as a highly tunable optoelectronic device such as optical filter, broad-band modulator, plasmonic switches and buffers.

  11. Investigation of the writing mechanism of electric-arc-induced long-period fiber gratings.

    PubMed

    Malki, Abdelrafik; Humbert, Georges; Ouerdane, Youcef; Boukhenter, Aziz; Boudrioua, Azzedine

    2003-07-01

    The mechanism for inscription of electric-arc-induced long-period gratings in SMF28 fiber was studied. The refractive-index profiles of irradiated fiber samples were measured, and their structures were investigated by Raman and luminescence spectroscopy. Slight geometrical deformations of the irradiated fiber were measured. A significant change in the Raman spectrum range from 200 to 700 cm(-1) caused by the electric arc is reported. The results show a decrease in the intensity of this band, indicating a modification, such as densification, of the glass structure. No modification of the fictive temperature was measured. A large increase in the red luminescence band was also observed and attests to the creation of defects in the fiber network structure.

  12. 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.

  13. 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)].

  14. Anomalous optical diffraction by a phase grating induced by a local field effect in semiconductor quantum dots

    NASA Astrophysics Data System (ADS)

    Mitsumori, Yasuyoshi; Watanuki, Tetsuya; Sato, Yuki; Edamatsu, Keiichi; Akahane, Kouichi; Yamamoto, Naokatsu

    2017-04-01

    We demonstrate the use of laser-induced phase gratings to control the emission characteristics of self-assembled semiconductor quantum dots. The microscopic Coulomb interaction between the photoinduced charge densities in a dot, referred to as the local field effect, affects the macroscopic optical properties of a dot ensemble even with inhomogeneous broadening, and forms a phase grating by spatially modulating the exciton resonant frequency. In the low excitation regime, the diffracted light intensity (observed using photon echoes) gradually rose with time delay—a result very different from the conventional instantaneous response to pulse excitation. With increasing excitation intensity, the response of the diffracted signal became more immediate and exhibited a biexponential decay. The change in the temporal profile can be systematically explained by analyzing the dynamics of the phase grating. Our findings suggest an optical switching mechanism using this intrinsic property of semiconductor quantum dots.

  15. Tunable diffraction grating using ultraviolet-light-induced spatial phase modulation in dual-frequency liquid crystal

    SciTech Connect

    Lin, P.-T.; Liang Xiao; Ren Hongwen; Wu, S.-T.

    2004-08-16

    An electrically tunable diffraction phase grating using ultraviolet (UV)-light-induced spatial dielectric modulation of a dual-frequency liquid crystal (DFLC) cell is demonstrated. A photomask with transparent and opaque stripes was used for fabricating the grating. In the UV-exposed stripes, the negative dielectric anisotropy ({delta}{epsilon}) tolane compound of the DFLC mixture is partially polymerized resulting in a decreased threshold voltage as compared to that of the unexposed region. Upon applying a constant voltage, the phase difference between the adjacent pixels is produced. The first-order diffraction efficiency reaches {approx}60% which agrees well with the simulation results. Due to the dual-frequency addressing at 30 V{sub rms}, the response time of the DFLC phase grating was measured to be {approx}1 ms at room temperature.

  16. Temperature profile of ex-vivo organs during radio frequency thermal ablation by fiber Bragg gratings

    NASA Astrophysics Data System (ADS)

    Palumbo, Giovanna; Iadicicco, Agostino; Tosi, Daniele; Verze, Paolo; Carlomagno, Nicola; Tammaro, Vincenzo; Ippolito, Juliet; Campopiano, Stefania

    2016-11-01

    We report on the integration of fiber optic sensors with commercial medical instrumentation for temperature monitoring during radio frequency ablation for tumor treatment. A suitable configuration with five fiber Bragg grating sensors bonded to a bipolar radio frequency (RF) probe has been developed to monitor the area under treatment. A series of experiments were conducted on ex-vivo animal kidney and liver and the results confirm that we were able to make a multipoint measurement and to develop a real-time temperature profile of the area, with a temperature resolution of 0.1°C and a spatial resolution of 5 mm during a series of different and consecutive RF discharges.

  17. Fully distributed fiber-optic sensing based on acoustically induced long-period grating

    NASA Astrophysics Data System (ADS)

    Wang, Dorothy Y.; Wang, Yunmiao; Han, Ming; Gong, Jianmin; Wang, Anbo

    2011-05-01

    This paper gives a review of a proposed fully-distributed fiber-optic sensing technique based on a traveling long-period grating (LPG) in a single-mode optical fiber. The LPG is generated by pulsed acoustic waves that propagate along the fiber. Based on this platform, first we demonstrated the fully-distributed temperature measurement in a 2.5m fiber. Then by coating the fiber with functional coatings, we demonstrated fully-distributed biological and chemical sensing. In the biological sensing experiment, immunoglobulin G (IgG) was immobilized onto the fiber surface, and we showed that only specific antigen-antibody binding can introduce a measurable shift in the transmission optical spectrum of the traveling LPG when it passes through the pretreated fiber segment. In the hydrogen sensing experiment, the fiber was coated with a platinum (Pt) catalyst layer, which is heated by the thermal energy released from Pt-assisted combustion of H2 and O2, and the resulted temperature change gives rise to a measurable LPG wavelength shift when the traveling LPG passes through. Hydrogen concentration from 1% to 3.8% was detected in the experiment. This technique may also permit measurement of other quantities by changing the functional coating on the fiber; therefore it is expected to be capable of other fully-distributed sensing applications.

  18. Production of submicrometre fused silica gratings using laser-induced backside dry etching technique

    NASA Astrophysics Data System (ADS)

    Hopp, B.; Vass, Cs; Smausz, T.; Bor, Zs

    2006-11-01

    Laser micromachining of transparent materials is a promising technique for producing micro-optical elements. Several types of both direct (e.g. ablation) and indirect (e.g. laser-induced backside wet etching: LIBWE) procedures have already been developed and presented in the last two decades. Here we present a new method (laser-induced backside dry etching (LIBDE)) in the analogy of LIBWE for the micro and nanoprocessing of transparent materials. In our experiments 1 mm thick fused silica plates were used as transparent work pieces. The plates were covered with 100 nm thick silver layers. The metal absorbing films were irradiated through the fused silica by a KrF excimer laser beam (λ = 248 nm, FWHM = 30 ns). The illuminated area was 1.05 mm2 and the fluence on the silver-quartz interface varied in the range 0-1800 mJ cm-2. We have provided evidence that LIBDE is more effective and simple than LIBWE, its etch rate being much higher at a given laser fluence. Our interference experiments proved that the LIBDE etching technique is suitable to fabricate gratings displaying submicrometre periods in transparent materials. On the basis of all these, it is suggested that this method may be useful to produce other nano and microoptical elements, too.

  19. 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.

  20. Carbon Nanotubes as Thermally Induced Water Pumps.

    PubMed

    Oyarzua, Elton; Walther, Jens Honore; Megaridis, Constantine M; Koumoutsakos, Petros; Zambrano, Harvey A

    2017-09-29

    Thermal Brownian motors (TBMs) are nanoscale machines that exploit thermal fluctuations to provide useful work. We introduce a TBM-based nanopump which enables continuous water flow through a carbon nanotube (CNT) by imposing an axial thermal gradient along its surface. We impose spatial asymmetry along the CNT by immobilizing certain points on its surface. We study the performance of this molecular motor using molecular dynamics (MD) simulations. From the MD trajectories, we compute the net water flow and the induced velocity profiles for various imposed thermal gradients. We find that spatial asymmetry modifies the vibrational modes of the CNT induced by the thermal gradient, resulting in a net water flow against the thermal gradient. Moreover, the kinetic energy associated with the thermal oscillations rectifies the Brownian motion of the water molecules, driving the flow in a preferred direction. For imposed thermal gradients of 0.5-3.3 K/nm, we observe continuous net flow with average velocities up to 5 m/s inside CNTs with diameters of 0.94, 1.4, and 2.0 nm. The results indicate that the CNT-based asymmetric thermal motor can provide a controllable and robust system for delivery of continuous water flow with potential applications in integrated nanofluidic devices.

  1. 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.

  2. Bandpass filter with adjustable bandwidth based on a press-induced long-period twisted holey-fiber grating.

    PubMed

    Torres-Gómez, I; Martínez-Ríos, A; Ceballos-Herrera, D E; Mejía-Beltrán, E; Selvas-Aguilar, R

    2007-12-01

    A bandpass filter with adjustable bandwidth based on a press-induced long-period grating in a twisted holey fiber is presented. By twisting the holey fiber prior to the application of periodic pressure, each rejection band of the nontwisted induced long-period grating is split into two shifted rejection bands that move further apart as the twist ratio increases. This feature results in a wide bandpass filter with controllable bandwidth. A bandpass filter at 1523 nm with adjustable bandwidth from 15 to 65 nm with near-linear response and insertion loss lower than 0.7 dB is demonstrated. Additionally, the bandpass filter can be tuned over 100 nm.

  3. Light-induced spatial gratings created by unipolar attosecond pulses coherently interacting with a resonant medium

    NASA Astrophysics Data System (ADS)

    Arkhipov, R. M.; Arkhipov, M. V.; Pakhomov, A. V.; Babushkin, I.; Rosanov, N. N.

    2017-09-01

    Recently, the possibility of the creation, erasing and ultrafast control of polarization and population inversion gratings by sequences of few-cycle bipolar pulses interacting with a medium in a resonant and coherent way was predicted. In this case, the overlapping of pulses in the medium is not needed for the creation of gratings. In this paper, we study the possibility of the ultrafast creation and control of spatial periodic gratings in a resonant medium when subcycle unipolar pulses (that is ones containing the constant spectral component of an electric field) propagate in the coherent regime.

  4. 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.

  5. 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.

  6. Fabrication of arc-induced long-period gratings in different silica fibers

    NASA Astrophysics Data System (ADS)

    Ranjan, Rajeev; Esposito, Flavio; Campopiano, Stefania; Iadicicco, Agostino

    2017-05-01

    In this work, we report on recent results about the fabrication of Long Period Gratings (LPGs) in different single mode optical fibers, by means of Electric Arc Discharge (EAD) technique. In particular, the results are related to three optical fibers with different doping elements, i.e.: standard telecommunication Ge-doped SMF28, highly photosensitive B/Gecodoped PS1250/1500, and P-doped P-SM-5 fibers. EAD leads to a point-by-point LPG inscription, due to localized tapering of the transversal size of the core and cladding regions along the fiber, and to changes of the silica refractive index due to the stress relaxation induced by local hot spots. Here, we take into consideration both standard and unconventional silica fibers and the aim of the work is to identify an appropriate "recipe" for each fiber, for manufacturing LPGs with strong and narrow attenuation bands (depth higher than 25 dB) and trivial power losses (<0.5 dB). Indeed, a proper combination of arc power and duration, as well as fiber tension, allows for the appropriate core and cladding modulation and thus for the desired LPGs spectral features. The sensitivity characteristics towards surrounding refractive index (SRI) and temperature changes of these LPGs are also investigated, highlighting the effects of different kind of doping.

  7. 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

  8. Nonreciprocity of a six-wave mixing light droplet by a moving electromagnetically induced grating

    NASA Astrophysics Data System (ADS)

    Zhang, Yiqi; Wu, Zhenkun; Zheng, Huaibin; Wang, Zhiguo; Zhang, Yunzhe; Tian, Hao; Zhang, Yanpeng

    2014-04-01

    For the first time, we investigate the nonreciprocal generation of six-wave mixing (SWM) in an inverted-Y type four-level system with spatially uniform distribution of atoms. The nonreciprocity results from a moving electromagnetically induced grating (EIG) which is formed by two coupling beams with different frequencies. We demonstrate that the nonreciprocity can be controlled by the frequencies of the coupling fields and the powers of the dressing beams. As the distribution of atoms is uniform, the atomic density cannot affect the nonreciprocity, but it will affect the formation of the photonic band gap structure of the moving EIG. This research can be used to make optical diodes or optical isolators, because the moving EIG, the speed of which is related to the frequency difference of the two coupling beams, can break time-reversal symmetry. We also demonstrate that the nonreciprocal SWM can form a nonreciprocal light droplet when it propagates in atomic vapors with third- and fifth-order nonlinear susceptibilities.

  9. 100 nm period gratings produced by lithographically induced self-construction

    NASA Astrophysics Data System (ADS)

    Lei, Xinya; Wu, Lin; Deshpande, Paru; Yu, Zhaoning; Wu, Wei; Ge, Haixiong; Chou, Stephen Y.

    2003-07-01

    In this paper we report a technique that allows a fast replication of sub-100 nm scale patterns in a thin polymer film on a substrate from a patterned mask. Using the new pattern transfer technique, we fabricated 100 nm period polymer gratings with a 50 nm linewidth above a Si substrate as an example to demonstrate its capability of producing sub-100 nm nanostructures with direct industrial applications. In our technique, a mask with protruding patterns is used to induce similar pattern formation in the molten polymer film through an electrohydrodynamic instability process. A solid positive replica of the mask is obtained by cooling the polymer below its glass transition temperature. The mask is removed afterwards for the next fabrication procedure. The polymer structures formed can be used either directly as functional devices or as etching masks for further lithography processes. The mechanism that leads to the instability and subsequent pattern formation in the polymer layer is explained. Several important physical parameters that control the whole instability process are also identified. Our theory and experiments show that the pattern transfer technique developed here is well suited for the fabrication of sub-100 nm surface patterns in thin polymer films.

  10. Thermal characteristics analysis of an IGBT using a fiber Bragg grating

    NASA Astrophysics Data System (ADS)

    Bazzo, João Paulo; Lukasievicz, Tiago; Vogt, Marcio; de Oliveira, Valmir; Kalinowski, Hypolito José; da Silva, Jean Carlos Cardozo

    2012-02-01

    This paper proposes a new method to develop a thermal model of an insulated gate bipolar transistor (IGBT) employing an optical fiber sensor mounted on the chip structure. Some features of the sensor such as electromagnetic immunity, small size and fast response time, allow the identification of temperature changes generated by the energy loss during device operation through direct measurement. In fact, this measurement method is considered impossible with conventional sensors. The online monitoring of the junction temperature enables identify the thermal characteristics of the IGBT. The results are used to develop an accurate model to simulate the heat generated during the device conduction and switching processes. The model showed a difference of only 0.3% between the measured and simulated results, besides allowing evaluate separately the heat generated by each turn-ON/OFF process.

  11. 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.

  12. 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.

  13. 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.

  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. Measurement of the nonlinear refractive index of tellurite glass fiber by using induced grating autocorrelation technique

    NASA Astrophysics Data System (ADS)

    Traore, Aboubakar

    Nonlinear phenomena in optical fibers have been attracting considerable attention because of the rapid growth of the fiber optics communication industry. The increasing demand in internet use and the expansion of telecommunications in the developing world have triggered the need for high capacity and ultra-fast communication devices and also the need to increase the number of transmission channels in the fibers. Wavelength Division Multiplexing (WDM) and Dense Wavelength Division Multiplexing (DWDM) systems are capable of transmitting large volumes of data at very high rates into huge numbers of optical transmission channels. This ability is limited by the gain bandwidth of Silica based fiber optics amplifiers already installed in the communication networks. Tellurite based fiber amplifiers offer the necessary bandwidth for amplification of WDM and DWDM channels. To investigate the nonlinear properties of the optical fibers in this research, we used a 10 picoseconds pulse width passively mode-locked Nd:Vanadate ( Nd:YVO4) laser operating at 1342nm with a repetition rate of 76 MHz. We accurately measured the nonlinear refractive index of single mode silica fibers utilizing the Induced Grating Autocorrelation (IGA) technique. IGA technique was extended furthermore to study nonlinear effects in multimode fibers, and for the first time, we successfully measured the nonlinear refractive index (n2) of a multimode silica fiber. Confident of the ability of IGA technique for determining n 2 of multimode silica fibers, we measured the nonlinear refractive index of multimode Tellurite glass fibers with length as short as 0.5 meter. The goal of this work is to provide accurate and reliable information on the nonlinear optical properties of Tellurite glass fibers, novel fibers with promising future for developing ultrafast and high transmission capacity communication devices.

  16. 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.

  17. 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.

  18. Formation of photo-induced index grating in azo-carbazole dye-doped polymer

    NASA Astrophysics Data System (ADS)

    Kawabe, Yutaka; Fukuzawa, Kodai; Uemura, Takuya; Matsuura, Katsufumi; Yoshikawa, Toshio; Nishide, Jun-ichi; Sasabe, Hiroyuki

    2012-10-01

    An azo-carbazole dye, 3-[(4-Nitrophenyl)azo]-9H-carbazole-9-ethanol (NACzEtOH), and its relatives doped in polyacrylate films have been known to show `photorefractive' effect without external electric field even in symmetric optical alignment. We have already observed strong energy transfer due to phase-shifted grating by two-beam coupling experiments made for NACzEtOH doped PMMA films. Although the operation mechanism is still unknown, the high efficiency of diffraction is very promising for the application to real-time holography. For the convenience of analysis, we modified Kogelnik's theory for thick grating by correcting the constraint condition and applied it to evaluate refractive index modulation and other parameters quantitatively. In order to clarify the operation mechanism, we conducted the writing and erasing of gratings by using red and green laser beams and analyzed the diffraction magnitude and response dynamics, showing that the response time strongly depended on the writing wavelength, and that the grating formation and its phase shift were not always synchronized.

  19. Thermally induced evolution of hydrogenated amorphous carbon

    NASA Astrophysics Data System (ADS)

    Mangolini, Filippo; Rose, Franck; Hilbert, James; Carpick, Robert W.

    2013-10-01

    The thermally induced structural evolution of hydrogenated amorphous carbon (a-C:H) films was investigated in situ by X-ray photoelectron spectroscopy for annealing temperatures up to 500 °C. A model for the conversion of sp3- to sp2-hybridized carbon in a-C:H vs. temperature and time was developed and applied to determine the ranges of activation energies for the thermally activated processes occurring. The energies are consistent with ordering and clustering of sp2 carbon, scission of sp3 carbon-hydrogen bonds and formation of sp2 carbon, and direct transformation of sp3- to sp2-hybridized carbon.

  20. Negative mobility induced by colored thermal fluctuations.

    PubMed

    Kostur, M; Luczka, J; Hänggi, P

    2009-11-01

    Anomalous transport of non-Markovian thermal Brownian particle dynamics in spatially periodic symmetric systems that is driven by time-periodic symmetric driving and constant bias is investigated numerically. The Brownian dynamics is modeled by a generalized Langevin equation with exponentially correlated Gaussian thermal noise, obeying the fluctuation-dissipation theorem. We study the role of nonzero correlation time of thermal fluctuations for the occurrence of absolute negative (linear) mobility (ANM) near zero bias, negative-valued, nonlinear mobility (NNM), and negative differential mobility (NDM) at finite bias away from equilibrium. We detect that a nonzero thermal correlation time can either enhance or also diminish the value of ANM. Moreover, finite thermal noise correlation can induce NDM and NNM in regions of parameter space for which such ANM and NNM behaviors are distinctly absent for limiting white thermal noise. In parts of the parameter space, we find a complex structure of regions of linear and nonlinear negative mobility: islands and tongues which emerge and vanish under parameters manipulation. While certain such anomalous transport regimes fade away with increasing temperature some specific regions interestingly remain rather robust. Outside those regimes with anomalous mobility, the ac/dc driven transport is either normal or the driven Brownian particles are not transported at all.

  1. 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.

  2. Two-dimensional electromagnetically induced cross-grating in a four-level N-type atomic system

    NASA Astrophysics Data System (ADS)

    Wu, Jianchun; Ai, Baoquan

    2015-06-01

    We propose a scheme for a two-dimensional (2D) electromagnetically induced cross-grating (EICG) in a four-level N-type atomic system. By employing standing-wave fields interacting with the atomic system, the absorption and dispersion of the probe field will change with the spatial periodical modulation. The first-order diffraction intensity sensitively depends on the parameters (the probe detuning, and the amplitude and detuning of the standing-wave fields), and can reach its maximum on varying the system parameters. The present studies may be instructive to design new devices in all-optical switching and optical imaging.

  3. Self-scanned single-frequency operation of a fiber laser driven by a self-induced phase grating

    NASA Astrophysics Data System (ADS)

    Lobach, I. A.; Kablukov, S. I.; Podivilov, E. V.; Babin, S. A.

    2014-04-01

    The selector-free single-frequency operation of an Yb-doped fiber laser with scanning in the range of ˜20 nm is demonstrated. The frequency and intensity evolution is shown to be driven by a self-induced phase grating in the active fiber defined by gain saturation in a standing-wave. A theory has been developed that describes well the main features of the experiment and provides possibilities for optimization of laser parameters. Perspectives for utilizing the self-scanned laser in fundamental studies and practical applications are discussed.

  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. 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.

  6. Numerical simulation on the thermal radiative properties of a 2D SiO2/W/SiO2/W layered grating for thermophotovoltaic applications

    NASA Astrophysics Data System (ADS)

    Zhao, Yi; Fu, Ceji

    2016-10-01

    Tailoring the spectrum of thermal emission from the emitter is important for improving the performance of a thermophotovoltaic (TPV) system. In this work, a two-dimensional (2D) layered grating structure made of SiO2 and tungsten (W), which can realize wavelength-selective control of thermal emission, was proposed for a potential emitter in TPV applications. Numerical simulations of the spectral emissivity of the structure from the ultraviolet (UV) to the mid-infrared region reveals that the spectral-normal emissivity of the structure is enhanced to above 0.95 in the wavelength region from 0.55 μm to 1.9 μm for both TE and TM waves, but drops sharply at wavelength larger than 2 μm. Physical mechanisms responsible for the wavelength-selective emissivity were elucidated as due to resonance of magnetic polaritons (MPs) in the SiO2 spacer and in the grooves of the tungsten grating, Wood's anomaly (WA), excitation of surface plasmon polaritons (SPPs) and wave interference. Furthermore, the structure was found to exhibit quasi-diffuse and polarization-insensitive features of thermal emission, suggesting that the proposed structure can serve as the emitter in the design of high performance TPV systems.

  7. 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.

  8. Optically Induced Space-charge and Conductivity Gratings in Wide-bandgap Semiconductors

    NASA Astrophysics Data System (ADS)

    Bryushinin, M. A.; Karavaev, P. M.; Sokolov, I. A.

    We report optical excitation of space-charge and conductivity gratings in wide-bandgap semiconductors. The approach is based on the illumination of semiconductor material with an oscillating interference pattern formed of two light waves, one of which is phase modulated with frequency ω. The non-steady-state photocurrent flowing through the short-circuited semiconductor is the measurable quantity in this technique. The alternating current results from the periodic relative shifts of the photoconductivity and space charge electric field gratings which arise in the volume of the crystal under illumination. The experiments are carried out in β-Ga2O3 crystal and the main parameters of the photoinduced carriers are determined.

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

    NASA Astrophysics Data System (ADS)

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

    2015-11-01

    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.

  10. Understanding profile-induced group-delay ripple in Bragg gratings.

    PubMed

    Poladian, L

    2000-04-20

    The relationship between group-delay ripple and the apodization profile of chirped Bragg gratings is analyzed. Simple physical explanations are given for departures from ideal linear group delay by use of only the concepts of reflection at discontinuities and band gaps and the optical path lengths of cavities. Quantitative expressions are obtained for the amplitudes, phases, and periods of both the fast and slow components of the ripple.

  11. 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

  12. Ultrasonic sensitivity of strain-insensitive fiber Bragg grating sensors and evaluation of ultrasound-induced strain.

    PubMed

    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.

  13. The motion-induced shift in the perceived location of a grating also shifts its aftereffect

    PubMed Central

    Kosovicheva, Anna A.; Maus, Gerrit W.; Anstis, Stuart; Cavanagh, Patrick; Tse, Peter U.; Whitney, David

    2013-01-01

    Motion can bias the perceived location of a stationary stimulus, but whether this occurs at a high level of representation or at early, retinotopic stages of visual processing remains an open question. As coding of orientation emerges early in visual processing, we tested whether motion could influence the spatial location at which orientation adaptation is seen. Specifically, we examined whether the tilt aftereffect (TAE) depends on the perceived or the retinal location of the adapting stimulus, or both. We used the flash-drag effect (FDE) to produce a shift in the perceived position of the adaptor away from its retinal location. Subjects viewed a patterned disk that oscillated clockwise and counterclockwise while adapting to a small disk containing a tilted linear grating that was flashed briefly at the moment of the rotation reversals. The FDE biased the perceived location of the grating in the direction of the disk's motion immediately following the flash, allowing dissociation between the retinal and perceived location of the adaptor. Brief test gratings were subsequently presented at one of three locations—the retinal location of the adaptor, its perceived location, or an equidistant control location (antiperceived location). Measurements of the TAE at each location demonstrated that the TAE was strongest at the retinal location, and was larger at the perceived compared to the antiperceived location. This indicates a skew in the spatial tuning of the TAE consistent with the FDE. Together, our findings suggest that motion can bias the location of low-level adaptation. PMID:22895880

  14. Degradation of femtosecond petawatt laser beams: Spatio-temporal/spectral coupling induced by wavefront errors of compression gratings

    NASA Astrophysics Data System (ADS)

    Li, Zhaoyang; Tsubakimoto, Koji; Yoshida, Hidetsugu; Nakata, Yoshiki; Miyanaga, Noriaki

    2017-10-01

    Recently, several petawatt (PW, 1015 W) lasers with pulse duration of ∼20–30 fs have been introduced throughout the world, pushing the upper limit on laser peak power. However, besides well-known spatio-temporal coupling effects, such as residual spatial/angular chirps and pulsefront tilt/curvature, the spatio-temporal/spectral coupling in compressors induced by wavefront errors of gratings, which could dramatically distort ultra-intense pulses, has been neglected. In this work, for the first time we analyzed this phenomenon and the peak power/intensity degradation induced by it. Our results suggest that the actual performance of femtosecond PW lasers may be worse than previously estimated.

  15. Bragg gratings in ORMOCERs

    NASA Astrophysics Data System (ADS)

    Belenguer, Tomas; Cheben, Pavel; Moreno-Barriuso, Eva M.; Nunez, Armonia; Ulibarrena, Manuel; del Monte, Francisco; Levy, David

    1997-10-01

    Two novel holographic recording media based on silica gel methyl methacrylate (MMA) and hydroxy ethyl methacrylate (HEMA) organically modified ceramics (ORMOCERS) are presented and its holographic properties, inferred from the experimental data, are discussed. The recording of holographic gratings of both low-spatial frequency (50 lp/mm) and high-spatial frequency (1400 lp/mm) in a bulk ORMOCER matrix is reported. The gratings were recorded by UV irradiation-induced photopolymerization of the MMA or HEMA monomers embedded in the silica matrix. The Bragg gratings were successfully recorded by interference of two coherent beams of 351.1 nm wavelength. A linearly polarized He-Ne laser beam (632.8 nm) was used for continuous monitoring of the recording process by measurement of the diffraction efficiency and for enhancement of the grating creation process. High diffraction efficiencies (93%) and low absorption and scattering coefficients were measured during the holographic reconstruction by He-Ne laser beam. The most important holographic parameters of the gratings were inferred from the experimental data: diffraction efficiency, angular selectivity, refraction-index modulation amplitude, spectral sensitivity, the Klein-Cook parameter, and the environmental stability of the gratings.

  16. Gratings in polymeric waveguides

    NASA Astrophysics Data System (ADS)

    Mishakov, G.; Sokolov, V.; Kocabas, A.; Aydinli, A.

    2007-04-01

    Laser-induced formation of polymer Bragg grating filters for Dense Wavelength Division Multiplexing (DWDM) applications is discussed. Acrylate monomers halogenated with both fluorine and chlorine, which possess absorption losses less than 0.25 dB/cm and wide choice of refractive indices (from 1.3 to 1.5) in the 1.5 μm telecom wavelength region were used. The monomers are highly intermixable thus permitting to adjust the refractive index of the composition within +/-0.0001. Moreover they are photocurable under UV exposure and exhibit high contrast in polymerization. These properties make halogenated acrylates very promising for fabricating polymeric waveguides and photonic circuits. Single-mode polymer waveguides were fabricated on silicon wafers using resistless contact lithography. Submicron index gratings have been written in polymer waveguides using holographic exposure with He-Cd laser beam (325 nm) through a phase mask. Both uniform and apodized gratings have been fabricated. The gratings are stable and are not erased by uniform UV exposure. The waveguide gratings possess narrowband reflection spectra in the 1.5 μm wavelength region of 0.4 nm width, nearly rectangular shape of the stopband and reflectivity R > 99%. The fabricated Bragg grating filters can be used for multiplexing/demultiplexing optical signals in high-speed DWDM optical fiber networks.

  17. Tunable wavelength erbium doped fiber linear cavity laser based on mechanically induced long-period fiber gratings

    NASA Astrophysics Data System (ADS)

    Pérez Maciel, M.; Montenegro Orenday, J. A.; Estudillo Ayala, J. M.; Jáuregui-Vázquez, D.; Sierra-Hernandez, J. M.; Hernandez-Garcia, J. C.; Rojas-Laguna, R.

    2016-09-01

    Tunable wavelength erbium doped fiber linear cavity laser, based on mechanically induced long-period fiber gratings (MLPFG) is presented. The laser was tuned applying pressure over the MLPFG, in order to monitor this, pressure is applied over a plate with periodic grooves that has a short length, this pressure is controlled by a digital torque tester as a result tunable effect is observed. The grooves have a period of 620µm and the maximal pressure without breakpoint fiber is around 0.80lb-in2. Furthermore, the MLPFG used can be erased, reconfigured and exhibit a transmission spectra with termal stability, similar to high cost photoinduced long period gratings. In this work, by pressure increment distributed over the MLPFG from 0.40 lb-in2 to 0. 70 lb-in 2, tuned operation range of 14nm was observed and single line emission was tuned in the C telecommunication band. According to the stability analysis the signal to noise ratio was 29 dB and minimal wavelength oscillations of 0.29nm.

  18. Thermally induced coherent vibrations in DNA

    NASA Astrophysics Data System (ADS)

    Rasmussen, Kim O.; Kalosakas, George; Voulgarakis, N. K.; Bishop, Alan R.; Choi, C. H.; Usheva, A.

    2004-05-01

    We compare numerical calculations and experimental data showing that large, slow thermally-induced openings of double stranded DNA coincide with the location of functionally relevant sites for transcription. Investigating a bacteriophage DNA gene promoter segment, we find that the large opening tends to occur at the transcription start site. Other probable large openings appear to be related to other regulatory sites. Sequence specificity, nonlinearity and entropy, are the basic elements for controlling coherent dynamics. To further characterize the dynamics related to the bubble formation we investigate the temperature dependence on the dynamic structure factor. A distinct feature in the dynamics structure factor is identified and attributed to the denaturation bubbles.

