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1

Dynamic studies on laser-induced gratings in azobenzene-doped polymer film  

NASA Astrophysics Data System (ADS)

Studies on the dynamic behaviours of laser-induced gratings through two-photon absorption and single-photon absorption were carried out in an azobenzene-doped PMMA film. The experimental results exposed the structures of energy levels and the relaxation between them, in which different lifetimes of the triplet states of trans and cis isomers of azobenzene molecule were recognized. The temporal characteristics of the diffracted signal from the induced-gratings showed also the dynamic processes of the photoisomerization reaction between two isomers.

Zhao, J.; Dong, F.; Qu, H.; Ye, P.; Fu, X.; Qiu, L.; Shen, Y.

1995-10-01

2

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)

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.

Xia, Jiulin

3

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

SciTech Connect

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.

Pennington, D.M.

1992-04-01

4

Laser-Induced Grating Characteristics in Doped Lithium Niobate Crystals,  

National Technical Information Service (NTIS)

The properties of laser-induced gratings were characterized in doped LiNbO3 crystals using small-angle scattering pattern analysis, the analysis of erasure decay patterns, and two-beam mixing. The results show the usefulness of each of these types of expe...

L. Arizmendi M. J. Kliewer R. C. Powell

1987-01-01

5

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

NASA Astrophysics Data System (ADS)

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.

Behrens, Edward Grady

6

Properties of Laser-Induced Gratings in Eu-Doped Glasses.  

National Technical Information Service (NTIS)

The properties of permanent, laser-induced gratings were studied in Europium (3+) -doped glasses. These gratings are associated with a structural modification of the glass host in the local environment of the Eu(3+) ions, and we have investigated the effe...

E. G. Behrens F. M. Durville R. C. Powell D. H. Blackburn

1989-01-01

7

Oxygen concentration effects on laser-induced grating spectroscopy of toluene  

NASA Astrophysics Data System (ADS)

The effects of variation in oxygen concentration on laser-induced grating spectroscopy (LIGS) signals from toluene vapour in nitrogen/oxygen mixtures is investigated. The modulation of LIGS signals arising from the interference of counter-propagating acoustic waves with a stationary density perturbation induced by pulsed excitation of toluene by frequency quadrupled radiation from a Nd:YAG laser has been measured as a function of oxygen partial pressure at total gas pressures up to 8 bar. The modulation depth or signal contrast is found to vary in an unexpected way with oxygen partial pressure and the behaviour is ascribed to energy transfer to excited singlet states of the oxygen molecule and subsequent collisional quenching. A simple model of the energy transfer dynamics is presented that reproduces the observed behaviour and the potential for using the signal contrast of LIGS signals as a measure of oxygen concentration is discussed.

Williams, Ben; Ewart, Paul

2012-11-01

8

Properties of laser-induced gratings in Eu-doped glasses  

Microsoft Academic Search

The properties of permanent, laser-induced gratings were studied in Eu3+-doped glasses. These gratings are associated with a structural modification of the glass host in the local environment of the Eu3+ ions, and we have investigated the effects produced by altering the Eu3+ concentration and by changing the composition of the glass host. A two-level-system model is developed to explain the

Edward G. Behrens; Frederic M. Durville; Richard C. Powell; Douglas H. Blackburn

1989-01-01

9

Submicrometer grating fabrication in fused silica by interferometric laser-induced backside wet etching technique  

NASA Astrophysics Data System (ADS)

Submicrometer period fused silica gratings were produced by two-beam interferometric laser-induced backside wet etching technique (TWIN LIBWE). The fourth harmonic of a Nd:YAG laser beam was spatially filtered in two steps, and the smoothened beam was split into two parts and interfered at incident angles of 60°, 30°, 14°, and 7.7°, respectively, on the backsides of fused silica plates that were in contact with a liquid absorber. The periods of the produced fused silica gratings were, respectively, 154 nm, 266 nm, 550 nm, and 990 nm. In the next step, TWIN-LIBWE setup was completed by using a coupling rectangular prism in order to reach immersion setup, which made possible to fabricate 104 nm period fused silica grating. This is the smallest laser-generated grating constant in fused silica at present. The morphology of the etched gratings was characterized by atomic force microscope. Important parameters (modulation depth, low-pass filtered waviness, quality factor) of the produced gratings were determined. Evolution of the grating parameters was also studied in the 990 nm case: the dependence of modulation depth, waviness, and quality factor on the number of laser pulses was investigated.

Vass, Csaba; Osvay, Károly; Vés?, Tamás; Hopp, Béla; Bor, Zsolt

2008-10-01

10

Dynamic-grating lasers  

NASA Astrophysics Data System (ADS)

The performance characteristics of dynamic-grating lasers, or degenerate four-wave mixing (FWM) lasers, are examined. In particular, attention is given to the general designs of FWM lasers, new efficient nonlinear lasing media (e.g., Ba2NaNb5O15 crystals), and lasers based on anisotropic diffraction gratings in crystals with photogalvanic nonlinearity (e.g., LiNbO3:Cu). Lasers based on media with local nonlinear response are also discussed.

Odulov, S. G.; Soskin, M. S.; Khizhniak, A. I.

1988-02-01

11

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

SciTech Connect

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.

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

2010-05-01

12

Pulsed laser induced spontaneous gratings on a surface of azobenzene polymer  

NASA Astrophysics Data System (ADS)

Self-organized spontaneous gratings were induced on a surface of azobenzene polymer by an irradiation of frequency doubled neodymium doped yttrium-aluminum-garnet pulsed laser. Irradiation of uniform single laser beam at normal incidence induced periodic line shaped structures on a polymer surface. The structure is so-called laser induced periodic surface structure (LIPSS) which was formed along the direction parallel to the polarization direction of pulsed laser. The LIPSS was formed above the critical thickness around 60 nm. Irradiation of s-polarized holographic interference beams induced the distinguished holographic surface relief grating (SRG) structures. Irradiation of p-polarized holographic interference beams induced egg crate-like (ECL) structures. A combination of holographic SRG and sequential LIPSS is the likely cause of the ECL patterns observed in this work.

Tsutsumi, Naoto; Fujihara, Arata

2004-11-01

13

Multiband sensor using thick holographic gratings for sulfur detection by laser-induced breakdown spectroscopy.  

PubMed

Detection of sulfur by optical emission spectroscopy generally presents some difficulties because the strongest lines are in the vacuum UV below 185 nm and therefore are readily absorbed by oxygen molecules in air. A novel concept for a low-cost and efficient system to detect sulfur using near-IR bands by laser-induced breakdown spectroscopy is here proposed. This concept is based on customized thick holographic gratings as spectral filtering elements. The signal integration and the temporal synchronization are performed using built-in custom electronics that amplify and integrate or trigger photodiode output signals. In this work, we use the near-IR lines at 921.287 nm and a background reference at 900 nm. Preliminary results show a limit of detection comparable to that of a conventional high-end system. PMID:22410928

Gagnon, Daniel; Lessard, Simon; Verhaegen, Marc; Mutchmore, Patrick; Bouchard, Paul; Doucet, François R; Sabsabi, Mohamad

2012-03-01

14

Dynamical behavior of laser-induced nanoparticles during remote processing  

NASA Astrophysics Data System (ADS)

Laser remote processing is used in a wide field of industrial applications. Among other things, it is characterized by flexible beam guidance in combination with high processing velocities. But in most cases process gas support in the interaction zone is omitted. Consequently, interaction mechanism between the vapor plume and the incident laser radiation can dynamically affect the process stability. Referring to remote welding with high brilliant laser sources having a wavelength around 1 ?m, the interaction between the incident laser radiation and formed particles plays an important role. The presented work shows results of the investigation of the laser-induced particle formation during the laser welding of stainless steel with a 2 kW fiber laser under remote conditions. It is therefore concentrated on the dynamical behavior of the laser-induced particle formation and the dependence of the particle formation on the laser beam power. TEM images of formed particles were analyzed. In addition, the radiation of a LED was directed through the vapor plume. On the one hand, the dynamic of the attenuation was considered. On the other hand, the Rayleigh approximation was used in order to evaluate the detected signals.

Scholz, Tobias; Dickmann, Klaus; Ostendorf, Andreas

2014-02-01

15

Surface plasmon scattering on polymer-bimetal layer covered fused silica gratings generated by laser induced backside wet etching  

NASA Astrophysics Data System (ADS)

Large amplitude fused silica gratings are prepared by combining the UV laser induced backside wet etching technique (LIBWE) and the two-beam interference method. The periodic patterning of fused silica surfaces is realized by s-polarized fourth harmonic beams of a Nd:YAG laser, applying saturated solution of naphthalene in methyl-methacrylate as liquid absorber. Atomic force microscopy is utilized to analyze how the modulation amplitude of the grating can be controlled by the fluence and number of laser pulses. Three types of plasmonic structures are prepared by a bottom-up method, post-evaporating the fused silica gratings by gold-silver bimetal layers, spin-coating the metal structures by thin polycarbonate films, and irradiating the multilayers by UV laser. The effect of the bimetal and polymer-coated bimetal gratings on the surface plasmon resonance is investigated in a modified Kretschmann arrangement allowing polar and azimuthal angle scans. It is demonstrated experimentally that scattering on rotated gratings results in additional minima on the resonance curves of plasmons excited by second harmonic beam of a continuous Nd:YAG laser. The azimuthal angle dependence proves that these additional minima originate from back-scattering. The analogous reflectivity minima were obtained by scattering matrix method calculations realized taking modulation depths measured on bimetal gratings into account.

Tóháti, H.; Sipos, Á.; Szekeres, G.; Mathesz, A.; Szalai, A.; Jójárt, P.; Budai, J.; Vass, Cs.; K?házi-Kis, A.; Csete, M.; Bor, Zs.

2009-03-01

16

Determination of physicochemical parameters of ionic liquids and their mixtures with solvents using laser-induced gratings.  

PubMed

The laser-induced gratings (LIGs) technique has been applied for the simultaneous determination of sound speed and thermal diffusivity in the room temperature ionic liquid (RTIL) 1-ethyl-3-methylimidazolium ethylsulfate, [EMIm][EtSO(4)], its mixture with 85.68 mol % acetone, C(3)H(6)O, and pure acetone. The measurements have been performed in a quartz glass cuvette at ambient pressure and temperature. Radiation of a pulse-repetitive Q-switched Nd:YAG pump laser (1064 nm) effected quasi-resonant excitation of overtone-combinational vibrational states of the RTIL molecules followed by the appearance of laser-induced gratings. The temporal evolution of the transient gratings (oscillation and damping) was recorded using Bragg-diffraction of a continuous-wave probe laser radiation. From the LIG signals' temporal profiles, values of the sound speed and thermal diffusivity were determined and, in addition, the isentropic compressibility and thermal conductivity were derived. The results are in a reasonable agreement with those reported in the literature. Furthermore, since the data for the determination of the physicochemical properties can be obtained with a single laser pulse, the LIG technique has potential for applications where data acquisition at high repetition rates is desirable for example to monitor processes. PMID:21627147

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

2011-07-01

17

Optical performance and laser induced damage threshold improvement of diffraction gratings used as compressors in ultra high intensity lasers  

NASA Astrophysics Data System (ADS)

This paper studies gratings engraved in a multilayer dielectric stack for ultra high intensity laser compressors. A metal layer is inserted between the substrate and the dielectric stack to reduce the number of dielectric bilayers and thus the mechanical stress within the stack. A code taking account the fluctuation range of the geometrical parameters during the fabrication process is used to numerically optimize the mirror stack and study different groove profiles to increase the reflected efficiency and the laser induced damage threshold. It is evidenced that of all the profiles leading to good diffraction performances, those with the greatest groove depth and width values result in the smallest enhancement of the electric field square inside the grating with a decrease by a factor close to 2.5.

Bonod, Nicolas; Néauport, Jérôme

2006-04-01

18

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

Microsoft Academic Search

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

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

2006-01-01

19

Laser-Induced Refractive-Index Gratings in Eu-Doped Glasses.  

National Technical Information Service (NTIS)

Four-wave mixing techniques were used to establish and probe refractive-index gratings in Eu(3+)-doped silicate and phosphate glasses. When the Eu(3+) ions are resonantly excited, superimposed transient and permanent gratings are formed. The former are ch...

F. M. Durville E. G. Behrens R. C. Powell

1986-01-01

20

Time-resolved measurement of the local equivalence ratio in a gaseous propane injection process using laser-induced gratings.  

PubMed

For the first time laser-induced gratings (LIGs) have been used for the investigation of a non-stationary pulse-repetitive injection process of gaseous propane, C(3)H(8), into air. By recording and evaluating single-shot LIG signals it was possible to determine, on a cycle-averaged basis, the temporal evolution of the local (within a probe volume 300 microm in diameter and 10 mm in length) equivalence ratio and by this the fuel-air ratio. Two different data treatment strategies, subject to C(3)H(8) concentration range, were first tested at stationary conditions and then used to evaluate the LIG signals obtained during the injection process. The relative standard deviation of single-shot measurements were estimated to be 0.14 and 0.32 at 0.8 % and 10 % of propane concentration, respectively. PMID:19532193

Seeger, Thomas; Kiefer, Johannes; Weikl, Markus C; Leipertz, Alfred; Kozlov, Dimitrii N

2006-12-25

21

Femtosecond-laser-induced highly birefringent Bragg gratings in standard optical fiber.  

PubMed

We report highly birefringent fiber Bragg gratings in standard single-mode optical fiber realized with UV femtosecond pulses and line-by-line inscription. By controlling the three-dimensional positioning of the focused laser beam with respect to the fiber core, we achieve very high birefringence at the grating location in a single exposure. A maximum birefringence value of 7.93×10(-4) has been reached for 10th-order gratings when using 2 ?J pulses, which is to our knowledge the highest birefringence value reported so far. This birefringence results from UV-induced high-densification lines shifted from the center of the core, increasing the asymmetry of the induced-stress lines. With a Bragg wavelength spacing reaching more than 800 pm between polarization modes, such gratings are particularly well suited for selective filtering or, as demonstrated here, for temperature-insensitive transverse-strain measurements. PMID:23455147

Chah, Karima; Kinet, Damien; Wuilpart, Marc; Mégret, Patrice; Caucheteur, Christophe

2013-02-15

22

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

NASA Astrophysics Data System (ADS)

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.

Chen, Huxiong

1997-12-01

23

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

SciTech Connect

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)

Ivakin, E V; Sukhodolov, A V [B.I. Stepanov Institute of Physics, National Academy of Sciences of Belarus, Minsk (Belarus); Ralchenko, V G; Vlasov, A V [Natural Science Center, A.M. Prokhorov General Physics Institute, Russian Academy of Sciences, Moscow (Russian Federation); Khomich, A V [Institute of Radio Engineering and Electronics, Russian Academy of Sciences, Moscow (Russian Federation)

2002-04-30

24

Laser-induced transient gratings application for measurement of thermal conductivity of CVD diamond  

NASA Astrophysics Data System (ADS)

In-plane DII (kII) and normal D? (k?) thermal diffusivity (thermal conductivity) of CVD diamond plates have been measured by method of transient gratings and laser flash technique. Samples of insulating and semiconducting boron-doped polycrystalline diamond were synthesized in microwave plasma maintained in methane-hydrogen mixtures. Averaged over the film thickness kII values at room temperature are determined to be in the range of 15-20 W/cmK approaching to those known for single crystal diamonds. From comparison of kII and k? values a thermal anisotropy of 10-20% for in-plane and normal directions (k? > kII) is found, this being ascribed to specific columnar growth of diamond grains. A strong variation (up to 2.7 times) in thermal conductivity across film thickness is revealed for selected specimens using a quasi-surface thermal grating excitation in VUV spectral range. In this case an additional fast-decay diffraction is observed due to nonthermal, owing to generated free charge carriers, recording of the grating.

Ivakin, E. V.; Sukhadolau, A. V.; Ralchenko, Victor G.; Vlasov, A. V.

2003-09-01

25

Effect of pulse duration on laser induced damage threshold of multilayer dielectric gratings  

NASA Astrophysics Data System (ADS)

Multilayer dielectric gratings (MDGs) are more and more used to compress pulse in the next generation of chirped-pulse amplification (CPA) system for high-energy petawatt (HEPW)-class lasers due to their high efficiency and high damage threshold for picosecond pulses. The damage tests for MDGs were carried out with long pulse (12ns) in air and short pulse (0.66~9.7ps) in vacuum at 1053nm, respectively. The experiment methodologies and results were discussed. For both long and short pulse, the initial damage locates at the grating ridges opposite to the incoming wave, which is consistent with the maximum normalized electric field intensity (NEFI). For long pulse, the damage is characterized by melting and boiling. And for short pulse, the damage is ascribed to multiphoton-induced avalanche ionization because of the electric field enhancement in the grating groove structure. And Measurement results of the dependence of damage threshold on the pulse width are presented. And the damage threshold of MDG in beam normal is 4.4J/cm2 at 70° incidence angle for 9.7ps pulse.

Kong, Fanyu; Jin, Yunxia; Li, Dawei; Chen, Weixiao; Zhu, Meiping; Wang, Tao; Li, Chaoyang; He, Hongbo; Xu, Guang; Shao, Jianda

2012-11-01

26

Micro Dynamics of Pulsed Laser Induced Bubbles in Dusty Plasma Liquids  

Microsoft Academic Search

We experimentally study the micro dynamics of the laser induced plasma bubble in a dusty plasma liquid formed by negatively charged dust particles suspended in a low pressure rf Ar glow discharge. The plume from the ablation of the suspended dust particles pushes away dust particle and generates a dust-free plasma bubble. It then travels downward. The spatio-temporal evolution of

Lee-Wen Teng; Chen-Yu Tsai; Yu-Ping Tseng; Lin I

2008-01-01

27

Dynamic modeling of photothermal interactions for laser-induced interstitial thermotherapy: parameter sensitivity analysis  

Microsoft Academic Search

A two-dimensional model was developed to model the effects of dynamic changes in the physical properties on tissue temperature and damage to simulate laser-induced interstitial thermotherapy (LITT) treatment procedures with temperature monitoring. A modified Monte Carlo method was used to simulate photon transport in the tissue in the non-uniform optical property field with the finite volume method used to solve

S. C. Jiang; X. X. Zhang

2005-01-01

28

Laser Induced C60 Cage Opening Studied by Semiclassical Dynamics Simulation  

PubMed Central

Laser induced opening of the C60 cage is studied by a semiclassical electron-radiation-ion dynamics technique. The simulation results indicate that the C60 cage is abruptly opened immediately after laser excitation. The opening of the C60 cage induces a quick increase in kinetic energy and a sharp decrease in electronic energy, suggesting that the breaking of the C60 cage efficiently heats up the cluster and enhances the thermal fragmentation of C60 fullerene.

Tang, Hong; Li, Hongjian; Dou, Yusheng

2011-01-01

29

Dynamics of laser-induced spin reorientation in Co/SmFeO3 heterostructure  

NASA Astrophysics Data System (ADS)

Ultrafast control of a ferromagnet (FM) via exchange coupling with an antiferromagnet (AFM) is demonstrated in a Co/SmFeO3 heterostructure. Employing time-resolved photoemission electron microscopy combined with x-ray magnetic circular dichroism, a sub-100-ps change of the Co spins orientation by up to 10? driven by the ultrafast heating of the SmFeO3 orthoferrite substrate through its spin reorientation phase transition is revealed. Numerical modeling of the ultrafast-laser-induced heat profile in the heterostructure, and the subsequent coupled spins dynamics and equilibration of the spin systems suggest that the localized laser-induced spin reorientation is hindered compared with the static case. Moreover, numerical simulations show that a relatively small Co/SmFeO3 exchange interaction could be sufficient to induce a complete and fast spin reorientation transition (SRT).

Le Guyader, L.; Kleibert, A.; Nolting, F.; Joly, L.; Derlet, P. M.; Pisarev, R. V.; Kirilyuk, A.; Rasing, Th.; Kimel, A. V.

2013-02-01

30

Properties of polarized laser-induced birefringent gratings in azobenzene-doped poly(methyl methecrylate) optical fibers  

NASA Astrophysics Data System (ADS)

Birefringent gratings induced by 532 nm polarized laser in an azobenzene-doped polymethyl methacrylate (PMMA) fibers and blocks were investigated. Significant photo-induced birefringence with about 3.0×10 -5 has been observed from the fiber. It was found that there is an intensity threshold, which is 0.29 mW/cm2 at 532 nm. The birefringence decayed gradually when the writing laser turned off. So the dynamic process of the birefringence was studied. Both the rise and the decay processes of the birefringence include an initial "fast" response mode and a subsequent "slow" response mode. Both the fast response and the slow response become faster with increasing irradiating laser intensity. The birefringence was induced by the combination of the nonlinear absorption, linear absorption and thermal effect.

Xingsheng, Xu; Hai, Ming; Qijin, Zhang

2002-04-01

31

Dynamics of laser induced micro bubble clusters on tissue phantoms  

NASA Astrophysics Data System (ADS)

Selective retina treatment (SRT) is a laser based method to treat retinal diseases associated with disorders of the retinal pigment epithelium (RPE) while preserving photoreceptors and choroid. Applying microsecond laser pulses to the 100- 200 strongly absorbing melanin granules inside the RPE cells induces transient micro bubbles which disrupt the cells. Aim of this work is to understand bubble dynamics in clusters with respect to the influence of the adjacent retina. Bubble dynamics were investigated in vitro on porcine RPE. An about 200 ?m thick layer of agarose gel was applied to the RPE layer in order to simulate the mechanical properties of retina. Different laser pulse durations from 1 ns (532 nm, Nd:YAG) to 1.7 ?s (527 nm, Nd:YLF) were used. The bubbles were investigated interferometrically (fiber interferometer @ 830 nm) and with fast flash photography (25 ns flash duration). Bubble lifetimes were measured. The results show that with retina phantoms the bubble formation threshold was reached at 2.5 times higher irradiation than without retina phantom for 1.7 ?s laser pulses. The microbubbles generated with 1 ns laser pulses were almost not influenced by the agarose layer. Irradiation twofold over bubble formation threshold resulted in 3.5 times longer bubble lifetimes for ?s and 2 times longer for ns pulse durations, respectively.

Fritz, Andreas; Zegelin, Andrea; Ptaszynski, Lars; Birngruber, Reginald; Brinkmann, Ralf

2011-02-01

32

Molecular dynamics studies of ultrafast laser-induced nonthermal melting  

NASA Astrophysics Data System (ADS)

Molecular Dynamics (MD) is employed to investigate nonthermal melting triggered by coherent phonon excitation in bismuth telluride, which has Peierls distortion in the lattice structure. Results showed that the structural distortion caused by coherent phonons appears as early as 80 fs, while it takes several picoseconds for the whole phonon-excited area to evolve into a liquid state. It was also found that the temperature in the phonon-excited area rises quickly within tens of femtoseconds, while the rest of the lattice remains at the initial temperature even after several picoseconds, which is separated from the high temperature region across a thin transition area. This phenomenon is analogous to the heat transfer across a solid-liquid interface, even though in our case there is no abrupt solid-liquid interface between the cold lattice and the quasiliquid.

Wang, Y.; Xu, X.

2013-03-01

33

Dynamics of laser-induced transient micro bubble clusters  

NASA Astrophysics Data System (ADS)

Selective retina treatment (SRT) is a laser based therapy of retinal diseases associated with disorders of the retinal pigment epithelium (RPE) while preserving photoreceptors and choroid. Microsecond laser pulses applied to the 100-200 strongly absorbing melanin granules inside the RPE cells induce transient micro bubbles which disrupt the cells. Aim of this work is to understand bubble dynamics in clusters. Investigations were carried out on porcine RPE explants and on a floppy disc based model system. Laser pulse durations of 3 ns (532 nm, Nd:YAG) and 1.7 ?s (527 nm, Nd:YLF) were used. Bubble dynamics was explored with a fiber interferometer (830 nm) and fast flash photography (25 ns). Bubble sizes, velocities and lifetimes were measured. Single nucleation sites, which coalesce after some ?s, are observed with ns pulses. Using ?s pulses, fewer but larger cluster sites are observed which become two times bigger at the same factor above threshold. A linear increase of the bubble hight with radiant exposure is found for both pulse durations. RPE Bubble formation thresholds of 85 mJ/cm2 and 255 mJ/cm2 for ns and ?s pulses are found, respectively. Typical expansion velocities are 5 m/s while collapsing bubbles can reach 30 m/s. Bubble heights are up to 5 ?m. Earlier investigations on single melanosomes showed a bubble size limitation to 4 ?m with ?s pulses. The melanosome clusters do not show this size limit. It has to be investigated whether the results are transferable to whole eye globes.

Fritz, Andreas; Ptaszynski, Lars; Stoehr, Hardo; Brinkmann, Ralf

2009-07-01

34

Micro Dynamics of Pulsed Laser Induced Bubbles in Dusty Plasma Liquids  

SciTech Connect

We experimentally study the micro dynamics of the laser induced plasma bubble in a dusty plasma liquid formed by negatively charged dust particles suspended in a low pressure rf Ar glow discharge. The plume from the ablation of the suspended dust particles pushes away dust particle and generates a dust-free plasma bubble. It then travels downward. The spatio-temporal evolution of the dust density fluctuation surrounding the bubble is monitored by directly tracking dust motion through optical video microscopy. The micro dynamics of the bubble associated dust acoustic type solitary oscillation in the wake field is investigated and discussed.

Teng, L.-W.; Tsai, C.-Y.; Tseng, Y.-P.; I Lin [Department of Physics, National Central University, Jhungli, Taiwan 32001 (China)

2008-09-07

35

Dynamic characteristics of laser-induced vapor bubble formation in water based on high speed camera  

NASA Astrophysics Data System (ADS)

In clinical practice, laser ablation usually works under liquid environment such as water, blood or their mixture. Laser-induced vapor bubble or bubble formation and its consequent dynamics were believed to have important influence on tissue ablation. In the paper, the dynamic process of vapor bubble formation and consequently collapse induced by pulsed Ho:YAG laser in static water was investigated by using high-speed camera. The results showed that vapor channel / bubble can be produced with pulsed Ho:YAG laser, and the whole dynamic process of vapor bubble formation, pulsation and consequently collapse can be monitored by using high-speed camera. The dynamic characteristics of vapor bubble, such as pulsation period, the maximum depth and width were determined. The dependence of above dynamic parameters on incident radiant exposure was also presented. Based on which, the influence of vapor bubble on hard tissue ablation was discussed.

Zhang, Xian-zeng; Guo, Wenqing; Zhan, Zhenlin; Xie, Shusen

2013-08-01

36

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

NASA Astrophysics Data System (ADS)

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.

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

2012-02-01

37

Dynamic sampling of laser-induced vapor plumes by mass spectrometry  

NASA Technical Reports Server (NTRS)

Mass spectrometric techniques and instrumentation for the dynamic sampling of laser-induced vapor clouds during their submillisecond expansion periods are discussed. Illustrations are drawn primarily from the results of pulsed-laser heating of some oxides and graphites; these include comparisons of incident laser beam pulses with the resultant pulses of positive ions and selected neutral species. Observed characteristics of vapor pulses from graphite are shown to correlate with calculated surface temperature response. Dynamic velocity measurements of individual vapor species are described and, from these velocities, vaporization temperatures are derived and compared using four gas dynamic models for vapor expansion into vacuum. Additional measurements indicate that the laser beam may interact directly with the neutral vapors to produce ions.

Lincoln, K. A.; Covington, M. A.

1975-01-01

38

Laser-induced ultrafast spin dynamics in ErFeO3  

NASA Astrophysics Data System (ADS)

Using 100-fs optical laser pulses, we have been able to excite and probe spin dynamics in the rare-earth orthoferrite ErFeO3. The investigation was performed in a broad temperature range with the focus on the vicinities of the compensation point Tcomp?47K and the spin reorientation transition region in the interval 86K?T?99K. Spin precession excited by the laser pulse was present in a large part of the investigated temperature range, but was especially strong near the spin reorientation region. In this region the laser pulse also caused an ultrafast spin reorientation. By changing the laser pulse fluence, we could vary both the reorientation amplitude and the reorientation speed. We show that the laser-induced spin dynamics in ErFeO3 is caused in part by heating and in part by the inverse Faraday effect. Comparing to the results of similar experiments in other rare-earth orthoferrites, we found the speed of the laser-induced spin reorientation to be significantly lower. We attribute this finding to the weaker electron-phonon coupling of the Er3+ 4f electrons with the lattice.

de Jong, J. A.; Kimel, A. V.; Pisarev, R. V.; Kirilyuk, A.; Rasing, Th.

2011-09-01

39

Laser-Induced Fluorescence Photogrammetry for Dynamic Characterization of Transparent and Aluminized Membrane Structures  

NASA Technical Reports Server (NTRS)

Photogrammetry has proven to be a valuable tool for static and dynamic profiling of membrane based inflatable and ultra-lightweight space structures. However, the traditional photogrammetric targeting techniques used for solid structures, such as attached retro-reflective targets and white-light dot projection, have some disadvantages and are not ideally suited for measuring highly transparent or reflective membrane structures. In this paper, we describe a new laser-induced fluorescence based target generation technique that is more suitable for these types of structures. We also present several examples of non-contact non-invasive photogrammetric measurements of laser-dye doped polymers, including the dynamic measurement and modal analysis of a 1m-by-1m aluminized solar sail style membrane.

Dorrington, Adrian A.; Jones, Thomas W.; Danehy, Paul M.; Pappa, Richard S.

2003-01-01

40

Dynamics of dud, dut in superstrong laser fields for laser induced nuclear fusion  

NASA Astrophysics Data System (ADS)

Nuclear fusion occurs during the collision of selected isotopes of hydrogen with relative energy in the MeV(10**6 eV) regime. Such high energy ions can be generated by high power lasers applied to clusters [1] via the accumulated ponderomotive energies. However in such schemes laser induced collisions are random whereas as shown previously ultrashort superintense laser pulses can be used to control collisions in muonic molecules [2]. We present full 3-D dynamics from accurate Time-dependent Schroedinger equations, TDSE, s, of the isotopomers, pud, dud, dut in super intense laser pulses with intensities I 10**23 W/cm**2 to illustrate the possibility of inducing always head-on(zero-impact) collisions leading in principle to laser induced nuclear fusion, LINF. Due to its heavy mass(mu/me=185.8) the muonic molecular ions are stable to ionization up to intensities I=10**23 W/cm**2 and recollision of the heavy particles (p,td,t) will be shown to be controllable by few cycle superintense laser pulses leading to LINF.The nonsymmetric isotopomers dut and put manifest enhanced fusion due to the presence of permanent dipole moments.[4pt] [1] KWD Ledingham et al, Science 300, 1107 (2003)[0pt] [2] S Chelkowski, PB Corkum, AD Bandrauk, Phys Rev Lett 93, 083602(2004)

Bandrauk, Andre D.; Paramonov, Guennaddi

2012-03-01

41

Dynamic Brillouin gratings permanently sustained by chaotic lasers.  

PubMed

A method to induce only one permanent and localized dynamic Brillouin grating in polarization maintaining optical fibers is introduced. The generation of the grating exploits the thumbtack correlation of the chaotic laser signals. A numerical calculation, corroborated by a theoretical analysis, is performed and the grating properties, length, and reflectance determined. PMID:22378429

Santagiustina, M; Ursini, L

2012-03-01

42

Femtosecond laser-induced crystallization of amorphous Ga-Sb-Se films and coherent phonon dynamics.  

PubMed

Femtosecond laser-irradiation-induced phase change of new environment friendly Te-free amorphous Ga-Sb-Se films is studied by coherent phonon spectroscopy. New coherent optical phonons (COP) occur when laser irradiation power reaches some threshold, implying laser-induced phase change taken place. Pump power dependence of COP dynamics reveals the phase change as crystallization and crystallization quality is comparable to one of annealing crystallization, showing application potential of Ga-Sb-Se films in optical phase change memory. The laser-irradiated crystallization of different component Ga-Sb-Se films is studied. It is found crystallization threshold power depends on Sb content, implying Sb-content control of the crystallization temperature of Ga-Sb-Se films. PMID:23038497

Zhu, Weiling; Lu, Yegang; Li, Simian; Song, Zhitang; Lai, Tianshu

2012-08-13

43

Enhanced spontaneous backscattering in Brillouin dynamic gratings.  

PubMed

Spontaneous Brillouin backscattering, which accompanies the operation of Brillouin dynamic gratings (BDGs) setups, is investigated both theoretically and experimentally. It is shown that this noisy emission, which cannot be separated from the signal of interest, contains not only the probe spontaneous Brillouin backscattering but also a significant contribution from the spontaneous/stimulated acoustic field, originating from the high-frequency writing pump. In the absence of the low-frequency writing pump and for a strong enough high-frequency writing pump, the observed Stokes noise can exhibit an average backscattered power much higher than that from the probe alone. PMID:24281529

Yaron, L; Peled, Y; Langer, T; Tur, M

2013-12-01

44

Imaging ultrafast dynamics of molecules with laser-induced electron diffraction.  

PubMed

We introduce a laser-induced electron diffraction method (LIED) for imaging ultrafast dynamics of small molecules with femtosecond mid-infrared lasers. When molecules are placed in an intense laser field, both low- and high-energy photoelectrons are generated. According to quantitative rescattering (QRS) theory, high-energy electrons are produced by a rescattering process where electrons born at the early phase of the laser pulse are driven back to rescatter with the parent ion. From the high-energy electron momentum spectra, field-free elastic electron-ion scattering differential cross sections (DCS), or diffraction images, can be extracted. With mid-infrared lasers as the driving pulses, it is further shown that the DCS can be used to extract atomic positions in a molecule with sub-angstrom spatial resolution, in close analogy to the standard electron diffraction method. Since infrared lasers with pulse duration of a few to several tens of femtoseconds are already available, LIED can be used for imaging dynamics of molecules with sub-angstrom spatial and a few-femtosecond temporal resolution. The first experiment with LIED has shown that the bond length of oxygen molecules shortens by 0.1 Å in five femtoseconds after single ionization. The principle behind LIED and its future outlook as a tool for dynamic imaging of molecules are presented. PMID:22914800

Lin, C D; Xu, Junliang

2012-10-14

45

Density jumps in the plasma of a nanosecond laser-induced spark and their dynamics  

SciTech Connect

Experimental investigation of the structure of a laser-induced spark emerging in the focusing of 50-ns radiation pulses is described. Two density jumps were discovered in the plasma of the laser-induced spark. One of them is localised in the vicinity of the focal plane of the lens, the other propagates from this plane in the laser propagation direction at a constant velocity of {approx}7.5 km s{sup -1}. (laser plasma)

Malyutin, A A; Podvyaznikov, V A; Chevokin, V K [A M Prokhorov General Physics Institute, Russian Academy of Sciences, Moscow (Russian Federation)

2011-01-31

46

Laser-Induced Forward Transfer Using Triazene Polymer Dynamic Releaser Layer  

NASA Astrophysics Data System (ADS)

This article presents a short review of the use of triazene polymer as a dynamic release layer (DRL) for laser-induced forward transfer (LIFT), before looking at the latest research in more detail. The field of triazene polymer ablation only started around 20 years ago and has grown rapidly into a number of different application areas. Most promisingly, triazene ablation has been refined as a method for propulsion, bringing the benefits of LIFT to the deposition of sensitive transfer materials. The key to understanding LIFT with a triazene DRL is to understand the more fundamental nature of triazene polymer ablation in both frontside and backside orientations. This article focuses on the most recent experimental results on LIFT with a triazene DRL: the effect of picosecond pulse lengths compared with nanosecond pulse lengths; the effect of reduced air pressure; and the improvements in transfer in terms of range of transfer materials, and transfer across a gap. The results all help improve fundamental understanding of triazene-based LIFT, and the transfer of functioning OLEDs demonstrates the capability of the technique.

Stewart, James Shaw; Lippert, Thomas; Nagel, Matthias; Nüesch, Frank; Wokaun, Alexander

2010-10-01

47

Dynamics of laser-induced damage of spherical nanoparticles by high-intensity ultrashort laser pulses  

NASA Astrophysics Data System (ADS)

Damage of a metal spherical nanoparticle by femtosecond laser pulses is analyzed by splitting the overall process into two steps. The fast step includes electron photoemission from a nanoparticle. It takes place during direct action of a laser pulse and its rate is evaluated as a function of laser and particle parameters by two approaches. Obtained results suggest the formation of significant positive charge of the nanoparticles due to the photoemission. The next step includes ion emission that removes the excessive positive charge and modifies particle structure. It is delayed with respect to the photo-emission and is analyzed by a simple analytical model and modified molecular dynamics. Obtained energy distribution suggests generation of fast ions capable of penetrating into surrounding material and generating defects next to the nanoparticle. The modeling is extended to the case of a nanoparticle on a solid surface to understand the basic mechanism of surface laser damage initiated by nano-contamination. Simulations predict embedding the emitted ions into substrate within a spot with size significantly exceeding the original particle size. We discuss the relation of those effects to the problem of bulk and surface laser-induced damage of optical materials by single and multiple ultrashort laser pulses.

Komolov, Vladimir L.; Gruzdev, Vitaly E.; Przhibelskii, Sergey G.; Smirnov, Dmitry S.

2012-12-01

48

Ultrafast dynamics of the laser-induced solid-to-liquid phase transition in aluminum  

NASA Astrophysics Data System (ADS)

This dissertation reports the ultrafast dynamics of aluminum during the solid-to-liquid phase transition of melting after excitation by an intense femtosecond laser pulse. Photoexcitation with intense femtosecond laser pulses is known to create a novel melting mechanism called non-thermal melting. This mechanism has been observed repeatedly in semiconductors, but not yet in metals. We investigate the melting mechanism of aluminum by monitoring the reflectivity response following excitation by an intense laser pulse. We employ an optical pump-probe technique designed to measure broadband reflectivity across the visible spectrum with femtosecond time resolution. A non-thermal melting mechanism was proposed for aluminum by optical experiments that demonstrated transition of the optical properties from solid to liquid values within 500 fs after phototexcitation. This result was later challenged by electron diffraction experiments, which showed that the lattice loses long range order within 3.5 ps during photoinduced melting. This time scale implies conventional thermal melting. We find that the broadband optical properties during the solid-to-liquid phase transition in aluminum agree with the results obtained by the electron diffraction experiments. The transition of the broadband reflectivity from solid to liquid values is complete within 1.5--2 ps in our experiments, which is compatible with thermal melting. We don't observe time scales on the order of 500 fs. All the experimental evidence in this dissertation lead to the conclusion that the laser-induced, solid-to-liquid phase transition in aluminum is a thermal process.

Kandyla, Maria

49

Dynamics of impacting a bubble by another pulsed-laser-induced bubble: Jetting, fragmentation, and entanglement  

NASA Astrophysics Data System (ADS)

We investigate experimentally the detailed dynamics of how an existing microbubble B1 is impacted and shattered by another nearby pulsed-laser-induced microbubble B2 , and the backward interaction on B2 in a thin liquid layer. Mediated by the flow field, potential energy can be accumulated or lost through the alternate compression and expansion of the two bubbles. The symmetry breaking induced by the presence of the nearby counterbubble generates push-pull-type alternate forward and backward axial jetting on the compressed bubble associated with the elongated shape or even entrainment of the counterexpanding bubble into the jet-indented boundary. The strong penetrating axial jet through B1 , and its interplay with the transverse jets by the flow field surrounding B1 in the first compression stage and the second expanding stage of B1 lead to a complicated fragmentation pattern of B1 . Increasing the interbubble interaction by decreasing the interbubble distance causes B2 to become entangled with B1 through its entrainments into the backward axial jet-indented region of B2 , in the expansion phase of B2 . At the extreme of large laser energy for B2 , the leftward reexpansion of B1 is suppressed. The strong shear flow field generates many tiny bubbles around the liquid-gas boundaries of the two axial jet-induced major daughter bubbles from B1 . The detailed interaction behaviors over a broad range of the energy of B2 , 0.14- 0.55?J (corresponding to the maximum bubble expansion energy), and of the interbubble distance (170- 500?m ) are presented and discussed.

Chen, Yen-Hung; I, Lin

2008-02-01

50

Laser-induced UV photodissociation of 2-bromo-2-nitropropane: dynamics of OH and Br formation.  

PubMed

Photoexcitation of 2-bromo-2-nitropropane (BNP) at 248 and 193 nm generates OH, Br, and NO(2) among other products. The OH fragment is detected by laser-induced fluorescence spectroscopy, and its translational and internal state distributions (vibration, rotation, spin-orbit, and ?-doubling components) are probed. At both 248 and 193 nm, the OH fragment is produced translationally hot with the energy of 10.8 and 17.2 kcal?mol, respectively. It is produced vibrationally cold (v" = 0) at 248 nm, and excited (v" = 1) at 193 nm with a vibrational temperature of 1870 ± 150 K. It is also generated with rotational excitation, rotational populations of OH(v" = 0) being characterized by a temperature of 550 ± 50 and 925 ± 100 K at 248 and 193 nm excitation of BNP, respectively. The spin-orbit components of OH(X(2)?) are not in equilibrium on excitation at 193 nm, but the ?-doublets are almost in equilibrium, implying no preference for its ? lobe with respect to the plane of rotation. The NO(2) product is produced electronically excited, as detected by measuring UV-visible fluorescence, at 193 nm and mostly in the ground electronic state at 248 nm. The Br product is detected employing resonance-enhanced multiphoton ionization with time-of-flight mass spectrometer for better understanding of the dynamics of dissociation. The forward convolution analysis of the experimental data has provided translational energy distributions and anisotropy parameters for both Br((2)P(3?2)) and Br?((2)P(1?2)). The average translational energies for the Br and Br? channels are 5.0 ± 1.0 and 6.0 ± 1.5 kcal?mol. No recoil anisotropies were observed for these products. Most plausible mechanisms of OH and Br formation are discussed based on both the experimental and the theoretical results. Results suggest that the electronically excited BNP molecules at 248 and 234 nm relax to the ground state, and subsequently dissociate to produce OH and Br through different channels. The mechanism of OH formation from BNP on excitation at 193 nm is also discussed. PMID:21280734

Saha, Ankur; Kawade, Monali; Upadhyaya, Hari P; Kumar, Awadhesh; Naik, Prakash D

2011-01-28

51

Dynamics of primary and secondary microbubbles created by laser-induced breakdown of an optically trapped nanoparticle.  

PubMed

Laser-induced breakdown of an optically trapped nanoparticle is a unique system for studying cavitation dynamics. It offers additional degrees of freedom, namely the nanoparticle material, its size, and the relative position between the laser focus and the center of the optically trapped nanoparticle. We quantify the spatial and temporal dynamics of the cavitation and secondary bubbles created in this system and use hydrodynamic modeling to quantify the observed dynamic shear stress of the expanding bubble. In the final stage of bubble collapse, we visualize the formation of multiple submicrometer secondary bubbles around the toroidal bubble on the substrate. We show that the pattern of the secondary bubbles typically has its circular symmetry broken along an axis whose unique angle rotates over time. This is a result of vorticity along the jet towards the boundary upon bubble collapse near solid boundaries. PMID:22400669

Arita, Y; Antkowiak, M; Venugopalan, V; Gunn-Moore, F J; Dholakia, K

2012-01-01

52

Dynamics of primary and secondary microbubbles created by laser-induced breakdown of an optically trapped nanoparticle  

PubMed Central

Laser-induced breakdown of an optically trapped nanoparticle is a unique system for studying cavitation dynamics. It offers additional degrees of freedom, namely the nanoparticle material, its size, and the relative position between the laser focus and the center of the optically trapped nanoparticle. We quantify the spatial and temporal dynamics of the cavitation and secondary bubbles created in this system and use hydrodynamic modeling to quantify the observed dynamic shear stress of the expanding bubble. In the final stage of bubble collapse, we visualize the formation of multiple submicrometer secondary bubbles around the toroidal bubble on the substrate. We show that the pattern of the secondary bubbles typically has its circular symmetry broken along an axis whose unique angle rotates over time. This is a result of vorticity along the jet towards the boundary upon bubble collapse near solid boundaries.

Arita, Y.; Antkowiak, M.; Venugopalan, V.; Gunn-Moore, F. J.; Dholakia, K.

2012-01-01

53

Dynamics of interference of femtosecond laser-induced stress waves and crack formation inside a LiF single crystal  

NASA Astrophysics Data System (ADS)

When a femtosecond laser pulse is focused tightly inside a LiF single crystal, cracks are generated in the <100< directions from the photoexcited region. Previously, we found that cracks of different lengths are formed by simultaneous fs laser irradiation at multiple spots. To elucidate the mechanism of modulation in crack lengths, we observed the transient stress distributions after simultaneous fs laser irradiation at multiple spots inside a LiF single crystal. First, we found that stress amplitude can be doubled by the interference of fs laser induced stress waves. Next, we observed the dynamics of crack formation as well as the transient birefringence distribution. In the case in which one crack became shorter than other cracks, the observation of the crack dynamics showed that the compressive stress by a constrictive interference of stress waves at a crack tip prevented the crack from propagating further. However, In the case in which the elongation of one crack occurred, we could not find any relationship between the elongation of a crack and the interference of stress waves by the observed stress distribution. Based on the time-resolved observation, we discussed the mechanism of the modulation of the laser induced cracks by interference of stress waves.

Sakakura, Masaaki; Fukuda, Naoaki; Shimotsuma, Yasuhiko; Miura, Kiyotaka

2014-03-01

54

Demodulation System for Fiber Optic Bragg Grating Dynamic Pressure Sensing  

NASA Technical Reports Server (NTRS)

Fiber optic Bragg gratings have been used for years to measure quasi-static phenomena. In aircraft engine applications there is a need to measure dynamic signals such as variable pressures. In order to monitor these pressures a detection system with broad dynamic range is needed. This paper describes an interferometric demodulator that was developed and optimized for this particular application. The signal to noise ratio was maximized through temporal coherence analysis. The demodulator was incorporated in a laboratory system that simulates conditions to be measured. Several pressure sensor configurations incorporating a fiber optic Bragg grating were also explored. The results of the experiments are reported in this paper.

Lekki, John D.; Adamovsky, Grigory; Floyd, Bertram

2001-01-01

55

Dynamic Optical Grating Device and Associated Method for Modulating Light  

NASA Technical Reports Server (NTRS)

A dynamic optical grating device and associated method for modulating light is provided that is capable of controlling the spectral properties and propagation of light without moving mechanical components by the use of a dynamic electric and/or magnetic field. By changing the electric field and/or magnetic field, the index of refraction, the extinction coefficient, the transmittivity, and the reflectivity fo the optical grating device may be controlled in order to control the spectral properties of the light reflected or transmitted by the device.

Park, Yeonjoon (Inventor); Choi, Sang H. (Inventor); King, Glen C. (Inventor); Chu, Sang-Hyon (Inventor)

2012-01-01

56

Dynamic two-axis curvature measurement using multicore fiber Bragg gratings interrogated by arrayed waveguide gratings  

NASA Astrophysics Data System (ADS)

We describe the use of arrayed waveguide gratings (AWGs) in the interrogation of fiber Bragg gratings (FBGs) for dynamic strain measurement. The ratiometric AWG output was calibrated in a static deflection experiment over a ±200 ?? range. Dynamic strain measurement was demonstrated with a FBG in a conventional single-mode fiber mounted on the surface of a vibrating cantilever and on a piezoelectric actuator, giving a resolution of 0.5 ?epsi at 2.4 kHz. We present results of this technique extended to measure the dynamic differential strain between two FBG pairs within a multicore fiber. An arbitrary cantilever oscillation of the multicore fiber was determined from curvature measurements in two orthogonal axes at 1125 Hz with a resolution of 0.05 m-1.

Fender, Amanda; Rigg, Euan J.; Maier, Robert R. J.; MacPherson, William N.; Barton, James S.; Moore, Andrew J.; Jones, Julian D. C.; Zhao, Donghui; Zhang, Lin; Bennion, Ian; McCulloch, Scott; Jones, Ben J. S.

2006-12-01

57

Dynamic two-axis curvature measurement using multicore fiber Bragg gratings interrogated by arrayed waveguide gratings.  

PubMed

We describe the use of arrayed waveguide gratings (AWGs) in the interrogation of fiber Bragg gratings (FBGs) for dynamic strain measurement. The ratiometric AWG output was calibrated in a static deflection experiment over a +/-200 microepsilon range. Dynamic strain measurement was demonstrated with a FBG in a conventional single-mode fiber mounted on the surface of a vibrating cantilever and on a piezoelectric actuator, giving a resolution of 0.5 microepsilon at 2.4 kHz. We present results of this technique extended to measure the dynamic differential strain between two FBG pairs within a multicore fiber. An arbitrary cantilever oscillation of the multicore fiber was determined from curvature measurements in two orthogonal axes at 1125 Hz with a resolution of 0.05 m(-1). PMID:17151742

Fender, Amanda; Rigg, Euan J; Maier, Robert R J; MacPherson, William N; Barton, James S; Moore, Andrew J; Jones, Julian D C; Zhao, Donghui; Zhang, Lin; Bennion, Ian; McCulloch, Scott; Jones, Ben J S

2006-12-20

58

Laser beam-induced dynamic gratings in ?-quartz  

Microsoft Academic Search

Piezoelectric effect has been monitored and applied usually below the microwave frequencies. By propagation of the laser beam through ?-quartz, diffraction fringes were observed in the transmitted beam spot. The diffraction fringes are produced by the dynamic gratings induced by the electromagnetic field of the incident light, namely an optical piezoelectric effect in ?-quartz.