  19. Novel Programmable Shape Memory Polystyrene Film: A Thermally Induced Beam-power Splitter

    NASA Astrophysics Data System (ADS)

    Li, Peng; Han, Yu; Wang, Wenxin; Liu, Yanju; Jin, Peng; Leng, Jinsong

    2017-03-01

    Micro/nanophotonic structures that are capable of optical wave-front shaping are implemented in optical waveguides and passive optical devices to alter the phase of the light propagating through them. The beam division directions and beam power distribution depend on the design of the micro/nanostructures. The ultimate potential of advanced micro/nanophotonic structures is limited by their structurally rigid, functional singleness and not tunable against external impact. Here, we propose a thermally induced optical beam-power splitter concept based on a shape memory polystyrene film with programmable micropatterns. The smooth film exhibits excellent transparency with a transmittance of 95% in the visible spectrum and optical stability during a continuous heating process up to 90 °C. By patterning double sided shape memory polystyrene film into erasable and switchable micro-groove gratings, the transmission light switches from one designed light divided directions and beam-power distribution to another because of the optical diffraction effect of the shape changing micro gratings during the whole thermal activated recovery process. The experimental and theoretical results demonstrate a proof-of-principle of the beam-power splitter. Our results can be adapted to further extend the applications of micro/nanophotonic devices and implement new features in the nanophotonics.

  20. Novel Programmable Shape Memory Polystyrene Film: A Thermally Induced Beam-power Splitter

    PubMed Central

    Li, Peng; Han, Yu; Wang, Wenxin; Liu, Yanju; Jin, Peng; Leng, Jinsong

    2017-01-01

    Micro/nanophotonic structures that are capable of optical wave-front shaping are implemented in optical waveguides and passive optical devices to alter the phase of the light propagating through them. The beam division directions and beam power distribution depend on the design of the micro/nanostructures. The ultimate potential of advanced micro/nanophotonic structures is limited by their structurally rigid, functional singleness and not tunable against external impact. Here, we propose a thermally induced optical beam-power splitter concept based on a shape memory polystyrene film with programmable micropatterns. The smooth film exhibits excellent transparency with a transmittance of 95% in the visible spectrum and optical stability during a continuous heating process up to 90 °C. By patterning double sided shape memory polystyrene film into erasable and switchable micro-groove gratings, the transmission light switches from one designed light divided directions and beam-power distribution to another because of the optical diffraction effect of the shape changing micro gratings during the whole thermal activated recovery process. The experimental and theoretical results demonstrate a proof-of-principle of the beam-power splitter. Our results can be adapted to further extend the applications of micro/nanophotonic devices and implement new features in the nanophotonics. PMID:28276500

  1. 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

    2014-09-05

    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.

  2. 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

  3. Analysis of mechanical and thermal response of rock due to laser drilling using optical fiber Bragg grating sensors

    NASA Astrophysics Data System (ADS)

    Quintero, Sully M. M.; Patusco, Guilherme B.; da Silva, Hugo G.; Furtado, Felipe O.; Valente, Luiz C. G.; Braga, Arthur M. B.

    2015-09-01

    Optical fiber Bragg grating sensors (FBGs) were used to measure strain and the temperature field that develop during laser drilling of carbonate rock samples. The shear deformation and high temperature gradient measured are clearly correlated with traces of fractures observed. Beyond the volume directly evaporated by laser exposure, a greater volume around the drilling area was fractured. From the perforation process point of view, it results in an increase of efficiency.

  4. 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

  5. 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.

  6. 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.

  7. Study of Mass Diffusion and Relaxation Processes in Polymer Systems by Laser Induced Holographic Grating Relaxation and Dynamic Light Scattering.

    NASA Astrophysics Data System (ADS)

    Xia, Jiulin

    The diffusion of dye molecules in various polymer systems is studied using the Laser Induced Holographic Grating Relaxation technique. The diffusion coefficients of camphorquinone (CQ), thymoquinone (TQ), diacetyl (DA) and azo compounds in these polymers are studied as a function of temperature, properties of both the polymers and the dye molecules. The effects of additives are also investigated. Due to the chemical reversibility of the azo compounds, the kinetics of their chemical processes are also analyzed. The mutual diffusion coefficients in poly(methyl methacrylate) (PMMA) and poly(ethylene oxide) (PEO) compatible polymer blends are measured by dynamic light scattering as a function of the molecular weight of PEO while keeping the molecular weight of PMMA fixed. The polymer chain relaxation processes of poly(isobornyl methacrylate) (PIMA) are also studied by using dynamic light scattering.

  8. Time-resolved gas thermometry by laser-induced grating spectroscopy with a high-repetition rate laser system

    NASA Astrophysics Data System (ADS)

    Förster, Felix J.; Crua, Cyril; Davy, Martin; Ewart, Paul

    2017-07-01

    Thermometry using laser-induced grating spectroscopy (LIGS) is reported using a high-repetition rate laser system, extending the technique to allow time-resolved measurements of gas dynamics. LIGS signals were generated using the second harmonic output at 532 nm of a commercially available high-repetition rate Nd:YAG laser with nitrogen dioxide as molecular seed. Measurements at rates up to 10 kHz were demonstrated under static cell conditions. Transient temperature changes of the same gas contained in a cell subjected to rapid compression by injection of gas were recorded at 1 kHz to derive the temperature evolution of the compressed gas showing temperature changes of 50 K on a time-scale of 0.1 s with a measurement precision of 1.4%. The data showed good agreement with an analytical thermodynamic model of the compression process.

  9. 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.

  10. A combination of laser-induced grating and transient-absorption experiments for investigation of laser pulse properties and fast molecular relaxation processes

    NASA Astrophysics Data System (ADS)

    Jena, A.

    1981-09-01

    A repetitive low-power laser-pulse apparatus has been developped which allows both absorption relaxation and light-induced grating experiments without changing geometry or components. The influence of pulse width and coherence time on the diffracted intensity correlation function is discussed for a weak amplitude grating in terms of a simplified theory. From the corresponding absorption relaxation signals including the coherent coupling contribution some easy ways for detecting vibronic-relaxation, intersystem-crossing and orientational-relaxation times are deduced. The advantage of the in-situ measurement of the amplitude grating autocorrelation function leads to a precise zero-delay calibration of the transient absorption equipment. Furthermore one gets the response function for the absorption experiments from the grating experiments, if stable mode-locking operation of the argon laser is reached. This condition can be controlled either by the time course of the absorption or grating signals. A surprisingly short coherence length is detected for the cavity-dumped laser beam. A reliable check of the coherent-coupling theory confirms the theoretical assumptions incorporated into the fast-relaxation signal analysis. Experiments on dye molecules show high triplet yield of heavy-atom substituted dyes and fast rotational diffusion of oblong molecular rotors.

  11. 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.

  12. Ultrafast laser-induced reproducible nano-gratings on a molybdenum surface

    NASA Astrophysics Data System (ADS)

    Dar, Mudasir H.; Saad, Nabil A.; Sahoo, Chakradhar; Naraharisetty, Sri Ram G.; Rao Desai, Narayana

    2017-02-01

    Wavelength-dependent reproducible nano-gratings were produced on a bulk molybdenum surface upon irradiation with femtosecond laser pulses at near normal incidence in ambient air and water environments. The surface morphology of the irradiated surfaces was characterized by field emission scanning electron microscopy. The ripple spacing was observed to decrease by half when the surface was irradiated with the second harmonic of the fundamental 800 nm radiation. Careful choice of the laser parameters such as fluence, scanning speed, polarization and wavelength were observed to be important for the formation of smooth periodic ripples. The mechanism of formation of polarization-dependent periodic ripples is explained based on the interference model. We also demonstrated the use of a laser direct writing technique for the fabrication of periodic subwavelength structures that have potential applications in photonic devices.

  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. Real-time analysis of arc-induced Long Period Gratings under gamma irradiation

    PubMed Central

    Esposito, Flavio; Ranjan, Rajeev; Stăncălie, Andrei; Sporea, Dan; Neguţ, Daniel; Becherescu, Nicu; Campopiano, Stefania; Iadicicco, Agostino

    2017-01-01

    In this paper, we present a comparative experimental and theoretical study on gamma radiation sensitivity of Long Period Gratings (LPGs), fabricated by electric arc discharge technique, as monitored in three single mode optical fibers supplied by different manufacturers. A real-time measurement of LPGs’ wavelength shift was performed until a total dose of 35 kGy was reached, with average dose rate of 0.18 kGy/h, the irradiation being done at room temperature. In one case, a maximum radiation sensitivity of 1.34 nm/kGy was recorded for doses up to 0.5 kGy. Moreover, by combining experimental results with numerical simulations, it was found that changes occurred in the core refractive index of the irradiated optical fibers up to 2.5 ∙ 10−5. The increase of the core thermo-optic coefficient up to 1.5 ∙ 10−8/°C was observed as well. PMID:28262784

  15. Real-time analysis of arc-induced Long Period Gratings under gamma irradiation

    NASA Astrophysics Data System (ADS)

    Esposito, Flavio; Ranjan, Rajeev; Stăncălie, Andrei; Sporea, Dan; Neguţ, Daniel; Becherescu, Nicu; Campopiano, Stefania; Iadicicco, Agostino

    2017-03-01

    In this paper, we present a comparative experimental and theoretical study on gamma radiation sensitivity of Long Period Gratings (LPGs), fabricated by electric arc discharge technique, as monitored in three single mode optical fibers supplied by different manufacturers. A real-time measurement of LPGs’ wavelength shift was performed until a total dose of 35 kGy was reached, with average dose rate of 0.18 kGy/h, the irradiation being done at room temperature. In one case, a maximum radiation sensitivity of 1.34 nm/kGy was recorded for doses up to 0.5 kGy. Moreover, by combining experimental results with numerical simulations, it was found that changes occurred in the core refractive index of the irradiated optical fibers up to 2.5 • 10‑5. The increase of the core thermo-optic coefficient up to 1.5 • 10‑8/°C was observed as well.

  16. Effect of the refractive index change kinetics of photosensitive materials on the diffraction efficiency of reflecting Bragg gratings.

    PubMed

    Lumeau, Julien; Glebov, Leonid B

    2013-06-10

    Experimental and modeled dependencies of the induced refractive index on dosage of UV exposure in photo-thermo-refractive glass for different thermal treatment regimes are presented. Resulting spatial profiles of refractive index modulation in a reflecting Bragg grating recorded by a holographic technique are computed, and corresponding diffraction efficiencies are modeled. It is shown that nonlinearity of the photosensitivity response is responsible for spatial distortions of a recorded grating that result in a decrease of the diffraction efficiency.

  17. Anharmonicity induced thermal modulation in stressed graphene

    NASA Astrophysics Data System (ADS)

    Jiang, JianJun; Fu, WeiCheng; Chen, JiGe; Zhao, Hong

    2017-07-01

    Thermal properties are essentially decided by atomic geometry and thus stress is the most direct way for manipulating. In this paper, we investigate stress modulation of thermal conductivity of graphene by molecular dynamics simulations and discuss the underlying microscopic mechanism. It is found that thermal conductivity of flexural-free graphene increases with compression and decreases with strain, while thermal conductivity of flexural-included graphene decreases with both compression and strain. Such difference in thermal behavior originates from the changes in the anharmonicity of the interatomic potential, where the wrinkle scattering is responsible for the thermal conductivity diminishment in flexural-included graphene under strain. By comparing the results obtained from the Tersoff and AIREBO potentials, it is revealed that the degree of the symmetry of interatomic potential determines the thermal conductivity variation of graphene. Our results indicate that the symmetry of interatomic potential should be taken into careful consideration in constructing the lattice model of graphene.

  18. Tunable plasmon-induced transparency in a grating-coupled double-layer graphene hybrid system at far-infrared frequencies.

    PubMed

    Zhao, Xiaolei; Zhu, Lin; Yuan, Cai; Yao, Jianquan

    2016-12-01

    A grating-coupled double-layer graphene hybrid system is proposed to investigate the plasmon-induced transparency effect at far-infrared frequencies. Based on the guided mode resonance principle, a diffractive grating is used to couple the normally incident waves and excite the plasmonic resonances on two graphene films separated by a spacer, thereby avoiding the need for patterning graphene. It is found that the origin of the observed transparency window transforms from Autler-Townes splitting to electromagnetically induced transparency with the increase of the separation distance between the two graphene films. The tunability of this hybrid system is also investigated via varying the Fermi energy in graphene. The proposed hybrid system has potential applications in tunable switches, sensors, and slow light devices and may open up new avenues for constructing easy-to-fabricate graphene-based plasmonic devices.

  19. Fabrication of self-ruled micro grating on CR-39 using ArF laser-induced rippling

    NASA Astrophysics Data System (ADS)

    Refahizadeh, M.; Parvin, P.; Silakhori, K.; Mortazavi, S. Z.; Mehdilo, A.

    2017-06-01

    The excimer laser at 193 nm induces regular self-assembled microstructures on poly allyl diglycol carbonate PADC (or CR-39). This surface rippling is threshold-dependent and undergoes different features at low/high UV fluences. The microstructures are characterized by small/large aspect ratios (0.056-0.226) at low/high UV fluences of 40-1000 mJ cm-2. The self-aligning micro grooves show a strong sensitivity to the incident angles. As a consequence, the parameter of the fluence threshold drastically reduces in terms of the large incident angles, leading to parallelism over a broad treated area. In fact, the self-rippling at high UV fluences aligns with P-polarization of the incident beam. Conversely, the pattern appears in the orientation of the S-polarization under low fluences. This unique property of CR-39 is used to fabricate the micro gratings of 250-2900 lines mm-1, which certainly meets the criteria for high efficiency at small aspect ratios.

  20. 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.

  1. Asymmetric acoustic gratings

    NASA Astrophysics Data System (ADS)

    He, Zhaojian; Peng, Shasha; Ye, Yangtao; Dai, Zhongwei; Qiu, Chunyin; Ke, Manzhu; Liu, Zhengyou

    2011-02-01

    The unidirectional transmission of acoustic waves is realized by a simple geometrically asymmetric steel grating structure. This exotic phenomenon stems from the one-way diffraction effect induced by the different periods of the slits on the both surfaces of the sample. And the frequency range of unidirectional transmission is simply determined by the structure periods. The experimental results agree well with the theoretical simulation. This remarkable effect is expected potential applications in ultrasonic devices, such as acoustic rectifiers and acoustic diodes.

  2. The linewidth of distributed feedback resonators: the combined effect of thermally induced chirp and gain narrowing

    NASA Astrophysics Data System (ADS)

    Kores, Cristine C.; Geskus, Dimitri; Ismail, Nur; Dijkstra, Meindert; Bernhardi, Edward H.; Pollnau, Markus

    2017-02-01

    Distributed-feedback (DFB) laser resonators are widely recognized for their advantage of generating laser emission with extremely narrow linewidth. Our investigation concerns ytterbium-doped amorphous Al2O3 channel waveguides with a corrugated homogeneous Bragg grating inscribed into its SiO2 top cladding, in which a λ/4 phase-shift provides a resonance and allows for laser emission with a linewidth as narrow as a few kHz. Pump absorption imposes a thermal chirp of the grating period, which has implications for the spectral characteristics of the resonator. Thermal effects on the spectral response of a DFB passive resonator were investigated via simulations using Coupled Mode Theory by considering (i) a constant deviation of the grating period or (ii) a chirp with a linear profile. We report an increase of the resonance linewidth up to 15%. This result is due to two factors, namely changes of the grating reflectivity at the resonance frequency up to 2.4% and of the shift of resonance frequency up to 61 pm due to an accumulated phase shift imposed on the grating by the chirp profile. The linewidth decrease due to gain is on the order of 106, which is a much larger value. Nevertheless, according to the Schawlow-Townes equation the linewidth increase of the passive resonator due to a thermal chirp quadratically increases the laser linewidth.

  3. Fiber Bragg grating sensor monitoring with thermally tuned Fabry-Perot cavity integrated in an all-silicon rib waveguide

    NASA Astrophysics Data System (ADS)

    Coppola, Giuseppe; Iodice, Mario; Saffioti, Nunzia; Zaccuri, Rocco C.; Indolfi, Maurizio; Rendina, Ivo; Rocco, Alessandra; Ferraro, Pietro

    2005-03-01

    Fiber Bragg Gratings (FBG) sensors are a very promising solution for strain and/or temperature monitoring in hostile or hazardous environments. In particular, their typical immunity to EMI and the absence of electrical signals and cables, encourage the use of FBG sensors in aerospace structure. Moreover, FBG sensors can be embedded in composite materials, allowing the fabrication of the so-called smart-materials. In this paper we experimentally demonstrate that a Fabry-Perot cavity, integrated in a low-loss all-silicon rib waveguide, and realized by standard dry etching technique, is suitable for FBG monitoring. The reflected signal for the sensor passes through the cavity which is tuned by means of thermo-optic effect. The optical circuit ends with a photodetector that, for each tuning step, produces a photocurrent proportional to the convolution integral between the FBG and the FP spectral response. Because the finesse of a silicon FP cavity in air is not so high (about 2.5), it is advantageous an extended tuning over a wavelength range longer than the cavity free spectral range, that is convolving the FBG response with more than one FP transmission peak. The photodetector output signal, once acquired, is elaborated using standard FFT algorithm and pass-band filtered, in order to extract the main harmonic. After a final I-FFT step, a fitting procedure returns the FBG reflection peak position. The experimental accuracy, using as reference the peak wavelength measure made with a commercial high-performance Optical Spectrun Analizer, is in the order of few tenths of picometers.

  4. Thermal insulator transition induced by interface scattering

    NASA Astrophysics Data System (ADS)

    Slovick, Brian A.; Krishnamurthy, Srini

    2016-10-01

    We develop an effective medium model of thermal conductivity that accounts for both percolation and interface scattering. This model accurately explains the measured increase and decrease of thermal conductivity with loading in composites dominated by percolation and interface scattering, respectively. Our model further predicts that strong interface scattering leads to a sharp decrease in thermal conductivity, or an insulator transition, at high loadings when conduction through the matrix is restricted and heat is forced to diffuse through particles with large interface resistance. The accuracy of our model and its ability to predict transitions between insulating and conducting states suggest it can be a useful tool for designing materials with low or high thermal conductivity for a variety of applications.

  5. 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.

  6. Photorefractive optical fuzzy-logic processor based on grating degeneracy

    NASA Astrophysics Data System (ADS)

    Wu, Weishu; Yang, Changxi; Campbell, Scott; Yeh, Pochi

    1995-04-01

    A novel optical fuzzy-logic processor using light-induced gratings in photorefractive crystals is proposed and demonstrated. By exploiting grating degeneracy, one can easily implement parallel fuzzy-logic functions in disjunctive normal form.

  7. Study of thermally induced higher order microcantilever modes

    NASA Astrophysics Data System (ADS)

    Kadam, Ashwini

    Microcantilevers have been widely studied for sensing tiny quantities of chemical and biological analytes in both vapor and liquid media. They have been shown to respond to changes in chemical, biological, thermal and physical processes. The primary sensing mechanisms are static bending due to induced differential surface stress and changes in the fundamental resonant frequency upon mass uptake. Although the possibility of using thermally induced higher order modes has been suggested for sensing and for understanding the mechanical behavior of microcantilevers, experimental demonstrations have not been given in the literature. Studies of thermally induced spectra provide an alternate in-situ detection technique for microcantilever sensing that is attractive in that no external excitation mechanism is required. However, thermally induced higher order modes have smaller amplitudes than what is obtained with external excitation. This dissertation examines the use of thermally induced higher order microcantilever modes both for sensing and studying adsorption induced interfacial changes between the Au coated microcantilever surface and Hg. The use of a thermally induced spectrum takes advantage of the fact that no additional external components are necessary to study them when using the optical lever (AFM style) detection technique. A process to microfabricate rectangular microcantilever is optimized and demonstrated. Thermally induced higher order flexural modes are demonstrated for Hg sensing with Au coated microcantilevers. Furthermore Hg sensing is carried out with microcantilevers having different Au coverage to investigate the use of thermally induced higher order modes for sensing. Two different types of Au surfaces are employed for Hg sensing with microcantilevers, one obtained by thermally evaporating Au, and the other by sputtering Au. Although the conventionally used deflection signal showed similar trend to Hg with both these films, exactly the opposite

  8. Fabrication and characterization of a non-zero dispersion-shifted mechanically-induced long-period grating for optical fiber sensing

    NASA Astrophysics Data System (ADS)

    Gallegos-Arellano, E.; Mata Chávez, R. I.; Huerta-Mascotte, E.; Estudillo-Ayala, J. M.; Guzmán-Chávez, A. D.; Vargas-Rodriguez, E.; Sierra-Hernández, J. M.; Rojas-Laguna, R.; Guryev, I.

    2015-08-01

    We present the fabrication and characterization of a mechanically induced long period grating (MLPG) using a grating period of 400 μm and 1m of NZ-DSF. Pressure is gradually applied up to 120 Lb at different angles like 0, 30, 45 and 60 degrees. An attenuation band is observed centered at a wavelength around 1064nm using a fiber position of 30 degrees with respect to the gratinǵs metal plate and a maximum pressure of 145 Lb. The loss band presents a maximum depth of 22dB and a bandwidth of approximately 10nm. Torsion and curvature characterizations did not change the output spectrum of the optical grating. However, temperature characterization depicted a small shifting which could be insignificant for some applications. Still, there is 16dB attenuation as temperature increases in a range from room temperature up to 450°C. These preliminary studies show that this 1064 nm centered wavelength MILPG might be used in a low linear dynamic range with temperature (75-300)°C as a temperature sensor.

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

    PubMed

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

    2015-09-09

    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.

  10. 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

  11. 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.

  12. Thermally-Induced Structural Disturbances of Rigid Panel Solar Arrays

    NASA Technical Reports Server (NTRS)

    Johnston, John D.; Thornton, Earl A.

    1997-01-01

    The performance of a significant number of spacecraft has been impacted negatively by attitude disturbances resulting from thermally-induced motions of flexible structures. Recent examples of spacecraft affected by these disturbances include the Hubble Space Telescope (HST) and the Upper Atmosphere Research Satellite (UARS). Thermally-induced structural disturbances occur as the result of rapid changes in thermal loading typically initiated as a satellite exits or enters the Earth's shadow. Temperature differences in flexible appendages give rise to structural deformations, which in turn result in disturbance torques reacting back on the spacecraft. Structures which have proven susceptible to these disturbances include deployable booms and solar arrays. This paper investigates disturbances resulting from thermally-induced deformations of rigid panel solar arrays. An analytical model for the thermal-structural response of the solar array and the corresponding disturbance torque are presented. The effect of these disturbances on the attitude dynamics of a simple spacecraft is then investigated using a coupled system of governing equations which includes the effects of thermally-induced deformations. Numerical results demonstrate the effect of varying solar array geometry on the dynamic response of the system.

  13. Thermally-Induced Structural Disturbances of Rigid Panel Solar Arrays

    NASA Technical Reports Server (NTRS)

    Johnston, John D.; Thornton, Earl A.

    1997-01-01

    The performance of a significant number of spacecraft has been impacted negatively by attitude disturbances resulting from thermally-induced motions of flexible structures. Recent examples of spacecraft affected by these disturbances include the Hubble Space Telescope (HST) and the Upper Atmosphere Research Satellite (UARS). Thermally-induced structural disturbances occur as the result of rapid changes in thermal loading typically initiated as a satellite exits or enters the Earth's shadow. Temperature differences in flexible appendages give rise to structural deformations, which in turn result in disturbance torques reacting back on the spacecraft. Structures which have proven susceptible to these disturbances include deployable booms and solar arrays. This paper investigates disturbances resulting from thermally-induced deformations of rigid panel solar arrays. An analytical model for the thermal-structural response of the solar array and the corresponding disturbance torque are presented. The effect of these disturbances on the attitude dynamics of a simple spacecraft is then investigated using a coupled system of governing equations which includes the effects of thermally-induced deformations. Numerical results demonstrate the effect of varying solar array geometry on the dynamic response of the system.

  14. Full distortion induced by dispersion evaluation and optical bandwidth constraining of fiber Bragg grating demultiplexers over analogue SCM systems.

    PubMed

    Martinez, Alfonso; Pastor, Daniel; Capmany, Jose

    2002-12-30

    We provide a full analysis of the distortion effects produced by the first and second order in-band dispersion of fiber Bragg grating based optical demultiplexers over analogue SCM (Sub Carrier Multiplexed) signals. Optical bandwidth utilization ranges for Dense WDM network are calculated considering different SCM system cases of frequency extension and modulation conditions.

  15. Thermally induced vibrations due to internal heat generation

    NASA Astrophysics Data System (ADS)

    Blandino, Joseph Robert

    Virtually all previous research on thermally induced vibrations has investigated vibrations caused by surface heating. This is the first detailed study of a thermally induced vibration caused by surface cooling. The phenomenon is shown to be driven by thermal moments. The thermal moments are caused by convection because the vibrations occur in air but not in a vacuum. A mathematical model was developed to predict the thermal-structural behavior of an internally heated beam. The convection heat transfer for a vibrating beam is complex. In most cases it is neither completely natural nor completely forced convection. The convection heat transfer is a mix of both components. The convection is further complicated by the transition of the airflow along the beam from laminar to turbulent flow. An experimental heat transfer investigation was conducted to determine expressions for the natural and forced convection as functions of both position along the beam and velocity. The results from the model were verified using experimental data for an internally heated beam undergoing thermally induced vibrations. The model was shown to predict the steady-state temperatures accurately. The model adequately predicted the steady-state displacements, although it predicted the displacement histories with some error. The analysis showed that the thermal and structural problems are coupled by the forced convection. Once initiated, the amplitude of the vibration increases until the amplitude is such that the heat removed by convection balances the internal heating. The steady-state amplitude is not affected by the initial displacement of the beam. Thermally induced vibrations of internally heated beams belong to the class of vibrations called self-sustaining oscillations.

  16. Induced natural convection thermal cycling device

    DOEpatents

    Heung, Leung Kit [Aiken, SC

    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.

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

    PubMed

    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. 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.

  19. Turbulence-induced thermal signatures over evaporating bare soil surfaces

    NASA Astrophysics Data System (ADS)

    Haghighi, Erfan; Or, Dani

    2015-07-01

    Soil wetness and airflow turbulence are key factors affecting surface energy balance components thereby influencing surface skin temperature. Turbulent eddies interacting with evaporating surfaces often induce localized and intermittent evaporative and sensible heat fluxes that leave distinct thermal signatures. These surface thermal fluctuations observable by infrared thermography (IRT) offer a means for characterization of overlaying turbulent airflows and remote quantification of surface wetness. We developed a theoretical and experimental methodology for using rapid IR surface temperature measurements to deduce surface wetness and evaporative fluxes from smooth bare soils. The mechanistic model provides theoretical links between surface thermal fluctuations, soil, and aerodynamic properties enabling thermal inferences of soil wetness with explicit consideration of soil thermal capacity and airflow turbulence effects. The method potentially improves accuracy of soil wetness assessment by IRT-based techniques whose performance is strongly influenced by surface-turbulence interactions and offers new ways for quantifying fluxes directly at their origin.

  20. Absorption and scattering in photo-thermo-refractive glass induced by UV-exposure and thermal development

    NASA Astrophysics Data System (ADS)

    Lumeau, Julien; Glebova, Larissa; Glebov, Leonid B.

    2014-01-01

    Photo-thermo-refractive (PTR) glass is a multicomponent photosensitive silicate glass that, after successive UV-exposure and thermal treatment, exhibits a refractive index change that results from the precipitation of nano-crystalline NaF. This glass is successfully used for the fabrication of holographic optical elements (volume Bragg gratings) that dramatically enhance properties of numerous laser systems and spectrometers. In this paper, induced absorption and scattering that determine efficiency of such elements were studied. It is found that the main contribution to induced absorption is produced by several types of silver containing particles having absorption bands with maxima in the blue-green region with exponential tails extending to the near IR spectral region. Evolution of all absorption bands was studied for different conditions of UV exposure and thermal development. Complex mechanisms of interconversion of silver containing particles is demonstrated as well as the fact that some of these particles can be associated with catalyzers of the nucleation process. It is also found that induced scattering obeys the classic Rayleigh law with an intensity depending on the conditions of UV exposure and thermal development. For short development times, scattering increases with dosage because of increased volume fraction of crystalline phase. For long development times, scattering decreases with dosage because of decreased size of individual crystals.

  1. Negative thermal expansion induced by intermetallic charge transfer.

    PubMed

    Azuma, Masaki; Oka, Kengo; Nabetani, Koichiro

    2015-06-01

    Suppression of thermal expansion is of great importance for industry. Negative thermal expansion (NTE) materials which shrink on heating and expand on cooling are therefore attracting keen attention. Here we provide a brief overview of NTE induced by intermetallic charge transfer in A-site ordered double perovskites SaCu3Fe4O12 and LaCu3Fe4-x Mn x O12, as well as in Bi or Ni substituted BiNiO3. The last compound shows a colossal dilatometric linear thermal expansion coefficient exceeding -70 × 10(-6) K(-1) near room temperature, in the temperature range which can be controlled by substitution.

  2. Ferromagnetic ordering in Mn induced by thermal strain

    NASA Astrophysics Data System (ADS)

    Hwang, Younghun; Choi, Jeongyong; Hong, Soon Cheol; Cho, Sunglae; Han, Suk-Hee; Shin, Kyung-Ho; Jung, Myung-Wha

    2009-01-01

    We report that the thermal strain due to the thermal-expansion difference between a Mn film and a semiconductor substrate is strong enough to overcome the thermal energy for a paramagnetic (PM) state and also to break antiferromagnetic (AF) magnetic symmetry, inducing ferromagnetic (FM) ordering at high temperatures. A Mn film on GaAs (100) showed FM ordering up to 9000Å with a Curie temperature (TC) of over 750 K and a net magnetic moment of 0.33μB/Mn , instead of AF (Néel temperature, TN=95K ) and PM orderings in bulk.

  3. Peroxidase changes in barley induced by ionizing and thermal radiation.

    PubMed

    Sah, N K; Pramanik, S; Raychaudhuri, S S

    1996-01-01

    Thermal and ionizing (gamma-ray) radiations were used to induce damage to barley seeds (IB65). The activity and isozyme banding patterns of peroxidase were compared. It was found that both physical agents caused damage to barley seeds (as observed from seedling height), but their action on peroxidase activity is not similar. Gamma-Rays enhance peroxidase activity. Thermal radiation, on the other hand, tends to reduce it but fails to alter the number of peroxidase isozymes. It is conjectured that the pathways of damage by thermal and ionizing radiations are not the same.

  4. Optical cell with periodic resistive heating for the measurement of heat, mass, and thermal diffusions in liquid mixtures.

    PubMed

    Hartung, M; Köhler, W

    2007-08-01

    A new technique for the measurement of heat, mass, and thermal diffusions in liquids has been developed. Similar to laser induced dynamic gratings, a temperature grating is created in the sample. Thermal expansion transforms the temperature into a refractive-index grating, which is read by diffraction of a readout laser beam. In a multicomponent mixture an additional concentration grating is formed by thermal diffusion driven by the temperature gradients of the temperature grating. Differently to laser induced dynamic grating experiments we use Joule heating instead of optical heating. For that purpose we have built cuvettes which have a grating of transparent conducting strips on the inner side of one of their windows. If heated by an electric current a temperature grating will build up in the sample. Both the heat equation and the extended diffusion equation have been solved in two dimensions to allow for quantitative data analysis. Our apparatus and method of analysis have been validated by measurements of heat, mass, and thermal diffusions in pure and binary liquids. Heat diffusion can be correctly determined as was shown for pure toluene, pure dodecane, and the symmetric mixture of isobutylbenzene dodecane. Mass and thermal diffusions were studied in the three symmetric mixtures of dodecane, isobutylbenzene, and tetralin. The obtained diffusion and Soret coefficients agree with the literature values within the experimental errors. Uncompensated transient heating effects limit the resolution of the experimental technique.