C. Z Tan; H Chen; Z. G Liu

2002-01-01

59

Dynamics of Spatially and Temporally Resolved Laser Induced Al-plasma  

SciTech Connect

In the present study the temporal and spatial evolution of the plasma produced by interaction of Q-switched Nd:YAG laser pulses at 532 nm with pure aluminum target are investigated via optical emission spectroscopy (OES) in vacuum (10-5 torr). Comparison of the spectra taken at different distances from the target surface facilitates discussing fundamental concepts of the Laser Induced Plasma (LIP). Such measurements have been exploited to understand the main processes involved and must be taken into account for the analysis of this kind of plasma. The LIP mean expansion velocity has been determined by measuring the ionic emission temporal profiles usually referred to as the Time of Flight (TOF) profiles. The temporal behavior of the spectral emission has been explained and interpreted in view of the three body recombination processes. Problems concerning the existence of and departure from the local thermodynamic equilibrium (LTE) in the LIP are studied carefully as observed in the performed experiment.

Imam, H.; Harith, M. A.; E-El Gamal, Yosr [National Institute of Laser Enhanced Sciences (NILES) Cairo University (Egypt); Abdellatif, G. [Phys. Dept. Faculty of Science, Cairo University (Egypt); Palleschi, V. [IPCF/CNR, Applied Laser Spectroscopy Laboratory, Pisa (Italy)

2007-02-14

60

A simple model for flyer velocity from laser-induced forward transfer with a dynamic release layer  

NASA Astrophysics Data System (ADS)

A simple 1-D model has been developed for the velocity of flyers in vacuum generated by laser-induced forward transfer (LIFT) with a dynamic release layer (DRL). It is an extension of a laser ablation model for metal flyer plates based on the Gurney model of explosive output for driving metal fragments. The model has been extended to the bilayer system of a DRL overlain with a transfer layer. The suitability of the model has been checked with experimental velocity data obtained from shadowgraphy. The experiments used bilayer samples of triazene polymer/aluminium, ablated from the backside through the substrate at reduced pressure (5 × 10-2 mbar). The results suggest that the Gurney energy approach provides the basis of a viable, physically relevant, algebraic model for LIFT, but other loss mechanisms still need be incorporated, particularly thermal loss into the fused silica substrate.

Shaw-Stewart, James; Lippert, Thomas; Nagel, Matthias; Nüesch, Frank; Wokaun, Alexander

2012-09-01

61

High average power solid-state lasers on dynamic gratings  

Microsoft Academic Search

Self-starting laser with cavity completed by dynamic holographic gratings induced in the laser crystal by optical waves has recently demonstrated the capability of generating beams with more than two-hundred-Watt average power and a good quality. An important advantage of these lasers is the adaptive property of their cavity provided by the nonlinear dynamic mirror, which is a self-pumped phase-conjugate mirror.

O. L. Antipov; A. P. Zinoviev; O. N. Eremeykin; A. P. Savikin; G. E. Yudakin; A. V. Shmyikov

2003-01-01

62

Temperature-controlled fiber Bragg grating dynamic strain detection system  

Microsoft Academic Search

A fiber Bragg grating (FBG) measurement system for dynamic strain detection has been developed. It exploits a temperature-controlled FBG as a small-band filter to measure the strain-induced wavelength shift of structurally integrated FBG sensors. This interrogation method realizes an optimal dynamic performance of the sensor also under the influence of environmental temperature changes. This has been confirmed relative to a

Xiao-Dong Wu; Cornelia Schmidt-Hattenberger; Kay Krüger; Jun Chen

2005-01-01

63

High-resolution imaging of ejection dynamics in laser-induced forward transfer  

NASA Astrophysics Data System (ADS)

Laser-induced Forward Transfer (LIFT) is a 3D direct-write method suitable for precision printing of various materials. As the ejection mechanism of picosecond LIFT has not been visualized in detail, the governing physics are not fully understood yet. Therefore, this article presents an experimental imaging study on the ejection process of gold-based LIFT. The LIFT experiments were performed using a 6.7 picosecond Yb:YAG laser source equipped with a SHG. The beam was focused onto a 200 nm thick gold donor layer. The high magnification images were obtained using bright field illumination by a 6 ns pulsed Nd:YAG laser source and a 50× long-distance microscope objective that was combined with a 200 mm tube lens. For laser fluence levels up to two times the donor-transfer-threshold, the ejection of a single droplet was observed. The typical droplet radius was estimated to be less than 3 ?m. A transition of ejection features towards higher fluence, indicates a second fluence-regime in the ejection process. For higher laser fluence, the formation of an elongated gold jet was observed. This jet fragments into multiple relatively small droplets, resulting in a spray of particles on the receiving substrate.

Pohl, R.; Visser, C. W.; Römer, G. R. B. E.; Sun, C.; Huis in't Veld, A. J.; Lohse, D.

2014-03-01

64

A feasible method for measuring the blood flow velocity in superficial artery based on the laser induced dynamic thermography  

NASA Astrophysics Data System (ADS)

Infrared thermography has been proved to be a useful tool to detect thermal physiologic changes associated with various diseases. However, static and single point temperature mapping on skin surface provided by the infrared thermography has not been able to meet the requirements for evaluating the complicated physiological status of human body. In order to explore more physiological variables for possible disease diagnostics, the present paper has developed a laser induced dynamic thermographic modality to estimate the average velocity of the superficial blood flow by means of tracking thermal transport along blood flow direction. A conceptual in vivo experiment is designed to record dynamic temperature response of rabbit auricle skin by thermograph, which is then used to estimate the blood flow velocity through a derived theoretical model. In addition, the lumped parameter model is developed to calibrate the estimated error by compensating the thermal response time induced by the tissue temperature change that the current infrared thermal imaging system with limited thermal sensitivity may fail to capture. The final calibrated results are fitting well with that from the Doppler ultrasound measurement, which indeed verified the practicality and feasibility of the method developed in this work.

Jin, Chao; He, Zhizhu; Zhang, Shanshan; Qi, Minchao; Sun, Ziqiao; Di, Derui; Liu, Jing

2012-11-01

65

Self-Mixing-Based Demodulation Technique for Dynamic Fiber Bragg Grating Strain Sensors  

Microsoft Academic Search

We report a novel demodulation scheme for the detection of small Bragg wavelength shifts in a fiber Bragg grating strain sensor by exploiting the optical feedback reflected from the grating structure back into a 1310 nm laser diode integrating a photodiode. The dynamic strain generated by a mechanical vibrator is applied transversely to the fiber Bragg grating and the desired

H. C. Seat; Y. Wang; T. Bosch; W. Hu; X. Chen; L. Zhang

2006-01-01

66

Dynamic self-enhanced diffraction from written photorefractive gratings  

NASA Astrophysics Data System (ADS)

The self-enhanced diffraction with oscillatory behavior for unfixed holograms is observed and investigated in new photorefractive (K1-xNax)2m(Sr1-yBay)1-mNb2O6 crystals. The recorded diffraction efficiency can be increased 10 times during the readout process. The maximum peak diffraction efficiency obtained is close to unity. A closed solution of dynamic two-wave mixing equations and a coupling coefficient expression obtained from the standard band transport model are used to fit the observed results. The observed self-enhancement is caused by the interference between a new grating, formed by the reading beam and the diffracted signal, and the existing grating. The fitted results show that the internal space-charge field originating from the photovoltaic effect and the pyroelectric effect can reduce the phase shift.

Zhang, Liangmin; Prasad, Paras N.; Burzynski, Ryszard; Chen, Huanchu; Han, Jianru

2000-01-01

67

Laser Spectroscopy of the Potassium Dimer: Photodissociation Dynamics and Laser-Induced Fluorescence  

Microsoft Academic Search

Laser spectroscopy is a powerful tool in terms of unraveling both spectroscopic information and dynamic information (e.g. photodissociation). In the first part of this thesis we utilize the polarization of light emitted by the atomic product K* after photodissociation (of K _2). This elucidates the dynamics of photodissociation with emphasis on the \\

Vassilios Theodoros Zafiropulos

1988-01-01

68

Laser-induced nonlinear dynamics in a nematic liquid-crystal film  

Microsoft Academic Search

An elliptically polarized cw laser beam propagating in a nematic liquid-crystal film can induce molecular reorientation and lead the system through various dynamic regimes: torsional oscillations, precession, nutation with precession, and others.

E. Santamato; G. Abbate; P. Maddalena; L. Marrucci; Y. R. Shen

1990-01-01

69

Doppler Spectrometry for Ultrafast Temporal Mapping of Density Dynamics in Laser-Induced Plasmas  

SciTech Connect

We present high resolution measurements of the ultrafast temporal dynamics of the critical surface in moderately overdense, hot plasma by using two-color, pump-probe Doppler spectrometry. Our measurements clearly capture the initial inward motion of the plasma inside the critical surface of the pump laser which is followed by outward expansion. The measured instantaneous velocity and acceleration profiles are very well reproduced by a hybrid simulation that uses a 1D electromagnetic particle-in-cell simulation for the initial evolution and a hydrodynamics simulation for the later times. The combination of high temporal resolution and dynamic range in our measurements clearly provides quantitative unraveling of the dynamics in this important region, enabling this as a powerful technique to obtain ultrafast snapshots of plasma density and temperature profiles for providing benchmarks for simulations.

Mondal, S.; Lad, Amit D.; Ahmed, Saima; Narayanan, V.; Pasley, J.; Rajeev, P. P.; Robinson, A. P. L.; Kumar, G. Ravindra [Tata Institute of Fundamental Research, 1 Homi Bhabha Road, Colaba, Mumbai-400005 (India); Department of Physics, University of York, Heslington, York (United Kingdom); Central Laser Facility, Rutherford-Appleton Laboratory, Chilton, Oxfordshire (United Kingdom); Central Laser Facility, Rutherford-Appleton Laboratory, Chilton, Oxfordshire (United Kingdom); Tata Institute of Fundamental Research, 1 Homi Bhabha Road, Colaba, Mumbai-400005 (India)

2010-09-03

70

Doppler spectrometry for ultrafast temporal mapping of density dynamics in laser-induced plasmas.  

PubMed

We present high resolution measurements of the ultrafast temporal dynamics of the critical surface in moderately overdense, hot plasma by using two-color, pump-probe Doppler spectrometry. Our measurements clearly capture the initial inward motion of the plasma inside the critical surface of the pump laser which is followed by outward expansion. The measured instantaneous velocity and acceleration profiles are very well reproduced by a hybrid simulation that uses a 1D electromagnetic particle-in-cell simulation for the initial evolution and a hydrodynamics simulation for the later times. The combination of high temporal resolution and dynamic range in our measurements clearly provides quantitative unraveling of the dynamics in this important region, enabling this as a powerful technique to obtain ultrafast snapshots of plasma density and temperature profiles for providing benchmarks for simulations. PMID:20867525

Mondal, S; Lad, Amit D; Ahmed, Saima; Narayanan, V; Pasley, J; Rajeev, P P; Robinson, A P L; Kumar, G Ravindra

2010-09-01

71

Laser-triggered dynamic breakdown of gases and laser-induced prebreakdown signals  

Microsoft Academic Search

Dynamic breakdown of Ne and Ar gases biased to the prebreakdown stage, with and without absorption of very short duration incident N2 laser pulses, is studied. Effects of bias and incident laser intensity are seen to be complementary. Laser illumination of the interelectrode gap causes gas breakdown at the cathode to take place at a faster rate and at lower

N. Yackerson; N. S. Kopeika

1985-01-01

72

Trends in Ln(III) Sorption to Quartz Assessed by Molecular Dynamics Simulations and Laser Induced Flourescence Studies  

SciTech Connect

Molecular dynamics simulations were performed to examine trends in trivalent lanthanide [Ln(III)] sorption to quartz surface SiOH0 and SiO- sites across the 4f period. Complementary laser induced fluorescence studies examined Eu(III) sorption to quartz at varying ionic strength such that the surface sorbed species could be extrapolated at zero ionic strength, the conditions under which the simulations are performed. This allowed for direct comparison of the data, enabling a molecular understanding of the surface sorbed species and the role of the ion surface charge density upon the interfacial reactivity. Thus, this combined theoretical and experimental approach aids in the prediction of the fate of trivalent radioactive contaminants at temporary and permanent nuclear waste storage sites. Potential of mean force molecular dynamics, as well as simulations of pre-sorbed Ln(III) species agrees with the spectroscopic study of Eu(III) sorption, indicating that strongly bound inner-sphere complexes are formed upon sorption to an SiO- site. The coordination shell of the ion contains 6-7 waters of hydration and it is predicted that surface OH groups dissociate from the quartz and bind within the inner coordination shell of Eu(III). Molecular simulations predict less-strongly bound inner2 sphere species in early lanthanides and more strongly bound species in late lanthanides, following trends in the ionic radius of the 4f ions. The participation of surface dissociated OHgroups within the inner coordination shell of the Ln(III) ion is, however, consistent across the series studied. Sorption to a fully protonated quartz surface is not predicted to be favorable by any Ln(III), except perhaps Lu.

Kuta, Jadwiga; Wander, Matthew C F.; Wang, Zheming; Jiang, Siduo; Wall, Nathalie; Clark, Aurora E.

2011-11-08

73

Ab initio molecular dynamics simulation of femtosecond laser-induced structural modification in vitreous silica  

Microsoft Academic Search

Femtosecond laser pulse induced structural changes in silica glass and their role in changing the refractive index of the glass have been investigated using ab initio molecular dynamics simulation methods based on finite-temperature density functional theory. The average nearest-neighbor Si-O, Si-Si, and O-O distances are found to increase during laser irradiation due to the weakening of bonds resulting from the

S. Sen; J. E. Dickinson

2003-01-01

74

Dynamics Of A Laser-Induced Plume Self-Similar Expansion  

NASA Astrophysics Data System (ADS)

The dynamics of a laser ablation plume during the first stage of its expansion, just after the termination of the laser pulse is modeled. First, we suppose the laser fluence range low enough to consider a neutral vapor. The expansion of the evaporated material is described by one-component fluid and one-dimensional Euler equations. The vapor is assumed to follow an ideal gas flow. For high energetic ions, the charge separation can be neglected and the hydrodynamics equations can be solved using self-similar formulation. The obtained ordinary differential equations are solved numerically. Secondly, the effect of ionization is investigated when the evaporated gas temperature is sufficiently high. In this case, Saha equation is included in the formulation of the model. We find a self-similar solution for a finite value of the similarity variable which depends on the laser ablation parameters.

Bennaceur-Doumaz, D.; Djebli, M.

2008-09-01

75

Laser-induced damage in biological tissue: Role of complex and dynamic optical properties of the medium  

NASA Astrophysics Data System (ADS)

Since its invention in the early 1960's, the laser has been used as a tool for surgical, therapeutic, and diagnostic purposes. To achieve maximum effectiveness with the greatest margin of safety it is important to understand the mechanisms of light propagation through tissue and how that light affects living cells. Lasers with novel output characteristics for medical and military applications are too often implemented prior to proper evaluation with respect to tissue optical properties and human safety. Therefore, advances in computational models that describe light propagation and the cellular responses to laser exposure, without the use of animal models, are of considerable interest. Here, a physics-based laser-tissue interaction model was developed to predict the spatial and temporal temperature and pressure rise during laser exposure to biological tissues. Our new model also takes into account the dynamic nature of tissue optical properties and their impact on the induced temperature and pressure profiles. The laser-induced retinal damage is attributed to the formation of microbubbles formed around melanosomes in the retinal pigment epithelium (RPE) and the damage mechanism is assumed to be photo-thermal. Selective absorption by melanin creates these bubbles that expand and collapse around melanosomes, destroying cell membranes and killing cells. The Finite Element (FE) approach taken provides suitable ground for modeling localized pigment absorption which leads to a non-uniform temperature distribution within pigmented cells following laser pulse exposure. These hot-spots are sources for localized thermo-elastic stresses which lead to rapid localized expansions that manifest themselves as microbubbles and lead to microcavitations. Model predictions for the interaction of lasers at wavelengths of 193, 694, 532, 590, 1314, 1540, 2000, and 2940 nm with biological tissues were generated and comparisons were made with available experimental data for the retina, cornea or the skin. Good agreement between model and experimental results established the validity of the model.

Ahmed, Elharith M.

76

Dynamic features of a laser-induced cavitation bubble near a solid boundary.  

PubMed

This paper deals with detailed features of bubble dynamics near a solid boundary. The cavitation bubble was created by using a Q-switched Nd: YAG laser pulse and observed using a high-speed camera (up to 100,000 frames per second). A hydrophone system was employed to monitor the acoustic signals generated by the transient pressure impulses and estimate the bubble oscillation periods. Experimental observations were carried out for bubbles with various maximum expanded radius Rmax (between 1.0mm and 1.6mm) and stand-off distances, ds (defined as the distance between the solid boundary and the bubble center at inception) of 0.4???3.0, and ?=ds/Rmax. The existence of a solid boundary created asymmetry in the flow field and forced the bubble to collapse non-spherically, which finally brought forth the jet impact phenomenon. The dimensionless first and second oscillation periods were dependent on ?. A series of expansion and collapse of the bubble with cascading loss of energy were observed after the bubble had been generated. This study revealed that most bubbles lost about two-thirds of the total energy from the first maximum expansion to the second maximum expansion. PMID:23411165

Yang, Yuan Xiang; Wang, Qian Xi; Keat, T S

2013-07-01

77

Dynamics and detection of laser induced microbubbles in the retinal pigment epithelium (RPE)  

NASA Astrophysics Data System (ADS)

Selective Retina Treatment (SRT) is a new method to treat eye diseases associated with disorders of the RPE. Selective RPE cell damage is achieved by applying a train of 1.7 ?s laser pulses at 527 nm. The treatment of retinal diseases as e.g. diabetic maculopathy (DMP), is currently investigated within clinical studies, however 200 ns pulse durations are under investigation. Transient micro bubbles in the retinal pigment epithelium (RPE) are expected to be the origin of cell damage due to irradiation with laser pulses shorter than 50 ?s. The bubbles emerge at the strongly absorbing RPE melanosomes. Cell membrane disruption caused by the transient associated volume increase is expected to be the origin of the angiographically observed RPE leakage. We investigate micro bubble formation and dynamics in porcine RPE using pulse durations of 150 ns. A laser interferometry system at 830 nm with the aim of an online dosimetry control for SRT was developed. Bubble formation was detected interferometrically and by fast flash photography. A correlation to cell damage observed with a vitality stain is found. A bubble detection algorithm is presented.

Fritz, Andreas; Ptaszynski, Lars; Stoehr, Hardo; Brinkmann, Ralf

2007-06-01

78

TOPICAL REVIEW: Nonthermal optical control of magnetism and ultrafast laser-induced spin dynamics in solids  

NASA Astrophysics Data System (ADS)

Ultrafast laser control of magnetism is one of the most exciting and challenging issues in physics and technology. Such a technique may provide the solution to the need for an ever increasing speed of data storage and manipulation. This review summarizes the recent progress in the study of ultrafast nonthermal effects of light on magnetic materials. Beginning with an introduction, the paper focuses on three main routes for laser control of magnetism. First, it is shown that due to the inverse, opto-magnetic Faraday effect, circularly polarized light may magnetize a medium. Microscopically, this effect is explained in terms of stimulated Raman scattering, where a spin-flip process requires neither annihilation of a photon, nor loss of its angular momentum. The feasibility of the inverse Faraday effect in magnetically ordered materials is demonstrated on the examples of orthoferrites and garnets. In particular, the effect of a 100 fs optical pulse on spins in DyFeO3 is found to be equivalent to an equally short magnetic field pulse up to 1 T. Second, linearly polarized 100 fs laser pulses are shown to create a long-lived modification of the magnetocrystalline anisotropy in magnetic garnets via optically induced electron transfer between nonequivalent ion sites. Third, we show that a combination of two pump pulses and nonthermal effects can lead to coherent control of magnetization dynamics and ultrafast magnetization switching. The review concludes with a summary and an outlook to the feasibility of laser control of magnetism in a broad class of materials.

Kimel, Alexey V.; Kirilyuk, Andrei; Hansteen, Fredrik; Pisarev, Roman V.; Rasing, Theo

2007-01-01

79

Dynamic and interaction of fs-laser induced cavitation bubbles for analyzing the cutting effect  

NASA Astrophysics Data System (ADS)

A prominent laser based treatment in ophthalmology is the LASIK procedure which nowadays includes a cutting of the corneal tissue based on ultra short pulses. Focusing an ultra short laser pulse below the surface of biological tissue an optical breakdown is caused and hence a dissection is obtained. The laser energy of the laser pulses is absorbed by nonlinear processes. As a result a cavitation bubble expands and ruptures the tissue. Hence positioning of several optical breakdowns side by side generates an incision. Due to a reduction of the duration of the treatment the current development of ultra short laser systems points to higher repetition rates in the range of hundreds of KHz or even MHz instead of tens of kHz. This in turn results in a probable occurrence of interaction between different optical breakdowns and respectively cavitation bubbles of adjacent optical breakdowns. While the interaction of one single laser pulse with biological tissue is analyzed reasonably well experimentally and theoretically, the interaction of several spatial and temporal following pulses is scarcely determined yet. Thus the aim of this study is to analyse the dynamic and interaction of two cavitation bubbles by using high speed photography. The applied laser pulse energy, the energy ratio and the spot distance between different cavitation bubbles were varied. Depending on a change of these parameters different kinds of interactions such as a flattening and deformation of bubble shape or jet formation are observed. Based on these results a further research seems to be inevitable to comprehend and optimize the cutting effect of ultra short pulse laser systems with high (> 1 MHz) repetition rates.

Tinne, N.; Schumacher, S.; Nuzzo, V.; Ripken, T.; Lubatschowski, H.

2009-07-01

80

Generation of inhomogeneous plane shear acoustic modes by laser-induced thermoelastic gratings at the interface of transparent and opaque solids  

NASA Astrophysics Data System (ADS)

The detailed theoretical description of how picosecond plane shear acoustic fronts can be excited by ultrafast lasers at the interface of two isotropic media, a transparent medium and an opaque medium, is presented. The processes leading to the emission of inhomogeneous plane bulk shear acoustic modes from the interaction at the interface of plane inhomogeneous compression/dilatation modes thermoelastically generated by laser interference gratings are analyzed. The theory describes the basic features of the spectral transformation function of the laser light conversion into shear modes and predicts an interval of frequencies where it is possible to achieve the emission into the transparent medium of propagating shear inhomogeneous modes only, while the compression/dilatation inhomogeneous modes will be evanescent and will be localized at the interface. The guidelines for optimal choice of the materials, with the goal of improving the amplitude of the photoexcited picosecond shear acoustic fronts are proposed. All-optical monitoring, i.e., excitation and detection, by fs-ps laser pulses of picosecond plane inhomogeneous shear acoustic fronts propagating in thin films and substrates can be applied for the noncontact determination of shear rigidity of materials.

Kouyate, Mansour; Pezeril, Thomas; Mounier, Denis; Gusev, Vitalyi

2011-12-01

81

Fiber Bragg grating sensors for dynamic machining applications  

NASA Astrophysics Data System (ADS)

Fiber Bragg grating sensors have attracted considerable attention for measurement applications due to their greatly reduced size, low weight, and immunity to electromagnetic interference in comparison with traditional sensing methods. Dynamic measurement of industrial machine tools is useful for gauging surface accuracy, monitoring tool condition, and predicting process stability, but requires a robust sensing scheme. The small size and high natural frequencies of micro machining tools coupled with a harsh manufacturing environment can render traditional sensors ineffective. This work presents a new method for measuring tool motion with fiber Bragg grating strain sensors. The feasibility of the sensing scheme is first demonstrated with a simple bench-top cantilever beam experiment. Then, a method for potting the sensors in the through coolant holes of a 1/8" carbide end mill with a high-viscosity gap-filling cyanoacrylate is demonstrated. Comparative structural analysis tests demonstrate the effectiveness of the sensors. Measurements of tool motion during cutting are presented. Finally, methods of noise reduction and improving signal accuracy are discussed.

Bartow, Matthew J.; Calvert, Sean G.; Bayly, Philip V.

2003-11-01

82

Laser Induced Photochemistry.  

National Technical Information Service (NTIS)

Laser induced photochemistry is not in a position to make a major impact on industry in the next few years because of the high cost of laser photons. In the longer term, laser induced photochemistry probably will make a valuable contribution to industry. ...

W. Happer J. Chamberlain H. Foley N. Fortson J. Katz

1979-01-01

83

Bandwidth-adjustable dynamic grating in erbium-doped fiber by synthesis of optical coherence function.  

PubMed

We present an approach for bandwidth-adjustable optical filter with the dynamic grating in erbium-doped fiber (EDF). The dynamic grating is introduced by the interference of two coherent light beams counter-propagating in the pumped EDF per the phenomenon of gain saturation. The bandwidth of the grating is determined by the length of the grating, i.e., the length of the interference region. With the technique of synthesis of optical coherence function (SOCF), we localize the interference into a range at an arbitrary position along the fiber by modulating the frequency of the two interfering light beams. The length of the range is controlled by adjusting the frequency modulation parameter. In this way, the length of the dynamic grating is controlled and its reflection bandwidth then adjusted. The experimental demonstration is given. PMID:19498578

Fan, Xinyu; He, Zuyuan; Mizuno, Yosuke; Hotate, Kazuo

2005-07-25

84

Design considerations for a fibre Bragg grating interrogation system utilizing an arrayed waveguide grating for dynamic strain measurement  

NASA Astrophysics Data System (ADS)

Dynamic strain signals are important for many structural monitoring applications, but the high-speed interrogation of strain sensors based on fibre Bragg gratings (FBGs) remains a challenge. Arrayed waveguide grating (AWG) interrogation schemes have been proposed, and by using modelling and validation experiments several design considerations are investigated and their relationship to system performance indicators determined. The Bragg grating length has an impact on the ability of the grating to ‘observe’ the transient strain field, while the spectral widths of both the FBG and AWG influence the recovered strain resolution. The system performance was examined for both high frequency noise as well as the long-term drifts over an hour, with a strain resolution of 1.4 µ? observed and drift of less than 3.1 µ? h-1. The noise dependence on the relative overlap of the AWG and FBG spectra was found to be significant and the inclusion of a semiconductor optical amplifier to boost light intensity at the detectors was found to significantly improve performance with an improvement in the signal-to-noise ratio up to 200%.

John, R. N.; Read, I.; MacPherson, W. N.

2013-07-01

85

Nine Orders of Magnitude Dynamic Range: Picomolar to Millimolar Concentration Measurement in Capillary Electrophoresis with Laser Induced Fluorescence Detection Employing Cascaded Avalanche Photodiode Photon Counters  

PubMed Central

The dynamic range of capillary electrophoresis analysis is ultimately limited by molecular shot noise at low concentrations and by concentration-induced band broadening at high concentrations. We report a system that approaches these fundamental limits. A laser-induced fluorescence detector is reported that employs a cascade of four fiber-optic beam-splitters connected in series to generate a primary signal and four attenuated signals, each monitored by a single-photon counting avalanche photodiode. Appropriate scaling of the signals from the five photodiodes produces a linear optical calibration curve for 5-carboxyl-tetramethylrhodamine from the concentration detection limit of 1 pM to the upper limit of 1 mM. Mass detection limits are 120 yoctomoles (70 molecules) injected into the instrument. The very-wide dynamic range instrument was used to study the metabolic products of the fluorescently labeled glycosphingolipid GM1-TMR produced by single cells isolated from the rat cerebellum.

Dada, Oluwatosin O.; Essaka, David C.; Hindsgaul, Ole; Palcic, Monica M.; Prendergast, Jillian; Schnaar, Ronald L.

2011-01-01

86

Dynamic Landslide Deformation Monitoring with Fiber Bragg Grating Sensors  

NASA Astrophysics Data System (ADS)

Fiber optic (FO) strain sensors are a promising new technology for in-situ landslide monitoring. General performance advantages include high resolution, fast sampling rate, and insensitivity to electrical disturbances. Here we describe a new FO monitoring system based on long-gage fiber Bragg grating sensors installed at the Randa Rockslide Laboratory in southern Switzerland. We highlight the advantages and disadvantages of the system, describe relevant first results, and compare FO data to that from traditional instruments already installed on site. The Randa rock slope has been the subject of intensive research since its failure in 1991. Around 5 million cubic meters of rock remains unstable today, moving at rates up to 20 mm / year. Traditional in-situ monitoring techniques have been employed to understand the mechanics and driving forces of the currently unstable rock mass, however these investigations are limited by the resolution and low sampling rate of the sensors. The new FO monitoring system has micro-strain resolution and offers the capability to detect sub-micrometer scale deformations in both triggered-dynamic and continuous measurements. Two types of sensors have been installed: fully-embedded borehole sensors encased in grout at depths of 38, 40, and 68 m, and surface extensometers spanning active tension cracks. Dynamic measurements are triggered by sensor deformation and recorded at 100 Hz, while continuous measurements are logged every 5 minutes. Since installation in August 2008, the FO monitoring system has been operational 90% of the time. Time series deformation data show movement rates consistent with previous borehole extensometer surveys. Accelerated displacements following installation are likely related to long-term curing and dewatering of the grout. A number of interesting transients have been recorded, which in some cases were large enough to trigger rapid sampling. The combination of short- and long-term observation offers new insights into the deformation process. Controlled-source shotgun tests were performed to investigate the sensor response to dynamic inputs. These tests compared an independent measure of ground motion with the dynamic strain measured across a tension crack by the FO sensor. Low frequency signals are comparable but the fiber optic record suffers from aliasing, where undersampling of higher frequency signals generates false peaks in the spectrum. In the event of an earthquake, however, such high frequency energy will not be present and the FO sensors are expected to provide an accurate measure of dynamic strain.

Moore, J. R.; Gischig, V.; Button, E.; Loew, S.

2009-12-01

87

Time-resolved diffraction profiles and atomic dynamics in short-pulse laser-induced structural transformations: Molecular dynamics study  

SciTech Connect

The diffraction profiles and density correlation functions are calculated for transient atomic configurations generated in molecular dynamics simulations of a 20 nm Au film irradiated with 200 fs laser pulses of different intensity. The results of the calculations provide an opportunity to directly relate the detailed information on the atomic-level structural rearrangements available from the simulations to the diffraction spectra measured in time-resolved x-ray and electron diffraction experiments. Three processes are found to be responsible for the evolution of the diffraction profiles. During the first several picoseconds after the laser excitation, the decrease of the intensity of the diffraction peaks is largely due to the increasing amplitude of thermal atomic vibrations and can be well described by the Debye-Waller factor. The effect of thermoelastic deformation of the film prior to melting is reflected in shifts and splittings of the diffraction peaks, providing an opportunity for experimental probing of the ultrafast deformations. Finally, the onset of the melting process results in complete disappearance of the crystalline diffraction peaks. The homogeneous nucleation of a large number of liquid regions throughout the film is found to be more effective in reducing long-range correlations in atomic positions and diminishing the diffraction peaks as compared to the heterogeneous melting by melting front propagation. For the same fraction of atoms retaining the local crystalline environment, the diffraction peaks are more pronounced in heterogeneous melting. A detailed analysis of the real space correlations in atomic positions is also performed and the atomic-level picture behind the experimentally observed fast disappearance of the correlation peak corresponding to the second nearest neighbors in the fcc lattice during the laser heating and melting processes is revealed.

Lin, Zhibin; Zhigilei, Leonid V. [Department of Materials Science and Engineering, University of Virginia, 116 Engineer's Way, Charlottesville, Virginia 22904-4745 (United States)

2006-05-01

88

Dynamics of plasma gratings in atomic and molecular gases.  

PubMed

The decay of the plasma grating formed at the intersection of two femtosecond filaments is measured in several molecular and atomic gases. The grating evolution is ruled by ambipolar diffusion in atomic gases and by a combination of ambipolar diffusion and collision-assisted free electron recombination in molecular gases. Electron diffusion and recombination coefficients are extracted for Ne, Ar, Kr, Xe, N2, O2, CO2, and air at 1 bar. PMID:23031032

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

2012-09-01

89

Direct methods for dynamic monitoring of secretions from single cells by capillary electrophoresis and microscopy with laser-induced native fluorescence detection  

SciTech Connect

Microscale separation and detection methods for real-time monitoring of dynamic cellular processes (e.g., secretion) by capillary electrophoresis (CE) and microscopic imaging were developed. Ultraviolet laser-induced native fluorescence (LINF) provides simple, sensitive and direct detection of neurotransmitters and proteins without any derivatization. An on-column CE-LINF protocol for quantification of the release from single cell was demonstrated. Quantitative measurements of both the amount of insulin released from and the amount remaining in the cell ({beta}TC3) were achieved simultaneously. Secretion of catecholamines (norepinephrine (NE) and epinephrine (E)) from individual bovine adrenal chromaffin cells was determined using the on-column CE-LINF. Direct visualization of the secretion process of individual bovine adrenal chromaffin cells was achieved by LINF imaging microscopy with high temporal and spatial resolution. The secretion of serotonin from individual leech Retzius neurons was directly characterized by LINF microscopy with high spatial resolution.

Tong, W.

1997-10-08

90

Dynamic Monitoring of Grating Angle at the National Synchrotron Light Source  

SciTech Connect

We present a dynamic monitoring method and monitoring system of grating angle, referred to as the Precise Angle Monitor (PAM), at U4B, a soft x-ray spherical grating monochromator (SGM) beam line at the National Synchrotron Light Source (NSLS). In an SGM, a photon energy scan is accomplished by rotating the grating angle precisely. After several decades of service, the monochromator at U4B developed instabilities that severely impacted the experimental program. Over several hours, either the spectral shape experienced distortions or the spectral peak shifted. In order to directly monitor the grating motion during scans, the optical head of a portable long trace profiler (PTLTP) was installed on U4B as the PAM. We find that the grating rotational motion is not ideal: (1) the scan steps are not smooth and there are high-frequency step angle errors; (2) there is also a low-frequency angle error; and (3) an unstable thermal expansion produces extra rotational error. Measurements of dynamic monitoring are presented, including grating rotation repeatability and thermal instability. The results illustrate the utility of dynamic monitoring of monochromator motion during actual operation.

Qian, S.; Arena, D; Dvorak, J; Qian, K

2009-01-01

91

Dynamic fiber Bragg gratings based health monitoring system of composite aerospace structures  

Microsoft Academic Search

The main purpose of the current work is to develop a new system for structural health monitoring of composite aerospace structures based on real-time dynamic measurements, in order to identify the structural state condition. Long-gauge Fibre Bragg Grating (FBG) optical sensors were used for monitoring the dynamic response of the composite structure. The algorithm that was developed for structural damage

A. Panopoulou; T. Loutas; D. Roulias; S. Fransen; V. Kostopoulos

2011-01-01

92

Laser induced copper plating  

Microsoft Academic Search

Argon laser induced plating of copper spots and lines from copper sulfate solutions on glass and phenolic resin paper has been investigated. The substrates had to be precoated with an evaporated copper film. The highest plating rates have been obtained with a small film thickness of 25 nm. Spots with a thickness up to 30 ?m were plated.

A. K. Al-Sufi; H. J. Eichler; J. Salk; H. J. Riedel

1983-01-01

93

Dynamic Landslide Deformation Monitoring with Fiber Bragg Grating Sensors  

Microsoft Academic Search

Fiber optic (FO) strain sensors are a promising new technology for in-situ landslide monitoring. General performance advantages include high resolution, fast sampling rate, and insensitivity to electrical disturbances. Here we describe a new FO monitoring system based on long-gage fiber Bragg grating sensors installed at the Randa Rockslide Laboratory in southern Switzerland. We highlight the advantages and disadvantages of the

J. R. Moore; V. Gischig; E. Button; S. Loew

2009-01-01

94

Dynamics of ps-pulse induced gratings in LC panels  

NASA Astrophysics Data System (ADS)

In the present work we focused our attention on studies of PVK:TNF hybrid polymer liquid crystal panels under short pulse laser illumination conditions. The diffraction gratings in a LC panel were induced by crossed beams generated by doubled in frequency Nd:YAG laser ((lambda) equals 532 nm) delivering pulses of 20 ps duration. So induced gratings were read by a cw laser radiation coming from a weak power He-Ne laser working at (lambda) equals 632.8 nm. The temporal evolution of intensity of first order diffraction measured in PVK:TNF hybrid liquid crystal panels shows many interesting features and complexity dependent on various experimental conditions. The substantial diffraction is observed already in time less than 1 ms after the pulse and the grating decay is completed within hundreds of milliseconds. At least three different steps of grating build-up can be distinguished which depend in various ways on the experimental conditions. A tentative mechanism of the observed responses is discussed in connection with the photoconductive properties of polymeric layers and the optical and electrical properties of the used liquid crystal E-7 (Merck).

Bartkiewicz, Stanislaw; Miniewicz, Andrzej; Sahraoui, Bouchta; Kajzar, Francois

2002-06-01

95

Dynamic strain monitoring of an in-use interstate bridge using fiber Bragg grating sensors  

Microsoft Academic Search

We describe the monitoring of the dynamic strain response of an in-service I-10 interstate bridge due to traffic loading. FBG sensors were attached to the center support girder of one span of the structure. Using a fiber Bragg grating interrogation system based on a wavelength division multiplexer, the sensors were monitored for various vehicle loading conditions.

Michael A. Davis; Alan D. Kersey; Timothy A. Berkoff; R. T. Jones; Rola L. Idriss; M. Kodinduma

1997-01-01

96

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

National Technical Information Service (NTIS)

We report ultrafast measurements of the dynamic thermal expansion of a surface and the temperature dependent surface thermal diffusivity using a two-color reflection transient grating technique. Studies were performed on p-type, n-type, and undoped GaAs(1...

D. M. Pennington C. B. Harris

1993-01-01

97

Electrically tunable power efficient dispersion compensating fiber Bragg gratings for dynamic operation in nonlinear lightwave systems  

Microsoft Academic Search

We demonstrate a power efficient (<0.5 W) tunable dispersion compensating fiber Bragg grating device and show for the first time dynamic optimization of dispersion in a nonlinear lightwave system. Operation is demonstrated in a 20 Gbit\\/s single channel NRZ system where the device was used to adjust the dispersion to the power-dependent optimal dispersion required for optimum performance

B. J. Eggleton; J. A. Rogers; P. S. Westbrook; T. A. Strasser; T. N. Nielsen; P. B. Hansen; K. F. Dreyer

1999-01-01

98

Dynamic Strain Sensing in a Long-Span Suspension Bridge Using Fiber Bragg Grating Sensors  

Microsoft Academic Search

Optical fiber sensors are ideal for monitoring continuous deterioration conditions of civil infrastructure, especially of long-span bridges. Typically, a network of sensors is used to measure the strains or low frequency vibrational response of the structure. In this work, we demonstrate dynamic spectral demodulation of fiber Bragg grating (FBG) sensor responses with a stabilized Michelson interferometer for monitoring mechanical strains

Yinian Zhu; Yan-Jin Zhu; Oluwaseyi Balogun; Songye Zhu; You-Lin Xu; Sridhar Krishnaswamy

2011-01-01

99

Dynamic pressure measurement of shock waves in explosives by means of a fiber Bragg grating sensor  

Microsoft Academic Search

A new technique for the dynamic measurement of detonation pressures by use of a Fibre Bragg Grating (FBG) sensor is reported. A variation in pressure changes the wavelength of the FBG reflected light. In a detonation, the shock wave passes the explosive with a velocity of ca. 7 km\\/s and the pressure builds up to ca. 20 GPa within 100

P. G. van't Hof; L. K. Cheng; J. H. G. Scholtes; W. C. Prinse

2007-01-01

100

Dynamic pressure measurement of shock waves in explosives by means of a fiber Bragg grating sensor  

Microsoft Academic Search

A new technique for the dynamic measurement of detonation pressures by use of a Fibre Bragg Grating (FBG) sensor is reported. A variation in pressure changes the wavelength of the FBG reflected light. In a detonation, the shock wave passes the explosive with a velocity of ca. 7 km\\/s and the pressure builds up to ca. 20 GPa within 100

L. K. Cheng; W. C. Prinse

101

Toward the optimization of double-pulse LIBS underwater: effects of experimental parameters on the reproducibility and dynamics of laser-induced cavitation bubble.  

PubMed

Double-pulse laser-induced breakdown spectroscopy (LIBS) was recently proposed for the analysis of underwater samples, since it overcomes the drawbacks of rapid plasma quenching and of large continuum emission, typical of single-pulse ablation. Despite the attractiveness of the method, this approach suffers nevertheless from a poor spectroscopic reproducibility, which is partially due to the scarce reproducibility of the cavitation bubble induced by the first laser pulse, since pressure and dimensions of the bubble strongly affect plasma emission. In this work, we investigated the reproducibility and the dynamics of the cavitation bubble induced on a solid target in water, and how they depend on pulse duration, energy, and wavelength, as well as on target composition. Results are discussed in terms of the effects on the laser ablation process produced by the crater formation and by the interaction of the laser pulse with floating particles and gas bubbles. This work, preliminary to the optimization of the spectroscopic signal, provides an insight of the phenomena occurring during laser ablation in water, together with useful information for the choice of the laser source to be used in the apparatus. PMID:22410923

Cristoforetti, Gabriele; Tiberi, Marco; Simonelli, Andrea; Marsili, Paolo; Giammanco, Francesco

2012-03-01

102

Dynamic characterizations of high diffraction efficiency in volume Bragg grating formed by holographic photopolymerization  

NASA Astrophysics Data System (ADS)

Volume Bragg grating with 96% diffraction efficiency (DE) was efficiently formed by holographic photopolymerization in blend syrup of photocurable trimethylolpropane triacrylate monomer and nematic liquid crystal. The formation dynamics of the composite gratings was quantitatively characterized under the frame of one-dimensional reaction-diffusion model with a revision of individual decay constants for monomer diffusion and reaction. Initial parameters of diffusion and reaction were analytically determined from the measured first order DE at the beginning stage. Evolutions of the DE, both in curing and postcuring periods, were excellently simulated, especially with postcuring reaction been taken into account.

Pu, Haihui; Yin, Dejin; Gao, Bin; Gao, Hongyue; Dai, Haitao; Liu, Jianhua

2009-10-01

103

A dynamic mathematical model of the complete grate/kiln iron-ore pellet induration process  

NASA Astrophysics Data System (ADS)

Induration (drying and hardening) of iron ore pellets is an energy-intensive feed preparation step for both the blast furnace and direct reduction routes to iron. It is commonly carried out by a ‘grate/kiln’ process. A mathematical model of the process is described, in which mechanistic models of the grate furnace, kiln, and cooler are linked to enable simulation of the entire process. The model includes equations for the gas stream pressure balances and process controller responses, and provides dynamic solutions. The validation of the model for an operating plant is discussed and steady-state solutions are compared with data from the plant.

Thurlby, J. A.

1988-02-01

104

Laser-induced gas breakdown and ignition  

NASA Astrophysics Data System (ADS)

Laser-induced gas breakdown and ignition are studied in atmospheric pressure gas flow. The nanosecond-pulsed, 1064-nm Nd:YAG laser was used to create the cascade-type optical breakdown in air, oxygen, ammonia, and the combustible ammonia/oxygen mixture. We investigate the formation of the initial plasma and the chemical and gasdynamic development of the breakdown kernel. The spatial and temporal features of the energy deposition process are presented for laser breakdowns in still air. The generation of air-breakdown events is very stable between laser pulses when the incident laser power is two times larger than the threshold value. The effects associated with the ammonia flow-speed in the range of 1- 7 cm/sec are shown to be significant for the plasma. formation and stability of both laser-induced breakdown and ignition kernel, even though the flow field is laminar. The post-breakdown development of laser breakdown and ignition is studied using high-speed photographic and spectroscopic techniques including shadowgraphs, planar laser-induced fluorescence (PLIF), spontaneous emission and Rayleigh scattering. These time- resolved two-dimensional images provide gasdynamic, radiative and NH radical concentration and temperature information to aid the understanding of the kernel dynamics. The asymmetric feature of the initial plasma and the gas dynamics that leads to the backstreaming effect in laser-induced breakdown is suggested and evaluated.

Chen, Ying-Ling Ann

105

Detection, Evaluation, and Optimization of Optical Signals Generated by Fiber Optic Bragg Gratings Under Dynamic Excitations  

NASA Technical Reports Server (NTRS)

The dynamic response of a fiber optic Bragg grating to mechanical vibrations is examined both theoretically and experimentally. The theoretical expressions describing the consequences of changes in the grating's reflection spectrum are derived for partially coherent beams in an interferometer. The analysis is given in terms of the dominant wavelength, optical bandwidth, and optical path difference of the interfering signals. Changes in the reflection spectrum caused by a periodic stretching and compression of the grating were experimentally measured using an unbalanced Michelson interferometer, a Michelson interferometer with a non-zero optical path difference. The interferometer's sensitivity to changes in dominant wavelength of the interfering beams was measured as a function of interferometer unbalance and was compared to theoretical predictions. The theoretical analysis enables the user to determine the optimum performance for an unbalanced interferometer.

Adamovsky, Grigory; Lekki, John; Lock, James A.

2002-01-01

106

Ultrafast dynamics of high-contrast nano-grating formation on gold film induced by temporally shaped femtosecond laser  

NASA Astrophysics Data System (ADS)

We theoretically investigated the ultrafast dynamics of high-contrast nano-grating formation on gold film surface with respect to non-equilibrium thermal excitation processes. It is proposed that the high-contrast nano-grating can be desirably achieved by optimizing the non-equilibrium thermal dynamics processes. The grating contrast can be largely promoted by 64% with adjusting thermal dynamics via tailoring temporally shaped femtosecond laser. The results are attributed to the competitive energy transfer routes between electrons thermal diffusion and electron-phonon relaxation processes during grating formation, which can be well manipulated by temporally shaped femtosecond laser. The study provides for strategy for production of high-quality periodic surface structures with sharp grating profiles.

Du, Guangqing; Chen, Feng; Yang, Qing; Ou, Yan; Wu, Yanmin; Lu, Yu; Bian, Hao; Hou, Xun

2014-03-01

107

Hybrid Raman/fiber Bragg grating sensor for distributed temperature and discrete dynamic strain measurements.  

PubMed

We propose and experimentally demonstrate a hybrid fiber optic sensing technique that effectively combines Raman optical time domain reflectometry and in-line time-division-multiplexing for fiber Bragg grating (FBG) dynamic interrogation. The highly integrated proposed scheme employs broadband apodized low reflectivity FBGs with a single narrowband optical source and a shared receiver block, allowing for simultaneous measurements of distributed static temperature and discrete dynamic strain, over the same sensing fiber. PMID:23114320

Toccafondo, Iacopo; Taki, Mohammad; Signorini, Alessandro; Zaidi, Farhan; Nannipieri, Tiziano; Faralli, Stefano; Di Pasquale, Fabrizio

2012-11-01

108

Dynamic post dispersion optimization at 40 Gb\\/s using a tunable fiber Bragg grating  

Microsoft Academic Search

A compact tunable fiber Bragg grating that uses distributed thin-film heaters on the surface of the fiber is used to dynamically optimize the post dispersion compensation of a multi-span 40-Gb\\/s nonreturn-to-zero (NRZ) transmission system. Dynamic post dispersion compensation with this device enables the system to operate over a much wider range of launch power than is otherwise possible with simple,

T. N. Nielsen; B. J. Eggleton; J. A. Rogers; P. S. Westbrook; P. B. Hansen; T. A. Strasser

2000-01-01

109

Dynamics of laser-induced bubble and nanoparticles generation during ultra-short laser ablation of Pd in liquid  

NASA Astrophysics Data System (ADS)

In this work, the dynamics of multiple cavitation bubbles produced by femtosecond laser ablation of a palladium target submerged in acetone is studied by means of time-resolved fast shadowgraphy technique. The data have evidenced the periodic growth and collapse of the bubbles and the consequent emission of material together with the role played by the laser focus position. Comparing the results with the previsions of the Rayleigh-Plesset model a good agreement is found. The nanoparticles obtained under different focusing conditions are characterized by means of TEM analysis. Their dimension and distribution are correlated with the bubbles dynamics.

De Bonis, A.; Sansone, M.; D'Alessio, L.; Galasso, A.; Santagata, A.; Teghil, R.

2013-11-01

110

Asymmetrisation of the profile of a thin dynamic holographic grating in a TV-locked optical feedback loop  

SciTech Connect

A system for recording a dynamic holographic grating in an optically addressed liquid-crystal spatial light modulator is studied. The system provides the asymmetrisation of the grating profile by using a TV-locked optical feedback loop (nonlinear or adaptive interferometer). (laser applications and other topics in quantum electronics)

Venediktov, Vladimir Yu; Ivanova, Natalya L; Freigang, N N [Research Center 'Vavilov State Optical Institute', St.Petersburg (Russian Federation); Laskin, V A [St. Petersburg State University, St. Petersburg (Russian Federation)

2009-10-31

111

Laser-induced artificial defects (LIADs): towards the control of the spatiotemporal dynamics in spin transition materials.  

PubMed

Micrometer-sized defects, induced by laser ablation, radically change the spatiotemporal dynamics of a first-order structural phase transition, in this case of a spin crossover material. This type of "domain engineering" is thus based on artificial defects, such as that in the image, which can serve either as nucleation sites or as pinning sites. The subsequent growth of the nucleated domains can also be guided to some extent. PMID:22488971

Bedoui, Salma; Lopes, Manuel; Zheng, Sipeng; Bonnet, Sylvestre; Molnár, Gábor; Bousseksou, Azzedine

2012-05-01

112

Dynamics of femtosecond laser-induced periodic surface structures on silicon by high spatial and temporal resolution imaging  

NASA Astrophysics Data System (ADS)

The formation dynamics of periodic ripples induced by femtosecond laser pulses (pulse duration ? = 50 fs and central wavelength ? = 800 nm) are studied by a collinear pump-probe imaging technique with a temporal resolution of 1 ps and a spatial resolution of 440 nm. The ripples with periods close to the laser wavelength begin to appear upon irradiation of two pump pulses at surface defects produced by the prior one. The rudiments of periodic ripples emerge in the initial tens of picoseconds after fs laser irradiation, and the ripple positions keep unmoved until the formation processes complete mainly in a temporal span of 1500 ps. The results suggest that the periodic deposition of laser energy during the interaction between femtosecond laser pulses and sample surface plays a dominant role in the formation of periodic ripples.

Jia, X.; Jia, T. Q.; Peng, N. N.; Feng, D. H.; Zhang, S. A.; Sun, Z. R.

2014-04-01

113

Laser-induced lightning  

NASA Astrophysics Data System (ADS)

The history of laser-induced discharges is reviewed, including the motivation for performing studies with femtosecond UV laser pulses. The development of the femtosecond UV source is outlined, discussing the relevant design parameters of each stage of the system. With such a system, detailed studies of multiphoton ionization at 248 nm were performed to refine our understanding of the ionization mechanism. In addition, a battery of high voltage breakdown tests were performed, examining variables such as: high voltage breakdown threshold, ionizing UV peak intensity, pressure dependence, and timing delay between ionization and discharge. The extrapolation of these experimental studies to longer gaps depends upon electron density loss mechanisms. One such loss mechanism, attachment, can be circumvented via photodetachment. An Alexandrite laser system for this purpose is developed, modeled, and tested.

Rambo, Patrick Kay

114

Control of the parameters of solid-state lasers by dynamic gratings in a DKDP crystal  

Microsoft Academic Search

Pulsed and cw Nd3+:YAG lasers were used in an experimental investigation of the influence of dynamic gratings in intracavity DKDP crystal elements on the main characteristics of the radiation emitted by solid-state lasers at room temperature. A hologram, formed in a DKDP crystal by a two-beam method, induced generation of pulsed laser radiation which had the spectral characteristics of a

B V Anikeev; S A Kutsenko; D V Sinko; V S Sukhorukov

1999-01-01

115

Control of the parameters of solid-state lasers by dynamic gratings in a DKDP crystal  

Microsoft Academic Search

Pulsed and cw Nd{sup 3+}:YAG lasers were used in an experimental investigation of the influence of dynamic gratings in intracavity DKDP crystal elements on the main characteristics of the radiation emitted by solid-state lasers at room temperature. A hologram, formed in a DKDP crystal by a two-beam method, induced generation of pulsed laser radiation which had the spectral characteristics of

B V Anikeev; S A Kutsenko; D V Sinko; V S Sukhorukov

1999-01-01

116

Laser-Induced Incandescence Calibration via Gravimetric Sampling  

NASA Technical Reports Server (NTRS)

Various beam imaging and/or sheet forming optics delivered light at 1064 nm from a pulsed Nd:YAG laser for use either as a beam of 3 mm radius or as a laser sheet. Imaging measurements were performed with a grated intensified array camera equipped with an ultraviolet f4.5 lens and a 40 mm extension tube. Point measurements were performed using an ultraviolet 250 mm focal length lens to collect and focus the laser induced incandescence (LII) signal into a 1 meter long quartz optical fiber which directed the LII signal to a 1/4 meter monochromator. An aperture preceding the lens restricted the signal collection region to 1 cm along the laser beam at the center of the gravimetric chimney. Signals from the PMT were processed by a boxcar integrator whereas the images were captured digitally using a frame-grabber with 16 MByte of on-board memory. Both 'point' and planar measurements were made with detector gates of 250 ns to minimize possible morphology bias in collection of the LII signal. Additionally, the imaging measurements were performed with broadband spectral collection of the LII signal to maximize the signal and again minimize any potential effects of morphology dependent heating and/or cooling rates. Digital delay generators controlled the firing of he laser, detector gates and data acquisition. Neutral density filters were used for both sets of measurements to maintain signal levels within linear dynamic ranges of the detectors, the range being determined prior to experiments.

VanderWal, R. L.; Zhou, Z.; Choi, M. Y.

1995-01-01

117

Dynamics of Jacobi's elliptic spatial waves in a nonlinear optical grating  

SciTech Connect

This paper presents the results of our study on the dynamics of Jacobi's elliptic spatial waves in a nonlinear optical grating based on a generalized coupled-mode model. We discuss the characteristics of their amplitudes, widths, and spatial periods as well as their bifurcation in the associated phase plane. Our study on the dynamical propagation of perturbed profiles reveal that these waves can suffer breathing and broadening due to the diffraction effect. A remarkable split-off phenomenon of a spatial wave with wide stripes into several narrow and shallow oblique stripes is observed, as well as their passing and bouncing collisions.

Alatas, Husin [Theoretical Physics Division, Department of Physics, Bogor Agricultural University, Jl. Meranti, Kampus IPB Darmaga, Bogor 16680 (Indonesia)

2011-04-15

118

Dynamics of the plume containing nanometric-sized particles ejected into the atmospheric air following laser-induced breakdown on the exit surface of a CaF2 optical window  

NASA Astrophysics Data System (ADS)

Laser induced breakdown on the output surface of calcium fluoride produces distinctive visualization of the gaseous material ejection via time-resolved shadowgraphy microscopy. This characteristic behavior allowed a detailed investigation of the directional expansion of the plume at ambient atmospheric conditions and its spatial separation and influence on the forming shockwave. The results also suggest that the material ejection is prolonged, extending more than 300 ns after the termination of the laser pulse. The dynamics of the backward motion of the gaseous material following its initial expansion is also resolved.

Demos, Stavros G.; Negres, Raluca A.; Rubenchik, Alexander M.

2014-01-01

119

Quantitative, dynamic fuel distribution measurements in combustion-related devices using laser-induced fluorescence imaging of biacetyl in iso-octane  

Microsoft Academic Search

Knowledge of in-situ fuel distributions in practical combustion devices, such as internal combustion engines, is crucial for research and devlopment purposes. Numerous imaging techniques, mostly based on laser-induced fluorescence (LIF), have been developed and yield high levels of 2-D spatial information, but generally lack the temporal resolution (frame rates) necessary to resolve important timescales at sub-millisecond levels for sustained times.

James D. Smith; Volker Sick

2007-01-01

120

Non-Bragg orders in dynamic self-diffraction on thick phase gratings in a photorefractive polymer  

NASA Astrophysics Data System (ADS)

We demonstrate that recording thick holographic phase gratings in photorefractive polymers can lead not only to very efficient Bragg diffraction but also to rather strong diffraction into non-Bragg orders. We show that this effect has features drastically different from those of Raman-Nath diffraction on thin gratings. We compare the experimental results with a model based on the theory of dynamic self-diffraction in a photorefractive medium. Applications of this effect in devices for optical image processing are proposed.

Volodin, B. L.; Kippelen, B.; Meerholz, K.; Kukhtarev, N. V.; Caulfield, H. John; Peyghambarian, N.

1996-04-01

121

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

NASA Astrophysics Data System (ADS)

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

Sreekumar, K.; Asokan, S.

2010-01-01

122

Control of the parameters of solid-state lasers by dynamic gratings in a DKDP crystal  

SciTech Connect

Pulsed and cw Nd{sup 3+}:YAG lasers were used in an experimental investigation of the influence of dynamic gratings in intracavity DKDP crystal elements on the main characteristics of the radiation emitted by solid-state lasers at room temperature. A hologram, formed in a DKDP crystal by a two-beam method, induced generation of pulsed laser radiation which had the spectral characteristics of a signal beam injected from outside in the form of radiation from a cw Nd{sup 3+}:YAG laser. In experiments on a cw Nd{sup 3+}:YAG laser the formation of a phase grating resulted in selection of transverse radiation modes. Such selection made the repetition period of the lasing spikes more regular and reduced their duration. A study was made of the dependence of the amplitude of a photoinduced electric field, inducing photorefraction, on the polarisation of the radiation of the 1.06 {mu}m wavelength. The formation of phase gratings in a DKDP crystal was the effect of excitation of impurity centres. The results obtained indicated feasibility of extending the range of control functions which can be performed by DKDP crystal elements. (control of laser radiation parameters)

Anikeev, B V; Kutsenko, S A; Sin'ko, D V; Sukhorukov, V S [Laser Physics Section, Volgograd State University, Volgograd (Russian Federation)

1999-04-30

123

Proceedings of Laser Induced Damage in Optical Materials: 1982 (14th) Held at Boulder, Colorado on November 16-17 1982.  

National Technical Information Service (NTIS)

Partial Contents: A Laser Damage Facility in the Ultra-Violet; Use of Hole Gratings in Laser Damage Testing; Float Polishing and Defects of Fused Silica; Pulsed laser Induced Optical Surface Damage Studies in Different Gases; Optical Figure Requirements f...

H. E. Bennett A. H. Guenther D. Milam B. E. Newnam

1984-01-01

124

Characterization of distributed modal birefringence in a few-mode fiber based on Brillouin dynamic grating.  

PubMed

We propose and demonstrate generation of Brillouin dynamic grating (BDG) in a few-mode fiber (FMF) with a Gaussian pulse pump and a counterpropagating continuous wave pump in LP01 mode. Brillouin optical time-domain analysis (BOTDA) is achieved by launching a third Gaussian pulse probe in LP11 mode. With coherent detection and time-domain analysis on the backreflected probe signal, the modal birefringence of the FMF is characterized via the distributed BDG with high spatial resolution and high accuracy. PMID:24876000

Li, An; Hu, Qian; Chen, Xi; Kim, Byoung Yoon; Shieh, William

2014-06-01

125

Efficient distributed feedback solid state dye laser with a dynamic grating  

Microsoft Academic Search

.   We present the first operation of a distributed feedback solid state dye laser with a dynamic, pump-induced grating. Broadly\\u000a tunable, narrow band operation in the region of 616 nm (604–649 nm) has been demonstrated with perylene red laser dye doped\\u000a in poly(methyl methacrylate) (PMMA), when pumped with a frequency doubled Nd:YAG laser. Conversion efficiencies of 20%, corresponding\\u000a to 35% optical-to-optical efficiency,

W. J. Wadsworth; I. T. McKinnie; A. D. Woolhouse; T. G. Haskell

1999-01-01

126

Dynamics of photo-induced terahertz optical activity in metal chiral gratings.  

PubMed

We investigated the dynamics of photo-induced optical activity of metal chiral gratings on an Si substrate for terahertz (THz) waves. We employed a new technique that enables optical-pump and THz-probe measurements via broadband THz spectroscopy at the microsecond time scale using a low-repetition-rate pump and a high-repetition-rate probe. We revealed that the THz optical activity decays as a result of the carrier diffusion effect because this optical activity is because of the presence of three-dimensional chiral structures of photo-carriers in the Si substrate. PMID:22940932

Kanda, Natsuki; Konishi, Kuniaki; Kuwata-Gonokami, Makoto

2012-09-01

127

Spatio-temporal mode analysis in self-organizing diode-pumped solid state lasers on dynamic gratings  

Microsoft Academic Search

A self-organizing laser based on a single diode-pumped Nd:YAG slab with reciprocal cavity completed by dynamic holographic gratings was created and studied. The temporal dynamics, frequency spectrum and spatial characteristics of the generated beam were examined.

Oleg L. Antipov; Oleg N. Eremeykin; Andrey P. Zinoviev; Alaxander P. Savikin

2004-01-01

128

Highly effective dynamic holographic gratings in doped bismuth titanate crystals and applications to metrology  

NASA Astrophysics Data System (ADS)

Highly efficient volume reflective, dynamical holographic gratings in doped Ti12TiO20 crystals have been observed. We demonstrated doped Ti12TiO20 single, electro-optical crystal and experimental set up, which combines high reversibility, small response time, high diffraction efficiency and practically unlimited number of cycles hologram recording, readout and erasing. It allows using doped Ti12TiO20 crystal as an attractive diffractive optical element in Dynamical Holographic Sensor -DHS for metrology applications. The high image contrast of the real time dynamical holographic interferograms without application of external electric field has been obtained for non transparent diffuse reflective objects using commercial available CW He-Ne laser. DHS applications for nondestructive test of the most vital parts engineering constructions to prevent premature failure have has been demonstrated. DHS application for visualization of cryogenic fields in the near zone of cryoultrasonic cancer tissue destructor has been presented.

Dovgalenko, George E.; Wu, Ying

2009-05-01

129

Laser-Induced Plasma In a Water Bubble  

SciTech Connect

In this work we present a theoretical study concerning the Laser Induced Breakdown Spectroscopy (LIBS) in water. The strong influence of chemical processes on the fluid dynamic expansion has been investigated. To this aim a fluid dynamic code has been developed and coupled with a chemical model, considering the plasma inside the bubble in local thermodynamic equilibrium (LTE)

Casavola, A.; Pesce, L. [Dipartimento di Chimica, Universita di Bari (Italy); Colonna, G. [CNR-IMIP, Bari section (Italy); Capitelli, M. [Dipartimento di Chimica, Universita di Bari (Italy); CNR-IMIP, Bari section (Italy)

2005-05-16

130

Vibrational Dynamics around the Conical Intersection Resulting from the tilde{A} ? tilde{X} Laser Induced Fluorescence of the Methoxy (CH_3O) Radical  

NASA Astrophysics Data System (ADS)

The results of a theoretical calculation of the spectra associated with the laser induced fluorescence tilde{A}^2A_1? tilde{X}^2E of both the methoxy molecule and CH_2DO are presented and discussed. The form of the vibronic dipole moment is determined by symmetry and the corresponding dipole expansion coefficients are calculated using ab initio methods. The calculated spectra include states up to 3000 Cm-1 above the zero point energy. We describe how the various features of the spectrum are related to coordinate dependent terms in the dipole expansion as well as the spin-orbit couplings, Jahn-Teller couplings, and vibrational anharmonicities.

Nagesh, Jayashree; Sibert, Edwin L. Sibert, III

2011-06-01

131

Femtosecond laser-induced two-photon polymerization: A new avenue towards microoptics and micromechanics  

Microsoft Academic Search

Various polymer micro-optical and mechanical components with complicated two and three-dimensional geometries have been prepared by femtosecond laser induced two-photon photopolymerization of resins, including aspheric micro lens and arrays, axicones, Dammann gratings, Fresnel lenses, Fractal zone plates, and integrated nanofiber sets.

Qi-Dai Chen; Hong Xia; Dong Wu; Juan Wang; Xiao-Feng Lin; Ye Tian; Hong-Bo Sun

2009-01-01

132

Laser-induced dispersion control.  

PubMed

An intense laser pulse is used to control the spectral phase of a weak probe pulse as they overlap in fused silica. The laser-induced linear chirp is controlled by the delay time between pulses. Dependence from intensity and spectral phase of the pump pulse is also studied. Experimental data is validated by numerical simulation based on optical Kerr effect. Results show that laser-induced pulse shaping is possible and may be useful for intracavity pulse compression and shaping in enhancement cavities. PMID:24876014

Rasskazov, Gennady; Ryabtsev, Anton; Lozovoy, Vadim V; Dantus, Marcos

2014-06-01

133

Investigation on the role of air in the dynamical evolution and thermodynamic state of a laser-induced aluminium plasma by spatial- and time-resolved spectroscopy  

NASA Astrophysics Data System (ADS)

The amount and the spatial distribution of air atoms and ions in a laser-induced plasma in ambient air provide important information about the formation of the plasma and its successive evolution history. For this reason, in the present work, the air mixing in a laser-induced plasma in air at atmospheric pressure and its influence on its thermodynamic evolution were studied. Information about spatial distributions of atoms and ions from Al, N and O were achieved by Abel-inverted spectra in the plume. The occurrence of LTE in the plume was also assessed by the utilization of theoretical criteria, and by the analysis of experimental spectra. Aluminium atoms and ions were found to be in LTE, while nitrogen and oxygen were not because of their longer times of relaxation toward equilibrium. Nitrogen was found to be over-ionized with respect to Saha-Eggert equilibrium, indicating that the plasma is recombining. Experimental observations suggest that the concentration of air species in the plasma is larger than that of aluminium, even in the region closer to the target, where the aluminium lines are stronger. In the front part of the plume only emission lines from air species were observed. The results suggest that a Laser-Supported Detonation (LSD) regime occurs during the trailing part of the laser pulse, resulting in the strong inclusion into the plasma of air elements. In this scenario, also the thermodynamic history of the plume is affected by the predominance of air species.

Cristoforetti, G.; Lorenzetti, G.; Legnaioli, S.; Palleschi, V.

2010-09-01

134

Gratings in polymeric waveguides  

NASA Astrophysics Data System (ADS)

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 ?m 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 ?m 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.

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

2007-04-01

135

Dynamics of electron transfer from high-potential cytochrome c to bacteriochlorophyll dimer in photosynthetic reaction centers as probed using laser-induced temperature jump.  

PubMed

Laser-induced temperature jump experiments were used for testing the rates of thermoinduced conformational transitions of reaction center (RC) complexes in chromatophores of Chromatium minutissimum. The thermoinduced transition of the macromolecular RC complex to a state providing effective electron transport from the multiheme cytochrome c to the photoactive bacteriochlorophyll dimer within the temperature range 220-280 K accounts for tens of seconds with activation energy 0.166 eV/molecule. The rate of the thermoinduced transition in the cytochrome-RC complex was found to be three orders of magnitude slower than the rate of similar thermoinduced transition of the electron transfer reaction from the primary to secondary quinone acceptors studied in the preceding work (Chamorovsky et al. in Eur Biophys J 32:537-543, 2003). Parameters of thermoinduced activation of the electron transfer from the multiheme cytochrome c to the photoactive bacteriochlorophyll dimer are discussed in terms of cytochrome c docking onto the RC. PMID:17262223

Chamorovsky, Sergei K; Chamorovsky, Constantine S; Knox, Peter P; Chizhov, Igor V; Zubov, Boris V

2007-07-01

136

Distributed discrimination of strain and temperature based on Brillouin dynamic grating in an optical fiber  

NASA Astrophysics Data System (ADS)

This paper reviews distributed discrimination of strain and temperature by use of an optical fiber based on fiber optic nerve systems. The preliminary method based on multiple resonance peaks of the Brillouin gain spectrum in a specially-designed fiber is firstly introduced. The complete discrimination of strain and temperature based on the Brillouin dynamic grating in a polarization maintaining fiber is extensively presented. The basic principle and two experimental schemes of distributed discrimination based on fiber optic nerve systems are demonstrated. The performance of the high discriminative accuracy (0.1 °C-0.3°C and 5 ??-12??) and high spatial resolution (˜10 cm) with the effective measurement points of about 50 for a standard system configuration or about 1000 for a modified one will be highly expected in real industry applications.

Hotate, Kazuo; Zou, Weiwen; Yamashita, Rodrigo Kendy; He, Zuyuan

2013-12-01

137

Beam dynamics and wakefield simulations of the double grating accelerating structure  

SciTech Connect

Laser-driven acceleration in dielectric structures can provide gradients on the order of GeV/m. The small transverse dimension and tiny feature sizes introduce challenges in design, fabrication, and simulation studies of these structures. In this paper we present the results of beam dynamic simulation and short range longitudinal wakefield simulation of the double grating structure. We show the linear trend of acceleration in a dielectric accelerator design and calculate the maximum achievable gradient equal to 0.47E{sub 0} where E0 is maximum electric field of the laser excitation. On the other hand, using wakefield simulations, we show that the loss factor of the structure with 400nm gap size will be 0.12GV/m for a 10fC, 100as electron bunch which is an order of magnitude less than expected gradient near damage threshold of the device.

Najafabadi, B. Montazeri; Byer, R. L.; Ng, C. K.; England, R. J.; Peralta, E. A.; Soong, K.; Noble, R.; Wu, Z. [Stanford University, Stanford, CA (United States); SLAC National Accelerator Laboratory, Menlo Park, CA (United States)

2012-12-21

138

Dynamic assessment of women pelvic floor function by using a fiber Bragg grating sensor system  

NASA Astrophysics Data System (ADS)

We present a novel sensing system consisting of an intravaginal probe and an optoelectronic measurement unit, which allows an easy, comfortable and quantitative dynamic evaluation of women pelvic floor muscle strength. The sensing probe is based on a silicone cylinder that transduces radial muscle pressure into axial load applied to a fiber Bragg grating strain sensor. The performance of a first sensor probe prototype with temperature referentiation and of the autonomous, portable optoelectronic measurement unit with data logging capabilities and graphical user interface is disclosed. The presented results refer to an ongoing collaboration work between researchers from the Medical, Optoelectronics and Mechanical areas, directed to the development of equipment that can assist in medical practice and help in the research of primary mechanisms responsible for several pelvic floor disorders, in particular urogenital prolapses.

Ferreira, Luis A.; Araújo, Francisco M.; Mascarenhas, Teresa; Natal Jorge, Renato M.; Fernandes, António A.

2006-03-01

139

Vibrational relaxation dynamics in transient grating spectroscopy studied by rate equations based on time-dependent correlation function  

NASA Astrophysics Data System (ADS)

A modified model, a set of rate equations based on time-dependent correlation function, is used to study vibrational relaxation dynamics in transient grating spectroscopy. The dephasing, the population dynamics, and the vibrational coherence concerning two vibrational states are observed respectively in organic dye IR780 perchlorate molecules doped polyvinyl alcohol matrix. The result shows that in addition to the information concerning system-environment interaction and vibrational coherence, the vibrational energy transfer can be described by this modified model.

Yu, Guo-Yang; Song, Yun-Fei; He, Xing; Zheng, Xian-Xu; Tan, Duo-Wang; Chen, Jun; Yang, Yan-Qiang

2012-04-01

140

Liquid Crystal Bragg Gratings: Dynamic Optical Elements for Spatial Light Modulators (Preprint).  

National Technical Information Service (NTIS)

Bragg gratings yield a single diffracted order when irradiated by a coherent beam at the appropriate Bragg angle. In many cases, nearly all of the energy of the incident beam can be coupled to the diffracted beam. Hence these gratings can form many useful...

J. M. Wofford L. V. Natarajan R. L. Sutherland S. Siwecki V. P. Tondiglia

2007-01-01

141

Dynamic dispersion compensation in a 10Gb\\/s optical system using a novel voltage tuned nonlinearly chirped fiber Bragg grating  

Microsoft Academic Search

We experimentally demonstrate dynamic dispersion compensation using a novel nonlinearly chirped fiber Bragg grating in a 10-Gb\\/s system. A single piezoelectric transducer continuously tunes the induced dispersion from 300 to 1000 ps\\/nm. The system achieves a bit-error rate=10-9 after both 50 and 104 km of single-mode fiber by dynamically tuning the dispersion of the grating between 500 and 1000 ps\\/nm,

K.-M. Feng; J.-X. Chai; V. Grubsky; D. S. Starodubov; M. I. Hayee; S. Lee; X. Jiang; A. E. Willner; J. Feinberg

1999-01-01

142

Dynamic fiber Bragg gratings based health monitoring system of composite aerospace structures  

NASA Astrophysics Data System (ADS)

The main purpose of the current work is to develop a new system for structural health monitoring of composite aerospace structures based on real-time dynamic measurements, in order to identify the structural state condition. Long-gauge Fibre Bragg Grating (FBG) optical sensors were used for monitoring the dynamic response of the composite structure. The algorithm that was developed for structural damage detection utilizes the collected dynamic response data, analyzes them in various ways and through an artificial neural network identifies the damage state and its location. Damage was simulated by slightly varying locally the mass of the structure (by adding a known mass) at different zones of the structure. Lumped masses in different locations upon the structure alter the eigen-frequencies in a way similar to actual damage. The structural dynamic behaviour has been numerically simulated and experimentally verified by means of modal testing on two different composite aerospace structures. Advanced digital signal processing techniques, e.g. the wavelet transform (WT), were used for the analysis of the dynamic response for feature extraction. WT's capability of separating the different frequency components in the time domain without loosing frequency information makes it a versatile tool for demanding signal processing applications. The use of WT is also suggested by the no-stationary nature of dynamic response signals and the opportunity of evaluating the temporal evolution of their frequency contents. Feature extraction is the first step of the procedure. The extracted features are effective indices of damage size and location. The classification step comprises of a feed-forward back propagation network, whose output determines the simulated damage location. Finally, dedicated training and validation activities were carried out by means of numerical simulations and experimental procedures. Experimental validation was performed initially on a flat stiffened panel, representing a section of a typical aeronautical structure, manufactured and tested in the lab and, as a second step, on a scaled up space oriented structure, which is a composite honeycomb plate, used as a deployment base for antenna arrays. An integrated FBG sensor network, based on the advantage of multiplexing, was mounted on both structures and different excitation positions and boundary conditions were used. The analysis of operational dynamic responses was employed to identify both the damage and its position. The system that was designed and tested initially on the thin composite panel, was successfully validated on the larger honeycomb structure. Numerical simulation of both structures was used as a support tool at all the steps of the work providing among others the location of the optical sensors used. The proposed work will be the base for the whole system qualification and validation on an antenna reflector in future work.

Panopoulou, A.; Loutas, T.; Roulias, D.; Fransen, S.; Kostopoulos, V.

2011-09-01

143

Visualization of laser-induced breakdown and ignition  

NASA Astrophysics Data System (ADS)

Laser-induced gas breakdown and ignition of atmospheric pressure NH3/O2 mixtures are investigated. The nanosecond-pulsed, 1064-nm Nd:YAG laser is used to create the cascade-type optical breakdown. The post-breakdown plasma and ignition are studied using spectroscopic techniques that include spontaneous emission and NH planar laser-induced fluorescence (PLIF). These time-resolved two-dimensional images provide not only radiative and gas dynamic information but also the space-time loci of the temperature and transient species concentrations. The results provide an understanding of the plasma kernel dynamics and the flame development that is essential to verify on-going simulation modeling of laser-ignition.

Chen, Ying-Ling A.; Lewis, J. W. L.

2001-09-01

144

A dynamic mathematical model of the complete grate\\/kiln iron–ore pellet induration process  

Microsoft Academic Search

Induration (drying and hardening) of iron ore pellets is an energy-intensive feed preparation step for both the blast furnace\\u000a and direct reduction routes to iron. It is commonly carried out by a ‘grate\\/kiln’ process. A mathematical model of the process\\u000a is described, in which mechanistic models of the grate furnace, kiln, and cooler are linked to enable simulation of the

J. A. Thurlby

1988-01-01

145

Dynamics of laser-induced channel formation in water and influence of pulse duration on the ablation of biotissue under water with pulsed erbium-laser radiation  

Microsoft Academic Search

The ability to use fiber-delivered erbium-laser radiation for non-contact arthroscopic meniscectomy in a liquid environment was studied. The laser radiation is transmitted through a water-vapor channel created by the leading part of the laser pulse. The dynamics of the channel formation around a submerged fiber tip was investigated with time-resolved flash photography. Strong pressure transients with amplitudes up to a

M. Ith; H. Pratisto; H. J. Altermatt; M. Frenz; H. P. Weber

1994-01-01

146

Fast dynamic interferometric lithography for large submicrometric period diffraction gratings production  

NASA Astrophysics Data System (ADS)

This paper describes a successful technological transfer, from a state laboratory to an industrial company, for writing long and large submicron period gratings (potentially square-meter sized), implemented in an industrial direct laser beam writing equipment at 355 nm wavelength (Dilase 750 from KLOE SA company). The writing head, which has been inserted in the machine, consists of a phase mask which enables it to project a set of fringes pattern of small area onto a photoresist-coated substrate. As the substrate is continuously moving, one-dimensional or two-dimensional gratings can be fabricated over large areas limited only by the machine's stage displacement range. The optical scheme is described from the beam shaping to the printing processes and the phase mask optimization. In order to demonstrate the technology, 600 nm period gratings of over 20 cm in length have been fabricated. Such submicron structures can be used in solar cell modules for photon trapping and as antireflection coatings.

Gâté, Valentin; Bernaud, Gerard; Veillas, Colette; Cazier, Anthony; Vocanson, Francis; Jourlin, Yves; Langlet, Michel

2013-09-01

147

New MLD gratings adapted for tiling in petawatt-class lasers  

NASA Astrophysics Data System (ADS)

Laser-induced damage threshold of gratings remains the main limiting factor towards generating higher-energy compressed pulses (terawatt and petawatt). HORIBA Jobin Yvon has first developed the manufacturing of large gold coated gratings, dimensions up to half a meter. Then we have developed large multilayer dielectric (MLD) gratings for working at 1.053 microns with 2 to 3 times higher damage threshold than gold coated gratings for ps pulses, and higher efficiency (up to 96% averaged over the full aperture). In addition these large MLD gratings are optimised for mosaic (tiling) configurations, in which the total useful grating length may reach 1 meter or more.

Flamand, J.; de Villèle, G.; Cotel, A.; Touzet, B.; Kane, S.

2006-06-01

148

Investigation of Laser-Induced Retinal Damage.  

National Technical Information Service (NTIS)

Laser-induced, photooxidative damage in ocular tissue was studied with a quantitative assay using high performance liquid chromatography (HPLC) to separate oxidized and reduced ascorbic acid in exposed tissue components. We demonstrated that ascorbic acid...

R. D. Glickman K. W. Lam

1992-01-01

149

Treatment of Laser Induced Retinal Injuries.  

National Technical Information Service (NTIS)

Previously we have shown that the ocular response to laser-induced ocular injury is characterized by an enhancement in arachidonic acid metabolism and that steroid treatment curtailed this response. In the present study we investigated the involvement of ...

M. Belkin N. Naveh

1989-01-01

150

Kinematics of Cold Excitons in the Laser Induced Exciton Trap  

NASA Astrophysics Data System (ADS)

We have recently demonstrated laser induced trapping of indirect excitons in coupled quantum wells [1]. An important advantage of the laser induced exciton trapping is the possibility of controlling the trap in-situ by varying the laser intensity in space and time. Moreover, the excitons at the trap center are cold since they are far from the hot area of the laser excitation. Here, we report the studies of exciton kinetics in the laser induced traps. In particular, the kinetics of the trap formation and the exciton collection to the trap center when the excitation is switched on, as well as the kinetics of the exciton cloud when the excitation and trap are switched off have been measured by ultrafast imaging spectroscopy. The dynamics of the degenerate Bose gas of excitons in the trap was measured and analyzed for the first time. [1] A.T. Hammack, M. Griswold, L.V. Butov, L.E. Smallwood, A.L. Ivanov, and A.C. Gossard, Phys. Rev. Lett. 96, 227402 (2006).

Hammack, A. T.; Butov, L. V.; Smallwood, L. E.; Mouchliadis, L.; Ivanov, A. L.; Gossard, A. C.

2007-03-01

151

Interaction dynamics of fs-laser induced cavitation bubbles and their impact on the laser-tissue-interaction of modern ophthalmic laser systems  

NASA Astrophysics Data System (ADS)

A today well-known laser based treatment in ophthalmology is the LASIK procedure which nowadays includes cutting of the corneal tissue with ultra-short laser pulses. Instead of disposing a microkeratome for cutting a corneal flap, a focused ultra-short laser pulse is scanned below the surface of biological tissue causing the effect of an optical breakdown and hence obtaining a dissection. Inside the tissue, the energy of the laser pulses is absorbed by non-linear processes; as a result a cavitation bubble expands and ruptures the tissue. Hence, positioning of several optical breakdowns side by side generates an incision. Due to a reduction of the amount of laser energy, with a moderate duration of treatment at the same time, the current development of ultra-short pulse laser systems points to higher repetition rates in the range of even Megahertz instead of tens or hundreds of Kilohertz. In turn, this results in a pulse overlap and therefor a probable occurrence of interaction between different optical breakdowns and respectively cavitation bubbles of adjacent optical breakdowns. While the interaction of one single laser pulse with biological tissue is analyzed reasonably well experimentally and theoretically, the interaction of several spatial and temporal following pulses is scarcely determined yet. Thus, the aim of this study is to analyse the dynamic and interaction of two cavitation bubbles by using high speed photography. The applied laser pulse energy, the energy ratio and the spot distance between different cavitation bubbles were varied. Depending on a change of these parameters different kinds of interactions such as a flattening and deformation of bubble shape or jet formation are observed. The effects will be discussed regarding the medical ophthalmic application of fs-lasers. Based on these results a further research seems to be inevitable to comprehend and optimize the cutting effect of ultra-short pulse laser systems with high (> 500 kHz) repetition rates.

Tinne, N.; Ripken, T.; Lubatschowski, H.; Heisterkamp, A.

2011-06-01

152

Theory of laser-induced demagnetization at high temperatures  

NASA Astrophysics Data System (ADS)

Laser-induced demagnetization is theoretically studied by explicitly taking into account interactions among electrons, spins, and lattice. Assuming that the demagnetization processes take place during the thermalization of the subsystems, the temperature dynamics is given by the energy transfer between the thermalized interacting baths. These energy transfers are accounted for explicitly through electron-magnon and electron-phonon interactions, which govern the demagnetization time scale. By properly treating the spin system in a self-consistent random phase approximation, we derive magnetization dynamic equations for a broad range of temperature. The dependence of demagnetization on the temperature and pumping laser intensity is calculated in detail. In particular, we show several salient features for understanding magnetization dynamics near the Curie temperature. While the critical slowdown in dynamics occurs, we find that an external magnetic field can restore the fast dynamics. We discuss the implication of the fast dynamics in the application of heat-assisted magnetic recording.

Manchon, A.; Li, Q.; Xu, L.; Zhang, S.

2012-02-01

153

Integrated hybrid Raman/fiber Bragg grating interrogation scheme for distributed temperature and point dynamic strain measurements.  

PubMed

We propose and experimentally demonstrate the feasibility of an integrated hybrid optical fiber sensing interrogation technique that efficiently combines distributed Raman-based temperature sensing with fiber Bragg grating (FBG)-based dynamic strain measurements. The proposed sensing system is highly integrated, making use of a common optical source/receiver block and exploiting the advantages of both (distributed and point) sensing technologies simultaneously. A multimode fiber is used for distributed temperature sensing, and a pair of FBGs in each discrete sensing point, partially overlapped in the spectral domain, allows for temperature-independent discrete strain measurements. Experimental results report a dynamic strain resolution of 7.8 n?/?Hz within a full range of 1700 ?? and a distributed temperature resolution of 1°C at 20 km distance with 2.7 m spatial resolution. PMID:23089781

Zaidi, Farhan; Nannipieri, Tiziano; Soto, Marcelo A; Signorini, Alessandro; Bolognini, Gabriele; Di Pasquale, Fabrizio

2012-10-20

154

The influence of ion gratings on rotational wavepacket dynamics inH2  

SciTech Connect

We generalize earlier work [V.G. Stavros, E. Harel, S.R.Leone, J. Chem. Phys. 122 (2005) 064301]by illustrating the plausiblerole ofion gratings in time-dependent degenerate four-wave mixing(TD-DFWM) experiments in H2. We postulate that at high laserintensities(1014 1015 W/cm2), H2+/H+ ions generate a static ion grating,it s signature manifested in the transformation from homodyne- toheterodyne-detection of the TD-DFWM signal, depending on laser intensity.The change in signal detection agrees with the calculated intensity forbarrier suppression ionization (BSI) in H2 and the reported onset ofsaturation for H2+ and H+, pointing towards the likely role of iongratings in intense laser field, FWM experiments.

Stavros, Vasilios G.; Leone, Stephen R.

2007-11-24

155

Interrogation of Fiber Bragg Grating Dynamic Strain Sensors by Self-Mixing Interferometry  

Microsoft Academic Search

An innovative investigation of optical feedback or self-mixing interference within the cavity of a single-longitudinal-mode laser is described as an integral part of a novel interrogation scheme to be employed in a fiber Bragg grating-based sensor for strain measurement. The entire sensor device simply consists of a laser diode with an integrated photodiode which is coupled to a fiber Bragg

Maha Suleiman; Han Cheng Seat; Thierry Bosch

2008-01-01

156

Role of laser-induced plasma in ultradeep drilling of materials by nanosecond laser pulses  

NASA Astrophysics Data System (ADS)

Radiative effects of the laser-induced ablative plasma on the heating and ablation dynamics of materials irradiated by nanosecond laser pulses are studied by the example of graphite ablation. On the basis of combined thermal and gas dynamic modeling, the laser-induced plasma plume is shown to be a controlling factor responsible for ultradeep laser drilling due to plasma radiation, both bremsstrahlung and recombinative. We demonstrate that plasma radiative heating of the target considerably deepens the molten layer, thus explaining the observed crater depths.

Bulgakova, Nadezhda M.; Evtushenko, Anton B.; Shukhov, Yuri G.; Kudryashov, Sergey I.; Bulgakov, Alexander V.

2011-10-01

157

Laser-Induced Underwater Plasma And Its Spectroscopic Applications  

SciTech Connect

Applications of Laser Induced Breakdown Spectroscopy (LIBS) for analysis of immersed solid and soft materials, and for liquid impurities are described. A method for improving the LIBS signal underwater and for obtaining quantitative analyses in presence of strong shot-to-shot variations of the plasma properties is proposed. Dynamic of the gas bubble formed by the laser pulse is also discussed, together with its importance in Double-Pulse (DP) laser excitation. Results of the studies relative to an application of multi-pulse sequence and its effects on the plasma and gas bubble formation are also presented.

Lazic, Violeta [ENEA, FIS-LAS, Via. E. Fermi 45, 00044 Frascati (Italy)

2008-09-23

158

New MLD gratings adapted for tiling in petawatt-class lasers  

Microsoft Academic Search

Laser-induced damage threshold of gratings remains the main limiting factor towards generating higher-energy compressed pulses (terawatt and petawatt). HORIBA Jobin Yvon has first developed the manufacturing of large gold coated gratings, dimensions up to half a meter. Then we have developed large multilayer dielectric (MLD) gratings for working at 1.053 microns with 2 to 3 times higher damage threshold than

J. Flamand; G. de Villèle; A. Cotel; B. Touzet; S. Kane

2006-01-01

159

Space charge field and dynamics of the grating formation in a photorefractive polymer-dispersed liquid crystal based on a photoconducting polysiloxane  

Microsoft Academic Search

A photorefractive system composed of liquid crystal droplets dispersed in a photoconducting polymer is characterized by means of two-beam coupling. The amplitudes and phases of the spatial variations of the refractive index and the absorption coefficient are measured using the moving grating technique. Dynamic measurements indicate that the phase of the refractive index modulation is nearly constant while the amplitude

Lutz Paelke; Heinz-S. Kitzerow

2006-01-01

160

Laser induced forward transfer of conducting polymers  

Microsoft Academic Search

We report on laser printing of conducting polymers directly from the solid phase. Laser induced forward transfer is employed\\u000a to deposit P3HT:PCBM films on glass\\/ITO\\/PEDOT:PSS substrates. P3HT:PCBM is widely used as the active material in organic solar\\u000a cells. Polyaniline films, which are also printed by laser induced forward transfer, find many applications in the field of\\u000a biotechnology. Laser printing parameters

M. Kandyla; S. Chatzandroulis; I. Zergioti

2010-01-01

161

Dynamic self-calibration of time grating sensors based on self-adaptive Kalman filter algorithm  

NASA Astrophysics Data System (ADS)

As regarding the errors caused by mechanical installation and signal processing, a novel self-adaptive kalman filter algorithm is proposed. According to kalman filter recursion formula, the current value can be estimated with the last estimated value and the current measured value. Therefore, the kalman filter algorithm does not need recorder the past series of the estimated value and the current measured value, the calculated load is not too heavy to implement. The respond speed and the quality of time grating can be improved significantly. Experiment results prove the valid of the proposed method.

Chen, Ziran

2013-10-01

162

Influence of nematic liquid crystal with dye and cell construction parameters on dynamic holographic grating formation  

NASA Astrophysics Data System (ADS)

We have described the relation between LC parameters and induced diffraction gratings recorded by light intensity pattern in dye-doped nematic liquid crystals sandwiched between two coating glass plates covered with ITO conductive and polyimide orientation layers. In our investigations we used the LC cells containing planary oriented nematic mixtures (low-angle rubbing, tilt 1.5 - 2%) doped with the antraquinone dyes (0.1 - 1% w/w). Nematic liquid crystal mixtures with different electrooptical threshold, optical anisotropy, viscosity and conductivity have been investigated. The influence of resistivity, optical anisotropy of LC mixtures and polyimide layers on diffraction efficiency and other parameters have been discussed.

Parka, Janusz; Miniewicz, Andrzej; Januszko, A.; Reznikov, Yuri A.; Dabrowski, Roman S.; Stolarz, Zofia

2000-05-01

163

Space charge field and dynamics of the grating formation in a photorefractive polymer-dispersed liquid crystal based on a photoconducting polysiloxane  

NASA Astrophysics Data System (ADS)

A photorefractive system composed of liquid crystal droplets dispersed in a photoconducting polymer is characterized by means of two-beam coupling. The amplitudes and phases of the spatial variations of the refractive index and the absorption coefficient are measured using the moving grating technique. Dynamic measurements indicate that the phase of the refractive index modulation is nearly constant while the amplitude increases gradually. The maximum value of the internal space charge field can be estimated from the amplitude of the phase grating and is found to be of the order of one-hundredth of the external bias field.

Paelke, Lutz; Kitzerow, Heinz-S.

2006-12-01

164

Laser-induced shock waves from structured surfaces  

NASA Astrophysics Data System (ADS)

We present our results on the expansion dynamics of laser induced plasma created shock wave from stainless steel alloy propagating into ambient air that are characterized by time resolved shadowgraphic imaging. A machinist's scale with periodic surface structures of 30 ?m depth and 240 +/- 20 ?m width having 25 and 64 lpi (lines per inch) is used as a target surface. Laser pulses from frequency doubled Nd:YAG (7ns, 532 nm) with 45 mJ energy per pulse focused to a beam diameter of ~ 1 mm on the target surface are used to generate laser induced shock waves. A fast ICCD camera (DH-734U, ANDOR) with 1.5 ns gating resolution is used to capture the time evolution of SWs into air. The properties of shock waves from structured surfaces are compared to that from a flat surface to understand the contribution of structured surface to shock wave dynamics. The SWs from a flat surface are observed to follow Sedov-Taylor solution during time delay of 0.2 to 20 ?s. Contact front discontinuity dynamics were studied at different time scales for flat and structured surfaces The maximum velocity of the SWs has increased from 2.75 to 4 km/s with increasing number of surface structures from 25 to 64 lpi. From the measured radius of curvature of SW's (RSW), the velocity, pressure and temperature associated with the micro explosion of metal surface is estimated using Counter Pressure Corrected Point Strong Explosion Theory.

Leela, Ch.; Kumar, V. Rakesh; Tewari, Surya P.; Kiran, P. Prem

2012-05-01

165

Treatment of Laser Induced Retinal Injuries.  

National Technical Information Service (NTIS)

This year's study consisted of two parts: 1. Completion of the study on steroid treatment of eyes 2. Study on Neodymium: yttrium aluminum garnet (YAG) laser induce retinal damage and its relationship with prostaglandin E2 (PGE2) and leukotrienes response....

M. Belkin N. Naveh

1987-01-01

166

Study Of Laser-Induced Copolymerization  

NASA Technical Reports Server (NTRS)

Report describes experiments on photopolymerization of styrene/maleic anhydride copolymer published as part of Laser Polymerization Program at NASA Langley Research Center. Presents basic study of copolymerization of styrene and maleic anhydride under laser-induced initiation and polymerization. Helps to clarify different theories on such initiation and represents significant advances in understanding of basic processes.

Miner, Gilda A.; Meador, Willard E.; Chang, C. Ken

1993-01-01

167

Multiple-photon laser-induced fluorescence. [HS and DS radicals  

SciTech Connect

The technique of multiple-photon laser-induced fluorescence has been used to study the spectroscopy and dynamics of atoms, molecules, and free radicals. Among the species investigated were iodine atoms (I), carbon monoxide (CO), molecular iodine (I/sub 2/), and HS and DS radicals. 7 figures.

Tiee, J.J.; Ferris, M.J.; Loge, G.W.; Wampler, F.B.; Hartford, A.

1982-01-01

168

Recent Applications of Laser-Induced Breakdown Spectrometry: A Review of Material Approaches  

Microsoft Academic Search

The use of laser?induced breakdown spectrometry (LIBS) has grown steadily, and it has proven to be a relatively dynamic research activity for performing direct spectrochemical elemental or metal analysis of a variety of materials, solids, liquids, and gases, with none or little sample pretreatment procedures. Significant progress has been made during the last several years on the diverse and versatile

Jianyong Wu; Joseph Sneddon

2004-01-01

169

Submerged laser-induced plasma amplification of shockwaves using shock tubes for nanoparticle removal  

Microsoft Academic Search

Amplifying the dynamic pressure of submerged laser-induced plasma (LIP) shockwaves using shock tubes is introduced and demonstrated. The higher the amplitude of the pressure generated, the smaller the particles that can be removed, thus proving more useful for a variety of nanoparticle removal applications. Limiting the expansion of the submerged LIP core with a shock tube is a non-contact approach

Thomas J. Dunbar; M. D. Murthy Peri; Ivin Varghese; Cetin Cetinkaya

2007-01-01

170

Pressure amplification of laser induced plasma shockwaves with shock tubes for nanoparticle removal  

Microsoft Academic Search

A method using shock tubes for amplifying the dynamic pressure of Laser Induced Plasma (LIP) shockwaves for removing sub-100-nm nanoparticles is introduced and demonstrated. The higher the amplitude of the pressure generated, the smaller the particles that can be removed and, thus the more useful for a variety of applications. Constraining the expansion of the LIP core with a shock

Thomas Dunbar; Brian Maynard; Derek A. Thomas; M. D. Murthy Peri; Ivin Varghese; Cetin Cetinkaya

2007-01-01

171

Femtosecond laser-induced breakdown in water  

NASA Astrophysics Data System (ADS)

Photodisruption is a commonly used opthalmic surgical technique which has proved immensely useful for such procedures as the removal of secondary cataracts and the incision of vitreous strands. Short laser pulses are focused to produce optical breakdown inside the eye. The absorption process is highly nonlinear, thus the region of breakdown is confined to the focal volume. It is believed that this localized, optically generated plasma evaporates tissue, providing a precise laser scalpel. The plasma, however, also produces a cavitation bubble and a shock wave which expands with supersonic speed then decays to a sonic wave after it propagates some distance. Both the bubble and the shock wave can cause collateral tissue damage, thus the "shock zone" (region of supersonic expansion and cavitation) limits the confinement of the photodisrupted region. Most clinical applications employ 10-ns pulses from Q-switched Nd: YAG lasers. For these lasers, the breakdown threshold is about 1 mJ and the shock zone is approximately 1 mm in diameter, thus limiting how close to critical tissues (eg. retina) this technique may be utilized. Recent experiments have shown that using shorter pulses significantly decreases the size of the shock zone. We present measurements of laser-induced breakdown in water using tightly focused (0.65 NA), 100-fs and 200-ps, 800-nm laser pulses from a Titanium: Sapphire laser system. Using a dark-field scattering technique we measure a sharp threshold for plasma formation of 0.12 ?J for 100-fs pulses and 2 ?J for 200-ps pulses. Acoustic measurements indicate pressure wave formation above 0.8 ?J for 100-fs pulses and 4 ?J for 200-ps pulses. Using a stroboscopic imaging technique to monitor the pressure wave expansion, we find that the shock zone has a diameter of only 11 ?m for 1-?J, 100-fs excitation pulses, increasing to 20 ?m for 30-?J, 100-fs pulses. Our ongoing measurements include imaging the dynamics from 100ps to 1ms after excitation to monitor cavitation bubble and shock formation, thermal effects, and bubble recollapse. The low threshold for plasma formation, and the small size of the photodisrupted region for femtosecond pulses, coupled with the simplification afforded by the all solid-state femtosecond systems now becoming available makes ultrashort pulse photodisruption both a worthwhile and practical alternative to the nanosecond techniques currently in use.

Schaffer, Chris B.

1997-04-01

172

Increasing dynamic range of a fibre Bragg grating edge-filtering interrogator with a proportional control loop  

NASA Astrophysics Data System (ADS)

We present a fibre Bragg grating (FBG) interrogator that uses a microcontroller board and a tunable optical filter in a proportional control loop to increase dynamic range and achieve high strain sensitivity. It is an edge-filtering interrogator with added proportional control loop that locks the operating wavelength to the mid-reflection point on the FBG spectrum. The interrogator separates low-frequency (LF) components of strain and measures them with extended dynamic range, while at the same time measuring high-frequency (HF) strain without loss in strain sensitivity. In this paper, we describe the implementation of the interrogator and analyse the characteristics of individual components, such as the speed and voltage resolution of the microcontroller and the tunable optical filter. We measure the performance of the proportional control loop at frequencies up to 1 kHz and characterize the system using control theory. We illustrate the limitation of the conventional interrogator to measure strains greater than 40 ?? and demonstrate successful application of the proposed interrogator for simultaneous measurement of 450 ?? LF strain at 50 Hz superimposed with 32 kHz HF strain.