  5. 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.

  6. Thermally induced currents in graphene-based heterostructure

    NASA Astrophysics Data System (ADS)

    Zeng, Minggang; Feng, Yuanping; Liang, Gengchiau

    2011-09-01

    We investigate thermally induced currents in a zigzag graphene nanoribbon (ZGNR) heterostructure, consisting of hydrogen-terminated ZGNR (ZGNR-H) and oxygen-terminated ZGNR (ZGNR-O), under different electronic and magnetic states. Compared to a pure ZGNR-H system, the heterostructure displays a considerably larger thermally induced current due to its asymmetric transmission spectrum. Moreover, the magnetized ZGNR-H/ZGNR-O shows spin filter and magnetoresistance effects, suggesting potential applications of the ZGNR-H/ZGNR-O heterostructures in thermoelectric and spintronics devices.

  7. Optical low coherence reflectometry for measuring a stationary Brillouin grating induced under uniform pumping in a short optical fiber

    NASA Astrophysics Data System (ADS)

    Takada, Kazumasa; Yasuno, Takahiro

    2017-01-01

    We demonstrate that valuable information on the distributed Brillouin spectra of an optical waveguide can be derived from a stationary Brillouin grating measurement under uniform pumping with optical low coherence reflectometry. We up-convert the frequencies of the probe and pump light waves by the Brillouin frequency and detect the Stokes light in the same way that we detect the Fresnel and Rayleigh backreflections in the fiber. The pump light wave that propagates toward the optical balanced mixer is blocked by using a polarization diversity technique and the distributed Brillouin gratings excited in an 82-cm long non-birefringent single mode fiber are measured at a spatial resolution of the order of 1 mm.

  8. Mechanical polishing to improve uniformity of beam sampling grating and its effects on laser-induced damage

    NASA Astrophysics Data System (ADS)

    Rao, Huanle; Liu, Zhengkun; Liu, Ying; Fu, Shaojun

    2012-01-01

    As an important optical element, beam sampling grating (BSG) is used in the terminal of inertial confinement fusion (ICF) drivers. It can provide a very slight sampling beam for the precision diagnosing of laser energy and wavefront distortion. However, in practice, its non-uniform diffraction efficiency seriously influences the accurate signal of sampling beam, and finally affects diagnostic ability. BSG is usually fabricated by holographic ion beam etched (HIBE) process. In this paper, a mechanical polishing processing technology was used to improve uniformity of the diffraction efficiency of BSG after HIBE. In the processing, cerium oxide (CeO2) was used to polish the local areas of grating where exhibit higher diffraction efficiency with the purpose of changing the depth of grating profile, and then they have similar efficiency with the surrounding areas. By iteration of the above process, BSG finally achieve the improved uniformity of diffraction efficiency over the area of a 430 x 430 mm2. The RMS of diffraction efficiency of BSG after mechanical polishing shows great reduction down to 4.8% as compared with that of the as-polished RMS of 21%. The effects of this processing on laser damage was characterized by the measuring the LIDT for the laser radiations of 355nm.

  9. Mechanical polishing to improve uniformity of beam sampling grating and its effects on laser-induced damage

    NASA Astrophysics Data System (ADS)

    Rao, Huanle; Liu, Zhengkun; Liu, Ying; Fu, Shaojun

    2011-11-01

    As an important optical element, beam sampling grating (BSG) is used in the terminal of inertial confinement fusion (ICF) drivers. It can provide a very slight sampling beam for the precision diagnosing of laser energy and wavefront distortion. However, in practice, its non-uniform diffraction efficiency seriously influences the accurate signal of sampling beam, and finally affects diagnostic ability. BSG is usually fabricated by holographic ion beam etched (HIBE) process. In this paper, a mechanical polishing processing technology was used to improve uniformity of the diffraction efficiency of BSG after HIBE. In the processing, cerium oxide (CeO2) was used to polish the local areas of grating where exhibit higher diffraction efficiency with the purpose of changing the depth of grating profile, and then they have similar efficiency with the surrounding areas. By iteration of the above process, BSG finally achieve the improved uniformity of diffraction efficiency over the area of a 430 x 430 mm2. The RMS of diffraction efficiency of BSG after mechanical polishing shows great reduction down to 4.8% as compared with that of the as-polished RMS of 21%. The effects of this processing on laser damage was characterized by the measuring the LIDT for the laser radiations of 355nm.

  10. Efficient Bragg gratings in phosphosilicate and germanosilicate photonic crystal fiber.

    PubMed

    Beugin, V; Bigot, L; Niay, P; Lancry, M; Quiquempois, Y; Douay, M; Mélin, G; Fleureau, A; Lempereur, S; Gasca, L

    2006-11-10

    We present ArF laser-induced dynamics of Bragg grating (BG) growths in phosphosilicate-doped or germanosilicate-doped core photonic crystal fibers (PCFs). To this end, we have adapted the technique of H2 loading, usually used in conventional fiber, to the case of microstructured fiber, allowing both the concentration of hydrogen in the PCFs to be kept nearly constant for the time of the exposure and the BG spectra to be easily recorded. We compared the characteristics of BG growths in the two types of PCF to those in conventional step-index fibers. We then conducted a study of the thermal stability of the BGs in PCFs through 30 min of isochronal annealing. At the same time we discuss the role played by the microstructuration and the doping with regard to the grating contrast and the Bragg wavelength stability.

  11. Efficient Bragg gratings in phosphosilicate and germanosilicate photonic crystal fiber

    NASA Astrophysics Data System (ADS)

    Beugin, V.; Bigot, L.; Niay, P.; Lancry, M.; Quiquempois, Y.; Douay, M.; Mélin, G.; Fleureau, A.; Lempereur, S.; Gasca, L.

    2006-11-01

    We present ArF laser-induced dynamics of Bragg grating (BG) growths in phosphosilicate-doped or germanosilicate-doped core photonic crystal fibers (PCFs). To this end, we have adapted the technique of H2 loading, usually used in conventional fiber, to the case of microstructured fiber, allowing both the concentration of hydrogen in the PCFs to be kept nearly constant for the time of the exposure and the BG spectra to be easily recorded. We compared the characteristics of BG growths in the two types of PCF to those in conventional step-index fibers. We then conducted a study of the thermal stability of the BGs in PCFs through 30 min of isochronal annealing. At the same time we discuss the role played by the microstructuration and the doping with regard to the grating contrast and the Bragg wavelength stability.

  12. 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.

  13. 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.

  14. Multilayer diffraction grating

    SciTech Connect

    Barbee, T.W., Jr.

    1988-10-18

    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 3000 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.

  15. Spatiotemporal Coherent Control of Thermal Excitations in Solids

    NASA Astrophysics Data System (ADS)

    Sander, M.; Herzog, M.; Pudell, J. E.; Bargheer, M.; Weinkauf, N.; Pedersen, M.; Newby, G.; Sellmann, J.; Schwarzkopf, J.; Besse, V.; Temnov, V. V.; Gaal, P.

    2017-08-01

    X-ray reflectivity measurements of femtosecond laser-induced transient gratings (TG) are applied to demonstrate the spatiotemporal coherent control of thermally induced surface deformations on ultrafast time scales. Using grazing incidence x-ray diffraction we unambiguously measure the amplitude of transient surface deformations with sub-Å resolution. Understanding the dynamics of femtosecond TG excitations in terms of superposition of acoustic and thermal gratings makes it possible to develop new ways of coherent control in x-ray diffraction experiments. Being the dominant source of TG signal, the long-living thermal grating with spatial period Λ can be canceled by a second, time-delayed TG excitation shifted by Λ /2 . The ultimate speed limits of such an ultrafast x-ray shutter are inferred from the detailed analysis of thermal and acoustic dynamics in TG experiments.

  16. Thermally induced fracture for core-veneered dental ceramic structures.

    PubMed

    Zhang, Zhongpu; Guazzato, Massimiliano; Sornsuwan, Tanapon; Scherrer, Susanne S; Rungsiyakull, Chaiy; Li, Wei; Swain, Michael V; Li, Qing

    2013-09-01

    Effective and reliable clinical uses of dental ceramics necessitate an insightful analysis of the fracture behaviour under critical conditions. To better understand failure characteristics of porcelain veneered to zirconia core ceramic structures, thermally induced cracking during the cooling phase of fabrication is studied here by using the extended finite element method (XFEM). In this study, a transient thermal analysis of cooling is conducted first to determine the temperature distributions. The time-dependent temperature field is then imported to the XFEM model for viscoelastic thermomechanical analysis, which predicts thermally induced damage and cracking at different time steps. Temperature-dependent material properties are used in both transient thermal and thermomechanical analyses. Three typical ceramic structures are considered in this paper, namely bi-layered spheres, squat cylinders and dental crowns with thickness ratios of either 1:2 or 1:1. The XFEM fracture patterns exhibit good agreement with clinical observation and the in vitro experimental results obtained from scanning electron microscopy characterization. The study reveals that fast cooling can lead to thermal fracture of these different bi-layered ceramic structures, and cooling rate (in terms of heat transfer coefficient) plays a critical role in crack initiation and propagation. By exploring different cooling rates, the heat transfer coefficient thresholds of fracture are determined for different structures, which are of clear clinical implication.

  17. High resolution temperature mapping of gas turbine combustor simulator exhaust with femtosecond laser induced fiber Bragg gratings

    NASA Astrophysics Data System (ADS)

    Walker, Robert B.; Yun, Sangsig; Ding, Huimin; Charbonneau, Michel; Coulas, David; Lu, Ping; Mihailov, Stephen J.; Ramachandran, Nanthan

    2017-04-01

    Femtosecond infrared (fs-IR) laser written fiber Bragg gratings (FBGs), have demonstrated great potential for extreme sensing. Such conditions are inherent in advanced gas turbine engines under development to reduce greenhouse gas emissions; and the ability to measure temperature gradients in these harsh environments is currently limited by the lack of sensors and controls capable of withstanding the high temperature, pressure and corrosive conditions present. This paper discusses fabrication and deployment of several fs-IR written FBG arrays, for monitoring exhaust temperature gradients of a gas turbine combustor simulator. Results include: contour plots of measured temperature gradients, contrast with thermocouple data.

  18. 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.

  19. Fabrication, measurement, and analysis of multilayer x- ray diffraction gratings

    NASA Astrophysics Data System (ADS)

    Hansen, Douglas P.

    1997-12-01

    I examine the theory and fabrication of lamellar multilayer x-ray diffraction gratings. I use current theory based on the Kirchoff Integral for amplitude gratings and a new equation for phase gratings to analyze current technology multilayer grating performance (where the period/λ exceeds 10). I examine the possible fabrication methods and define two general categories (additive: multilayer added to patterned substrate, subtractive: grating etched into multilayer). I conclude the additive approach is superior, leading to x-ray analogues to binary optics and holographic optical elements. I define an additive process in detail and demonstrate the serviceability of the key processes: thermal growth of silicon dioxide on silicon, lithography, a combined plasma-etch and wet-etch. Multilayer fabrication difficulties on patterned substrates are identified, including: mushroom cap growth, and filleting in the grooves. Measurements done at NSLS on 2 amplitude gratings and 1 phase grating are reported. The data is shown to be compatible with the Kirchoff theory.

  20. Photon-induced thermal effects in superconducting coplanar waveguide resonators

    NASA Astrophysics Data System (ADS)

    Wang, Yiwen; Zhou, Pinjia; Wei, Lianfu; Li, Haijie; Zhang, Beihong; Zhang, Miao; Wei, Qiang; Fang, Yurong; Cao, Chunhai

    2013-10-01

    We experimentally investigated the optical responses of a superconducting niobium resonator. It was found that, with increasing radiation power, the resonance frequency increases monotonically below around 500 mK, decreases monotonically above around 1 K, and exhibits a nonmonotonic behavior at around 700 mK. These observations show that one can operate the irradiated resonator in three temperature regimes, depending on whether two-level system (TLS) effects or kinetic inductance effects dominate. Furthermore, we found that the optical responses at ultra-low temperatures can be qualitatively regarded as a photon-induced thermalization effect of TLSs, which could be utilized to achieve thermal sensitive photon detections.

  1. Influence of absorption induced thermal initiation pathway on irradiance threshold for laser induced breakdown

    PubMed Central

    Varghese, Babu; Bonito, Valentina; Jurna, Martin; Palero, Jonathan; Verhagen, Margaret Hortonand Rieko

    2015-01-01

    We investigated the influence of thermal initiation pathway on the irradiance threshold for laser induced breakdown in transparent, absorbing and scattering phantoms. We observed a transition from laser-induced optical breakdown to laser-induced thermal breakdown as the absorption coefficient of the medium is increased. We found that the irradiance threshold after correction for the path length dependent absorption and scattering losses in the medium is lower due to the thermal pathway for the generation of seed electrons compared to the laser-induced optical breakdown. Furthermore, irradiance threshold gradually decreases with the increase in the absorption properties of the medium. Creating breakdown with lower irradiance threshold that is specific at the target chromophore can provide intrinsic target selectivity and improve safety and efficacy of skin treatment methods that use laser induced breakdown. PMID:25909007

  2. Twist Sensitivity of Cladding-Mode Resonances and Its Cross-Sensitivity to Strain and Temperature in a Mechanically Induced Long-Period Fiber Grating

    NASA Astrophysics Data System (ADS)

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

    2014-09-01

    Twist sensitivity of cladding-mode resonances in a mechanically induced long-period fiber grating formed over a single-mode fiber is experimentally demonstrated and theoretically analyzed. Of the two usual cladding-mode resonances corresponding to LP11 and LP12, higher-order mode LP12 is more sensitive to twist in comparison with the lower-order mode LP11. The extent of down-shifting of resonant wavelengths depends on twist-induced circular birefringence and the modal field distribution of the cladding-modes inside the fiber. When the fiber is severely twisted to 3.5 rad/cm, a shift sensitivity is observed of 1 nm/(rad/cm) for the LP11 mode and 4.23 nm/(rad/cm) for the LP12 mode. The fiber breaks when the twist rate exceeds 3.5 rad/cm. In comparison with LP12, the LP11 resonance is almost independent of the axial strain variation with an ultra-low sensitivity of 0.18 pm/με, and it is also almost insensitive to the temperature variation with a coefficient of 35 pm/°C. Forming the LP11 resonance far away from its cut-off wavelength, a widely tunable band-pass filter is also demonstrated with a very high twist sensitivity of 8.75 nm/(rad/cm) and negligible cross-sensitivity to strain and temperature. The experimental and theoretical results are very useful in selecting sensitive and stable cladding-mode resonances in the design of new mechanically induced long-period fiber gratings based torsion sensors and tunable band-pass filters.

  3. Thermal Effects Induced by Laser Irradiation of Solids

    SciTech Connect

    Galovic, S.

    2004-12-01

    A part of incident energy is absorbed within the irradiated sample when a solid is exposed to the influence of laser radiation, to more general electromagnetic radiation within the wide range of wavelengths (from microwaves, to infrared radiation to X-rays), or to the energy of particle beams (electronic, protonic, or ionic). The absorption process signifies a highly selective excitation of the electronic state of atoms or molecules, followed by thermal and non-thermal de-excitation processes. Non-radiation de-excitation-relaxation processes induce direct sample heating. In addition, a great number of non-thermal processes (e.g., photoluminescence, photochemistry, photovoltage) may also induce heat generation as a secondary process. This method of producing heat is called the photothermal effect.The photothermal effect and subsequent propagation of thermal waves on the surface and in the volume of the solid absorbing the exciting beam may produce the following: variations in the temperature on the surfaces of the sample; deformation and displacement of surfaces; secondary infrared radiation (photothermal radiation); the formation of the gradient of the refractivity index; changes in coefficients of reflection and absorbtion; the generation of sound (photoacoustic generation), etc. These phenomena may be used in the investigation and measurement of various material properties since the profile and magnitude of the generated signal depend upon the nature of material absorbing radiation. A series of non-destructive spectroscopic, microscopic and defectoscopic detecting techniques, called photothermal methods, is developed on the basis of the above-mentioned phenomena.This paper outlines the interaction between the intensity modulated laser beam and solids, and presents a mathematical model of generated thermal sources. Generalized models for a photothermal response of optically excited materials have been obtained, including thermal memory influence on the propagation

  4. Catwalk grate lifting tool

    DOEpatents

    Gunter, Larry W.

    1992-01-01

    A device for lifting catwalk grates comprising an elongated bent member with a handle at one end and a pair of notched braces and a hook at the opposite end that act in conjunction with each other to lock onto the grate and give mechanical advantage in lifting the grate.

  5. Catwalk grate lifting tool

    DOEpatents

    Gunter, L.W.

    1992-08-11

    A device is described for lifting catwalk grates comprising an elongated bent member with a handle at one end and a pair of notched braces and a hook at the opposite end that act in conjunction with each other to lock onto the grate and give mechanical advantage in lifting the grate. 10 figs.

  6. 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.

  7. Negative thermal expansion induced by intermetallic charge transfer

    PubMed Central

    Azuma, Masaki; Oka, Kengo; Nabetani, Koichiro

    2015-01-01

    Suppression of thermal expansion is of great importance for industry. Negative thermal expansion (NTE) materials which shrink on heating and expand on cooling are therefore attracting keen attention. Here we provide a brief overview of NTE induced by intermetallic charge transfer in A-site ordered double perovskites SaCu3Fe4O12 and LaCu3Fe4−xMnxO12, as well as in Bi or Ni substituted BiNiO3. The last compound shows a colossal dilatometric linear thermal expansion coefficient exceeding −70 × 10−6 K−1 near room temperature, in the temperature range which can be controlled by substitution. PMID:27877801

  8. Domes on Europa: The Role of Thermally Induced Compositional Diapirism

    NASA Technical Reports Server (NTRS)

    Pappalardo, R. T.; Barr, A.C.

    2004-01-01

    The surface of Europa is peppered by topographic domes, interpreted as sites of intrusion and extrusion. Diapirism is consistent with dome morphology, but thermal buoyancy alone cannot produce sufficient driving pressures to create the observed dome elevations. Instead, we suggest that diapirs may initiate by thermal convection that induces compositional segregation within Europa's ice shell. This double-diffusive convection scenario allows sufficient buoyancy for icy plumes to create the observed surface topography, if the ice shell has a very small effective elastic thickness (approximately 0.1 to 0.5 km) and contains low-eutectic-point impurities at the percent level. Thermal buoyancy, compositional buoyancy and double-diffusive convection are discussed.

  9. Development of Aspherical Active Gratings at NSRRC

    SciTech Connect

    Tseng, T.-C.; Wang, D.-J.; Perng, S.-Y.; Chen, C.-T.; Lin, C.-J.; Kuan, C.-K.; Ho, H.-C.; Wang, J.; Fung, H.S.; Chang, S.-H.

    2007-01-19

    An active grating based on a novel optical concept with bendable polynomial surface profile to reduce the coma and defocus aberrations had been designed and proved by the prototype testing. Due to the low glass transition temperature of the glue and the difference of thermal expansion coefficient between the 17-4 steel bender and silicon, the prototype distorted from flat polished condition when thermally de-blocked the polishing pitch. To improve the thermal deformation of the active grating in the polishing process, a new invar bender and high curing temperature glue were adapted to glue a silicon substrate on the bender. After some tests and manufacturer polishing, it showed acceptable conditions. In this paper we will present the design and preliminary tests of the invar active grating. Meanwhile, the design and analysis of a new 17-4 PH steel bender to be electro-less nickel plating and mechanical ruling for a new beamline will also be discussed.

  10. Development of Aspherical Active Gratings at NSRRC

    NASA Astrophysics Data System (ADS)

    Tseng, Tse-Chuan; Wang, Duan Jen; Perng, Shen-Yaw; Chen, Chien-Te; Lin, Chia-Jui; Kuan, Chien-Kuang; Ho, His-Chou; Wang, Jeremy; Fung, H. S.; Chang, Shuo-Hung

    2007-01-01

    An active grating based on a novel optical concept with bendable polynomial surface profile to reduce the coma and defocus aberrations had been designed and proved by the prototype testing. Due to the low glass transition temperature of the glue and the difference of thermal expansion coefficient between the 17-4 steel bender and silicon, the prototype distorted from flat polished condition when thermally de-blocked the polishing pitch. To improve the thermal deformation of the active grating in the polishing process, a new invar bender and high curing temperature glue were adapted to glue a silicon substrate on the bender. After some tests and manufacturer polishing, it showed acceptable conditions. In this paper we will present the design and preliminary tests of the invar active grating. Meanwhile, the design and analysis of a new 17-4 PH steel bender to be electro-less nickel plating and mechanical ruling for a new beamline will also be discussed.

  11. Temperature-induced transient noise of pyroelectric thermal detector

    NASA Astrophysics Data System (ADS)

    Lee, Muno; Bae, Seong-Ho

    2000-11-01

    An analysis of temperature-induced transient noise for a thermal detector prepared with Pb(Zr,Ti)O3-Pb(Sb0.5Nb0.5)O3 (PZT-PSN) pyroelectric ceramics as the sensing element is conducted by measuring its oven noise as a function of the junction field-effect transistor (JFET) characteristics, gate resistance, low-temperature heat treatment, chemical composition and the grain size of the pyroelectric ceramic. Pyroelectric wafers are prepared by the mixed oxide technique, and thermal sensors are fabricated with a PZT-PSN ceramic wafer, JFET, chip-type gate resistor, alumina PCB (printed circuit board) and a TO- 5 package with antireflective (AR)-coated Si window. Thermal detector noise depends on the chemical composition of the pyroelectric sensing element. The temperature-induced transient JFET noise varies with its characteristics and gate resistance and is reduced by connecting a pyroelectric sensing element with high capacitance. The pyroelectric ceramic sensing element generates burst noise in the region from 7 to -10 degree(s)C during cooling, which is remarkably reduced by reducing the grain size of the pyroelectric ceramic and/or by cyclic heat treatment at a low temperature. Thus, burst noise as a strong relationship with the elastic energies within the ceramic sensing element and the bonding material between the sensing wafer and the PCB, originating in the different thermal expansion between pyroelectric sensing wafer and alumina PCB.

  12. 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.

  13. 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.

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

    NASA Astrophysics Data System (ADS)

    Tompkins, Stephen S.

    1994-07-01

    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.

  15. 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.

  16. Incoherent combining of 100-W Yb-fiber laser beams by PTR Bragg grating

    NASA Astrophysics Data System (ADS)

    Ciapurin, Igor V.; Glebov, Leonid B.; Glebova, Larissa N.; Smirnov, Vadim I.; Rotari, Eugeniu V.

    2003-07-01

    Volume diffractive gratings (Bragg gratings) in photo-thermo-refractive (PTR) inorganic glass are proposed for incoherent laser beam combining because they have narrow spectral selectivity and diffraction efficiency greater than 95% from visible to near IR regions. They showed no laser-induced damage, no thermal lens, and no Bragg angle shift under CW Yb-fiber laser (1096 nm) irradiation at 100 kW/cm2. It opens the way to rugged, low-cost, efficient optics for high-power laser systems. Based on theoretical modeling of PTR Bragg gratings, we have designed a high-efficient technology for incoherent combining of two or several laser beams with certain wavelength shift. Two 100 W beams of Yb-fiber lasers in the range of 1080-1100 nm with the wavelength separation of 11 nm were combined with efficiency exceeding 75% while material losses did not exceed 2-4%. No fading or parameter change of PTR Bragg grating working in two 100 W beams were found. It was found that the process limiting efficiency of incoherent beam combining is the spectral widening of radiation of Yb-doped fiber lasers. At high power, their spectral width exceeds spectral selectivity of Bragg grating and causes a decrease of diffraction efficiency.

  17. 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.

  18. 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.

  19. 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

  20. 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.

  1. Cell membrane thermal gradients induced by electromagnetic fields

    NASA Astrophysics Data System (ADS)

    Garner, Allen L.; Deminsky, Maxim; Bogdan Neculaes, V.; Chashihin, V.; Knizhnik, Andrey; Potapkin, Boris

    2013-06-01

    While electromagnetic fields induce structural changes in cell membranes, particularly electroporation, much remains to be understood about membrane level temperature gradients. For instance, microwaves induce cell membrane temperature gradients (∇T) and bioeffects with little bulk temperature change. Recent calculations suggest that nanosecond pulsed electric fields (nsPEFs) may also induce such gradients that may additionally impact the electroporation threshold. Here, we analytically and numerically calculate the induced ∇T as a function of pulse duration and pulse repetition rate. We relate ∇T to the thermally induced cell membrane electric field (Em) by assuming the membrane behaves as a thermoelectric such that Em ˜ ∇T. Focusing initially on applying nsPEFs to a uniform membrane, we show that reducing pulse duration and increasing pulse repetition rate (or using higher frequency for alternating current (AC) fields) maximizes the magnitude and duration of ∇T and, concomitantly, Em. The maximum ∇T initially occurs at the interface between the cell membrane and extracellular fluid before becoming uniform across the membrane, potentially enabling initial molecular penetration and subsequent transport across the membrane. These results, which are equally applicable to AC fields, motivate further studies to elucidate thermoelectric behavior in a model membrane system and the coupling of the Em induced by ∇T with that created directly by the applied field.

  2. 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.

  3. Self-induced thermal distortion effects on target image quality.

    PubMed

    Gebhardt, F G

    1972-06-01

    Experimental results are reported that show the effects of the self-induced thermal lens due to a high power laser beam on imaging or tracking systems viewing along the same propagation path. The thermal distortion effects of a wind are simulated with a low power ( less, similar 3-W) CO(2) laser beam propagating through a cell of liquid CS(2) moving across the beam. The resulting image distortion includes a warping effect analogous to the deflection of the CO(2) beam, together with a pronounced demagnification of the central portion of the object. An active optical tracker is simulated with a He-Ne laser beam propagating collinearly with the CO(2) beam. The He-Ne beam pattern returned from a specular target is distorted and sharply confined to the outline of the crescent shaped CO(2) beam. Simple ray optics models are used to provide qualitative explanations for the experimental results.

  4. Long period grating response to gamma radiation

    NASA Astrophysics Data System (ADS)

    Sporea, Dan; Stǎncalie, Andrei; Neguţ, Daniel; Delepine-Lesoille, Sylvie; Lablonde, Laurent

    2016-04-01

    We report the evaluation of one long period grating (LPG) and one fiber Bragg grating (FBG) under gamma irradiation. The LPG was produced by the melting-drawing method based on CO2 laser assisted by a micro-flame and was engraved in a commercial single mode fiber SMF28 from Corning, grating length 25 mm, grating pitch of 720 μm. After the manufacturing of the grating, the fiber was re-coated with Acrylate and the grating was inserted into special ceramic case transparent to gamma radiation. The FBG is commercialized by Technica SA, and it is written in SMF-28 optical fiber (λ= 1546 nm; grating length of 12 mm; reflectivity > 80 %; bandwidth - BW @3 dB < 0.3 nm; side lobe suppress ratio - SLSR >15 dB; Acrylate recoating). By on-line monitoring of the LPG wavelength deep with an optical fiber interrogator during the irradiation exposure and pauses, both the irradiation induced shift (maximum 1.45 nm) and the recovery (in the range of 200 pm) phenomena were observed. Temperature sensitivity of the LPS was not affected by gamma irradiation.

  5. Multiplexed volume Bragg gratings for spectral beam combining of high power fiber lasers

    NASA Astrophysics Data System (ADS)

    Divliansky, Ivan; Ott, Daniel; Anderson, Brian; Drachenberg, Derrek; Rotar, Vasile; Venus, George; Glebov, Leonid

    2012-02-01

    The recent development of kW fiber laser sources makes the concept of laser systems operating at power levels from tens of kilowatts up to 100-kilowatt levels a reality. The use of volume Bragg gratings for spectral beam combining is one approach to achieve that goal. To make such systems compact, lower the complexity and minimize the induced thermal distortions we propose and demonstrate the use of special volume Bragg elements which have several Bragg gratings written inside as combining optical components. The multiplexed volume Bragg gratings (MVBGs) were recorded in photo-thermo refractive glass and three beams with total power of 420 W were successfully combined using one MVBG. The combining efficiency was 97% and there was no significant beam quality degradation. The results demonstrated that the approach of using multiplexed volume Bragg gratings for spectral beam combining is an excellent extension to the current state of the art combining techniques. Especially valuable is the capability to reduce the number of optical elements in the system and while being able to manage the expected thermal load when kilowatt level sources are used for beam combining.

  6. Imaging laser-induced thermal fields and effects

    NASA Astrophysics Data System (ADS)

    Verdaasdonck, Rudolf M.

    1995-05-01

    Laser light interaction with biological tissues is a combination of optical, thermal and mechanical effects depending on the energy applied per unit of volume per unit of time. Visualization of the phenomena with a high temporal and spatial resolution, contributes to a better understanding of the mechanism of action, especially when pulsed lasers are involved. For this goal, setups were developed based on Schlieren techniques to image the interaction of pulsed (CO2, Holmium and Excimer) and CW (CO2, Nd:YAG, Cu-vapor) lasers with physiological media and biological tissues. In a 'fast' Schlieren setup, images of shock waves and fast expanding and imploding vapor bubbles were captured using very short light flashes (10 ns-10 microseconds). These recordings suggest that these explosive vapor bubbles seem to be the main dynamism for tissue ablation. In a 'color' Schlieren setup, very small changes in optical density of the media induced by temperature gradients, were color coded. Calibration of the color images to absolute temperatures were performed by using calculated temperature distributions and by thermocouple measurements. Cameras with high speed shutters (0.1-50 ms) enabled the recording of dynamic images of the thermal relaxation and heat diffusion in tissues during variation of pulse length and repetition rate. Despite pulse lengths < ms, heat generation in tissue was considerable already at pulse repetition rates above a few Hz. Similar Schlieren techniques were applied to study the thermal characteristics of laser probes, e.g. for the treatment of Benign Prostatic Hyperplasia (BPH). In combination with thermal modeling an optimal therapy might be predicted. Schlieren techniques, generating high-speed and 'thermal' images, can provide a good understanding of the ablation mechanism and the thermo-dynamics during laser-tissue interaction with continuous wave and pulse lasers.

  7. 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.

  8. Biopolymer holographic diffraction gratings

    NASA Astrophysics Data System (ADS)

    Savić Šević, Svetlana; Pantelić, Dejan

    2008-03-01

    Surface-relief diffraction gratings are holographically recorded in dextran sensitized with ammonium dichromate (DCD). DCD was exposed with single-frequency 200 mW diode pumped ND-YAG laser, at 532 nm. The diffraction grating profiles were analyzed by atomic force microscopy (AFM). It was found that different surface profiles could be obtained. Gratings with 330 lines/mm spatial frequencies were made. Existence of higher harmonics in Fourier Transform of non-sinusoidal profiles shows that DCD is capable of recording spatial frequencies up to 1320 lines/mm (four times fundamental frequency). The measured maximum relief depth of the DCD grating is 402 nm.