Stan, Nikola; Bailey, D. C.; Chadderdon, S. L.; Webb, S.; Zikry, M.; Peters, K. J.; Selfridge, R. H.; Schultz, S. M.

2014-06-01

173

Carrier dynamics in quantum-dot sensitized solar cells measured by transient grating and transient absorption methods.  

PubMed

Carrier dynamics in quantum-dot sensitized solar cells (QDSSCs) was clarified by combining the information obtained by the heterodyne transient grating (HD-TG), transient absorption (TA) and transient photocurrent (TP) measurements under the short circuit conditions in the time range from microseconds to seconds. The HD-TG signal is sensitive to the ionic species at the electrode/electrolyte interface, and the electrons in the titanium oxide layer injected from quantum dots (QDs) were monitored by the TA signal, and the photocurrent as a final output was monitored by the TP signal. By using the compensating information, the whole picture of the charge dynamics was obtained in the time region after the initial electron injection from QDs into the titanium oxide layer. In the former part of this paper, the assignment of the responses for each measurement was clarified based on the previous paper on dye sensitized solar cells (S. Kuwahara, et al. Phys. Chem. Chem. Phys., 2013, 15(16), 5975-5981). In the latter part, the effect of the device parameters for actual QDSSCs, such as electrolyte concentrations, and coating times of surface passivation of QDs were investigated. PMID:23712641

Maeda, Naotaka; Hata, Hiroaki; Osada, Naoya; Shen, Qing; Toyoda, Taro; Kuwahara, Shota; Katayama, Kenji

2013-07-14

174

Laser-induced regeneration of cartilage  

NASA Astrophysics Data System (ADS)

Laser radiation provides a means to control the fields of temperature and thermo mechanical stress, mass transfer, and modification of fine structure of the cartilage matrix. The aim of this outlook paper is to review physical and biological aspects of laser-induced regeneration of cartilage and to discuss the possibilities and prospects of its clinical applications. The problems and the pathways of tissue regeneration, the types and features of cartilage will be introduced first. Then we will review various actual and prospective approaches for cartilage repair; consider possible mechanisms of laser-induced regeneration. Finally, we present the results in laser regeneration of joints and spine disks cartilages and discuss some future applications of lasers in regenerative medicine.

Sobol, Emil; Shekhter, Anatoly; Guller, Anna; Baum, Olga; Baskov, Andrey

2011-08-01

175

Planar laser induced fluorescence in aqueous flows  

Microsoft Academic Search

Planar laser-induced fluorescence (PLIF) is a non-intrusive technique for measuring scalar concentrations in fluid flows.\\u000a A fluorescent dye is used as a scalar proxy, and local fluorescence caused by excitation from a thin laser sheet can be related\\u000a to dye concentration. This review covers quantitative PLIF in aqueous flows, with discussions of fluorescence theory, experimental\\u000a methods and equipment, image processing

J. P. Crimaldi

2008-01-01

176

Applications of Laser-Induced Breakdown Spectrometry  

Microsoft Academic Search

When a high-powered laser beam is focused onto a small area or spot of a solid surface, the temperature of the locally heated region rises rapidly to the vaporization temperature of the solid material and an optically induced plasma, frequently called a laser-induced plasma (LIP) or laser-ablated plasma (LAP) or laser spark is formed at the surface. The plasma will

Kyuseok Song; Yong-Ill Lee; Joseph Sneddon

1997-01-01

177

Laser induced modification of surface structures  

Microsoft Academic Search

The results on surface modification of materials of different structures; morphology, grain sizes, density and porosity by exposure to nanosecond laser light are given. Laser induced changes in their surface characteristics are presented. Surface layers of Si3N4, SiC dense ceramics and BN graphite and turbostratic pressed powders are studied by scanning electron microscopy to reveal the new nanostructures (nanowires or

L. L. Sartinska; S. Barchikovski; N. Wagenda; B. M. Rud’; I. I. Timofeeva

2007-01-01

178

Conformational relaxation dynamics of a poly(N-isopropylacrylamide) aqueous solution measured using the laser temperature jump transient grating method.  

PubMed

We observed phase transition and phase relaxation processes of a poly(N-isopropylacrylamide) (PNIPAM) aqueous solution using the heterodyne transient grating (HD-TG) method combined with the laser temperature jump technique. The sample temperature was instantaneously raised by about 1.0 K after irradiation of a pump pulse to crystal violet (CV) molecules for heating, and the phase transition was induced for the sample with an initial temperature just below the lower critical solution temperature (LCST); the following phase relaxation dynamics was observed. Turbidity relaxation was observed in both the turbidity and HD-TG responses, while another relaxation process was observed only in the HD-TG response, namely via the refractive index change. It is suggested that this response is due to formation of globule molecules or their assemblies since they would have nothing to do with turbidity change but would affect the refractive index, which is dependent on the molar volume of a chemical species. Furthermore, the grating spacing dependence of the HD-TG responses suggests that the response was caused by the counter propagating diffusion of the coil molecules as a reactant species and the globule molecules as a product species and the lifetime of the globule molecules ranged from 1.5 to 5 seconds. Thus, we conclude that the turbidity reflects the dynamics of aggregate conditions, not molecular conditions. The coil and globule sizes were estimated from the obtained diffusion coefficient. The sizes of the coil molecules did not change at the initial temperatures below the LCST but increased sharply as it approaches LCST. We propose that the coil-state molecules associate due to hydrophobic interaction when the initial temperature was higher than LCST minus 0.5 K and that the globule-state molecules generated from the coil-state molecules showed a similar trend in temperature. The phase transition was also induced by heating under a microscope, and the relaxation process was followed using the fluorescence peak shift of a fluorescent molecule-labeled PNIPAM. The result also supports the existence of a globule molecule or its assembly remains for several seconds in the phase relaxation. PMID:22422215

Inoue, Hayato; Katayama, Kenji; Iwai, Kaoru; Miura, Atsushi; Masuhara, Hiroshi

2012-04-28

179

CONTROL OF LASER RADIATION PARAMETERS: Control of the parameters of solid-state lasers by dynamic gratings in a DKDP crystal  

Microsoft Academic Search

Pulsed and cw Nd3+:YAG lasers were used in an experimental investigation of the influence of dynamic gratings in intracavity DKDP crystal elements on the main characteristics of the radiation emitted by solid-state lasers at room temperature. A hologram, formed in a DKDP crystal by a two-beam method, induced generation of pulsed laser radiation which had the spectral characteristics of a

B. V. Anikeev; S. A. Kutsenko; D. V. Sin'ko; V. S. Sukhorukov

1999-01-01

180

Laser-induced damage of diamond films  

NASA Astrophysics Data System (ADS)

The laser-induced damage thresholds of diamond films deposited on silicon substrates were investigated. Experiments were performed with both CW and pulsed lasers operating at a wavelength of 10. 6 jim. Analytical studies were conducted to determine the thermal and thermomechanical states as well as the electric field strengths of the films and the substrates at the damage thresholds in an effort to identify the damage mechanism. The evidence suggests that the diamond films are damaged by stress-induced cracking which occurs when the underlying silicon approaches melt. 1 .

Read, Harold E.; Merker, M.; Gurtman, Gerry A.; Wilson, Russell S.

1991-06-01

181

Laser induced fluorescence of trapped molecular ions  

SciTech Connect

An experimental apparatus for obtaining the optical spectra of molecular ions is described. The experimental technique includes the use of three dimensional ion trapping, laser induced fluorescence, and gated photon counting methods. The ions, which are produced by electron impact, are confined in a radio-frequency quadrupole ion trap of cylindrical design. Because the quadrupole ion trap allows mass selection of the molecular ion desired for study, the analysis of the spectra obtained is greatly simplified. The ion trap also confines the ions to a region easily probed by a laser beam. 18 references.

Grieman, F.J.

1979-10-01

182

Laser-induced water condensation in air  

NASA Astrophysics Data System (ADS)

Triggering rain on demand is an old dream of mankind, with a huge potential socio-economical benefit. To date, efforts have mainly focused on cloud-seeding using silver salt particles. We demonstrate that self-guided ionized filaments generated by ultrashort laser pulses are also able to induce water-cloud condensation in the free, sub-saturated atmosphere. Potential contributing mechanisms include photo-oxidative chemistry and electrostatic effects. As well as revealing the potential for influencing or triggering water precipitation, laser-induced water condensation provides a new tool for the remote sensing of nucleation processes in clouds.

Rohwetter, Philipp; Kasparian, Jérôme; Stelmaszczyk, Kamil; Hao, Zuoqiang; Henin, Stefano; Lascoux, Noëlle; Nakaema, Walter M.; Petit, Yannick; Queißer, Manuel; Salamé, Rami; Salmon, Estelle; Wöste, Ludger; Wolf, Jean-Pierre

2010-07-01

183

Laser-induced fluorescence of atherosclerotic plaques  

NASA Astrophysics Data System (ADS)

In vitro laser-induced fluorescence (LIF) spectra and lifetimes of normal and atherosclerotic tissues are reported. The experimental arrangement conceived to measure LIF contained a 700 ps nitrogen pulsed laser (337.1 nm) and two quartz optical fibers to induce and respectively collect the fluorescence of normal and diseased samples. With UV laser excitation we found proeminent differences both in spectral and temporal range between normal artery and atherosclerotic plaques which was standard pathological classified in five types such as: normal artery, fibrous plaque, atherosclerotic plaque, calcified plaque and ulcerated plaque. As for statistics, the total number of measurements performed on each of the five mentioned types of tissues was 25.

Moise, N.; Pascu, Mihai L.; Carp, C.; Volvoreanu, C.

1998-07-01

184

Modeling of Laser-Induced Metal Combustion  

SciTech Connect

Experiments involving the interaction of a high-power laser beam with metal targets demonstrate that combustion plays an important role. This process depends on reactions within an oxide layer, together with oxygenation and removal of this layer by the wind. We present an analytical model of laser-induced combustion. The model predicts the threshold for initiation of combustion, the growth of the combustion layer with time, and the threshold for self-supported combustion. Solutions are compared with detailed numerical modeling as benchmarked by laboratory experiments.

Boley, C D; Rubenchik, A M

2008-02-20

185

Femtosecond laser induced breakdown for combustion diagnostics  

NASA Astrophysics Data System (ADS)

The focused beam of a 100 fs, 800 nm laser is used to induce a spark in some laminar premixed air-methane flames operating with variable fuel content (equivalence ratio). The analysis of the light escaping from the plasma revealed that the Balmer hydrogen lines, H? and H?, and some molecular origin emissions were the most prominent spectral features, while the CN (?2?+-?2?+) band intensity was found to depend linearly with methane content, suggesting that femtosecond laser induced breakdown spectroscopy can be a useful tool for the in-situ determination and local mapping of fuel content in hydrocarbon-air combustible mixtures.

Kotzagianni, M.; Couris, S.

2012-06-01

186

Pressure effects in laser-induced plasmas of trinitrotoluene and pyrene by laser-induced breakdown spectroscopy (LIBS).  

PubMed

The influence of the ambient atmosphere on the dynamics of plasma expansion, besides the interaction between excited plasma and gas molecules, has been studied for specific organic aromatic compounds. To analyze the influence of air on the formation pathways of atomic and molecular species inside the plasma plume, the spectral emissions in laser-induced breakdown spectroscopy (LIBS) of 2,4,6-trinitrotoluene (TNT) and pyrene were compared at different pressure environments, from high vacuum to atmospheric pressure. Pelletized samples of the compounds were introduced in a vacuum chamber for excitation with the fourth harmonic output of an Nd : YAG laser (266 nm). The optical emission signal was collected with an optical fiber connected to a spectrograph fitted with a intensified charge-coupled device detector. Results from LIBS spectra indicate that changes in pressure level affect the kinetics of the characteristic excited species and their spatial distribution inside the plasma plume. PMID:24405951

Delgado, Tomás; Vadillo, José M; Laserna, J Javier

2014-01-01

187

Fiber grating sensors  

Microsoft Academic Search

We review the recent developments in the area of optical fiber grating sensors, including quasi-distributed strain sensing using Bragg gratings, systems based on chirped gratings, intragrating sensing concepts, long period-based grating sensors, fiber grating laser-based systems, and interferometric sensor systems based on grating reflectors

Alan D. Kersey; Michael A. Davis; Heather J. Patrick; Michel LeBlanc; K. P. Koo; C. G. Askins; M. A. Putnam; E. Joseph Friebele

1997-01-01

188

Methodology for analyzing laser induced structural damage  

SciTech Connect

The analysis of laser-induced structural damage requires the merging of a thermal analysis which includes the characterization of the laser damage with a structural analysis which enables the determination of the deformation and the residual load carrying ability. Three types of laser-induced damage are considered: loss of structure due to melting, change of material properties due to temperature changes, and addition of load due to thermal stress. The thermal solution is calculated from a set of finite difference equations obtained from heat balances performed at successive finite time increments on an array of finite cells. The structural analysis is performed by a re-analysis technique, applicable when changes in structural stiffness are small compared to the initial value. The combined procedure for evaluating laser damage is applied to two structures, representing two levels of complexity. The first was a simple two-dimensional plate and the second a three-dimensional wing structure. The displacement solutions were compared to results obtained from NASTRAN to determine the accuracy of the iterative solution technique. The procedure was found to be efficient, and permits the parametric studies needed for a-priori estimates of the effectiveness of potential laser weapons systems. 10 references.

Bryan, S.K.; Torvik, P.J.; Venkayya, V.B.

1984-01-01

189

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

Microsoft Academic Search

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

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

2003-01-01

190

Toward standardization in laser-induced damage testing  

Microsoft Academic Search

The need to develop standard methods for determining and reporting laser-induced damage thresholds is examined. Data from an international laser-induced damage testing experiment conducted in 1982 aimed at evaluating various experimental approaches for their compatibility are discussed. The recommendations for the standardization of damage testing derived from the experiment are presented. New developments in exposure methodology, damage detection, and calibration

Steven C. Seitel; Karl H. Guenther

1986-01-01

191

Elemental chemical analysis of submerged targets by double-pulse laser-induced breakdown spectroscopy.  

PubMed

Double-pulse laser-induced plasma spectroscopy (DP-LIPS) is applied to submerged targets to investigate its feasibility for elemental analysis. The role of experimental parameters, such as inter-pulse delay and detection time, has been discussed in terms of the dynamics of the laser-induced bubble produced by the first pulse and its confinement effect on the plasma produced by the second laser pulse. The analytical performance of this technique applied to targets in a water environment are discussed. The elemental analysis of submerged copper alloys by DP-LIPS has been compared with conventional (single-pulse) LIBS in air. Theoretical investigation of the plasma dynamics in water bubbles and open air has been performed. PMID:16544131

De Giacomo, A; Dell'Aglio, M; Casavola, A; Colonna, G; De Pascale, O; Capitelli, M

2006-05-01

192

In Search of Multi-Peaked Reflective Spectrum with Optic Fiber Bragg Grating Sensor for Dynamic Strain Measurement  

NASA Technical Reports Server (NTRS)

In a typical optic fiber Bragg grating (FBG) strain measurement, unless in an ideal static laboratory environment, the presence of vibration or often disturbance always exists, which often creates spurious multiple peaks in the reflected spectrum, resulting in a non-unique determination of strain value. In this report we attempt to investigate the origin of this phenomenon by physical arguments and simple numerical simulation. We postulate that the fiber gratings execute small amplitude transverse vibrations changing the optical path in which the reflected light traverses slightly and non-uniformly. Ultimately, this causes the multi-peak reflected spectrum.

Tai, Hsiang

2006-01-01

193

Femtosecond laser diagnostics of ultrafast laser-induced melting of the GaAs surface  

Microsoft Academic Search

The authors report the experimental results of second harmonic generation (SHG) and linear reflectivity studies of the dynamics of laser-induced melting of a GaAs surface layer under subpicosecond pulsed laser excitation. The SH intensity drops less than 100 fs after excitation, while the linear reflectivity reaches a value characteristic of molten GaAs in about 1 ps. Thus, the experimental results

S. V. Govorkov; V. I. Emel'Yanov; I. L. Shumay; Wolfgang Rudolph; Thomas Schroeder

1992-01-01

194

Shadowgraphic studies of triazene assisted laser-induced forward transfer of ceramic thin films  

NASA Astrophysics Data System (ADS)

The laser-induced forward transfer process of solid ceramic donor materials (gadolinium gallium oxide and ytterbium doped yttrium aluminium oxide) was studied using triazene polymer as a sacrificial layer by means of a time-resolved nanosecond-shadowgraphy technique. The dependence of the ablation dynamics and quality of the ejected donor material on the laser fluence and thickness of the sacrificial and donor layers were investigated and discussed.

Kaur, K. S.; Fardel, R.; May-Smith, T. C.; Nagel, M.; Banks, D. P.; Grivas, C.; Lippert, T.; Eason, R. W.

2009-06-01

195

Laser-induced autofluorescence of caries  

NASA Astrophysics Data System (ADS)

The laser induced autofluorescence from carious regions of human teeth was studied using a krypton ion laser at 407 nm as an excitation source, a fiberoptical detection system combined with a polychromator and an optical multichannel analyzer. In addition, time-resolved and time-gated fluorescence measurements in the nanosecond range were carried out. It was found that carious regions contain different fluorophores which emit in the red spectral range. The emission spectra with maxima around 590 nm, 625 nm and 635 nm are typical for metalloporphyrins, copro- and protoporphyrin. During excitation the fluorescence was bleached. Non-carious regions showed a broad fluorescence band with a maximum in the short-wavelength spectral region with shorter fluorescence decay times than the carious regions. Therefore, caries can be detected by spectral analysis of the autofluorescence as well as by determination of the fluorescence decay times or by time-gated imaging.

Koenig, Karsten; Hibst, Raimund; Flemming, Gabriela; Schneckenburger, Herbert

1993-07-01

196

Laser Induced Fluorescence Measurements in HELIX  

NASA Astrophysics Data System (ADS)

To noninvasively measure the perpendicular and parallel ion temperatures, a laser induced fluorescence diagnostic has been installed on the West Virginia University Hot hELIcon eXperiment (HELIX). The HELIX experiment is unique in that the ions are heated by additional ion cyclotron resonant heating (ICRH). We present the first measurements, with and without ICRH, of the perpendicular ion temperature for argon HELIX plasmas. The ion temperature is investigated as a function of ICRH power, plasma density, and helicon source driving frequency. During ICRH, the change in the electron temperature due to collisional equilibration with the ions is measured with a RF compensated Langmuir probe. If completed in time, measurements of the parallel ion temperature will also be presented.

Scime, Earl E.; Balkey, Matthew M.; Keiter, Paul A.

1996-11-01

197

Laser-induced thrombosis in zebrafish.  

PubMed

In the event of injury to the vasculature in vertebrate organisms bleeding is stopped by a defense mechanism called hemostasis. Even though biochemical studies characterized a number of factors, classical genetic methods have not been applied to study hemostasis. We introduced zebrafish as an animal model to study genetics of hemostasis. To conduct genetic studies of hemostasis, we required a global screening method to address all the factors of hemostasis such as those present in plasma, in platelets or those present in the endothelium. Therefore, we developed a global laser induced thrombosis method which can assay all these components. In this paper, we describe the principle of this method as well as provide the detailed protocol so this could be used as a screening tool to measure hemostasis in any laboratory. PMID:21550445

Jagadeeswaran, Pudur; Carrillo, Maira; Radhakrishnan, Uvaraj P; Rajpurohit, Surendra K; Kim, Seongcheol

2011-01-01

198

Laser induced fluorescence of dental caries  

NASA Technical Reports Server (NTRS)

Significant differences between the optical spectra taken from sound regions of teeth and carious regions have been observed. These differences appear both in absorption and in laser induced fluorescence spectra. Excitation by the 488 nm line of an argon ion laser beam showed a peak in the emission intensity around 553 nm for the sound dental material while the emission peak from the carious region was red-shifted by approximately 40 nm. The relative absorption of carious region was significantly higher at 488 nm; however its fluorescence intensity peak was lower by an order of magnitude compared to the sound tooth. Implications of these results for a safe, reliable and early detection of dental caries are discussed.

Albin, S.; Byvik, C. E.; Buoncristiani, A. M.

1988-01-01

199

Femtosecond laser induced breakdown for combustion diagnostics  

SciTech Connect

The focused beam of a 100 fs, 800 nm laser is used to induce a spark in some laminar premixed air-methane flames operating with variable fuel content (equivalence ratio). The analysis of the light escaping from the plasma revealed that the Balmer hydrogen lines, H{sub {alpha}} and H{sub {beta}}, and some molecular origin emissions were the most prominent spectral features, while the CN ({Beta}{sup 2}{Sigma}{sup +}-{Chi}{sup 2}{Sigma}{sup +}) band intensity was found to depend linearly with methane content, suggesting that femtosecond laser induced breakdown spectroscopy can be a useful tool for the in-situ determination and local mapping of fuel content in hydrocarbon-air combustible mixtures.

Kotzagianni, M. [Department of Physics, University of Patras, 26504 Patras (Greece); Institute of Chemical Engineering and High Temperature Chemical Processes (ICE-HT), Foundation for Research and Technology-Hellas (FORTH), 26504 Patras (Greece); Couris, S. [Department of Physics, University of Patras, 26504 Patras (Greece); Institute of Chemical Engineering and High Temperature Chemical Processes (ICE-HT), Foundation for Research and Technology-Hellas (FORTH), 26504 Patras (Greece); Laboratoire Interdisciplinaire Carnot de Bourgogne (ICB), Universite de Bourgogne, 21078 Dijon Cedex (France)

2012-06-25

200

Laser-Induced Incandescence: Detection Issues  

NASA Technical Reports Server (NTRS)

Experimental LII (laser-induced incandescence) measurements were performed in a laminar gasjet flame to test the sensitivity of different LII signal collection strategies to particle size. To prevent introducing a particle size dependent bias in the LII signal, signal integration beginning with the excitation laser pulse is necessary . Signal integration times extending to 25 or 100 nsec after the laser pulse do not produce significant differences in radial profiles of the LII signal due to particle size effects with longer signal integration times revealing a decreased sensitivity to smaller primary particles. Long wavelength detection reduces the sensitivity of the LII signal to primary particle size. Excitation of LII using 1064 nm light is recommended to avoid creating photochemical interferences thus allowing LII signal collection to occur during the excitation pulse without spectral interferences.

VanderWal, Randall L.

1996-01-01

201

Femtosecond laser-induced crystallization of amorphous Sb2Te3 film and coherent phonon spectroscopy characterization and optical injection of electron spins  

NASA Astrophysics Data System (ADS)

A femtosecond laser-irradiated crystallizing technique is tried to convert amorphous Sb2Te3 film into crystalline film. Sensitive coherent phonon spectroscopy (CPS) is used to monitor the crystallization of amorphous Sb2Te3 film at the original irradiation site. The CPS reveals that the vibration strength of two phonon modes that correspond to the characteristic phonon modes (A1g1 and Eg) of crystalline Sb2Te3 enhances with increasing laser irradiation fluence (LIF), showing the rise of the degree of crystallization with LIF and that femtosecond laser irradiation is a good post-treatment technique. Time-resolved circularly polarized pump-probe spectroscopy is used to investigate electron spin relaxation dynamics of the laser-induced crystallized Sb2Te3 film. Spin relaxation process indeed is observed, confirming the theoretical predictions on the validity of spin-dependent optical transition selection rule and the feasibility of transient spin-grating-based optical detection scheme of spin-plasmon collective modes in Sb2Te3-like topological insulators.

Li, Simian; Huang, Huan; Zhu, Weiling; Wang, Wenfang; Chen, Ke; Yao, Dao-Xin; Wang, Yang; Lai, Tianshu; Wu, Yiqun; Gan, Fuxi

2011-09-01

202

[Research on radiation intensity of nanosecond pulse laser-induced soil plasma].  

PubMed

To improve the quality of laser-induced breakdown spectroscopy, nanosecond pulse laser generated by Nd : YAG laser was used to excite soil sample. The laser-induced plasma spectrum was observed using a grating spectrometer and a photoelectric detection system. The influence of laser output energy ranging from 100 to 500 mJ on the radiation intensity of plasma was studied. The results show that both the line intensity and signal-to-background ratio can be enhanced under the optimized condition that the laser energy is 200 mJ. The quality of spectrum was further improved after the laser beam used to excite the sample was defocused properly. When the defocusing position is + 6 mm, the spectral lines intensity of element Mg, Al, K and Fe increased about 46%, 63%, 59% and 45% compared to that without defocusing respectively. The spectral signal-to-background ratio increased about 11%, 31%, 35% and 38% respectively. This lays a foundation for detection of trace impurity element in soil. PMID:22497122

Chen, Jin-zhong; Song, Guang-ju; Sun, Jiang; Li, Xu; Wei, Yan-hong

2012-01-01

203

Laser-induced periodic nanoparticle patterns  

NASA Astrophysics Data System (ADS)

Creating the conditions so that matter naturally self-arranges at the nanoscale under a homogeneous excitation is an exciting challenge for the development of efficient and cost-effective processes. Sub-micrometer periodic templates can be formed spontaneously on materials by low-energy ion sputtering or with lasers. In the latter case, the formation of self-organized grating-like structures requires a high temperature rise and generally results from interactions with ultrashort laser pulses. Recently, a few studies have dealt with self-formed periodic patterns of metal nanoparticle assemblies, but they only reported changes in the spatial and size distributions of metal nanoparticles deposited on surfaces prior to interaction with femtosecond lasers. Here, we show that metal nanoparticles can grow in a selforganized manner within a waveguide illuminated from free-space by a continuous wave visible laser. We report the conditions that give rise to the generation of such 1D nanoparticle gratings and describe the parameters that influence the grating characteristics. We explain the mechanisms involved in the formation of such nanostructures on the basis of interference phenomena between the incident wave and guided modes.

Destouches, N.; Vitrant, G.; Crespo-Monteiro, N.; Liu, Z.; Lefkir, Y.; Vocanson, F.; Epicier, T.

2014-03-01

204

Ultra-fast Diagnostics of Laser-induced Melting of Matter in ns to ?s Time-scales  

Microsoft Academic Search

The interaction of laser radiation with dielectrics and metals is detected with femtosecond reso- lution by pump&probe techniques (t = 80 fs or 3 ps, ? = 810 nm). Even with femtosecond laser ra- diation melt ejection dynamics can be observed by irradiating metals like copper or aluminium us- ing time-resolved shadowgraphy. Laser-induced melt ejection has been observed in the

Alexander Horn; Ilja MINGAREEV; Isamu MIYAMOTO

2006-01-01

205

Probing electron correlations by laser-induced tunnel ionization  

NASA Astrophysics Data System (ADS)

Pairwise electron correlation has been intensely studied by projecting two electrons to the continuum simultaneously via a well controlled perturbation, e.g. a collision with an energetic electron, a fast ion or a single XUV photon. Electron correlation studies using multiphoton ionization remain an exception. One reason may be that recollision aside, studies in rare gas atoms have largely suggested that multiphoton multiple ionization in the tunneling limit proceeds sequentially - each successive ionization stage loosing memory of previous electronic correlations. On the other hand, laser tunnel ionization has been known to access multiple electronic states. Recent evidence, corroborating the notion that tunneling can prepare these correlated multielectron states in a coherent superposition, suggests that sequential multiple ionization may provide insight into dynamical correlations in the parent ion. Here, we demonstrate how dynamics of electron correlation can be investigated using laser-induced tunnel ionization by interrogating valence shell electrons in rare gas atoms with intense laser pulses. We find a strong spatial propensity in the sequential double tunnel ionization regime. For instantaneous emission, we find that the two electrons are preferentially emitted in perpendicular directions. Applying laser scanning tunneling microscopy in a pump-probe scheme we directly observe the periodic charge redistribution in the valence shell of singly charged noble gas atoms that was predicted by Santra and coworkers and recently inferred in an attosecond pump-probe experiment using XUV probe pulses. In contrast to single photon ionization, tunneling is highly directional. Here, we exploit that property of tunnel ionization to remove an electron from a rare gas atom along a specific spatial direction. We then probe the correlation by ionizing a second electron via a laser-induced tunneling gate. Since our tunneling gates are optically controlled, the second gate can be opened at any angle and at any time relative to the first. Hence, not only spatial but also temporal variations of the correlation can be probed. We demonstrate the generality of this concept by extending our measurements to a small molecule (HCl).

Staudte, André.

2011-03-01

206

Acoustic Emission Detection Using Fiber Bragg Gratings.  

National Technical Information Service (NTIS)

A systematic study of acoustic emission detection using fiber Bragg grating sensors is presented. In this, we attempt to use the fiber Bragg grating to sense the dynamic strain created by a passing ultrasonic wave signal. Our goal is to see if such a sens...

E. Udd H. Cui I. Perez

2001-01-01

207

Acoustic emission detection using fiber Bragg gratings  

Microsoft Academic Search

A systematic study of acoustic emission detection using fiber Bragg grating sensors has been carried out over the last year. In this, we attempt to use the fiber Bragg grating to sense the dynamic strain created by a passing ultrasonic wave signal. Our goal here is to see if such a sensor is possible, and if so, what the detection

Ignacio M. Perez; Hong-Liang Cui; Eric Udd

2001-01-01

208

Laser-Induced Incandescence in Microgravity  

NASA Technical Reports Server (NTRS)

Knowledge of soot concentration is important due to its presence and impact upon a wide range of combustion processes ranging from diffusion to premixed flames, laminar to turbulent processes and homogeneous to heterogeneous combustion. Measurement of soot volume fraction (f(sub v)) is essential to discerning its formation and growth. The presence of soot also affects other physical and chemical properties of combustion thereby affecting studies not directly concerned with either its formation or growth, such as radiative heat transfer, CO oxidation and fuel vaporization or pyrolysis rates. Microgravity offers unique opportunities for studying both soot growth and the effect of soot radiation upon flame structure and spread. Spatial scales and residence time scales are greatly extended in 0-g facilitating soot growth studies. With the varied geometries, short duration microgravity test times and time-varying processes there is a demand for measurement of f(sub v) with high spatial and temporal resolution. Laser-induced incandescence (LII) has advanced f(sub v) measurements in many 1-g combustion processes. To create laser-induced incandescence, a pulsed high intensity laser heats soot to incandescence temperatures. Using appropriate spectral and temporal detection conditions, the resulting incandescence can be selectively detected apart from the non-laser-heated soot and flame gases. Theoretical modelling and experiments have shown that the resulting incandescence is representative of f(sub v). Using an intensified array camera and a laser sheet for excitation, one- and two-dimensionally resolved LII images of f(sub v) have been obtained in 1-g. LII has been characterized and developed at NASA-Lewis for soot volume fraction determination in a wide range of 1-g combustion applications. Broadly grouped, the characterization work has included studies of excitation intensity, excitation wavelength and the optimum temporal and spectral detection conditions to enable an accurate representation of soot volume fraction by LII. Tests for special requirements imposed by different combustion processes have been performed in laminar and turbulent diffusion flames, rich sooting premixed flames, single droplet combustion, and other heterogeneous combustion. These studies demonstrated LII's high sensitivity, temporal and spatial capabilities and its geometric versatility. In contrast to the advantages offered to combustion studies by a microgravity environment, advanced diagnostics, specifically those requiring pulsed laser diagnostics have been limited due to the size, weight and power limitations in a low-gravity environment. Reported here are the first demonstrations of LII performed in a microgravity environment. Examples are shown for laminar and turbulent gas-jet diffusion flames in 0-g.

VanderWal, Randy L.

1997-01-01

209

Dynamic evolution of the spectrum of long-period fiber Bragg gratings fabricated from hydrogen-loaded optical fiber by ultraviolet laser irradiation  

NASA Astrophysics Data System (ADS)

Long-period fiber Bragg gratings fabricated by exposure of hydrogen-loaded fiber to UV laser light exhibit large-scale dynamic evolution for approximately two weeks at room temperature. During this time two distinct features show up in their spectrum: a large upswing in wavelength and a substantial deepening of the transmission minimum. The dynamic evolution of the transmission spectrum is explained quantitatively by use of Malo's theory of UV-induced quenching [Electron. Lett. 30, 442 (1994)] followed by refilling of hydrogen in the fiber core and the theory of hydrogen diffusion in the fiber material. The amount of hydrogen quenched by the UV irradiation is 6% of the loaded hydrogen.

Fujita, Keio; Masuda, Yuji; Nakayama, Keisuke; Ando, Maki; Sakamoto, Kenji; Mohri, Jun-Pei; Yamauchi, Makoto; Kimura, Masanori; Mizutani, Yasuo; Kimura, Susumu; Yokouchi, Takashi; Suzaki, Yoshifumi; Ejima, Seiki

2005-11-01

210

Surface relief gratings in azobenzene supramolecular systems based on polyimides  

NASA Astrophysics Data System (ADS)

The paper describes formation of new supramolecular azopolymers based on hydrogen bonds as perspective materials for laser induced surface relief gratings (SRGs) and for polarization gratings. Supramolecular films were built on the basis of hydrogen bonds between the functional groups of polymer and azobenzene derivatives, that is 4-[4-(3-hydroxypropyloxy)phenylazo]-pyridine and 4-[4-(6-hydroxyhexyloxy)phenylazo]pyridine. Polymers with imide rings, i.e., poly(esterimide)s and poly(etherimide)s, with phenolic hydroxyl or carboxylic groups were applied as matrixes for polymer-dye supramolecular systems. They revealed glass transition temperatures (Tg) in the range of 170-260 °C, whereas supramolecular systems exhibited lower Tg (88-187 °C). The polymers were easily soluble in aprotic polar solvents and exhibited remarkable good film forming properties. Moreover, new chromophore 4-[4-(3-hydroxypropyloxy)phenylazo]pyridine was synthesized and characterized. The light induced SRGs formation and simultaneous formation of the polarization gratings were explored in prepared polymer-chromophore assembles films using a holographic grating recording technique. First time to the best of our knowledge SRGs were formed in hydrogen-bonded supramolecular systems based on polyimides. The highest SRG amplitude and thus the highest diffraction efficiency were obtained in poly(esterimide)s with the hydroxyl functional group. Additionally, the thermal stability of the photoinduced surface gratings and polarization gratings were tested revealing in the case of the SRGs partial stability and almost complete erasure of the polarization gratings.

Schab-Balcerzak, Ewa; Sobolewska, Anna; Stumpe, Joachim; Hamryszak, Lukasz; Bujak, Piotr

2012-12-01

211

Laser-induced crystallization and crystal growth.  

PubMed

Recent streams of laser studies on crystallization and crystal growth are summarized and reviewed. Femtosecond multiphoton excitation of solutions leads to their ablation at the focal point, inducing local bubble formation, shockwave propagation, and convection flow. This phenomenon, called "laser micro tsunami" makes it possible to trigger crystallization of molecules and proteins from their supersaturated solutions. Femtosecond laser ablation of a urea crystal in solution triggers the additional growth of a single daughter crystal. Intense continuous wave (CW) near infrared laser irradiation at the air/solution interface of heavy-water amino acid solutions results in trapping of the clusters and evolves to crystallization. A single crystal is always prepared in a spatially and temporally controlled manner, and the crystal polymorph of glycine depends on laser power, polarization, and solution concentration. Upon irradiation at the glass/solution interface, a millimeter-sized droplet is formed, and a single crystal is formed by shifting the irradiation position to the surface. Directional and selective crystal growth is also possible with laser trapping. Finally, characteristics of laser-induced crystallization and crystal growth are summarized. PMID:21721131

Sugiyama, Teruki; Masuhara, Hiroshi

2011-11-01

212

Peroxy Radical Measurements via Laser Induced Fluorescence  

NASA Astrophysics Data System (ADS)

We present a newly built Laser Induced Fluorescence (LIF) system to measure the sum of all peroxy radicals (RO2) utilizing chemical conversion to OH. This instrument operates in two different modes: the ROx mode (sum of OH, HO2, and RO2) and the HOx mode (sum of OH and HO2). The HOx mode is used to derive the RO2 data from the ROx measurements. A model approach was used during instrumental development to identify the key parameters needed for the conversion process in front of the detection area and to optimize sensitivity. The instrument was then carefully characterized in various lab experiments, where it could be shown that the wall losses for HO2 are negligible and that nearly all HO2 is converted to OH in front of the detection zone. The pressure and temperature dependencies were also analyzed and assured that the instrument does not show any photolytical interference. As the instrument is calibrated with only one kind of peroxy radicals it was very important that the differences in sensitivity for different peroxy radicals are acceptable. Lab experiments as well as first results from the HOPE 2012 intensive field campaign, which took place in summer 2012 at the Global Atmosphere Watch (GAW) station of the German Weather Service, will be discussed.

Trawny, Katrin; Tatum Ernest, Cheryl; Novelli, Anna; Elste, Thomas; Plaß-Dülmer, Christian; Rudolf, Markus; Martinez, Monica; Harder, Hartwig; Lelieveld, Jos

2013-04-01

213

Laser-Induced Fluorescence in Plasma Processing  

NASA Astrophysics Data System (ADS)

Laser-induced fluorescence (LIF) has been used over 20 years in basic plasma physics and occasionally in plasma processing about 10 years. LIF gives non-perturbing time/space-resolved ion velocity distributions for thermodynamic and transport phenomena and can calibrate energy analyzers and mass flow probes. Complexity and expense limit LIF use; future diode lasers may permit real-time processing metrology. Here LIF examined a Veeco/Ion Tech RF ion beam source and plasma sheaths, comparing LIF distributions to energy analyzer and manufacturer's estimates. LIF distributions show narrower beam spread than energy analyzers (8 vs. 13 eV). Total beam-ion energy, from accelerating grids and plasma potential (frequently not negligible) within the RF source, is found without using manufacturer's estimate. LIF spatial resolution permits measurement of ion flow velocities in the sheath (to 6 km/s) and presheath near a boundary. LIF typically is done on metastable populations of argon, sharing some ground-state ion properties but variations may occur (e.g. metastable population quenching in neutral gas plume outside RF ion beam source). Talk slides at http://HAL9000.ps.uci.edu.

McWilliams, R.; Boehmer, H.; Edrich, D.; Heidbrink, W.; Zhao, L.; Zimmerman, D.

2004-11-01

214

Baicalin attenuates laser-induced choroidal neovascularization.  

PubMed

Abstract Purpose: To determine whether intravitreally-injected baicalin inhibits the growth of choroidal neovascularization (CNV) experimentally induced via laser photocoagulation through analysis of angiogenic factors. Materials and methods: Six CNVs were induced in the left eyes of 8-week-old male Brown Norway rats. Immediately after the induction of CNV, 4??l of baicalin solution (0.1, 1 or 5?nmol) and 4??l of a solution containing 100??g of bevacizumab were slowly injected into the vitreous cavity under direct observation with an operating microscope. At 14 days after CNV induction, fluorescein angiography (FA) was performed, and choroidal flat mounts were produced for quantitative assessment of CNV. The levels of the anti-angiogenic proteins vascular endothelial growth factor (VEGF), platelet-derived growth factor (PDGF) and matrix metalloproteinase-2 (MMP-2) were determined via Western blot analysis. Results: FA of bevacizumab- and baicalin-treated rats showed significantly reduced CNV and leakage from the CNV lesions compared to control rats at day 14. Choroidal flat mounts revealed that baicalin inhibited the growth of CNV lesions in a dose-dependent manner. Western blot analysis demonstrated that baicalin significantly attenuated the up-regulation of VEGF, PDGF and MMP-2. Conclusion: Baicalin suppressed laser-induced CNV formation in rats. These results suggest that baicalin should be considered as a candidate drug for treating exudative age-related macular degeneration. PMID:24502359

Yang, Sung Jae; Jo, Hyoung; Kim, June-Gone; Jung, Sang Hoon

2014-07-01

215

Laser-induced lipolysis on adipose cells  

NASA Astrophysics Data System (ADS)

Recently, a new liposuction technique, using a low-level laser (LLL) device and Ultrawet solution prior to the procedure, demonstrated the movement of fat from the inside to the outside of the adipocyte (Neira et al., 2002). To determine the mechanisms involved, we have performed Scanning and Transmission Electron Microscopy studies; Light transmittance measurements on adipocyte dilutions; and a study of laser light propagation in adipose tissue. This studies show: 1. Cellular membrane alterations. 2. LLL is capable to reach the deep adipose tissue layer, and 3. The tumescence solution enhances the light propagation by clearing the tissue. MRI studies demonstrated the appearance of fat on laser treated abdominal tissue. Besides, adipocytes were cultivated and irradiated to observe the effects on isolated cells. These last studies show: 1. 635 nm-laser alone is capable of mobilizing cholesterol from the cell membrane; this action is enhanced by the presence of adrenaline and lidocaine. 2. Intracellular fat is released from adipocytes by co joint action of adrenaline, aminophyline and 635 nm-laser. Results are consistent with a laser induced cellular process, which causes fat release from the adipocytes into the intercellular space, besides the modification of the cellular membranes.

Solarte, Efrain; Gutierrez, O.; Neira, Rodrigo; Arroyave, J.; Isaza, Carolina; Ramirez, Hugo; Rebolledo, Aldo F.; Criollo, Willian; Ortiz, C.

2004-10-01

216

Laser-induced breakdown spectroscopy: Sparking new applications  

NASA Astrophysics Data System (ADS)

Previously regarded as a laboratory method for the characterization of metal alloys, laser-induced breakdown spectroscopy is now showing great potential for field-based environmental monitoring and biohazard analysis.

Kearton, Bob; Mattley, Yvette

2008-09-01

217

Laser Induced Breakdown in High Pressure Noble Gases.  

National Technical Information Service (NTIS)

Laser induced breakdown is studied both experimentally and analytically in high pressure helium, neon, and argon gases. It is shown that an analysis based on balancing electron production against electron loss yields good agreement with experimental data ...

A. A. Dougal G. W. Haynes

1971-01-01

218

Vacuum ultraviolet laser induced fluorescence on a Si atomic beam  

NASA Technical Reports Server (NTRS)

A broadly applicable vacuum ultraviolet experiment is described for measuring radiative lifetimes of neutral and singly-ionized atoms in a beam environment to 5-percent accuracy using laser induced fluorescence. First results for neutral Si are reported.

O'Brian, T. R.; Lawler, J. E.

1991-01-01

219

Laser-induced synthesis, deposition and etching of materials  

Microsoft Academic Search

The field of laser-induced synthesis, deposition and etching of materials is reviewed with an emphasis on the emerging trends\\u000a and novel adaptations of the basic laser processing concepts. A number of examples are cited to illustrate the issues involved.\\u000a These include rapid synthesis of titanium nitride by pulsed laser induced reactive quenching at Ti:liquid NH3 interface, laser deposition of good

S B Ogale

1988-01-01

220

Nanoscale laser-induced forward transfer through patterned Cr films  

NASA Astrophysics Data System (ADS)

The resolution enhancement of laser-induced forward transfer (LIFT) is investigated through the pre-patterning of Cr on the donor substrate. 85 nm dots are first patterned on a microscope slide, and an 800 nm wavelength and 130 fs pulse laser with a beam waist of ˜9 ?m is used to transfer the Cr dots to an acceptor substrate. The threshold fluence is found to be ˜0.15 the threshold fluence of a similar continuous film, which is thought to be due to the fact that no force is needed to tear away Cr from the film itself, unlike in a continuous film experiment. Since the volume of the material limits the transfer feature sizes instead of the laser parameters, as in a continuous film system, minimum transferable feature diameters are significantly lower compared to the continuous film case. Also, the transferred feature diameters are not dependent on the laser parameters, so the diameters are consistent across a wide range of fluences. The force per unit area generated by the laser at threshold fluence is estimated to be ˜3 GPa, which is consistent with previous results in the literature. The simplified model that our pre-patterned Cr LIFT experiment represents would make it an ideal case for benchmarking molecular dynamics simulations of femtosecond laser ablation.

Sametoglu, V.; Sauer, V.; Tsui, Y. Y.

2013-03-01

221

Laser-Induced Ignition Modeling and Comparison with Experiments  

NASA Astrophysics Data System (ADS)

We have studied experimentally the ignition resulting from optical breakdowns in mixtures of oxygen and the fuel ammonia induced by a 10 nanosecond pulsewidth laser for a time of hundreds of milliseconds using laser spectroscopy. In these studies, we have for the first time characterized the laser-induced plasma, the formation of the combustion radicals, the detonation wave, the flame front and the combustion process itself. The objective of the modeling is to understand the fluid dynamic and chemical kinetic effects following the nominal 10 ns laser pulse until 1 millisecond after laser breakdown. The calculated images match the experimentally recorded data sets and show spatial details covering volumes of 1/10000 cc to 1000 cc. The code was provided by CFD Research Corporation of Huntsville, Alabama, and was appropriately augmented to compute the observed phenomena. The fully developed computational model now includes a kinetic mechanism that implements plasma equilibrium kinetics in ionized regions, and non-equilibrium, multistep, finite rate reactions in non-ionized regions. The predicted fluid phenomena agree with various flow patterns characteristic of laser spark ignition as measured in the CLA laboratories. Comparison of calculated and measured OH and NH concentration will be presented.

Dors, Ivan; Qin, W.; Chen, Y.-L.; Parigger, C.; Lewis, J. W. L.

2000-11-01

222

Holographic Gratings for Optical Processing  

NASA Technical Reports Server (NTRS)

Investigation of astronomical objects and tracking of man-made space objects lead to generation of huge amount of information for optical processing. Traditional big-size optical elements (such as optical telescopes) have a tendency for increasing aperture size in order to improve sensitivity. This tendency leads to increasing of weight and costs of optical systems and stimulate search for the new, more adequate technologies. One approach to meet these demands is based on developing of holographic optical elements using new polymeric materials. We have investigated possibility to use new material PQ-PMMA (phenantrenequinone-doped PMMA (Polymethyl Methacrylate)) for fabrication of highly selective optical filters and fast spatial-temporal light modulators. This material was originally developed in Russia and later was tested in CalTech as a candidate material for optical storage. Our theoretical investigation predicts the possibility of realization of fast spatial and temporal light modulation, using volume reflection-type spectral filter. We have developed also model of holographic-grating recording in PQ-PMMA material, based on diffusional amplification. This mechanism of recording allow to receive high diffraction efficiency during recording of reflection-type volume holographic grating (holographic mirror). We also investigated recording of dynamic gratings in the photorefractive crystals LiNbO3 (LN) for space-based spectroscopy and for adaptive correction of aberrations in the telescope's mirrors. We have shown, that specific 'photogalvanic' mechanism of holographic grating recording in LN allow to realize recording of blazed gratings for volume and surface gratings. Possible applications of dynamic gratings in LN for amplification of images, transmitted through an imaging fiber guide was also demonstrated.

Kukhtarev, Nickolai

2002-01-01

223

Dynamic Sensing Performance of a Point-Wise Fiber Bragg Grating Displacement Measurement System Integrated in an Active Structural Control System  

PubMed Central

In this work, a fiber Bragg grating (FBG) sensing system which can measure the transient response of out-of-plane point-wise displacement responses is set up on a smart cantilever beam and the feasibility of its use as a feedback sensor in an active structural control system is studied experimentally. An FBG filter is employed in the proposed fiber sensing system to dynamically demodulate the responses obtained by the FBG displacement sensor with high sensitivity. For comparison, a laser Doppler vibrometer (LDV) is utilized simultaneously to verify displacement detection ability of the FBG sensing system. An optical full-field measurement technique called amplitude-fluctuation electronic speckle pattern interferometry (AF-ESPI) is used to provide full-field vibration mode shapes and resonant frequencies. To verify the dynamic demodulation performance of the FBG filter, a traditional FBG strain sensor calibrated with a strain gauge is first employed to measure the dynamic strain of impact-induced vibrations. Then, system identification of the smart cantilever beam is performed by FBG strain and displacement sensors. Finally, by employing a velocity feedback control algorithm, the feasibility of integrating the proposed FBG displacement sensing system in a collocated feedback system is investigated and excellent dynamic feedback performance is demonstrated. In conclusion, our experiments show that the FBG sensor is capable of performing dynamic displacement feedback and/or strain measurements with high sensitivity and resolution.

Chuang, Kuo-Chih; Liao, Heng-Tseng; Ma, Chien-Ching

2011-01-01

224

Dynamic sensing performance of a point-wise fiber Bragg grating displacement measurement system integrated in an active structural control system.  