  9. 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.

  10. Fast fiber-optic tunable filter based on axial compression on a fiber Bragg grating.

    PubMed

    Zu, Wen; Gu, Xijia

    2006-09-01

    We describe the design, fabrication, and performance of a fiber Bragg grating-based tunable optic filter. The filter, driven by two piezostacks, consists of a flexural hinge structure for displacement magnification and a fiber-ferrule assembly for axial compression of the fiber grating. Finite-element analysis was used to design the mechanical structure to achieve the required displacement magnification and the force for grating compression. A passive thermal compensation design was implemented to reduce thermal-induced wavelength drift. A feedback control system with a linear variable differential transformer was employed to control the displacement for accurate wavelength tuning and fine-tuning resolution. This tunable filter has achieved a closed-loop switching time of 17.3 ms, and a passive thermal compensation that reduced the thermal drift of the Bragg wavelength to 1.5 pm/C. The flexural-hinge structure that offers negligible backlash, noise-free motion, no need of lubricants, and no wear ensures its long-term reliability.

  11. Dual-twist fiber long period gratings

    NASA Astrophysics Data System (ADS)

    Churikov, Victor M.; Kopp, Victor I.; Genack, A. Z.

    2009-02-01

    Long period fiber gratings couple core and co-propagating cladding modes to produce dips in the transmission spectrum and have been widely utilized as sensors and filters. We have recently developed a new approach to long period fiber gratings utilizing optical fibers, which are uniformly twisted at elevated temperatures to produce double or single helices. Because these fibers are not manufactured by exposing photosensitive glass to patterned UV illumination, as is the case for traditional fiber Bragg gratings (FBGs) or long period gratings (LPGs), they are more robust in harsh thermal and chemical environments. Double helix fibers are polarization sensitive and are fabricated by twisting fiber preforms with high-index noncircular cores while single helix gratings are polarization insensitive and are created by twisting standard optical fibers with cores that are not perfectly centered. Here, we present a new approach to single-helix chiral long-period gratings (CLPGs). The CLPG is created in a glassforming process in which two optical fibers are twisted together to form a helix in the signal fiber as the fibers pass through a miniature oven. "Dual-twist" CLPGs may be fabricated from any conventional or specialty fiber and provide reproducible spectra that may be tailored to specific applications.

  12. 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.

  13. 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.

  14. 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.

  15. Laser-induced thermal desorption of aniline from silica surfaces

    NASA Astrophysics Data System (ADS)

    Voumard, Pierre; Zenobi, Renato

    1995-10-01

    A complete study on the energy partitioning upon laser-induced thermal desorption of aniline from silica surfaces was undertaken. The measurements include characterization of the aniline-quartz adsorption system using temperature-programmed desorption, the extrapolation of quasiequilibrium desorption temperatures to the regime of laser heating rates on the order of 109-1010 K/s by computational means, measurement of the kinetic energy distributions of desorbing aniline using a pump-probe method, and the determination of internal energies with resonance-enhanced multiphoton ionization spectroscopy. The measurements are compared to calculations of the surface temperature rise and the resulting desorption rates, based on a finite-difference mathematical description of pulsed laser heating. While the surface temperature of laser-heated silica reaches about 600-700 K at the time of desorption, the translational temperature of laser-desorbed aniline was measured to be Tkin=420±60 K, Tvib was 360±60 K, and Trot was 350±100 K. These results are discussed using different models for laser-induced thermal desorption from surfaces.

  16. 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.

  17. Apodized Volume Bragg Gratings

    NASA Astrophysics Data System (ADS)

    Mokhov, Sergiy

    2015-03-01

    Reflective and transmissive volume Bragg grating (VBGs) are widely used in high power laser applications because of their large operational aperture and robustness. They are fabricated in photosensitive material through holographic recording of uniform interference pattern of two overlapping coherent waves obtained by splitting a flat-top shaped laser beam. The following thermal treatment produces permanent refractive index modulation (RIM). Reflective VBGs have fringes parallel to operational anti-reflective coated surfaces and they demonstrate narrow reflection bandwidth. Transmissive VBGs are cut with fringes perpendicular to surfaces and they are characterized by narrow angular selectivity. Uniform RIM causes secondary lobes in corresponding reflection and transmission spectra due to sharp boundary conditions for volume Bragg diffraction. We propose to create apodization of RIM by recording two interference patterns with slightly different parameters in the same volume which would create slow varying moire envelope of amplitude of RIM. Cutting the specimen at zeros of moire envelope with one sine semi-period thickness will produce VBGs apodized at sides which will reduce parasitic secondary lobes in spectra. In reflection geometry, two patterns of the same orientation with slightly different periods are required for apodization along Bragg wave vector. In transmission case, recording of the same interference patterns with small mutual rotation angle provides apodization in direction perpendicular to Bragg wave vector. Modeling results show significant improvement in selective properties of VBGs with such moire apodization.

  18. Bragg Grating Simulation Software

    DTIC Science & Technology

    2008-02-01

    Organisation DSTO-TN-0800 ABSTRACT (U) This document is a user manual for a software application that predicts the complex reflection spectrum of...fibre Bragg gratings, given user defined input parameters. The software is designed primarily to complement the joint DSTO/Swinburne grating writing

  19. Thermal-Performance Instability in Piezoresistive Sensors: Inducement and Improvement

    PubMed Central

    Liu, Yan; Wang, Hai; Zhao, Wei; Qin, Hongbo; Fang, Xuan

    2016-01-01

    The field of piezoresistive sensors has been undergoing a significant revolution in terms of design methodology, material technology and micromachining process. However, the temperature dependence of sensor characteristics remains a hurdle to cross. This review focuses on the issues in thermal-performance instability of piezoresistive sensors. Based on the operation fundamental, inducements to the instability are investigated in detail and correspondingly available ameliorative methods are presented. Pros and cons of each improvement approach are also summarized. Though several schemes have been proposed and put into reality with favorable achievements, the schemes featuring simple implementation and excellent compatibility with existing techniques are still emergently demanded to construct a piezoresistive sensor with excellent comprehensive performance. PMID:27886125

  20. 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.

  1. Charge-induced optical bistability in thermal Rydberg vapor

    NASA Astrophysics Data System (ADS)

    Weller, Daniel; Urvoy, Alban; Rico, Andy; Löw, Robert; Kübler, Harald

    2016-12-01

    We investigate the phenomenon of optical bistability in a driven ensemble of Rydberg atoms. By performing two experiments with thermal vapors of rubidium and cesium, we are able to shed light on the underlying interaction mechanisms causing such a nonlinear behavior. Due to the different properties of these two atomic species, we conclude that the large polarizability of Rydberg states in combination with electric fields of spontaneously ionized Rydberg atoms is the relevant interaction mechanism. In the case of rubidium, we directly measure the electric field in a bistable situation via two-species spectroscopy. In cesium, we make use of the different sign of the polarizability for different l states and the possibility of applying electric fields. Both these experiments allow us to rule out dipole-dipole interactions and support our hypothesis of a charge-induced bistability.

  2. 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.

  3. Microscopic calculation of thermally induced spin-transfer torques

    NASA Astrophysics Data System (ADS)

    Kohno, Hiroshi; Hiraoka, Yuuki; Hatami, Moosa; Bauer, Gerrit E. W.

    2016-09-01

    Spin-transfer torques, both reactive and dissipative, induced by temperature gradients in conducting ferromagnets are calculated microscopically for smooth magnetization textures. Temperature gradients are treated à la Luttinger by introducing a fictitious gravitational field that couples to the energy density. The thermal torque coefficients obtained by the Kubo formula contain unphysical terms that diverge towards zero temperature. Such terms are caused by equilibrium components and should be subtracted before applying the Einstein-Luttinger relation. Only by following this procedure a familiar Mott-like formula is obtained for the dissipative spin-transfer torque. The result indicates that a fictitious field that couples to the entropy rather than energy would solve the issue from the outset.

  4. 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.

  5. Thermal-Performance Instability in Piezoresistive Sensors: Inducement and Improvement.

    PubMed

    Liu, Yan; Wang, Hai; Zhao, Wei; Qin, Hongbo; Fang, Xuan

    2016-11-24

    The field of piezoresistive sensors has been undergoing a significant revolution in terms of design methodology, material technology and micromachining process. However, the temperature dependence of sensor characteristics remains a hurdle to cross. This review focuses on the issues in thermal-performance instability of piezoresistive sensors. Based on the operation fundamental, inducements to the instability are investigated in detail and correspondingly available ameliorative methods are presented. Pros and cons of each improvement approach are also summarized. Though several schemes have been proposed and put into reality with favorable achievements, the schemes featuring simple implementation and excellent compatibility with existing techniques are still emergently demanded to construct a piezoresistive sensor with excellent comprehensive performance.

  6. Substrate-induced reduction of graphene thermal conductivity

    NASA Astrophysics Data System (ADS)

    Koniakhin, S. V.; Utesov, O. I.; Terterov, I. N.; Nalitov, A. V.

    2017-01-01

    We develop a theory of heat conductivity in supported graphene, accounting for coherent phonon scattering on disorder induced by an amorphous substrate. We derive spectra for in-plane and out-of-plane phonons in the framework of Green's function approach. The energy parameters of the theory are obtained using molecular dynamics simulations for graphene on a SiO2 substrate. The heat conductivity is calculated by the Boltzmann transport equation. We find that the interaction with the substrate drastically reduces the phonon lifetime and completely suppresses the contribution of flexural (ZA) phonons to the heat conductivity. As a result, the total heat conductivity is reduced by several times, which matches with the tendency observed in the available experimental data. The considered effect is important for managing the thermal properties of graphene-based electronic devices.

  7. Unidirectional thermal effects in current-induced domain wall motion.

    PubMed

    Torrejon, J; Malinowski, G; Pelloux, M; Weil, R; Thiaville, A; Curiale, J; Lacour, D; Montaigne, F; Hehn, M

    2012-09-07

    We report experimental evidence of thermal effects on the displacement of vortex walls in NiFe nanostrips. With the use of nanosecond current pulses, a unidirectional motion of the magnetic domain walls towards the hotter part of the nanostrips is observed, in addition to current-induced domain wall motion. By tuning the heat dissipation in the samples and modeling the heat diffusion, we conclude that this unidirectional motion can only be explained by the presence of a temperature profile along the nanostrip. A quantitative analysis of the experiments shows that, on top of the classical thermodynamic pressure on the domain wall, another force, probably the magnonic spin Seebeck effect, is displacing the domain walls.

  8. Spontaneous thermally-induced delamination of polymer films

    NASA Astrophysics Data System (ADS)

    Kohli, Punit; Jiao, Kexin; Zhou, Chuanhong; Wynne, Jared; Poude, Anish; Chu, Philip; Chemistry; Biochemistry Collaboration; Mechanical Engineering Collaboration

    In this talk, we will discuss spontaneous thermally-induced biaxial delamination of thin polymer films from flat surfaces. The delamination results in the formation of ultra-high aspect ratio (up to 1000) of micro-ribbons of polydimethylsiloxane. The thickness, width, and length of the micro-ribbons is about 10 μm, 100 μm, and up to many centimeter respectively. We will demonstrate that the formation of polymer micro-ribbons can be experimentally controlled. Specifically, the thickness and mechanical properties of polymer, and geometrical and physical properties of the substrate played crucial roles in defining the delamination process. From the practical viewpoint, we demonstrate the use of the micro-ribbons for imaging and separation applications. NSF, NIH, and SIUC.

  9. 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.

  10. 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.

  11. 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.

  12. Dynamic studies of holographic gratings in dye-doped liquid-crystal films.

    PubMed

    Fuh, A Y; Liao, C C; Hsu, K C; Lu, C L; Tsai, C Y

    2001-11-15

    The dynamic behavior of a holographic grating induced in a homeotropically aligned dye-doped liquid-crystal film is investigated. In the presence of an applied dc voltage, photoexcited azo dyes induce a photorefractive grating and then diffuse and are adsorbed onto cell substrates. The reorientation of liquid crystals as a result of adsorbed dyes leads to a phase grating that is phase shifted 90 degrees from the photorefractive grating. Competition of these two gratings induces two-beam coupling of the writing beams, initially transferring energy from beam 1 to beam 2 and then, after a pause, from beam 2 to beam 1.

  13. Aluminum nitride grating couplers.

    PubMed

    Ghosh, Siddhartha; Doerr, Christopher R; Piazza, Gianluca

    2012-06-10

    Grating couplers in sputtered aluminum nitride, a piezoelectric material with low loss in the C band, are demonstrated. Gratings and a waveguide micromachined on a silicon wafer with 600 nm minimum feature size were defined in a single lithography step without partial etching. Silicon dioxide (SiO(2)) was used for cladding layers. Peak coupling efficiency of -6.6 dB and a 1 dB bandwidth of 60 nm have been measured. This demonstration of wire waveguides and wideband grating couplers in a material that also has piezoelectric and elasto-optic properties will enable new functions for integrated photonics and optomechanics.

  14. 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).

  15. 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)

  16. 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

  17. 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.

  18. Visualization of fiber Bragg gratings of type II induced by radiation of an ArF excimer laser in an anisotropic single-mode optical fiber with an elliptical stress cladding

    NASA Astrophysics Data System (ADS)

    Gribaev, A. I.; Varzhel, S. V.; Petrov, A. A.; Palandzhyan, D. A.; Konnov, K. A.

    2017-07-01

    results in visualization of fiber Bragg gratings of type II recorded in birefringent single-mode optical fibers with an elliptical stress cladding with a high concentration of germanium dioxide are shown. Periodic structures of the induced refractive index are inscribed by a single pulse of an excimer laser with a working- gas mixture of ArF using the phase mask. Fiber Bragg gratings into anisotropic optical fiber were investigated by optical and scanning-probe microscopes. It is shown that single-pulse recording by ArF excimer laser creates in the fiber, both inside and on the surface of the quartz cladding, periodic structures, the spatial period of which corresponds to the period of the phase mask, optimized for the +1/-1 diffraction order.

  19. Tunable resonance-domain diffraction gratings based on electrostrictive polymers.

    PubMed

    Axelrod, Ramon; Shacham-Diamand, Yosi; Golub, Michael A

    2017-03-01

    Critical combination of high diffraction efficiency and large diffraction angles can be delivered by resonance-domain diffractive optics with high aspect ratio and wavelength-scale grating periods. To advance from static to electrically tunable resonance-domain diffraction grating, we resorted to its replication onto 2-5 μm thick P(VDF-TrFE-CFE) electrostrictive ter-polymer membranes. Electromechanical and optical computer simulations provided higher than 90% diffraction efficiency, a large continuous deflection range exceeding 20°, and capabilities for adiabatic spatial modulation of the grating period and slant. A prototype of the tunable resonance-domain diffraction grating was fabricated in a soft-stamp thermal nanoimprinting process, characterized, optically tested, and provided experimental feasibility proof for the tunable sub-micron-period gratings on electrostrictive polymers.

  20. 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.

  1. Grating Beam Combiner.

    DTIC Science & Technology

    1982-12-01

    Contract Number: F30602-80-C-0241 Effective Date of Contract: 15 July 1980 Contract Expiration Date: 1 August 1982 Short Title of Work: Grating...performed. Measurements of the efficiency, diffracted wavefront quality, frequency ratio, and skew are described. Analysis of the effects of nonzero...Section 2.5) for grating groove depth can be understood in terms of their effect on efficiency at the two wavelengths and tolerances thereon. Groove

  2. 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.

  3. 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.

  4. 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.

  5. Thermally induced proliferation of pores in a model fluid membrane.

    PubMed Central

    Shillcock, J C; Seifert, U

    1998-01-01

    The growth of thermally induced pores in a two-dimensional model fluid membrane is investigated by Monte Carlo simulation. Holes appear in the membrane via an activated process, and their subsequent growth is controlled by an edge energy per unit length or line tension. The barrier height and line tension, together with a lateral tension, are the independent parameters of the model. In the resulting phase diagram, a rupture transition separates an intact membrane from a disintegrated state. The approach to the ruptured state shows distinct regimes. Reducing the barrier height at large line tension produces multiple, quasi-independent, small holes whose behavior is dominated by their edge energy, whereas at lower line tensions shape fluctuations of the holes facilitate their coalescence into a single large hole. At a small value of line tension and large barrier height, a single hole spontaneously permeabilizes the membrane in an entropically driven phase transition. Entropy dominates pore growth for line tensions not far below those measured for artificial vesicles. Permeabilization of lipid bilayers by certain peptides involves perturbing lipid-lipid cohesive energies, and our simulations show that at small line tensions the entropy of hole shape fluctuations destroys the model membrane's stability. PMID:9545038

  6. 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).

  7. 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).

  8. 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.

  9. 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.

  10. 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.

  11. 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.

  12. 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.

  13. 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.

  14. Method for measuring ocular aberrations induced by thermal lensing in vivo

    NASA Astrophysics Data System (ADS)

    Vincelette, Rebecca; Oliver, Jeff; Noojin, Gary; Schuster, Kurt; Shingledecker, Aurora; Welch, Ashley J.

    2010-02-01

    An adaptive optics imaging system was used to qualitatively observe the types of aberrations induced by an infrared laser in a rhesus eye. Thermal lensing was induced with an infrared laser radiation wavelength of 1150-nm. The adaptive optics system tracked the temporal response of the aberrations at a frequency of 30 Hz for continuous-wave exposures. Results are compared against thermal lensing aberrations induced in an artificial eye.

  15. Hydrogen-loaded fiber Bragg grating for high-temperature sensor applications

    NASA Astrophysics Data System (ADS)

    Zhang, Bowei; Kahrizi, Mojtaba

    2004-11-01

    Bragg gratings have widespread applications in the rapidly growing field of optical sensors. Although fiber Bragg gratings are often referring to permanent refractive index structures, exposure in increased temperature usually results the decay of the refractive index modulation. Basically, the stability of the grating competence at high temperature is an important criterion for high temperature sensor applications. This report is a part on going research to develop high temperature optical sensors. We report our design and analyze of a hydrogen loaded fiber Bragg grating temperature sensor range from room temperature to around 1000°C. A basic setup has been built in our lab to examine the performance of the point temperature sensor based on the hydrogen loaded fiber Bragg grating. Until now, a grating has been shown to stabilize at temperatures in excess of 700°C and to survive at temperatures in excess of 930°C. The tested operation gratings around 700°C retain up to 80% reflectivity after one and a half hours. The thermal treatment of the tested hydrogen loaded fiber Bragg gratings is demonstrated capable to enhance effectively the grating's thermal stability. Our experimental results provide a better understanding of thermal response to the hydrogen loaded fiber Bragg gratings and their decay behavior at elevated temperatures.

  16. Effect of thermally induced strain on optical fiber sensors embedded in cement-based composites

    NASA Astrophysics Data System (ADS)

    Yuan, Li-bo; Zhou, Li-min; Jin, Wei; Lau, K. T.; Poon, Chi-kin

    2003-04-01

    A critical issue in developing a fiber-optic strain gauge is its codependency on temperature and strain. Any changes in the output of the optical fiber sensor due to its own thermal sensitivity and the thermal expansion of the most material will be misinterpreted as a change in shape-induced strain in the structure. This codependence is often referred to as thermally induced apparent strain or simply apparent strain. In this paper, an analytical model was developed to evaluate the thermally induced strain in fiber optic sensors embedded in cement-based composites. The effects of thermal induced strain on embedded optical fiber were measured with a white-light fiber-optic Michelson sensing interferometer for a number of cement-based host materials.

  17. Compact grating interferometer for producing photoresist gratings with incoherent light.

    PubMed

    Post, D; Patorski, K; Ning, P

    1987-03-15

    An achromatic interferometer was developed to produce 1200-lines/mm crossed-line photoresist gratings with a mercury arc light source. It is a compact reflection system of outstanding stability. Alignment procedures are described. The most stringent requirement, coplanar alignment of two folding gratings, was accomplished with the aid of a Twyman-Green interferometer. The grating interferometer produced crossed-line photoresist gratings with first-order diffraction efficiency exceeding 20%.

  18. Electro-Optic Diffraction Grating Tuned Laser.

    DTIC Science & Technology

    The patent concerns an electro - optic diffraction grating tuned laser comprising a laser medium, output mirror, retro-reflective grating and an electro - optic diffraction grating beam deflector positioned between the laser medium and the reflective diffraction grating. An optional angle multiplier may be used between the electro - optic diffraction grating and the reflective grating.

  19. Birefringence Bragg Binary (3B) grating, quasi-Bragg grating and immersion gratings

    NASA Astrophysics Data System (ADS)

    Ebizuka, Noboru; Morita, Shin-ya; Yamagata, Yutaka; Sasaki, Minoru; Bianco, Andorea; Tanabe, Ayano; Hashimoto, Nobuyuki; Hirahara, Yasuhiro; Aoki, Wako

    2014-07-01

    A volume phase holographic (VPH) grating achieves high angular dispersion and very high diffraction efficiency for the first diffraction order and for S or P polarization. However the VPH grating could not achieve high diffraction efficiency for non-polarized light at a large diffraction angle because properties of diffraction efficiencies for S and P polarizations are different. Furthermore diffraction efficiency of the VPH grating extinguishes toward a higher diffraction order. A birefringence binary Bragg (3B) grating is a thick transmission grating with optically anisotropic material such as lithium niobate or liquid crystal. The 3B grating achieves diffraction efficiency up to 100% for non-polarized light by tuning of refractive indices for S and P polarizations, even in higher diffraction orders. We fabricated 3B grating with liquid crystal and evaluated the performance of the liquid crystal grating. A quasi-Bragg (QB) grating, which consists long rectangle mirrors aligned in parallel precisely such as a window shade, also achieves high diffraction efficiency toward higher orders. We fabricated QB grating by laminating of silica glass substrates and glued by pressure fusion of gold films. A quasi-Bragg immersion (QBI) grating has smooth mirror hypotenuse and reflector array inside the hypotenuse, instead of step-like grooves of a conventional immersion grating. An incident beam of the QBI grating reflects obliquely at a reflector, then reflects vertically at the mirror surface and reflects again at the same reflector. We are going to fabricate QBI gratings by laminating of mirror plates as similar to fabrication of the QB grating. We will also fabricate silicon and germanium immersion gratings with conventional step-like grooves by means of the latest diamond machining methods. We introduce characteristics and performance of these gratings.

  20. Charged particle accelerator grating

    DOEpatents

    Palmer, Robert B.

    1986-01-01

    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.

  1. 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.

  2. An elastomeric grating coupler

    NASA Astrophysics Data System (ADS)

    Kocabas, Askin; Ay, Feridun; Dâna, Aykutlu; Aydinli, Atilla

    2006-01-01

    We report on a novel nondestructive and reversible method for coupling free space light to planar optical waveguides. In this method, an elastomeric grating is used to produce an effective refractive index modulation on the surface of the optical waveguide. The external elastomeric grating binds to the surface of the waveguide with van der Waals forces and makes conformal contact without any applied pressure. As a demonstration of the feasibility of the approach, we use it to measure the refractive index of a silicon oxynitride film. This technique is nondestructive, reversible, low cost and can easily be applied to the characterization of optical materials for integrated optics.

  3. Circular Fibonacci gratings.

    PubMed

    Gao, Nan; Zhang, Yuchao; Xie, Changqing

    2011-11-01

    We introduce circular Fibonacci gratings (CFGs) that combine the concept of circular gratings and Fibonacci structures. Theoretical analysis shows that the diffraction pattern of CFGs is composed of fractal distributions of impulse rings. Numerical simulations are performed with two-dimensional fast Fourier transform to reveal the fractal behavior of the diffraction rings. Experimental results are also presented and agree well with the numerical results. The fractal nature of the diffraction field should be of great theoretical interest, and shows potential to be further developed into practical applications, such as in laser measurement with wideband illumination.

  4. 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.

  5. Grating interferometer for flatness testing.

    PubMed

    de Groot, P J

    1996-02-01

    Two diffraction gratings placed in front of a f lat surface generate an interference pattern representing the surface deformations. The interference pattern is achromatic and has an equivalent wavelength between 4 and 40 microm, depending on the grating frequencies and the viewing angle. Using phase-shifting techniques, the grating interferometer provides high-precision profile measurements of both smooth and rough surfaces.

  6. 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.

  7. Hybrid grating reflectors: Origin of ultrabroad stopband

    SciTech Connect

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

    2016-04-04

    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.

  8. 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.

  9. 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.

  10. Properties of diffraction gratings holographically recorded in poly(ethylene glycol)dimethacrylate-ionic liquid composites

    NASA Astrophysics Data System (ADS)

    Ellabban, Mostafa A.; Glavan, Gašper; Flauger, Peter; Klepp, Jürgen; Fally, Martin

    2017-05-01

    We investigated recording and readout of transmission gratings in composites of poly(ethylene glycol) dimethacrylate (PEGDMA) and ionic liquids (IL) in detail. Gratings were recorded using a two-wave mixing technique for different grating periods, exposures and a series of film thicknesses. The recording kinetics as well as the post-exposure behavior of the gratings were studied by diffraction experiments. We found that - depending on the parameters - different grating types (pure phase or mixed) are generated, and at elevated thicknesses strong light-induced scattering develops. Gratings with thicknesses up to 85 micrometers are of the required quality with excellent optical properties, thicker gratings exhibit strong detrimental light-induced scattering. The obtained results are particularly valuable when considering PEGDMA-ionic liquid composites for applications as e.g., holographic storage materials or as neutron optic diffractive elements.

  11. Thermally induced spin rate ripple on spacecraft with long radial appendages

    NASA Technical Reports Server (NTRS)

    Fedor, J. V.

    1983-01-01

    A thermally induced spin rate ripple hypothesis is proposed to explain the spin rate anomaly observed on ISEE-B. It involves the two radial 14.5 meter beryllium copper tape ribbons going in and out of the spacecraft hub shadow. A thermal lag time constant is applied to the thermally induced ribbon displacements which perturb the spin rate. It is inferred that the averaged thermally induced ribbon displacements are coupled to the ribbon angular motion. A possible exponential build up of the inplane motion of the ribbon which in turn causes the spin rate ripple, ultimately limited by damping in the ribbon and spacecraft is shown. It is indicated that qualitative increase in the oscillation period and the thermal lag is fundamental for the period increase. found that numerical parameter values required to agree with in orbit initial exponential build up are reasonable; those required for the ripple period are somewhat extreme.

  12. Evaluation of thermally induced non-Fourier stress wave disturbances via tailored hybrid transfinite element formulations

    NASA Technical Reports Server (NTRS)

    Tamma, Kumar K.; Railkar, Sudhir B.

    1989-01-01

    Accurate solutions have been obtained for a class of non-Fourier models in dynamic thermoelasticity which are relevant to the understanding of thermally-induced stress wave disturbances. The method employs tailored hybrid formulations based on the transfinite element approach. The results show that significant thermal stresses may arise due to non-Fourier effects, especially when the speeds of propagation of the thermal and stress waves are equal.

  13. Tunable air-suspended polymer grating couplers

    NASA Astrophysics Data System (ADS)

    Prokop, Christoph; Schmalz, Tobias; Kleessen, Philipp; Laegel, Bert; Wolff, Sandra; Mitchell, Arnan; Karnutsch, Christian

    2017-06-01

    We present thermal tuning of air-suspended SU-8 polymer waveguide grating couplers for TE-polarized light. Numerical simulations have been performed to estimate the wavelength shift caused by the change of temperature. Due to the small positive thermal expansion and large negative thermo-optic coefficient of SU-8, a shift toward shorter wavelengths is expected. In the experimental evaluation, a negative wavelength shift from 1542 nm at 20°C toward 1527 nm at 56°C is obtained with approximately -0.42 nm K-1 matching the theoretical considerations.

  14. Gratings and waveguides

    NASA Technical Reports Server (NTRS)

    Bates, K. A.; Erwin, J. K.; Li, L.; Burke, J. J.; Ramanujam, N.

    1993-01-01

    Our immediate objective is to understand the limitations of guided-wave and grating coupler devices in their application to optical data storage. Our long-range goal is to develop and validate design codes for integrated optic devices. The principal research activity was in the development of numerical models for the design of a blue wavelength integrated optical source for data storage applications.

  15. Double groove broadband gratings.

    PubMed

    Pietarinen, Juha; Vallius, Tuomas

    2008-09-01

    Waveguiding in periodical structures of the size of the wavelength is applied to increase the functional spectral band of diffractive optics. The deviation of the effective refractive index between waveguides as a function of the wavelength is utilized to compensate the strong wavelength dependence of the efficiency of diffraction gratings.

  16. Wavelength tunable long period gratings based on silica waveguide geometric modulation

    NASA Astrophysics Data System (ADS)

    Jiang, Jia; Callender, Claire L.; Ledderhof, Christopher J.; Ding, Jianfu

    2011-03-01

    This paper presents planar long period grating (LPG) devices based on a periodic thickness variation in the waveguide core, fabricated by etching into the lower cladding layer prior to definition of the waveguide layer. This periodic geometric change results in a stable grating structure and a permanent refractive index modulation of 10-4 or higher, which is comparable to the index modulation in Ge-doped silica material induced by photo irradiation techniques widely used in fiber grating fabrication. This grating produces a strong resonance at a particular wavelength in the transmission spectrum, enabling a range of applications from wavelength filtering to signal distribution in communication networks. In this work, a polymer and silica hybrid architecture has been implemented in order to achieve wavelength tunability. Using a thermally oxidized silicon layer as a lower cladding, a Ge-doped silica ridge is patterned using conventional photolithography and reactive ion etching to form the waveguide core, which is then covered with a low index fluorinated polymer cladding. While the silica waveguides offer a lower propagation loss and an easy processability, the top polymer allows the device to be thermally tuned over a wide wavelength range by exploiting the opposite thermo-optic coefficient between fluorinated polymer and silica, and the high sensitivity of the underlying LPG to the refractive index of the cladding layer. Strong rejection bands have been demonstrated in the C+L band, in good agreement with theoretical calculations. Corrugated structures have been defined across an extended area under multiple waveguides resulting in coupling of light from the fundamental mode into cladding modes and back into the neighboring waveguides located far from the evanescent coupling distance. This kind of coupler can facilitate devices that require extraction and control of a particular waveguide mode for applications such as multiple channel signal distribution and

  17. 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.

  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. 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.

  20. Temperature of thermal spikes induced by swift heavy ions

    NASA Astrophysics Data System (ADS)

    Matsuzaki, S.; Hayashi, H.; Nakajima, K.; Matsuda, M.; Sataka, M.; Tsujimoto, M.; Toulemonde, M.; Kimura, K.

    2017-09-01

    Few-nm sized gold, platinum and palladium nanoparticles were deposited on amorphous silicon nitride films. These films were irradiated with 420 MeV Au and 100 MeV Xe ions. Temperature distributions of thermal spikes produced by these ions were evaluated by observing desorption of the nanoparticles from the target surfaces upon ion impact. It was found that the temperature of the thermal spike produced by 420 MeV Au is higher than 100 MeV Xe. The observed temperature of the thermal spike at the entrance surface is slightly lower than that at the exit surface both for 420 MeV Au and 100 MeV Xe ions. These results can be well explained by the inelastic thermal spike model.

  1. 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.

  2. Sensored fiber reinforced polymer grate

    DOEpatents

    Ross, Michael P.; Mack, Thomas Kimball

    2017-08-01

    Various technologies described herein pertain to a sensored grate that can be utilized for various security fencing applications. The sensored grate includes a grate framework and an embedded optical fiber. The grate framework is formed of a molded polymer such as, for instance, molded fiber reinforced polymer. Further, the grate framework includes a set of elongated elements, where the elongated elements are spaced to define apertures through the grate framework. The optical fiber is embedded in the elongated elements of the grate framework. Moreover, bending or breaking of one or more of the elongated elements can be detected based on a change in a characteristic of input light provided to the optical fiber compared to output light received from the optical fiber.

  3. Optical control of plasmonic grating transmission by photoinduced anisotropy

    NASA Astrophysics Data System (ADS)

    Palto, Sergey P.; Draginda, Yulia A.; Artemov, Vladimir V.; Gorkunov, Maxim V.

    2017-07-01

    Light transmission through subwavelength silver slit gratings coated with Langmuir-Blodgett films of an azo-dye compound was studied. While the coating was found to dramatically enhance the TM-polarized grating transmittance, it also enabled its low-intensity optical control: the photoinduced alignment of the azo-dye molecules yielded a significant (˜ 40 nm) shift of the extraordinary transmission peaks to shorter or longer wavelengths depending on the orientation of the induced optical axis with respect to the gratings.

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

    SciTech Connect

    Qiao, Jie; Papa, J.; Liu, X.

    2015-09-24

    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. Moreover, 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.

  5. 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.

  6. Optical fiber Bragg gratings. Part II. Modeling of finite-length gratings and grating arrays

    NASA Astrophysics Data System (ADS)

    Passaro, Vittorio M. N.; Diana, Roberto; Armenise, Mario N.

    2002-09-01

    A model of both uniform finite-length optical fiber Bragg gratings and grating arrays is presented. The model is based on the Floquet-Bloch formalism and allows rigorous investigation of all the physical aspects in either single- or multiple-periodic structures realized on the core of a monomodal fiber. Analytical expressions of reflectivity and transmittivity for both single gratings and grating arrays are derived. The influence of the grating length and the index modulation amplitude on the reflected and transmitted optical power for both sinusoidal and rectangular profiles is evaluated. Good agreement between our method and the well-known coupled-mode theory (CMT) approach has been observed for both single gratings and grating arrays only in the case of weak index perturbation. Significant discrepancies exist there in cases of strong index contrast because of the increasing approximation of the CMT approach. The effects of intragrating phase shift are also shown and discussed.

  7. Estimating the thermally induced acceleration of the New Horizons spacecraft

    NASA Astrophysics Data System (ADS)

    Guerra, André G. C.; Francisco, Frederico; Gil, Paulo J. S.; Bertolami, Orfeu

    2017-06-01

    Residual accelerations due to thermal effects are estimated through a model of the New Horizons spacecraft and a Monte Carlo simulation. We also discuss and estimate the thermal effects on the attitude of the spacecraft. The work is based on a method previously used for the Pioneer and Cassini probes, which solve the Pioneer anomaly problem. The results indicate that after the encounter with Pluto there is a residual acceleration of the order of 10-9 m/s 2 , and that rotational effects should be difficult, although not impossible, to detect.

  8. 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.

  9. 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.

  10. Thermal effects on photon-induced quantum transport in a single quantum dot.

    PubMed

    Assunção, M O; de Oliveira, E J R; Villas-Bôas, J M; Souza, F M

    2013-04-03

    We theoretically investigate laser induced quantum transport in a single quantum dot attached to electrical contacts. Our approach, based on a nonequilibrium Green function technique, allows us to include thermal effects on the photon-induced quantum transport and excitonic dynamics, enabling the study of non-Markovian effects. By solving a set of coupled integrodifferential equations, involving correlation and propagator functions, we obtain the photocurrent and the dot occupation as a function of time. Two distinct sources of decoherence, namely, incoherent tunneling and thermal fluctuations, are observed in the Rabi oscillations. As temperature increases, a thermally activated Pauli blockade results in a suppression of these oscillations. Additionally, the interplay between photon and thermally induced electron populations results in a switch of the current sign as time evolves and its stationary value can be maximized by tuning the laser intensity.

  11. Laser-induced thermocapillary convection in thin liquid layers: effect of thermal conductivity of substrates

    NASA Astrophysics Data System (ADS)

    Zykov, A. Yu.; Ivanova, N. A.

    2017-09-01

    The effect of the thermal conductivity of solid substrates on the thermocapillary convection induced by the thermal action of a laser beam in a thin liquid layer is studied experimentally. A diameter of photothermocapillary signal presenting a circular interference pattern formed on a screen by a probe laser beam reflected from the thermocapillary dimple is used for quantitative analysis. It is shown that diameter of the photothermocapillary signal changes with the thermal conductivity of substrates as k - n . This suggests that the thermal conductivity of substrate strongly affects the curvature of thermocapillary dimple. An influence of the power of the heating laser beam and the liquid layer thickness on the sensitivity of the thermocapillary effect to the thermal conductivity of substrates is also studied. It was shown that the sensitivity of the photothermocapillary effect to the thermal conductivity of substrates increases with the power of the heating laser beam and decreases with increasing the thickness of the liquid layer.

  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. Mechanically Induced Scission and Subsequent Thermal Remending of Perfluorocyclobutane Polymers

    DTIC Science & Technology

    2011-10-03

    first reported by Wudl and co-workers, who devised a polymeric material that would fail through a thermally reversible retro- Diels Alder reaction when...similar to that of other retro- Diels Alder chain scission mechanisms,9,18 but is shown here to proceed through a reactive intermediate that can

  14. Thermally induced magnetic switching in bit-patterned media

    NASA Astrophysics Data System (ADS)

    Pfau, B.; Günther, C. M.; Hauet, T.; Eisebitt, S.; Hellwig, O.

    2017-07-01

    We have studied the thermal variation of the switching field of magnetic islands at room temperature. A model bit-pattern media composed of an assembly of islands with 80 nm width was fabricated by sputter deposition onto a pre-patterned substrate. Using direct magnetic-contrast imaging of the islands under applied field, we extract the switching probabilities of individual islands. Based on an analytical model for the thermally activated switching of the islands, we are able to determine the intrinsic magnetic anisotropy of each island and, consequentially, a distribution of anisotropies for the island ensemble investigated. In the distribution, we identify a separated group of islands with a particularly small anisotropy. We attribute this group to islands containing misaligned grains triggering the magnetic reversal. At room temperature and slow field sweep rates, the observed thermal broadening of the switching-field distribution is small compared to the intrinsic broadening. However, we illustrate that thermal fluctuations play a crucial role at high sweep rates by extrapolating our results to technological relevant regimes.

  15. Evaluating thermal damage induced by pulsed light with multiphoton microscopy

    NASA Astrophysics Data System (ADS)

    Gong, Wei; Xie, Shusen; Huang, Yimei

    2009-02-01

    Nonablative skin remodeling is a new light treatment approach for photodamaged skin. Compared to ablative CO2 or Er:YAG laser resurfacing, dermabrasion, and chemical peels, the clinical objective of nonablative skin remodeling is to maximize thermal damage to upper dermis while minimizing injury to the epidermis and surrounding tissue, consequently decreasing potential complications and shortening long recuperation periods. Histological analysis of preoperative and postoperative biopsies using H&E or special stains has indicated the dermal thermal injury, which resulting in collagen denaturation, is the most important mechanism of nonablative skin remodeling for improving skin situation. And the extent of improvement of skin situation corresponded to the formation of a new band of dense, compact collagen bundles in the papillary dermis. The diversity of individual skin condition influences the choice of pulsed light treatment parameters, and further influences the degree of dermal thermal damage, thus the efficacy of nonablative skin remodeling remains unstable. Recently, multiphoton microscopy has show a promising application for monitoring skin thermal damage, because collagen could produce strong second harmonic generation (SHG). And SHG intensity is presumably proportional to the percentage of collagen in dermis. In this paper, the auto-fluorescence (AF) intensity and SHG intensity of mice skin irradiated by pulsed Nd:YAG laser were measured and imaged with multiphoton microscope, and the results show the ratio of SHG to AF decreases with the increase of irradiation exposure dose, and could be a quantitative technique to assess dermal thermal damage, and could further benefit the choice of light treatment parameters.

  16. Size scaling and bursting activity due to thermally induced cracking

    NASA Astrophysics Data System (ADS)

    Kun, F.; Yoshioka, N.; Ito, N.

    2012-04-01

    Sub-critical rupture, occurring under a constant load below the fracture strength of materials, is of fundamental importance in a wide range of physical, biological, and geological systems. During the last decade major progress has been achieved in the understanding of the role of quenched disorder in the size scaling of materials strength. However, under sub-critical loads, the interplay of annealed disorder (thermal noise) and of the inhomogeneous stress field in the rupture process still remained an open fundamental problem. We study sub-critical fracture driven by thermally activated crack nucleation in the framework of fiber bundle models. Based on analytic calculations and computer simulations we show that in the presence of stress inhomogeneities, thermally activated cracking results in an anomalous size effect, i.e. the average lifetime of the system decreases as a power law of the system size, where the exponent depends on the external load and on the temperature. We propose a modified form of the Arrhenius law which provides a comprehensive description of thermally activated breakdown. On the microlevel, thermal fluctuations trigger bursts of breakings which proved to have a power law size distribution. We compare analytic results obtained in the mean field limit to the computer simulations of localized load redistribution to reveal the effect of the range of interaction on the time evolution. Focusing on the waiting times between consecutive bursts we show that the time evolution has two distinct forms: at high load values the breaking process continuously accelerates towards macroscopic failure, however, for low loads and high enough temperatures the acceleration is preceded by a slow-down. Analyzing the structural entropy and the location of consecutive bursts we show that in the presence of stress concentration the early acceleration is the consequence of damage localization. The distribution of waiting times has a power law form with an exponent

  17. Therapeutic role of Cuminum cyminum on ethanol and thermally oxidized sunflower oil induced toxicity.

    PubMed

    Aruna, K; Rukkumani, R; Varma, P Suresh; Menon, Venugopal P

    2005-05-01

    Ethanol is one of the most widely used and abused drugs, increasing lipid levels in humans and experimental animals. Heating of oil rich in polyunsaturated fatty acids (PUFA) produces various lipid peroxidative end products that can aggravate the pathological changes produced by ethanol. In the present communication, the effect of Cuminum cyminum was investigated on alcohol and thermally oxidized oil induced hyperlipidaemia. The results showed increased activity of aspartate transaminase (AST), alkaline phosphatase (ALP) and gamma glutamyl transferase (GGT) and increased levels of cholesterol, triglycerides and phospholipids in the plasma of rats given alcohol, thermally oxidized oil and alcohol+thermally oxidized oil when compared with the normal control group. The levels of tissue (liver and kidney) cholesterol and triglycerides were increased significantly in rats groups given alcohol, thermally oxidized oil and alcohol+thermally oxidized oil when compared with the normal control rats. The levels were decreased when cumin was given along with alcohol and thermally oxidized oil. The level of phospholipids decreased significantly in the liver and kidney of groups given alcohol, thermally oxidized oil and alcohol+thermally oridized oil when compared with the normal control rats. The level increased when cumin was administered along with alcohol and thermally oxidized oil. The activity of phospholipase A and C increased significantly in the liver of groups given alcohol, thermally oxidized oil and alcohol+thermally oxidized oil when compared with the normal control rats, whereas the activity was decreased with the cumin treatment. The results obtained indicate that cumin can decrease the lipid levels in alcohol and thermally oxidized oil induced hepatotoxicity.

  18. Duration of Venodilation for Peripheral Intravenous Cannulation, as Induced by a Thermal Stimulus on the Forearm.

    PubMed

    Tokizawa, Yuki; Tsujimoto, Tomomi; Inoue, Tomoko

    2017-03-01

    Application of a thermal stimulus is a common procedure used to promote venodilation for peripheral intravenous cannulation (PIVC); however, the effects of thermal stimulation on the duration of venodilation and skin temperature of the forearm are unclear. To investigate the duration of venodilation induced by a thermal stimulus on the forearm. Healthy female adults ( N = 40) from Japan participated in this study from November to December 2013. A heat pack was warmed to 40°C ± 2°C and placed over the forearm for 15 min. Vein diameter was measured via ultrasound and skin temperature via temperature sensor at six time points: before application of the thermal stimulus and at 1-min intervals for 5 min upon removal of the thermal stimulus. The main outcomes were vein diameter, proportional change in vein diameter, and skin temperature. We calculated proportional change in vein diameter after application of the thermal stimulus using vein diameter before the thermal stimulus to represent 100%. Compared with vein diameter before thermal stimulus, the diameter at each time point after thermal stimulus was significantly increased ( p < .05) as were proportional change in vein diameter ( p < .05) and skin temperature. A thermal stimulus of 40°C ± 2°C on the forearm dilated veins significantly for PIVC, and the effect persisted for at least 5 min.

  19. 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

  20. 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.

  1. Tactile hyperesthesia, altered epidermal innervation and plantar nerve injury in the hindfeet of rats housed on wire grates.

    PubMed

    Mizisin, A P; Kalichman, M W; Garrett, R S; Dines, K C

    1998-03-30

    The effects of wire grates on nerve injury and recovery were examined in rats housed in cages with sawdust-covered solid flooring. For the first 3 weeks of the study, 20 rats were housed on sawdust alone and 20 rats were housed in cages with wire grates placed over the sawdust. For the remaining 9 weeks, 10 animals housed on sawdust had wire grates added to their cages, while grates were removed from the cages of 10 animals. The effects of tactile stimulation on hindpaw plantar skin was measured weekly using the Von Frey filament test. Intraepidermal innervation using PGP 9.5 immunostaining and plantar nerve histology were assessed at the end of the 12-week study. After just 1 week on grates, hindpaw withdrawal thresholds were already markedly decreased and remained low until the grates were removed at 3 weeks. Thresholds returned to normal by 4 weeks after removal of the grates. Wire grates also induced increases in PGP 9.5 immunoreactive intraepidermal fine nerve endings that were normalized after grate removal. Demyelination, Wallerian degeneration and Renaut bodies were induced in the medial plantar nerve in rats housed in cages with wire-grate flooring. Nerve injury was largely resolved after 9 weeks on sawdust flooring. These data demonstrate that wire grates rapidly induce hindpaw tactile hyperesthesia and plantar neuropathy in rats and emphasize a risk of using wire-grate cage flooring in studies assessing hindlimb function and structure.

  2. Thermally induced micromechanical stresses in ceramic/ceramic composites

    SciTech Connect

    Li, Zhuang ); Bradt, R.C. . Mackay School of Mines)

    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.

  3. 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.

  4. Thermal induced structural transformation of bimetallic AuPd nanoparticles

    NASA Astrophysics Data System (ADS)

    Bruma, A.; Li, Z. Y.

    2014-06-01

    High Angle Annular Dark Field Scanning Transmission Electron Microscope (HAADF-STEM) has been employed for the study of thermal effects of structural transformation of AuPd nanoparticles produced by physical vapour deposition. Depending on the duration of annealing at a temperature of 500 K, atomic resolved imaging analysis reveals the formation of various structure morphologies from the ordered L12 superlattice to the core-shell structure. The effects of Pd-oxides are also discussed.

  5. Thermal-Induced Stress of Plasmonic Magnetic Nanocomposites

    NASA Astrophysics Data System (ADS)

    Phan, Anh D.; Do, Nghia C.; Nga, Do T.

    2017-08-01

    We present theoretical calculations to interpret optical and mechanical properties of Ag@Fe3O4 nanoflowers. The microstructures and nature of optical peaks of nanoflowers are determined by means of the Mie theory associated with effective dielectric approximation and the experimental absorption spectrum. Under laser illumination, the thermal strain fields inside and outside the structure due to the absorbed optical energy are studied using continuum mechanics approach. Our findings provide simple but comprehensive description of the elastic behaviors of previous experiments.

  6. The kinetics of thermal stress induced denaturation of Aquaporin 0.

    PubMed

    Hansen, John E; Leslie, Logan; Swamy-Mruthinti, Satyanarayana

    2014-08-08

    Aquaporin 0 (AQP0) is an integral membrane protein that facilitates water transport and cellular adhesion in the lens. Its dysfunction has been associated with cataractogenesis. Our earlier studies showed AQP0 undergoes aggregation when subjected to thermal stress and this aggregation seems to have been facilitated by mechanical agitation brought about by gentle stirring. The purpose of this study is to determine the secondary structural changes that precede aggregation and the role that α-crystallin plays in inhibiting those structural changes. Detergent solubilized calf lens AQP0 was subjected to thermal stress at 50°C for varying times. Secondary structural changes were measured by Circular Dichroism (CD) spectropolarimetry. Convex constraint analysis was used to deconvolute the CD spectra into pure component curves representing the secondary structural elements. Our results showed that under thermal stress, the α-helix content of AQP0 decreased from 50% to 7% with a concomitant increase from 0% to 52% in β-sheet content. The time-dependent loss of α-helical structure and gain of β-sheet structure appear to follow first-order kinetics with very similar values (∼30min) suggesting a single transition. In the presence of α-crystallin, this conversion to β-sheet is minimized, suggesting that the protein structure that binds to the molecular chaperone is mostly the α-helical structure of AQP0. Copyright © 2014 Elsevier Inc. All rights reserved.

  7. Helicity induced thermal conductivity reduction in superlattice nanowires

    NASA Astrophysics Data System (ADS)

    Varshney, Vikas; Roy, Ajit K.; Lee, Jonghoon; Dudis, Douglas S.; Farmer, Barry L.

    2012-12-01

    In this study, we have performed non-equilibrium molecular dynamics (NEMD) simulations to investigate thermal transport properties of 'model' bi-component helical nanowires. The results indicate that significant reduction in thermal conductivity, similar to that of flat superlattice nanostructures, can be achieved using a helical geometric configuration. The reduction is attributed to a plethora of transmissive and reflective phonon scattering events resulting from the steady alteration of phonon propagating direction that emerges from the continuous rotation of the helical interface. We also show that increasing the relative mass ratio of the two components lowers the phonon energy transmission at the interface (differences in vibrational frequency spectrum), thereby relatively 'easing' the phonon energy propagation along the helical pathway. While the proposed mechanisms result in a reduced lattice thermal conductivity, the continuous nature of the bi-component nanowire would not be expected to significantly reduce its electrical counterpart, as often occurs in superlattice/alloy nanostructures. Hence, we believe that the helical configuration of atomic arrangement should be a very attractive, general approach for improved thermoelectric material assemblies independent of the specific chemical composition.

  8. 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.

  9. Determination of heterogeneous thermal parameters using ultrasound induced heating and MR thermal mapping.

    PubMed

    Huttunen, Janne M J; Huttunen, Tomi; Malinen, Matti; Kaipio, Jari P

    2006-02-21

    In this paper, a method for the determination of spatially varying thermal conductivity and perfusion coefficients of tissue is proposed. The temperature evolution in tissue is modelled with the Pennes bioheat equation. The main motivation here is a model-based optimal control for ultrasound surgery, in which the tissue properties are needed when the treatment is planned. The overview of the method is as follows. The same ultrasound transducers, which are eventually used for the treatment, are used to inflict small temperature changes in tissue. This temperature evolution is monitored using MR thermal imaging, and the tissue properties are then estimated on the basis of these measurements. Furthermore, an approach to choose transducer excitations for the determination procedure is also considered. The purpose of this paper is to introduce a method and therefore simulations are used to verify the method. Furthermore, computations are accomplished in a 2D spatial domain.

  10. 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.

  11. Hybrid-type fiber Bragg gratings and their applications

    NASA Astrophysics Data System (ADS)

    Shu, Xuewen; Sugden, Kate; Zhao, Donghui; Floreani, Filip; Zhang, Lin; Bennion, Ian

    2002-09-01

    Fiber Bragg gratings (FBGs) have attracted a lot of attention in recent years due to their wide applications in optical telecommunications and smart sensing. They have been used as DWDM filters, dispersion compensators, gain flattening filters, optical switch and connection devices, and temperature/strain sensors. FBGs have been found to exhibit four different type structures according to their different growth mechanisms. Each type of FBG exhibits unique thermal and strain properties. Generally, the Type I gratings in hydrogenated and hydrogen-free fibers are used most for applications. However, some novel devices may be achieved by combinational structure of different types of gratings in the future. In this paper, we propose a novel concept of fabrication and application of FBGs with hybrid grating types. We have observed a complex growth behavior of a hybrid-type grating in the UV exposure to a B/Ge codoped fiber through a phase mask. A new model has been developed to simulate the complex growth behavior of the hybrid-type gratings, giving results in excellent agreement with experiment.

  12. 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.

  13. Thermal gradient induced tweezers for the manipulation of particles and cells.

    PubMed

    Chen, Jiajie; Cong, Hengji; Loo, Fong-Chuen; Kang, Zhiwen; Tang, Minghui; Zhang, Haixi; Wu, Shu-Yuen; Kong, Siu-Kai; Ho, Ho-Pui

    2016-11-17

    Optical tweezers are a well-established tool for manipulating small objects. However, their integration with microfluidic devices often requires an objective lens. More importantly, trapping of non-transparent or optically sensitive targets is particularly challenging for optical tweezers. Here, for the first time, we present a photon-free trapping technique based on electro-thermally induced forces. We demonstrate that thermal-gradient-induced thermophoresis and thermal convection can lead to trapping of polystyrene spheres and live cells. While the subject of thermophoresis, particularly in the micro- and nano-scale, still remains to be fully explored, our experimental results have provided a reasonable explanation for the trapping effect. The so-called thermal tweezers, which can be readily fabricated by femtosecond laser writing, operate with low input power density and are highly versatile in terms of device configuration, thus rendering high potential for integration with microfluidic devices as well as lab-on-a-chip systems.

  14. 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

  15. Thermal gradient induced tweezers for the manipulation of particles and cells

    NASA Astrophysics Data System (ADS)

    Chen, Jiajie; Cong, Hengji; Loo, Fong-Chuen; Kang, Zhiwen; Tang, Minghui; Zhang, Haixi; Wu, Shu-Yuen; Kong, Siu-Kai; Ho, Ho-Pui

    2016-11-01

    Optical tweezers are a well-established tool for manipulating small objects. However, their integration with microfluidic devices often requires an objective lens. More importantly, trapping of non-transparent or optically sensitive targets is particularly challenging for optical tweezers. Here, for the first time, we present a photon-free trapping technique based on electro-thermally induced forces. We demonstrate that thermal-gradient-induced thermophoresis and thermal convection can lead to trapping of polystyrene spheres and live cells. While the subject of thermophoresis, particularly in the micro- and nano-scale, still remains to be fully explored, our experimental results have provided a reasonable explanation for the trapping effect. The so-called thermal tweezers, which can be readily fabricated by femtosecond laser writing, operate with low input power density and are highly versatile in terms of device configuration, thus rendering high potential for integration with microfluidic devices as well as lab-on-a-chip systems.

  16. Thermal gradient induced tweezers for the manipulation of particles and cells

    PubMed Central

    Chen, Jiajie; Cong, Hengji; Loo, Fong-Chuen; Kang, Zhiwen; Tang, Minghui; Zhang, Haixi; Wu, Shu-Yuen; Kong, Siu-Kai; Ho, Ho-Pui

    2016-01-01

    Optical tweezers are a well-established tool for manipulating small objects. However, their integration with microfluidic devices often requires an objective lens. More importantly, trapping of non-transparent or optically sensitive targets is particularly challenging for optical tweezers. Here, for the first time, we present a photon-free trapping technique based on electro-thermally induced forces. We demonstrate that thermal-gradient-induced thermophoresis and thermal convection can lead to trapping of polystyrene spheres and live cells. While the subject of thermophoresis, particularly in the micro- and nano-scale, still remains to be fully explored, our experimental results have provided a reasonable explanation for the trapping effect. The so-called thermal tweezers, which can be readily fabricated by femtosecond laser writing, operate with low input power density and are highly versatile in terms of device configuration, thus rendering high potential for integration with microfluidic devices as well as lab-on-a-chip systems. PMID:27853191

  17. 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.

  18. Thermally induced magnon accumulation in two-sublattice magnets

    NASA Astrophysics Data System (ADS)

    Ritzmann, Ulrike; Hinzke, Denise; Nowak, Ulrich

    2017-02-01

    We present a temperature-dependent study of the thermal excitation of a magnon accumulation in two-sublattice magnetic materials. Using atomistic spin model simulations, we study the local magnetization profiles sublattice-wise in the vicinity of a temperature step in antiferromagnets, as well as in ferrimagnets. It is shown that the strength of the magnon accumulation in these systems scales with the derivative of the magnetization with respect to the temperature. These results give an insight into the complex temperature dependence of the magnon accumulation by making a direct link to the macroscopic behavior of the magnetization.

  19. Thermal Model of Laser-Induced Eye Damage

    DTIC Science & Technology

    1974-10-08

    Measurement of the Choroidal Blood j Flow in the Rabbit Using 85-Krpton," Exp. Eye Res._ 16, pp 421- 425 (1973) 15. "Thermal Problems in Biotechnology ...QM VIH 8- 1. ALLLN ET AL LCL1PSt bNUkNS IN h’UMANS AN)LAf5,)kATORPY mL AS LIE MLNT IN H A fif.1 $* S A M-1.L 01 (Ay Y 6w 2a ALLLN LT AL HUL’m CT Iij

  20. Laser-induced thermal desorption facilitates postsource decay of peptide ions.

    PubMed

    Kim, Shin Hye; Lee, Aera; Song, Jae Yong; Han, Sang Yun

    2012-05-01

    We investigated the thermal mechanism involved in laser desorption/ionization (LDI) of thermally labile molecules from the flat surfaces of amorphous Si (a-Si) and crystalline Si (c-Si). a-Si was selected for this study because of its thermal property, such as low thermal conductivity; thus, it was predicted to be highly susceptible to laser-induced surface heating. By virtue of lack of surface nanostructures, the flat surfaces offer a simple model system to focus on the thermal mechanism, avoiding other effects, including possible non-thermal contributions that can arise from the physical existence of surface nanostructures. For the energetics study, the internal energies of substituted benzylpyridinium ions produced by LDI on the bare and coated surfaces of a-Si and c-Si were obtained using the survival yield method. The results, including LDI thresholds, ion yields, and internal energies all suggested that the LDI mechanism would be indeed thermal, which is most likely promoted by thermal desorption caused by laser-induced surface heating. In addition, the LDI process driven by laser-induced thermal desorption (LITD) was also found to be capable of depositing an excessive internal energy in resulting LDI ions, which underwent a dissociation. It exhibited the essentially same features as in postsource decay (PSD) in MALDI-TOF/TOF mass spectrometry. We report that the LDI process by LITD offers not only a way of intact ionization but also a facile means for PSD of peptide ions, which this work demonstrates is well suited to peptide sequencing using TOF/TOF mass spectrometry.

  1. Thermally induced transverse cracking in graphite-epoxy cross-ply laminates

    NASA Technical Reports Server (NTRS)

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

    1986-01-01

    Thermally induced transverse cracking in T300/5208 graphite-epoxy cross-ply laminates was investigated experimentally and theoretically. The six laminate configurations studied were: 0/90(3)s, 0(2)/90(2)s, 0(3)/90s, 90/0(3)s, 90(2)/0(2)s, and 90(3)/0s. The thermal load required to initiate transverse cracking was determined experimentally and compared to a theoretical prediction. Experimental results for the accumulation of transverse cracks under cyclic thermal loading between - 250 and 250 F for up to 500 thermal cycles are presented. The calculated in situ transverse-lamina strength was determined to be at least 1.9 times the unidirectional-lamina transverse tensile strength. All laminate configurations exhibited an increase in crack density with increasing thermal cycles.

  2. Improved resistance of chemically-modified nanocellulose against thermally-induced depolymerization.

    PubMed

    Agustin, Melissa B; Nakatsubo, Fumiaki; Yano, Hiroyuki

    2017-05-15

    The study demonstrated the improvement in the resistance of nanocellulose against thermally-induced depolymerization by esterification with benzoyl (BNZ) and pivaloyl (PIV). The change in the degree of polymerization (DP) and molecular weight distribution (MWD) after thermal treatment in nitrogen and in air was investigated using viscometry and gel permeation chromatography. BNZ and PIV nanocellulose esters without α-hydrogens gave higher DP and narrower MWD than pure bacterial cellulose; and the acetyl and myristoyl esters, which possess α-hydrogens. Results also showed that when depolymerization is suppressed, thermal discoloration is also reduced. Resistance against depolymerization inhibits the formation of reducing ends which can be active sites for thermal discoloration. Finally, the findings suggest that benzoylation and pivaloylation can be an excellent modification technique to improve the thermal stability of nanocellulose.

  3. 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.

  4. Unraveling the nucleation and growth of spontaneous surface relief gratings

    NASA Astrophysics Data System (ADS)

    Mazaheri, Leila; Sabat, Ribal Georges; Lebel, Olivier; Nunzi, Jean-Michel

    2016-12-01

    Nucleation and growth of spontaneous surface relief gratings (SSRGs) on a Disperse Red 1 (DR1) glass-forming derivative were investigated. No interference pattern is applied and surface patterning is induced using single-beam irradiation: the gratings are self-organized. Grating growth is assumed to initiate from an interference pattern formed between the incident light beam and waves scattered at grazing angle by surface defects. However, the mechanism is not yet fully understood and there is not a comprehensive explanation of the structure formation process. Herein, the grating formation procedure is studied by monitoring the surface topology of thin films exposed to one writing beam for various periods of time, under both linear and circular polarizations, using AFM. Even in the absence of surface defects on the initial film, irradiation produces light-induced surface defects due to the reorientation and mass movement of the azo molecules. These defects act as seeds for SSRG around which gratings gradually emerge and propagate throughout the sample. To consolidate this hypothesis, the formation of gratings was studied on samples with controlled surface roughness. Pore-shaped defects do not diffract light on top of the sample, and thus have no impact on SSRG growth, while for hill-shaped defects, growth rate decreases sharply with defect sizes larger than the writing beam wavelength. Two other analogous glass-forming azobenzene derivatives were studied, and in all cases, SSRG formation was correlated with the induction of birefringence in the early stages of the irradiation.

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

    SciTech Connect

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

    2015-06-30

    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.

  6. 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.

  7. Polarization independent blue phase liquid crystal gratings based on periodic polymer slices structure

    NASA Astrophysics Data System (ADS)

    Yan, Jing; Li, Qing; Hu, Kai

    2013-10-01

    A polarization independent switchable phase grating based on polymer stabilized blue phase liquid crystal is proposed. A high efficiency of the phase grating has been achieved because of the sharp rectangular phase profile which shows good agreement with the simulation results. The diffraction efficiency of the 1st order is 38%, the response time is in the submillisecond range, and the phase grating is independent of the polarization of the incident light. The voltage-induced hysteresis characteristics are also investigated.