PubMed

In this work, a fiber Bragg grating (FBG) sensing system which can measure the transient response of out-of-plane point-wise displacement responses is set up on a smart cantilever beam and the feasibility of its use as a feedback sensor in an active structural control system is studied experimentally. An FBG filter is employed in the proposed fiber sensing system to dynamically demodulate the responses obtained by the FBG displacement sensor with high sensitivity. For comparison, a laser Doppler vibrometer (LDV) is utilized simultaneously to verify displacement detection ability of the FBG sensing system. An optical full-field measurement technique called amplitude-fluctuation electronic speckle pattern interferometry (AF-ESPI) is used to provide full-field vibration mode shapes and resonant frequencies. To verify the dynamic demodulation performance of the FBG filter, a traditional FBG strain sensor calibrated with a strain gauge is first employed to measure the dynamic strain of impact-induced vibrations. Then, system identification of the smart cantilever beam is performed by FBG strain and displacement sensors. Finally, by employing a velocity feedback control algorithm, the feasibility of integrating the proposed FBG displacement sensing system in a collocated feedback system is investigated and excellent dynamic feedback performance is demonstrated. In conclusion, our experiments show that the FBG sensor is capable of performing dynamic displacement feedback and/or strain measurements with high sensitivity and resolution. PMID:22247683

Chuang, Kuo-Chih; Liao, Heng-Tseng; Ma, Chien-Ching

2011-01-01

225

Formation of laser-induced periodic surface structures on niobium by femtosecond laser irradiation  

NASA Astrophysics Data System (ADS)

The surface morphology of a Niobium sample, irradiated in air by a femtosecond laser with a wavelength of 800 nm and pulse duration of 100 fs, was examined. The period of the micro/nanostructures, parallel and perpendicularly oriented to the linearly polarized fs-laser beam, was studied by means of 2D Fast Fourier Transform analysis. The observed Laser-Induced Periodic Surface Structures (LIPSS) were classified as Low Spatial Frequency LIPSS (periods about 600 nm) and High Spatial Frequency LIPSS, showing a periodicity around 300 nm, both of them perpendicularly oriented to the polarization of the incident laser wave. Moreover, parallel high spatial frequency LIPSS were observed with periods around 100 nm located at the peripheral areas of the laser fingerprint and overwritten on the perpendicular periodic gratings. The results indicate that this method of micro/nanostructuring allows controlling the Niobium grating period by the number of pulses applied, so the scan speed and not the fluence is the key parameter of control. A discussion on the mechanism of the surface topology evolution was also introduced.

Pan, A.; Dias, A.; Gomez-Aranzadi, M.; Olaizola, S. M.; Rodriguez, A.

2014-05-01

226

Single cell transfection by laser-induced breakdown of an optically trapped gold nanoparticle  

NASA Astrophysics Data System (ADS)

Cell selective introduction of therapeutic agents remains a challenging problem. Cavitation-based therapies including ultrasound-induced sonoporation and laser-induced optoporation have led the way for novel approaches to provide the potential of sterility and cell selectivity compared with viral or biochemical counterparts. Acoustic streaming, shockwaves and liquid microjets associated with the cavitation dynamics are implicated in gene and drug delivery. These approaches, however, often lead to non-uniform and sporadic molecular uptake that lacks refined spatial control and suffers from a significant loss of cell viability. Here we demonstrate spatially controlled cavitation instigated by laser-induced breakdown of an optically trapped single gold nanoparticle. Our unique approach employs optical tweezers to trap a single nanoparticle, which when irradiated by a nanosecond laser pulse is subject to laser-induced breakdown followed by cavitation. Using this method for laser-induced cavitation, we can gain additional degrees of freedom for the cavitation process - the particle material, its size, and its position relative to cells or tissues. We show the energy breakdown threshold of gold nanoparticles of l00nm with a single nanosecond laser pulse at 532 nm is three orders of magnitude lower than that for water, which leads to gentle nanocavitation enabling single cell transfection. We optimize the shear stress to the cells from the expanding bubble to be in the range of 1-10 kPa for transfection by precisely positioning a trapped gold nanoparticle, and thus nanobubble, relative to a cell of interest. The method shows transfection of plasmid-DNA into individual mammalian cells with an efficiency of 75%.

Arita, Yoshihiko; Ploschner, Martin; Antkowiak, Maciej; Gunn-Moore, Frank; Dholakia, Kishan

2014-03-01

227

Fiber grating spectra  

Microsoft Academic Search

In this paper, we describe the spectral characteristics that can be achieved in fiber reflection (Bragg) and transmission gratings. Both principles for understanding and tools for designing fiber gratings are emphasized. Examples are given to illustrate the wide variety of optical properties that are possible in fiber gratings. The types of gratings considered include uniform, apodized, chirped, discrete phase-shifted, and

T. Erdogan

1997-01-01

228

Self-excitation of lasing in lithium niobate during recording of dynamic phase gratings by circular photogalvanic currents  

NASA Astrophysics Data System (ADS)

Lasing in plane-parallel lithium niobate samples doped with 0.03 wt pct Fe was observed and investigated for the first time. It was excited by focused radiation from a helium-cadmium laser with the ordinary polarization. It was found that lasing was a consequence of formation of a volume phase holographic grating by the excitation of circular photogalvanic currents oscillating in space. Measurements of the threshold angles of lasing yielded the maximum gain and internal losses in the resonator of such a lithium niobate laser.

Odulov, S. G.

1984-03-01

229

ARTICLES: Self-excitation of lasing in lithium niobate during recording of dynamic phase gratings by circular photogalvanic currents  

NASA Astrophysics Data System (ADS)

Lasing in plane-parallel lithium niobate samples doped with 0.03 wt. % Fe was observed and investigated for the first time. It was excited by focused radiation from a helium-cadmium laser with the ordinary polarization. It was found that lasing was a consequence of formation of a volume phase holographic grating by the excitation of circular photogalvanic currents oscillating in space. Measurements of the threshold angles of lasing yielded the maximum gain and internal losses in the resonator of such a lithium niobate laser.

Odulov, S. G.

1984-03-01

230

Diffraction gratings for optical sensing  

NASA Astrophysics Data System (ADS)

The following document summarizes a journey through the world of diffraction gratings, covering topics such as their history, fabrication, metrology, and uses in some of the most precise scientific experiments ever proposed. Though diffraction gratings have long been used for spectroscopy and pulse compression, it was not until recently that researchers have explored their ability to split and recombine single-frequency CW laser sources for high-precision interferometry. Gravitational-wave detection, one of the most challenging sensing applications to date, is being investigated by the Laser Interferometer Gravitational-Wave Observatory (LIGO) and Laser Interferometer Space Antenna (LISA) projects. Future generations of LIGO and LISA detectors may incorporate gratings as key optical components. This thesis describes the ways gratings can improve interferometer performance by simplifying thermal management and discusses the essential challenges that must be overcome before they can be adopted. The use of gratings requires new interferometer geometries. We show cases where these can be implemented simply and compactly. Gravitational-wave interferometry imposes many requirements on grating components. Using improved metrology methods, we demonstrate that large dielectric gratings with uniformly high efficiency can be fabricated and validated. In particular, we measure the diffraction efficiency of two 20-cm-scale gratings over their entire apertures. The values taken from across their surfaces collectively had means and standard deviations of mu = 99.293% and sigma = 0.164%, and mu =99.084% and sigma =0.079%. We also present simplified models of thermal distortions in gratings, and show them to be in good agreement with measurements conducted by a wavefront sensor. Special focus is given to experimental demonstrations that have achieved highly precise measurements of translational and rotational motion, also known as displacement and angular sensing. For the former, resonant-cavity methods that have achieved both high sensitivity and high dynamic range (10 pm/?Hz at 1 Hz over 620 nm) are described. For the latter, a novel device known as the grating angular sensor that has achieved a sensitivity level of 0.2 nrad/?Hz at 1 kHz is presented.

Lu, Patrick P.

231

Laser-Induced Fluorescence Diagnostics in Plasmas  

NASA Astrophysics Data System (ADS)

Laser-Induced Fluorescence (LIF) diagnostics in plasmas constitutes a largish corpus of techniques which may be thought of as active forms of spectroscopy, or the exploitation of atomic physics developments for plasma physics purposes. Starting from first principles, we will derive the fundamental concepts and equations underlying typical LIF schemes. We also present the basics of popular applications such as the measurement of ion temperatures and electric and magnetic fields, discuss basic technological developments and realistically confront limitations. In the simplest LIF scheme, a "pump" laser tuned to resonance with an atomic transition is beamed into the plasma containing atomic or ionic "target" particles prepared in an appropriate initial quantum state. Absorption of a pump photon changes the target particle's quantum state, e.g. to a short-lived intermediate level which decays to a final state, emitting a second photon. The relationship between absorbed and re-radiated radiation spectra and directions yields a vast range of plasma properties which cannot be measured non-perturbatively in any other way. For instance, the spectrum of the re-radiated photons in low-density plasmas is dominated by the Doppler effect, and is easily unfolded to yield the Boltzmann velocity distribution. From the quantum viewpoint, the preceding is evidently a two-photon process. A direct approach to the rate or cross-section for this class of processes, which also includes well-known phenomena such as Rayleigh and Raman scattering, is through the use of the Kramers-Heisenberg formula, which we work out from first principles. Due to the extremely high value of the cross-sections for resonance fluorescence, typically 6 orders of magnitude larger than atomic cross-sections, relatively modest laser intensities suffice to generate large signals. One can therefore use narrow laser beams and short-duration pulses to achieve diagnostics with exceptionally high space and time resolution. Note also that the diagnostic scheme, which alters only the quantum nature of the plasma particles, does not affect (except in extreme cases) the classical plasma properties, and is therefore eminently non-perturbative. Work supported by the National Science Foundation under Grant No. PHY-9215015

Stern, R. A.

1997-11-01

232

Laser-Induced Damage of Calcium Fluoride  

SciTech Connect

As advances continue to be made in laser technology there is an increasing demand for materials that have high thresholds for laser-induced damage. Laser damage occurs when light is absorbed, creating defects in the crystal lattice. These defects can lead to the emission of atoms, ions and molecules from the sample. One specific field where laser damage is of serious concern is semiconductor lithography, which is beginning to use light at a wavelength of 157 nm. CaF2 is a candidate material for use in this new generation of lithography. In order to prevent unnecessary damage of optical components, it is necessary to understand the mechanisms for laser damage and the factors that serve to enhance it. In this research, we study various aspects of laser interactions with CaF2, including impurity absorbance and various forms of damage caused by incident laser light. Ultraviolet (UV) laser light at 266 nm with both femtosecond (fs) and nanosecond (ns) pulse widths is used to induce ion and neutral particle emission from cleaved samples of CaF2. The resulting mass spectra show significant differences suggesting that different mechanisms for desorption occur following excitation using the different pulse durations. Following irradiation by ns pulses at 266 nm, multiple single-photon absorption from defect states is likely responsible for ion emission whereas the fs case is driven by a multi-photon absorption process. This idea is further supported by the measurements made of the transmission and reflection of fs laser pulses at 266 nm, the results of which reveal a non-linear absorption process in effect at high incident intensities. In addition, the kinetic energy profiles of desorbed Ca and K contaminant atoms are different indicating that a different mechanism is responsible for their emission as well. Overall, these results show that purity plays a key role in the desorption of atoms from CaF2 when using ns pulses. On the other hand, once the irradiance reaches high levels, like that of the fs case, significant desorption is possible due to multi-photon absorption by the intrinsic material.

Espana, A.; Joly, A.G.; Hess, W.P.; Dickinson, J.T.

2004-01-01

233

Advanced experimental applications for x-ray transmission gratings spectroscopy using a novel grating fabrication method  

SciTech Connect

A novel fabrication method for soft x-ray transmission grating and other optical elements is presented. The method uses focused-ion-beam technology to fabricate high-quality free standing grating bars on transmission electron microscopy grids. High quality transmission gratings are obtained with superb accuracy and versatility. Using these gratings and back-illuminated CCD camera, absolutely calibrated x-ray spectra can be acquired for soft x-ray source diagnostics in the 100-3000 eV spectral range. Double grating combinations of identical or different parameters are easily fabricated, allowing advanced one-shot application of transmission grating spectroscopy. These applications include spectroscopy with different spectral resolutions, bandwidths, dynamic ranges, and may serve for identification of high-order contribution, and spectral calibrations of various x-ray optical elements.

Hurvitz, G.; Ehrlich, Y.; Shpilman, Z.; Levy, I.; Fraenkel, M. [Plasma Physics Department, Applied Physics Division, Soreq NRC, Yavne (Israel); Strum, G. [Solid State Department, Applied Physics Division, Soreq NRC, Yavne (Israel)

2012-08-15

234

Laser-induced breakdown spectroscopy analysis of asbestos  

NASA Astrophysics Data System (ADS)

Laser-induced breakdown spectroscopy was applied to test the possibility of detecting and identifying asbestos in different samples in view of the perspective at field operation without sample preparation which is peculiar to this technique. Several like-resin materials were first investigated by laser-induced breakdown spectroscopy, in order to find an asbestos container assuring safe laboratory operation during the material characterization aimed to identify indicators suitable for a quick identification on field. Successively, spectra of asbestos samples of both in serpentine and amphibole forms were measured and the variability in elemental composition was calculated from the emission spectra. Ratios of intensities of characteristic elements were tested as indicators for asbestos recognition. Laser-induced breakdown spectroscopy results were compared with those obtained by analyzing the same asbestos samples with a scanning electron microscopy equipped with an energy dispersive X-ray spectroscopy, a good correlation was found for Mg/Si and Fe/Si, thus showing the capability of laser-induced breakdown spectroscopy as a diagnostic tool for this category of materials. In particular, it was demonstrated that the method based on two indicators derived from laser-induced breakdown spectroscopy intensity ratios allows to discriminate between asbestos and cements in single shot measurements suitable to field operation.

Caneve, L.; Colao, F.; Fabbri, F.; Fantoni, R.; Spizzichino, V.; Striber, J.

2005-08-01

235

Diffractive coherence in multilayer dielectric gratings  

SciTech Connect

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.

Shore, B.W.; Feit, M.D.; Perry, M.D.; Boyd, R.D.; Britten, J.A. [Lawrence Livermore National Lab., CA (United States); Li, Lifeng [Arizona Univ., Tucson, AZ (United States). Optical Sciences Center

1995-05-26

236

Multilayer diffraction grating  

DOEpatents

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.

Barbee, T.W. Jr.

1990-04-10

237

Multilayer diffraction grating  

DOEpatents

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.

Barbee, Jr., Troy W. (Palo Alto, CA)

1990-01-01

238

Polymer micro-fiber Bragg grating.  

PubMed

Polymer micro-fibers with inscribed Bragg gratings are reported in this Letter. Starting with a single-mode polymer optical fiber and implementing a two-stage tapering process, a 16 ?m diameter micro-fiber is fabricated and a Bragg grating is inscribed in it that exhibits a peak reflected wavelength circa 1530 nm. The growth dynamics of the polymer micro-fiber Bragg grating are also observed and analyzed. A maximum reflectivity of 5% is obtained after an exposure time of 3 min to a 50 mW power He-Cd laser of 325 nm wavelength. The temperature and strain characterization results of the micro-fiber Bragg grating with different diameters are also presented. Such polymer micro-fiber Bragg gratings can be used as sensors for high-sensitivity measurements in a number of application areas. PMID:23988957

Rajan, Ginu; Noor, Muhammad Yusof Mohd; Lovell, Nigel H; Ambikaizrajah, Eliathamby; Farrell, Gerald; Peng, Gang-Ding

2013-09-01

239

Estimation of mechanical properties of a viscoelastic medium using a laser-induced microbubble interrogated by an acoustic radiation force.  

PubMed

An approach to assess the mechanical properties of a viscoelastic medium using laser-induced microbubbles is presented. To measure mechanical properties of the medium, dynamics of a laser-induced cavitation microbubble in viscoelastic medium under acoustic radiation force was investigated. An objective lens with a 1.13 numerical aperture and an 8.0 mm working distance was designed to focus a 532 nm wavelength nanosecond pulsed laser beam and to create a microbubble at the desired location. A 3.5 MHz ultrasound transducer was used to generate acoustic radiation force to excite a laser-induced microbubble. Motion of the microbubble was tracked using a 25 MHz imaging transducer. Agreement between a theoretical model of bubble motion in a viscoelastic medium and experimental measurements was demonstrated. Young's modulii reconstructed using the laser-induced microbubble approach were compared with those measured using a direct uniaxial method over the range from 0.8 to 13 kPa. The results indicate good agreement between methods. Thus, the proposed approach can be used to assess the mechanical properties of a viscoelastic medium. PMID:21973379

Yoon, Sangpil; Aglyamov, Salavat R; Karpiouk, Andrei B; Kim, Seungsoo; Emelianov, Stanislav Y

2011-10-01

240

Laser-induced fluorescence of space-exposed polyurethane  

NASA Technical Reports Server (NTRS)

The object of this work was to utilize laser-induced fluorescence technique to characterize several samples of space-exposed polyurethane. These samples were flown on the Long Duration Exposure Facility (LDEF), which was in a shuttle-like orbit for nearly 6 years. Because of our present work to develop laser-induced-fluorescence inspection techniques for polymers, space-exposed samples and controls were lent to us for evaluation. These samples had been attached to the outer surface of LDEF; therefore, they were subjected to thermal cycling, solar ultraviolet radiation, vacuum, and atomic oxygen. It is well documented that atomic oxygen and ultraviolet exposure have detrimental effects on many polymers. This was a unique opportunity to make measurements on material that had been naturally degraded by an unusual environment. During our past work, data have come from artificially degraded samples and generally have demonstrated a correlation between laser-induced fluorescence and tensile strength or elasticity.

Hill, Ralph H., Jr.

1993-01-01

241

Sticking of droplets on slippery superhydrophobic surfaces by laser induced forward transfer  

NASA Astrophysics Data System (ADS)

Liquid jets created by the Laser Induced Forward Transfer (LIFT) technique can reach extremely high speeds exceeding 270 m/s. The impact of such a jet on a solid surface can create a dynamic pressure of 35 MPa, enabling the LIFT process to stick liquid droplets on highly slippery superhydrophobic surfaces. In this letter, we demonstrate how LIFT printing can be utilized in order to achieve selective sticky behavior on slippery surfaces, valuable for many biosensor applications, and we suggest it as a tool of evaluating the thermodynamic robustness of the so called Fakir states on various rough hydrophobic surfaces.

Boutopoulos, Christos; Papageorgiou, Dimitrios P.; Zergioti, Ioanna; Papathanasiou, Athanasios G.

2013-07-01

242

Quantitative characterization of a nonreacting, supersonic combustor flowfield using unified, laser-induced iodine fluorescence  

NASA Technical Reports Server (NTRS)

A calibrated, nonintrusive optical technique, laser-induced iodine fluorescence (LIIF) was used to quantify the steady, compressible flowfield of a nonreacting, supersonic combustor. The combustor was configured with single and staged, transverse-air injection into a supersonic-air freestream behind a rearward-facing step. Pressure, temperature, two-velocity components, and injectant mole fraction were measured with high spatial resolution in the three-dimensional flowfields. These experimental results provide a benchmark set of data for validation of computational fluid dynamic (CFD) codes being developed to model supersonic combustor flowfields.

Fletcher, D. G.; Mcdaniel, J. C.

1989-01-01

243

Molecular-level mechanisms of nanoparticle detachment in laser-induced plasma shock waves  

SciTech Connect

Detachment and detachment mechanisms of nanoparticles from flat surfaces subjected to shock waves are investigated by employing molecular gas dynamic simulations using the direct simulation Monte Carlo method and experimental transient pressure data. Two mechanisms for nanoparticle detachment based on rolling moment resistance of the adhesion bond and the elastic restitution effect are introduced. As a result of present simulations, it is computationally demonstrated that the pulsed laser-induced shock waves can generate sufficient rolling moments to detach sub-100-nm particles and initiate removal. The transient moment exerted on a 60 nm polystyrene latex particle on a silicon substrate is presented and discussed.

Zhou Dong; Cetinkaya, Cetin [Department of Mechanical and Aeronautical Engineering, Center for Advanced Materials Processing, Clarkson University, Potsdam, New York 13699-5725 (United States)

2006-04-24

244

Fiber-bragg grating-loop ringdown method and apparatus  

DOEpatents

A device comprising a fiber grating loop ringdown (FGLRD) system of analysis is disclosed. A fiber Bragg grating (FBG) or Long-Period grating (LPG) written in a section of single mode fused silica fiber is incorporated into a fiber loop. By utilizing the wing areas of the gratings' bandwidth as a wavelength dependent attenuator of the light transmission, a fiber grating loop ringdown concept is formed. One aspect of the present invention is temperature sensing, which has been demonstrated using the disclosed device. Temperature measurements in the areas of accuracy, stability, high temperature, and dynamic range are also described.

Wang, Chuji (Starkville, MS) [Starkville, MS

2008-01-29

245

Laser-induced crystalline optical waveguide in glass fiber format.  

PubMed

We report on the first fabrication of a glass fiber based laser-induced crystalline waveguide. The glass and crystal are based on the stoichiometric composition of (La,Yb)BGeO(5). A laser induced waveguide has been fabricated on the surface of a ribbon glass fiber using milliwatt-level continuous wave UV laser radiation at a fast scanning speed. Evidence of crystallinity in the created structure was observed using micro-Raman spectroscopy and scanning electron microscopy. Preliminary investigations on the waveguiding behavior and the nonlinear performance in the crystalline waveguide are reported. PMID:23262917

Feng, Xian; Shi, Jindan; Huang, Chung-Che; Horak, Peter; Teh, Peh Siong; Alam, Shaif-ul; Ibsen, Morten; Loh, Wei H

2012-12-10

246

Femtosecond laser induced surface melting and nanojoining for plasmonic circuits  

NASA Astrophysics Data System (ADS)

Femtosecond laser induced nonthermal processing is an emerging nanofabrication technique for delicate plasmonic devices. In this work we present a detailed investigation on the interaction between ultra-short pulses and silver nanomaterials, both experimentally and theoretically. We systematically study the laser-silver interaction at a laser fluent from 1 J/m2 to 1 MJ/m2. The optimal processing window for welding of silver nanowires occurs at fluences of 200-450 J/m2. The femtosecond laser-induced surface melting allows precise welding of silver nanowires for "T" and "X" shape circuits. These welded plasmonic circuits are successfully applied for routining light propagation.

Hu, A.; Deng, G. L.; Courvoisier, S.; Reshef, O.; Evans, C. C.; Mazur, E.; Zhou, Y.

2013-09-01

247

Physical model for the laser induced forward transfer process  

NASA Astrophysics Data System (ADS)

This paper presents a numerical model which describes the underlying physical processes during laser induced forward transfer. The laser induced forward transfer uses a pulsed laser to transfer thin layers from a transparent support to a substrate. The model predicts the threshold energies Eth as well as the blow-off time tblow, thus allowing a profound physical understanding of the transfer process. The good agreement of simulated with measured Eth and tblow of thin nickel layers demonstrates the accuracy of the model. The model shows that gasification of the soda-lime glass support is the main driving force of the transfer process.

Röder, Tobias C.; Köhler, Jürgen R.

2012-02-01

248

Study on characteristics of optical bistable devices based on fiber Bragg grating  

NASA Astrophysics Data System (ADS)

The simulation model to bistable characteristics of grating is established by numerically solving the nonlinear coupledmode equations of Fiber Bragg Grating using 3-stage 4-order semi-implicit Runge - Kutta method. The impact of the grating parameters and operating point on S-shaped hysteresis loop parameters is researched. The results show that the area of S-shaped hysteresis loop, bistable operating condition, bistable threshold and dynamic range can be adjusted by changing the operating wavelength and grating parameters, such as grating length, grating apodization and average refractive index modulation depth of grating.

Peng, Yongjun; Qiu, Kun; Wu, Baojian; Ji, Siwei

2009-11-01

249

Design of a novel laser-induced fluorescence spectrophotometer for water quality monitor based on virtual instrument and linear CCD  

NASA Astrophysics Data System (ADS)

Since the water resource is being seriously polluted with the development of the human society, the monitoring of the available water resource is an impending task. The concentration of the dissolved organic matter, oxygen and inorganic salt in water can be checked by means of some methods, e.g. electrolysis, electrochemical method, colorimetry. But because some drawbacks are existed in these methods, the laser-induced fluorescence (LIF) spectrophotometry method is adopted into this paper. And a novel LIF spectrophotometer for water quality monitor (WQM) is designed. In this WQM, the 3rd harmonic of the Q switched Nd:YAG laser is used as the induced fluorescence light-source. And for the splitting-light system of the spectrophotometer for WQM, in order to improve the resolution and light-passing efficiency, a novel volume holography transmissive(VHT) grating is used as the diffraction grating instead of the plane or holography grating. Meanwhile, the linear CCD with combined data acquisition (DAQ) card is used as the fluorescence spectral detection system and virtual instrument (VI) technology based on LabVIEW is used to control the spectral acquisition and analysis. Experimental results show that the spatial resolution of the novel spectrophotometer for WQM is improved, its resolution can reach 2nm. And the checking accuracy of this WQM is higher than others. Therefore, the novel LIF spectrophotometer for WQM has the potential value in the water quality monitoring and biochemical application.

Ren, Zhong; Huang, Shuanggen; Liu, Guodong; Huang, Zhen; Zeng, Lvming

2011-06-01

250

Laser Induced Aluminum Surface Breakdown Model.  

National Technical Information Service (NTIS)

Laser powered propulsion systems involve complex fluid dynamics, thermodynamics and radiative transfer processes. Based on an unstructured grid, pressure-based computational aerothermodynamics; platform, several sub-models describing such underlying physi...

Y. S. Chen J. Liu S. Zhang

2002-01-01

251

Cooled Echelle Grating Spectrometer.  

National Technical Information Service (NTIS)

A cooled echelle grating spectrometer for detecting wavelengths between one micrometers and fifteen micrometers is described. More specifically, a spectrometer is disclosed, having a cross-dispersing grating for ordering infrared energy, and an echelle gr...

R. Beer

1978-01-01

252

Improved Performance (Transmission) Gratings.  

National Technical Information Service (NTIS)

Results of the study produced the following conclusions: higher line density gratings could be produced immediately by superimposing existing gratings (after reducing wire widths); unwanted higher orders could be reduced by chemical treatment of existing ...

P. L. Csonka

1978-01-01

253

Concave Diffraction Gratings.  

National Technical Information Service (NTIS)

The report summarizes the need for concave diffraction gratings in ultraviolet, visible, and near infra-red spectroscopy, and provides a brief resume of the relative merits of ruled gratings and those generated using interference or 'holographic' techniqu...

M. C. Hutley

1985-01-01

254

Detection of uranium in solids by using laser-induced breakdown spectroscopy combined with laser-induced fluorescence  

SciTech Connect

Detection of uranium in solids by using laser-induced breakdown spectroscopy has been investigated in combination with laser-induced fluorescence. An optical parametric oscillator wavelength-tunable laser was used to resonantly excite the uranium atoms and ions within the plasma plumes generated by a Q-switched Nd:YAG laser. Both atomic and ionic lines can be selected to detect their fluorescence lines. A uranium concentration of 462 ppm in a glass sample can be detected by using this technique at an excitation wavelength of 385.96 nm for resonant excitation of U II and a fluorescence line wavelength of 409.0 nm from U II.

Shen, X. K.; Lu, Y. F

2008-04-10

255

Adaptable Diffraction Gratings With Wavefront Transformation  

NASA Technical Reports Server (NTRS)

Diffraction gratings are optical components with regular patterns of grooves, which angularly disperse incoming light by wavelength. Traditional diffraction gratings have static planar, concave, or convex surfaces. However, if they could be made so that they can change the surface curvature at will, then they would be able to focus on particular segments, self-calibrate, or perform fine adjustments. This innovation creates a diffraction grating on a deformable surface. This surface could be bent at will, resulting in a dynamic wavefront transformation. This allows for self-calibration, compensation for aberrations, enhancing image resolution in a particular area, or performing multiple scans using different wavelengths. A dynamic grating gives scientists a new ability to explore wavefronts from a variety of viewpoints.

Iazikov, Dmitri; Mossberg, Thomas W.; Greiner, Christoph M.

2010-01-01

256

Short-pulse Laser Induced Transient Structure Formation and Ablation Studied with Time-resolved Coherent XUV-scattering  

NASA Astrophysics Data System (ADS)

The structural dynamics of short-pulse laser irradiated surfaces and nano-structures has been studied with nm spatial and ultrafast temporal resolution by means of single-shot coherent XUV-scattering techniques. The experiments allowed us to time-resolve the formation of laser-induced periodic surface structures, and to follow the expansion and disintegration of nano-objects during laser ablation.

Sokolowski-Tinten, Klaus; Barty, Anton; Boutet, Sebastien; Shymanovich, Uladzimir; Chapman, Henry; Bogan, Mike; Marchesini, Stefano; Hau-Riege, Stefan; Stojanovic, Nikola; Bonse, Jörn; Rosandi, Yudi; Urbassek, Herbert M.; Tobey, Ra'anan; Ehrke, Henri; Cavalleri, Andrea; Düsterer, Stefan; Redlin, Harald; Frank, Matthias; Bajt, Sasa; Schulz, Joachim; Seibert, Marvin; Hajdu, Janos; Treusch, Rolf; Bostedt, Christoph; Hoener, M.; Möller, T.

2010-10-01

257

Catwalk grate lifting tool  

DOEpatents

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.

Gunter, L.W.

1992-08-11

258

Modern topics in standardized laser-induced damage threshold measurements  

Microsoft Academic Search

Although the measurement of the laser-induced damage threshold is a field of permanent research effort since the late 1960s, the optimization of the damage handling capability is still a key issue for the development of high performance laser systems. In conjunction with the ever increasing demand for lasers with high average power, energy, extreme wavelengths or short pulses, the resistance

K. Starke; H. Blaschke; M. Jupé; M. Lappschies; D. Ristau

2005-01-01

259

Laser induced amplification of hypersound in nondegenerate semiconductor superlattices  

NASA Astrophysics Data System (ADS)

Laser induced amplification of hypersound in a nondegenerate semiconductor superlattice has been studied. It is shown that there exists a threshold laser field intensity E0 for which the hypersound attenuation coefficient ?q may change sign and thus become amplified. It is also noted that the superlattice, while amplifying, also serves as a filter, i.e. allows waves of definite frequencies.

Mensah, S. Y.; Allotey, F. K. A.; Mensah, N. G.; Elloh, V. W.

2003-01-01

260

Laser-Induced Instabilities in Raman-Active Media.  

National Technical Information Service (NTIS)

Laser-induced instabilities in Raman-active media are studied. The stimulated Raman scattering process is found to be important in benzene even for a Stokes conversion rate of a few percent. Growth rates are obtained by numerical analysis, using equations...

K. A. Brueckner S. S. Rangnekar

1968-01-01

261

Laser–Induced Fluorescence Detection of Carbamates Traces in Water  

Microsoft Academic Search

The absorption and fluorescence spectra of carbaryl (CB), carbofuran (CF) and carbendazim (MBC) have been studied. Fluorescence lifetime and fluorescence quantum yields are also reported as well as the influence of pH, solvent and presence of humic acids on fluorescence. The limit of detection (LD) of the three compounds has been measured by direct analysis by laser-induced fluorescence (LIF) using

Laure Burel-Deschamps; Philippe Giamarchi; Ludovic Stephan; Yves Lijour; Alain Le Bihan

2006-01-01

262

Laser-induced multiphoton dissociation of n-butyl ether  

NASA Astrophysics Data System (ADS)

The pulsed CO 2-laser-induced multiphoton dissociation of n-butyl vinyl ether is studied. Comprehensive measurements have been performed for 9.6.?m and 10.6 ?m irradiation. The corresponding dissociation product distributions show distinct differences for the two irradiation wavelengths, the most important finding being that acetylene is only produced at 9.6 ?m.

Hofmann, Hubert; Kl?ffer, Waiter; Sch?fer, Gerhard; Gloor, Jean

1981-04-01

263

Plasma erosion rate diagnostics using laser-induced fluorescence  

NASA Technical Reports Server (NTRS)

An optical technique for measuring the sputtering rate of a molybdenum surface immersed in a xenon plasma has been developed and demonstrated. This approach, which may be useful in real-time wear diagnostics for ion thrusters, relies on laser-induced fluorescence to determine the density of sputtered molybdenum atoms.

Gaeta, C. J.; Turley, R. S.; Matossian, J. N.; Beattie, J. R.; Williamson, W. S.

1992-01-01

264

Laser-induced fluorescence of HCF and HCCl  

NASA Astrophysics Data System (ADS)

We report the first observation of the laser-induced fluorescence excitation spectrum of the à 1A'(000)-X˜ 1A'(010) vibronic band of HCF and some subbands of the à 1A'(030) and à 1A'(040)-X˜ 1A'(000) vibronic bands of HCCl, using the technique of molecular beams.

Qiu, Yuanwu; Zhou, Shikang; Shi, Jiliang

1987-04-01

265

Laser-Induced Damage Measurements with 266-NM Pulses.  

National Technical Information Service (NTIS)

The results of a survey of laser-induced damage thresholds for optical components at 266 nm are reported. The thresholds were measured at two pulse durations--0.150 ns and 1.0 ns. The 30 samples tested include four commercial dielectric reflectors, three ...

T. F. Deaton W. L. Smith

1980-01-01

266

Isotope-selective measurements in a laser-induced plasma  

Microsoft Academic Search

In laser induced plasma spectroscopy (LIPS), a laser beam of sufficient energy is focused onto the surface of a solid sample in order to produce a plasma. The plasma can be monitored by several spectroscopic techniques. However, optical emission spectroscopy has by far been the most popular method of choice. The goal of this work was to evaluate the use

Leslie Anthony King

1998-01-01

267

Quantitative analysis using remote laser-induced breakdown spectroscopy (LIBS)  

Microsoft Academic Search

A measurement system for quantitative, remote materials analysis has been realised. It is based on the method of laser-induced breakdown spectroscopy (LIBS), utilising an optical fibre system, both to deliver the laser radiation to the sample specimen and to collect the light emission from the luminous plasma plume. Distances of up to 100 m between the remote location and the

C. M. Davies; H. H. Telle; D. J. Montgomery; R. E. Corbett

1995-01-01

268

Mechanisms of pulsed laser induced damage to optical coatings  

Microsoft Academic Search

Laser induced damage in optical components is the limiting factor in the design of high power lasers. This problem is addressed with special emphasis placed on the optical coatings used on the components. A theoretical model is developed assuming basic mechanisms which lead to damage of the coatings. Numerical results are generated and compared with experimental data. The basic procedure

Michael R. Lange

1986-01-01

269

Analysis of Atomic Beams Produced by Laser-Induced Ablation  

Microsoft Academic Search

Pulsed atomic beams with flux densities above 1016 cm-2 s-1 have been produced in vacuum with high reproducibility by laser induced ablation from titanium and iron targets. The power of the TEA CO2 laser was kept at a level where plasma production at the target surface was avoided: no ions were detectable. The beams were analysed by laser fluorescence. The

K P Selter; H-J Kunze

1982-01-01

270

Metal pattern deposition by laser-induced forward transfer  

Microsoft Academic Search

Results of a systematic study on laser-induced transfer of metal patterns are summarized. The pulse width of the lasers used in the experiments was scaled from a few nanoseconds to one millisecond to discover the different time-dependent processes determining ablation and transfer of thin films of a variety of metals. The physical events were followed by optical and electron microscopy

Z. Kántor; Z. Tóth; T. Szörényi

1995-01-01

271

Overview of applications of Laser-Induced Breakdown Spectroscopy (LIBS)  

SciTech Connect

Laser-induced breakdown spectroscopy (LIBS) is a method of performing elemental analyses of solids, liquids, and gases using the microplasma produced by a focused laser pulse. Because the microplasma is formed by optical radiation, LIBS has some important advantages compared to conventional laboratory based analytical methods. Three applications are discussed which use the LIBS method. 6 refs., 8 figs., 2 tabs.

Cremers, D.A.

1987-01-01

272

Laser-Induced Breakdown Spectroscopy of Trace Metals  

NASA Technical Reports Server (NTRS)

An alternative approach for laser-induced breakdown spectroscopy (LIBS) determination of trace metal determination in liquids is demonstrated. The limits of detection (LOD) for the technique ranged from 10 ppb to 10 ppm for 15 metals metals (Mg, Al, Si, Ca, Ti, Cr, Fe, Co, Ni, Cu, Zn, As, Cd, Hg, Pb) tested.

Simons, Stephen (Technical Monitor); VanderWal, Randall L.; Ticich, Thomas M.; West, Joseph R., Jr.

2004-01-01

273

Neuroprotective Therapy for Argon-Laser Induced Retinal Injury  

Microsoft Academic Search

Laser photocoagulation treatment of the central retina is often complicated by an immediate side effect of visual impairment, caused by the unavoidable laser-induced destruction of the normal tissue lying adjacent to the lesion and not affected directly by the laser beam. Furthermore, accidental laser injuries are at present untreatable. A neuroprotective therapy for salvaging the normal tissue might enhance the

M. ROSNER; Y. SOLBERG; J. TURETZ; M. BELKIN

1997-01-01

274

Double pulse laser ablation and plasma: Laser induced breakdown spectroscopy signal enhancement  

Microsoft Academic Search

A review of recent results of the studies of double laser pulse plasma and ablation for laser induced breakdown spectroscopy applications is presented. The double pulse laser induced breakdown spectroscopy configuration was suggested with the aim of overcoming the sensitivity shortcomings of the conventional single pulse laser induced breakdown spectroscopy technique. Several configurations have been suggested for the realization of

V. I. Babushok; F DELUCIAJR; J. L. Gottfried; C. A. Munson; A. W. Miziolek

2006-01-01

275

Investigating the role of superdiffusive currents in laser induced demagnetization of ferromagnets with nanoscale magnetic domains.  

PubMed

Understanding the loss of magnetic order and the microscopic mechanisms involved in laser induced magnetization dynamics is one of the most challenging topics in today's magnetism research. While scattering between spins, phonons, magnons and electrons have been proposed as sources for dissipation of spin angular momentum, ultrafast spin dependent transport of hot electrons has been pointed out as a potential candidate to explain ultrafast demagnetization without resorting to any spin dissipation channel. Here we use time resolved magneto-optical Kerr measurements to extract the influence of spin dependent transport on the demagnetization dynamics taking place in magnetic samples with alternating domains with opposite magnetization directions. We unambiguously show that whatever the sample magnetic configuration, the demagnetization takes place during the same time, demonstrating that hot electrons spin dependent transfer between neighboring domains does not alter the ultrafast magnetization dynamics in our systems with perpendicular anisotropy and 140 nm domain sizes. PMID:24722395

Moisan, N; Malinowski, G; Mauchain, J; Hehn, M; Vodungbo, B; Lüning, J; Mangin, S; Fullerton, E E; Thiaville, A

2014-01-01

276

Investigating the role of superdiffusive currents in laser induced demagnetization of ferromagnets with nanoscale magnetic domains  

PubMed Central

Understanding the loss of magnetic order and the microscopic mechanisms involved in laser induced magnetization dynamics is one of the most challenging topics in today's magnetism research. While scattering between spins, phonons, magnons and electrons have been proposed as sources for dissipation of spin angular momentum, ultrafast spin dependent transport of hot electrons has been pointed out as a potential candidate to explain ultrafast demagnetization without resorting to any spin dissipation channel. Here we use time resolved magneto-optical Kerr measurements to extract the influence of spin dependent transport on the demagnetization dynamics taking place in magnetic samples with alternating domains with opposite magnetization directions. We unambiguously show that whatever the sample magnetic configuration, the demagnetization takes place during the same time, demonstrating that hot electrons spin dependent transfer between neighboring domains does not alter the ultrafast magnetization dynamics in our systems with perpendicular anisotropy and 140?nm domain sizes.

Moisan, N.; Malinowski, G.; Mauchain, J.; Hehn, M.; Vodungbo, B.; Luning, J.; Mangin, S.; Fullerton, E. E.; Thiaville, A.

2014-01-01

277

Novel immersion grating, VPH grating, and quasi-Bragg grating  

Microsoft Academic Search

We have successfully fabricated germanium immersion gratings with resolving power of 45,000 at 10 mum by using a nano precision 3D grinding machine and ELID (ELectrolytic In-process Dressing) method. However the method spends large amount of machine times. We propose grooves shape with a new principle for a solid grating, which achieves high performance and lower cost. We have developed

Noboru Ebizuka; Keiko Oka; Akiko Yamada; Masako Kashiwagi; Kashiko Kodate; Koji S. Kawabata; Mariko Uehara; Chie Nagashima; Kotaro Ichiyama; Takashi Ichikawa; Tomoyuki Shimizu; Shinya Morita; Yutaka Yamagata; Hitoshi Omori; Hitoshi Tokoro; Yasuhiro Hirahara; Shuji Sato; Masanori Iye

2006-01-01

278

Multilayer dielectric diffraction gratings  

DOEpatents

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.

Perry, Michael D. (Livermore, CA); Britten, Jerald A. (Oakley, CA); Nguyen, Hoang T. (Livermore, CA); Boyd, Robert (Livermore, CA); Shore, Bruce W. (Livermore, CA)

1999-01-01

279

Multilayer dielectric diffraction gratings  

DOEpatents

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.

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

1999-05-25

280

Investigation of the early stages in laser-induced ignition by Schlieren photography and laser-induced fluorescence spectroscopy  

Microsoft Academic Search

Laser ignition has been discussed widely as a potentially superior ignition source for technical appliances such as internal combustion engines. Ignition strongly affects overall combustion, and its early stages in particular have strong implications on subsequent pollutant formation, flame quenching, and extinction. Our research here is devoted to the experimental investigation of the early stages of laser-induced ignition of CH4\\/air

Maximilian Lackner; S. Charareh; F. Winter; K. F. Iskra; D. Rüdisser; T. Neger; H. Kopecek; E. Wintner

2004-01-01

281

[Simultaneous quantitative analysis of multielements in Al alloy samples by laser-induced breakdown spectroscopy].  

PubMed

The multielement components of some aluminium alloy samples were quantified by using laser-induced breakdown spectroscopy (LIBS). The Nd : YAG pulsed laser was used to produce plasma in ambient air. The spectral range of 200-980 nm was simultaneously obtained through a multichannel grating spectrometer and CCD detectors. The authors studied the influences of time delays, energy of the laser, and depth profile of elements in samples on spectral intensity, and optimized the experimental parameters based on the influence analysis. With the optimal experimental parameters, the authors made the calibration curves by four certified aluminum alloy samples for eight elements, Si, Fe, Cu, Mn, Mg, Zn, Sn, and Ni, and quantified the composition of an aluminum sample. The obtained maximum relative standard deviation (RSD) was 5.89%, and relative errors were--20.99%-15%. Experimental results show that LIBS is an effective technique for quantitative analysis of aluminum alloy samples, though the improved accuracy of the quantitative analysis is necessary. PMID:20210173

Sun, Lan-Xiang; Yu, Hai-Bin

2009-12-01

282

Laser-induced IR fluorescence spectra of simulant chemical threat agent and exhaust vapors. Technical report  

SciTech Connect

Infrared (IR) fluorescence spectra have been measured for several agent/exhaust simulants illuminated by a slowly (10-200 Hz) chopped infrared absorption spectra when excited by a grating tuned 5 watt CO{sub 2} (9 - 11 microns) laser. Utilizing a calibrated spectral measurement apparatus, the spectra are presented in terms of the actual quantity of fluorescence energy emitted from a unit volume of vapor and wavelength span for a given set of excitation conditions (laser wavelength, power, and chop frequency) and simulant pressure. The addition of air to small quantities (10 - 30 Torr) of the simulants quenches, but does not completely extinguish, the fluorescence. A linear increase in the infrared fluorescence intensity with laser chopping period is observed along with very slow (msec) rise and decay times of the fluorescence signal. These observations are attributed to the bulk heating of the vapor or vapor-air mixture along the laser beam path due to the slow chopping frequencies. These results indicate the possible utilization of laser-induced infrared fluorescence in remote sensing of chemical vapors of interest to the Army (agents/vehicle exhausts).

Bossoli, R.B.; Thomson, G.M.

1990-04-01

283

Measurement of Fluorescence Spectra from Ambient Aerosol Particles Using Laser-induced Fluorescence Technique  

NASA Astrophysics Data System (ADS)

To obtain the information of composition of organic aerosol particles in atmosphere, we developed an instrument using laser-induced fluorescence (LIF) technique. To measure the fluorescence from a particle, we employed two lasers. Scattering light signal derived from a single particle upon crossing the 635nm-CW laser triggers the 266nm-pulsed laser to excite the particle. Fluorescence from the particle in the wavelength range 300-600nm is spectrally dispersed by a grating spectrometer and then detected by a 32-Ch photo-multiplier tube(PMT). The aerosol stream is surrounded by a coaxial sheath air flow and delivered to the optical chamber at atmospheric pressure. Using PSL particles with known sizes, we made a calibration curve to estimate particle size from scattering light intensity. With the current setup of the instrument we are able to detect both scattering and fluorescence from particles whose diameters are larger than 0.5um. Our system was able to differentiate particles composed of mono-aromatic species (e.g. Tryptophan) from those of Riboflavin, by their different fluorescence wavelengths. Also, measurements of fluorescence spectra of ambient particles were demonstrated in our campus in Yokosuka city, facing Tokyo bay in Japan. We obtained several types of florescence spectra in the 8 hours. Classification of the measured fluorescence spectra will be discussed in the presentation.

Taketani, F.; Kanaya, Y.; Nakamura, T.; Moteki, N.; Takegawa, N.

2011-12-01

284

Laser Induced Aluminum Surface Breakdown Model  

NASA Technical Reports Server (NTRS)

Laser powered propulsion systems involve complex fluid dynamics, thermodynamics and radiative transfer processes. Based on an unstructured grid, pressure-based computational aerothermodynamics; platform, several sub-models describing such underlying physics as laser ray tracing and focusing, thermal non-equilibrium, plasma radiation and air spark ignition have been developed. This proposed work shall extend the numerical platform and existing sub-models to include the aluminum wall surface Inverse Bremsstrahlung (IB) effect from which surface ablation and free-electron generation can be initiated without relying on the air spark ignition sub-model. The following tasks will be performed to accomplish the research objectives.

Chen, Yen-Sen; Liu, Jiwen; Zhang, Sijun; Wang, Ten-See (Technical Monitor)

2002-01-01

285

Laser Induced Aluminum Surface Breakdown Model  

NASA Technical Reports Server (NTRS)

Laser powered propulsion systems involve complex fluid dynamics, thermodynamics and radiative transfer processes. Based on an unstructured grid., pressure-based computational aerothermodynamics, platform, several sub-nio"'dels describing such underlying physics as laser ray tracing and focusing, thermal non-equilibrium, plasma radiation and air spark ignition have been developed. This proposed work shall extend the numerical platform and existing sub-models to include the aluminum wall surface Inverse Bremsstrahlung (113) effect from which surface ablation and free-electron generation can be initiated without relying on the air spark ignition sub-model. The following tasks will be performed to accomplish the research objectives.

Chen, Yen-Sen; Liu, Jiwen; Zhang, Sijun; Wnag, Ten-See (Technical Monitor)

2001-01-01

286

Quantifying pulsed laser induced damage to graphene  

NASA Astrophysics Data System (ADS)

As an emerging optical material, graphene's ultrafast dynamics are often probed using pulsed lasers yet the region in which optical damage takes place is largely uncharted. Here, femtosecond laser pulses induced localized damage in single-layer graphene on sapphire. Raman spatial mapping, SEM, and AFM microscopy quantified the damage. The resulting size of the damaged area has a linear correlation with the optical fluence. These results demonstrate local modification of sp2-carbon bonding structures with optical pulse fluences as low as 14 mJ/cm2, an order-of-magnitude lower than measured and theoretical ablation thresholds.

Currie, Marc; Caldwell, Joshua D.; Bezares, Francisco J.; Robinson, Jeremy; Anderson, Travis; Chun, Hayden; Tadjer, Marko

2011-11-01

287

Temporal behavior of neutral and ionic lines emitted from a laser induced plasma on an aqueous surface  

NASA Astrophysics Data System (ADS)

The temporal behavior of spectral lines emitted from a laser induced plasma has been studied. The plasma was created by using a Nd:YAG pulsed laser in air at atmospheric pressure focused on the surface of an aqueous solution. This work is an extension of previous published work [J. Ben Ahmed, Z. Ben Lakhdar, G. Taieb, Kinetics of laser induced plasma on an aqueous surface, Laser chem. 20 (2002) 123-134.]. The time evolution of lines intensities emitted from Ca, Ca +, Mg and Mg + has been experimentally observed and simulated using a simple theoretical approach based on electron-ion recombination. It was shown that the plasma temperature and electron density are correlated to the dynamics of plasma emission. Finally, the time evolution of the optical depth of Ca + resonance line at 393.4 nm was also studied.

Ahmed, J. Ben; Jaïdane, N.

2009-05-01

288

Laser-induced multi-energy processing in diamond growth  

NASA Astrophysics Data System (ADS)

Laser-induced multi-energy processing (MEP) introduces resonant vibrational excitations of precursor molecules to conventional chemical vapor deposition methods for material synthesis. In this study, efforts were extended to explore the capability of resonant vibrational excitations for promotion of energy efficiency in chemical reactions, for enhancement of diamond deposition, and for control of chemical reactions. The research project mainly focused on resonant vibrational excitations of precursor molecules using lasers in combustion flame deposition of diamond, which led to: 1) promotion of chemical reactions; 2) enhancement of diamond growth with higher growth rate and better crystallizations; 3) steering of chemical reactions which lead to preferential growth of {100}-oriented diamond films and crystals; and 4) mode-selective excitations of precursor molecules toward bond-selective control of chemical reactions. Diamond films and crystals were deposited in open air by combustion flame deposition through resonant vibrational excitations of precursor molecules, including ethylene (C2H4) and propylene (C3H 6). A kilowatt wavelength-tunable CO2 laser with spectral range from 9.2 to 10.9 microm was tuned to match vibrational modes of the precursor molecules. Resonant vibrational excitations of these molecules were achieved with high energy efficiency as compared with excitations using a common CO2 laser (fixed wavelength at 10.591microm). With resonant vibrational excitations, the diamond growth rate was increased; diamond quality was promoted; diamond crystals with lengths up to 5 mm were deposited in open air; preferential growth of {100}-oriented diamond films and single crystals was achieved; mode-selective excitations of precursor molecules were investigated toward control of chemical reactions. Optical emission spectroscopy (OES), mass spectrometry (MS), and molecular dynamic simulations were conducted to obtain an in-depth understanding of the resonant vibrational excitations. Species concentrations in flames without and with laser excitations under different wavelengths were investigated both experimentally and theoretically. Detection of C2, CH, and OH radicals, as well as CxHy species and their oxides (CxH yO) (x=1, 2; y=0˜5) using OES and MS, together with reaction pathway simulations, were used to explain the effect of vibrational excitations of precursor molecules on chemical reactions and on diamond depositions.