  8. High-resolution liquid-crystal phase grating formed by fringing fields from interdigitated electrodes.

    PubMed

    Lindquist, R G; Kulick, J H; Nordin, G P; Jarem, J M; Kowel, S T; Friends, M; Leslie, T M

    1994-05-01

    We report the formation of thin anisotropic phase gratings in a nematic liquid-crystalline film by use of lateral (fringing) electric fields induced by transparent interdigitated electrodes. These gratings yield high diffraction efficiency (>30%) with a strong dependence on the readout beam incidence angle. In addition, the formation of a defect wall is observed that has a significant effect on the diffraction properties of the phase grating.

  9. 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

  10. 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.

  11. 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}.

  12. 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.

  13. 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).

  14. 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.

  15. 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.

  16. 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.

  17. 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.

  18. Grating-based red lasers

    NASA Astrophysics Data System (ADS)

    Pezeshki, Bardia; Hagberg, Mats; Zelinski, Michael; Zou, Sarah; Kolev, Emil I.

    1999-04-01

    We have demonstrated a number of high power and single- frequency lasers at 635 - 680 nm by incorporating a grating reflector within the device, including DBRs, tunable DBRs, monolithic MOPAs, DFBs, and angled-grating DFBs. The DBR laser, with an unpumped grating as the rear reflector, is the simplest single-frequency structure, with about 20 mW output power. The device can be tuned about 3 nm by injecting current in the rear grating. Higher output power can be obtained by combining the DBR with a flared amplifier to form a monolithic MOPA with over 250 mW CW output power. Unlike DBR structures, the DFBs have a grating throughout their gain region, and therefore show no mode hops. Wavelengths as short as 634 nm and output powers as high as 90 mW have been obtained with DFBs. An angle-grating DFB is a broad area device where the angled grating forces lasing in a single spatial and longitudinal mode. More than 400 mW in single-frequency power has been obtained at 660 nm from such a structure. In general, grating-based red lasers are useful for interferometry, spectroscopy, and fiber-coupling applications.

  19. 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)

  20. Thermal conductivity enhancement of laser induced graphene foam upon P3HT infiltration

    NASA Astrophysics Data System (ADS)

    Smith, M. K.; Luong, D. X.; Bougher, T. L.; Kalaitzidou, K.; Tour, J. M.; Cola, B. A.

    2016-12-01

    Significant research has been dedicated to the exploration of high thermal conductivity polymer composite materials with conductive filler particles for use in heat transfer applications. However, poor particle dispersibility and interfacial phonon scattering have limited the effective composite thermal conductivity. Three-dimensional foams with high ligament thermal conductivity offer a potential solution to the two aforementioned problems but are traditionally fabricated through expensive and/or complex manufacturing methods. Here, laser induced graphene foams, fabricated through a simple and cost effective laser ablation method, are infiltrated with poly(3-hexylthiophene) in a step-wise fashion to demonstrate the impact of polymer on the thermal conductivity of the composite system. Surprisingly, the addition of polymer results in a drastic (250%) improvement in material thermal conductivity, enhancing the graphene foam's thermal conductivity from 0.68 W/m-K to 1.72 W/m-K for the fully infiltrated composite material. Graphene foam density measurements and theoretical models are utilized to estimate the effective ribbon thermal conductivity as a function of polymer filling. Here, it is proposed that the polymer solution acts as a binding material, which draws graphene ligaments together through elastocapillary coalescence and bonds these ligaments upon drying, resulting in greatly reduced contact resistance within the foam and an effective thermal conductivity improvement greater than what would be expected from the addition of polymer alone.

  1. 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.

  2. Slow plasmons in grating cavities

    NASA Astrophysics Data System (ADS)

    Aydinli, Atilla; Karademir, Ertugrul; Balci, Sinan; Kocabas, Coskun

    2016-03-01

    Recent research on surface plasmon polaritons and their applications have brought forward a wealth of information and continues to be of interest to many. In this report, we concentrate on propagating surface plasmon polaritons (SPPs) and their interaction with matter. Using grating based metallic structures, it is possible to control the electrodynamics of propagating SPPs. Biharmonic gratings loaded with periodic Si stripes allow excitation of SPPs that are localized inside the band gap with grating coupling. The cavity state is formed due to periodic effective index modulation obtained by one harmonic of the grating and loaded Si stripes. More complicated grating structures such as metallic Moiré surfaces have also been shown to form a localized state inside the band gap when excited with Kretschmann configuration.

  3. 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.

  4. Structure-induced enhancement of thermal conductivities in electrospun polymer nanofibers

    NASA Astrophysics Data System (ADS)

    Zhong, Zhenxin; Wingert, Matthew C.; Strzalka, Joseph; Wang, Hsien-Hau; Sun, Tao; Wang, Jin; Chen, Renkun; Jiang, Zhang

    2014-06-01

    Polymers that are thermally insulating in bulk forms have been found to exhibit higher thermal conductivities when stretched under tension. This enhanced heat transport performance is believed to arise from the orientational alignment of the polymer chains induced by tensile stretching. In this work, a novel high-sensitivity micro-device platform was employed to determine the axial thermal conductivity of individual Nylon-11 polymer nanofibers fabricated by electrospinning and post-stretching. Their thermal conductivity showed a correlation with the crystalline morphology measured by high-resolution wide-angle X-ray scattering. The relationship between the nanofiber internal structures and thermal conductivities could provide insights into the understanding of phonon transport mechanisms in polymeric systems and also guide future development of the fabrication and control of polymer nanofibers with extraordinary thermal performance and other desired properties.Polymers that are thermally insulating in bulk forms have been found to exhibit higher thermal conductivities when stretched under tension. This enhanced heat transport performance is believed to arise from the orientational alignment of the polymer chains induced by tensile stretching. In this work, a novel high-sensitivity micro-device platform was employed to determine the axial thermal conductivity of individual Nylon-11 polymer nanofibers fabricated by electrospinning and post-stretching. Their thermal conductivity showed a correlation with the crystalline morphology measured by high-resolution wide-angle X-ray scattering. The relationship between the nanofiber internal structures and thermal conductivities could provide insights into the understanding of phonon transport mechanisms in polymeric systems and also guide future development of the fabrication and control of polymer nanofibers with extraordinary thermal performance and other desired properties. Electronic supplementary information (ESI

  5. Laser induced unzipping: A thermal route to polymer ablation

    NASA Astrophysics Data System (ADS)

    Blanchet, Graciela B.; Fincher, C. R., Jr.

    1994-09-01

    The data presented here show that polytetrafluoroethylene (PTFE) and polymethylmethacrylate (PMMA) can be ablated by the evaporation of solid polymer targets with a pulsed ultraviolet laser. In situ measurements of the plume composition show that the products emitted under laser irradiation are primarily monomer and other species resulting from energetic collisions within the plasma. The similarities between the ablative and pyrolisis mass spectra suggest that ablation of PTFE and PMMA occur through a laser induced pyrolitic decomposition.

  6. 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

    2016-04-04

    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.

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

    DOE PAGES

    Qiao, Jie; Papa, J.; Liu, X.

    2015-09-24

    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. Moreover, a 1.5-meter deformable gratingmore » 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.« less

  8. Heat-induced darkening and spectral broadening in photodarkened ytterbium-doped fiber under thermal cycling.

    PubMed

    Söderlund, Mikko J; Montiel i Ponsoda, Joan J; Koplow, Jeffrey P; Honkanen, Seppo

    2009-06-08

    We study thermal bleaching of photodarkening-induced loss in a 20-microm core diameter, large-mode-area ytterbium-doped silica fiber. Pristine and photodarkened samples are subjected to thermal cycling pulses. Recovery of the photodarkened fiber absorption coefficient initiates at approximately 350 degrees C and complete recovery is reached at approximately 625 degrees C. However, prior to recovery, the photodarkened fiber exhibits further heat-induced increase of absorption loss. This increase of loss is attributed to both a permanent increase of loss-inducing color centers and a temperature-dependent broadening of the absorption spectrum. Post-irradiation heat-induced formation of color centers suggests the presence of an intermediate energy state in the near-infrared photochemical mechanism for photodarkening.

  9. 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.

  10. 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.

  11. 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

    NASA Astrophysics Data System (ADS)

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

    2015-02-01

    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.

  12. Period doubling induced by thermal noise amplification in genetic circuits

    PubMed Central

    Ruocco, G.; Fratalocchi, A.

    2014-01-01

    Rhythms of life are dictated by oscillations, which take place in a wide rage of biological scales. In bacteria, for example, oscillations have been proven to control many fundamental processes, ranging from gene expression to cell divisions. In genetic circuits, oscillations originate from elemental block such as autorepressors and toggle switches, which produce robust and noise-free cycles with well defined frequency. In some circumstances, the oscillation period of biological functions may double, thus generating bistable behaviors whose ultimate origin is at the basis of intense investigations. Motivated by brain studies, we here study an “elemental” genetic circuit, where a simple nonlinear process interacts with a noisy environment. In the proposed system, nonlinearity naturally arises from the mechanism of cooperative stability, which regulates the concentration of a protein produced during a transcription process. In this elemental model, bistability results from the coherent amplification of environmental fluctuations due to a stochastic resonance of nonlinear origin. This suggests that the period doubling observed in many biological functions might result from the intrinsic interplay between nonlinearity and thermal noise. PMID:25404210

  13. Thermally induced crystallization in NbO2 thin films

    NASA Astrophysics Data System (ADS)

    Zhang, Jiaming; Norris, Kate J.; Gibson, Gary; Zhao, Dongxue; Samuels, Katy; Zhang, Minxian Max; Yang, J. Joshua; Park, Joonsuk; Sinclair, Robert; Jeon, Yoocharn; Li, Zhiyong; Williams, R. Stanley

    2016-09-01

    Niobium dioxide can exhibit negative differential resistance (NDR) in metal-insulator-metal (MIM) devices, which has recently attracted significant interest for its potential applications as a highly non-linear selector element in emerging nonvolatile memory (NVM) and as a locally-active element in neuromorphic circuits. In order to further understand the processing of this material system, we studied the effect of thermal annealing on a 15 nm thick NbO2 thin film sandwiched inside a nanoscale MIM device and compared it with 180 nm thick blanket NbOx (x = 2 and 2.5) films deposited on a silicon dioxide surface as references. A systematic transmission electron microscope (TEM) study revealed a similar structural transition from amorphous to a distorted rutile structure in both cases, with a transition temperature of 700 °C for the NbO2 inside the MIM device and a slightly higher transition temperature of 750 °C for the reference NbO2 film. Quantitative composition analysis from electron energy loss spectroscopy (EELS) showed the stoichiometry of the nominal 15 nm NbO2 layer in the as-fabricated MIM device deviated from the target 1:2 ratio because of an interaction with the electrode materials, which was more prominent at elevated annealing temperature.

  14. Thermally induced crystallization in NbO2 thin films

    PubMed Central

    Zhang, Jiaming; Norris, Kate J.; Gibson, Gary; Zhao, Dongxue; Samuels, Katy; Zhang, Minxian Max; Yang, J. Joshua; Park, Joonsuk; Sinclair, Robert; Jeon, Yoocharn; Li, Zhiyong; Williams, R. Stanley

    2016-01-01

    Niobium dioxide can exhibit negative differential resistance (NDR) in metal-insulator-metal (MIM) devices, which has recently attracted significant interest for its potential applications as a highly non-linear selector element in emerging nonvolatile memory (NVM) and as a locally-active element in neuromorphic circuits. In order to further understand the processing of this material system, we studied the effect of thermal annealing on a 15 nm thick NbO2 thin film sandwiched inside a nanoscale MIM device and compared it with 180 nm thick blanket NbOx (x = 2 and 2.5) films deposited on a silicon dioxide surface as references. A systematic transmission electron microscope (TEM) study revealed a similar structural transition from amorphous to a distorted rutile structure in both cases, with a transition temperature of 700 °C for the NbO2 inside the MIM device and a slightly higher transition temperature of 750 °C for the reference NbO2 film. Quantitative composition analysis from electron energy loss spectroscopy (EELS) showed the stoichiometry of the nominal 15 nm NbO2 layer in the as-fabricated MIM device deviated from the target 1:2 ratio because of an interaction with the electrode materials, which was more prominent at elevated annealing temperature. PMID:27682633

  15. Period doubling induced by thermal noise amplification in genetic circuits.

    PubMed

    Ruocco, G; Fratalocchi, A

    2014-11-18

    Rhythms of life are dictated by oscillations, which take place in a wide rage of biological scales. In bacteria, for example, oscillations have been proven to control many fundamental processes, ranging from gene expression to cell divisions. In genetic circuits, oscillations originate from elemental block such as autorepressors and toggle switches, which produce robust and noise-free cycles with well defined frequency. In some circumstances, the oscillation period of biological functions may double, thus generating bistable behaviors whose ultimate origin is at the basis of intense investigations. Motivated by brain studies, we here study an "elemental" genetic circuit, where a simple nonlinear process interacts with a noisy environment. In the proposed system, nonlinearity naturally arises from the mechanism of cooperative stability, which regulates the concentration of a protein produced during a transcription process. In this elemental model, bistability results from the coherent amplification of environmental fluctuations due to a stochastic resonance of nonlinear origin. This suggests that the period doubling observed in many biological functions might result from the intrinsic interplay between nonlinearity and thermal noise.

  16. Period doubling induced by thermal noise amplification in genetic circuits

    NASA Astrophysics Data System (ADS)

    Ruocco, G.; Fratalocchi, A.

    2014-11-01

    Rhythms of life are dictated by oscillations, which take place in a wide rage of biological scales. In bacteria, for example, oscillations have been proven to control many fundamental processes, ranging from gene expression to cell divisions. In genetic circuits, oscillations originate from elemental block such as autorepressors and toggle switches, which produce robust and noise-free cycles with well defined frequency. In some circumstances, the oscillation period of biological functions may double, thus generating bistable behaviors whose ultimate origin is at the basis of intense investigations. Motivated by brain studies, we here study an ``elemental'' genetic circuit, where a simple nonlinear process interacts with a noisy environment. In the proposed system, nonlinearity naturally arises from the mechanism of cooperative stability, which regulates the concentration of a protein produced during a transcription process. In this elemental model, bistability results from the coherent amplification of environmental fluctuations due to a stochastic resonance of nonlinear origin. This suggests that the period doubling observed in many biological functions might result from the intrinsic interplay between nonlinearity and thermal noise.

  17. 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; Pinto, L F Ribeiro

    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 1 ppm, 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 4 weeks) and at a higher frequency (4-fold increase at 16 weeks) 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. Copyright © 2016. Published by Elsevier Inc.

  18. Cryo-Induced Thermal Wounds: A Human Acute Wound Model.

    PubMed

    Vivas, Alejandra; Fox, Joshua D; Baquerizo Nole, Katherine L; Maderal, Andrea D; Badiavas, Evangelos; Cargill, D Innes; Slade, Herbert B; Feldman, Steven R; Kirsner, Robert S

    2015-07-01

    Clinical models are invaluable in studying wound healing. Challenges in studying human wounds include heterogeneity of patients and wounds, as well as prolonged study time, resulting in high costs. Animal models are an efficient method to study wound healing, but often lack correlation with human acute wound healing. Human wound models can be created using sharp instruments, suction, acids, heat and cold. In this observational study, we propose a practical human acute wound model where partial thickness wounds are induced by cryosurgery to create wounds that could facilitate wound healing research and development. On forearms of 8 healthy adult volunteers, freeze injuries were induced using liquid nitrogen spray delivered onto a target area of a 1 cm circular opening at a distance from the cryo-device to the skin of 0.5-1 cm. Several freeze-thaw time cycles were implemented by administering pulses ranging from 3 to 12 seconds. Clinical evaluation was performed at a 24-hour follow-up period. Blister roofs were histologically analyzed by a blinded dermatophathologist. Clinical assessment of time to heal was determined. Freeze-times greater than 5 seconds caused a majority of subjects to develop blisters, and freeze-times greater than 8 seconds resulted in uniform blister formation. Consistent histology of full thickness necrotic epidermis with intact detached basement membrane with minimal acute neutrophilic inflammatory infiltrate was observed in all blister specimens examined. The 8-second freeze-time group had a time to heal of 13-14 days, while the 12-second freeze-time group required 3 weeks to heal. After healing, an area of hypopigmented skin and slightly hypertrophic scarring remained. This novel cryo-induced wound model is a potential simple, efficient and reliable model for studying the dynamic processes involved in acute wound healing and to aid in the development of new wound healing therapies. Clinicaltrials.gov identifier: NCT01253135.

  19. Electronically reconfigurable superimposed waveguide long-period gratings

    NASA Astrophysics Data System (ADS)

    Kulishov, Mykola; Daxhelet, Xavier; Gaidi, Mounir; Chaker, Mohamed

    2002-08-01

    The perturbation to the refractive index induced by a periodic electric field from two systems of interdigitated electrodes with the electrode-finger period l is analyzed for a waveguide with an electro-optically (EO) active core-cladding. It is shown that the electric field induces two superimposed transmissive refractive-index gratings with different symmetries of their cross-section distributions. One of these gratings has a constant component of an EO-induced refractive index along with its variable component with periodicity l, whereas the second grating possesses only a variable component with periodicity 2l. With the proper waveguide design, the gratings provide interaction between a guided fundamental core mode and two guided cladding modes. Through the externally applied electric potential, these gratings can be independently switched ON and OFF, or they can be activated simultaneously with electronically controlled weighting factors. Coupling coefficients of both gratings are analyzed in terms of their dependence on the electrode duty ratio and dielectric permittivities of the core and cladding. The coupled-wave equations for the superimposed gratings are written and solved. The spectral characteristics are investigated by numerical simulation. It is found that the spectral characteristics are described by a dual-dip transmission spectrum with individual electronic control of the dip depths and positions. Within the concept, a new external potential application scheme is described in which the symmetry of the cross-sectional distribution of the refractive index provides coupling only between the core mode and the cladding modes, preventing interaction of the cladding modes with each another. This simple concept opens opportunities for developing a number of tunable devices for integrated optics by use of the proposed design as a building block.

  20. Spectral combining of high-power fiber laser beams using Bragg grating in PTR glass

    NASA Astrophysics Data System (ADS)

    Ciapurin, Igor V.; Glebov, Leonid B.; Smirnov, Vadim I.

    2004-06-01

    High-efficient volume Bragg gratings (VBG) in inorganic photo-thermo-refractive (PTR) glass were recently reported for the use in high-power laser systems. Both transmission and reflection gratings have shown diffraction efficiency greater than 95% from visible to near IR spectra in a wide range of spatial frequencies. Those gratings have exhibited perfect thermal, optical and mechanical stability. Spectral beam combining (SBC) using PTR Bragg grating with efficiency more than 92% for two 100 W Yb-fiber-laser beams with the 11 nm wavelength separation between them is reported. The paper presents results of modeling and experimental study of a beam combiner for high-power lasers with the only passive PTR grating component in it. Two laser beams illuminate a thick Bragg grating which has only two symmetric resonant angles providing total diffraction of a beam with a certain wavelength. Incidence angle for all transmitting beams should correspond to the Bragg angle for the diffracted beam. Transmitting beams are not diffracted by grating if spectral sift corresponds to zeros in a spectral selectivity curve, and propagate in the same direction as a diffracted beam. It is shown the efficient trade-off between grating period and refractive index modulation allows modeling of high-efficient combining setup for each of arbitrary chosen grating thickness. Comparison between calculation results and experimental data is given.

  1. Acetylsalicylic acid reduces viral shedding induced by thermal stress.

    PubMed

    Gebhardt, Bryan M; Varnell, Emily D; Kaufman, Herbert E

    2004-01-01

    To investigate the effect of acetylsalicylic acid on ocular shedding of herpes simplex virus type 1 (HSV-1). Mice that were latent for the McKrae strain of HSV-1 were treated with acetylsalicylic acid, a nonspecific inhibitor of cyclooxygenases, either prophylactically or at the time of heat stress-induced viral reactivation. The effect of the drug on viral shedding in the tear film, infectious virus in the cornea and trigeminal ganglion, and viral DNA in the cornea and trigeminal ganglion was determined. Acetylsalicylic acid inhibited heat stress-induced shedding of virus in the tears and reduced the numbers of corneal and trigeminal ganglion homogenates containing virus. Intraperitoneal therapeutic and oral prophylactic plus therapeutic treatments were similar in their ability to inhibit reactivation. The results indicate that a cyclooxygenase inhibitor such as acetylsalicylic acid can reduce recurrent viral infection in mice. These findings may implicate prostaglandins as agents in the viral reactivation process and suggest that therapy to suppress viral reactivation using nontoxic inhibitors of prostaglandin synthesis may be effective in humans.

  2. Dislocated double-layer metal gratings: an efficient unidirectional coupler.

    PubMed

    Liu, Tianran; Shen, Yang; Shin, Wonseok; Zhu, Qiangzhong; Fan, Shanhui; Jin, Chongjun

    2014-07-09

    We propose theoretically and demonstrate experimentally a dislocated double-layer metal grating structure, which operates as a unidirectional coupler capable of launching surface plasmon polaritons in a desired direction under normal illumination. The structure consists of a slanted dielectric grating sandwiched between two gold gratings. The upper gold grating has a nonzero lateral relative displacement with respect to the lower one. Numerical simulations show that a grating structure with 7 periods can convert 49% of normally incident light into surface plasmons with a contrast ratio of 78 between the powers of the surface plasmons launched in two opposite directions. We explain the unidirectional coupling phenomenon by the dislocation-induced interference of the diffracted waves from the upper and lower gold gratings. Furthermore, we developed a simple and cost-effective technique to fabricate the structure via tilted two-beam interference lithography and subsequent shadow deposition of gold. The experimental results demonstrate a coupling efficiency of 36% and a contrast ratio of 43. The relatively simple periodic nature of our structure lends itself to large-scale low-cost fabrication and simple theoretical analysis. Also, unlike the previous unidirectional couplers based on aperiodic structures, the design parameters of our unidirectional coupler can be determined analytically. Therefore, this structure can be an important component for surface-plasmon-based nanophotonic circuits by providing an efficient interface between free-space and surface plasmon waves.

  3. Population difference gratings produced by unipolar subcycle pulses in a resonant medium

    NASA Astrophysics Data System (ADS)

    Arkhipov, R. M.; Arkhipov, M. V.; Babushkin, I.; Pakhomov, A. V.; Rosanov, N. N.

    2017-07-01

    We demonstrate the possibility of inducing, erasing and extra rapidly controlling population difference gratings resulting from coherent interaction of unipolar subcycle pulses with a resonant medium. Gratings can be produced without overlap of pulses in the medium, which is an important distinction of the proposed approach from the traditional one, in which gratings are produced using interference of two or more overlapping quasi-monochromatic light beams. The use of unipolar subcycle pulses ensures faster control over gratings in comparison with bipolar pulses studied by us previously.

  4. UV-Writing of a Superstructure Waveguide Bragg Grating in a Planar Polymer Substrate.

    PubMed

    Rosenberger, Manuel; Schmauss, Bernhard; Hellmann, Ralf

    2017-08-25

    We report on the fabrication of a superstructure Bragg grating in a planar polymer substrate. Based on a twofold illumination process an integrated waveguide and a superstructure Bragg grating are subsequently written into bulk polymethylmethacrylate by UV-induced refractive index modification. The measured reflected spectrum of the superstructure Bragg grating exhibits multiple reflection peaks and is in good agreement with performed standard simulations based on the beam propagation method and coupled mode theory algorithms. By applying a varying tensile load we determine the strain sensitivity to be about 1.10 pm/µε and demonstrate the applicability of the superstructure Bragg grating for strain measurements with redundant sensing signals.

  5. Modified growth kinetics of ion induced yttrium--silicide layers during subsequent thermal annealing

    SciTech Connect

    Alford, T.L.; Mayer, J.W. )

    1991-12-02

    Yttrium and amorphous silicon bilayers were irradiated with 600-keV inert ions between {minus}190 and 265 {degree}C. Ion-induced YSi{sub 1.7} layers occurred in those samples irradiated above {ge} (R18)205 {degree}C. These ion-mixed samples were thermally annealed at temperatures between 325 and 380 {degree}C. The diffusion-limited growth was observed only in those samples which had an ion-induced YSi{sub 1.7} layer present prior to thermal annealing. This type of growth is distinctly different from the interface limited, nonuniform, and irreproducible growth seen during typical thermal annealing of yttrium and silicon bilayers. This type of growth still occurred in those samples annealed after ion irradiations at {le}190 {degree}C.

  6. Thermally induced structural changes of intrinsically disordered small heat shock protein Hsp22.

    PubMed

    Kazakov, Alexey S; Markov, Denis I; Gusev, Nikolai B; Levitsky, Dmitrii I

    2009-12-01

    We applied different methods (differential scanning calorimetry, circular dichroism, Fourier transform infrared spectroscopy, and intrinsic fluorescence) to investigate the thermal-induced changes in the structure of small heat shock protein Hsp22. It has been shown that this protein undergoes thermal-induced unfolding that occurs within a very broad temperature range (from 27 degrees C to 80 degrees C and above), and this is accompanied by complete disappearance of alpha-helices, significant decrease in beta-sheets content, and by pronounced changes in the intrinsic fluorescence. The results confirm predictions that Hsp22 belongs to the family of intrinsically disordered proteins (IDP) with certain parts of its molecule (presumably, in the alpha-crystallin domain) retaining folded structure and undergoing reversible thermal unfolding. The results are also discussed in terms of downhill folding scenario.

  7. Study on a gas transport system based on thermal induced flow

    NASA Astrophysics Data System (ADS)

    Matsumoto, Hiroaki; Mihara, Kai; Yamagishi, Daigo; Morokuma, Takayuki

    2016-11-01

    In this study, the performance of a rarefied gas transport system which works by thermal induced flow was studied experimentally. The driving force of the pump system presented in this study is thermal creep flow around the edge of a small circular plate. The thermal induced flow is generated by irradiating the plates, which are colored black on one side and white on the other. The system was constructed by arranging a series of such plates in a glass pipe which was connected to two vessels and irradiated with an infrared lamp. It was observed that the ratio of pressures in the two vessels was about 96% when the temperature difference between the black and white surfaces of the plates was about 40 °C.

  8. Thermally Induced Phase Transitions of CsHSO 4: A Reexamination

    NASA Astrophysics Data System (ADS)

    Rangavittal, N.; Row, T. N. Guru; Rao, C. N. R.

    1995-07-01

    A reexamination of the thermally induced phase transitions of CsHSO4 shows that the room-temperature phase IV transforms to II around 373 K. Phase III is, however, not obtained by heating IV to 340 K. Phases IV and III can coexist at room temperature under certain conditions; and phase III appears to transform to II at 340 K.

  9. Evaluation on thermal explosion induced by slightly exothermic interface reaction.

    PubMed

    Yu, Ma-Hong; Li, Yong-Fu; Sun, Jin-Hua; Hasegawa, Kazutoshi

    2004-09-10

    An asphalt-salt mixture (ASM), which once caused a fire and explosion in a reprocessing plant, was prepared by imitating the real bituminization process of waste on a lab scale to evaluate its actual thermal hazards. Heat flux reaction calorimeters were used to measure the release of heat for the simulated ASM at a constant heating rate and at a constant temperature, respectively. Experimental results show that the reaction in the ASM below about 250 degrees C is a slightly exothermic interface reaction between the asphalt and the salt particles contained in the asphalt, and that the heat release rate increases sharply above about 250 degrees C due to melting of the salt particles. The reaction rates were formulated on the basis of an assumed reaction model, and the kinetic parameters were determined. Using the model with the kinetic parameters, temperature changes with time and drum-radius axes for the ASM-filled drum were numerically simulated assuming a one-dimensional infinite cylinder system, where the drum was being cooled at an ambient temperature of 50 degrees C. The minimum filling temperature, at which the runaway reaction (MFTRR) can occur for the simulated ASM in the drum is about 194 degrees C. Furthermore, a very good linear correlation exists between this MFTRR and the initial radius of salt particles formed in the bituminization product. The critical filling temperature to the runaway reaction is about 162 degrees C for the asphalt-salt mixture, containing zero-size salt particles, filled in the same drum at an ambient temperature of 50 degrees C. Thus, the runaway reaction will never occur in the drum filled with the asphalt-salt mixture under the conditions of the filling temperature below 162 degrees C and a constant ambient temperature of 50 degrees C. As a consequence, the ASM explosion occurred in the reprocessing plant likely was due to a slightly exothermically reaction and self heating.

  10. Thermally induced filter bias in TEOM mass measurement.

    PubMed

    Page, Steven J; Tuchman, Donald P; Vinson, Robert P

    2007-07-01

    Researchers at the National Institute for Occupational Safety and Health (NIOSH) have long used stationary tapered element oscillating microbalances (TEOMs) in laboratory settings. They have served to assess the mass concentration of laboratory-generated particulates in experimental dust chambers and they provide a reference method for comparison with other particulate-measuring instruments. Current NIOSH research is focused on further adapting TEOM technology as a wearable personal dust monitor (PDM) for coal mining occupations. This investigation's goal is to help identify, quantify, and provide means for resolving certain TEOM-related error. The present research investigated bias caused by thermal effects on filter assemblies. New filters used in the PDM for 8 h tests show an average positive bias of 25.5 microg, while similar tests of equivalent filters used in two 1400A model TEOMs show an average positive bias of 34.3 microg. The derived bias values allow correction of previously collected biased data. Also, pre-heating the filters for 24 h at 46 degrees C shows significant bias reduction, with PDM pre-heated filters subsequently averaging -3.3 microg and 1400A TEOM filters averaging 5.9 microg. On a single-point comparison to gravimetric sampling, a 25.5 microg bias is only significant at low mass loadings. At 2.5 mg, this bias represents a negligible 1% of the mass measurement. If ordinary linear regression is used, the bias is still insignificant. However, if the more valid weighted linear regression is used, it gives more weight to the smaller dependent variable values, which are more impacted by the bias. Consequently, what is 1% bias on a single high-mass value can translate into a larger bias percentage at high-mass values when performing a weighted regression on data that include a large number of low-mass values.

  11. 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.

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

    PubMed Central

    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

  13. Magnetic field induced augmented thermal conduction phenomenon in magneto-nanocolloids

    NASA Astrophysics Data System (ADS)

    Katiyar, Ajay; Dhar, Purbarun; Nandi, Tandra; Das, Sarit K.