Xie, Zhiqiang

289

Validation of Laser-Induced Fluorescent Photogrammetric Targets on Membrane Structures  

NASA Technical Reports Server (NTRS)

The need for static and dynamic characterization of a new generation of inflatable space structures requires the advancement of classical metrology techniques. A new photogrammetric-based method for non-contact ranging and surface profiling has been developed at NASA Langley Research Center (LaRC) to support modal analyses and structural validation of this class of space structures. This full field measurement method, known as Laser-Induced Fluorescence (LIF) photogrammetry, has previously yielded promising experimental results. However, data indicating the achievable measurement precision had not been published. This paper provides experimental results that indicate the LIF-photogrammetry measurement precision for three different target types used on a reflective membrane structure. The target types were: (1) non-contact targets generated using LIF, (2) surface attached retro-reflective targets, and (3) surface attached diffuse targets. Results from both static and dynamic investigations are included.

Jones, Thomas W.; Dorrington, Adrian A.; Shortis, Mark R.; Hendricks, Aron R.

2004-01-01

290

Flame-enhanced laser-induced breakdown spectroscopy.  

PubMed

Flame-enhanced laser-induced breakdown spectroscopy (LIBS) was investigated to improve the sensitivity of LIBS. It was realized by generating laser-induced plasmas in the blue outer envelope of a neutral oxy-acetylene flame. Fast imaging and temporally resolved spectroscopy of the plasmas were carried out. Enhanced intensity of up to 4 times and narrowed full width at half maximum (FWHM) down to 60% for emission lines were observed. Electron temperatures and densities were calculated to investigate the flame effects on plasma evolution. These calculated electron temperatures and densities showed that high-temperature and low-density plasmas were achieved before 4 µs in the flame environment, which has the potential to improve LIBS sensitivity and spectral resolution. PMID:24718144

Liu, L; Li, S; He, X N; Huang, X; Zhang, C F; Fan, L S; Wang, M X; Zhou, Y S; Chen, K; Jiang, L; Silvain, J F; Lu, Y F

2014-04-01

291

Probing nanotubes and red blood cells with laser-induced cavitation bubbles  

NASA Astrophysics Data System (ADS)

A spatial light modulator (SLM) is used to simultaneously create arrays of laser-induced cavitation bubbles. The different bubble geometries result in the creation of a directed, transient and strong liquid flow. Due to the fast dynamics of the cavitation bubbles the flow is actuated on very short temporal (?s) and spatial (?m) scales. We show two examples of the use of laser-induced cavitation bubbles to probe and manipulate small objects: multiwalled carbon nanotubes (MWCNT) and red blood cells (RBCs). In the case of MWCNT, we use a pair of bubbles to displace and bend the nanotubes. By measuring the time it takes for the nanotube to recover its original shape we can estimate the flexural rigidity and the bending modulus. The shape recovery is recorded with a high-speed camera at up to 300,000 frames per second (fps). We found the flexural rigidity to be on the range of 0.98 -- 6.6 x 10-19 Nm^2 and the Young's modulus on the order of 0.06-0.6 TPa for MWCNT with an average diameter of 117.8 ± 6.7 nm and a thickness of 4.6 ± 0.75 nm. A similar approach is used to study the mechanical properties of RBC's, where multiple cells are elongated due to the radial flow induced by a single bubble. We study the shape recovery of the RBCs and find a significant difference when they are treated with an enzyme.

Quinto-Su, Pedro; Huang, Xiaohu; Kuss, Claudia; Gonzalez, Roberto; Preiser, Peter; Wu, Tom; Ohl, Claus-Dieter

2009-11-01

292

Planar laser-induced fluorescence imaging in shock tube flows  

Microsoft Academic Search

The planar laser-induced fluorescence (PLIF) imaging method was used to perform flow visualization and quantitative planar\\u000a thermometry in shock tube flow fields using toluene as a fluorescence tracer in nitrogen. Fluorescence quantum yield values\\u000a needed to quantify PLIF images were measured in a static cell at low pressures (<1 bar) for various toluene partial pressures\\u000a in nitrogen bath gas. Images behind

J. Yoo; D. Mitchell; D. F. Davidson; R. K. Hanson

2010-01-01

293

Laser-induced fluorescence spectroscopy for combustion diagnostics  

NASA Technical Reports Server (NTRS)

The types of spectroscopic and collisional measurements that are needed to develop laser-induced fluorescence as a diagnostic technique are discussed, with emphasis placed on combustion measurements. The spectroscopic measurements under collision-free conditions include production of radicals, excitation scan studies, lifetime measurements, and fluorescence scans. The collisional studies discussed here are quenching, energy transfer, and polarization phenomena. The results of recent laboratory experiments are presented.

Crosley, D. R.; Smith, G. P.

1983-01-01

294

Laser-induced incandescence applied to droplet combustion  

NASA Technical Reports Server (NTRS)

Laser-induced incandescence (LII) is ideally suited for obtaining high temporally and spatially resolved measurements of soot volume fraction in transient combustion phenomena. We demonstrate qualitative two-dimensional nonintrusive optical measurements of the soot evolution versus time from single fiber-supported burning fuel droplets of heptane and decane. Quantitative measurement of the soot volume fraction is also demonstrated through calibration of the LII signal against a small coflow ethylene diffusion flame.

VanderWal, Randall L.; Dietrich, Daniel L.

1995-01-01

295

Excimer laser induced etching of InP  

Microsoft Academic Search

We report 193 nm ArF excimer laser induced etching of InP in Cl2. Etching occurs by desorption of an In-chloride layer, as evidenced by an etch rate which increases linearly with laser repetition rate and is nearly pressure independent between 2 and 50 mTorr Cl2. At substrate temperatures near 150 °C, the etch rate increases above a ‘‘threshold’’ fluence of

V. M. Donnelly; T. R. Hayes

1990-01-01

296

Laser-induced single step micro\\/nanopatterning  

Microsoft Academic Search

Recent achievements in laser-induced surface patterning obtained in our group are summarized. Here, we have employed both a SNOM-type setup and two-dimensional lattices of SiO2 microspheres formed by self-assembly processes. With the SNOM-type setup we have demonstrated nanoscale photochemical and photothermal etching, mainly of Si in Cl2 atmosphere. With 2D lattices of microspheres a large number of single features can

Dieter Bäuerle; Gerard Wysocki; Lars Landström; Johannes Klimstein; Klaus Piglmayer; Johannes Heitz

2003-01-01

297

Laser-Induced Fluorescence Helps Diagnose Plasma Processes  

NASA Technical Reports Server (NTRS)

Technique developed to provide in situ monitoring of rates of ion sputter erosion of accelerator electrodes in ion thrusters also used for ground-based applications to monitor, calibrate, and otherwise diagnose plasma processes in fabrication of electronic and optical devices. Involves use of laser-induced-fluorescence measurements, which provide information on rates of ion etching, inferred rates of sputter deposition, and concentrations of contaminants.

Beattie, J. R.; Mattosian, J. N.; Gaeta, C. J.; Turley, R. S.; Williams, J. D.; Williamson, W. S.

1994-01-01

298

Detection of beryllium by laser-induced-breakdown spectroscopy  

NASA Astrophysics Data System (ADS)

Using the new technique of laser-induced-breakdown spectroscopy (LIBS) a limit of detection was measured for beryllium in air of 0.5 ng/g ( w/w), which is one-third of the OSHA limit for the 8-h average exposure to beryllium. Approximately linear working curves were obtained over the concentration range 0.5 to 2 × 10 4 ng g -1. The potential application of this technique to a beryllium monitoring instrument is discussed.

Radziemski, Leon J.; Cremers, David A.; Loree, Thomas R.

299

Hydrodynamic efficiency of laser-induced transfer of matter  

SciTech Connect

A one-dimensional analytic hydrodynamic model of the direct laser-induced transfer of matter is considered. The efficiency of pulsed laser radiation energy conversion to the kinetic energy of the ejected matter is determined. It is shown that the hydrodynamic efficiency of the process for the layers of matter of thickness exceeding the laser radiation absorption depth is determined by the adiabatic index of the evaporated matter. (laser applications and other topics in quantum electronics)

Isakov, Vladimir A; Kanavin, Andrey P; Nasibov, A S [P.N. Lebedev Physics Institute, Russian Academy of Sciences, Moscow (Russian Federation)

2007-04-30

300

Laser-induced chemistry of the allyl halides  

NASA Astrophysics Data System (ADS)

The continuous wave CO2 laser-induced chemistry of several allyl halides has been studied at various pressures and laser powers. The majority of products observed in these reactions are also reported in gas phase pyrolysis. From the kinetic studies of allyl chloride and bromide, overall reaction orders were determined. New reaction mechanisms for formation of cyclic products based upon results obtained in these reactions have been proposed.

McDonald, J. K.; Merritt, J. A.; McManus, S. P.

1986-08-01

301

Laser-induced gas breakdown - Spectroscopic and chemical studies.  

NASA Technical Reports Server (NTRS)

Discussion of the results of several experimental investigations on laser-induced gas breakdown. The experiments included time-resolved spectroscopy, direct detection of H atoms with a TiO2 probe, and chemical reactions; each of them provided insight into the behavior of the medium at different times. Chemical reactions and explosions have been initiated by the laser beam when a plasma was created. No primary multiphotonic absorption and no macroscopic chemical reactions were observed below the breakdown threshold.

De Montgolfier, PH.; Dumont, P.; Mille, Y.; Villermaux, J.

1972-01-01

302

Laser-induced luminescence of xenon implanted natural diamond  

Microsoft Academic Search

We report here on laser-induced luminescence studies of the Xe ion related optical center in diamond. The sample with the Xe center was a natural diamond (type Ia) irradiated with 500keV Xe ions at room temperature with the dose 1×1013cm?2 and annealed at 1400C. The Xe center exhibits an isolated zero phonon line (ZPL) at 811.7nm (1.527eV) and a weak

V. A. Martinovich; A. A. Gorokhovsky

2004-01-01

303

Laser-induced surface modification and metallization of polymers  

Microsoft Academic Search

Laser-induced surface modification of different polymers is presented as a suitable pretreatment of surfaces in a two-step metallization process. Materials such as polyamide (PA), polypropylene (PP), polystyrene (PS), polycarbonate (PC), acrylbutadienestyrene (ABS), styreneacrylnitrile (SAN), polybutadieneterephthalate (PBT), and polyoxymethylene (POM) were treated by excimer-laser radiation at 248 nm in air. The aim of this study is to investigate different processing regimes

H. Frerichs; J. Stricker; D. A. Wesner; E. W. Kreutz

1995-01-01

304

Laser-induced fluorescence of the CD2CFO radical  

Microsoft Academic Search

The laser-induced fluorescence spectrum of the B~ 2A''-->X~ 2A'' transition of the CD2CFO radical has been observed in the region 316-335 nm. The radical was produced by 193 nm photolysis or by fluorine atom reaction with acetyl-d3 fluoride. The spectrum of CD2CFO was similar to that of CH2CFO reported previously except for small isotope shifts in the range 7-343 cm-1.

Satoshi Inomata; Masashi Furubayashi; Takashi Imamura; Nobuaki Washida; Makoto Yamaguchi

1999-01-01

305

Study of fast laser induced cutting of silicon materials  

NASA Astrophysics Data System (ADS)

We report on a fast machining process for cutting silicon wafers using laser radiation without melting or ablating and without additional pretreatment. For the laser induced cutting of silicon materials a defocused Gaussian laser beam has been guided over the wafer surface. In the course of this, the laser radiation caused a thermal induced area of tension without affecting the material in any other way. With the beginning of the tension cracking process in the laser induced area of tension emerged a crack, which could be guided by the laser radiation along any direction over the wafer surface. The achieved cutting speed was greater than 1 m/s. We present results for different material modifications and wafer thicknesses. The qualitative assessment is based on SEM images of the cutting edges. With this method it is possible to cut mono- and polycrystalline silicon wafers in a very fast and clean way, without having any waste products. Because the generated cracking edge is also very planar and has only a small roughness, with laser induced tension cracking high quality processing results are easily accessible.

Weinhold, S.; Gruner, A.; Ebert, R.; Schille, J.; Exner, H.

2014-03-01

306

Atomic and molecular emissions in laser-induced breakdown spectroscopy  

NASA Astrophysics Data System (ADS)

This article summarizes measurements and analysis of hydrogen Balmer series atomic lines following laser-induced optical breakdown. Electron number density on the order of 1 × 1025 m- 3 can be measured using H? Stark width and shift in the analysis of breakdown plasma in 1 to 1.3 × 105 Pa, gaseous hydrogen. The H? line can be utilized for electron number density up to 7 × 1023 m- 3. The historic significance is elaborated of accurate H? measurements. Electron excitation temperature is inferred utilizing Boltzmann plot techniques that include H? atomic lines and further members of the Balmer series. Laser ablation of aluminum is discussed in view of limits of application of the Balmer series. H? and H? lines show presence of molecular carbon in a 2.7 and 6.5 × 105 Pa, expanding methane flow. Diagnostic of such diatomic emission spectra is discussed as well. Laser-induced breakdown spectroscopy historically embraces elemental analysis, or atomic spectroscopy, and to a lesser extent molecular spectroscopy. Yet occurrence of superposition spectra in the plasma decay due to recombination or due to onset of chemical reactions necessitates consideration of both atomic and molecular emissions following laser-induced optical breakdown. Molecular excitation temperature is determined using so-called modified Boltzmann plots and fitting of spectra from selected molecular transitions. The primary interest is micro-plasma characterization during the first few micro-seconds following optical breakdown, including shadowgraph visualizations.

Parigger, Christian G.

2013-01-01

307

Laser-Induced Modification Of Energy Bands Of Transparent Solids  

SciTech Connect

Laser-induced variations of electron energy bands of transparent solids significantly affect the initial stages of laser-induced ablation (LIA) influencing rates of ionization and light absorption by conduction-band electrons. We analyze fast variations with characteristic duration in femto-second time domain that include: 1) switching electron functions from bonding to anti-bonding configuration due to laser-induced ionization; 2) laser-driven oscillations of electrons in quasi-momentum space; and 3) direct distortion of the inter-atomic potential by electric field of laser radiation. Among those effects, the latter two have zero delay and reversibly modify band structure taking place from the beginning of laser action. They are of special interest due to their strong influence on the initial stage and threshold of laser ablation. The oscillations modify the electron-energy bands by adding pondermotive potential. The direct action of radiation's electric field leads to high-frequency Franz-Keldysh effect (FKE) spreading the allowed electron states into the forbidden-energy bands. FKE provides decrease of the effective band gap while the electron oscillations lead either to monotonous increase or oscillatory variations of the gap. We analyze the competition between those two opposite trends and their role in initiating LIA.

Gruzdev, Vitaly [Department of Mechanical and Aerospace Engineering, College of Engineering University of Missouri, Columbia, MO 65211 (United States)

2010-10-08

308

Dynamic measurements on narrow linewidth complex coupled 1.55 ?m DFB lasers with gain and index grating in antiphase  

Microsoft Academic Search

We report on dynamic measurements on antiphase complex coupled 1.55 ?m DFB lasers. The antiphase complex coupling mechanism is realized by periodically etching the active layer and quarternary InGaAsP overgrowth. This new fabrication approach results in very narrow linewidths measured on devices with rather short resonator lengths. The minimum linewidth for a 375 ?m long ridge waveguide laser was only

R. Schreiner; M. Mulot; J. Wiedmann; W. Coenning; J. Porsche; J. L. Gentner; M. Berroth; F. Scholz; H. Schwizer

1999-01-01

309

Non-linear optical studies of adsorbates: Spectroscopy and dynamics  

SciTech Connect

In the first part of this thesis, we have established a systematic procedure to apply the surface optical second-harmonic generation (SHG) technique to study surface dynamics of adsorbates. In particular, we have developed a novel technique for studies of molecular surface diffusions. In this technique, the laser-induced desorption with two interfering laser beams is used to produce a monolayer grating of adsorbates. The monolayer grating is detected with diffractions of optical SHG. By monitoring the first-order second-harmonic diffraction, we can follow the time evolution of the grating modulation from which we are able to deduce the diffusion constant of the adsorbates on the surface. We have successfully applied this technique to investigate the surface diffusion of CO on Ni(111). The unique advantages of this novel technique will enable us to readily study anisotropy of a surface diffusion with variable grating orientation, and to investigate diffusion processes of a large dynamic range with variable grating spacings. In the second part of this work, we demonstrate that optical infrared-visible sum-frequency generation (SFG) from surfaces can be used as a viable surface vibrational spectroscopic technique. We have successfully recorded the first vibrational spectrum of a monolayer of adsorbates using optical infrared-visible SFG. The qualitative and quantitative correlation of optical SFG with infrared absorption and Raman scattering spectroscopies are examined and experimentally demonstrated. We have further investigated the possibility to use transient infrared-visible SFG to probe vibrational transients and ultrafast relaxations on surfaces. 146 refs.

Zhu, Xiangdong.

1989-08-01

310

Reflective diffraction grating  

DOEpatents

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.

Lamartine, Bruce C. (Los Alamos, NM)

2003-06-24

311

X-ray reflection by multilayer surface gratings  

NASA Astrophysics Data System (ADS)

X-ray reflection by multilayer gratings has been investigated theoretically and experimentally. A theoretical treatment based on the DWBA method has been developed and compared with the full dynamical and the kinematical approaches. All three theories are treated in one uniform formalism, removing the usual restrictions of the Fraunhofer approximation in order to simplify the direct numerical comparison. Contrary to the wide spread opinion the DWBA shows good agreement especially for the intense grating truncation rods. The regions of validity of the DWBA are proved by exact dynamical calculations. The dynamical diffraction by the multilayered grating has been formulated by a matrix formalism generalizing the Fresnel transmission and reflection coefficients for diffraction, which describe the interaction of the scattering by different grating truncation rods. The concept of Ewald's sphere allows a transparent interpretation of the different scattering phenomena and the influence of Umweganregung on the scattering pattern. The theories are applied on first experimental results of epitaxial multilayer gratings.

Mikul?´k, Petr; Baumbach, Tilo

1998-06-01

312

Integrated Grating Spectrometer  

NASA Technical Reports Server (NTRS)

Proposed integrated grating spectrometer made in waveguide layer on silicon wafer. Occupies area of about 2 centimeters to 2nd power on wafer 0.4 mm thick. Operates in visible spectrum (wavelengths of 400 to 700 nm) and blazed to diffract in first order. Array of integrated grating spectrometers performs spectral analysis of picture elements along line. Optical fiber couples light from each picture element into separate integrated spectrometer. Technique enables continous independent variation, along grating, of pitch, curvature, and blaze angle. Grating designed to have large numerical aperture, zero aberration at two selected wavelengths, and very low aberration at intermediate wavelengths.

Lang, Robert J.

1990-01-01

313

Polarimetry of transmission gratings  

NASA Astrophysics Data System (ADS)

We have investigated the polarizing properties of gold wire gratings in the resonance domain. The partial polarizing properties of 1- mu m period gratings in the near IR are then used to orient the wire structure of transmission grating facets parallel to each other by means of an alignment polarimeter technique. The absolute alignment accuracy for these gratings is limited by the influence of the support structure on the orientation of the polarization ellipse. If the polarizing properties of this perturbative component are known, the accuracy can be enhanced by treating the polarization by means of the Mueller calculus.

Lochbihler, Hans; Polnau, Ernst; Predehl, Peter

1995-09-01

314

Quantitative measurement of transverse injector and free stream interaction in a nonreacting SCRAMJET combustor using laser-induced iodine fluorescence  

NASA Technical Reports Server (NTRS)

A preliminary quantitative study of the compressible flowfield in a steady, nonreacting model SCRAMJET combustor using laser-induced iodine fluorescence (LIIF) is reported. Measurements of density, temperature, and velocity were conducted with the calibrated, nonintrusive, optical technique for two different combustor operating conditions. First, measurements were made in the supersonic flow over a rearward-facing step without transverse injection for comparison with calculated pressure profiles. The second configuration was staged injection behind the rearward-facing step at an injection dynamic pressure ratio of 1.06. These experimental results will be used to validate computational fluid dynamic (CFD) codes being developed to model supersonic combustor flowfields.

Fletcher, D. G.; Mcdaniel, J. C.

1987-01-01

315

Collective Spin Hall Effect for Electron-Hole Gratings  

NASA Astrophysics Data System (ADS)

We show that an electric field parallel to the wave fronts of an electron-hole grating in a GaAs quantum well generates, via the electronic spin Hall effect, a spin grating of the same wave vector and with an amplitude that can exceed 1% of the amplitude of the initial density grating. We refer to this phenomenon as the “collective spin Hall effect.” A detailed study of the coupled spin-charge dynamics for quantum wells grown in different directions reveals rich features in the time evolution of the induced spin density, including the possibility of generating a helical spin grating.

Shen, Ka; Vignale, G.

2013-09-01

316

Near-field optical properties of wide bandwidth metal multi-layer dielectric gratings for pulse compressor  

NASA Astrophysics Data System (ADS)

Metal multi-layer dielectric gratings (MMDG) for pulse compressors in high-energy laser systems should provide broad bandwidth as well as high laser-induced damage thresholds. The non-uniform optical near-field distribution of MMDG is an important factor that limits damage resistant capabilities. MMDG for pulse compressors operating at 800 nm with a corrugated SiO2 layer are designed by using a genetic algorithm and the Fourier mode method. The diffraction efficiency, bandwidth, and near-field distribution of the MMDG are theoretically investigated. For the single dielectric match layer grating, the bandwidth is 140 nm, if the thickness and refractive index of the match layer are changed, the maximum electric field in the grating ridge, match layer, and metal layer of the grating increases with the decrease in grating diffraction efficiency. For the multi-dielectric match layer grating, the bandwidth and the maximum electric field in the metal layer decrease with the increase in high- and low-index material pairs, and the maximum electric field in the grating ridge and match layer initially decreases and then increases. Over a wide wavelength range, the maximum electric field in the grating ridge, match layer, and metal layer is minimal near the central wavelength. Moreover, MMDG should be used at larger incident angles while keeping enough bandwidth to reduce the electric field in the grating.

Guan, Heyuan; Jin, Yunxia; Liu, Shijie; Kong, Fanyu; Du, Yin; He, Kai; Yi, Kui; Shao, Jianda

2014-03-01

317

Micromachined Vibratory Diffraction Grating Scanner for Multiwavelength Collinear Laser Scanning  

Microsoft Academic Search

This paper presents an effective method to achieve multiwavelength collinear laser scanning using micromachined vibratory grating scanners, which have the potential to scan at high frequencies without the optical performance degradation resulting from dynamic nonrigid-body deformation. An optical simulation model has been developed to predict the scanning patterns of the vibratory grating scanners. The proposed multiwavelength collinear scanning method was

Guangya Zhou; Fook Siong Chau

2006-01-01

318

Enhancement of airborne shock wave by laser-induced breakdown of liquid column in laser shock cleaning  

SciTech Connect

In laser shock cleaning (LSC), the shock wave is generated by laser-induced breakdown of the ambient gas. The shock wave intensity has thus been a factor limiting the performance of the LSC process. In this work, a novel method of amplifying a laser-induced plasma-generated shock wave by the breakdown of a liquid column is proposed and analyzed. When the laser beam is focused on a microscale liquid column, a shock wave having a significantly amplified intensity compared to that generated by air breakdown alone can be generated in air. Therefore, substantially amplified cleaning force can be obtained. The dynamics of a shock wave induced by a Q-switched Nd:YAG laser was analyzed by laser flash shadowgraphy. The peak pressure of the laser-induced shock wave was approximately two times greater than that of air breakdown at the same laser fluence. The proposed method of shock wave generation is expected to be useful in various applications of laser shock processing, including surface cleaning.

Jang, Deoksuk; Kim, Dongsik [Department of Mechanical Engineering POSTECH, 790-784, Pohang (Korea, Republic of); Park, Jin-Goo [Department of Materials Engineering, Hanyang University, 426-791, Ansan (Korea, Republic of)

2011-04-01

319

DYNAMICS OF X-RAY-EMITTING EJECTA IN THE OXYGEN-RICH SUPERNOVA REMNANT PUPPIS A REVEALED BY THE XMM-NEWTON REFLECTION GRATING SPECTROMETER  

SciTech Connect

Using the unprecedented spectral resolution of the reflection grating spectrometer (RGS) on board XMM-Newton, we reveal dynamics of X-ray-emitting ejecta in the oxygen-rich supernova remnant Puppis A. The RGS spectrum shows prominent K-shell lines, including O VII He{alpha} forbidden and resonance, O VIII Ly{alpha}, O VIII Ly{beta}, and Ne IX He{alpha} resonance, from an ejecta knot positionally coincident with an optical oxygen-rich filament (the so-called {Omega} filament) in the northeast of the remnant. We find that the line centroids are blueshifted by 1480 {+-} 140 {+-} 60 km s{sup -1} (the first and second term errors are measurement and calibration uncertainties, respectively), which is fully consistent with that of the optical {Omega} filament. Line broadening at 654 eV (corresponding to O VIII Ly{alpha}) is obtained to be {sigma} {approx}< 0.9 eV, indicating an oxygen temperature of {approx}< 30 keV. Analysis of XMM-Newton MOS spectra shows an electron temperature of {approx}0.8 keV and an ionization timescale of {approx}2 Multiplication-Sign 10{sup 10} cm{sup -3} s. We show that the oxygen and electron temperatures as well as the ionization timescale can be reconciled if the ejecta knot was heated by a collisionless shock whose velocity is {approx}600-1200 km s{sup -1} and was subsequently equilibrated due to Coulomb interactions. The RGS spectrum also shows relatively weak K-shell lines of another ejecta feature located near the northeastern edge of the remnant, from which we measure redward Doppler velocities of 650 {+-} 70 {+-} 60 km s{sup -1}.

Katsuda, Satoru; Tamagawa, Toru [RIKEN - Institute of Physical and Chemical Research, 2-1 Hirosawa, Wako, Saitama 351-0198 (Japan); Ohira, Yutaka [Department of Physics and Mathematics, Aoyama Gakuin University, 5-10-1 Fuchinobe Sagamihara 252-5258 (Japan); Mori, Koji [Department of Applied Physics, Faculty of Engineering, University of Miyazaki, 1-1 Gakuen Kibana-dai Nishi, Miyazaki 889-2192 (Japan); Tsunemi, Hiroshi; Koyama, Katsuji [Department of Earth and Space Science, Graduate School of Science, Osaka University, 1-1 Machikaneyama, Toyonaka, Osaka 60-0043 (Japan); Uchida, Hiroyuki [Department of Physics, Kyoto University, Kitashirakawa-oiwake-cho, Sakyo, Kyoto 606-8502 (Japan)

2013-05-10

320

Simulation and characterization of laser induced deformation processes  

NASA Astrophysics Data System (ADS)

Laser induced deformation processes include laser forming (LF) and laser shock processing. LF is a recently developed and highly flexible thermal forming technique, and laser shock processing is an innovative mechanical process in which shock waves up to 10GPa are generated by a confined laser ablation process. The generated high pressure imparts beneficial residual stress into the surface layer of metal parts as well as shapes thin metal parts. In laser forming, it has been known that microstructural evolution has an important effect on the deformation process, and that the typical thermal cycles in laser forming are much steeper than those in other thermal mechanical processes like welding and hot rolling. In this study, microstructural evolution in laser forming has been investigated, and a thermal-microstructural-mechanical model is developed to predict microstructural changes (phase transformations and recrystallization) and their effects on flow behavior and deformation. Grain structure and phase transformation in heat affected zone (HAZ) is experimentally characterized, and measurement of bending curvature also helps to validate the proposed model. Based on the similar methodology, two different materials have been studied: AISI 1010 low carbon steel and Ti-6Al-4V alloy. In the case of Ti-6A1-4V alloy, the initial phase ratio of Ti-alpha and Ti-beta need to be measured by X-ray diffraction. In laser shock processing, under shock loading solid material behavior is fluidlike and shock-solid interactions play a key role in determining the induced residual stress distributions and the final deformed shape. In this work shock-solid interactions under high pressure and thus high strain rate in laser shock processing are studied and simulated based on conservation's law, equation of state and elastoplasticity of material. A series of carefully controlled experiments, including spatially resolved residual stress measurement by synchrotron X-ray diffraction and measurement of local & global bending curvatures, is conducted to validate the model. Based on numerical results, the attenuation and shock velocity variation of shock wave in laser shock processing are further analyzed. In addition, based on the well validated shock wave propagation model, opposing dual sided laser shock peening has also been investigated. In opposing dual sided LSP, the workpiece can be simultaneously irradiated or irradiated with different time lags to create different surface residual stress patterns by virtue of the interaction between the opposing shock waves. In order to better understand the wave-wave interactions under different conditions, the residual stress profiles corresponding to various workpiece thicknesses and various irradiation times were evaluated. The dynamics and anisotropy in micro scale laser peen forming of single crystal Al has been also studied based on meso scale crystal plasticity integrated with consideration of dynamics and pressure dependent crystal elastic moduli.

Fan, Yajun

321

An elastomeric grating coupler  

Microsoft Academic Search

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

Askin Kocabas; Feridun Ay; Aykutlu Dâna; Atilla Aydinli

2006-01-01

322

Torus Grating Spectrometer.  

National Technical Information Service (NTIS)

Calculations are given for the design of a spectrometer having fixed slits and a concave grating of toroidal surface in which the grating is rotated to vary the wavelength. Conditions are stated to obtain minimum astigmatism, and from these the most favor...

H. Greiner, E. Schaffer

1977-01-01

323

Diffraction grating lens array  

NASA Astrophysics Data System (ADS)

We have proposed a new type of camera module with a thin structure and distance-detection capability. This camera module has a four-lens-array with diffraction gratings (one for blue, one for red, and two for green). The diffraction gratings on the mold are formed mechanically, and the plastic lens array is fabricated by injection molding. The two green images are compared to detect parallax, and parallax-corrected blue, red and green images are then composed to generate a color image. We have developed new design software and molding technologies for the grating lenses. The depth and period of blazed gratings and the shapes of aspheric lenses are optimized; and blue, red and two green aspheric lenses with gratings are molded as a single four-lens-array. The diffraction gratings on both surfaces of each lens act to improve field curvature and realize wide-angle imaging. However, blazed gratings sometimes cause unnecessary diffraction lights that impede the formation ofhigh-resolution images. We have developed a new method to measure necessary first-order diffraction lights and unnecessary diffraction lights separately. Use of this method allows the relationship between molding conditions and necessary/unnecessary diffraction lights to be shown. Unnecessary diffraction lights can be diminished by employing the optimal molding processes, allowing our grating lenses to be used for image capture.

Korenaga, Tsuguhiro; Ando, Takamasa; Moriguchi, Seiji; Takami, Fuminori; Takasu, Yoshifumi; Nishiwaki, Seiji; Suzuki, Masa-aki; Nagashima, Michiyoshi

2007-03-01

324

A comparative study of single and double pulse of laser induced breakdown spectroscopy of silver  

SciTech Connect

We present a comparative study of the collinear and orthogonal pre-ablation dual pulse configurations of laser induced breakdown spectroscopy (LIBS) of silver using Nd:YAG lasers. The effect of the inter-pulse delay and the ratio of the laser pulse energies on the signal intensity enhancement for both the dual pulse configurations have been investigated. Using the first laser at 532 nm and second laser at 1064 nm delayed by 5 {mu}s, we achieved nearly 2 times signal enhancement in the collinear double-pulsed configuration and nearly 12 times in the pre-ablation orthogonal configuration as compared to SP LIBS. It is ascertained that at the optimized value of the inter-pulse delay between the two lasers, the intensity ratio of the neutral silver lines follows the local thermo dynamical equilibrium (LTE) condition and it is also in excellent agreement with that of the relative transitions probabilities ratio listed in the NIST data base.

Rashid, Babar; Ahmed, Rizwan; Ali, Raheel; Baig, M. A. [Atomic and Molecular Physics Laboratory, Department of Physics, Quaid-i-Azam University, 45320 Islamabad (Pakistan)

2011-07-15

325

Thermal accommodation coefficients for laser-induced incandescence sizing of metal nanoparticles in monatomic gases  

NASA Astrophysics Data System (ADS)

The capabilities of time-resolved laser-induced incandescence (TiRe-LII), a combustion diagnostic used almost exclusively to measure soot primary particles, could potentially be extended to size aerosolized metal nanoparticles. In order to do this, however, it is necessary to characterize the thermal accommodation coefficient, ?, which specifies the heat conduction rate between the laser-energized nanoparticles and the surrounding gas. This paper extends a molecular dynamics (MD) methodology to calculate ? for Fe/He, Fe/Ar, Mo/He, and Mo/Ar systems. A comparative analysis of the results shows that ? is most strongly influenced by the potential well between the gas molecule and nanoparticle surface. Finally, the MD-derived value for ? is used to recover the nanoparticle size distribution for TiRe-LII measurements made on molybdenum nanoparticles in argon.

Daun, K. J.; Sipkens, T. A.; Titantah, J. T.; Karttunen, M.

2013-09-01

326

Laser-induced forward transfer of focussed ion beam pre-machined donors  

NASA Astrophysics Data System (ADS)

In this paper we report femtosecond laser-induced forward transfer (LIFT) of pre-machined donor films. 1 ?m thick zinc oxide (ZnO) films were first machined using the focussed ion beam (FIB) technique up to a depth of 0.8 ?m. Debris-free micro-pellets of ZnO with extremely smooth edges and surface uniformity were subsequently printed from these pre-machined donors using LIFT. Printing results of non-machined ZnO donor films and films deposited on top of a polymer dynamic release layer (DRL) are also presented for comparison, indicating the superior quality of transfer achievable and utility of this pre-machining technique.

Kaur, K. S.; Feinaeugle, M.; Banks, D. P.; Ou, J. Y.; Di Pietrantonio, F.; Verona, E.; Sones, C. L.; Eason, R. W.

2011-05-01

327

Experimental investigation of a supersonic swept ramp injector using laser-induced iodine fluorescence  

NASA Technical Reports Server (NTRS)

Planar measurements of injectant mole fraction and temperature have been conducted in a nonreacting supersonic combustor configured with underexpanded injection in the base of a swept ramp. The temperature measurements were conducted with a Mach 2 test section inlet in streamwise planes perpendicular to the test section wall on which the ramp was mounted. Injection concentration measurements, conducted in cross flow planes with both Mach 2 and Mach 2.9 free stream conditions, dramatically illustrate the domination of the mixing process by streamwise vorticity generated by the ramp. These measurements, conducted using a nonintrusive optical technique (laser-induced iodine fluorescence), provide an accurate and extensive experimental data base for the validation of computation fluid dynamic codes for the calculation of highly three-dimensional supersonic combustor flow fields.

Hartfield, Roy J.; Hollo, Steven D.; Mcdaniel, James C.

1990-01-01

328

On laser induced single bubble near a solid boundary: Contribution to the understanding of erosion phenomena  

NASA Astrophysics Data System (ADS)

Cavitation erosion is an especially destructive and complex phenomenon. In order to understand its basic mechanism, the dynamics of laser-induced vapor bubbles have been investigated. Special experimental devices have been used to record ultrafast visualizations and pressure measurements. From these measurements, the different sources of stresses, induced on the solid wall by the presence of the bubble (shock wave, microjet), have been characterized. The ``water hammer'' pressure associated with the microjet velocity varies up to 210 MPa. When the bubble collapses near a solid wall, the pressure emitted is less than in an infinite medium. Pressure values up to 2.5 MPa have been found. These values have been associated with the duration of the pressure applied to the solid wall, which is about 30 ns for the microjet and more than 300 ns for the shock wave. These results have been correlated with the analysis of damage created on the surface sample.

Isselin, Jean-Christophe; Alloncle, Anne-Patricia; Autric, Michel

1998-11-01

329

Optoelectronic microwave switching via laser-induced plasma tapers in GaAs microstrip sections  

NASA Astrophysics Data System (ADS)

This paper presents a new type of high-speed optoelectronic GaAs microstrip switch controlled by a pulse-operated laser diode via substrate-edge excitation. The exponential decay of photoconductivity across a longitudinal section of the microstrip forms a laser-induced electron-hole plasma wedge that works as a lossy tapered transmission line. The dynamics of carrier generation and recombination as well as the overall performance of the switch are quantitatively analyzed and optimized. This device is capable of switching with subnanosecond precision as well as with optical pulse energies in the order of 1 microJ. Theoretical and experimental results were found to be in good agreement.

Platte, W.

1981-10-01

330

Effect of damping on the laser induced ultrafast switching in rare earth-transition metal alloys  

NASA Astrophysics Data System (ADS)

In this paper, we present simulations of thermally induced magnetic switching in ferrimagnetic systems performed with a Landau-Lifshitz-Bloch (LLB) equation for damping constant in a wide range of values. We have systematically studied the GdFeCo ferrimagnet with various concentrations of Gd and compared for some values of parameters the LLB results with atomistic simulations. The agreement is remarkably good, which shows that the dynamics described by the ferrimagnetic LLB is a reasonable approximation of this complex physical phenomenon. As an important element, we show that the LLB is able to also describe the intermediate formation of a ferromagnetic state which seems to be essential to understand laser induced ultrafast switching. The study reveals the fundamental role of damping during the switching process.

Oniciuc, Eugen; Stoleriu, Laurentiu; Cimpoesu, Dorin; Stancu, Alexandru

2014-06-01

331

A comparative study of single and double pulse of laser induced breakdown spectroscopy of silver  

NASA Astrophysics Data System (ADS)

We present a comparative study of the collinear and orthogonal pre-ablation dual pulse configurations of laser induced breakdown spectroscopy (LIBS) of silver using Nd:YAG lasers. The effect of the inter-pulse delay and the ratio of the laser pulse energies on the signal intensity enhancement for both the dual pulse configurations have been investigated. Using the first laser at 532 nm and second laser at 1064 nm delayed by 5 ?s, we achieved nearly 2 times signal enhancement in the collinear double-pulsed configuration and nearly 12 times in the pre-ablation orthogonal configuration as compared to SP LIBS. It is ascertained that at the optimized value of the inter-pulse delay between the two lasers, the intensity ratio of the neutral silver lines follows the local thermo dynamical equilibrium (LTE) condition and it is also in excellent agreement with that of the relative transitions probabilities ratio listed in the NIST data base.

Rashid, Babar; Ahmed, Rizwan; Ali, Raheel; Baig, M. A.

2011-07-01

332

Investigation of laser-induced iodine fluorescence for the measurement of density in compressible flows  

NASA Technical Reports Server (NTRS)

Laser induced fluorescence is an attractive nonintrusive approach for measuring molecular number density in compressible flows although this technique does not produce a signal that is directly related to the number density. Saturation and frequency detuned excitation are explored as means for minimizing the quenching effect using iodine as the molecular system because of its convenient absorption spectrum. Saturation experiments indicate that with available continuous wave laser sources of Gaussian transverse intensity distribution only partial saturation could be achieved in iodine at the pressures of interest in gas dynamics. Using a fluorescence lineshape theory, it is shown that for sufficiently large detuning of a narrow bandwidth laser from a molecular transition, the quenching can be cancelled by collisional broadening over a large range of pressures and temperatures. Experimental data obtained in a Mach 4.3 underexpanded jet of nitrogen seeded with iodine for various single mode argon laser detunings from a strong iodine transition at 5145 A are discussed.

Mcdaniel, J. C., Jr.

1982-01-01

333

Spectroscopic investigation of laser-induced plasma in laser beam welding  

Microsoft Academic Search

The contribution deals with the diagnostics of laser induced plasma (LIP) by optical emission spectroscopy. Laser induced plasma occurs during laser welding and reveals important information about technological process. The performed experiments were concerned with in-time spectral analysis (wavelength range: 200-800 nm) of laser induced plasma of austenitic steel (18% Cr, 9% Ni) during cw CO2 laser welding. Circumstances of

J. Bruncko; Frantisek Uherek; Dusan Chorvat; Miroslav Michalka; P. Fodrek

2002-01-01

334

Search for Laser-Induced Formation of Antihydrogen Atoms  

SciTech Connect

Antihydrogen can be synthesized by mixing antiprotons and positrons in a Penning trap environment. Here an experiment to stimulate the formation of antihydrogen in the n=11 quantum state by the introduction of light from a CO{sub 2} continuous wave laser is described. An overall upper limit of 0.8% with 90% C.L. on the laser-induced enhancement of the recombination has been found. This result strongly suggests that radiative recombination contributes negligibly to the antihydrogen formed in the experimental conditions used by the ATHENA Collaboration.

Amoretti, M.; Macri, M.; Testera, G.; Variola, A. [Istituto Nazionale di Fisica Nucleare, Sezione di Genova, 16146 Genova (Italy); Amsler, C.; Pruys, H.; Regenfus, C. [Physik-Institut, Zuerich University, 8057 Zuerich (Switzerland); Bonomi, G. [Dipartimento di Ingegneria Meccanica, Universita di Brescia, 25123 Brescia (Italy); Istituto Nazionale di Fisica Nucleare, Universita di Pavia, 27100 Pavia (Italy); Bowe, P. D.; Ejsing, A. M.; Hangst, J. S.; Madsen, N. [Department of Physics and Astronomy, University of Aarhus, 8000 Aarhus C (Denmark); Canali, C.; Carraro, C.; Lagomarsino, V.; Manuzio, G. [Istituto Nazionale di Fisica Nucleare, Sezione di Genova, 16146 Genova (Italy); Dipartimento di Fisica, Universita di Genova, 16146 Genova (Italy); Cesar, C. L. [Instituto de Fisica, Univesidade Federal do Rio de Janeiro, Rio de Janeiro 21945-970 (Brazil); Charlton, M.; Joergensen, L. V.; Mitchard, D. [Department of Physics, University of Wales Swansea, Swansea SA2 8PP (United Kingdom)] (and others)

2006-11-24

335

Laser induced fluorescence of barium evaporating from a dispenser cathode  

NASA Astrophysics Data System (ADS)

A continuous wave dye laser is used to induce resonance fluorescence in Ba atoms evaporating from a thermionic dispenser cathode. The laser is tuned to the 553.5 microns Ba I line by making use of the optogalvanic effect in a hollow cathode discharge tube. Photon counting equipment is used to measure the Ba fluorescent intensity as a function of cathode temperature and laser power. Ba concentrations and evaporation rates as functions of temperature are derived from the fluorescent intensity. Laser induced fluorescence is established as a technique for examining various species evaporating from cathodes. The technique can be used in attempts to determine cathode failure mechanisms.

Zemyan, S. M.

1982-03-01

336

Nanosecond polarization-resolved laser-induced breakdown spectroscopy.  

PubMed

It is shown that the continuum emission produced in the ablation of an Al target with nanosecond laser pulses is much more strongly polarized than the discrete line emission. This effect may be utilized to improve the resolution of the laser-induced breakdown spectroscopy spectrum by using a polarizer to filter out the continuum background. The effects of laser fluence and focal position are also reported. It is further shown that the lifetime of the emission closely tracks the intensity spectrum. PMID:20081938

Liu, Yaoming; Penczak, John S; Gordon, Robert J

2010-01-15

337

Remote sensing of phytoplankton using laser-induced fluorescence  

SciTech Connect

The results of remote laser sensing of brackish-water phytoplankton on board a research vessel are presented. Field data of laser-induced fluorescence of phytoplankton obtained during the several cruises in the mouth of tile Gulf of Finland are compared with the results of standard chlorophyll a analysis of water samples and phytoplankton species determination by microscopy. The approach of fluorescence excitation by tunable laser radiation is applied to study the spatial distribution of a natural phytoplankton community. The remote analysis of the pigment composition of a phytoplankton community using the method of selective pigment excitation is described. The possibility of elaborating methods of quantitative laser remote biomonitoring is discussed.

Babichenko, S.; Poryvkina, L.; Arikese, V. (Inst. of Ecology and Marine Research, Tallinn (Estonia)); Kaitala, S. (Univ. of Helsinki (Finland)); Kuosa, H. (Tvaerminne Zoological Station, Hanko (Finland))

1993-06-01

338

Spatial confinement effects in laser-induced breakdown spectroscopy  

SciTech Connect

The spatial confinement effects in laser-induced breakdown of aluminum (Al) targets in air have been investigated both by optical emission spectroscopy and fast photography. A KrF excimer laser was used to produce plasmas from Al targets in air. Al atomic emission lines show an obvious enhancement in the emission intensity when a pair of Al-plate walls were placed to spatially confine the plasma plumes. Images of the Al plasma plumes showed that the plasma plumes evolved into a torus shape and were compressed in the Al walls. The mechanism for the confinement effects was discussed using shock wave theory.

Shen, X. K.; Sun, J.; Ling, H.; Lu, Y. F. [Department of Electrical Engineering, University of Nebraska-Lincoln, Lincoln, Nebraska 68588-0511 (United States)

2007-08-20

339

Evidence of laser induced degradation and graphitization of aromatic pollutants  

NASA Astrophysics Data System (ADS)

The laser-induced photodecomposition and graphitization of polynuclear aromatic hydrocarbons is investigated by irradiating solid pollutant samples with an Nd-YAG laser, leaving a carbon-rich, black powder. The irradiation of anthracene and benzopyrene forms the ions Cn(+)-, CnH(+)-, and CnH2(+)- in a wide plume produced by a pulsed-CO2 laser. The tendency of aromatic compounds to fragment is noted, and the notion that ion formation is governed by the mechanism that produces ablation in the laser cloud is suggested. Optical multichannel analyzer emission spectra indicate the production of the Cn species, suggesting applications to the treatment of aromatic product wastes.

Mele, A.; Letardi, T.; di Lazarro, P.

340

Anomalous laser-induced group velocity dispersion in fused silica.  

PubMed

We present 20fs(2) accuracy laser-induced group velocity dispersion (LI-GVD) measurements, resulting from propagation of a femtosecond laser pulse in 1mm of fused silica, as a function of peak intensity. For a 5.5 × 10(11) W/cm(2) peak intensity, LI-GVD values are found to vary from -3 to + 15 times the material GVD. Normal induced dispersion can be explained by the Kerr effect, but anomalous LI-GVD, found when the input pulses have negative pre-chirp, cannot. These findings have significant implications regarding self-compression and the design of femtosecond lasers. PMID:23938642

Rasskazov, Gennady; Ryabtsev, Anton; Pestov, Dmitry; Nie, Bai; Lozovoy, Vadim V; Dantus, Marcos

2013-07-29

341

Towards Friction Control using laser-induced periodic Surface Structures  

NASA Astrophysics Data System (ADS)

This paper aims at contributing to the study of laser-induced periodic surface structures (LIPSS) and the description of their tribological properties in order to facilitate the knowledge for contact mechanical applications. To obtain laser parameters for LIPSS formation, we propose to execute two D2-Experiments. For the transfer of results from static experiments to areas of LIPSS we propose the discrete accumulation of fluences. Areas covered by homogeneously distributed LIPSS were machined. Friction force of these areas was measured using a tribometer in a ball on flat configuration. The friction force was found to be higher on the structured area than on the initial surface.

Eichstädt, J.; Römer, G. R. B. E.; Veld, A. J. Huis in't.

342

Laser Induced Fluorescence of Biochemical for UV LIDAR Application.  

PubMed

Laser induced fluorescence spectroscopy in the ultraviolet regime has been used for the detection of biochemical through a fiber coupled CCD detector from a distance of 2 m. The effect of concentration and laser excitation energy on the fluorescence spectra of nicotinamide adenine dinucleotide (NADH) has been investigated. The signature fluorescence peak of NADH was centred about 460 nm. At lower concentration Raman peak centred at 405 nm was also observed. The origin of this peak has been discussed. Detection limit with the proposed set up is found to be 1 ppm. PMID:24337816

Gupta, L; Sharma, R C; Razdan, A K; Maini, A K

2014-05-01

343

Laser-induced shock waves effects in materials  

SciTech Connect

A review of the effects of pressure pulses on materials is presented with an orientation toward laser-induced shock wave effects in biological tissue. The behavior is first discussed for small amplitudes, namely sound waves, since many important features in this region are also applicable at large amplitudes. The generation of pressure pulses by lasers is discussed along with amplitudes. The origin and characteristic properties of shock waves are discussed along with the different types of effects they can produce. The hydrodynamic code techniques required for shock wave calculations are discussed along with the necessary empirical data base and methods for generating that data base. 7 refs., 15 figs.

Dingus, R.S.; Shafer, B.P.

1990-01-01

344

Trace metal mapping by laser-induced breakdown spectroscopy  

SciTech Connect

Abstract: Laser-Induced Breakdown Spectroscopy (LIBS) is a sensitive optical technique capable of fast multi-elemental analysis of solid, gaseous and liquid samples. The potential applications of lasers for spectrochemical analysis were developed shortly after its invention; however the massive development of LIBS is connected with the availability of powerful pulsed laser sources. Since the late 80s of 20th century LIBS dominated the analytical atomic spectroscopy scene and its application are developed continuously. Here we review the utilization of LIBS for trace elements mapping in different matrices. The main emphasis is on trace metal mapping in biological samples.

Kaiser, Jozef [ORNL; Novotny, Dr. Karel [Masaryk University; Hrdlicka, A [Brno University of Technology, Czech Republic; Malina, R [Brno University of Technology, Czech Republic; Hartl, M [Brno University of Technology, Czech Republic; Kizek, R [Mendel University of Brno; Adam, V [Mendel University of Brno

2012-01-01

345

Tissue discrimination by laser-induced fluorescence method  

NASA Astrophysics Data System (ADS)

On the basis of the differentiation of molecular structures between healthy and diseased tissue, spectroscopic information could be used for tissue discrimination. The experimental results on laser induced fluorescence of atherosclerotic deposits through the new exogenous photosensitizer Hypocrellin A (HA) was reported and algorithms implemented to on the arterial fluorescence system has been developed to be capable of discriminating normal from atherosclerotic tissue in this paper, indicating that Hypocrellin (HA) could be used as a clinical probe for both atherosclerotic lesions. Better discriminatory effect was found on fatty and calcified tissue.

Liu, Weiqing; Zhang, Yijun; Kuze, Hiroki; Takeuchi, Nobuo

1999-09-01

346

High time resolution laser induced fluorescence in pulsed argon plasma  

SciTech Connect

A submillisecond time resolution laser induced fluorescence (LIF) method for obtaining the temporal evolution of the ion velocity distribution function in pulsed argon plasma is presented. A basic LIF system that employs a continuous laser wave pumping and lock-in aided detection of the subsequent fluorescence radiation is modified by addition of a high frequency acousto-optic modulator to provide measurements of the ion flow velocity and ion temperature in a helicon generated pulsed argon plasma with temporal resolutions as high as 30 {mu}s.

Biloiu, Ioana A.; Sun Xuan; Scime, Earl E. [Department of Physics, West Virginia University, Morgantown, West Virginia 26506-6315 (United States)

2006-10-15

347

Characterization of Arcjet Flows Using Laser-Induced Fluorescence  

NASA Technical Reports Server (NTRS)

A sensor based on laser-induced fluorescence has been installed at the 20-MW NASA Ames Aerodynamic Heating Facility. The sensor has provided new, quantitative, real-time information about properties of the arcjet flow in the highly dissociated, partially ionized, nonequilibrium regime. Number densities of atomic oxygen, flow velocities, heavy particle translational temperatures, and collisional quenching rates have been measured. These results have been used to test and refine computational models of the arcjet flow. The calculated number densities, translational temperatures, and flow velocities are in moderately good agreement with experiment

Bamford, Douglas J.; O'Keefe, Anthony; Babikian, Dikran S.; Stewart, David A.; Strawa, Anthony W.

1995-01-01

348

Laser-induced breakdown spectroscopy of alcohols and protein solutions  

SciTech Connect

We report on the use of laser-induced breakdown spectroscopy for the study of organic samples that exhibit similar elemental composition. We evaluate the method for its potential application for the measurement of small spectroscopic differences between samples such as alcohols and water solution of proteins. We measure differences in the relative amplitudes of the oxygen peaks for alcohols and find that these correlate with the relative amount of oxygen atoms within the molecule. We also show that the spectra of proteins reveal differences that can be used for their detection and identification.

Melikechi, N.; Ding, H.; Marcano, O. A.; Rock, S. [Center for Research and Education in Optical Science and Applications, Applied Optics Center, and Department of Physics and Pre-Engineering, Delaware State University, 1200 N DuPont Highway, Dover, Delaware 19901 (United States)

2008-04-15

349

Colloid formation and laser-induced bleaching in fluorite  

SciTech Connect

Colloid formation and subsequent laser-induced bleaching in fluorite has been studied by transmission electron microscopy and electron diffraction. At high incident electron-beam (e-beam) energies, Ca colloids with diameter {approx}10 nm form a simple cubic superlattice with lattice parameter a{approx}18 nm. The colloids themselves are topotactic with the fluorite matrix forming low-energy interfaces close to a {sigma}=21 special grain boundary in cubic materials. Laser irradiation using {lambda}=532 nm has been shown to effectively bleach the e-beam-irradiated samples returning the fluorite to its monocrystalline state. The bleached samples appear more resistant to further colloid formation.

LeBret, Joel B.; Cramer, Loren P.; Norton, M. Grant; Dickinson, J. T. [School of Mechanical and Materials Engineering, Washington State University, Pullman, Washington 99164 (United States); Materials Science Program, Washington State University, Pullman, Washington 99164 (United States); School of Mechanical and Materials Engineering, Washington State University, Pullman, Washington 99164 (United States); Materials Science Program, Washington State University, Pullman, Washington 99164 (United States)

2004-11-08

350

H sup minus beam characterization using laser-induced neutralization  

SciTech Connect

The Laser-induced neutralization techniques, LINDA, is important as a noninterceptive diagnostic for quantitatively measuring beam emittance values. It is also valuable for its capability to characterize, both quantitatively and qualitatively, the performance and match of linac components. In this paper we present LINDA experimental results that show how the output beam of a radio-frequency quadrupole (RFQ) and drift-tube linac (DTL) combination changes with the variation of RFQ-DTL relative phase and of DTL cavity power. We also present results showing the effect of a longitudinal buncher on beam emissions. 2 refs., 4 figs.

Yuan, V.W.; Garcia, R.; Johnson, K.F.; Saadatmand, K.; Sander, O.R.; Sandoval, D.; Shinas, M.

1991-01-01

351

Quasiadiabatic approach for laser-induced single-bubble sonoluminescence.  

PubMed

The luminescence parameters of laser-induced bubble in the presence of an acoustic field in water are studied. A comparison is made between parameters such as bubble radius, interior temperature, and pressure of the bubble induced by laser and an acoustic field influenced by different driving pressure amplitudes. It is found that the bubble volume induced by laser at the collapse instant is more than 10(6) times larger than the one induced by an acoustic field. It is also noticed, by increasing the driving pressure amplitude, the bubble radius decreases in both cases, however, the bubble interior pressure and temperature increase. PMID:22400653

Sadighi-Bonabi, Rasoul; Razeghi, Fatemeh; Ebrahimi, Homa; Fallahi, Shadi; Lotfi, Erik

2012-01-01

352

Quasiadiabatic approach for laser-induced single-bubble sonoluminescence  

NASA Astrophysics Data System (ADS)

The luminescence parameters of laser-induced bubble in the presence of an acoustic field in water are studied. A comparison is made between parameters such as bubble radius, interior temperature, and pressure of the bubble induced by laser and an acoustic field influenced by different driving pressure amplitudes. It is found that the bubble volume induced by laser at the collapse instant is more than 106 times larger than the one induced by an acoustic field. It is also noticed, by increasing the driving pressure amplitude, the bubble radius decreases in both cases, however, the bubble interior pressure and temperature increase.

Sadighi-Bonabi, Rasoul; Razeghi, Fatemeh; Ebrahimi, Homa; Fallahi, Shadi; Lotfi, Erik

2012-01-01

353

Electrically-programmable diffraction grating  

DOEpatents

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).

Ricco, Antonio J. (Albuquerque, NM) [Albuquerque, NM; Butler, Michael A. (Albuquerque, NM) [Albuquerque, NM; Sinclair, Michael B. (Albuquerque, NM) [Albuquerque, NM; Senturia, Stephen D. (Brookline, MA) [Brookline, MA

1998-01-01

354

Temperature measurement of Ho:YAG laser induced bubble in water using silver halide IR optical fiber  

NASA Astrophysics Data System (ADS)

We measured the localized transient temperature of Ho:YAG laser induced bubble in water by infrared radiation measurement with a infrared optical fiber to study heat effect/damage of this bubble for vascular therapeutic applications. Although there have been many reports regarding to the temperature in the Ho:YAG laser induced bubble by both theoretical and experimental approaches, we can not find well-time-response reliable temperature in the laser induced bubble. We constructed the remote temperature measurement system to obtain the temperature of the laser induced bubble with the infrared optical fiber (Optran MIR, CeramOptec) made of AgCl/AgBr with 1mm in core diameter. The flash lamp excited Ho: YAG laser (IH102, NIIC,?=2.1?m) beam was delivered through a silica optical fiber (core diameter: 600?m) and was irradiated from the fiber tip in water. The tip position of the infrared optical fiber against the silica glass fiber was changed to measure local bubble temperature. The sidewall of the infrared optical fiber tip was covered by a black rubber tube to prevent the collection of the Ho:YAG laser into the infrared fiber. The infrared radiation delivered through the infrared optical fiber was measured by the HgCdTe infrared detector (KMPC12-2-J1, Kolmar Technologies, rise time:500ns). This fiber optic radiation detection system was calibrated before the bubble temperature measurement. Since the bubble boundary location and its shape were changed with time, we corrected influences of these factors. We finally obtained the peak temperature of 61.7+/-2.8°C at the top surface in the laser induced bubble with 800mJ/pulse. This temperature was 10 degree lower than that of reported. The temperature at the top of the bubble was approximately 9.8 degree higher than that at the bubble side. Obtained temperature distribution with time may be available to study bubble dynamics necessary for our vascular applications.

Iwasaki, Takehiro; Nakatani, Eriko; Arai, Tsunenori

2008-03-01

355

Direct probing of chromatography columns by laser-induced fluorescence  

SciTech Connect

This report summarizes the progress and accomplishments of this research project from September 1, 1989 to February 28, 1993. During this period, we have accomplished all of the primary scientific objectives of the research proposal: (1) constructed and evaluated a laser-induced fluorescence detection system that allows direct examination of the chromatographic column, (2) examined nonequilibrium processes that occur upon solute injection and elution, (3) examined solute retention in liquid chromatography as a function of temperature and pressure, (4) examined solute zone dispersion in liquid chromatography as a function of temperature and pressure, and (5) developed appropriate theoretical models to describe these phenomena. In each of these studies, substantial knowledge has been gained of the fundamental processes that are responsible for chromatographic separations. In addition to these primary research objectives, we have made significant progress in three related areas: (1) examined pyrene as a fluorescent polarity probe insupercritical fluids and liquids as a function of temperature and pressure, (2) developed methods for the class-selective identification of polynuclear aromatic hydrocarbons in coal-derived fluids by microcolumn liquid chromatography with fluorescence quenching detection, and (3) developed methods for the determination of saturated and unsaturated (including omega-3) fatty acids in fish oil extracts by microcolumn liquid chromatography with laser-induced fluorescence detection. In these studies, the advanced separation and detection techniques developed in our laboratory are applied to practical problems of environmental and biomedical significance.

McGuffin, V.L.

1992-12-07

356

Laser-induced fluorescence detection of stomach cancer using hypericin  

NASA Astrophysics Data System (ADS)

Natural photodynamic pigment hypericin having intrinsic antitumor properties was applied for fluorescence detection of cancer. Clinical investigation of hypericin was performed to ensure high tumor/normal fluorescence contrast in digestion organs. Laser-induced autofluorescence and exogenous fluorescence analysis of normal tissue and stomach adenocarcinoma was performed using helium-cadmium laser (8 mW, 442 nm). Twenty-one patients have undergone procedure of fluorescence detection of tumors before and after photosensitization. For sensitization of patients we used five or seven capsules containing hypericin in amount of 1 mg which have been administered orally. Strong yellow-red fluorescence of hypericin in tissue with maximum at 603 nm and autofluorescence peak at 535 nm gives an intensity ratio I(603 nm)/I(535 nm) of 2 - 2.5 from cancerous tissue and provides 85% specificity. Preliminary in vivo results of auto- and fluorescence analysis using hypericin photosensitization from one patient with esophageal cancer and eleven patients with stomach cancer proven histologically are encouraging and indicate the high reliability of laser-induced fluorescence technique with hypericin in detection of early stage malignant lesions.

Dets, Sergiy M.; Buryi, Alexander N.; Melnik, Ivan S.; Joffe, Alexander Y.; Rusina, Tatyana V.

1996-12-01

357

Femtosecond laser-induced refractive index modification in multicomponent glasses  

NASA Astrophysics Data System (ADS)

We present a comprehensive study on femtosecond laser-induced refractive index modification in a wide variety of multicomponent glasses grouped as borosilicate, aluminum-silicate, and heavy-metal oxide glasses along with lanthanum-borate and sodium-phosphate glasses. By using high-spatial resolution refractive index profiling techniques, we demonstrate that under a wide range of writing conditions the refractive index modification in multicomponent glasses can be positive, negative, or nonuniform, and exhibits a strong dependence on the glass composition. With the exception of some aluminum-silicate glasses all other glasses exhibited a negative/nonuniform index change. We also demonstrate direct writing of waveguides in photosensitive Foturan® glass with a femtosecond laser without initiating crystallization by thermal treatment. Upon ceramization of lithium-aluminum-silicate glasses such as Foturan®, Zerodur®, and Robax® we observe switching of laser-induced refractive index change from being positive to negative. The measured transmission losses in the waveguides at 1550 nm agree with the index profile measurements in alkali-free aluminum-silicate glasses.

Bhardwaj, V. R.; Simova, E.; Corkum, P. B.; Rayner, D. M.; Hnatovsky, C.; Taylor, R. S.; Schreder, B.; Kluge, M.; Zimmer, J.

2005-04-01

358

Amorphous carbon film deposition by laser induced C 60 fragmentation  

NASA Astrophysics Data System (ADS)

It is demonstrated that a pure carbon (fullerene) precursor, C 60, is appropriate for laser-induced carbon film deposition. Amorphous carbon films were obtained on Si and SiO 2 substrates upon ArF excimer laser induced fragmentation of gas phase C 60. The depositions were performed in Ar and H 2 ambient in a hot-wall reactor at 550°C. Strong C 2 emission bands were observed by optical emission spectroscopy during the deposition process indicating that C 2 dimers are used for film formation, however, thermal decomposition of C 58, C 56, etc. high-mass fragments may also contribute to the layer development. Raman and TEM studies showed amorphous (highly disordered, turbostratic) character of the films. Optical absorption spectroscopy indicated semiconductor feature of the layers with optical band gap of 0.7 and 0.9 eV for the films deposited in Ar and H 2 ambient, respectively. For the films deposited in H 2 atmosphere, changes in the Raman spectrum and an upshift of the optical band gap of the layer indicate amorphous hydrogenated film with diamond-like character, however, degree of the sp 3 hybridisation was estimated to be low. The deposition rate was measured to be ˜200 Å/min at 500°C and 400 mJ/cm 2 laser fluence. AFM measurements showed smooth films with low surface roughness, ˜1 nm on 1 ?m scale length.

Heszler, P.; Carlsson, J. O.; Lu, J.

1997-02-01

359

Detection of explosives with laser-induced breakdown spectroscopy  

NASA Astrophysics Data System (ADS)

Our recent work on the detection of explosives by laser-induced breakdown spectroscopy (LIBS) is reviewed in this paper. We have studied the physical mechanism of laser-induced plasma of an organic explosive, TNT. The LIBS spectra of TNT under single-photon excitation are simulated using MATLAB. The variations of the atomic emission lines intensities of carbon, hydrogen, oxygen, and nitrogen versus the plasma temperature are simulated too. We also investigate the time-resolved LIBS spectra of a common inorganic explosive, black powder, in two kinds of surrounding atmospheres, air and argon, and find that the maximum value of the O atomic emission line SBR of black powder occurs at a gate delay of 596 ns. Another focus of our work is on using chemometic methods such as principle component analysis (PCA) and partial least squares discriminant analysis (PLS-DA) to distinguish the organic explosives from organic materials such as plastics. A PLS-DA model for classification is built. TNT and seven types of plastics are chosen as samples to test the model. The experimental results demonstrate that LIBS coupled with the chemometric techniques has the capacity to discriminate organic explosive from plastics.

Wang, Qian-Qian; Liu, Kai; Zhao, Hua; Ge, Cong-Hui; Huang, Zhi-Wen

2012-12-01

360

Laser-induced breakdown spectroscopy of tantalum plasma  

SciTech Connect

Laser Induced Breakdown spectroscopy (LIBS) of Tantalum (Ta) plasma has been investigated. For this purpose Q-switched Nd: YAG laser pulses (?? 1064 nm, ?? 10 ns) of maximum pulse energy of 100 mJ have been employed as an ablation source. Ta targets were exposed under the ambient environment of various gases of Ar, mixture (CO{sub 2}: N{sub 2}: He), O{sub 2}, N{sub 2}, and He under various filling pressure. The emission spectrum of Ta is observed by using LIBS spectrometer. The emission intensity, excitation temperature, and electron number density of Ta plasma have been evaluated as a function of pressure for various gases. Our experimental results reveal that the optical emission intensity, the electron temperature and density are strongly dependent upon the nature and pressure of ambient environment. The SEM analysis of the ablated Ta target has also been carried out to explore the effect of ambient environment on the laser induced grown structures. The growth of grain like structures in case of molecular gases and cone-formation in case of inert gases is observed. The evaluated plasma parameters by LIBS analysis such as electron temperature and the electron density are well correlated with the surface modification of laser irradiated Ta revealed by SEM analysis.

Khan, Sidra; Bashir, Shazia; Hayat, Asma; Khaleeq-ur-Rahman, M.; Faizan–ul-Haq [Centre for Advanced Studies in Physics, GC University, Lahore (Pakistan)] [Centre for Advanced Studies in Physics, GC University, Lahore (Pakistan)

2013-07-15

361

Calibration analysis of zeolites by laser induced breakdown spectroscopy  

NASA Astrophysics Data System (ADS)

Laser induced breakdown spectroscopy was used for calibration analysis of different types of microporous crystalline aluminosilicates with exactly ordered structure — zeolites. The LIBS plasma was generated using a Q-switched Nd:YAG laser operating at the wavelength of 532 nm and providing laser pulses of 4 ns duration. Plasma emission was analysed by echelle type emission spectrometer, providing wide spectral range 200-950 nm. The spectrometer was equipped with intensified CCD camera providing rapid spectral acquisition (gating time from 5 ns). The optimum experimental conditions (time delay, gate width and laser pulse energy) have been determined for reliable use of LIBS for quantitative analysis. Samples of different molar ratios of Si/Al were used to create the calibration curves. Calibration curves for different types of zeolites (mordenite, type Y and ZSM-5) were constructed. Molar ratios of Si/Al for samples used for calibration were determined by classical wet chemical analysis and were in the range 5.3-51.8 for mordenite, 2.3-12.8 for type Y and 14-600 for ZSM-5. Zeolites with these molar ratios of Si/Al are usually used as catalysts in alkylation reactions. Laser induced breakdown spectroscopy is a suitable method for analysis of molar ratio Si/Al in zeolites, because it is simple, fast, and does not require sample preparation compared with classical wet chemical analysis which are time consuming, require difficult sample preparation and manipulation with strong acids and bases.

Hor?á?ková, M.; Grolmusová, Z.; Hor?á?ek, M.; Rakovský, J.; Hudec, P.; Veis, P.

2012-08-01

362

Probing Electron Correlation with Sequential Laser--Induced Tunnel ionization  

NASA Astrophysics Data System (ADS)

Since 1964 we have known that multiphoton ionization could be approximated by tunnel ionization for long wavelength light. Aside from re-collision, since then multiple ionization has been treated as successive, independent single ionization events. Our results show that this long-held belief is false. Tunnelling is highly directional and highly sensitive to the ionization potential (Ip) of the accessible ionic states (which itself can depend on the direction of ionization). Using rare gas atoms as examples, we show that laser induced tunnelling is suppressed or enhanced depending on how the field is applied. We image the hole left by the first tunnelling electron by measuring in the spatial correlation of the second electron. Laser induced tunnelling gives us experimental access to one of the most difficult to measure properties of matter -- electron-electron correlations [1]. [4pt] [1] A. Fleischer, H.J. W"orner, L. Arissian, L.R. Liu, M. Meckel, A. Rippert, R. D"orner, D.M. Villeneuve, A. Staudte and P.B. Corkum, unpublished results.

Corkum, Paul

2011-03-01

363

Laser-induced breakdown spectroscopy of tantalum plasma  

NASA Astrophysics Data System (ADS)

Laser Induced Breakdown spectroscopy (LIBS) of Tantalum (Ta) plasma has been investigated. For this purpose Q-switched Nd: YAG laser pulses (? ~ 1064 nm, ? ~ 10 ns) of maximum pulse energy of 100 mJ have been employed as an ablation source. Ta targets were exposed under the ambient environment of various gases of Ar, mixture (CO2: N2: He), O2, N2, and He under various filling pressure. The emission spectrum of Ta is observed by using LIBS spectrometer. The emission intensity, excitation temperature, and electron number density of Ta plasma have been evaluated as a function of pressure for various gases. Our experimental results reveal that the optical emission intensity, the electron temperature and density are strongly dependent upon the nature and pressure of ambient environment. The SEM analysis of the ablated Ta target has also been carried out to explore the effect of ambient environment on the laser induced grown structures. The growth of grain like structures in case of molecular gases and cone-formation in case of inert gases is observed. The evaluated plasma parameters by LIBS analysis such as electron temperature and the electron density are well correlated with the surface modification of laser irradiated Ta revealed by SEM analysis.

Khan, Sidra; Bashir, Shazia; Hayat, Asma; Khaleeq-ur-Rahman, M.; Faizan-ul-Haq

2013-07-01

364

Direct probing of chromatography columns by laser-induced fluorescence  

NASA Astrophysics Data System (ADS)

This report summarizes the progress and accomplishments of this research project from 1 Sep. 1989 to 28 Feb. 1993. During this period, we have accomplished all of the primary scientific objectives of the research proposal: (1) constructed and evaluated a laser-induced fluorescence detection system that allows direct examination of the chromatographic column, (2) examined nonequilibrium processes that occur upon solute injection and elution, (3) examined solute retention in liquid chromatography as a function of temperature and pressure, (4) examined solute zone dispersion in liquid chromatography as a function of temperature and pressure, and (5) developed appropriate theoretical models to describe these phenomena. In each of these studies, substantial knowledge has been gained of the fundamental processes that are responsible for chromatographic separations. In addition to these primary research objectives, we have made significant progress in three related areas: (1) examined pyrene as a fluorescent polarity probe in supercritical fluids and liquids as a function of temperature and pressure, (2) developed methods for the class-selective identification of polynuclear aromatic hydrocarbons in coal-derived fluids by microcolumn liquid chromatography with fluorescence quenching detection, and (3) developed methods for the determination of saturated and unsaturated (including omega-3) fatty acids in fish oil extracts by microcolumn liquid chromatography with laser-induced fluorescence detection. In these studies, the advanced separation and detection techniques developed in our laboratory are applied to practical problems of environmental and biomedical significance.

McGuffin, V. L.

1992-12-01

365

Time-resolved X-Ray diffraction from coherent phonons during a laser-induced phase transition  

PubMed

Time-resolved x-ray diffraction with picosecond temporal resolution is used to observe scattering from impulsively generated coherent acoustic phonons in laser-excited InSb crystals. The observed frequencies and damping rates are in agreement with a model based on dynamical diffraction theory coupled to analytic solutions for the laser-induced strain profile. The results are consistent with a 12 ps thermal electron-acoustic phonon coupling time together with an instantaneous component from the deformation-potential interaction. Above a critical laser fluence, we show that the first step in the transition to a disordered state is the excitation of large amplitude, coherent atomic motion. PMID:11015847

Lindenberg; Kang; Johnson; Missalla; Heimann; Chang; Larsson; Bucksbaum; Kapteyn; Padmore; Lee; Wark; Falcone

2000-01-01

366

Planar measurement of flow field parameters in a nonreacting supersonic combustor using laser-induced iodine fluorescence  

NASA Technical Reports Server (NTRS)

A nonintrusive optical technique, laser-induced iodine fluorescence, has been used to obtain planar measurements of flow field parameters in the supersonic mixing flow field of a nonreacting supersonic combustor. The combustor design used in this work was configured with staged transverse sonic injection behind a rearward-facing step into a Mach 2.07 free stream. A set of spatially resolved measurements of temperature and injectant mole fraction has been generated. These measurements provide an extensive and accurate experimental data set required for the validation of computational fluid dynamic codes developed for the calculation of highly three-dimensional combustor flow fields.

Hartfield, Roy J., Jr.; Hollo, Steven D.; Mcdaniel, James C.

1990-01-01

367

Enthalpy Distributions of Arc Jet Flow Based on Measured Laser Induced Fluorescence, Heat Flux and Stagnation Pressure Distributions  

NASA Technical Reports Server (NTRS)

The centerline total enthalpy of arc jet flow is determined using laser induced fluorescence of oxygen and nitrogen atoms. Each component of the energy, kinetic, thermal, and chemical can be determined from LIF measurements. Additionally, enthalpy distributions are inferred from heat flux and pressure probe distribution measurements using an engineering formula. Average enthalpies are determined by integration over the radius of the jet flow, assuming constant mass flux and a mass flux distribution estimated from computational fluid dynamics calculations at similar arc jet conditions. The trends show favorable agreement, but there is an uncertainty that relates to the multiple individual measurements and assumptions inherent in LIF measurements.

Suess, Leonard E.; Milhoan, James D.; Oelke, Lance; Godfrey, Dennis; Larin, Maksim Y.; Scott, Carl D.; Grinstead, Jay H.; DelPapa, Steven

2011-01-01

368

Plume splitting and rebounding in a high-intensity CO{sub 2} laser induced air plasma  

SciTech Connect

The dynamics of plasma plume formed by high-intensity CO{sub 2} laser induced breakdown of air at atmospheric pressure is investigated. The laser wavelength is 10.6 {mu}m. Measurements were made using 3 ns gated fast photography as well as space and time resolved optical emission spectroscopy. The behavior of the plasma plume was studied with a laser energy of 3 J and 10 J. The results show that the evolution of the plasma plume is very complicated. The splitting and rebounding of the plasma plume is observed to occur early in the plumes history.

Chen Anmin; Jiang Yuanfei; Liu Hang; Jin Mingxing; Ding Dajun [Institute of Atomic and Molecular Physics, Jilin University, Changchun 130012 (China)

2012-07-15

369

Quantitative local equivalence ratio determination in laminar premixed methane-air flames by laser induced breakdown spectroscopy (LIBS)  

NASA Astrophysics Data System (ADS)

Laser induced breakdown spectroscopy has been used in order to obtain quantitative local equivalence ratio measurements in laminar premixed methane-air Bunsen flames. The total emission intensities of the 656.3 nm H ? and the 777 nm O(I) atomic spectral lines were simultaneously measured and a linear relation of the H/O intensity ratio with the flame equivalence ratio ? was established. Axial and radial profiles of local equivalence ratio were thus obtained for both lean and rich flames and were used to provide information regarding flame structure and dynamics.

Stavropoulos, P.; Michalakou, A.; Skevis, G.; Couris, S.

2005-03-01

370

Noble gas halogen laser induced fluorescence of benzene: Some of its derivatives, difluoromethyl radicals; and carbon monoxide  

NASA Astrophysics Data System (ADS)

The dynamics of molecules excited by laser absorption into well defined vibrational states were investigated. An apparatus was built in order to study laser induced fluorescence. A noble gas halogen excimer laser (pulse energy 10 mJ for KrF) was also constructed. Fluorescence of gaseous or liquid substances was examined by a high resolution monochromator, a transient recorder and a computer. Through absorption of the KrF line (248.4 nm) of the excimer laser by benzene and its fluor derivatives, vibrationally excited levels in the first electronically excited singulet state were populated and the concomitant fluorescence was observed and resolved in spectrum and time.

Langel, W.

1980-12-01

371

Femtosecond laser damage threshold of pulse compression gratings for petawatt scale laser systems.  

PubMed

Laser-induced femtosecond damage thresholds of Au and Ag coated pulse compression gratings were measured using 800 nm laser pulses ranging in duration from 30 to 200 fs. These gratings differ from conventional metal-on-photoresist pulse compression gratings in that the gratings patterns are generated by etching the fused silica substrate directly. After etching, the metal overcoating was optimized based on diffraction efficiency and damage threshold considerations. The experiment on these gratings was performed under vacuum for single-shot damage. Single-shot damage threshold, where there is a 0% probability of damage, was determined to be within a 400-800 mJ/cm(2) range. The damage threshold exhibited no clear dependence on pulse width, but showed clear dependence on gold overcoat surface morphology. This was confirmed by electromagnetic field modeling using the finite element method, which showed that non-conformal coating morphology gives rise to significant local field enhancement near groove edges, lowering the diffraction efficiency and increasing Joule heating. Large-scale gratings with conformal coating have been installed successfully in the 500 TW Scarlet laser system. PMID:24216857

Poole, Patrick; Trendafilov, Simeon; Shvets, Gennady; Smith, Douglas; Chowdhury, Enam

2013-11-01

372

Optimizing a cleaning process for multilayer-dielectric- (MLD) diffraction gratings  

NASA Astrophysics Data System (ADS)

A critical component for the OMEGA EP short-pulse petawatt laser system is the grating compressor chamber (GCC). This large (12,375 ft3) vacuum chamber contains critical optics where laser-pulse compression is performed at the output of the system on two 40-cm-sq-aperture, IR (1054-nm) laser beams. Critical to this compression, within the GCC, are four sets of tiled multilayer-dielectric- (MLD) diffraction gratings that provide the capability for producing 2.6-kJ output IR energy per beam at 10 ps. The primary requirements for these large-aperture (43-cm × 47-cm) gratings are diffraction efficiencies greater than 95%, peak-to-valley wavefront quality of less than ?/10 waves, and laser-induced-damage thresholds greater than 2.7 J/cm2 at 10-ps measured beam normal. Degradation of the grating laser-damage threshold due to adsorption of contaminants from the manufacturing process must be prevented to maintain system performance. In this paper we discuss an optimized cleaning process to achieve the OMEGA EP requirements. The fabrication of MLD gratings involves processes that utilize a wide variety of both organic materials (photoresist processes) and inorganic materials (metals and metal oxides) that can affect the final cleaning process. A number of these materials have significant optical absorbance; therefore, incomplete cleaning of these residues may result in the MLD gratings experiencing laser damage.

Ashe, B.; Giacofei, C.; Myhre, G.; Schmid, A. W.

2008-01-01

373

Detection of trace phosphorus in steel using laser-induced breakdown spectroscopy combined with laser-induced fluorescence  

SciTech Connect

Monitoring of light-element concentration in steel is very important for quality assurance in the steel industry. In this work, detection in open air of trace phosphorus (P) in steel using laser-induced breakdown spectroscopy (LIBS) combined with laser-induced fluorescence (LIF) has been investigated. An optical parametric oscillator wavelength-tunable laser was used to resonantly excite the P atoms within plasma plumes generated by a Q-switched Nd:YAG laser. A set of steel samples with P concentrations from 3.9 to 720 parts in 10{sup 6}(ppm) were analyzed using LIBS-LIF at wavelengths of 253.40 and 253.56 nm for resonant excitation of P atoms and fluorescence lines at wavelengths of 213.55 and 213.62 nm. The calibration curves were measured to determine the limit of detection for P in steel, which is estimated to be around 0.7 ppm. The results demonstrate the potential of LIBS-LIF to meet the requirements for on-line analyses in open air in the steel industry.

Shen, X. K.; Wang, H.; Xie, Z. Q.; Gao, Y.; Ling, H.; Lu, Y. F.

2009-05-01

374

Blazed phononic crystal grating  

NASA Astrophysics Data System (ADS)

It is well known that blazed optical diffraction gratings can significantly increase the diffraction efficiency of plane waves for a selected angle of incidence. We show that by combining blazing with a phononic band gap, diffraction efficiency approaching 100% can be achieved for acoustic waves. We obtain experimentally 98% diffraction efficiency with a two-dimensional phononic crystal of rotated steel rods of square cross-section immersed in water. This result opens the way toward the design of efficient phononic crystal gratings.

Moiseyenko, Rayisa P.; Liu, Jingfei; Declercq, Nico F.; Laude, Vincent

2013-01-01

375

Diffraction grating lens array  

Microsoft Academic Search

We have proposed a new type of camera module with a thin structure and distance-detection capability. This camera module has a four-lens-array with diffraction gratings (one for blue, one for red, and two for green). The diffraction gratings on the mold are formed mechanically, and the plastic lens array is fabricated by injection molding. The two green images are compared

Tsuguhiro Korenaga; Takamasa Ando; Seiji Moriguchi; Fuminori Takami; Yoshifumi Takasu; Seiji Nishiwaki; Masa-aki Suzuki; Michiyoshi Nagashima

2007-01-01

376

Diffraction Gratings WDM Components  

Microsoft Academic Search

Diffraction grating WDM components have tremendous capability in number of channels (160 channel components and more with\\u000a bi-directionality are commercially available and components with two times more channels have been demonstrated experimentally).\\u000a They have a high free spectral range (typically 775 nm with gratings working in the first order). Small spacing such as 25\\u000a GHz is commercially available and 5

Jean-Pierre Laude

377

Radial Variation of Refractive Index, Plasma Frequency and Phase Velocity in Laser Induced Air Plasma  

Microsoft Academic Search

Laser-induced breakdown spectroscopy (LIBS) is a nonintrusive technique that needs no sample preparation and even recently, quantitative measurements were done without the need for calibration standards. Much research has been done on the laser induced air plasma to study the spatial variation of plasma parameters in the axial direction of the laser beam. In this paper, we report investigation on

Manny Mathuthu; Rita M. Raseleka; Andrew Forbes; Nicholas West

2006-01-01

378

Laser ablation laser induced fluorescence for sensitive detection of heavy metals in water  

Microsoft Academic Search

Laser Induced Breakdown Spectroscopy LIBS is a fast non-contact technique for the analysis of the elemental composition using spectral information of the emission from a laser-induced plasma. For the LIBS studies in this thesis the focus has been in using very low energy, microjoule pulses in order to give high spatial resolution and minimize the laser system requirements. This is

Yogesh Godwal

2010-01-01

379

Laser-induced breakdown versus self-focusing for focused picosecond pulses in water  

NASA Astrophysics Data System (ADS)

We present numerical studies of nonlinear propagation for picosecond pulses focused in water. Depending on the pulse duration and focusing conditions, for some input powers self-focusing may precede laser-induced breakdown and vice versa. We derive a criterion that predicts the relative roles of laser-induced breakdown and self-focusing.

Feng, Q.; Moloney, J. V.; Newell, A. C.; Wright, E. M.

1995-10-01

380

Laser induced damage thresholds and laser safety levels. Do the units of measurement matter?  

Microsoft Academic Search

The commonly used units of measurement for laser induced damage are those of peak energy or power density. However, the laser induced damage thresholds, LIDT, of all materials are well known to be absorption, wavelength, spot size and pulse length dependent. As workers using these values become divorced from the theory it becomes increasingly important to use the correct units

R. M. Wood

1998-01-01

381

Highly refractive index sensitive femtosecond laser inscribed long period gratings  

NASA Astrophysics Data System (ADS)

The distinct behaviour of femtosecond laser inscribed long period gratings, with a non-uniform index perturbation within the optical fibre core, has been studied experimentally. The non-uniform laser-induced perturbation results in light coupling from the core mode to a greater number of cladding modes than is the case with their UV laser inscribed counterparts, and this is made evident from the surrounding refractive index (SRI) grating response. Femtosecond inscribed long period gratings are shown to simultaneously couple to multiple sets of cladding modes. A 400?m LPG is shown to result in attenuation peaks that have both blue and red wavelength shifts over a 1250nm to 1700nm wavelength range. This gives rise to SRI sensitivities far greater than anything achievable by monitoring a single attenuation peak. The maximum sensitivity produced by monitoring a single attenuation peak was 1106nm/RIU, whereas monitoring opposing wavelength shifts resulted in a significantly improved sensitivity of 1680nm/RIU.

Davies, Edward; Kalli, Kyriacos; Koutsides, Charalambos; Zhang, Lin

2011-05-01

382

Neuroprotective therapy for argon-laser-induced retinal injury  

NASA Astrophysics Data System (ADS)

Laser photocoagulation treatment of the central retina is often complicated by an immediate side effect of visual impairment, caused by the unavoidable laser-induced destruction of the normal tissue lying adjacent to the lesion and not affected directly by the laser beam. Furthermore, accidental laser injuries are at present untreatable. A neuroprotective therapy for salvaging the normal tissue might enhance the benefit obtained from treatment and allow safe perifoveal photocoagulation. We have developed a rat model for studying the efficacy of putative neuroprotective compounds in ameliorating laser-induced retinal damage. Four compounds were evaluated: the corticosteroid methylprednisolone, the glutamate-receptor blocker MK-801, the anti-oxidant enzyme superoxide dismutase, and the calcim-overload antagonist flunarizine. The study was carried out in two steps: in the first, the histopathological development of retinal laser injuries was studied. Argon laser lesions were inflicted in the retinas of 18 pigmented rats. The animals were sacrificed after 3, 20 or 60 days and their retinal lesions were evaluated under the light microscope. The laser injury mainly involved the outer layers of the retina, where it destroyed significant numbers of photoreceptor cells. Over time, evidence of two major histopathological processes was observed: traction of adjacent nomral retinal cells into the central area of the lesion forming an internal retinal bulging, and a retinal pigmented epithelial proliferative reaction associated with subretinal neovascularization and invations of the retinal lesion site by phagocytes. The neuroprotective effects of each of the four compounds were verified in a second step of the study. For each drug tested, 12 rats were irradiated wtih argon laser inflictions: six of them received the tested agent while the other six were treated with the corresponding vehicle. Twenty days after laser expsoure, the rats were sacrificed and their lesions were subjected to image-analysis morphometry. The extent of retianl damage was assessed by measuring the lesion diameter and the amount of photoreceptor cell loss in the outer nuclear layer. Methylprednisolone and MI-801 were shown to ameliorate laser-induced retinal damage, whereas both superoxide dismutase and flunarizine were ineffective. Furthermore, MK-801 diminished the proliferative reaction of the retinal pigment epithelial cells. On the basis of our results we suggest that the pigmented rat model is suitable for studying and screening various compounds for their neuroprotective efficacy in treating retinal laser injury. We further suggest that glutamate might play a key role in mediating retinal injury induced by laser irradiation.

Belkin, Michael; Rosner, Mordechai; Solberg, Yoram; Turetz, Yosef

1999-06-01

383

Laser-induced plasma generation and evolution in a transient spray.  

PubMed

The behaviors of laser-induced plasma and fuel spray were investigated by visualizing images with an ultra-high-speed camera. Time-series images of laser-induced plasma in a transient spray were visualized using a high-speed color camera. The effects of a shockwave generated from the laser-induced plasma on the evaporated spray behavior were investigated. The interaction between a single droplet and the laser-induced plasma was investigated using a single droplet levitated by an ultrasonic levitator. Two main conclusions were drawn from these experiments: (1) the fuel droplets in the spray were dispersed by the shockwave generated from the laser-induced plasma; and (2) the plasma position may have shifted due to breakdown of the droplet surface and the lens effect of droplets. PMID:24921999

Kawahara, Nobuyuki; Tsuboi, Kazuya; Tomita, Eiji

2014-01-13

384

Defect geometries and laser-induced damage in multilayer coatings  

SciTech Connect

A correlation between laser-induced damage and the height of a coating defect was found from an examination of HfO{sub 2}/SiO{sub 2} mirrors made by three different coating vendors. The nodular defects in these reactive e-beam deposited mirrors were studied using the combination of SEM, optical microscopy, FIB and AFM techniques. Each vendor had small defects in common, but characteristically different large defects. Also the majority of seeds that caused the defects were made of hafnia, not silica. The apparent mechanical stability of the defects within the coating plays a major role in the laser resistance (1064 nm and l0ns) of a high damage threshold coating.

Tench, R.J.; Kozlowski, M.R.; Chow, R.

1994-07-01

385

Defect geometries and laser-induced damage in multilayer coatings  

NASA Astrophysics Data System (ADS)

A correlation between laser-induced damage and the height of a coating defect was found from an examination of HfO2/SiO2 mirrors made by three different coating vendors. The nodular defects in these reactive e-beam deposited mirrors were studied using the combination of scanning electron microscopy (SEM), optical microscopy, focused ion beam (FIB) and atomic force microscopy (AFM) techniques. Each vendor has small defects in common, but characteristically different large defects. also the majority of seeds that caused the defects were made of hafnia, not silica. The apparent mechanical stability of the defects within the coating plays a major role in the laser resistance (1064 nm and 10 ns) of a high damage threshold coating.

Tench, Robert J.; Kozlowski, Mark R.; Chow, Robert

1994-09-01

386

Laser-induced photo-thermal magnetic imaging  

NASA Astrophysics Data System (ADS)

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.

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

2012-08-01

387

Ultraviolet-laser-induced permanent electrical conductivity in polyimide  

NASA Astrophysics Data System (ADS)

When polyimide (Kapton) is irradiated by a krypton fluoride (KrF) laser, an increase of the electrical conductivity of up to 16 orders of magnitude is observed. In the high conduction regime, the resistivity is about 0.1 ? cm, the current voltage characteristic is ohmic and the contacts of gold and silver with the irradiated conducting polymer are also ohmic. The conduction mechanism is phonon-assisted variable range hopping, evident from the observed temperature and electric field dependence of the resistivity at low conductivities. The laser-induced conductivity depends on the ambient atmosphere during irradiation. Transmission spectroscopy in the visible region and infrared Fourier transform spectroscopy have been used to characterize the material. A thermal mechanism is proposed for the formation of conducting polyimide, by excimer-laser irradiation.

Feurer, T.; Sauerbrey, R.; Smayling, M. C.; Story, B. J.

1993-03-01

388

Laser-induced breakdown spectroscopy (LIBS): applications in environmental issues  

NASA Astrophysics Data System (ADS)

Results are presented from three different applications of laser induced breakdown spectroscopy (LIBS) in problems of environmental interest. In one case, LIBS is applied in the on-line control of the nickel recovery process, by monitoring the nickel content of molten ferronickel slabs, in a laboratory scale experiment. In a second case, LIBS is used in the identification of polymer materials, and on the basis of spectral features, criteria are proposed for the distinction among different types of plastic materials. Also, in preliminary experiments, the use of LIBS with respect to the detection of heavy and toxic metals in paints and the possibility of performing depth profile analysis of multiple paint layers is examined.

Couris, Stelios; Hatziapostolou, A.; Anglos, Dmitrios; Mavromanolakis, A.; Fotakis, Costas

1996-11-01

389

Terahertz generation in multiple laser-induced air plasmas  

SciTech Connect

An investigation of the terahertz wave generation in multiple laser-induced air plasmas is presented. First, it is demonstrated that the intensity of the terahertz wave increases as the number of air plasmas increases. Second, the physical mechanism of this enhancement effect of the terahertz generation is studied by quantitatively measuring the intensity of the generated terahertz wave as a function of phase difference between adjacent air plasmas. It is found out that the superposition is the main mechanism to cause this enhancement. Thus, the results obtained in this paper not only provide a technique to generate stronger terahertz wave but also enable a better understanding of the mechanism of the terahertz generation in air plasma.

Chen, M.-K.; Kim, Jae Hun; Yang, C.-E.; Yin, Stuart Shizhuo [Department of Electrical Engineering, The Pennsylvania State University, University Park, Pennsylvania 16802 (United States); Hui Rongqing [Department of Electrical Engineering and Computer Science, University of Kansas, Lawrence, Kansas 66045 (United States); Ruffin, Paul [US Army Aviation and Missile Research Development and Engineering Center, Redstone Arsenal, Alabama 35898 (United States)

2008-12-08

390

Laser-induced photo-thermal magnetic imaging.  

PubMed

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. PMID:22991481

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

2012-08-20

391

Laser induced extraplanar propulsion for three-dimensional microfabrication  

SciTech Connect

The laser induced extraplanar propulsion process is presented for the creation of controllable three-dimensional deformation of on-substrate components. It is demonstrated that the process is compatible with transparent substrates and ductile materials and is highly controllable in terms of the desired deformation via the adjustment of incident laser energy density. Copper films with thicknesses varying from 0.1-1 {mu}m are deformed over bending angles ranging from 0 deg. - 180 deg. A 355 nm laser at fluences ranging from 10-40 mJ/cm{sup 2} is used in conjunction with an indium-tin-oxide propulsion layer to demonstrate the process. Characterization is performed via electron and laser confocal microscopy.

Birnbaum, A. J.; Pique, A. [Materials Science and Technology Division, Code 6364, Naval Research Laboratory, Washington, DC 20375 (United States)

2011-03-28

392

Two-Photon/Laser-Induced Fluorescence (TP/LIF) sensor  

NASA Technical Reports Server (NTRS)

The Two-Photon/Laser-Induced Fluorescence (TP/LIF) technique is based on the stepwise excitation of the OH transitions, X(exp 2)II, v(exp '') = 0 yields X(exp 2)II, v(exp '') = 1 (lambda = 2.9 microns) and X(exp 2)II v(exp '') = 1 yields A(exp2)Sigma, v' = 0 (lambda = 345 nm) with background free fluorescence monitoring of the A(exp 2)Sigma, v' = 0 yields X(exp 2)II, v(exp '') = 0 transition near 309 nm. This technique has awaited the advent of a suitable mid-infrared (2.9 microns) laser source. Turnable mid-IR lasers now exist that are capable of meeting the specifications required of a high sensitivity TP/LIF OH sensor.

Bradshaw, John D.

1994-01-01

393

[Influence factors analysis for laser-induced plasma spectroscopy measurements].  

PubMed

An experimental equipment has been set up for laser-induced plasma spectroscopic (LIPS) measurement based on a Nd: YAG Q-switched solid laser (average single pulse energy is 38 mJ) as exciting light source and the copper alloy as sample. The instrument time distribution of Cu radiation was obtained, and the software and hardware influence factors on the measured spectra were analyzed. The experiments proved that the fluctuation of laser output energy, average number of each datum, the position between the target surface and the lens focus, the position between the optical fiber bundle for receiving the radiation and the normal of the target surface, and the effective receiving area of the optical fiber bundle all influence the intensity of spectra and the reproducibility of measurement. PMID:16544468

Li, Jing; Lin, Chang-He; Li, Sheng-Li

2005-12-01

394

Diagnostics for the detection and evaluation of laser induced damage  

NASA Astrophysics Data System (ADS)

The Laser Damage and Conditioning Group at LLNL is evaluating diagnostics which will help make damage testing more efficient and reduce the risk of damage during laser conditioning. The work to date has focused on photoacoustic and scattered light measurements on 1064-nm wavelength HfO2/SiO2 multilayer mirror and polarizer coatings. Both the acoustic and scatter diagnostics have resolved 10 micron diameter damage points in these coatings. Using a scanning stage, the scatter diagnostic can map both intrinsic and laser-induced scatter. Damage threshold measurements obtained using scatter diagnostics compare within experimental error with those measured using 100x Nomarski microscopy. Scatter signals measured during laser conditioning can be used to detect damage related to nodular defects.

Sheehan, L.; Kozlowski, M.; Rainer, F.

1995-01-01

395

Laser-induced periodic surface structures: Fingerprints of light localization  

NASA Astrophysics Data System (ADS)

The finite-difference time-domain (FDTD) method is used to study the inhomogeneous absorption of linearly polarized laser radiation below a rough surface. The results are first analyzed in the frequency domain and compared to the efficacy factor theory of Sipe and coworkers. Both approaches show that the absorbed energy shows a periodic nature, not only in the direction orthogonal to the laser polarization, but also in the direction parallel to it. It is shown that the periodicity is not always close to the laser wavelength for the perpendicular direction. In the parallel direction, the periodicity is about ?/Re(ñ), with ñ being the complex refractive index of the medium. The space-domain FDTD results show a periodicity in the inhomogeneous energy absorption similar to the periodicity of the low- and high-spatial-frequency laser-induced periodic surface structures depending on the material's excitation.

Skolski, J. Z. P.; Römer, G. R. B. E.; Obona, J. V.; Ocelik, V.; Huis in't Veld, A. J.; de Hosson, J. Th. M.

2012-02-01

396

MoI density measurements by laser induced fluorescence spectroscopy  

NASA Astrophysics Data System (ADS)

The density of molybdenum atoms produced by sputtering of a TZM (molybdenum) target by Ar+ ions is measured by laser induced fluorescence (LIF) using tunable dye laser. The excitation transition involved is a7S3-z5P30 at 345.64 nm, while the fluorescence signal is from the decay z5P30-a5S2 at 550.6 nm. The LIF measurements are carried out by varying the laser power incident on Mo atoms by means of neutral density filters. An absolute calibration of the detection system together with the realization of a well defined optical probe volume allows for the determination of the density of the emitting atoms. An evaluation of LIF diagnostic performance on Frascati Tokamak upgrade put a lower limit of 2.5×1014 atoms/m3 on the detectable local density of MoI close to the toroidal limiter.

Orsitto, F.; Borra, M.; Coppotelli, F.; Gatti, G.; Neri, E.