    2016-12-01

    Magnetic field induced augmented thermal conductivity of magneto-nanocolloids involving nanoparticles, viz. Fe2O3, Fe3O4, NiO and Co3O4 dispersed in different base fluids have been reported. Experiments reveal the augmented thermal transport under external applied magnetic field. A maximum thermal conductivity enhancement ∼114% is attained at 7.0 vol% concentration and 0.1 T magnetic flux density for Fe3O4/EG magneto-nanocolloid. However, a maximum ∼82% thermal conductivity enhancement is observed for Fe3O4/kerosene magneto-nanocolloid for the same concentration but relatively at low magnetic flux density (∼0.06 T). Thereby, a strong effect of fluid as well as particle physical properties on the chain formation propensity, leading to enhanced conduction, in such systems is observed. Co3O4 nanoparticles show insignificant effect on the thermal conductivity enhancement of MNCs due to their minimal magnetic moment. A semi-empirical approach has been proposed to understand the mechanism and physics behind the thermal conductivity enhancement under external applied magnetic field, in tune with near field magnetostatic interactions as well as Neel relaxivity of the magnetic nanoparticles. Furthermore, the model is able to predict the phenomenon of enhanced thermal conductivity as a function of physical parameters and shows good agreement with the experimental observations.

  14. 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

    2014-01-15

    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.

  15. 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.

  16. Temperature-induced gene expression associated with different thermal reaction norms for growth rate.

    PubMed

    Ellers, Jacintha; Mariën, Janine; Driessen, Gerard; van Straalen, Nico M

    2008-03-15

    Although nearly all organisms are subject to fluctuating temperature regimes in their natural habitat, little is known about the genetics underlying the response to thermal conditions, and even less about the genetic differences that cause individual variation in thermal response. Here, we aim to elucidate possible pathways involved in temperature-induced phenotypic plasticity of growth rate. Our model organism is the collembolan Orchesella cincta that occurs in a wide variety of habitats and is known to be adapted to local thermal conditions. Because sequence information is lacking in O. cincta, we constructed cDNA libraries enriched for temperature-responsive genes using suppression subtractive hybridization. We compared gene expression of O. cincta with steep thermal reaction norms (high plasticity) to those with flat thermal reaction norms (low plasticity) for juvenile growth after exposure to a temperature switch composed of a cooling or a warming treatment. Using suppression subtractive hybridization, we found differential expression of ten nuclear genes, including several genes involved in energy metabolism, such as pantothenate kinase and carbonic anhydrase. In addition, seven mitochondrial genes were found in the cloned subtracted library, but further analysis showed this was caused by allelic variation in mitochondrial genes in our founder population, and that a specific haplotype was associated with high thermal responsiveness. Future work will focus on candidate genes from pathways such as the oxidative phosphorylation and biosynthesis of coenzyme A which are possibly involved in thermal responsiveness of juvenile growth rate.

  17. High-Average-Power Diffraction Pulse-Compression Gratings Enabling Next-Generation Ultrafast Laser Systems

    SciTech Connect

    Alessi, D.

    2016-11-01

    Pulse compressors for ultrafast lasers have been identified as a technology gap in the push towards high peak power systems with high average powers for industrial and scientific applications. Gratings for ultrashort (sub-150fs) pulse compressors are metallic and can absorb a significant percentage of laser energy resulting in up to 40% loss as well as thermal issues which degrade on-target performance. We have developed a next generation gold grating technology which we have scaled to the petawatt-size. This resulted in improvements in efficiency, uniformity and processing as compared to previous substrate etched gratings for high average power. This new design has a deposited dielectric material for the grating ridge rather than etching directly into the glass substrate. It has been observed that average powers as low as 1W in a compressor can cause distortions in the on-target beam. We have developed and tested a method of actively cooling diffraction gratings which, in the case of gold gratings, can support a petawatt peak power laser with up to 600W average power. We demonstrated thermo-mechanical modeling of a grating in its use environment and benchmarked with experimental measurement. Multilayer dielectric (MLD) gratings are not yet used for these high peak power, ultrashort pulse durations due to their design challenges. We have designed and fabricated broad bandwidth, low dispersion MLD gratings suitable for delivering 30 fs pulses at high average power. This new grating design requires the use of a novel Out Of Plane (OOP) compressor, which we have modeled, designed, built and tested. This prototype compressor yielded a transmission of 90% for a pulse with 45 nm bandwidth, and free of spatial and angular chirp. In order to evaluate gratings and compressors built in this project we have commissioned a joule-class ultrafast Ti:Sapphire laser system. Combining the grating cooling and MLD technologies developed here could enable petawatt laser systems to

  18. 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.

  19. Fabrication of Polymer Optical Fibre (POF) Gratings

    PubMed Central

    Luo, Yanhua; Yan, Binbin; Zhang, Qijin; Peng, Gang-Ding; Wen, Jianxiang; Zhang, Jianzhong

    2017-01-01

    Gratings inscribed in polymer optical fibre (POF) have attracted remarkable interest for many potential applications due to their distinctive properties. This paper overviews the current state of fabrication of POF gratings since their first demonstration in 1999. In particular we summarize and discuss POF materials, POF photosensitivity, techniques and issues of fabricating POF gratings, as well as various types of POF gratings. PMID:28273844

  20. High-efficiency and fast-response tunable phase grating using a blue phase liquid crystal.

    PubMed

    Yan, Jin; Li, Yan; Wu, Shin-Tson

    2011-04-15

    We demonstrate a tunable phase grating using a polymer-stabilized blue phase liquid crystal. Because of the electric-field-induced rectangularlike phase profile, a high diffraction efficiency of 40% is achieved. Moreover, this device shows submillisecond response time. The proposed tunable phase grating holds great potential for photonics and display applications.

  1. 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

  2. Performance evaluation of fiber Bragg gratings at elevated temperatures

    NASA Astrophysics Data System (ADS)

    Juergens, Jeffrey; Adamovsky, Grigory; Floyd, Bertram

    2004-03-01

    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

  3. 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.

  4. 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

  5. Study of the thermal effect on silicon surface induced by ion beam from plasma focus device

    NASA Astrophysics Data System (ADS)

    Ahmad, Z.; Ahmad, M.; Al-Hawat, Sh.; Akel, M.

    2017-04-01

    Structural modifications in form of ripples and cracks are induced by nitrogen ions from plasma focus on silicon surface. The investigation of such structures reveals correlation between ripples and cracks formation in peripheral region of the melt spot. The reason of such correlation and structure formation is explained as result of thermal effect. Melting and resolidification of the center of irradiated area occur within one micro second of time. This is supported by a numerical simulation used to investigate the thermal effect induced by the plasma focus ion beams on the silicon surface. This simulation provides information about the temperature profile as well as the dynamic of the thermal propagation in depth and lateral directions. In accordance with the experimental observations, that ripples are formed in latter stage after the arrival of last ion, the simulation shows that the thermal relaxation takes place in few microseconds after the end of the ion beam arrival. Additionally, the dependency of thermal propagation and relaxation on the distance of the silicon surface from the anode is presented.

  6. 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.

  7. 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.

  8. Thermally induced mode distortion and its limit to power scaling of fiber lasers.

    PubMed

    Ke, Wei-Wei; Wang, Xiao-Jun; Bao, Xian-Feng; Shu, Xiao-Jian

    2013-06-17

    A general model is proposed to describe thermal-induced mode distortion in the step-index fiber (SIF) high power lasers. Two normalized parameters in the model are able to determine the mode characteristic in the heated SIFs completely. Shrinking of the mode fields and excitation of the high-order modes by the thermal-optic effect are investigated. A simplified power amplification model is used to describe the output power redistribution under various guiding modes. The results suggest that fiber with large mode area is more sensitive on the thermally induced mode distortion and hence is disadvantaged in keeping the beam quality in high power operation. The model is further applied to improve the power scaling analysis of Yb-doped fiber lasers. Here the thermal effect is considered to couple with the optical damage and the stimulated Raman scattering dynamically, whereas direct constraint from the thermal lens is relaxed. The resulting maximal output power is from 67kW to 97kW, depending on power fraction of the fundamental mode.

  9. Effect of acyclovir on thermal stress-induced herpesvirus reactivation.

    PubMed

    Gebhardt, Bryan M; Kaufman, Herbert E; Hill, James M

    2004-01-01

    Acyclovir has been shown to be effective in preventing recurrent herpes simplex virus lesions of the genitalia and oral labia. The purpose of the current study was to determine the effect of acyclovir on the appearance of infectious virus in the peripheral nervous system and in an end organ, the eye. Mice latent for the McKrae strain of herpes simplex virus type 1 were given 3.5 mg/ml acyclovir in their drinking water. Control animals received water without drug. Acyclovir treatment was continued for 4 successive days. On the third day, the mice were subjected to a brief period of hyperthermic stress to induce viral reactivation. Twenty-four hours after stress induction, swabs of the ocular surface and homogenates of the cornea and trigeminal ganglia were analyzed for the presence of infectious herpes simplex virus type 1 and viral DNA. Acyclovir treatment significantly decreased the frequency of infectious virus in the ocular tear film and the cornea but not in the trigeminal ganglion. The corneal homogenates of acyclovir-treated animals contained smaller amounts of viral DNA compared with untreated controls, whereas the amounts of viral DNA in the trigeminal ganglia of acyclovir-treated and untreated animals were similar. These results suggest that oral administration of acyclovir, at least at the dose used in this study, is effective in modestly reducing viral replication in peripheral tissues such as the eye but is not effective in inhibiting viral reactivation and viral DNA synthesis in the peripheral nervous system in mice subjected to induction of reactivation by hyperthermic stress.

  10. The use of MRI-guided laser-induced thermal ablation for epilepsy.

    PubMed

    Tovar-Spinoza, Zulma; Carter, David; Ferrone, David; Eksioglu, Yaman; Huckins, Sean

    2013-11-01

    Epilepsy surgery is constantly researching for new options for patients with refractory epilepsy. MRI-guided laser-induced thermal ablation for epilepsy is an exciting new minimally invasive technology with an emerging use for lesionectomy of a variety of epileptogenic focuses (hypothalamic hamartomas, cortical dysplasias, cortical malformations, tubers) or as a disconnection tool allowing a new option of treatment without the hassles of an open surgery. MRI-guided laser interstitial thermal therapy (MRgLITT) is a procedure for destroying tissue-using heat. To deliver this energy in a minimally invasive fashion, a small diameter fiber optic applicator is inserted into the lesion through a keyhole stereotactic procedure. The thermal energy induces damage to intracellular DNA and DNA-binding structures, ultimately leading to cell death. The ablation procedure is supervised by real-time MRI thermal mapping and confirmed by immediate post-ablation T1 or FLAIR MRI images. The present report includes an overview of the development and practice of an MR-guided laser ablation therapy known as MRI-guided laser interstitial thermal therapy (MRgLITT). The role of modern image-guided trajectory planning in MRgLITT will also be discussed, with particular emphasis on the treatment of refractory epilepsy using this novel, minimally invasive technique. MRI-guided laser-induced thermal ablation for epilepsy is an exciting new minimally invasive technology that finds potential new applications every day in the neurosurgical field. It certainly brings a new perspective on the way we practice epilepsy surgery even though long-term results should be properly collected and analyzed.

  11. Naringenin improves the healing process of thermally-induced skin damage in rats.

    PubMed

    Al-Roujayee, Abdulaziz S

    2017-04-01

    Objective To evaluate the effect of the phenolic compound naringenin on thermal burn-induced inflammatory responses and oxidative stress in rats. Methods First degree thermal burn injuries were induced in shaved rats by 10 s immersion of the back surface in water at 90℃. Naringenin treatment (25, 50 and 100 mg/kg/day) was initiated 24 h following burn injury, and continued for 7 days. On treatment day 7, serum tumour necrosis factor (TNF)-α, interleukin (IL)-1β, IL-6, nitric oxide (NO), prostaglandin (PG)E2, caspase-3, leukotriene (LT)-B4 and nuclear factor (NF)-κB levels were quantified. Skin sample glutathione (GSH) and thiobarbituric acid reactive substances (TBARS) levels, and catalase, superoxide dismutase (SOD), glutathione-S-transferase (GST) and glutathione peroxidase (GPx) activities, were also measured. Results Serum inflammatory biomarkers were significantly increased in thermal-burn injured rats versus uninjured controls. Naringenin significantly inhibited the increased proinflammatory markers at day 7 of treatment. Increased TBARS levels and decreased GSH levels in wounded skin were significantly restored by naringenin treatment at day 7. SOD, catalase, GPx and GST activities were markedly inhibited in wounded skin tissues, and were significantly increased in naringenin-treated rats. Conclusion Naringenin treatment showed anti-inflammatory and antioxidant effects in rats with thermal burn-induced injury.

  12. PFC2D simulation of thermally induced cracks in concrete specimens

    NASA Astrophysics Data System (ADS)

    Liu, Xinghong; Chang, Xiaolin; Zhou, Wei; Li, Shuirong

    2013-06-01

    The appearance of cracks exposed to severe environmental conditions can be critical for concrete structures. The research is to validate Particle Flow Code(PFC2D) method in the context of concrete thermally-induced cracking simulations. First, concrete was discreted as meso-level units of aggregate, cement mortar and the interfaces between them. Parallel bonded-particle model in PFC2D was adapted to describe the constitutive relation of the cementing material. Then, the concrete mechanics meso-parameters were obtained through several groups of biaxial tests, in order to make the numerical results comply with the law of the indoor test. The concrete thermal meso-parameters were determined by compared with the parameters in the empirical formula through the simulations imposing a constant heat flow to the left margin of concrete specimens. At last, a case of 1000mm×500mm concrete specimen model was analyzed. It simulated the formation and development process of the thermally-induced cracks under the cold waves of different durations and temperature decline. Good agreements in fracture morphology and process were observed between the simulations, previous studies and laboratory data. The temperature decline limits during cold waves were obtained when its tensile strength was given as 3MPa. And it showed the feasibility of using PFC2D to simulate concrete thermally-induced cracking.

  13. 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.

  14. 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.

  15. Lycopene ameliorates thermal hyperalgesia and cold allodynia in STZ-induced diabetic rat.

    PubMed

    Kuhad, Anurag; Chopra, Kanwaljit

    2008-02-01

    Peripheral neuropathy is one of the common complications of diabetes mellitus. It is frequently associated with debilitating pain. The present study was designed to investigate effect of Lycopene, a carotenoid found in tomatoes, on hyperalgesia and cold allodynia in streptozotocin (STZ) induced diabetic rats. After 4-weeks of STZ injection, diabetic mice exhibited a significant thermal hyperalgesia cold allodynia, hyperglycemia and loss of body weights as compared with control rats. Chronic treatment of lycopene for 4 weeks significantly attenuated the cold allodynia and thermal hyperalgesia. The results emphasize the role of antioxidant such as lycopene as an adjuvant therapy in the treatment of diabetic neuropathy.

  16. Thermally-induced, geometrically nonlinear response of symmetrically laminated composite plates

    NASA Technical Reports Server (NTRS)

    Meyers, C. A.; Hyer, M. W.

    1992-01-01

    This paper discusses the thermally-induced geometrically nonlinear response of symmetrically laminated composite plates. The plate response is due to a temperature increase that is uniform in the plane of the plate but has a slight gradient through the thickness. The case of a completely uniform temperature increase but with an initial out-of-plane imperfection in the plate is also considered. Because they are closely allied problems, thermal buckling and postbuckling are discussed. Using variational methods in conjunction with a Rayleigh-Ritz formulation, these responses are investigated for two laminates, a (+/- 45/0/90)s and a (+/- 45/02)s, under two different simple support conditions.

  17. Analysis of Heavy Ion Irradiation Induced Thermal Damage in SiC Schottky Diodes

    NASA Astrophysics Data System (ADS)

    Abbate, C.; Busatto, G.; Cova, P.; Delmonte, N.; Giuliani, F.; Iannuzzo, F.; Sanseverino, A.; Velardi, F.

    2015-02-01

    A study is presented aimed at describing phenomena involved in Single Event Burnout induced by heavy ion irradiation in SiC Schottky diodes. On the basis of experimental data obtained for 79Br irradiation at different energies, electro-thermal FEM is used to demonstrate that the failure is caused by a strong local increase of the semiconductor temperature. With respect to previous studies the temperature dependent thermal material properties were added. The critical ion energy calculated by this model is in agreement with literature experimental results. The substrate doping dependence of the SEE robustness was analyzed, proving the effectiveness of the developed model for device technological improvements.

  18. Observation of thermally induced tuning of lasing emission from melamine–formaldehyde resin microspheres

    NASA Astrophysics Data System (ADS)

    Li, Hanyang; Liu, Shuangqiang; Peng, Feng; Yang, Jun; Li, Jin; Zhang, Yundong

    2017-03-01

    We report on the observation of the thermally induced tuning of the whispering gallery mode lasing emission from active microcavities. Melamine–formaldehyde resin microspheres were doped with a fluorescent dye and pumped by a 532 nm pulse laser. We show that microspheres with different sizes display lasing emissions in different parts of the spectrum, with a varying number of lasing modes present in the spectrum. The dominant thermo-optic effect leads to a blue shift of the whispering gallery mode lasing. The thermal sensing with a sensitivity of 0.33 nm/°C is higher than that of conventional polymer microcavities.

  19. Origin of Domes on Europa: The Role of Thermally Induced Compositional Buoyancy,

    NASA Technical Reports Server (NTRS)

    Pappalardo, R. T.; Barr, A. C.

    2004-01-01

    The surface of Jupiter's moon Europa is peppered by topographic domes, interpreted as sites of intrusion and extrusion. Diapirism is consistent with dome morphology, but thermal buoyancy alone cannot produce sufficient driving pressures to create the observed dome elevations. Instead, diapirs may initiate by thermal convection that induces compositional segregation. Exclusion of impurities from warm upwellings allows sufficient buoyancy for icy plumes to create the observed surface topography, provided the ice shell has a small effective elastic thickness (0.2 to 0.5 km) and contains low-eutectic point impurities at the few percent level. This model suggests that the ice shell may be depleted in impurities over time.

  20. 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.

  1. Laser-induced thermal dynamics and temperature localization phenomenon in tissues and cells doped with nanoshells

    NASA Astrophysics Data System (ADS)

    Yakunin, Alexander N.; Avetisyan, Yury A.; Tuchin, Valery V.

    2012-03-01

    Paper presents and discusses the features of laser-induced thermal dynamics of the gold nanoshells, which is associated with their relatively large size and layered structure. Unlike bulk nanoparticles the existence of a novel thermal phenomenon - hoop-shaped narrow hot zone on the nanoshell surface - is found. It is caused by spatial-temporal inhomogeneities of light field diffracted by a nanoshell and corresponding absorption of laser radiation. The numerical solution of time-dependent heat conduction equation accounting for corresponding spatially inhomogeneous distribution of heating sources is presented.

  2. Origin of Domes on Europa: The Role of Thermally Induced Compositional Buoyancy,

    NASA Technical Reports Server (NTRS)

    Pappalardo, R. T.; Barr, A. C.

    2004-01-01

    The surface of Jupiter's moon Europa is peppered by topographic domes, interpreted as sites of intrusion and extrusion. Diapirism is consistent with dome morphology, but thermal buoyancy alone cannot produce sufficient driving pressures to create the observed dome elevations. Instead, diapirs may initiate by thermal convection that induces compositional segregation. Exclusion of impurities from warm upwellings allows sufficient buoyancy for icy plumes to create the observed surface topography, provided the ice shell has a small effective elastic thickness (0.2 to 0.5 km) and contains low-eutectic point impurities at the few percent level. This model suggests that the ice shell may be depleted in impurities over time.

  3. Waveguide silicon nitride grating coupler

    NASA Astrophysics Data System (ADS)

    Litvik, Jan; Dolnak, Ivan; Dado, Milan

    2016-12-01

    Grating couplers are one of the most used elements for coupling of light between optical fibers and photonic integrated components. Silicon-on-insulator platform provides strong confinement of light and allows high integration. In this work, using simulations we have designed a broadband silicon nitride surface grating coupler. The Fourier-eigenmode expansion and finite difference time domain methods are utilized in design optimization of grating coupler structure. The fully, single etch step grating coupler is based on a standard silicon-on-insulator wafer with 0.55 μm waveguide Si3N4 layer. The optimized structure at 1550 nm wavelength yields a peak coupling efficiency -2.6635 dB (54.16%) with a 1-dB bandwidth up to 80 nm. It is promising way for low-cost fabrication using complementary metal-oxide- semiconductor fabrication process.

  4. 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.

  5. 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.

  6. Gratings, photosensitivity, and poling in silica optical waveguides with 157-nm fluorine laser radiation

    NASA Astrophysics Data System (ADS)

    Chen, Peng (Kevin)

    2002-08-01

    The energetic 7.9-eV photons of the F2 laser directly access bandgap states in germanosilicate glasses to drive one-photon processes for inducing strong refractive index changes in silica optical waveguides. In this thesis, the author carried out the first comprehensive F2-laser photosensitivity studies with an aim to assess prospects for shaping useful photonic structures directly inside the germanosilicate waveguides. Both planar waveguides and standard telecommunication fibers were examined. Large effective index change (>10-3) was induced in both fibers and planar waveguides without any enhancement technique. With the use of hydrogen loading enhancement, asymmetric refractive index profiles were noted by atomic force microscopy and microreflection microscopy, having a peak index change of larger than 0.01 in the fiber core. The 157-nm laser radiation is effective in rapidly forming long-period gratings in standard fibers. Grating formation is over 250 times faster than that with the 248-nm KrF laser constituting the fastest photosensitivity response ever reported. For planar lightwave circuits (PLCs), the 157-nm laser exposure generate narrow profiles of large index changes (Deltan ˜ 10 -2) that is useful in trimming phase errors and controlling birefringence in frequency domain modulators (FDMs) and interleavers. The large vacuum-ultraviolet-induced birefringence was used to completely compensate the intrinsic birefringence of Deltan ˜ 10-4 in typical PLCs. With hydrogen soaking, modest 157-nm pre-irradiation (accumulated fluence >3 J/cm2) was found to 'lock-in' a permanent photosensitivity enhancement in the germanosilica, permitting the formation of strong (40 dB) and stable fiber Bragg gratings with 248-nm-KrF laser light. The F2-laser photosensitivity locking was 300-time more effective than with KrF-laser pretreatment. The practical trimming applications in PLCs were demonstrated in PLC interleavers and FDMs. The 157-nm laser pre-radiation was found to

  7. Comparative study of 1,064-nm laser-induced skin burn and thermal skin burn.

    PubMed

    Zhang, Yi-Ming; Ruan, Jing; Xiao, Rong; Zhang, Qiong; Huang, Yue-Sheng

    2013-01-01

    Infrared lasers are widely used in medicine, industry, and other fields. While science, medicine, and the society in general have benefited from the many practical uses of lasers, they also have inherent safety issues. Although several procedures have been put forward to protect the skin from non-specific laser-induced damage, individuals receiving laser therapy or researchers who use laser are still at risk for skin damage. This study aims to understand the interaction between laser and the skin, and to investigate the differences between the skin damage caused by 1,064-nm laser and common thermal burns. Skin lesions on Wistar rats were induced by a 1,064-nm CW laser at a maximum output of 40 W and by a copper brass bar attached to an HQ soldering iron. Histological sections of the lesions and the process of wound healing were evaluated. The widths of the epidermal necrosis and dermal denaturalization of each lesion were measured. To observe wound healing, the epithelial gap and wound gap were measured. Masson's trichrome and picrosirius red staining were also used to assess lesions and wound healing. The thermal damage induced by laser intensified significantly in both horizontal dimension and in vertical depth with increased duration of irradiation. Ten days after wounding, the dermal injuries induced by laser were more severe. Compared with the laser-induced skin damage, the skin burn induced by an HQ soldering iron did not show a similar development or increased in severity with the passage of time. The results of this study showed the pattern of skin damage induced by laser irradiation and a heated brass bar. This study also highlighted the difference between laser irradiation and thermal burn in terms of skin damage and wound healing, and offers insight for further treatment.

  8. 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.

  9. Extraordinary optical transmission and enhanced magneto-optical effects induced by hybrid waveguide-surface plasmon polariton mode in bilayer metallic grating

    NASA Astrophysics Data System (ADS)

    Lei, Chengxin; Wang, Sihao; Tang, Zhixiong; Li, Daoyong; Chen, Leyi; Tang, Shaolong; Du, Youwei

    2017-03-01

    We predict theoretically a significant enhancement of the magneto-optical Faraday rotation and extraordinary optical transmission in the bilayer metallic grating. Calculations, based on the extended finite difference time domain method, demonstrate that in such structures the Faraday rotation spectrum has several resonant peaks in a broad spectrum spanning visible to near-infrared frequencies, some of them coinciding with transmittance peaks, providing simultaneously an up to 44-fold Faraday rotation enhancement and high transmittance of 57%, which is quite favorable for the potential application of novel optical and magneto-optical devices. Meanwhile, two pairs of resonant Faraday rotation angles whose signs are opposite can be achieved in the visible and near-infrared wavelength ranges. It is most important that the wavelength position and amplitude of the transmittance and Faraday rotation can be simply tailored by the incident angle of incident light, the period of the designed system, and so on. We research the implied physical mechanism of the resonance characteristics of transmittance and Faraday rotation by investigating the influences of different incident angles and periods on them and the electromagnetic field distributions at the location of resonance. It is found that the resonant peaks and dips are determined by different hybrid modes of waveguide resonance mode and surface plasmon polariton mode, and the conversion of the TM- and TE-mode in the magnetic dielectric layer mostly governs the enhancement of the Faraday rotation. These research findings will be useful for the design of novel surface plasmon magneto-optical devices in the future.

  10. Non-diffusive thermal transport in GaAs at micron length scales

    SciTech Connect

    Johnson, Jeremy A.; Eliason, Jeffrey K.; Maznev, Alexei A.; Luo, Tengfei; Nelson, Keith A.

    2015-10-21

    We use a transient thermal grating technique in reflection geometry to measure the effective thermal diffusivity in GaAs as a function of heat transfer distance at three temperatures. Utilizing heterodyne detection, we isolate the “amplitude” grating contribution of the transient grating signal, which encodes the thermal transport dynamics. As the thermal grating period decreases, and thus the heat-transfer distance, we observe a reduction in the effective thermal diffusivity, indicating a departure from diffusive behavior. Non-diffusive behavior is observed at room temperature, as well as low temperature (180 K) and high temperature (425 K). At the shortest thermal grating period measured corresponding to a heat transfer distance of approximately 1 μm, the effective diffusivity drops to a value roughly 50% of the bulk thermal diffusivity. These measurements show the utility of the reflection transient thermal grating technique to measure thermal transport properties of opaque materials.

  11. Simultaneous dispersion compensation and polarization mode dispersion compensation using linearly chirped fiber Bragg grating

    NASA Astrophysics Data System (ADS)

    Li, Zhiquan; Chen, Ying; Xu, Mingyan; Zhu, Qiguang

    2005-01-01

    A composite structure based on linearly chirped fiber Bragg grating which can compensate for dispersion and polarization mode dispersion simultaneously has been proposed and characterized. On one hand, a chirped fiber Bragg grating can be regarded as a filter that is composed of several uniform sub-gratings. Therefore, optical signals with different wavelengths can be reflected at different points of the grating, which will result in different time delays, by which the dispersion compensation can be implemented easily. On the other hand, a chirped fiber Bragg grating has the pressure-induced birefringence effect. In the experiment, a piezoelectric transducer is used to apply the pressure on the linearly chirped fiber Bragg grating. Then the change of reflection spectra can be obtained when the pressure is applied at different points of the grating. From the reflection spectra response, the transverse pressure is found to lead to the split of the spectra of the grating. Through the observation of the group delay characteristics, we find that the differential group delay moves towards a bigger value with the increased voltage, and the maximal range of differential group delay (DGD) is 50 ps. By consequence, first-order polarization mode dispersion (PMD) can be compensated for with linearly chirped fiber Bragg grating. Thus, when the data rate of the fiber communication system is above 10 Gb/s and below 40 Gb/s, the simultaneous compensation of DGD and PMD is necessary and can be achieved by the composite structure.

  12. Modeling of Thermally Induced Stresses in Three-Dimensional Bonded Integrated Circuit Wafers

    NASA Astrophysics Data System (ADS)

    Zhang, Jing

    2011-05-01

    A finite-element model has been developed to investigate the potential reliability issues of thermally induced stresses in interwafer Cu via structures in three-dimensional (3D) integrated circuit (IC) wafers. The model is first partially validated by comparing computed results against experimental data on via test structures from planar ICs. Computed von Mises stresses show that the predicted failure agrees with the results of thermal cycle experiments. The model is then employed to study thermal stresses in interwafer Cu vias in 3D bonded IC structures. The results illustrate that there is a concern regarding the stability of interwafer Cu vias. Simulations show that the von Mises stresses in interwafer Cu vias decrease with decreasing pitch length at constant via size, increase with decreasing via size at constant pitch, and decrease with decreasing bonding thickness.

  13. High-strength and thermally stable bulk nanolayered composites due to twin-induced interfaces.

    PubMed

    Zheng, Shijian; Beyerlein, Irene J; Carpenter, John S; Kang, Keonwook; Wang, Jian; Han, Weizhong; Mara, Nathan A

    2013-01-01

    Bulk nanostructured metals can attribute both exceptional strength and poor thermal stability to high interfacial content, making it a challenge to utilize them in high-temperature environments. Here we report that a bulk two-phase bimetal nanocomposite synthesised via severe plastic deformation uniquely possesses simultaneous high-strength and high thermal stability. For a bimetal spacing of 10 nm, this composite achieves an order of magnitude increase in hardness of 4.13 GPa over its constituents and maintains it (4.07 GPa), even after annealing at 500 °C for 1 h. It owes this extraordinary property to an atomically well-ordered bimaterial interface that results from twin-induced crystal reorientation, persists after extreme strains and prevails over the entire bulk. This discovery proves that interfaces can be designed within bulk nanostructured composites to radically outperform previously prepared bulk nanocrystalline materials, with respect to both mechanical and thermal stability.

  14. Fluctuation of a Piston in Vacuum Induced by Thermal Radiation Pressure

    NASA Astrophysics Data System (ADS)

    Inui, Norio

    2017-10-01

    We consider the displacement of a piston dividing a vacuum cavity at a finite temperature T induced by fluctuations in the thermal radiation pressure. The correlation function of the thermal radiation pressure is calculated using the theoretical framework developed by Barton, which was first applied to the fluctuation of the Casimir force at absolute zero. We show that the variance of the radiation pressure at a fixed point is proportional to T8 and evaluate the mean square displacement for a piston with a small cross section in a characteristic correlation timescale ħ/(kBT). At room temperature, the contribution of the thermal radiation to the fluctuation is larger than that of the vacuum fluctuation.

  15. 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.

  16. Laser induced fluorescence imaging of thermal damage in polymer matrix composites

    SciTech Connect

    Wachter, E.A.; Fisher, W.G.; Meyer, K.E.

    1996-12-31

    A simple, fluorescence-based imaging system was developed for identifying regions of thermal damage in polymer-matrix composites (PMCs). PMCs have important applications where low weight and high mechanical strength are needed. One concern in the aerospace industry is the tendency of some PMC materials to become irreversibly damaged when exposed to high temperatures. Traditional nondestructive evaluation (NDE) techniques are capable of detecting physical flaws, such as cracks and delaminations, but have not proven effective for detecting initial heat damage, which occurs on a molecular scale. Spectroscopic techniques such as laser-induced fluorescence provide an attractive means for detecting thermal damage on large, irregularly shaped surfaces. This paper describes instrumentation capable of rapidly detecting thermal damage in graphite/epoxy components.