1999-01-01

397

Laser-induced damage measurements with 266-nm pulses  

SciTech Connect

The results of a survey of laser-induced damage thresholds for optical components at 266 nm are reported. The thresholds were measured at two pulse durations--0.150 ns and 1.0 ns. The 30 samples tested include four commercial dielectric reflectors, three metallic reflectors, two anti-reflection films, a series of eight half-wave oxide and fluoride films, and twelve bare surfaces (fluoride crystals, silica, sapphire, BK-7 glass, CD*A and KDP). The 266-nm pulses were obtained by frequency-quadrupling a Nd:YAG, glass laser. Equivalent plane imagery and calorimetry were used to measure the peak fluence of each of the UV pulses with an accuracy of +- 15%; the uncertainty in the threshold determinations is typically +- 30%.

Deaton, T.F.; Smith, W.L.

1980-01-23

398

An investigation of laser induced surface damage in glass  

NASA Astrophysics Data System (ADS)

Laser-induced plasma surface damage in a transparent dielectric is investigated. The possible occurrence of unipolar arcing as a damage mechanism in nonconductors is examined. Experiments were conducted using a neodymium glass laser in a Q-switched mode to create a hot plasma. The plasma damage on both entrance and exit surfaces was examined. The morphology of damage is qualitatively analyzed. Several theories are applied in explanation of the damage obtained. The appearance of micropitting at the periphery of the laser impact area of the targets indicates the possible occurrence of unipolar arcing as a damage mechanism. Other damage mechanisms include thermal stress, electron avalanche, particle deposition, and micropitting from particle inclusions or surface imperfections.

Uyak, R. D.

1985-06-01

399

Laser-induced photo-thermal magnetic imaging  

PubMed Central

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.

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

2012-01-01

400

Laser-induced breakdown spectroscopy analysis of energetic materials  

NASA Astrophysics Data System (ADS)

A number of energetic materials and explosives have been studied by laser-induced breakdown spectroscopy (LIBS). They include black powder, neat explosives such as TNT, PETN, HMX, and RDX (in various forms), propellants such as M43 and JA2, and military explosives such as C4 and LX-14. Each of these materials gives a unique spectrum, and generally the spectra are reproducible shot to shot. We observed that the laser-produced microplasma did not initiate any of the energetic materials studied. Extensive studies of black powder and its ingredients by use of a reference spectral library have demonstrated excellent accuracy for unknown identification. Finally, we observed that these nitrogen- and oxygen-rich materials yield LIBS spectra in air that have correspondingly different O:N peak ratios compared with air. This difference can help in the detection and identification of such energetic materials.

de Lucia, Frank C.; Harmon, Russell S.; McNesby, Kevin L.; Winkel, Raymond J.; Miziolek, Andrzej W.

2003-10-01

401

Laser-induced breakdown spectroscopy expands into industrial applications  

NASA Astrophysics Data System (ADS)

This paper presents R&D activities in the field of laser-induced breakdown spectroscopy for industrial applications and shows novel LIBS systems running in routine operation for inline process control tasks. Starting with a comparison of the typical characteristics of LIBS with XRF and spark-discharge optical emission spectrometry, the principal structure of LIBS machines embedded for inline process monitoring will be presented. A systematic requirement analysis for LIBS systems following Ishikawa's scheme was worked out. Stability issues are studied for laser sources and Paschen-Runge spectrometers as key components for industrial LIBS systems. Examples of industrial applications range from handheld LIBS systems using a fiber laser source, via a set of LIBS machines for inline process control tasks, such as scrap analysis, coal analysis, liquid slag analysis and finally monitoring of drill dust.

Noll, Reinhard; Fricke-Begemann, Cord; Brunk, Markus; Connemann, Sven; Meinhardt, Christoph; Scharun, Michael; Sturm, Volker; Makowe, Joachim; Gehlen, Christoph

402

Evaluation of Laser-Induced Breakdown Spectroscopy as Technetium Monitor  

SciTech Connect

The analytical figure of merit of a laser-induced breakdown (LIBS) system was evaluated for technetium measurements in liquid. LIBS data of elements that have similar properties to Tc such as Cr, Mn, and Re were studied. Various optical geometries which produce the laser spark in and at the liquid sample were tested. The calibration curve for Mn, Cr, and Re were obtained at the optimized experimental conditions with bulk liquid and liquid jet. We found that measurements using a liquid jet provide better detection limits than the bulk liquid measurements. The detection limits of Mg, Cr, Mn, and Re in a liquid jet measurement are found to be 0.1, 0.4, 0.7, and 10 ppm, respectively.

Spencer, W.A.; Yueh, F.Y.; Sharma, R.C.; Singh, J.P.; Zhang, H.

2000-11-14

403

Quantitative analysis of gallstones using laser-induced breakdown spectroscopy  

SciTech Connect

The utility of laser-induced breakdown spectroscopy (LIBS) for categorizing different types of gallbladder stone has been demonstrated by analyzing their major and minor constituents. LIBS spectra of three types of gallstone have been recorded in the 200-900 nm spectral region. Calcium is found to be the major element in all types of gallbladder stone. The spectrophotometric method has been used to classify the stones. A calibration-free LIBS method has been used for the quantitative analysis of metal elements, and the results have been compared with those obtained from inductively coupled plasma atomic emission spectroscopy (ICP-AES) measurements. The single-shot LIBS spectra from different points on the cross section (in steps of 0.5 mm from one end to the other) of gallstones have also been recorded to study the variation of constituents from the center to the surface. The presence of different metal elements and their possible role in gallstone formation is discussed.

Singh, Vivek K.; Singh, Vinita; Rai, Awadhesh K.; Thakur, Surya N.; Rai, Pradeep K.; Singh, Jagdish P

2008-11-01

404

Laser induced extraplanar propulsion for three-dimensional microfabrication  

NASA Astrophysics Data System (ADS)

The laser induced extraplanar propulsion process is presented for the creation of controllable three-dimensional deformation of on-substrate components. It is demonstrated that the process is compatible with transparent substrates and ductile materials and is highly controllable in terms of the desired deformation via the adjustment of incident laser energy density. Copper films with thicknesses varying from 0.1-1 ?m are deformed over bending angles ranging from 0°-180°. A 355 nm laser at fluences ranging from 10-40 mJ/cm2 is used in conjunction with an indium-tin-oxide propulsion layer to demonstrate the process. Characterization is performed via electron and laser confocal microscopy.

Birnbaum, A. J.; Piqué, A.

2011-03-01

405

Diagnostics for the detection and evaluation of laser induced damage  

SciTech Connect

The Laser Damage and Conditioning Group at LLNL is evaluating diagnostics which will help make damage testing more efficient and reduce the risk of damage during laser conditioning. The work to date has focused on photoacoustic and scattered light measurements on 1064-nm wavelength HfO{sub 2}/SiO{sub 2} multilayer mirror and polarizer coatings. Both the acoustic and scatter diagnostics have resolved 10 {mu}m diameter damage points in these coatings. Using a scanning stage, the scatter diagnostic can map both intrinsic and laser-induced scatter. Damage threshold measurements obtained using scatter diagnostics compare within experimental error with those measured using 100x Nomarski microscopy. Scatter signals measured during laser conditioning can be used to detect damage related to nodular defects.

Sheehan, L.; Kozlowski, M.; Rainer, F.

1995-01-03

406

Prediction of absorption coefficients by pulsed laser induced photoacoustic measurements  

NASA Astrophysics Data System (ADS)

In the current study, a pulsed laser induced photoacoustic spectroscopy setup was designed and developed, aiming its application in clinical diagnostics. The setup was optimized with carbon black samples in water and with various tryptophan concentrations at 281 nm excitations. The sensitivity of the setup was estimated by determining minimum detectable concentration of tryptophan in water at the same excitation, and was found to be 0.035 mM. The photoacoustic experiments were also performed with various tryptophan concentrations at 281 nm excitation for predicting optical absorption coefficients in them and for comparing the outcomes with the spectrophotometrically-determined absorption coefficients for the same samples. Absorption coefficients for a few serum samples, obtained from some healthy female volunteers, were also determined through photoacoustic and spectrophotometric measurements at the same excitations, which showed good agreement between them, indicating its clinical implications.

Priya, Mallika; Satish Rao, B. S.; Ray, Satadru; Mahato, K. K.

2014-06-01

407

Evaluating Photodynamic Therapy Efficacy Using Laser Induced Breakdown Spectroscopy  

NASA Astrophysics Data System (ADS)

Laser-induced breakdown spectroscopy (LIBS), is an excellent tool for trace elemental analysis, was exploited for a detecting concentrations of calcium and magnesium in malignant tissues before and after PDT. Calcium and magnesium concentrations are known tobe high in malignancy. Tissues were injected with methylene blue photosensitizer with concentrations 0.5%, 1% and 2%. Two different light sources were used with two different energy densities/each light sources. The results showed a decrease in tissue elements content after PDT application for both calcium and magnesium compared to before PDT application as shown in the tissue spectral lines' intensities which has been reflected in. Type of light source showed no effect on tissue elements content which showed slight differences among the different energy densities. It has been shown that LIBS technique can be adopted method to monitor tumor photodynamic therapy applications.

Fekry, O.; El-Batanouny, M. H.; El-Begawy, M. B.; Harith, M. A.

2011-09-01

408

Optical properties of laser induced oxynitride films on titanium  

NASA Astrophysics Data System (ADS)

This paper presents a study of the optical properties and chemical composition of laser-induced color oxynitride films formed on titanium substrates in a normal-pressure atmospheric environment. The samples were investigated by spectroscopic ellipsometry and X-ray photoelectron spectroscopy. The influence of the laser fluence F on the optical properties of oxynitride films has been found. The thickness of the layers ranges from ?20 nm to ?40 nm and increases linearly with F. The determined complex dielectric functions demonstrate two absorption bands, one of them appears in the visible-light wavelength range. We show that the color created by oxynitride films formed on the titanium surface depends not only on the interference effect as commonly assumed, but is also a function of the changes of the optical properties of these coatings.

Skowro?ski, ?.; Anto?czak, A. J.; Trzcinski, M.; ?azarek, ?.; Hiller, T.; Bukaluk, A.; Wronkowska, A. A.

2014-06-01

409

Laser-induced fluorescence spectroscopy in tissue local necrosis detection  

NASA Astrophysics Data System (ADS)

The recent effort leads to reliable imaging techniques which can help to a surgeon during operations. The fluorescence spectroscopy was selected as very useful online in vivo imaging method to organics and biological materials analysis. The presented work scopes to a laser induced fluorescence spectroscopy technique to detect tissue local necrosis in small intestine surgery. In first experiments, we tested tissue auto-fluorescence technique but a signal-to-noise ratio didn't express significant results. Then we applied a contrast dye - IndoCyanine Green (ICG) which absorbs and emits wavelengths in the near IR. We arranged the pilot experimental setup based on highly coherent extended cavity diode laser (ECDL) used for stimulating of some critical areas of the small intestine tissue with injected ICG dye. We demonstrated the distribution of the ICG exciter with the first file of shots of small intestine tissue of a rabbit that was captured by high sensitivity fluorescent cam.

Cip, Ondrej; Buchta, Zdenek; Lesundak, Adam; Randula, Antonin; Mikel, Bretislav; Lazar, Josef; Veverkova, Lenka

2014-03-01

410

Elemental analysis of slurry samples with laser induced breakdown spectroscopy  

SciTech Connect

Direct analysis of wet slurry samples with laser induced breakdown spectroscopy (LIBS) is challenging due to problems of sedimentation, splashing, and surface turbulence. Also, water can quench the laser plasma and suppress the LIBS signal, resulting in poor sensitivity. The effect of water on LIBS spectra from slurries was investigated. As the water content decreased, the LIBS signal was enhanced and the standard deviation was reduced. To improve LIBS slurry analysis, dried slurry samples prepared by applying slurry on PVC coated slides were evaluated. Univariate and multivariate calibration was performed on the LIBS spectra of the dried slurry samples for elemental analysis of Mg, Si, and Fe. Calibration results show that the dried slurry samples give a good correlation between spectral intensity and elemental concentration.

Eseller, Kemal E.; Tripathi, Markandey M.; Yueh, Fang-Yu; Singh, Jagdish P.

2010-05-01

411

Alloying aluminum with Fe using laser induced plasma technique  

NASA Astrophysics Data System (ADS)

A new surface modification technique is demonstrated using laser induced plasma (LIP) to increase the hardness of the surface layer. This LIP treatment provides a very high heating and fast cooling mechanism that can be used to form alloyed layer on a material surface. The hardness of the alloyed material is measured and the results show that the alloyed surface is 3 times as hard as the un-treated surface and a single Fe alloyed aluminum surface is harder than the one formed by the mixture of Fe and Cu. The micro-hardness of the alloy increases with the number of pulses at a rate of around 4 HV/pulse. The maximum hardness of 93.0 HV is obtained with the use of single Fe after exposure to 7 pulses of the laser.

Alwafi, Y. A.; Bidin, N.; Gustiono, D.; Harun, S. W.

2012-08-01

412

Femtosecond laser-induced microwelding of silver and copper.  

PubMed

Femtosecond (fs) laser irradiation has been shown to be effective for welding transparent materials and for transparent materials to metals. However, to date there is little work regarding similar applications in welding/bonding of metals. In this article, we for the first time to the best of our knowledge report on fs laser-induced microwelding of Ag microwires and Cu substrates. The influence of laser pulse number and fluence on fs laser microwelding is studied to explore an optimum welding window. Morphology analysis indicates that the primary weld of the Ag microwire and the Cu substrate was located at the edge of the Ag microwire and produced via the redeposition and local melting-induced welding of the ablated materials. PMID:23434991

Huang, Hong; Hu, Anming; Peng, Peng; Duley, Walter Winston; Zhou, Yunhong

2013-02-20

413

Titanium monoxide spectroscopy following laser-induced optical breakdown  

SciTech Connect

This work investigates Titanium Monoxide (TiO) in ablation-plasma by employing laser-induced breakdown spectroscopy (LIBS) with 1 to 10 TW/cm{sup 2} irradiance, pulsed, 13 nanosecond, Q-switched Nd:YAG laser radiation at the fundamental wavelength of 1064 nm. The analysis of TiO is based on our first accurate determination of transition line strengths for selected TiO A-X, B-X, and E-X transitions, particularly TiO A-X {gamma} and B-X {gamma} Prime bands. Electric dipole line strengths for the A{sup 3}{Phi}-X{sup 3}{delta} and B{sup 3}{Pi}-X{sup 3}{delta} bands of TiO are computed. The molecular TiO spectra are observed subsequent to laser-induced breakdown (LIB). We discuss analysis of diatomic molecular spectra that may occur simultaneously with spectra originating from atomic species. Gated detection is applied to investigate the development in time of the emission spectra following LIB. Collected emission spectra allow one to infer micro-plasma parameters such as temperature and electron density. Insight into the state of the micro-plasma is gained by comparing measurements with predictions of atomic and molecular spectra. Nonlinear fitting of recorded and computed diatomic spectra provides the basis for molecular diagnostics, while atomic species may overlap and are simultaneously identified. Molecular diagnostic approaches similar to TiO have been performed for diatomic molecules such as AlO, C{sub 2}, CN, CH, N{sub 2}, NH, NO and OH.

Parigger, Christian G.; Woods, Alexander C.; Keszler, Anna; Nemes, Laszlo; Hornkohl, James O. [The University of Tennessee/UT Space Institute, Center for Laser Applications, 411 B.H. Goethert Parkway, Tullahoma, TN 37388-9700 (United States); Chemical Research Center of the Hungarian Academy of Sciences, Institute of Materials and Environmental Chemistry, Pusztaszeri ut 59-67, H-1025 Budapest (Hungary); Chemical Research Center of the Hungarian Academy of Sciences, Laser Spectroscopy Laboratory, Pusztaszeri ut 59-67, H-1025 Budapest (Hungary); Hornkohl Consulting, Tullahoma, TN 37388 (United States)

2012-07-30

414

Nanosecond laser-induced synthesis of nanoparticles with tailorable magneticanisotropy  

NASA Astrophysics Data System (ADS)

Controlling the magnetic orientation of nanoparticles is important for many applications. Recently, it has been shown that single domain ferromagnetic hemispherical Co nanoparticles prepared by nanosecond laser-induced self-organization, show magnetic orientation that was related to the negative sign of the magnetostrictive coefficient ?S [J. Appl. Phys. v103, p073902, 2008]. Here we have extended this work to the Fe 50Co 50 alloy, which has a positive ?S and Ni, which has a negative ?S. Patterned arrays of ferromagnetic nanoparticles of Fe 50Co 50, Ni, (and Co) were synthesized from their ultrathin metal films on SiO 2 substrate by nanosecond laser-induced self-organization. The morphology, nanostructure, and magnetic behavior of the nanoparticle arrays were investigated by a combination of electron microscopy, atomic force microscopy, and magnetic force microscopy techniques. Transmission electron microscopy investigations revealed a granular polycrystalline nanostructure, with the number of grains inside the nanoparticle increasing with their diameter. Magnetic force measurements showed that the magnetization direction of the hemispherical Co and Ni nanoparticles was predominantly out-of-plane while those for the Fe 50Co 50 alloy was in the plane of the substrate. Finite element analysis was used to estimate the average residual strain in the nanoparticles, following laser processing. The difference in behavior is due to the dominating influence of magnetostrictive energy on the magnetization as a result of residual thermal strain following fast laser processing. Since ?S is negative for polycrystalline Co and Ni, and positive for Fe 50Co 50, the tensile residual strain forces the magnetization direction to out-of-plane and in-plane, respectively. This work demonstrates a cost-effective non-epitaxial technique for the synthesis of magnetic nanoparticles with tailored magnetization orientations.

Krishna, H.; Gangopadhyay, A. K.; Strader, J.; Kalyanaraman, R.

2011-02-01

415

Kr II laser-induced fluorescence for measuring plasma acceleration  

SciTech Connect

We present the application of laser-induced fluorescence of singly ionized krypton as a diagnostic technique for quantifying the electrostatic acceleration within the discharge of a laboratory cross-field plasma accelerator also known as a Hall effect thruster, which has heritage as spacecraft propulsion. The 728.98 nm Kr II transition from the metastable 5d{sup 4}D{sub 7/2} to the 5p{sup 4}P{sub 5/2}{sup Ring-Operator} state was used for the measurement of laser-induced fluorescence within the plasma discharge. From these measurements, it is possible to measure velocity as krypton ions are accelerated from near rest to approximately 21 km/s (190 eV). Ion temperature and the ion velocity distributions may also be extracted from the fluorescence data since available hyperfine splitting data allow for the Kr II 5d{sup 4}D{sub 7/2}-5p{sup 4}P{sub 5/2}{sup Ring-Operator} transition lineshape to be modeled. From the analysis, the fluorescence lineshape appears to be a reasonable estimate for the relatively broad ion velocity distributions. However, due to an apparent overlap of the ion creation and acceleration regions within the discharge, the distributed velocity distributions increase ion temperature determination uncertainty significantly. Using the most probable ion velocity as a representative, or characteristic, measure of the ion acceleration, overall propellant energy deposition, and effective electric fields may be calculated. With this diagnostic technique, it is possible to nonintrusively characterize the ion acceleration both within the discharge and in the plume.

Hargus, W. A. Jr. [AFRL/RQRS, Edwards AFB, California 93524 (United States); Azarnia, G. M.; Nakles, M. R. [ERC, Inc., Edwards AFB, California 93524 (United States)

2012-10-15

416

Effects of pulse width on nascent laser-induced bubbles for underwater laser-induced breakdown spectroscopy  

NASA Astrophysics Data System (ADS)

The reason for the significant advantage offered by long-pulse (150 ns) irradiation in underwater laser-induced breakdown spectroscopy (LIBS) is investigated from the point of view of the behavior of nascent cavitation bubbles. Shadowgraphs of nascent bubbles generated by pulsed laser irradiation of Cu targets in water were observed for two different pulse widths, 20 ns and 150 ns. It is clearly seen that the nascent bubble is formed at the leading edge of the laser pulse profile, regardless of the pulse width. Bubbles generated by a 20-ns pulse are characterized by a flat-shape filled with dense matter with intense optical emission, which is in contrast to more hemispherical low-density bubbles observed under the irradiation by a 150-ns pulse. The behavior of the nascent bubbles is consistent with the behavior of the later plasma in the bubbles, which is crucial for observation of well-defined atomic spectral lines for underwater LIBS.

Sakka, Tetsuo; Tamura, Ayaka; Matsumoto, Ayumu; Fukami, Kazuhiro; Nishi, Naoya; Thornton, Blair

2014-07-01

417

Immersion grating and etched gratings for infrared astronomy  

Microsoft Academic Search

An immersion grating with a high refractive index, n, increases the spectral resolution by a factor n over that of a reflective surface grating of equal length. A silicon immersion grating has been developed and tested; initial results are reported here.

Guenter R. Wiedemann; Hemant H. Dave; Donald E. Jennings

1993-01-01

418

High speed inscription of uniform, large-area laser-induced periodic surface structures in Cr films using a high repetition rate fs laser.  

PubMed

We report on the fabrication of laser-induced periodic surface structures in Cr films upon high repetition rate fs laser irradiation (up to 1 MHz, 500 fs, 1030 nm), employing beam scanning. Highly regular large-area (9??cm2) gratings with a relative diffraction efficiency of 42% can be produced within less than 6 min. The ripple period at moderate and high fluences is 0.9 ?m, with a small period of 0.5 ?m appearing at lower energies. The role of the irradiation parameters on the characteristics of the laser-induced periodic surface structures (LIPSS) is studied and discussed in the frame of the models presently used. We have identified the polarization vector orientation with respect to the scan direction as a key parameter for the fabrication of high-quality, large-area LIPSS, which, for perpendicular orientation, allows the coherent extension of the sub-wavelength structure over macroscopic distances. The processing strategy is robust in terms of broad parameter windows and applicable to other materials featuring LIPSS. PMID:24979026

Ruiz de la Cruz, A; Lahoz, R; Siegel, J; de la Fuente, G F; Solis, J

2014-04-15

419

Multiplexing fiber bragg grating sensors  

Microsoft Academic Search

Bragg reflection gratings and out-coupling taps for sensors can be written holographically within the core of many commercial fibers available today. The gratings appear to be permanent and have been tested to temperatures in excess of 500°C. Quasi-distributed temperature, strain, pressure, chemical, and interferometric sensors can be made with the wavelength selective, reflection gratings, and taps. The fiber gratings, and

W. W. Morey; J. R. Dunphy; G. Meltz

1991-01-01

420

Laser-induced-fluorescence studies of fragment ions: CH/sup +/ and CD/sup +/  

SciTech Connect

The dynamics of ion-molecule interactions within a mass selective rf quadrupole ion trap are studied for several ion-molecule systems. Laser induced fluorescence is used as a probe of the internal energy distributions of molecular ions under collision free conditions and under controlled collision conditions. The effects of collisions at near thermal energies (0.3 to 0.5 eV) are easily understood in terms of processes such as charge transfer and other energy transfer mechanisms. The A/sup 1/PI - X/sup 1/..sigma../sup +/ system of CH/sup +/ and CD/sup +/ has been examined under collision free conditions. The ions were produced from methane through electron impact ionization/dissociation. The observed energy distributions reflect the dynamical partitioning of dissociation exothermicity, excepting short lived electronic states. Many new transitions belonging to this electronic system have been observed and a reliable vibrational frequency for the X/sup 1/..sigma../sup +/ state has been obtained. The radiative lifetimes of CH/sup +/ and CD/sup +/ A/sup 1/PI(v = 0) states have been measured and a revised oscillator strength for the A-X transition has been derived from this data.

O'Keefe, A.

1981-08-01

421

Sectioned thin-film grating  

Microsoft Academic Search

The resolving power of metallic linear gratings deposited on a dielectric thin-film waveguide can be increased by separating sections of the grating by blank spaces. Because of the high coupling efficiencies of gratings deposited directly on the waveguide, the effects of the blank spaces cannot be observed for such guides. If a dielectric film with an index of refraction less

W. D. Westwood; J. W. Y. Lit

1974-01-01

422

An elastomeric grating coupler  

NASA Astrophysics Data System (ADS)

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.

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

2006-01-01

423

Subwavelength grating filtering devices.  

PubMed

We propose and simulate the characteristics of optical filters based on subwavelength gratings. In particular, we demonstrate through numerical simulations the feasibility of implementing SWG Bragg gratings in silicon-on-insulator (SOI). We also propose SWG ring resonators in SOI and verify their operation using numerical simulations and experiments. The fabricated devices exhibit an extinction ratio as large as 30 dB and a Q-factor as high as ~20,000. These fundamental SWG filters can serve as building blocks for more complex devices. PMID:24977793

Wang, Junjia; Glesk, Ivan; Chen, Lawrence R

2014-06-30

424

Charged particle accelerator grating  

DOEpatents

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.

Palmer, Robert B. (Shoreham, NY)

1986-01-01

425

Detection of zinc and lead in water using evaporative preconcentration and single-particle laser-induced breakdown spectroscopy  

NASA Astrophysics Data System (ADS)

A novel laser-induced breakdown spectroscopy (LIBS)-based measurement method for metals in water is demonstrated. In the presented technology a small amount of sodium chloride is dissolved in the sample solution before spraying the sample into a tubular oven. After water removal monodisperse dry NaCl aerosol particles are formed where trace metals are present as additives. A single-particle LIBS analysis is then triggered with a scattering based particle detection system. Benefits are the highly increased metal concentration in the LIBS focal volume and the static NaCl-matrix which can be exploited in the signal processing procedure. Emitted light from the emerged plasma plume is collected with wide angle optics and dispersed with a grating spectrometer. In an aqueous solution, the respective limits of detection for zinc and lead were 0.3 ppm and 0.1 ppm using a relatively low 14 mJ laser pulse energy. Zn/Na peak intensity ratio calibration curve for zinc concentration was also determined and LIBS signal dependence on laser pulse energy was investigated.

Järvinen, Samu T.; Saarela, Jaakko; Toivonen, Juha

2013-08-01

426

Line selection and parameter optimization for trace analysis of uranium in glass matrices by laser-induced breakdown spectroscopy (LIBS).  

PubMed

Laser-induced breakdown spectroscopy (LIBS) has been evaluated for the determination of uranium in real-world samples such as uraninite. NIST Standard Reference Materials were used to evaluate the spectral interferences on detection of uranium. The study addresses the detection limit of LIBS for several uranium lines and their relationship to non-uranium lines, with emphasis on spectral interferences. The data are discussed in the context of optimizing the choice of emission lines for both qualitative and quantitative analyses from a complex spectrum of uranium in the presence of other elements. Temporally resolved spectral emission intensities, line width, and line shifts were characterized to demonstrate the parameter influence on these measurements. The measured uranium line width demonstrates that LIBS acquired with moderately high spectral resolution (e.g., by a 1.25 m spectrometer with a 2400 grooves/mm grating) can be utilized for isotope shift measurements in air at atmospheric pressure with single to tens of parts per million (ppm) level detection limits, as long as an appropriate transition is chosen for analysis. PMID:24160879

Choi, Inhee; Chan, George C-Y; Mao, Xianglei; Perry, Dale L; Russo, Richard E

2013-11-01

427

Simultaneous Raman spectroscopy-laser-induced breakdown spectroscopy for instant standoff analysis of explosives using a mobile integrated sensor platform.  

PubMed

A novel experimental design combining Raman spectroscopy and laser-induced breakdown spectroscopy (LIBS) in a unique integrated sensor is described. The sensor presented herein aims to demonstrate the applicability of a hybrid dual Raman-LIBS system as an analytical tool for the standoff analysis of energetic materials. Frequency-doubled 532 nm Nd:YAG nanosecond laser pulses, first expanded and then focused using a 10x beam expander on targets located at 20 m, allowed simultaneous acquisition of Raman-LIBS spectra for 4-mononitrotoluene (MNT), 2,6-dinitrotoluene (DNT), 2,4,6-trinitrotoluene (TNT), cyclotrimethylenetrinitramine (RDX), C4 and H15 (plastic explosives containing 90% and 75% of RDX by weight, respectively), and Goma2-ECO (Spanish denominated dynamite class high explosive mainly composed of ammonium nitrate, nitroglycol, and dinitrotoluene among other compounds), sodium chlorate, and ammonium nitrate. With the use of a Cassegrain telescope, both Raman and LIBS signals from the same laser pulses were collected and conducted through a bifurcated optical fiber into two identical grating spectrographs coupled to intensified charge-coupled device (iCCD) detectors. With the use of the appropriate timing for each detection mode, adjustment of the laser power on the beam focal conditions is not required. The ability of the present single hybrid sensor to simultaneously acquire, in real time, both molecular and multielemental information from the same laser pulses on the same cross section of the sample at standoff distances greatly enhances the information power of this approach. PMID:20085236

Moros, Javier; Lorenzo, Juan Antonio; Lucena, Patricia; Tobaria, Luciano Miguel; Laserna, José Javier

2010-02-15

428

Minimizing contamination to multilayer dielectric diffraction gratings within a large vacuum system  

NASA Astrophysics Data System (ADS)

The University of Rochester's Laboratory for Laser Energetics (LLE) has recently completed the construction of the OMEGA EP short-pulse, petawatt laser system. A major structure for OMEGA EP is the grating compressor chamber (GCC). This large (15,750-ft3) vacuum chamber contains numerous optics used in laser-pulse compression of two 40-cm-sq-aperture, IR (1054-nm) laser beams. Critical to this compression, within the GCC, are eight sets (four per beamline) of tiled (e.g., three optical elements precisely held side by side to act as one element) multilayer-dielectric (MLD)-diffraction-grating assemblies (three gratings per assembly) that provide the capability for producing 2.6-kJ output IR energy per beam at 10 ps. The primary requirements for each of the 24 large-aperture (43-cm × 47-cm) gratings are a high diffraction efficiency greater than 95%, a peak-to-valley wavefront quality of less than ?/4 waves at 1054 nm, and a laser-induced-damage threshold greater than 2.7 J/cm2 at 10-ps pulse width (measured at normal beam incidence). Degradation of grating laser-damage thresholds due to adsorption of contaminants must be prevented to maintain system performance.

Ashe, B.; Marshall, K. L.; Mastrosimone, D.; McAtee, C.

2008-08-01

429

Dark current and light illumination effects on grating formation during periodic long-term operation in photorefractive polymers  

NASA Astrophysics Data System (ADS)

Photorefractive grating formation dynamics in long-timescale writing and the effects of periodic writing through the control of writing beam irradiation or electric field application were investigated using typical photorefractive polymers. Both dark current and writing beam irradiation affected grating formation dynamics. Dark current in polymers changed the effective trap density over time through deep trap filling and/or detrapping and thus affected grating formation considerably. The writing beam irradiation also affected grating development in the presence of an electric field owing to the accumulation of filled deep traps. However, grating development recovered after the elimination of the electric field freed up the filled deep traps.

Fujihara, T.; Mamiya, J.; Kawamoto, M.; Sassa, T.

2014-01-01

430

Development of laser induced breakdown spectroscopy instrumentatin for safeguards applications  

SciTech Connect

In September 2006, a Technical Meeting on Application of Laser Spectrometry Techniques in IAEA Safeguards was held at IAEA headquarters (HQ). One of the principal recommendations from this meeting was the need to 'pursue the development of novel complementary access instrumentation based on laser induced breakdown spectroscopy (LIBS) for the detection of gaseous and solid signatures and indicators of nuclear fuel cycle processes and associated materials.' Pursuant to this recommendation the Department of Safeguards (SG) under the Division of Technical Support (SGTS) convened the Experts and Users Advisory Meeting on Laser Induced Breakdown Spectroscopy (LIBS) for Safeguards Applications. This meeting was held at IAEA HQ from July 7-11,2008 and hosted by the Novel Technologies Unit (NTU). The meeting was attended by 12 LIBS experts from the Czech Republic, the European Commission, France, the Republic of Korea, the United States of America, Germany, the United Kingdom of Great Britain, Canada, and Northern Ireland. After a presentation of the needs of the IAEA inspectors, the LIBS experts were in agreement that needs as presented could be partially or fully fulfilled using LIBS instrumentation. The needs of the IAEA inspectors were grouped in the following broad categories: (1) Improvements to in-field measurements/environmental sampling; (2) Monitoring status of activity in a Hot Cell; (3) Verifying status of activity at a declared facility via process monitoring; and (4) Need for pre-screening of environmental samples before analysis. Under the Department of Energy/National Nuclear Security Administration (DOE/NNSA) Next Generation Safeguards Initiative (NGSI) Los Alamos National Laboratory is exploring three potential applications of LIBS for international safeguards. As part of this work, we are developing: (1) a user-friendly man-portable LIBS system to characterize samples across a wide range of elements in the periodic table from hydrogen up to heavy elements like plutonium and uranium; (2) a LIBS system that can be deployed in harsh environments such as gloveboxes and hot cells providing relative compositional analysis of process streams for example ratios like Cm/Pu and Cm/U; and (3) an inspector field deployable system that can be used to analyze the elemental composition of microscopic quantities of samples containing plutonium and uranium. In this paper we will describe our current development and performance testing results both in a fixed lab and measurements in field deployable configurations using LIBS instrumentation developed for applications to international safeguards.

Barefield Il, James E [Los Alamos National Laboratory; Clegg, Samuel M [Los Alamos National Laboratory; Le, Loan A [Los Alamos National Laboratory; Lopez, Leon N [Los Alamos National Laboratory

2010-01-01

431

Echelle gratings acting as one  

NASA Astrophysics Data System (ADS)

A new device for producing order-sortable echelle spectra by use of consecutive diffractions in several echelle grating surfaces is described. This echelle emulating device (EED) comprises a prism placed in the path between a pair of echelle grating surfaces. The refractive angle of the prism is fixed through a simple relation. The device reproduces all the main properties of a single virtual echelle, obtained from a simple grating equation describing the combined action of the gratings and the prism. The spectral order of the EED is the sum of the spectral orders of the individual gratings. A spectrograph that utilizes the device is described, and several applications are discussed.

Lindblom, Peter

2003-08-01

432

Cryogenic Grating Spectrometer.  

National Technical Information Service (NTIS)

The Cryogenic Grating Spectrometer (CGS) first flew on the KAO in 1982 December and has been open to guest investigators since 1984 October. In the past 12 years it has completed over 100 research flights supporting 13 different principal investigators st...

E. F. Erickson, M. R. Haas, S. W. J. Colgan, J. P. Simpson, R. H. Rubin

1995-01-01

433

Influence of oscillating features of a laser-induced bubble on laser propulsion in water environment near different interfaces  

NASA Astrophysics Data System (ADS)

Laser propulsion in a water environment is influenced by oscillating features of a laser-induced bubble. In our study an optical beam deflection method is used to investigate dynamics of laser-induced semispherical cavitation bubbles near three different interfaces: the rigid boundary (water-solid interface), the free surface (water-air interface) and the liquid-liquid interface (water-soybean oil interface), and in the bulk. The maximum radius of the first bubble oscillation Rmax1 was widened and the collapse time T1 is prolonged in the case of the rigid boundary. Rmax1 is diminished and T1 is shortened in the case of the free surface and the water-oil interface, among which the latter makes Rmax1 even smaller. In order to get the maximum propelling force in different distances near different medium interfaces, different pulse energy of the laser is used. The bubble moves toward the rigid boundary and moves away from the free surface during its oscillations. This will change the application point of the propelling force on the object, and cause a change in the propelling direction of the object.

Chen, J.; Han, B.; Dou, L.; Pan, Y.-X.; Shen, Z.-H.; Lu, J.; Ni, X.-W.

2010-12-01

434

Laser-induced microjet: wavelength and pulse duration effects on bubble and jet generation for drug injection  

NASA Astrophysics Data System (ADS)

The expansion of the laser-induced bubble is the main mechanism in the developed microjet injector. In this study, Nd:YAG and Er:YAG lasers are used as triggers of the bubble formation. The impact of the laser parameters on the bubble dynamics is studied and the performance of the injector is evaluated. We found that the main cause of the differences in the bubble behavior comes from the pulse duration and wavelength. For Nd:YAG laser, the pulse duration is very short relative to the bubble lifetime making the behavior of the bubble close to that of the cavitation bubble, while in Er:YAG case, the high absorption in the water and long pulse duration change the initial behavior of the bubble making it close to a vapor bubble. The contraction and subsequent rebound are typical for cavitation bubbles in both cases. The results show that the laser-induced microjet injector generates velocity which is sufficient for the drug delivery for both laser beams of different pulse duration. We estimate the typical velocity within 30-80 m/s range and the breakup length to be larger than 1 mm suitable for trans-dermal drug injection.

Jang, Hun-jae; Park, Mi-ae; Sirotkin, Fedir V.; Yoh, Jack J.

2013-12-01

435

Forensic comparative glass analysis by laser-induced breakdown spectroscopy  

NASA Astrophysics Data System (ADS)

Glass samples of four types commonly encountered in forensic examinations have been analyzed by laser-induced breakdown spectroscopy (LIBS) for the purpose of discriminating between samples originating from different sources. Some of the glass sets were also examined by laser ablation-inductively coupled plasma-mass spectrometry (LA-ICP-MS). Refractive index (RI) measurements were also made on all glass samples and the refractive index data was combined with the LIBS and with the LA-ICP-MS data to enhance discrimination. The glass types examined included float glass taken from front and side automobile windows (examined on the non-float side), automobile headlamp glass, automobile side-mirror glass and brown beverage container glass. The largest overall discrimination was obtained by employing RI data in combination with LA-ICP-MS (98.8% discrimination of 666 pairwise comparisons at 95% confidence), while LIBS in combination with RI provided a somewhat lower discrimination (87.2% discrimination of 1122 pairwise comparisons at 95% confidence). Samples of side-mirror glass were less discriminated by LIBS due to a larger variance in emission intensities, while discrimination of side-mirror glass by LA-ICP-MS remained high.

Bridge, Candice M.; Powell, Joseph; Steele, Katie L.; Sigman, Michael E.

2007-12-01

436

Development and applications of laser-induced incandescence  

NASA Technical Reports Server (NTRS)

Several NASA-funded investigations focus on soot processes and radiative influences of soot in diffusion flames given their simplicity, practical significance, and potential for theoretical modeling. Among the physical parameters characterizing soot, soot volume fraction, f(sub v), a function of particle size and number density, is often of chief practical interest in these investigations, as this is the geometrical property that directly impacts radiative characteristics and the temperature field of the flame and is basic to understanding soot growth and oxidation processes. Diffusion flames, however, present a number of challenges to the determination of f(sub v) via traditional extinction measurements. Laser-induced incandescence (LII) possesses several advantages compared to line-of-sight extinction techniques for determination of f(sub v). Since LII is not a line-of-sight technique, similar to fluorescence, it possesses geometric versatility allowing spatially resolved measurements of f(sub v) in real time in nonaxisymmetric systems without using deconvolution techniques. The spatial resolution of LII is determined by the detector and imaging magnification used. Neither absorption by polycyclic aromatic hydrocarbons (PAH's) nor scattering contributes to the signal. Temporal capabilities are limited only by the laser pulse and camera gate duration, with measurements having been demonstrated with 10 ns resolution. Because of these advantages, LII should be applicable to a variety of combustion processes involving both homogeneous and heterogeneous phases. Our work has focussed on characterization of the technique as well as exploration of its capabilities and is briefly described.

Vanderwal, Randy L.; Dietrich, Daniel L.; Zhou, Zhiquang; Choi, Mun Y.

1995-01-01

437

Thermal cleavage on glass by a laser-induced plume  

NASA Astrophysics Data System (ADS)

We developed a thermal cleaving process on glass using an infrared-laser-induced plume. A pulsed ytterbium fiber laser with a wavelength of 1070 nm and a laser pulse energy of 40 µJ was used to produce a plasma plume on a carbon-coated sacrificial glass substrate. The induced plasma plume affected the surface of the target glass substrate and changed its optical properties locally. The laser beam that was subsequently absorbed in the modified zone induced localized heating, which led to micro-crack initiation for the glass cleaving. Various processing parameters, such as the laser's power and pulse width, and the distance between the coating layer and the target glass substrate were investigated to optimize the quality of the glass cleave. The quality of the cutting edges and cross sections with respect to these parameters were examined. Numerical simulations of the micro-crack initiation due to heat accumulation were performed to investigate the fracture mechanism and to estimate the expected glass-cleaving line. The limits and applications of the process are also discussed.

Choi, Won Seok; Kim, Jong Hyeong; Kim, Joohan

2014-02-01

438

Laser-induced periodic surface structures, modeling, experiments, and applications  

NASA Astrophysics Data System (ADS)

Laser-induced periodic surface structures (LIPSSs) consist of regular wavy surface structures, or ripples, with amplitudes and periodicity in the sub-micrometer range. A summary of experimentally observed LIPSSs is presented, as well as our model explaining their possible origin. Linearly polarized continuous wave (cw) or pulsed laser light, at normal incidence, can produce LIPSSs with a periodicity close to the laser wavelength, and direction orthogonal to the polarization on the surface of the material. Ripples with a periodicity (much) smaller than the laser wavelength develop when applying laser pulses with ultra-short durations in the femtosecond and picosecond regime. The direction of these ripples is either parallel or orthogonal to the polarization direction. Finally, when applying numerous pulses, structures with periodicity larger than the laser wavelength can form, which are referred to as "grooves". The physical origin of LIPSSs is still under debate. The strong correlation of the ripple periodicity to the laser wavelength, suggests that their formation can be explained by an electromagnetic approach. Recent results from a numerical electromagnetic model, predicting the spatially modulated absorbed laser energy, are discussed. This model can explain the origin of several characteristics of LIPSSs. Finally, applications of LIPSSs will be discussed.

Römer, G. R. B. E.; Skolski, J. Z. P.; Obo?a, J. Vincenc; Ocelík, V.; de Hosson, J. T. M.; Huis in't Veld, A. J.

2014-03-01

439

Dust Removal on Mars Using Laser-Induced Breakdown Spectroscopy  

NASA Technical Reports Server (NTRS)

Dust coatings on the surface of Mars complicate and, if sufficiently thick, mask the spectral characteristics and compositional determination of underlying material from in situ and remote sensing instrumentation. The Laser-Induced Breakdown Spectroscopy (LIBS) portion of the Chemistry & Camera (ChemCam) instrument, aboard the Mars Science Laboratory (MSL) rover, will be the first active remote sensing technique deployed on Mars able to remove dust. ChemCam utilizes a 5 ns pulsed 1067 nm high-powered laser focused to less than 400 m diameter on targets at distances up to 7 m [1,2]. With multiple laser pulses, dust and weathering coatings can be remotely analyzed and potentially removed using this technique [2,3]. A typical LIBS measurement during MSL surface operations is planned to consist of 50 laser pulses at 14 mJ, with the first 5 to 10 pulses used to analyze as well as remove any surface coating. Additionally, ChemCam's Remote Micro-Imager (RMI) is capable of resolving 200 m details at a distance of 2 m, or 1 mm at 10 m [1,4]. In this study, we report on initial laboratory experiments conducted to characterize the removal of dust coatings using similar LIBS parameters as ChemCam under Mars-like conditions. These experiments serve to better understand the removal of surface dust using LIBS and to facilitate the analysis of ChemCam LIBS spectral data and RMI images.

Graff, T. G.; Morris, R. V.; Clegg, S. M.; Wiens, R. C.; Anderson, R. B.

2011-01-01

440

The LILIA (laser induced light ions acceleration) experiment at LNF  

NASA Astrophysics Data System (ADS)

Laser-matter interaction at relativistic intensities opens up new research fields in the particle acceleration and related secondary sources, with immediate applications in medical diagnostics, biophysics, material science, inertial confinement fusion, up to laboratory astrophysics. In particular laser-driven ion acceleration is very promising for hadron therapy once the ion energy will attain a few hundred MeV. The limited value of the energy up to now obtained for the accelerated ions is the drawback of such innovative technique to the real applications. LILIA (laser induced light ions acceleration) is an experiment now running at LNF (Frascati) with the goal of producing a real proton beam able to be driven for significant distances (50-75 cm) away from the interaction point and which will act as a source for further accelerating structure. In this paper the description of the experimental setup, the preliminary results of solid target irradiation and start to end simulation for a post-accelerated beam up to 60 MeV are given.

Agosteo, S.; Anania, M. P.; Caresana, M.; Cirrone, G. A. P.; De Martinis, C.; Delle Side, D.; Fazzi, A.; Gatti, G.; Giove, D.; Giulietti, D.; Gizzi, L. A.; Labate, L.; Londrillo, P.; Maggiore, M.; Nassisi, V.; Sinigardi, S.; Tramontana, A.; Schillaci, F.; Scuderi, V.; Turchetti, G.; Varoli, V.; Velardi, L.

2014-07-01

441

Laser-induced fluorescence for discrimination of crops and weeds  

NASA Astrophysics Data System (ADS)

This paper reports the use of Laser Induced Fluorescence (LIF) of plants to discriminate between crops and weeds for potential use in an intelligent crop spraying system. Past and current work in intelligent crop spraying has concentrated on using multi-spectral reflectance data in particular using near infrared (NIR) and color. Texture and shape image processing has also been used with limited success and is usually computationally expensive. Also, most of these approaches are error prone since they rely on ambient solar illumination and so are susceptible to errors caused by cloud variations, shadows and other non-uniformities. There are several commercial spraying systems available that detect presence or absence of plants using the NIR 'red-edge' effect without discrimination between species. 'Weedseeker' and 'Detectspray' are two examples of such systems, the 'Weedseeker' system being one of the few active systems, incorporating its own light source. However, both systems suffer from poor spatial resolution. The use of plant or chlorophyll fluorescence for discrimination between species is a relatively under researched area. This paper shows that LIF of several crops and weeds can be used to discriminate between species. Spectra are presented for two crop and two weed species over a range of discrete laser excitation wavelengths. The technique can be directly implemented with a laser imaging system for real-time detection and discrimination of crops and weeds.

Hilton, Peter J.

2000-11-01

442

Laser-Induced Temperature Jump Infrared Measurements of RNA Folding  

PubMed Central

Probing a sample using infrared spectroscopy following a laser-induced temperature jump is a powerful method to monitor fast relaxation kinetics. Here, we describe how this approach is used to study the kinetics of RNA folding. We begin with a concise summary of the infrared spectral properties of RNA in the 1500–1800 cm?1 region. The infrared transitions in this region are directly related to the double bond stretching vibrations and ring modes of the nucleotide bases. When RNA undergoes a conformational change, the local environments of the nucleotides are altered. Consequently, the changes in the corresponding infrared spectrum are associated with the structural changes. Experimentally, temperature is used to systematically vary the RNA structure. When a short laser pulse is used to produce a rapid temperature increase in the sample, the structural changes that ensue can be followed in real time. In this contribution, we discuss experimental methods including sample preparation, instrumentation, and data analysis. We conclude with several experimental examples that highlight usefulness of the technique.

Dyer, R. Brian; Brauns, Eric B.

2011-01-01

443

Adhesion of polymer coatings studied by laser-induced delamination  

SciTech Connect

This paper concentrates on the laser-induced delamination technique, aimed at measuring the practical work of adhesion of thin polymer coatings on metal substrates. In this technique an infrared laser-pulsed beam is used to create an initial blister. Upon increasing the pulse intensity, the size of the blister grows, resulting in partial delamination of the film. In this work the blister profiles and the blister pressure were obtained from independent measurements. Alongside experiments, a simple model is developed to provide the equations necessary for calculating the blister strain energy, height, and the gas pressure inside the blister. The model is essentially based on an elastic behavior of the polymer film. The blister height and the blister pressure predicted by the model were confronted with the experimental observations and a fair agreement was found. The adhesion properties of the polyethylene terephthalate films on a steel substrate were characterized in terms of the maximum stress required for delamination and the practical work of adhesion. The relation between the two are discussed. Because the blister formation and subsequent delamination take place on a time scale of microseconds, it is argued that the viscous properties of the film do not manifest on this time scale and the contribution of plastic deformation of the film is rather small.

Fedorov, A.; Hosson, J.Th.M. de [Department of Applied Physics, Materials Science Centre, and the Netherlands Institute for Metals Research, University of Groningen, Nijenborgh 4, 9747 AG Groningen (Netherlands)

2005-06-15

444

Laser-induced breakdown spectroscopy of molten aluminum alloy.  

PubMed

We have demonstrated that a fiber-optic laser-induced breakdown spectroscopy (LIBS) probe is suitable for measuring the concentration of minor constituents of a molten Al alloy in a laboratory furnace. For the first time to our knowledge we are able to record the LIBS spectra in several spectral regions of seven different molten Al alloy samples by inserting the LIBS probe inside the molten alloys, allowing us to obtain a ratio calibration curve for minor constituents (Cr, Mg, Zn, Cu, Si, etc.), using Fe as a reference element. A ratio calibration curve for Fe with a major element (Al) can also be obtained with which the concentration of Fe in the alloy can be determined. The effects of the surrounding atmosphere on the LIBS spectra of the molten alloy were investigated. Effects of focal length of the lens on the LIBS signals were also studied. LIBS spectra of a solid Al alloy recorded with the same LIBS probe were compared with the LIBS spectra of the molten alloy. Our results suggest that the LIBS probe is useful for monitoring the elemental composition of an Al melt in an industrial furnace at different depths and different positions inside the melt. PMID:12716148