  17. 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.

  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.

  19. 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.

  20. Hot colors: the nature and specificity of color-induced nasal thermal sensations.

    PubMed

    Michael, George A; Galich, Hélène; Relland, Solveig; Prud'hon, Sabine

    2010-03-05

    The nature of the recently discovered color-induced nasal thermal sensations was investigated in four Experiments. Subjects were required to fixate a bottle containing a red or green solution presented centrally (Exp1 and Exp4) or laterally (Exp2) and to sniff another bottle, always the same one, but which they were not allowed to see, containing 10 ml of a colorless, odorless and trigeminal-free solution. Each nostril was tested separately, and subjects were asked whether the sniffed solution induced warming or cooling sensations (plus an ambient sensation in Exp4) in the nasal cavity. The results of Experiments 1 and 2 confirmed the warming/left nostril-cooling/right nostril dissociation, suggesting the existence of different lateralized processes for thermal processing. However, Experiment 2 failed to demonstrate dominance of warming responses when subjects' eyes were directed to the left or cooling responses when they were directed to the right. Nor did gaze direction interact with the tested nostril. This suggests that the color-induced thermal sensations are specifically related to the nasal trigeminal system, rather than a general process related to general hemispheric activity. When the exposed bottles were colorless (Exp3), no lateralized patterns were observed, suggesting, in combination with the results of Experiments 1 and 2, that both color cues and nasal stimulations are necessary for lateralized patterns to arise. Rendering the temperature judgment even more difficult (Exp4), made the lateralized patterns shift towards the associated (i.e., ambient) responses. The results are discussed in a general framework which considers that, even in the absence of real thermal stimulus, preparing to process thermal stimuli in the nasal cavity may activate the underlying lateralized neural mechanisms, and that those mechanisms are reflected in the responses.

  1. Optical fiber Bragg gratings. Part I. Modeling of infinitely long gratings

    NASA Astrophysics Data System (ADS)

    Passaro, Vittorio M. N.; Diana, Roberto; Armenise, Mario N.

    2002-09-01

    We present an accurate numerical method based on the Floquet-Bloch formalism to analyze the propagation properties and the radiation loss in infinitely long uniform fiber Bragg gratings. The model allows us to find all the propagation characteristics including the propagation constants, the space harmonics and the total field distribution, the guided and radiated power, and the modal loss induced by the periodic structure. The influence of the geometrical and physical parameters on the performance of the Bragg gratings has been established. A clear explanation of the physical phenomena related to the index modulation amplitude changes is presented, including the photonic bandgap effect, which is not easily described by the finite-difference time-domain method and cannot be described by the widely used coupled-mode theory.

  2. Rear side gratings for silicon solar cells: efficiency enhancement finally demonstrated

    NASA Astrophysics Data System (ADS)

    Bläsi, Benedikt; Tucher, Nico; Eisenlohr, Johannes; Lee, Benjamin G.; Benick, Jan; Hauser, Hubert; Hermle, Martin; Goldschmidt, Jan Christoph

    2016-04-01

    After more than 20 years of research on rear side gratings for light trapping in solar cells, we have been able to demonstrate enhanced efficiencies for crystalline silicon solar cells with two different grating concepts and solar cell architectures. In both cases planar front sides have been used. With hexagonal sphere gratings and the tunnel oxide passivated contact (TOPCon) concept, a grating induced Jsc increase of 1.4 mA/cm2 and an efficiency increase of 0.8%absolute could be achieved. With binary crossed gratings fabricated by a nanoimprint based process chain, a grating induced Jsc gain of 1.2 mA/cm2 and an efficiency gain of 0.7% absolute could be achieved. For the binary grating concept, cell thickness variations have also been performed. The increasing importance of the light trapping properties towards low solar cell thicknesses could be confirmed by an enhanced EQE in the long wavelength region (Jsc increase: 1.6 mA/cm2 for 150 μm and 1.8 mA/cm2 for 100 μm thick solar cells). The results are in very good agreement with simulations using the OPTOS modeling formalism. OPTOS enables the further analysis and optimization of grating concepts in silicon solar cells and modules. So a grating induced Jsc gain of 0.8 mA/cm2 is forecast for solar cells with pyramidal front side texture. On module level, still a grating induced Jsc gain of 0.6 mA/cm2 can be expected.

  3. Measurement of delayed-neutron yield from {sup 237}Np fission induced by thermal neutrons

    SciTech Connect

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

    2007-06-15

    The delayed-neutron yield from thermal-neutron-induced fission of the {sup 237}Np 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 {sup 237}Np fission induced by thermal neutrons is {nu}{sub d} = 0.0110 {+-} 0.0009. This study was performed at the Frank Laboratory of Neutron Physics (JINR, Dubna)

  4. Martian mesoscale circulations induced by variations in surface optical and thermal characteristics: A numerical study

    NASA Technical Reports Server (NTRS)

    Siili, Tero; Savijarvi, H.

    1993-01-01

    According to Mariner 9 and Viking observations the surface albedo and the thermal inertia of Mars' surface vary substantially, and fairly large gradients also occur. The Syrtis Major region is bounded in the west by high-albedo cratered terrain and in the east by Isidis Planitia, a high-albedo plateau. Sinus Meridiani, centered at 0 degrees W 5 degrees S, is almost surrounded by higher albedo regions with sharp boundaries, and Acidalia Planitia, between 10 and 50 degrees W and north of 35 degrees N, has sharp albedo boundaries to the east and west. Observational and modeling studies, e.g., on Australian dry salt lake coasts, have shown that discontinuities and gradients in surface properties can induce mesoscale circulations. We have used a version of the DMUH mesoscale model to simulate atmospheric circulations induced by variations in the reflectivity and in the thermal inertia of the martian surface.

  5. Quantitative analysis of thermally-induced alterations of corneal stroma by second-harmonic generation imaging

    NASA Astrophysics Data System (ADS)

    Matteini, P.; Rossi, F.; Ratto, F.; Cicchi, R.; Kapsokalyvas, D.; Pavone, F. S.; Pini, R.

    2010-02-01

    Thermal modifications induced in the corneal stroma were investigated by means of second harmonic generation (SHG) imaging. Whole fresh cornea samples were heated in a water bath at temperatures in the 35-80 °C range for a 4-min time. SHG images of the structural modifications induced at each temperature were acquired from different areas of cross-sectioned corneal stroma by using an 880 nm linearly- and circularly-polarized excitation light emitted by a mode-locked Ti:Sapphire laser. The SHG images were then analyzed by means of both an empirical approach and a 2D-theoretical model. The proposed analyses provide a detailed description of the changes occurring in the structural architecture of the cornea during the thermal treatment. Our results allow us to depict a temperature-dependent biochemical model for the progressive destructuration occurring to collagen fibrils and nonfibrillar components of the stroma.

  6. Negative Gaussian curvature induces significant suppression of thermal conduction in carbon crystals.

    PubMed

    Zhang, Zhongwei; Chen, Jie; Li, Baowen

    2017-09-28

    From the mathematic category of surface Gaussian curvature, carbon allotropes can be classified into three types: zero curvature, positive curvature, and negative curvature. By performing Green-Kubo equilibrium molecular dynamics simulations, we found that surface curvature has a significant impact on the phonon vibration and thermal conductivity (κ) of carbon crystals. When curving from zero curvature to negative or positive curvature structures, κ is reduced by several orders of magnitude. Interestingly, we found that κ of negatively curved carbon crystals exhibits a monotonic dependence on curvature. Through phonon mode analysis, we show that curvature induces remarkable phonon softening in phonon dispersion, which results in the reduction of phonon group velocity and flattening of phonon band structure. Furthermore, the curvature was found to induce phonon mode hybridization, leading to the suppression of phonon relaxation time. Our study provides physical insight into thermal transport in curvature materials, and will be valuable in the modulation of phonon activity through surface curvature.

  7. 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.

  8. Synchronization of electrically coupled stochastic magnetic oscillators induced by thermal and electrical noise

    NASA Astrophysics Data System (ADS)

    Mizrahi, A.; Locatelli, N.; Grollier, J.; Querlioz, D.

    2016-08-01

    Superparamagnetic tunnel junctions are nanostructures that auto-oscillate stochastically under the effect of thermal noise. Recent works showed that despite their stochasticity, such junctions possess a capability to synchronize to subthreshold voltage drives, in a way that can be enhanced or controlled by adding noise. In this work, we investigate a system composed of two electrically coupled junctions, connected in series to a periodic voltage source. We make use of numerical simulations and of an analytical model to demonstrate that both junctions can be phase locked to the drive, in phase or in antiphase. This synchronization phenomenon can be controlled by both thermal and electrical noises, although the two types of noises induce qualitatively different behaviors. Namely, thermal noise can stabilize a regime where one junction is phase locked to the drive voltage while the other is blocked in one state; on the contrary, electrical noise causes the junctions to have highly correlated behaviors and thus cannot induce the latter. These results open the way for the design of superparamagnetic tunnel junctions that can perform computation through synchronization, and which harvest the largest part of their energy consumption from thermal noise.

  9. 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.

  10. Vibration sensor based on highly birefringent Bragg gratings written in standard optical fiber by a femtosecond laser

    NASA Astrophysics Data System (ADS)

    Chah, Karima; Bueno, Antonio; Kinet, Damien; Caucheteur, Christophe; Chluda, Cédric; Mégret, Patrice; Wuilpart, Marc

    2014-05-01

    We present a vibration sensor based on highly birefringent fiber Bragg gratings written in standard single mode optical fiber and realized with UV femtosecond pulses. This vibration sensor takes advantage of the stress-induced phase shift between the two orthogonally polarized fiber eigenmodes which induces intensity distribution changes in the two fiber Bragg grating reflection modes. The gratings are inscribed with the femtosecond line by line technique and have a birefringence value of 6 10-4. We demonstrate that theses gratings are temperature birefringence insensitive and ideal for vibration measurements.

  11. Thermally induced optical bistability in a new polymeric blend at room temperature

    NASA Astrophysics Data System (ADS)

    Bernini, U.; de Stefano, L.; Mormile, P.; Pierattini, G.; Russo, P.

    1993-09-01

    The transition from the transmission to the reflection regime for an Ar+-laser beam propagating in the new polymeric blend PMMA-EVA at a nonlinear interface has been observed. A comparison between the experimental data and a calculation of the input optical intensity at which this transition should occur (1.45×107 W m-2) is presented using Kaplan's theory. The results suggest the presence of thermally induced optical bistability in PMMA-EVA.

  12. Irradiation-Induced Thermal Effects in Alloyed Metal Fuel of Fast Reactors

    NASA Astrophysics Data System (ADS)

    Kryukov, F. N.; Nikitin, O. N.; Kuzmin, S. V.; Belyaeva, A. V.; Gilmutdinov, I. F.; Grin, P. I.; Zhemkov, I. Yu

    2017-01-01

    The paper presents the results of studying alloyed metal fuel after irradiation in a fast reactor. Determined is the mechanism of fuel irradiation swelling, mechanical interaction between fuel and cladding, and distribution of fission products. Experience gained in fuel properties and behavior under irradiation as well as in irradiation-induced thermal effects occurred in alloyed metal fuel provides for a fuel pin design to have a burnup not less than 20% h. a.

  13. A Novel Combination of Thermal Ablation and Heat-Inducible Gene Therapy for Breast Cancer Treatment

    DTIC Science & Technology

    2008-04-01

    STATEMENT Approved for Public Release; Distribution Unlimited 13. SUPPLEMENTARY NOTES 14. ABSTRACT High intensity focused ultrasound ...focused ultrasound (HIFU) thermal ablation and HIFU-induced gene therapy represents a promising approach in improving the overall efficacy and quality...R3230Ac cells with concentration from 0.5x106 /ml to 5x106/ml. The speed of sound and attenuation were measured in a broadband transmission ultrasound

  14. Influence of the thermal contact resistance in current-induced domain wall depinning

    NASA Astrophysics Data System (ADS)

    López, Cristina; Ramos, Eduardo; Muñoz, Manuel; Kar-Narayan, S.; Mathur, N. D.; Prieto, José L.

    2017-08-01

    In this work we study the influence of the thermal contact resistance on the temperature of a typical nanostripe used in current induced magnetic domain wall movement or depinning. The thermal contact resistance arises from an imperfect heat transport across the interface between the metallic ferromagnetic nanostripe and the substrate. We show that this parameter, which is likely non-zero in any experimental device, increases the temperature in the nanostripe considerably. When the current is injected in the nanostripe in nanosecond long pulses, the larger temperature also implies a reduction of the effective current density delivered by the pulse generator. Both the thermal contact resistance and the dynamic response of the pulse generator are usually neglected in theoretical estimations of the influence of spin transfer torque on domain wall displacement and depinning. Here we show that only if the thermal contact resistance and the electric resistivity of the ferromagnetic nanostripe are optimized to the best values reported in the bibliography, the Joule heating may not be so crucial for current densities of the order of 108 A cm-2. Also, the use of physical constrictions (notch) to pin the magnetic domain wall may complicate the interpretation of the results as they always come together with relevant thermal gradients.

  15. 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.

  16. Laser-induced thermal characterization of nano Ag metal dispersed ceramic alumina matrix

    NASA Astrophysics Data System (ADS)

    George, Sajan D.; Anapara, Aji A.; Warrier, K. G. K.; Radhakrishnan, P.; Vallabhan, C. P. G.; Nampoori, V. P. N.

    2003-04-01

    In this paper, we report the measurements of thermal diffusivity of nano Ag metal dispersed ceramic alumina matrix sintered at different temperatures using laser induced non-destructive photoacoustic technique. Measurements of thermal diffusivity also have been carried out on specimens with various concentration of nano metal. Analysis of the data is done on the basis of one-dimensional model of Rosencwaig and Gersho. The present measurements on the thermal diffusivity of nano metal dispersed ceramic alumina shows that porosity has a great influence on the heat transport and the thermal diffusivity value. The present analysis also shows that the inclusion of nano metal into ceramic matrix increases its interconnectivity and hence the thermal diffusivity value. The present study on the samples sintered at different temperature shows that the porosity of the ceramics varies considerably with the change in sintering temperature. The results are interpreted in terms of phonon assisted heat transfer mechanism and the exclusion of pores with the increase in sintering temperature.

  17. Induced thermal stress fields for three-dimensional distortion control of Si wafer topography

    NASA Astrophysics Data System (ADS)

    Schaper, Charles D.; Chen, Been-Der; Pease, R. Fabian W.

    2004-06-01

    Localized, controlled heating can induce a thermal stress field in silicon wafers and displace the surface topography in three dimensions, which is useful for nanoscale regulation of overlay in microcontact printing systems. Simulation and experimental results are presented to demonstrate the use of a thermal array consisting of a dense distribution of independent heating elements to locally displace silicon wafer alignment microstructures. An experimental apparatus comprised of a 7×7 array of thermal cycling sources is used to control the absolute three-dimensional position of surface microstructures. The system is used to demonstrate out-of-plane sensitivity of 1.4 μm/°C by thermomechanical displacement contributions from thermal expansion of the heating element. Rolloff in out-of-plane displacement of 200 nm/mm/°C in silicon at the boundary between heated and nonheated regions in this apparatus is exhibited. Dynamic real-time control of the substrate flatness is thus feasible and is demonstrated with the apparatus using feedback from three alignment microscopes, to sub-100 nm levels of regulation. Control of the in-plane microstructure position is achieved by stabilizing the vertical displacement with a mechanical nanopositioning stage, while establishing a thermal stress field to produce displacement sensitivity of 70 nm/°C. Real-time feedback control of the in-plane microstructure position is demonstrated, also within sub-100 nm of the target regulation level.

  18. Error analysis and method of calibration for linear time grating displacement sensor

    NASA Astrophysics Data System (ADS)

    Gao, Zhonghua; Zheng, Fangyan; Chen, Xihou; Chen, Ziran; Peng, Donglin

    2013-01-01

    A combination method for calibrating the errors of linear time grating displacement sensor is presented. Based on further analysis of time grating, periodic errors, Abbe errors and thermal expansion errors are integrated to obtain error curve for setting up error model, which is adopted to compensate errors using Fourier harmonic analysis and the principle of liner expansion, respectively. Results prove that this method solves the difficult issues about error separation in the linear measurement, and significantly improves the accuracy of linear time grating. Furthermore, this method also solves the issues about continuous automatic sampling with computer, so that the calibration efficiency has been greatly enhanced.

  19. Transmitting volume Bragg gratings in PTR glass written with femtosecond Bessel beams

    NASA Astrophysics Data System (ADS)

    Cheng, G. H.; Zhang, Y. J.; Liu, Q.

    2017-05-01

    Transmitting volume Bragg gratings were fabricated in photo-thermo-refractive glass using femtosecond laser Bessel beams and thermal treatment. The phase contrast images of gratings under different writing power were investigated before and after annealing. Microstructures composed of nano-sized crystals were observed in the exposed regions. Optimized writing power (100 mW) achieved dense nano-crystals distribution. A maximum diffraction efficiency of 92.36% was achieved with 1 mm grating thickness at period of 5 μm.

  20. Thermally induced shape modification of free-standing nanostructures for advanced functionalities.

    PubMed

    Cui, Ajuan; Li, Wuxia; Shen, Tiehan H; Yao, Yuan; Fenton, J C; Peng, Yong; Liu, Zhe; Zhang, Junwei; Gu, Changzhi

    2013-01-01

    Shape manipulation of nanowires is highly desirable in the construction of nanostructures, in producing free-standing interconnect bridges and as a building block of more complex functional structures. By introducing asymmetry in growth parameters, which may result in compositional or microstructural non-uniformity in the nanowires, thermal annealing can be used to induce shape modification of free-standing nanowires. We demonstrate that such manipulation is readily achieved using vertically grown Pt-Ga-C composite nanowires fabricated by focused-ion-beam induced chemical vapor deposition. Even and controllable bending of the nanowires has been observed after a rapid thermal annealing in a N2 atmosphere. The mechanisms of the shape modification have been examined. This approach has been used to form electrical contacts to freestanding nano-objects as well as nano-'cages' for the purpose of securing ZnO tubs. These results suggest that thermally induced bending of nanowires may have potential applications in constructing three-dimensional nanodevices or complex structures for the immobilization of particles and large molecules.

  1. Thermally Induced Shape Modification of Free-standing Nanostructures for Advanced Functionalities

    NASA Astrophysics Data System (ADS)

    Cui, Ajuan; Li, Wuxia; Shen, Tiehan H.; Yao, Yuan; Fenton, J. C.; Peng, Yong; Liu, Zhe; Zhang, Junwei; Gu, Changzhi

    2013-08-01

    Shape manipulation of nanowires is highly desirable in the construction of nanostructures, in producing free-standing interconnect bridges and as a building block of more complex functional structures. By introducing asymmetry in growth parameters, which may result in compositional or microstructural non-uniformity in the nanowires, thermal annealing can be used to induce shape modification of free-standing nanowires. We demonstrate that such manipulation is readily achieved using vertically grown Pt-Ga-C composite nanowires fabricated by focused-ion-beam induced chemical vapor deposition. Even and controllable bending of the nanowires has been observed after a rapid thermal annealing in a N2 atmosphere. The mechanisms of the shape modification have been examined. This approach has been used to form electrical contacts to freestanding nano-objects as well as nano-`cages' for the purpose of securing ZnO tubs. These results suggest that thermally induced bending of nanowires may have potential applications in constructing three-dimensional nanodevices or complex structures for the immobilization of particles and large molecules.

  2. Experimental investigation of thermally induced core laser leakage in large mode area single trench fiber

    NASA Astrophysics Data System (ADS)

    Kong, Lingchao; Huang, Liangjin; Gu, Shaoyi; Leng, Jinyong; Guo, Shaofeng; Zhou, Pu; Xu, Xiaojun; Jiang, Zongfu

    2016-11-01

    We demonstrated a new phenomenon, namely, thermally induced core laser leakage in single trench fiber (STF), for the first time. The STF provides very high loss and power delocalization of higher order mode (HOM) and maintain the effective single mode operation. However these properties are chartered only under low power situations. In this paper we established a 976nm directly pumped high power co-pumping fiber amplifier based on the STF. The maximum output power was 1022W with a slope efficiency of 76%. Further increase the pump power will leads to the output power decrease. Meanwhile a micro second Level noise like power fluctuation was observed. No resonance frequency was observed in frequency domain indicating the mode instability is not triggered. We believe that it is the thermally induced waveguide index profile change due to the excessively heat load in the front section of STF that leads to the failure of HOM suppression and the power of FM was coupled into the HOM. However the heat load in the rear section of STF was relatively low and the HOM leaked into the cladding due to the bending loss. We provide a mitigating method by pumping with pump light of smaller absorption. A maximum power of 1330W was achieved without power decrease via pumping the STF with 905nm and 976nm pump light (same amplifier). To our best knowledge, this is the first demonstration of thermally induced core laser leakage in STF and the pertinent results can provide significant reference for future optimization.

  3. Thermally Induced Shape Modification of Free-standing Nanostructures for Advanced Functionalities

    PubMed Central

    Cui, Ajuan; Li, Wuxia; Shen, Tiehan H.; Yao, Yuan; Fenton, J. C.; Peng, Yong; Liu, Zhe; Zhang, Junwei; Gu, Changzhi

    2013-01-01

    Shape manipulation of nanowires is highly desirable in the construction of nanostructures, in producing free-standing interconnect bridges and as a building block of more complex functional structures. By introducing asymmetry in growth parameters, which may result in compositional or microstructural non-uniformity in the nanowires, thermal annealing can be used to induce shape modification of free-standing nanowires. We demonstrate that such manipulation is readily achieved using vertically grown Pt-Ga-C composite nanowires fabricated by focused-ion-beam induced chemical vapor deposition. Even and controllable bending of the nanowires has been observed after a rapid thermal annealing in a N2 atmosphere. The mechanisms of the shape modification have been examined. This approach has been used to form electrical contacts to freestanding nano-objects as well as nano-‘cages' for the purpose of securing ZnO tubs. These results suggest that thermally induced bending of nanowires may have potential applications in constructing three-dimensional nanodevices or complex structures for the immobilization of particles and large molecules. PMID:23938336

  4. 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.

  5. 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.

  6. A directly cooled grating substrate for ALS (Advanced Light Source) undulator beam lines

    SciTech Connect

    DiGennaro, R.; Swain, T.

    1989-08-01

    Design analyses using finite element methods are presented for thermal distortion of water-cooled diffraction grating substrates for a potential application at the LBL Advanced Light Source, demonstrating that refinements in cooling channel configuration and heat flux distribution can significantly reduce optical surface distortion with high heat loads. Using an existing grating substrate design, sensitivity of tangential slope errors due to thermal distortion is evaluated for a variety of thermal boundary conditions, including coolant flow rate and heat transfer film coefficients, surface illumination area and heat distribution profile, and location of the convection cooling surfaces adjacent to the heated region. 1 ref., 5 figs., 2 tabs.

  7. Germanium implanted Bragg gratings in silicon on insulator waveguides

    NASA Astrophysics Data System (ADS)

    Loiacono, Renzo; Reed, Graham T.; Gwilliam, Russell; Mashanovich, Goran Z.; O'Faolain, Liam; Krauss, Thomas; Lulli, Giorgio; Jeynes, Chris; Jones, Richard

    2010-02-01

    Integrated Bragg gratings are an interesting candidate for waveguide coupling, telecommunication applications, and for the fabrication of integrated photonic sensors. These devices have a high potential for optical integration and are compatible with CMOS processing techniques if compared to their optical fibre counterpart. In this work we present design, fabrication, and testing of Germanium ion implanted Bragg gratings in silicon on insulator (SOI). A periodic refractive index modulation is produced in a 1μm wide SOI rib waveguide by implanting Germanium ions through an SiO2 hardmask. The implantation conditions have been analysed by 3D ion implantation modelling and the induced refractive index change has been investigated on implanted samples by Rutherford Backscattering Spectroscopy (RBS) and ellipsometry analysis. An extinction ratio of up to 30dB in transmission, around the 1.55μm wavelength, has been demonstrated for Germanium implanted gratings on SOI waveguides.

  8. 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.

  9. Vibrational spectroscopy at electrolyte/electrode interfaces with graphene gratings

    PubMed Central

    Bie, Ya-Qing; Horng, Jason; Shi, Zhiwen; Ju, Long; Zhou, Qin; Zettl, Alex; Yu, Dapeng; Wang, Feng

    2015-01-01

    Microscopic understanding of physical and electrochemical processes at electrolyte/electrode interfaces is critical for applications ranging from batteries, fuel cells to electrocatalysis. However, probing such buried interfacial processes is experimentally challenging. Infrared spectroscopy is sensitive to molecule vibrational signatures, yet to approach the interface three stringent requirements have to be met: interface specificity, sub-monolayer molecular detection sensitivity, and electrochemically stable and infrared transparent electrodes. Here we show that transparent graphene gratings electrode provide an attractive platform for vibrational spectroscopy at the electrolyte/electrode interfaces: infrared diffraction from graphene gratings offers enhanced detection sensitivity and interface specificity. We demonstrate the vibrational spectroscopy of methylene group of adsorbed sub-monolayer cetrimonium bromide molecules and reveal a reversible field-induced electrochemical deposition of cetrimonium bromide on the electrode controlled by the bias voltage. Such vibrational spectroscopy with graphene gratings is promising for real time and in situ monitoring of different chemical species at the electrolyte/electrode interfaces. PMID:26123807

  10. 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.

  11. Vibrational spectroscopy at electrolyte/electrode interfaces with graphene gratings

    NASA Astrophysics Data System (ADS)

    Bie, Ya-Qing; Horng, Jason; Shi, Zhiwen; Ju, Long; Zhou, Qin; Zettl, Alex; Yu, Dapeng; Wang, Feng

    2015-06-01

    Microscopic understanding of physical and electrochemical processes at electrolyte/electrode interfaces is critical for applications ranging from batteries, fuel cells to electrocatalysis. However, probing such buried interfacial processes is experimentally challenging. Infrared spectroscopy is sensitive to molecule vibrational signatures, yet to approach the interface three stringent requirements have to be met: interface specificity, sub-monolayer molecular detection sensitivity, and electrochemically stable and infrared transparent electrodes. Here we show that transparent graphene gratings electrode provide an attractive platform for vibrational spectroscopy at the electrolyte/electrode interfaces: infrared diffraction from graphene gratings offers enhanced detection sensitivity and interface specificity. We demonstrate the vibrational spectroscopy of methylene group of adsorbed sub-monolayer cetrimonium bromide molecules and reveal a reversible field-induced electrochemical deposition of cetrimonium bromide on the electrode controlled by the bias voltage. Such vibrational spectroscopy with graphene gratings is promising for real time and in situ monitoring of different chemical species at the electrolyte/electrode interfaces.

  12. The in-focus variable line spacing plane grating monochromator

    NASA Astrophysics Data System (ADS)

    Reininger, R.

    2011-09-01

    The in-focus variable line spacing plane grating monochromator is based on only two plane optical elements, a variable line spacing plane grating and a plane pre-mirror that illuminates the grating at the angle of incidence that will focus the required photon energy. A high throughput beamline requires only a third optical element after the exit slit, an aberration corrected elliptical toroid. Since plane elements can be manufactured with the smallest figure errors, this monochromator design can achieve very high resolving power. Furthermore, this optical design can correct the deformations induced by the heat load on the optics along the dispersion plane. This should allow obtaining a resolution of 10 meV at 1 keV with currently achievable figure errors on plane optics. The position of the photon source when an insertion device center is not located at the center of the straight section, a common occurrence in new insertion device beamlines, is investigated.

  13. 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

  14. Fiber Bragg grating multichemical sensor

    NASA Astrophysics Data System (ADS)

    Boland, Patrick; Sethuraman, Gopakumar; Mendez, Alexis; Graver, Tom; Pestov, Dmitry; Tait, Gregory

    2006-10-01

    Fiber optic-based chemical sensors are created by coating fiber Bragg gratings (FBG) with the glassy polymer cellulose acetate (CA). CA is a polymeric matrix capable of localizing or concentrating chemical constituents within its structure. Some typical properties of CA include good rigidity (high modulus) and high transparency. With CA acting as a sensor element, immersion of the gratings in various chemical solutions causes the polymer to expand and mechanically strain the glass fiber. This elongation of the fiber sections containing the grating causes a corresponding change in the periodicity of the grating that subsequently results in a change in the Bragg-reflected wavelengths. A high-resolution tunable fiber ring laser interrogator is used to obtain room-temperature reflectance spectrograms from two fiber gratings at two different wavelengths - 1540nm and 1550nm. The graphical representation from this device enables the display of spectral shape, and not merely shifts in FBG central wavelength, thereby allowing for more comprehensive analysis of how different physical conditions cause the reflectance profile to move and alter overall form. Wavelength shifts on the order of 1 to 80 pm in the FBG transition edges and changes in spectral shape are observed in both sensors upon immersion in a diverse selection of chemical analytes.

  15. A half-period surface relief grating formed by bicolor interferences in thin azopolymer films

    NASA Astrophysics Data System (ADS)

    Apostoluk, Aleksandra; Fiorini-Debuisschert, Celine; Nunzi, Jean-Michel

    2003-07-01

    All optical poling technique allows orientation of dye molecules in a polymer matrix by purely optical means. The coherent superposition of two beams at fundamental (FUND)and second harmonic (SH)frequencies results in the presence of the polar field E(t) inside the material, able to break the centrosymmetry of the medium. The temporal average cube t of this field E(t) = Eω(t)+E2ω(t), is non-zero, which leads to an orientation-selective excitation of molecules and the second order χ(2)-susceptibility grating is encoded, with a period satisfying the phase matching condition for SH generation. The physical origin of the effect lies in the orientational hole-burning in the initially isotropic distribution of dye molecules (via trans-cis trans photoisomerisation). We investigate other phenomena responsible for the SHG in polymer films like the electron transfer between a polymer matrix (donor of electrons) and a dye molecule (electron acceptor) and processes which accompany polar orientation mechanism like the one-direction photoinduced molecular migration. The stability of the induced polar order after orientation has been also studied and the crosslinkable polymer system has been developed D side chain molecules with ends can thermally react with epoxy groups were randomly inserted in the side groups of the polymer backbone, which leads to the reticulation and enhancement of the rotational stability. After poling the second order nonlinear response exhibits a much longer relaxation time. In the set-up configuration used we monitor non-perturbatively the all optical poling and there is no necessity of taking into account the phase difference between writing beams (fundamental and SH). The periodical modulation of the relative phase provides the desired control on the polar order at the molecular level as well as the possibility of encoding surface relief gratings with a period equal to the half of the period of the χ(2) grating.

  16. 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.

  17. 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.

  18. 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.

  19. 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.

  20. A phenomenological expression to describe the temperature dependence of pressure-induced softening in negative thermal expansion materials.

    PubMed

    Fang, Hong; Dove, Martin T

    2014-03-19

    By exploring a simple model of a negative thermal expansion (NTE) system, we introduce a phenomenological expression to describe the temperature dependence of the pressure-induced softening in NTE structures.